asian urban research network - ubc scarp · 5.6. wastewater disposal: recover and reuse 38 5.6.1....

Asian Urban Research Network

ISSN 1190-8971

Sanitation Infrastructure:A Handbook of Wastewater Technologyand Management Systems

AURNWP#25 October 1999Annwen Rowe-Evans,Matsumura Shigehisa, and Tam Pham

Centre for Human SettlementsSchool of Community and Regional Planning

The University of British ColumbiaVancouver, Canada

A.UR.N.The Asian Urban Research Network is part ofthe Centre of Excellence Project on HumanSettlements Development sponsored by theCanadian International Development Agency.

—

Our relationship to environmental issues is as old as civilizationitself Advances and regressions in managing health throughenvironmental practices occurred throughout the quest forbetter health. At first, mankind dealt with health- andenvironmental-related problems in terms of magic, mysticism,and a great deal of trial and error. Then, through theevolutionary process, the scientWc method radually emerged.Finally, engineering provided yredictive reliability.., byeliminating vector- and water-borne diseases, sanitaryengineering, the forerunner of modern-day environmentalengineering set a precedent of serving civilization throughtechnology.

Earnest Gloyna

Our society values growth but looks upon the processes andproducts ofdecay as waste.

Bill Roley

Though their health needs d[fer drastically, the rich and thepoor do have one thing in common: both die unnecessarily. Therich die of heart disease and cancer, the poor of dysenterydisease, diarrhea, and cholera.

William Chandler

CONTENTS

1. ...... 1

2. ASPECISS OF .n.4

3. OF .. ...5

4. 11()IJ_F’I . ..... . 8

4.1. Historical aspects of toilet systems 84.2. “Dry” or non-water--dependent systems 8

4.2.1. Bucket latrines 84.2.2. Pit latrine systems 94.2.3. Composting toilets 14

4.3. “Wet” or water-dependent systems 154.3.1. Overhung latrines 154.3.2. Pow-flush latrines 164.3.3. Vault toilets and cartage 174.3.4. Aqua privies 174.3.5. Cistern-flush toilets 19

4.4. Septic tank systems 19

4.5. Other simple on—site disposal systems 224.5.1. Leaching pits and cesspools; 224.5.2. Sullage 23

4.6 A comparison of toilet systems 23

5. SEWERAGE: TIlE COLLECTION, TREATMENT, AND DISPOSAL OFDO1’{ES’I’IC VVAS’1i’1A’rEIt ....E... 23

5.1 Characteristics ofdomestic wastewater 25

5.2. Wastewater collection systems 255.2.1. Conventional sewer systems 255.2.2. Small-bore sewer systems 285.2.3. Shallow sewer systems 28

5.3. Wastewater treatment systems 295.3.1. Primary treatment 29

5.3.2. Secondary treatment 305.3.3. Advanced or tertiary treatment 31

5.4. Alternative treatment systems 315.4.1. Waste stabilization ponds and lagoons 325.4.2. Wetland systems 3354.3. Aquaculture systems 36

5.5. Disinfection techniques 38

ii Contents

5.6. Wastewater disposal: recover and reuse 385.6.1. Effluent reuse 395.6.2 Sludge reuse 405.6.3. Biogas reuse 40

6. Ir’])US’II.I.IsI.. 41

6.1. Characteristics of industrial wastewater 416.1.1. Petroleum industry 416.1.2. Iron and steel industry 42.6.1.3. Non-ferrous metal production 426.1.4. Chemical industry 436.1.5. Food industry 456.1.6. Pulp and paper industry 456.1.7. Textile industry 46

6.2. Treatment and disposal of industrial wastewaters 466.2.1. Options for the treatment of industrial wastewaters 466.2.2. Special treatment techniques for industrial wastewaters 49

7. (C)Ii’R.OL 4.r.{D 1]3G1_JL,A.I’IOl% OF VAShIEVnIFR 50

7.1. Point source and nonpoint source wastewater 50

7.2. Control ofnonpoint and point source wastewater 51

8. Ol”1DLIJSION . 52

. .... ........... 54

FIGURES AN]) TABLES

Table 1.1 Water Supply and Sanitation Coverage, 1980-2000 2

Table 3.1 Common Diseases Transmitted by Polluted Water (Domestic Sources) 6

Table 3.2 Health Effects of Conimon Chemical Water Contaminants (Industrial Sources) 6

Table 3.3 Common Types of Water Pollutants 7

Table 4.1 Comparison of Toilet Systems 24

Table 5.1 Summary Analysis of Wastewater Collection Systems 26

Table 5.2 Advanced or Tertiary Treatment Techniques and Methods 31

Table 5.3 Advantages and Limitations ofVarious Treatment Systems 37

Table 5.4. Disinfection Techniques 39

Table 6.1 Types and Sources of Liquid Effluent 41

Table 6.2 Liquid Effluents From Major Inorganic Chemical Products 43

Table 6.3 Liquid Effluents From Major Organic Chemical Products 44

Table 6.4 Industrial Wastewater: Components, Effects, and Typical Sources 47

Table 6.5 Major Industrial Treatment Methods 50

Pham, Rowe-Evans, andShigehisa

FIGURES

‘U

Figure 1.1

Figure 4.1

Figure 4.2

Figure 4.3a

Figure 4.3b

Figure 4.4

Figure 4.5

Figure 4.6

Figure 4.7

Figure 4.8

Figure 4.9

Figure 4.10

Figure 5.1

Figure 5.2

Figure 5.3

Figure 5.4

Figure 5.5

Figure 6.1

Figure 7.1

Trends in Water Supply and Sanitation Coverage 3Construction Details of a Pit Latrine 10Collapsed Traditional Pit Latrine 11Reed Odourless Earth Closet (ROEC) Pit Latrine 13Ventilated Improved Pit (VIP) Latrine 13Overhung Latrine 15Pour-Flush Latrine 16Botswana Type B Aqua Privy 18Septic Tank System 20Details for Small Septic Tanks 20Septic System Absorbtion Trench 21Seepage Pit 22Shallow Sewer and Conventional Sewer Systems 27Primary and Secondary Treatment Processes in Conventional Systems 29Persistent Chemicals and Bacteria 30Schematic Diagram ofDigester and Stabilization Ponds 34Wetland Systems 35Separated and Combined Storm and Sewer Systems 48Point and Nonpoint Sources of Water Pollution 51

1. INTRODUCTION

Sanitation infrastructure, in essence, responds to the need to remove waste produced by humansin any given settlement. Sanitation constitutes “the effective use of measures that create andmaintain healthy environmental conditions. Among these measures are the safeguarding of foodand water, proper sewage and excreta disposal, and the control of disease carrying insects andanimals” (Salvato, 1992, 9). This handbook deals with virtually all of these components in anattempt to review and assess the various technological responses to the problems of sanitation.For our purposes here, sanitation may be viewed as the collection and appropriate disposal ofhuman-made waste, both residential and industrial, excluding garbage, but including both blackand grey water, that is, toilet wastes and wastewater. Although important to the infrastructureequation, agricultural waste is to a large degree beyond the scope ofthis current work.

The question of sanitation is expressed worldwide in very different ways and in varying degrees.As Table 1.1 indicates, while the percentage of the global rural population covered by sanitationservices has grown and continues to grow quite dramatically, urban sanitation services havestagnated for some time at roughly 70% coverage. This lack of truly substantial progress inproviding universal access to sanitation is further demonstrated in Figure 1.1. Whereas bothwater supply and sanitation were available to roughly half of the population in developingcountries in 1980, access to water has spread much faster than access to sanitation. The gapbetween the number of individuals in developing nations with access to sanitation and the totalnumber of individuals living in such countries must be addressed through increased efficiency ofsanitation services as well as greater investment in this area.

When examining the issue of sanitation, it is worthwhile to keep a number of important factors inmind, beyond the obvious technological elements involved. The first of these considerationspertains to the physical environment. Relevant issues include: geographical location, density ofsettlement, protection of water supply, integration with other infrastructure and recyclabiity ofsystem elements. The second set of considerations entails an emphasis on public health benefits,that is, an improvement in the physical quality of human life through freedom from disease,death and general misery. It is interesting and important to note that, providing the system iscorrectly built, maintained and used, there is very little difference in health benefits between themost simple sanitation systems and complex, expensive ones (Cairncross and Feachem, 1983,146). Thirdly, there are an enormous quantity and variety of social factors that impact upon thediscussion of sanitation, including cultural habits, convenience, aesthetics and communityparticipation. The fmal consideration to keep in mind throughout the discussion that follows isessentially “the bottom line,” or cost, of sanitation projects. Over the years, sanitation indeveloping countries has been high in cost and low in efficiency and reliability. For significantimprovements in the fmancial realm of sanitation infrastructure, the World Bank and UnitedNations have made the following suggestions:

• infrastructure must be made available at an acceptable cost within the competingdemands of the domestic, industrial and agricultural sector;

• correct incentives are needed to improve the effectiveness of actors and institutions thatprovide, manage, and maintain infrastructure to make the service sustainable;

(Popula

tion

inm

illi

on

s)

1980

1990

,20

00.

No.

No,

“No

.N

o.N

o.N

o.R

eg

ion

/secto

r.P

opula

tion

cov

erag

eS

erved

unse

rved

Popula

tion

cov

erag

ese

rved

un

serv

edP

op

ula

tio

nco

ver

age

serv

edu

nse

rved

Arj

cs

V

Urb

anw

atd

r1

19

.77

83

.99

.41

20

.36

20

2.5

4.

871

76

.21

26

.33

332.4

976

253.0

179.4

8R

ura

lw

ater

332.8

3‘3

3,

10

9..3

223.0

0409.6

442

,1

72

.05

23.5

9496.5

947

234.2

7.

262.3

2U

rban

sanit

ati

on

.1

19

.77

657

7.8

.41.9

2.

V

202.5

479

160.0

142.5

3.

33

2.4

973

242.1

790.3

2R

ura

lsa

nit

ati

on

332.8

318

59

.91

272.9

2409.6

426

106,5

1303.1

3496.5

931

153.1

1343.4

8

,ati

nA

mer

ica

and

the

Car

ibb

ean

VVV

Urb

anw

ater

236.7

282

194.1

14

2.6

13

24

.08

872

81

.95

42

.13

416.7

989

369.7

947.0

0R

ura

lw

ater

V 124.9

1V

58.7

1.

66.2

01

23

.87

627680

47

.07

122.8

477

94

.89

27.9

5U

rban

sanit

ati

on

23

6.7

278

18

4.6

452.0

8V

324.0

879

25

6.0

268.0

6416.7

979

327.4

089.3

9R

ura

lsa

nit

ati

on

12

4.9

122

27

.48

97.4

31

23

.87

3745,8

378.0

41

22

.84

52.6

4.1

858.6

6

£%si

aan

dth

eV

Pacif

ic.

.V

VU

rban

wat

er349.4

473

.401.0

9148.3

5761.1

8V

77586.1

1175.0

71

083.5

671

771.7

1314.4

3R

ura

lw

ater

1823.3

0VV

28510.5

21

312.7

82

099.4

067

1406.6

0692.8

02

320.7

999

2302.6

810.1

1U

rban

sanit

ati

on

549.4

465

35

7.1

4192.3

07

61

.18

63494.7

72

66

.41

1085.5

658

63

2.4

04

53

.16

Rura

lsa

nit

ati

on

1823.3

042

763

.79

.1057.5

i2

099.4

054

11

33

.68

9.65

.72

2320.7

963

3.501.3

78

19

.22

Wes

tern

Asi

a

Urb

anw

ater

27

.54

9526.1

61

.38

44.4

210

044.2

5V

0.1

767.2

610

067.2

60.0

0R

ura

lw

ater

21.9

551

11

.19

10.7

625.6

056

14

.34

11.2

630.6

657

17.4

813.1

8U

rban

sanit

ati

on

27.5

479

21.7

63

.78

44

.42

100

44.4

20

.00

67.2

610

067.2

60.0

0R

ura

lsa

nit

ati

on

21.9

.534

7.4

614.4

92

3.6

034

8.7

016.9

030.6

6.

329.9

420.7

2

Glo

bal

tota

lsV

.V

Urb

anw

ater

933.4

777

720.7

7:

21

2.7

01

332.2

282

10

88

.52

243.7

03.

90

2,1

077

1456.2

74

45

.83

Ru

ral

wat

erV

2302.9

930

690.2

51

63.2

.74

26

38

.51

631

669.7

998

8472

2970.8

889

26

49

.33

321.5

5U

rban

sanit

ati

on

V933.4

769

64

1.3

9292.0

81

332.2

272

95

5.2

237,0

01

90

2.1

067

12

69

.05

633.0

5R

ura

lsa

nit

ati

on

2302.9

937

86

0.6

41

442.3

52

65

8.3

149

12

94

.72

13.

63.7

92

970,8

838

17

28

.80

12

42

.88

Tab

le1.

1W

ater

Supp

lyan

dSa

nita

tion

Cov

erag

e,19

80-2

000

Sour

ce:

Uni

ted

Nat

ions

,19

90,

20.

I

All developing countries (population in billions)..

• Population ‘Water * Sanitation — — — connuation of present liend -- acceleraonn.eded for universal coverage

Figure 11 Trends in Water Supply and Sanitation CoverageSource: United Nations, 1995; 9.

Pham, Rowe-Evans, andShigehisa 3

6

5 . ... 4.9

• . .

• —4.——

I — — 4-.’ —

-4 -4-4

4

•———-4 -.4..

4.

q •1. •-—--4.-..

2.7: .---

2_ -4 -4

-4 -4 — —

— — ——

11.3

0 .I.

1980-

20001990

4 Sanitation Infrastructure

• environmentally sustainable methods must be given primacy, for reasons of both goodecological and economic feasibility. Environmentally destructive methods have cost ushuge sums ofmoney to correct; and,

• the required level of financial resources to provide sanitation services must be continuallyavailable and accessible.

Finally, it is important to realize that the ability to provide or access sanitation services bearswith it a certain power. This is a power that is not equally shared throughout a given society andmay silence the voices of certain individuals within that society. These main considerations,amongst others, must be kept in mind when examining any and all aspects of the sanitationquestion.

In view of these considerations, this handbook will begin with an historical overview ofsanitation engineering, then proceed to an examination of the effects of wastewater on bothhumans and the physical environment. It will then examine the variety of.tecbnology associatedwith sanitation, including toilet systems, sewerage and industrial wastewater treatment Finally,the control and regulation ofwastewater will be discussed and conclusions drawn pertinent to theissue at hand.

2. ifiSTORICAL ASPECTS OF SANITATION

We can trace the history of sanitation back to ancient times, more than several millennia ago..Throughout history, impure water has been a leading cause of fatal disease in humans. In moremodern times, however, wastewater has remained an issue, particularly in urban settlements.The earliest drainage systems, constructed in the 16th.and 17th centuries, carried off storm runofffrom built-up areas protecting them against inundation. Privies and cesspools were often usedfor the disposal of human excreta; household wastes were often thrown into the street, creatingdeplorable sanitary conditions (Gloyna, 1986, 8 12-814). Waterbome diseases such as typhoidfever and dysentery were still common in developed countries less than a century ago. It wasn’tuntil the mid-nineteenth century when the great typhoid epidemic swept London that the perils ofwater pollution gained substantial recognition and organizational steps to combat it werelaunched (Bervy and Horton, 1974, 167-168).

Examples of the history of sanitation problems abound. In 1900, the United States death ratefrom typhoid fever, a waterbome disease, was 35.8 per 100,000 people. If such a rate persistedtoday, the death rate from typhoid would far exceed those deriving from automobile accidents.In Great Britain, the Thames River was little more than a flowing anaerobic sewer until the latel950s. As for industrial waste, the risk of toxic chemical contamination of the food supply firstcame to the forefront in Japan in the 1950s. The most affected region, Minamata, lent its nameto the disease which is characterized by pustulous legions covering the entire body (Ellis, 1989,3 8-39).

Fortunately, advances in sanitation technology, as well as increasing awareness of the linksbetween human health and water quality, contributed to the fight against waterbome diseases. In

Pham, Rowe-Evans, and Shigehisa 5

comparison to the early 1 900s, the Thames River of the 1 980s made a remarkable recovery, butonly after more than three decades of effort, US$ 250 million of taxpayers’ money, and millionsmore spent by concerned industries. It was mainly in the 1970s that many full-scale efforts forcontrolling wastewater in developed countries began. In the case of the United States, the firstpermanent legislation for wastewater control was passed in 1956. However, it wasn’t actuallyuntil the 1970s that broadened water pollution control laws greatly increased the number andquality of wastewater treatment plants. These laws have also required industries to reduce oreliminate point source discharge into surface waters. Pollution control laws since the 1970s havealso led to improvements in dissolved oxygen content in many rivers and streams in Canada,Japan, and most western European countries (Miller, 1990, 520-522).

On the other hand, in most developing countries many cities are still without adequate watersupply, and wastewater is not properly handled or treated. Waterborne diseases still rank highamong the leading causes of death and debility. In India, more than two-thirds of water resourcesare polluted. Of India’s 3,119 towns and cities, only 218 have any type of sewage treatmentfacilities. India’s Ganges River, in which millions of Hindus regularly immerse themselves towash away their sins, is highly contaminated. It receives untreated sewage and industrial wastesfrom millions of people in 114 cities, as well as pesticide and fertilizer runoff. In China, only 2%ofwastewater is treated. Of the 78 rivers monitored in China, 54 are seriously polluted. In LatinAmerica and Africa, many rivers are also severely contaminated (Miller, 1990, 523).

In developed and developing countries alike, there is much to be done in improving the waterquality of rivers, lakes and oceans. Due to increased residential outputs, industrial wastes andagricultural chemicals, inputs of nitrates, phosphates, pesticides, and other toxic chemicals haveincreased in many rivers since the 1 970s. These chemicals continue to contaminate drinkingwater as well as decimate wildlife. More effective and appropriate means of dealing withsanitation problems worldwide are needed to both improve human health and further minimizethe enormous impact we have made on our environment.

3. EFFECTS OF WASTEWATER

Water pollution has been defined as “any alteration of the chemical, physical or biologicalquality of water, which results in an unacceptable depreciation of its utility or environmentalvalue” (Fish, 1972, 647-657). This defmition embraces not only the more traditional chemicaland bacteriological aspects of water quality associated with human health and disease, but alsoall the factors which may affect the overall environmental characteristics of the water. As thedefinition implies, water pollution can be classified into three main types:

• chemical pollution: chemical additions to water result in a direct or indirect depreciationof the water quality;

• physical pollution: alteration of volume, topography or temperature of the water oradditions of solids causes an unacceptable depreciation in water value;

• biological pollution: certain living organisms added to water results in a depreciation ofits value (United Nations, 1982, 293).


The effects of wastewater are broad and extensive. The following five categories roughlyrepresent the potential range of effects: human health, amenity (smell and aesthetics), fish andother animals (fauna), plants (flora), and fresh water and ocean ecosystems.

Among these consequences, human health effects have perhaps the most direct and personalimpact. Tables 3.1 and 3.2 show the major effects ofwater pollution on human health: Table 3.1shows human health effects of domestic wastes, and Table 3.2, those of industrial wastes.

Table 3.1 Common Diseases Transmitted by Polluted Water (Domestic Sources)

Type of Organism Disease EffectsBacteria • Typhoid fever • Diarrhea, severe vomiting, enlarged spleen,

• Cholera inflamed intestine; often fatal ifuntreated• Bacterial • Diarrhea, severe vomiting, dehydration; often

dysentery fatal• Enteritis • Diarrhea; rarely fatal except in infants without

proper treatment. Severe stomach pain, nausea, vomiting; rarely

fatalViruses • Infectious • Fever, severe headache, loss of appetite, abdo

hepatitis miiial pain, jaundice, enlarged liver; rarely fatal• Polio • High fever, severe headache, sore throat, stiff

neck, deep muscle pain, severe weakness,tremors

Parasitic protozoa • Amebic • Severe diarrhea, headache, abdominal pain,dysentery chills, fever, if untreated liver abscess, bowel

perforationParasitic worm • Schistosomiasis • Abdominal pain, skin rash, anemia, chronic

fatigueSource: Miller, 1990.

Table 3.2 Health Effects of Common Chemical Water Contaminants (Industrial Sources)

Contaminant EffectsInorganicSubstances: • Cancer, damage to liver, kidney, blood, and nervous system,. Arsenic anemia, pulmonary problems, high blood pressure• Cadmium • Nervous system and kidney damage, biologically amplified in• Mercury food, respiratory distress, possible death in infants and fetus• NitrateOrganic Substances:. Benzene • Chromosomal damage, anemia, blood disorders, and leukemia• Dioxins • Skin disorders, cancer, and genetic mutations• PCBs • Liver, kidney, and pulmonary damage• Vinyl chloride • Liver, kidney, lung damage, and cancer and suspected mutationsSource: Miller, 1990

Pham, Rowe-Evans, and Shigehisa. 7

Effects to the amenity of water also comprise a crucial issue, particularly for the urban livingenvironment. For example, in most cities in developing countries, rivers and streams flowing inresidential areas constitute a general nuisance due to their odor and physical condition.However, it is harder to identify the precise effects of polluted wastewater on the environment,including fauna, flora, and water ecosystems. Nevertheless, the long-term accumulation of toxicchemicals in fish or bird populations will eventually directly affect humans.

The effect of wastewater on the environment, including human beings, can be further brokendown into eight common types of water pollutants (as shown in Table 3.3).

Table 3.3 Common Types ofWater Pollutants

1. Disease-causing agents • bacteria, viruses, protozoa, parasitic worms2. Oxygen-demanding wastes • organic wastes, which degraded by oxygen-consuming

bacteria3. Water-soluble inorganic • acids, salts, compounds oftoxic metals (lead, mercury etc.)

chemicals4. Inorganic plant nutrients • water-soluble nitrate and phosphate5. Organic chemicals • oil, gasoline, plastics, pesticides, cleaning solvents,

detergents6. Sediment or suspended • insoluble particles of soil, silt, and other solid inorganic

matter and organic materials7. Radioactive substances • radioisotopes8. Heat • heated water

Source: Miller, 1990

1) In developing countries, disease-causing agents are the major cause of sickness and death,killing an average of 25,000 people each day.

2) Oxygen-demanding wastes can deplete water of dissolved oxygen gas.3) High levels of water-soluble inorganic chemicals make water unfit to drink, harm fish and

other aquatic life, depress crop yields, and accelerate corrosion ofequipment that uses water.4) Water-soluble nitrate and phosphate cause excessive growth of algae and other aquatic plants.

Excessive levels of these in drinking water can reduce the oxygen carrying capacity of theblood and kill unborn and newborn children. Nitrates may contribute to the greenhouseeffect.

5) Organic chemicals threaten human health and harm fish and other aquatic life. In the UnitedStates, organic chemicals in underground water cause kidney disorders, birth defects andvarious types of cancer.

6) Suspended particulate matter destroys the ecosystem of fauna and flora in lakes, reservoirs,river and stream channels, and harbours. These reduce photosynthesis by aquatic plants,disrupts aquatic food webs, and clogs the gills of fish and the filters of shellfish.

7) Ionizing radiation from isotopes causes DNA mutations, leading to birth defects, cancer, andgenetic damage.


8) Increases in water temperatures result in lower dissolved oxygen content and make aquaticorganisms more vulnerable to disease, parasite, and toxic chemicals (Miller, 1990, 518-522).

4. TOILET SYSTEMS

Now that a brief historical overview of sanitation and a discussion of the effects of wastewaterhas been provided, this handbook will now turn to the examination of basic sanitation systems.Throughout time, the issue of sanitation, whether or not it was recognized as such, has been ofconcern to human populations. This has become increasingly so with the rise of humansettlements and the preponderance of urbanization. This section deals with the most personaland most basic of responses to the issue ofhuman waste disposal, namely latrine and septic toiletsystems.

4.1. Historical aspects of toilet systems

With the move from principally nomadic to sedentary lifestyles, human beings encountered theneed to systematize the disposal of bodily wastes and wastewater. Where before, humandefecation and urination had occurred on a more or less random and ad hoc basis, permanentconcentrations of people demanded disposal methods. In the ease of wastewater, this was oftentaken care of by simple disposal onto and absorption into nearby ground. In the case of humanexcreta, some form of pit was usually dug in order to minimize the offensive effects (Seabloomand Carison, 1986, 60). The construction of such pits heralded the birth of latrine systems. Theadvent of the more complicated septic-type systems constituted an addition to, rather than atransformation of, the sanitation process. In latrine systems, human waste was absorbed directlyfrom the pit into the surrounding ground, with the introduction of septic tanks an intermediarystep was added between disposal and absorption, namely that of temporary storage,sedimentation and digestion (Ehiers and Steel, 1965, 112-113).

4.2. “Dry” or non-water-dependent systems

4.2.1. Bucket latrines

The collection of human excrement for later disposal at a consolidated site has throughout historybeen the most prevalent method for dealing with such types of waste (McGarry, 1977, 254). Abucket latrine in its physical form, remains principally consistent over time and across space; itconsists of a container, directly over which is placed a squatting slab or seat. It usually takes theaverage family several days to fill the container, with collection occurring at least once a week.The container may be located in a position near to an access path or road in order to facilitatecollection. At the time of collection, the container is often emptied on the spot into a cart andmay or may not be rinsed; in either case it usually involves some spillage and regularizedcontamination of the area. On a larger scale, similar conditions are present at the collectiondepot. (Ehiers and Steel, 1965, 150; McGarry, 1977,254; Cairncross and Feachem, 1983, 130).

Pham, Rowe-Evans, and Shigehisa. 9

The advantages of using bucket latrines include; affordability, accessibility, and job creationthrough a labour-intensive collection system. The concerns with this system are: its “aestheticallyunpleasing” nature which has a resulting impact on the stratification of sanitation-related labourby class; its unhygenic nature due to its easy accessibility to microorganisms and rodents; and theeffects of spillage and rinsing. Recommendations for realistic standards and improvements to thesystem concern the following: sealing and removal of the container and hence sanitry transportto the collection depot/disposal site, replacement of the original container with a disinfected one,and daily collection schedules (McGarry, 1977, 254; Cairncross and Feachem, 1983,. 130).

Costs to either the user or the municipality of a bucket latrine system are often relatively low,with minimum capital outlay for containers, collection equipment and cost recovery possible ona fee-per-container-collected basis. The major cost factor is usually involved in the operatingexpenses of labour and disinfectant. The principal technological elements required include awaterproof container and a collection cart. Collected wastes may be disposed of directly into alandifil or into a sewer system. In the former case, concern should be expressed for the quality ofthe local groundwater which may be contaminated by disposal, and a distinct method of dealingwith the waste water from cooking and washing activities must be designed and implemented.The efficiency of the system varies greatly from place to place. It is usually dependent upon thefunctioning of the collection system as well as the degree of contamination through spillage andrinsing. It has in fact, been recommended that a bucket system only be implemented “undersituations of tight institutional control, where all operations are carefully supervised” (Cairncrossand Feachem, 1983, 130), and consequently the flexibility of the system on the collection end isquestionable. However, there is room for the community to become involved in the supervisionof the latrine system. People can be educated on the health aspects of maintaining the containerand, provided that some sort of standards be set and their adherence monitored, the communitycan take over the actual collection and disposal duties. The recycling aspects of nightsoilcollection, where human excreta are returned to the ground as fertilizer, may also be consideredin the implementation of a bucket latrine system.

4.2.2. Pit latrine systems

The general designation of “pit latrine” applies to all types of human waste disposal technologiesthat are comprised of a hole dug into the ground, a covering platform, a superstructure forprivacy, and which are intended to accommodate a “dry” or “waterless” excreting process (seeFigure 4.1). In its most basic form the pit latrine may consist of a hand-dug pit, 3’ by 4’ and 6’deep or a 14” to 18” diameter hole bored to a depth of 15’ to 25’ with a simple slab andsuperstructure (Salvato, 1992, 651). The most basic pit latrine is however, often improved uponby considering several simple factors.

The first consideration lies with the fact that the latrine-type system is low-cost and easy tomaintain; technical additions may provide significant improvements without substantially raisingcosts or maintenance. In technical terms, it is recommended that the pit be as deep as is feasiblewith a reinforcing lining in the upper portion of the pit (the lining must not prevent seepage offluids into adjacent ground). For reasons of hygiene and durability, the covering slab

fJ ‘0

a

I-’

Fig

ure

42

Col

laps

edT

radi

tion

alP

itL

atri

neSo

urce

:R

ajes

war

y,19

92,

13.

I

12 Scmitation Infrastructure

should be made of concrete rather than wood. This not only makes for higher structural safety,thus preventing latrine collapse, (see Figure 4.2) but also prevents hookworm transmission. A lidhelps to control insect populations and lessens the likelihood of children falling in. With theaddition of a seat, the latrine is less likely to be fouled by excreta “missing the mark” and avoids

the problem of floor sweepings being brushed into the hole (Cairncross and Feachem, 1983, 114-

117; Ehlers and Steel, 1965, 146-149; and Salvato, 1992, 650-651).

When considering the interaction of water with the pit latrine, contamination of ground and

surface water must be strictly avoided; locating the latrine downstream from water sources is

highly recommended. There ought to be little water deposited into the latrine and ventilation

should be incorporated to keep the pit dry and small in bulk. Standing water in the pit can inducecollapse and is highly unsanitary, not to mention providing an excellent breeding ground for

insects. Finally, latrines should be constructed, as indicated above, with serious thought topreventing contact with insects. This will inevitably reduce transmission of disease and make

the latrine much more pleasant to use. One way to ensure this would be through a. tight sealbetween the joints of the cover slabs. Prevention of insect breeding in the latrine is much moreeffective than the later destruction of insects. The application of insecticide is the short termsolution to killing flies and other insects, however, by reducing the number of predators andcompetitors, the population of insects will only increase in the long run (Caimcross andFeachem, 1983, 114-117; Ehlers and Steel, 1965,146-149; Salvato, 1992, 650-651; Wilson,1980a, 14).

In all, the assessment of latrines is best viewed from the vantage point of the VentilatedImproved Pit latrine (see Figure 4.3b), a type that incorporates suggested improvements andaddresses serious disadvantages of pit-type latrines. First serious attempts at majorimprovements to the pit latrine came in the form of the Reed odourless earth closet (ROEC), aprecursor to the Ventilated Improved Pit variety (see Figure 4.3a). The placement of thesuperstructure adjacent to the pit with a connecting chute greatly eliminated the likelihood ofcollapse and allowed easier access to the pit for removal of contents. However, the majorconcern was the fouling of the .chute due to excreta buildup and either the inadequate cleaning ofthe chute or the overuse ofwater in attempts to clean it (Wilson, 1980a, 14).

The Ventilated Improved Pit latrine places the superstructure and pit slightly closer together so

that the back of the superstructure overhangs the pit by nearly hail obviating the need for achute. Local materials may be used in some construction, such as that of the superstructure (mudand wattle walls), or it may be more suitable to use higher technology materials (concrete slabcovers, or thin fibreglass disposable pit liners in the case of unstable ground conditions). In

essence, the main features of the VIP latrine are as follows:• dual pit structure to allow for extended use (alternating over the long run between pits

allows time for removal of the contents of one while the other is in use);• masonry collar lining around the upper portion of the pit; concrete squatting slab or seat,

reinforced with steel or cast in a cone or dome shape;• ventilation pipe for odour dispersion, designed to suck air through the drop hole and pit,

and out the pipe with a sufficiently large opening for sunlight to attract flies out of the pit;and,

Figu

re4.

3aR

eed

Odo

urle

ssE

arth

Clo

set

(RO

EC

)Pi

tLat

rine

Figu

re43

bV

entil

ated

Impr

oved

Pit (

VIP

)L

atri

ne

I c •4

.

Sun

nysi

de

Bla

ckve

ntpi

pew

ithfly

scre

en

ir

Doo

r

Sea

tan

dco

ver

-,

V..

Sun

nysi

de

Bla

ckve

ntpi

pew

ithfly

scre

ens

Con

cret

eac

cess

cove

rs,

V

pain

ted

blac

k

Air

I

L-s

hape

dw

all

jC

tba

ckfi

llF

Pre

fabr

icat

edch

ute

plas

ter

Con

cret

eba

ckfi

ll

Rei

nfor

cing

bars

Sour

ce:

Wik

son,

1980

1,, 1

4.


• non-corrosive gauze screen covering for the top of the ventilation pipe to prevent theentry of flies or trap their exit (effectively starving them to death).

The advantages of the VIP latrine are, low cost and ease of construction/maintenance, minimalwater use and potential for upgrading. The disadvantages include construction and structuralintegrity of the pit in either very rocky or very sandy soils, inappropriately high water table levelsor water contamination, lack of suitability for very high density areas, and relatively strictemptying requirements (Sinnatamby, 1990, 132-134; Cairncross and Feachem, 1983, 117-121;Wilson, 1980a, 14-15).

The above discussion has not yet dealt with two fundamental elements, namely the emptying ofpits and the disposal of suilage. In the case of single-pit latrines, the sanitary dangers ofemptying the pit are considerable, a vacuum tanker rather than personal contact is recommended.In that case, water must be added before emptying can occur and a pit lining is virtually essential.However, dual-pit latrines do not require linings and hence can act as leaching pits, ridding thepits of some of their contents. One pit can be emptied by hand after 12 months of inactivity andthe resulting humus used as fertilizer.

In the case of sullage, or the wastewater resulting from food preparation and washing activities, adisposal method must be identified and appropriately administered. Contamination and otherconcerns identified in the discussion of latrines must be taken into consideration. With theexception of disposal into a sewer system, sullage demands the construction of a soakaway pitwith suitable reinforcement for sandy soils and emptying for low permeability soil types(Sinnatamby, 1990, 132-134; Cairneross and Feachem, 1983, 117-121; Wilson, 1980a, 14-15,59-60).

In the final assessment, the pit latrine in its most improved form can satisfy many of theassessment criteria. Costs of installation are reasonably low when compared to other sanitationsystems, a general cost range of US$ 68-175 is estimated (Sinnatamby, 1990, 156). However,such an expense can vary greatly depending on the construction materials and labour and thesystem used to empty the pit(s). Very little technical knowledge is required for either theconstruction or maintenance phases. Although the system can in its various modifications beextremely efficient and safe, unfortunately, it is not integrated with water supply or sullagedisposal. Beyond the concern for not contaminating the local water table or sources, alternatesullage disposal methods must be undertaken. Given the appropriate adaptation of the latrinedesign to local conditions, the environmental impact is also relatively small. Finally, it should beobvious that, given adequate enforcement of standards, the system is imminently adaptable, andhence flexible to community and individual needs, with many possibilities for devolution of allproject phases to the community level.

4.2.3. Composting toilets

Although the composting toilet is a simple adaptation of the pit latrine, this technology deservesa brief treatment here due to its recent rise in Western nations as an “environmentally-friendly”


technology. Designed in Sweden for use in country cottages, the composting toilet comprises avault design over a smaller than usual pit. An air ventilation system aids in the aerobic andanaerobic digestion of the wastes and emptying takes place on a more regular basis. The supportsystem required for this type of technology (communication, education and evaluation for properuse) can make it unsuitable for certain situations in a majority of world nations (McGarry, 1977,258).

4.3. “Wet” or water-dependent systems

4.3.1. Overhung latrines

Overhung latrines may be used in those human settlement areas immediately adjoiningcirculating water. The overhung latrine is, very simply, an outhouse structure with the seat oropen hole located directly above a body of water such as a tidal fiat, beach, river, canal or lake(see Figure 4.4). In some cases, the wastes fall directly into the body of water, in others, theyremain on the surface of the ground until the tide carries them away. This system involvesminimal cost, labour and technology and is very flexible in terms of system construction andmanagement as the only required “equipment” is the outhouse superstructure. The overhunglatrine system works exceptionally well where: the wastes disposed of are entirely organic (i.e.water disposal may also be used for solid waste provided this is true); if the circulation of thewater is sufficient to ensure proper dilution and removal; and if the body of water is saline, thuspreventing its use as drinking Water. However, in the case of freshwater rivers, overhung latrinesand water disposal of wastes is often inappropriate as it will result in dangerous contamination ofdrinking and bathing water (McGarry 1977, 247-248).

Figure 4.4 Overhung Latrine (discharging directly into an open canal)Source: McGarry, 1977, 247.


4.3.2. Pour-flush latrines

Pour-flush latrines are distinguished from the sanitation technology discussed above in that theyemploy a water seal. A pour-flush latrine is comprised of a seat or squatting pan with a “steeplysloped base,” a water-seal trap in the form of a U-pipe filled with water, and a pipe (maximumlength 8 metres) leading to a soakage pit or septic tank (see Figure 4.5). In the case of a soakagepit, it is recommended that a twin pit system be used, taking into consideration of course the easeof pit emptying, the system used to empty the pit (manual or mechanical) and whether there issufficient space in high density areas. These details have all been discussed in above sections.Pour-flush tanks are most appropriate in situations where anal cleansing with water is the nonn(e.g. many Asian countries) and where a low volume of water use for flushing is desired. Theadvantages of the pow-flush system include: lack of insect and odour problems; the ability tolocate the latrine inside a building and on levels above the ground floor, the flatness of thegradients required, avoiding deep excavation and pumping; and potential for upgrading to sewerconnection. Disadvantages include: lack of suitability in areas where bulky anal cleansingmaterials are the norm and the requirement of a reliable, if small, water supply.

110 600

Earth fillin 20mm fine sandlayer over SOnnbroken bricks

Open brickwork

_____________

4A

1000

Figure 4.5 Pour-Flush LatrineSource: Cairncross and Feachem, 1983, 125.

Installation and maintenance costs are reasonably low, similar to that of a Ventilated ImproyedPit latrine (IJS$ 75-150) and one quarter of the cost of a waterbome sewage system—providedthat the latrine is connected to a soakage pit and not a septic tank or sewer system. The systemdoes however, require a minimum of technology: a deep squatting pan, pipes and pit reinforcingmaterials. With a strong educational component and technical supervision, sanitation projectsusing pour-flush latrines can be devolved to the community level. Given a reliable water supplyand regular pit emptying, this system works very effectively, and can easily accommodatewastewater being discharged into the system where ground conditions have decent absorptionrates (Cairncross and Feachem, 1983, 124-126; Sinnatamby, 1990, 136-142).


4.3.3. Vault toilets and cartage

The vault toilet is in essence a pour flush system with the addition of a watertight privy vault(tank) to store toilet wastes for several weeks. Removal every two to four weeks by a vacuumtanker is then required. With this system and other receptacles requiring periodic emptying,there are related concerns; although emptying removes human wastes from the immediate livingarea, it can induce unhygenic and offensive circumstances. Appropriate cartage, or the system oftank/pit emptying through mechanical pumping and removal by vehicle for treatment elsewhere,can be an effective response. Cartage has the advantage of being easily adaptable to changes indensity of land use and, technologically, can range from a simple animal-drawn cart with a smalltank and manual hand pump to a large vacuum tanker truck. However, in terms of technology, aseat/squatting pan and watertight tank are required. Cartage has the disadvantage of tendingtowards higher operating costs than on-site disposal and certainly requires more organizationaleffort on the part of municipal authorities. Access to the tanks may be difficult if care is nottaken to keep a suitably-sized path open and traffic congestion may slow the cartage process.Addition of grey water to the tank would dramatically increase the required emptying frequency(Caimcross and Feachem, 1983, 127).

4.3.4. Aqua privies

In its traditional design, the aqua privy consists of a squatting pan/seat, a vertical chute or drop-pipe 100-150 mm in diameter, and a watertight simple (septic) tank. The liquid waste level mustremain at all times at least 100-150 mm above the end of the pipe in order to maintain the waterseal necessary to protect the user from the tank contents. A ventilation pipe, allowing gas to passout of the tank, is also appropriate. The aqua privy requires the addition of approximately 18litres of water per day to replace tank losses via the chute. The tank itselfperforms in the mannerof a septic tank where solid wastes sink to the bottom and are digested by anaerobic bacteria toform gas and semiliquid. Tank overflow is disposed of through a soakaway pit and the tankrequires emptying (desludging) when it becomes two thirds full. Conventionally, aqua privies donot account for the disposal of sullage.

Advantages of the aqua privy include its suitability in areas where anal cleansing using water iscommon and its sanitary quality high when properly managed. However, significant problemswith the operation of the privy have been far too common. ‘Where the water seal is notmaintained, the privy ceases to function properly and becomes attractive to insects and rodents inaddition to emitting unpleasant odours. This can occur either through a crack in the tank orthrough a failure on the part of the users to maintain the water level. If a reliable and easilyaccessible water supply is not readably available or if there is a social stigma attached to carryingwater to the privy (most aqua privies are located outside the house for cost, sanitary, cultural andsituational reasons), a water seal failure is almost inevitable. Also, soakage pits in inappropriatesoils are frequently clogged especially when overused through attempting to introduce sullagedisposal into the system (Caimcross and Feachem, 1983, 130-13 1; McGarry, 1977, 255; Kaoma,1980, 41-47; and Wilson, 1980b, 48-49).


Given the considerable problemsassociated with the conventionallydesigned aqua privy, importantmodifications and improvements werenecessary to overcome the basic flaws.The following type of aqua privy isderived from the combined eqeiieixeswith Zambia’s self-topping aqua privyand the Botswana “Type B” one (seeFigure 4.6). As a top priority, theimproved design must first incorporatethe discharge of household wastewaterinto the privy, which has theadvantages of being both an integratedmethod as well as keeping consistentwater levels in the tank. In fact,

__________

washing facilities (for both bathing and

______

household washing) can be constructedimmediately adjacent to the privy, andmay be fed through the toilet itself tohelp clean it.

•

Secondly, since the use of soakage pitshas resulted in a number of problems,the improved design is directlyconnected to a covered sewer system.The tank is still used in thesedimentation process for solids and topretreat organic solids so that they arein a suitable form for transportation inthe sewer. In addition, it may form thestructural foundation for the toiletfwashing building. The sewers carry the

wastes to stabilization ponds, since anaerobic pretreatment has occurred in the tank a muchhigher number of individuals can be served by a smaller pond. Since there are no solid-catchingtraps throughout the system and since stones and sand are not present in the effluent destined forthe ponds, flow problems are few and infrequent. However, the tank still requires regularmonitoring and desludging when necessary. The main advantages of the improved design includea properly functioning (and hence very sanitary) water seal; savings on sewer lines due toreduced pipe size and velocity of flow (due to high liquidity of effluent) and reduced total pipelength (due to ability to locate odourless ponds near the source of waste); water savings sinceonly waste water is used to “flush” the privy; and potential devolution of much of themaintenance work to the community level for unskilled workers. The disadvantages of thedesign, under decent conditions, are usually limited to problems with irregular sludge removal

Sunny side

Black ventpipe withfly screen

ManholelSink

___

4 V77

cover III I rvateriev.ej.Jf ior slab

IILJ’ —To soakaway U Chute r -

1 1 Sand/cement-tBackfillrendering _j;I—I Blocks4

Figure 4.6 .Botswana Type B Aqua PrivySource: Wilson, 1980a, 48.


and a relatively high construction cost, usually comparable to a flush toilet/wash basin unitconnected to a sewer system (Kaoma, 1980,41-47 and Wilson, 1980b, 48-49).

4.3.5. Cistern-flush toilets

The cistern-flush toilet is easily conceived--one need only to envisage the averge Westernbathroom to picture this type of sanitation device. The most common form involves a base withseat (and often lid) with a cistern or water holding tank. Although this system is very sanitaryand is able to accommodate the addition of items other than human body waste (toilet paper,etc.), it is relatively costly, tends to use a large amount ofwater per flush and is dependent upon areliable water supply and sewer system.

4.4. Septic tank systems

First introduced in England in 1895 by Donald Cameron, the septic tank system consists of atoilet feeding into a large watertight tank usually placed below ground, which in turn feeds into adisposal field or sewer (see Figure 4.7). The tank receives grey and black water, that ishousehold wastewater and toilet wastes, by means of a short sewer pipe. The tank itself isintended to slow down the movement of the wastes into the absorption mechanism or sewer, andso prevent premature clogging, by settling out the solid matter, and breaking it down throughliquefaction and anaerobic bacterial action (see Figure 4.8). The solids ferment on the bottom ofthe tank (and must be removed on an infrequent basis) while the effluent passes on, within 24hours, into a sewer system or, more likely, into a soil absorption system (Cairncross andFeachem, 1983, 127-129; Ehlers and Steel, 1965, 112-119; McGarry, 1977, 251; Salvato, 1992,512, 519-520, 523).

For a private home, inspection of the tank should occur annually and desludging every three tofive years by a vacuum truck, depending on tank size and use. There is no need to add heavyduty cleaning solvents to the tank, in fact, these may only succeed in causing solids to be carriedover in to the absorption field, and the clogging of the field itself. Care should also be taken toensure that the following problems do not arise: excessive water overloading of the tank, unevensettlement of the tank or associated equipment, and failure due to improper or inadequatemaintenance. In addition, the septic tank system itself is relatively high in cost and is thus onlysuitable for middle to upper income neighbourhoods of developing countries. The one basiclimiting factor for the use of septic tanks in urban areas is density. Usually, tanks are suitableonly in low-density areas with less than 100 persons per hectare. However, through the use ofthree-compartment tanks where household wastewater is fed in only in the third and last settlingtank, the septic tank method is safe and efficient in communities with two to three times thatdensity. Savings might also be realized through the use of large multi-family tanks, such as theImlioff tank (Cairncross and Feachem, 1983, 127-129; Ehlers and Steel, 1965, 112-119;McGarry, 1977, 251; Wolde-Gabriel, 1980, 50-51; Salvato, 1992, 512, 519-520, 523).

Once effluent exits the septic tank, if it does not enter a sewer system, it is deposited into anabsorption field--the most common form being a tile disposal field. This end of the system

20

Figure 4.8 Details for Small Septic TanksSource: Salvato, 1992, 516.

Scmitation Infrastructure

• Septic tank (Larger solids settle to bottom. Greases and oilsrise to top, are trapped, and are periodically removedby pumping to prevent overflow and backup into house.)

Household

Pforatedpi

-Nonperforated pipe

on box

—

Gravel or

-

Drain ILmicroorganis

outi particles)..

.....•.- ‘

Figure 4.7 Septic Tank SystemSource. Miller, 1990,540.

Section on


consists of a distribution box, which evenly distributes effluent to a series of concrete or claypiping, laid with open joints so that the effluent percolates into the soil and is absorbed. Thefiltration removes suspended materials while aerobic bacteria in the soil stabilize organic matter,either suspended or dissolved. For the latter reason, subsurface absorption fields are normallylaid at depths of 24 to 30 inches. In order to ensure absorption, soil must be permeable andsufficiently well-drained (determinable through a soil percolation test and dependent on the rateof sewage flow from the attached dwelling). The open-joint pipe should be laid in a layer ofclean gravel, crushed stone or broken brick, with a layer of straw, hay or untreated building paperseparating the absorption layer from the earth backfill on top of it (see Figure 4.9). Attentionmust also be paid to the laying of absorption pipes on careful grades (Ehlers and Steel, 1965,127-130; Sinnatamby, 1990, 143; Wolde-Gabriel, 1980,50-51; Salvato, 1992,538-574).

Overfill lo oThiw for sWlkmerilr-2’o/slraw, elc., or

untreated building paper

f 7 1/ III .

f 0 0 I /Earth backfill ‘

.7 f’ f 6NlOl2v

,y,

I/i.• J 2L

U —

4 06”min.

Opening (10 [.—.72’1o 36—j

Figure 4.9 Septic System Absorption TrenchSource: Ehlers and Steel, 1965, 125.

Obvious advantages tÔ the septic system include on-site treatment producing higher qualityeffluent and adaptability to absorption field or sewer system (and hence upgradability).Disadvantages include the often prohibitively high cost of installation, skilled labour and costrequired in upkeeR (monitoring, desludging, etc.); inappropriate soil conditions; insufficient land(absorption fields require substantial amounts) and hence inappropriateness for high densityareas; potential contamination of ground or surface water; municipal abrogation of serviceprovision responsibility since the system is so easily relegated to private responsibility; and the

• requirement of substantial amounts of water. However, certain responses may answer several ofthose disadvantages. Firstly, soil condition problems can be overcome through the constructionof raised bed absorption-evapotranspiration systems or mound systems in those areas where thesoil cannot sufficiently absorb the effluent. Multiple-family tanks may help to solve spaceproblems and reduce per capita tank cost, but will necessarily involve increased total pre-tankpipe length and will entail different management arrangements (Ehiers and Steel, 1965, 127-130;Sinnatamby, 1990, 143; Wolde-Gabriel, 1980, 50-51; Salvato, 1992, 53 8-574).


4.5. Other simple on-site disposal systems

4.5.1. Leaching pits and cesspools

Leaching or seepage pits are used in the disposal of settled, but treated, sewage (see Figure 4.10).They are particularly useful in those instances where the upper soil layer is impervious butpermeable soil exists below. These on-site disposal systems consist of covered pits, where

the earth sidewalls ofthepit have•not been sealed in the digging orboring process but remain penneable

pijr, ,emovawe for inspeclion and where the walls are subsequently

-- ... . lined with bricks laid withoutmortar. The bottom ofthe pit must

:7:2 cemenimrtc7r be no less than two feet above the

ground water level to avoidIntel pie (reinforcing bar contamination. Cesspools, also a

• - covered chamber designed to receive

: waste, differ from leaching pits in: that they receive untreated wastes

• E directly from the household (in fact,—No rnprlar a septic tank is an improved and

o In joints watertight form of cesspool). Ifused- - ,, ,- ., as a means ofallowing waste

Avot7ab/e 0 - - —6 of to! . -

Ie; : — J rack or gravel absorption mto nearby soil,o cesspools may eventually block the

pores of the soil and cause overflow.= : Since leaching pits and cesspools in

radiallyconcentrated pollution source, they

..—FirsI layer ofbricks essence constitute a highly

ought not be employed at all in areaswhere groundwater is the source of

- 24 drinking water. They are also often0 attractions for insects and a source of

• — unpleasant odour. In general,taielo groond although leaching pits and cesspools

2ff rn!afnwm are easily constructed andmaintained at low cost, they canhave huge environmental impactsand are limited in what they may

Figure 4.10 Seepage Pit reasonably be used for (CairnorossSource: Ehiers and Steel, 1965, 125.

and Feachem, 1983, 131-l32;Ehlersand Steel, 1965, 112, 123-125;Salvato, 1992, 534-537).


4.5.2. Sullage

Sullage, by common definition, consists of all household wastes excluding toilet wastes (blackwater) and may alternately be called grey water. Methods for sullage disposal include grounddisposal (on or off-site) in permeable soil areas; leaching pits; pit latrines; open drains; covereddrains or sewers. Since all sullage contains some pathogens, it always constitutes a potentialhealth risk. It may be a breeding ground for (disease-carrying) insects when left to stand in poolsor a potential groundwater contaminant from leaching pits. Disposal through drains, either openor covered, must also account for sufficient velocities in dry seasons to carry the wastewaterAlthough usually not of the same biological toxicity as black water, sullage disposal can easilyrun into the same problems as disposal of toilet wastes. Costs and technical requirements varyenormously with the chosen means of disposal. Sullage disposal methods may or may not beintegrated with black water disposal, environmentally sustainable, or able to be devolved to thecommunity level (Douglas, 1983, 148 and Njau, 1980, 59-60).

4.6 A comparison of toilet systems

As was indicated in the introduction of this handbook, there are a multitude of considerations indealing with sanitation technology. This section on toilet systems has attempted to present anumber of these considerations when dealing with each separate system. With such a hugevariety of possible systems and an equal variety of locations and local circumstances, it mightseem impossible to productively compare the different toilet systems. Table 4.1, however, is anattempt to do just that. What is important to note is that there are a variety of choices and tradeoffs to be made when selecting a given system for implementation, and that these factors canvary from constructing and operating costs to average water requirements.

5. SEWERAGE: THE COLLECTION, TREATMENT, AND DISPOSAL OFDOMESTIC WASTEWATER

In the previous. section, various in situ sanitation technologies were discussed, ranging fromsimple systems, such as pit latrines, to more sophisticated systems, such as Inthoff (septic) tanks.By virtue of their relative simplicity and scale, these sanitation systems are most suited forserving remote areas and lower-density or small communities.

Having different performance requirements than those in remote or smaller communities, higher-density urban sanitation infrastructure generally relies on technologies that are moremechanically advanced. Not only must the system serve a much larger population base, but itmust also serve a more complex and vast geographical area. To this end, sewerage systems arethe conventions by which cities collect, treat, and dispose of domestic as well as industrialwastewater. This section of the handbook will deal primarily with conventional as well asunconventional methods of handling domestic wastewater. Within a sustainability context, thesection will also examine the possibility of recovering and reusing both effluent and sludge (aby-product of the treatment process). The next section of the handbook will deal with industrialwastewater.


Table 4.1 Comparison of Toilet Systems

Sanitation Rural Urban Construc- Operating Ease of Water Integratedsystem applica- applica- tion cost cost construc- requirem with other

tion tion lion ent infrastructure

. systemsBucket suitable suitable low medium very easy none nolatrines -

Pit suitable not low low very easy, none nolatrines suitable in depending

high- on soildensity conditionsareas

Compost- not suitable not high high none noing toilets suitable in

high-densityareas

Overhung suitable may be low low very easy requires a may belatrines suitable circulatin integrated

g water withbody organic

solid wastedisposal

Pour- suitable suitable medium low requires water near may beflush builder toilet possibletoiletsSewered not suitable suitable high medium requires water integratedpour- engineer piped to with waterflush building supplytoiletsVault not suitable suitable medium very high requires minimal may betoilets where builder possibleand access andcartage mainten

ance arereasonabiy possible

Aqua not suitable suitable medium to high requires reliable may bepnvies high builder supply or possible

water neartoilet

Cistern not suitable suitable very high high requires water integratedflush where engineer piped to with watertoilets affordable building supplySeptic suitable suitable in high high requires water integratedtank low- builder piped to with watersystems density building supply

areas

Source: Cairncross and Feachem, 1983, 147.


5.1 Characteristics of domestic wastewater

Domestic wastewater contains primarily organic and inorganic matter as suspended, colloidal,and dissolved solids from garbage, food preparation, household chores (cleaners and detergents),and human wastes (Arceivalla, 1981, 131). Their concentration in the wastewater depends on anumber of factors, namely, the original concentration in the water supply; the climate; and thewealth, health, and habits of people. Of the variety of organic matter that is introduced into thedomestic waste stream, human excreta is of chief concern because it contains a concentratedpopulation of pathogens (disease-causing agents), the major categories of which include:viruses, bacteria, protozoa, and helminths (parasitic worms) (Hammer and Hammer, 1996, 59).As previously mentioned, typhoid, cholera, bacterial dysentery, polio, and infectious hepatitis aresome of the common diseases caused by pathogens that are transmissible through contaminatedwater. Because sewage-contaminated water is a threat to public health, periodic tests are madefor the presence of sewage. Although many different microorganisms thrive in sewage, thecommon intestinal bacterium Escherichia coli is typically used as an indication of the amount ofsewage present in water and as an indirect measure of the presence of disease-causing agents(Miller, 1990, 518).

Another chief concern is the nonliving organic matter present in sewage because of the decayingprocess it undergoes. Microorganisms use oxygen dissolved in the water when they degradeorganic material. As the microorganisms metabolize the organic matter, they use up theavailable oxygen. When oxygen is depleted, anaerobic bacteria take over the decay process andproduce a by-product that has a foul odor.

5.2. Wastewater collection systems

Although there are in existence several methods of collecting wastewater, only the more commonsystems will be discussed here. These include conventional, small-bore, and shallow seweragesystems (see Table 5.1).

5.2.1. Conventional sewer systems

In most urban areas, waterborne wastes from households, industries, and storm runoff areconveyed by gravity flow through a network of underground, watertight conduits to centralwastewater treatment plants or to points of disposal off site. This network of pipes, or simplyput, sewer system, can either be combined or separated. The combined system is less expensiveto build but the main drawback is its performance during extended periods of copious rainfall,when the total volume of wastewater and stormwater flowing through the system usually exceedsthe processing capacity of treatment plants. Consequently, the overflow, which containsuntreated sewage, is discharged directly into surface watercourses (Miller, 1990, 541). Incontrast to the combined system, storm sewers in the separate system carries only surface runoffand other relatively uncontaminated waters to natural channels directly, while sanitary sewers


Table 5.1 Summary Analysis of Wastewater Collection Systems

Conventional Small-bore ShallowCharacter- • large diameter • 4 to 6 inch diameter • small diameter conduitsistics conduits (minimum conduits laid at flatter (2 to 4 inches) laid out

8 inches up to gradient and connected to in shallow trenches (1several feet) mterceptor tanks to 2 ft below grade)installed at slope • wastewater carried by • branch networkdeep below grade pipes is partially treated connection requinng

: minimal pipmg. . wastewatercarried by

pipes is partiallytreated

Cost • $ 800 - 1200 • if retrofitted, can cost less • costs range from $ 65 -

US/house in than$ 100 - 500 325 US/house indeveloping countries US/house developing countries

. up to $ 5000 • ifnew, can cost almost as • costs per householdUS/house in much as conventional decrease as densitiesdeveloped countries systems in developing increase

countriesLimitations • not appropriate for • cost-effective only as • cost-effective in areas

small, remote or retrofit system of high density (190poor communities • require additional land inhabitants/hectare)

. expensive and area for interceptor tanks; • require hiEh frequencydifficult to repair not appropriate where ofwater flowing

• intensive processes land shortage is a through pipe systems torequiring skilled problem prevent solidsdesign and careful • difficult to access and accumulation; the moreoperation remove sludge from densely populated the

• no preliminary interceptor tanks area, the better thetreatment; 100% system worksreliance on off-sitetreatment

. lengthy constructionor connection period

Integration • can be easily and feasibly • can be easily integratedretrofitted to upgrade with existing systems

—--- existing on-site sanitary • add-on connections forschemes new households are

inexpensive and simpleEfficiency • 3ppropriate for high • appropriate for high • no risks of pipe

density urban density settlements blockage; wastewater issettlements • almost no risk of system filtered through grit

. self-cleaning; failure due to clogging and grease traprequires low- • can reduce off-site • repairs can be easilymaintenance treatment requirements and inexpensively

• high performance, by 40 to 60% effected - no disruptionlow rate of failure to surroundings and nobut standard require- impairment to entirements are excessive block systemcontributing to highmaterial andconstruction costs

Management • public work • public authorities • public authoritiescentrally managed responsible only for responsible only forby municipal submain and main sewers relatively short lengthsauthorities in public right-of-way of street or block

• permit management at sewerscommunity level; local • households entirelyinitiation and responsible formaintenance of project maintenance and repaircost 75% less than public of sewer segments laidprovision of same service on their property

Source: Hammer and Hammer, 1996 and Sinnatamby, 1990.


convey domestic and industrial -wastewaters (separately) to treatment works for processing priorto their disposal (Hammer and Hammer, 1996,320-322).

Waste discharges from households are collected and carried by street laterals (up to 8 inches indiameter) to branch sewers. There are no tributary sewer lines; each house has its own serviceconnection to the branch or submain lines, which then convey the wastewater received to largemains (see Figure 5.lb). In turn, main sewers, also referred to as trunlç or outfall sewers, finallycany the discharge by gravity flow or pressure to central treatment plants.

__/

___________—,

‘—

!‘!!%--

To S(reet sewer

b

Figure 5.1 Shallow Sewer and Conventional Sewer SystemsSource: Sinnatamby, 1990, 149.

By and large, conventional sewer systems have proven to be highly effective and efficient incities of developed cáuntries. However, because of their high capital and operational costs, aswell as technological complexity, their transference to most developing countries would be.highly inappropriate (refer to Table 5.1 for a comparison with other systems). In terms of costs,rigid construction standards and design specifications combine to make this technologyprohibitively expensive for most cities in the developing world. For example:

• the minimum recommended size for laterals is 8 inches, even though pipes half thespecified diameter have been proven to be equally effective (Hammer & Hammer 1996,333);

• the volume of wastewater from a community normally varies from 50 to 250 gal percapita per day (gpcd); a common value for domestic wastewater flow is 120 gpcd (450lipid), assuming that the dwellings have modern water-using appliances, such asautomatic washing machines. Most sewer systems, however, are by requirementdesigned forfiows in excess of400 gpcd (Hammer and Hammer, 1996,334);

II


• a minimum gradient requirement of 1 in 70 is specified for the connection of 20households to a 4 in street lateral. But in some communities (of developing countries), agradient of 1 in 167 has proven to be successful for up to 60 households connected to a 4in street lateral, over a period ofmany years (Sinnatamby, 1990, 147); and,

• where velocities are greater than 10 fl/see, special provisions are required to protect pipesand manholes against displacement by erosion. Studies, however, have shown that sewerwear from velocities twice as great has been negligible (Sinnatamby, 1990, 148).

In terms of technological complexity, most developing countries have neither the requiredequipment nor the skilled manpower readily available to build or operate these systems.Consequently, they must purchase equipment or hire consultants from industrialized countries atexorbitant prices and fees. For cities or communities where limiting factors such as these exist,alternative systems such as small-bore and shallow sewers are more appropriate.

5.2.2. Small-bore sewer systems

An alternative to conventional sewerage is the small-bore sewer system. Where on-site sanitaryschemes, such as leachpits or soakaways already exist, small-bore sewer systems can beretrofitted to transport and dispose of effluents that have been partially treated. Prior to reachingsewer pipes, effluents pass through interceptor tanks, like leachpits, where large debris, grosssolids, grit, and grease are removed. When the effluents finally enter the network of pipes, theyare free of solid matters which can accumulate thus permitting small diameter pipes (2 inchescompared with 6 to 8 inches in conventional systems) to be used and laid at flatter gradients.The implications here are significant cost-savings for both material and excavation work, inaddition to savings which arise chiefly from having to process effluents that are 40 to 50 per centcleaner (Sinnatamby, 1990, 144).

5.2.3. Shallow sewer systems

The shallow sewer system is another alternative to conventional sewerage and is essentially amodification of the conventional system itself. It has been adapted to suit particular needs oflow-income and high density communities. Similar to conventional sewerage, domesticwastewater is directly collected and transported by a network of underground, watertightconduits for treatment and disposal off-site. Unlike the parent system, however, sullage isfiltered through inexpensive grit and grease traps (installed in each household) before enteringthe sewer network. Consequently, wastewater flowing through the pipes is free of debris andsolids, thus permitting the use of narrower pipes, up to 4 inches in diameter, and installation atflatter gradients (in backyards and narrow alleyways of houses). The branch-layout of the pipes,as opposed to the conventional circuit layout, permits easy household add-ons and reducesoverall pipe lengths (see Figure 5.la). Another cost-saving feature of this system is its location.By locating sewers away from paths and roads with heavy imposed loads, pipes can be laid inshallow trenches 1 to 2 feet below grade, instead of 11 feet as is required for conventionalsystems.


In summary, compared to conventional sewerage, shallow sewerage inherently has the followingadvantages (Sinnatamby, 1990, 150):

• reduced water requirement - relying on frequency (arising from density) rather thanvolume (arising from high consumption) ofwater flows for self-cleaning operations;

• reduced overall length ofpipes - by 50%;• reduced construction costs through reduced depths and lengths ofpipes;• reduced material costs through use of smaller pipes and easily accessible inspection

chambers;• reduced maintenance costs - less possibility of solid deposition through frequent water

flows ensured by pipe layout; and,• high connection rates resulting from simultaneous construction ofblock and street sewers

5.3. Wastewater treatment systems

Once the waste-laden water has been collected and transported by sewers to a treatment plant, itcan undergo up to three levels of purification to prevent environmental and public healthproblems. The three levels of sewage treatment are classified as primary, secondary, andadvanced (or tertiary). Once the wastewater is treated to the level of purity desired, it isdisinfected before being returned to the environment (Miller, 1990, 541).

5.3.1. Primary treatment

Primary treatment includes the removal of suspended and floating particles such as sand and siltby the mechanical processes of screening and gravitational settling. Once the suspendedparticles have settled at the bottom of the sedimentation tanlc, pond, or lagoon, water is removedfrom the top for secondary treatment (see Figure 5.2). In some developing countries however,this water is released into the environment without further treatment (Enger, 1992,465-466).

Scteen Pniñaiy Aeradon tank Secoiiday t1toinator

Ra

t.Slj::;tdr

Sludge

.1 Digested sewage sludge

Figure 5.2. Primary and Secondary Treatment Processes in Conventional SystemsSource: Enger, 1992, 355.


Although primary treatment removes up to 60 per cent of solids, it only removes 25 to 40 percent of oxygen demanding wastes (Enger, 1992, 354). Thus, a heavy load of organic matter,

such as dissolved salts, bacteria, and other microorganisms, is still carried by the water. Incrowded areas where several municipalities take in water and return it to a lake, river, or streamwithin a few kilometers ofeach other, primary treatment is not adequate.

5.3.2. Secondary treatment

Secondary treatment usually follows primary treatment, it is a biological process relying onmicroorganisms to decompose the remaining suspended organic matter in the wastewater. Toencourage this action, the wastewater is mixed with large quantities ofhighly oxygenated water,or the water is aerated directly, as in a trickling filter system. In this system, wastewater issprayed over a large vat of rocks, as it trickles through bacteria and other microorganismsdecompose the organic materials contained in it. In another type of secondaiy treatment knownas activated sludge, water is aerated and circulated through bacteria-rich particles; the bacteriadecompose suspended organic material (see Figure 5.2). After several hours, the particles andmicroorganisms are allowed to settle out forming sewage sludge, a slimy mixture of bacteria-laden solids (Enger, 1992,356).

Even after primary andsecondary treatment, waste-water still contains detectablelevels of pollutants, includingviruses and pathogens, whichcan have harmful effects onhumans and the bioticenvironment (see Figure 5.3).Yet, most cities, even thosein developed countries, stoptreatment at this phasebecause tertiary treatmentplants cost twice as much tobuild and four times as muchto operate as secondaryfacilities (Miller, 1990, 543).

ucae :: -

‘ip.Q,kciaioa

enc

Figure 5.3 Persistent Chemicals and BacteriaSource: Miller, 1990,544.

Although secondary treatment is effective in removing up to 90 per cent of suspended solids andorganic waste, it is only effective in removing 30 per cent of phosphorous (an algae promotingagent), and 5 per cent of heavy metals, radioactive isotopes and pesticides. In communitieswhere these pollutants are likely to be present in high concentrations, or in areas where treated

wastewater is injected directly into deep wells to replenish depleted aquifers, a third treatment

process is necessary to avoid contamination and minimize the risk of waterbome disease

outbreaks (Miller, 1990, 544).


5.3.3. Advanced or tertiary treatment

Advanced or tertiary treatment methods include a variety of biological, chemical, and physicalprocesses that remove dissolved pollutants left after primary and secondary treatments. A singleprocess or a combination of these processes may be used (see Table 5.2).

Table 5.2 Advanced or Tertiary Treatment Techniques and Methods

Technique Problem Methodschemicals

Biological Phosphorous 1. Large ponds are used to allow aquatic plants toand nitrogen assimilate the nitrogen and phosphorus compoundscompounds from the water before the water is released.

2. Columns containing denitrifying bacteria are used toconvert nitrogen compounds into atmosphericnitrogen.

Chemical Phosphates 1. Water can be filtered through calcium carbonate. Theand industrial phosphate substitutes for the carbonate ion, and thepollutants calcium phosphate can be removed.

2. Specific industrial pollutants, which arenonbiodegradable, may be removed by a variety ofspecific chemical processes.

Physical Primary 1. Distillation.industrial 2. Water can be passed between electrically chargedpollutants plates to remove ions.

3. High-pressure filtration through small-pored filters.4. Ion-exchange columns.

Source: Enger, 1992, 359.

5.4. Alternative treatment systems

Although the mechanical biological treatment of sewage has become standard practice in mostdeveloped countries, this method is not suitable for developing countries where shortages ofcapital, scientific knowledge and skilled labour currently exist. As methods of treatment becomemore and more sophisticated, it tends to be forgotten that simple, low-cost wastewater treatmentmethods can also be relied upon to deliver high quality treatment, particularly in societies whereimpediments exist to the adequate provision of sanitary services. Some of the simpler and morecommon methods include ponds, lagoons, wetlands, and aquaculture.


5.4.1. Waste stabilization ponds and lagoons

Employed for treatment of wastewaters for over 3000 years, waste stabilization ponds are thesimplest and, consequently, least expensive form of treatment techniques (Smith-Vargo, 1991,27). They can be used alone or in combination with other wastewater treatment processes andcan function under a wide range of climatic conditions ranging from tropical to arctic. Thismethod of treatment involves holding the wastewater in shallow ponds for a sufficient detentionperiod to render the wastes stable and inoffensive for discharge to receiving watercourses or land.Stabilization is assisted by various physical, chemical and biological processes commonlyreferred to as self purification. This process results in organic matter being broken down throughbacterial activity to become more stable end products. With the exception of the aerated types,pond systems operate under entirely natural conditions without the benefit of any man-madeaccelerating devices, such as heating and mechanical aeration. The advantages anddisadvantages ofpond systems are described below (Smith, 1987, 345-347).

The advantages of pond systems stem from their extreme simplicity and reliability of operation;there is no equipment to fail and no tricks to successful operation. But nature takes time,requiring long detention periods which in turn imply large land requirements. Biological aetivityis also considerably affected by temperature, more so in the pond’s natural conditions. Thus,waste stabilization ponds are most appropriate where land is inexpensive, climate favorable, anda simple method of treatment that does not require equipment and operating skills is possible.

The cost of waste stabilization ponds is generally very competitive as long as land costs are notexcessive. Construction is simple involving mostly earthwork and operating costs are practicallynegligible compared with other conventional methods of treatment. Like all other treatmentsystems, ponds also have their limitations, although in terms of performance they are almost likea conventional system. Their low cost has sometimes led some to feel that ponds may be inferiorin performance, but this is not generally the case. Often ponds have proved more reliable in thelong run than other methods (Arcievala, 1981, 741-743).

Stabilization ponds and lagoons are classified by type of biological reaction, duration, or theextent of treatment of wastewaters before entering the pond. The most basic types are:

1. Facultative ponds, also known as oxidation ponds, sewage lagoons, and photosyntheticponds. These are the most common type and are usually 4 to 8 ft in depth, with anaerobic layer overlying an anaerobic layer, which often contains sludge deposits. Theusual detention time is 5 to 30 days. The key to facultative operation is oxygenproduction by photosynthetic algae and surface reaeration. The oxygen is used by theaerobic bacteria in stabilizing the organic material in the upper layer. The algae arenecessary for oxygen production, but their presence in the fmal effluent represents one ofthe most serious performance problems associated with facultative ponds. Despite thisproblem, there is an advantage to this situation. Algae are rich in protein and if harvestedand sterilized by heat treatment they can provide a source of high protein food foranimals (Arceivala, 1981, 746-750).


2. Aerated ponds, usually followed by facultative ponds, are used for first-stage treatmentof high-strength municipal wastewaters and for pretreatment of industrial wastewaters.The basins are generally 10 to 12 ft deep with detention times of 3 to 10 days. The chiefadvantage of aerated ponds is that they require less land area, but because they aremechanically aerated, they require a constant input of energy (Arceivala, 1981, 750-752).

3. Aerobic ponds are shallow ponds of about 1 to 1.5 ft depth with a retention period of 3 to5 days. Being limited to warm sunny climates, they are designed to maximize lightpenetration and growth of algae through photosynthetic action. Aerobic conditions aremaintained throughout the depth of the pond at all times, and the wastes are stabilizedentirely through aerobic microorganisms. Aerobic ponds are useful where the ultimateharvesting of algae is desired, but their use in waste treatment has not been widespread(Hammer and Hammer, 1996,403).

4. Anaerobic ponds require no dissolved oxygen for microbial activity. Anaerobicorganisms use oxygen from compounds such as nitrates and sulfates which areabundantly available in the waste, and produce end products such as methane and carbondioxide. They are usually 8 to 16 ft in depth and have detention times of 20 to 50 days.Anaerobic ponds are usually used for treatment of strong industrial and agriculturalwastes or as a pretreatment step where an industry is a significant contributor to amunicipal system. Their effluents are generally not fit for discharge without furthertreatment, and are therefore, often provided in tandem with facultative ponds whichfollow them (Dixo, Gambrill and Catunda, 1995, 275-277).

5. Maturation ponds, also referred to as tertiary ponds, receive wastewaters which havebeen pretreated either in ponds or conventional treatment plants. They are generallydesigned to have a retention period of 3 to 7 days with a depth of 3 to 5 ft. The effluentsreceived from secondary treatment processes are exposed for a further period of time withthe main purpose of removing enteric bacteria and viruses through bacterial die-off. Inwarm climates, these ponds may constitute an economically feasible alternative todisinfection by chlorine (Nurdogan and Oswald, 1995, 34-36).

A series of conventional stabilization ponds normally consists of; an anaerobic pond, whichfunctions like a septic tank to sediment sewage solids, followed by facultative and maturationponds (see Figure 5.4). If designed properly, this system can be nearly as effective asconventional primary and secondary treatment methods, but will only cost a fraction of theamount required to build a conventional treatment plant (Dixo, Gambrill, and Catunda, 1995,279-280).

5.4.2. Wetland systems

Another low-cost alternative to conventional treatment plants are wetlands which are simple tooperate and maintain (see Figure 5.5). In particular, they are attractive alternatives for small,poor, or remote communities to meet their domestic wastewater treatment and water qualityneeds. More importantly, they require relatively low capital and operating costs in comparisonwith conventional systems. Wetland systems are typically characterized by emergent aquaticvegetation such as cattails, rushes, buirushes, sedges, and reeds which, symbiotically, are

BIOG

ASOF

F

U3.(JA

W

Uot

uroU

onpo

nd2

Fig

ure

5.4

Sche

mat

icD

iagr

amof

Dig

este

ran

dSt

abif

izat

ioli

Pon

dsSo

urce

:D

ixo,

Gam

brill

and

Cat

unda

,19

95,

280.

SCRE

EN

WAS

TEW

ATER

FLUM

E

F’ p2Su

bmer

3ble

pum

pM

eter

ing

pum

p

p1

8T F, U,

8o1a

ncng

tank

Seco

ndar

yfo

culto

Uve

pond

Mat

urat

ion

pond

SUPE

RNAT

ANT

Uat

uroU

onpo

nd3

tJpf

lowan

aero

bic

ztud

gebl

anke

tre

acto

r

7/S

LU

DG

EBt

.ANK

EI/7

1

is .1

Pham, Rowe-Evans, and Shigehisa

a viable, feasible, and environmentally sensitive method oftreating municipal wastewater(Bhamidimani et al, 1991, 24S-250).

Both natural and constructedwetlands can be effectivelyemployed in a treatmentprogram, but the concept mostlikely to offer a cost-effectivetreatment alternative is the use ofconstructed wetlands. Constructing a wetland avoids regulatoryentanglements associated with

_______ ______

discharge quality standards innatural wetlands and allowsdesign of the wetland foroptimum wastewater treatment(Bhamidimani et al, 1991, 250-253). Essentially, a constructedwetland is an artificial complexof saturated substrates, emergentand submergent vegetation,animal life, and water. in this

______

system, three major combinations involving wastewater andwetlands can be observed:• disposal of partially treated

effluents into wetlands• use of effluents or partially

treated wastewater forenhancement, restoration, orcreation ofwetlands; and,

• use of constructed wetlandsas a wastewater treatmentprocess.

All three categories provide some degree of wastewatôr treatment, either directly or indirectly.The fundamental mechanism which facilitates biodegradation in this system is the diffusion of•waste components into the bioflims on the submerged stems and roots of plants. But the processof nutrient uptake is likely to be minimal unless the plants are periodically harvested andreplaced. Other system components having some influence in the treatment process are soils,

capable of coliform reduction, nutrient removal, and polishing treatment of primary effluent.Although natural wetlands have been used by a number of small communities to purify water forat least a hundred years, only recently have they been recognized by the scientific community as

35

Surracejiow Wetland

Sutsurrace-Flow Vetlnd

4I4rVertical-Flow Wetland

Figure 5.5 Wetland SystemsSource: Bhamidimarri eta!, 1991, 248.


bacteria, and animals (Bhamidimarri et al, 1991, 253). Their function and the systemperformance are in turn influenced by water depth, temperature, and dissolved oxygenconcentration (see Table 5.1 for a summary analysis of the system).

5.4.3. Aquaculture systems

Aquaculture systems offer yet another alternative to conventional treatment methods and can beeither designed to serve the singular purpose of treating wastewater, or the dual purpose oftreating wastewater and rearing fish or other forms of aquatic biomass. In developed countries, itis common to find systems designed for the singular purpose, but in developing countries, it ismore common to find systems designed for both purposes.

Aquaculture systems can also be designed for different treatment requirements, for example; inthe treatment of raw wastewater, primary effluent, upgrading of existing secondary treatmentsystems, or for advanced secondary or even tertiary treatment. In the case of secondary treatmentrequirements, the design for aquaculture systems is essentially the same as that for facultativeponds but the performance of the former is significantly better than the latter owing to theaddition ofplants and animals.

Similar to wetland systems, aquaculture systems rely on aquatic plants and animals to naturallypurify wastewater. One major type of plant or animal, as in a monoculture operation, or a varietyof plants and animals, as in a polyculture operation, can be employed. The major biologicalcomponents in this treatment process include floating plants, fish and other animals, planktonicorganisms, and submerged plants. Emergent plants can also be used, but these are morecharacteristic of wetland systems. The treatment responses in aquaculture systems are due eitherto the direct uptake of material by the plants or animals and by the presence of the biota alteringthe physical environment in the system. Or, as is the case of water hyacinths, the plant’s rootsact as the host substrate for attached microbial organisms which provide a very significant degreeof treatment. All of these plants and animals have specific environmental requirements that mustbe maintained for their successful use, and in some cases a regular harvest is necessary to ensureoptimum performance. Harvested materials, such as hyacinths, have beneficial secondary uses.They can be dried and composted, and then used for soil conditioner or fertilizer (Kumar andGarde, 1990, 153-156; and Roseland, 1992).

The construction of pond systems in developing countries, namely those with tropical climates,may provide an environment for the breeding of vectors, particularly mosquitoes that cantransmit disease agents such as malaria and filariasis. The addition of fish to ponds, however,diminishes this danger since mosquito larvae are consumed by the fish. The waste-fed fishthemselves are an important source of protein, and in most cases are suitable for humanconsumption. Although the practice of recycling wastes to add nutrients to and improve theprotein production in aquaculture ponds is an ancient practice in many developing countries,there is still some social resistance, primarily from developed countries which view it as anunsanitary practice. The very idea of consuming fish raised on human or other wastes may be an


Table 5.3 Advantages and Limitations of Various Treatment Systems

Treatment Advantages LimitationsSystemsConventiona • Do not require vast land areas • Prohibitively expensive for developing1 Systems • Old technology, results are predictable countries & extremely energy intensive

• Best for large and high density urban • Susceptible to ‘shock loading’ orareas sudden inflows of toxins resulting in

discharge ofuntreated effluent inreceiving waterways

. Produce large quantities of toxic sludgePond and • Low capital and operating costs • Requires large land takeLagoon • Simple to operate and maintain • Loss ofwater through evaporation orSystems • Constant availability of treatment, no seepage

risk of system failure • High algal growth content of effluent,. Good pathogen removal risk of eutrophication in receiving• Rely on unlimited solar energy waterbodies. Capable ofwater reclamation • Uncertain and variable effluent quality• Recycle nutrients • Suitable for areas with high incidence• Algae can be combined with grains to of sunlight

produce valuable feedWetland • Require low energy input • Require a lot of landSystems • Simple to operate and maintain • Cannot treat effluent with high algal

• Low capital and operating costs content. Environmentally sensitive • Not suitable for cold climates. Provide habitat for wildlife • Decrease in efficiency over time due to• More attractive than treatment plants; accumulation of dead plants

can include ornamental plants • Require regular plant harvest• Produce biomass which can be • Suitable for small, low density

composted and used as soil communitiesconditioner or fertilizer • Slow process

• No sludge production • Require supplemental disinfection. . Good removal of some toxic • Can only remove degradable pollutants

chemicals and trace organics and some toxic chemicals• Used as secondary/advanced treatment • Possibility of mosquito and rodent

without chemicals or a lot of energy problemsAquaculture • Can be easily integrated into low cost • Sensitivity to low temperatures. RequireSystems sanitation systems temperature above 10 degrees Celsius

• Less land consuming than wetlands • May provide breeding ground for• Basic system simple to disease vectors such as mosquitoes

operate/maintain • Health hazards associated with• Promote recycling and reuse of handling and preparation of

organic waste material and water contaminated products• Fish used in system is rich source of • Solar aquatics built in greenhouses still

protein for human diets at experimental stages in developed• Plants used in system can be countries and require expertise

composted and used as fertilizerSource: Smith-Vargo, 1991; Smith 1987; Bhamidimarri eta!, 1991; and Edwards, 1985.


abhorrence to societies that can afford conventional treatment methods and fish raised on “fishfood,” but for societies in developing nations, the reuse of wastewater for aquaculture, followedby irrigation of crops, offers attractive benefits. These benefits include the increase in watersupplies for productive agricultural use and the addition of valuable fertilizers and micronutrientsto maintain aquaculture growth and later soil fertility, while at the same time contributing to thereduction of pollution of surface water sources (Edwards, 1985, 22-33). However, whileaquaculture systems have a number of benefits, they also have a numberof limitations (see Table5.3).

5.5. Disinfection techniques

Following collection, wastewater is treated by one or a combination of the methods describedpreviously. It is then disinfected by either chlorination or radiation before being discharged intoa waterbody (Miller, 1991, 576).

At all three stages of treatment, i.e. primary, secondary, and tertiary, chlorine may be used toeliminate disease-causing bacteria and inactivate some viruses. In general, chlorination iseffective in removing these pathogens but some may be protected in suspended and colloidalsolids if the wastewater has not been filtered first for turbidity removal. Cysts of protozoa andhelminth eggs are resistant to chlorine and need to be physically removed by effective chemicalcoagulation and granular-media filtration. Disinfection by chlorination presents yet anotherpotential problem; the formation of small amounts of chioro-organic compounds which arecarcinogenic. In small amounts, these compounds are harmless but their cumulative effects arestill not known (Maarschalkerweerd et al, 1990, 145-150).

Two alternative methods of disinfection currently exist, but their development and technology isstill relatively new and experimental. They include; disinfection by ultraviolet rays--a physicalprocess relying on transference of electromagnetic energy from source (lamp) to organisms’genetic material, and by ozonation, also a physical process using ozone. See Table 5.4 for asummary analysis ofthese systems.

5.6. Wastewater disposal: recover and reuse

In the wake of diminishing resources and growing populations, the principle of recover and reuseshould be inviolate. For many societies in developing nations, it is the only means ofsafeguarding their natural stock from further depletion. It is also the primary means of achievingeconomic and social benefits.

Sustainable resource recovery activities in the developing world entail the recycling and reuse ofliquid wastes from municipal and commercial sources. A number of possible uses are discussedin the next section.


Table 5.4. Disinfection Techniques

Disinfection Advantages Disadvantages / LimitationsMethodsChlorination • Kill most bacteria and viruses • Chlorine residuals in

• Simple method wastewater can havedeleterious effects on aquaticbiota in receivingwatercourses -.

. Produce chlorinatedcompounds which may betoxic to humans and animals

Liv • Disinfect but do not chemically alter • Lack ofmeasurable residualswastewater, exhibit no toxicity • Possible occurrence of

• UV equipment occupies little space photoreactivation which can. Inexpensive compared to chlorination repair damage done by UV

and ozonation light• Can be retrofitted into existing chlorine • Technology still in its infancy

contact chamber• Not complex to operate, in essence a

lighting system with lamps immersed ineffluent

• System has component with 20 yearlifespan

Ozonation • Not toxic to humans or other living • Still experimentalorganisms • Very costly

Source: Maarschalkerweerd et a!. 1990, 145-151.

5.6.1. Effluent reuse

Treated effluent is a valuable source of water for irrigation or agricultural purposes, particularlyin arid and warm climates. Disposal of effluent through this method has a number of advantages:

• returning solids back to the land and reusing the wastewater wherever feasible is anecologically sound solution;

• land application of wastewater leads to groundwater recharge and evapotranspiration;• land application provides an additional but natural method of treating wastewater through

percolation and infiltration;• provides natural fertilizing constituents for crops; and,• enhances conditioning properties of soil for crops.

Although there are a number of benefits derived from the application of effluent for agriculturalpurposes, there are also a number of limitations or disadvantages associated with it, including:

• contamination and pollution hazards likely in regard to agricultural workers and cropconsumers; and,

• possible chemical effects of the wastewater on the soil and groundwater (Escritt, 1984,375-385).


5.6.2. Sludge reuse

Sludges are a common by-product from all waste treatment systems, including some of thenatural processes discussed earlier. They contain a high proportion of the organic mattercontained in the sewage liquor before treatment, concentrated in a fluid containing between 2 and5 per cent suspended solids. The sludges have similar characteristics to that of night-soil comingfrom wet latrines, and thus have a significant manurial value and can be used for land irrigationor agricultural purposes (Pickford, 1995, 37). -

There are five possible ways to handle sewage sludge. They include: anaerobic digestion,composting, incineration, disposal in a sanitary landfill, and ocean dumping. In anaerobicdigestion, the sewage sludge is placed in large circular digesters and kept warm. This allowsanaerobic bacteria to break down the organic material into gases such as methane and carbondioxide; the methane can then be recycled and burned to heat the digesters. After a few weeks ofdigestion, the sewage sludge resembles humus and can be used as a soil conditioner. Sewagesludge can also be dried and used as a fertilizer. However, as it is rich in plant nutrients, it maysometimes contain too many heavy metals to be used commercially, a result of sewer systemsmixing industrial waste which may contain toxic substances with household waste. Farmers indeveloped countries are sometimes reluctant to use sewage sludge fertilizer out of concern thatconsumers will not purchase the food grown in it. But in developing nations, where night soil isoften applied directly to agricultural land, processed sludge fertilizer presents an important andvaluable resource (Pickford, 1995, 38-41 and Miller, 1990, 580).

Although sewage sludge can be used to condition soil, in developed countries it is generallytreated as a solid waste. Dried sewage sludge is often incinerated, which contributes to airpollution, although sometimes the heat produced by this process is used constructively.Alternatively, sewage sludge can be disposed of in sanitary landfills. This, however, is not arecommended method for developing countries where resources are in short supply and sanitarylandfills are non-existent or full beyond capacity. Prior to legislation banning ocean dumping,sewage sludge was often disposed of along coastal lines. This too, is not an ecologically soundway of handling a potentially valuable resource in either the developed or developing world(Miller, 1990, 582).

5.6.3. Biogas reuse

Biogas is naturally produced from sewage sludge treated in digesters under anaerobic conditions.The sewage sludge or the contents of wet latrines from a population of 10,000 produces enoughgas to drive a 20 horse power engine all day long. Animal wastes also provide an importantsource of natural energy. It is estimated that ‘the dung from one cow will yield enough gas toprovide the domestic power needed for a family of three and that the stock from a farm would beable to provide all the power required for the numerous farming processes. Despite theenormous potentials of this natural resource, the technology and processes for harnessing it isstill in its infancy. Most developing nations do not have adequate funds for research anddevelopment in this area. The developed nations that do have the adequate funds have no


incentives to research and develop this area because they have alternative energy resources torely on and enough money to import if they do not (Pickford, 1995, 37-42).

6. INDUSTRIAL WASTEWATER

The effects of industrial wastewater on human health have afready been noted, including theserious nature of materials used in industrial processes. In developing countries in particular,both the urban environment and human health are dramatically impacted by industrialwastewater. In Indonesia, for example, the unregulated establishment of factories in the middleof rice fields aggravates both the urban and rural environment. Wastewater dumped intowatercourses becomes a major public health risk in adjacent urban areas, where rivers constitutethe main raw water source for the municipal water treatment plants (World Bank, 1994, 3-4).However, the mechanism of waste generation and associated character of industrial waste arequite different depending on the individual industry. Industrial wastewater, therefore, is bestdescribed using the following seven categories.

6.1. Characteristics of industrial wastewater

6.1.1. Petroleum industry

Oil refineries and petrochemical plants produce an astounding number of different pollutants,including hydrocarbons, acids, ailcalis, cyanides, numerous sodium salts, phenolic compounds,numerous inorganic and organic sulfur compounds, and halogenated and nitrogenated hycfrocarbons (Hodges, 1973, 168). Uncontaminated but heated waste water also constitutes a disposalproblem (Cardon and Klein, 1977, 78-80). Possible sources of effluent are given in Table 6.1.

Table 6.1 Types and Sources of Liquid Effluent

Waste SourceOil rainwater from tank farms, pipe-tracks and product(accidental contamination) dispatch areasOil rainwater from processing areas, tank drain water,(continuous contamination) deballasting water, cooling water, blow-down,

flushing and cleaning water, crude desaltingOrganic material e.g.: phenols, process water from steam striping, crude oilthiophenols, organic acids washing, chemical oil treatment process, crudeInorganic material e.g.: ammonium desalting, thermal cracking; catalytic crackingsulfide, inorganic salts, metalsElevated water temperature I boiler blow-down, boiler feed water, make up units,uncontaminated water cooling water, rainwater from oil free areasSource: United Nations, 1982.


Recycling of process water is a significant feature of modem refmery practice, and extensivewater treatment is, therefore, carried out. Primary treatment includes the removal of suspendedsolids and undissolved oils by sedimentation and gravity separation. Secondary treatment byfiltration, flocculation or flotation remove additional oil and dissolved organic substances aretaken out by biological oxidation treatment techniques (United Nations, 1982, 2-10).

6.1.2. Iron and steel industry

Iron and steel manufacturing may be grouped into the following six distinct sequentialoperations: 1) coke production and by-product recovery; 2) ore preparation, including sinteringoperations; 3) pig iron manufacturing in blast furnaces; 4) steel-making processes using basicoxygen, electric arc and open hearth furnaces; 5) casting and rolling mill operations; and, 6)finishing operations. With the exceptions of coke production and by-product recovery, waterpollution sources originate principally from the washing of exit gases to control air emissions.Coke production is a net producer of wastewater, most of which results from water in the coalcharged to the ovens (United Nations, 1982, 11-17).

These wastes tend to be acidic and contain cyanogen, phenol, ore, coke limestone, alkali, oil, millscale, and fine suspended solids. Larger mills may recover by-products but smaller mills do notfind this economical. They may simply neutralize the acidity with lime which can lead to a largevolume of sludge (Hodges, 1973, 168-169).

6.1.3. Non-ferrous metal production

Large amounts of liquid effluent are a frequent result of non-ferrous metal production. Thiseffluent tends to contain significant concentrations of dissolved and suspended solids --

chromium, lead, nickel cadmium, zinc, copper, silver, etc. -- as well as grease and oil and pHfluctuations, both alkaline and acidic. Metal salts or oxides are often encountered in. the wastestreams, and cooling water requirement can add significantly to the quantity of the effluent.These pollutants are generated at most stages of the process.

In some cases, the quantities of liquid effluent and suspended solids are enormous. For example,the aluminum production industry can generate huge amounts of a sludge effluent known as ‘redmud’ because of its colour and texture, and liquid effluents (spent solution containing sodiumaluminate or calcium fluoride and sodium / calcium sulfate).

Water pollutants from aluminum production suöh as dissolved solids and ferric oxides aresometimes effectively treated by reverse osmosis, coagulation, electro-dialysis and activatedcarbon. All of these processes assure 95 -100 % treatment efficiency levels. Dissolved solidsand BOD (Biological Oxygen Demand -- the amount of oxygen needed by microorganisms todecompose the organic material in a given volume of water) are effectively treated by lagooning.The major environmental problems are therefore associated with the discharge of gaseousemissions (fluorides and particulate) and the disposal of sludge (United Nations, 1982,22-44).


6.1.4. Chemical industry

Potential waste from chemical industries is high, but because of the nature of the compounds thiswaste is usually recovered as a matter of economic necessity. In other cases, the chemicalmanufacturing operation is run in a closed system allowing little or no escape. However, thewaste in liquid effluents, which are primarily dissolved and suspended solids, can present largeproblems in terms of environmental hazard (United Nations, 1982, 47). The formation andrelease of pollutants valy according to the raw materials used and the manufacturing process. Inorder to examine the liquid waste of chemical industries, industrial processes may be dividedalong the following lines: inorganic, organic, and plastics and other chemical industries.

An assessment of typical discharged pollutants and the environmental problems caused by agiven process is relatively straight forward. This, however, usually applies to the major commonpollutants discharged in large quantities. There is very little information available for tracingother discharges. This is partly due to the difficulties in their detection as well as the scarcity ofknowledge on their effect (United Nations, 1982, 48).

(1) Inorganic chemical industriesMajor inorganic chemicals such as acids, alkalis, soda and chlorine, phosphate fertilizers,ammonium nitrate and others are produced in large quantities by the inorganic chemical industry.Despite advances in manufacturing process efficiencies and pollution control technologies,which result in lower specific rates of discharge, (the sheer tonnage that is being produced)significant absolute quantities continue to be released. Furthermore, on a local scale the potentialof a concentrated point source discharge can aggravate the environmental problems that surrounda chemical plant.

Table 6.2 Liquid Effluents From Major Inorganic Chemical Products

Product Liquid effluentsodium carbonate suspended solid, silica; brine; magnesium and calcium, other impurities,(soda ash) saltssodium hydroxide suspended and dissolved solid; NaOH; NaCL;H2S04;CaCO3;Ca(OC1)2;and chlorine filter acids; mercury; carbon; chlorinated hydrocarbons.sulfuric acid minimal discharge (mostly recycled cooling water), suspended and

dissolved solids and acidity.nitric acid suspended solids; dissolved solids; sulfuric acid; chlorinephosphoric acid suspended solids, gypsum; phosphorus; fluorides;ammonia ammonia, carbon dioxide, oil, monoethanolamine, BOD, CODtitanium dioxide suspended solid, siliceous sludge, ferrous sulfate, acid, magnesium and

aluminum sulfate, titanium dioxide, waste coke, metal saltssodium sodium chloride, sodium sulfate, suspended solids, chromate ions, ferricdichromate and magnesium salt

Source: United Nations, 1982.


Production efficiency in organic chemical industries is generally within the rage of 97 to 99 %.The remaining 1 to 3 % are emitted into the biosphere in the form of gases, dispersed liquids andparticles. Of these processes, phosphate fertilizers and sulfuric acid have undergone the mostsignificant change because of the increasing demand for agricultural products (United Nations,1982,49-54). Table 6.2 shows liquid effluents from each major inorganic chemical product.

The advent of many sulfur dioxide recovery plants has changed competition in the marketplaceconsiderably. Recovery plants are expected to continue to operate at full capacity in order toconform to pollution control regulations, regardless of the market price of acid (United Nations, -

1982, 48-53).

(2) Organic chemical industriesLiquid waste presents the greatest problem in the organic chemical industry. The source ofliquid waste streams can be divided into five general categories: 1) waste containing a principalraw material or product resulting from the stripping of the product from solution; 2) by-productsproduced during reactions; 3) cooling water and boiler blow-down, steam condensate, watertreatment waste and general wash water, 4) spills, wash-downs, vassal cleanouts, sampleoverflows; 5) rain, and stormwater. The principal contaminants in the effluents include organicchemicals from residual products and by-products, oils from the bottom of distillation andstripping columns, suspended solids, and catalysts. Table 6.3 shows liquid effluents for majororganic chemical products.

Table 6.3 Liquid Effluents From Major Organic Chemical Products

Product Liquid effluentsethylene dichioride chlorine, ethylene dichloride, HCL, vinyl chloride, methyl chloride,

ethyl chloride, sodium hydroxide, sodium chlorideurea ammonia, carbon dioxide, ammonia carbonatemethanol oils, metals, high boiling point organic, COD, BOD, TOCstyrene COD, BOD, TOCethylbenzene benzene, hydrogen chloride, tarry materials, COD, BOD, TOCvinyl chloride chlorinated organic, suspended solids, vinylchlorideacetone acetone, isopropanol, COD, BOD, TOCacrylonitrile ammonia sulfate, acetonitrilecarbon tetrachioride sodium chloride, perchloroethylene, hexachioroethan

Source: United Nations, 1982.

(3) Plastics and other chemical industriesMuch of the wastewater in plastic manufacturing originates from processes where streams are indirect contact with water. Wastewater may also be formed during the course of a chemicalreaction. It may arise from cleaning process vessels, area housekeeping, utility boiler andcooling water blow-down, and other sources such as laboratories. The contaminants in the waste


water include organic reactants, monomers, oligomers, polymers, salts, BOD5, COD, andsuspended solids.

Wastewater produced by organic dyes and pigments present perhaps the most importantproblems. Waste consists of brine solutions and dilute streams of acids and bases contaminatedwith toxic and explosive organic compounds. The waste solutions also contain metal or metalsalts used as catalysts for various reactions (United Nations, 1982, 8 1-99).

6.1.5. Food industry

Wastes from the food processing industry -- meat and daiiy products, beet sugar refining,brewing and distilling, canning, etc. -- tend to be troublesome mainly because of the high contentof decomposable organic substance, which can lead to oxygen depletion and water supplyimpairment in the same way as domestic sewage. The meat processing wastes come fromstockyards, slaughterhouses, packing plants, and rendering plants. These contain blood, fat,proteins, feathers, and other organic wastes. The dairy industry produces organic wastes high inprotein, fat, and lactose from milk and cheese processing. Whey from the production of cheese isan important BOD source in areas with an established cheese industry. The beet sugar refiningindustry produces wastes of high BOD content, including sugar and protein. Breweries anddistilleries produce organic solids containing nitrogen and fermented starches from grainprocessing and alcohol distilling. The processing of food to produce canned or frozen productsleads to enormous amounts of wet solid wastes. Food processing often involves some danger ofinfectious disease (Hodges, 1973, 166-167).

6.1.6. Pulp and paper industry

Pulp and paper processing, in addition to being a notorious source of air pollution, produces agreat amount of water pollution.. In the 1970s, the MacMillan Bloedel mill at Port Albemi,British Columbia, produced about 1650 metric tons of pulp and paper daily, using 160,000 m3 offresh water and dumping about the same amount of polluted water. The industry produces twomain effluents, that is, pulp mill and paper mill wastes. Waste characteristics vary dependingupon the manufacturing processes used, end products manufactured and degree of productrecovery (Hodges, 1973, 167).

Pulp mill wastes are generated from debarking, girding, digested cooking, washing, bleaching,chemical recovery and de-inking. These effluents can contain spent cooking liquor, fine fibres,ligneous compounds, bleaching chemicals, organosulfur compounds sodium sulfides, carbonatesand hydroxides. Paper mill wastes originate in water which passes through the wire screens,showers and felts of the paper machines. The wastes (whitewater) can contain fine fibres, sizing,dye, casein, clay ink, waxes, grease, oil and other materials, depending upon the additives used inthe paper production (United Nations, 1982, 143-162).


6.1.7. Textile industry

Textile mill wastes, generated by cooking the fibres and de-sizing the fabrics, have a highBiological Oxygen Demand and are quite alkaline, requiring neutralization and other treatment.The wastes arise from impurities in the fibre and from the chemicals used in processing. Theproduction of 100 kg of wool leads typically to 1500 kg of impurities (wool fibres, sand, grease,burrs, etc.) and 300 to 600 kg of process chemicals, with a total of 200 to 250 kg BOD. Cottonprocessing leads to relatively less total BOD but the waste water may have 200 to 600 mgfl BOD(Hodges, 1972, 167).

As a summary analysis, Table 6.4 details the liquid wastes produced in different industries,arranging them by waste component group. It lists eight components of contaminants andpollutants all of which industrial wastewater cany in common with domestic wastewaters(Chanlett, 1979, 181).

6.2. Treatment and disposal of industrial wastewaters

As can be seen in the previous section, industrial wastewater varies more in character than doesdomestic sewage. In fact, when a town’s sewage is in any way abnormal, industrial wastewateris usually a major causative factor. Industrial waste always includes inorganic substances insuspension or solution, some of which may be poisonous or liable to inhibit the action ofbacteria; natural organic compounds; and synthetic organic compounds. The latter can induceproblems in both sewerage and sewage treatment (Escritt and Haworth, 1984, 466).

6.2.1. Options for the treatment of industrial wastewaters

In many industries, wastewaters are recycled out of economic necessity. In other cases,manufacturing operations are run in a closed system. It is however, difficult for industrial wastesto be treated 100% within a factory due to the cost and efficiency of treatment. Once wastewaterhas been produced it has to be treated in varying degrees according to the factory’s preciselocation within the system and the nature of the waste. In general, there are four options, notmutually exclusive, for the management of industrial wastewater. They are:

1. control at the point of generation within the plant;2. pretreatment for discharge to public sanitary sewers;3. discharge to public sewers for combined treatment at the municipal treatment works; and,4. on-site treatment with discharge or with further treatment (Chanlett, 1979, 184-191)

Management often tends towards the third option even at the cost of special charges as it avoidsgetting into waste treatment as a plant responsibility. Resorting to option four is not as commonas may be thought. In the case of the United States, there are many more partial treatmentprocedures, falling under option two, to modify wastewaters before discharge to public sewers(Chanlett, 1979, 184).

Phain, Rowe-Evans, and Shigehisa 47

Table 6.4 Industrial Wastewater: Components, Effects, and Typical Sources

Component group Effects Typical sources

Bio-oxidizables Deoxygenation, anaerobic Large amounts of solubleexpressed as conditions, fish kills, stinks carbohydrates, sugar refining,

BOD5 canning, distilleries, breweries, milk

processing, pulping, paper making

Primary Fish kills, cattle poisoning, Metal cleaning, plating, pickling,

toxicants; such plankton kills, accumulations in phosphate and bauxite refining,

as, CN, Cr, Cd, flesh of fish and mollusks chlorine generation, battery making,

Cu, F, Hg, Pb, Zn tanningAcids and Disruption ofpH buffer Coal-mine drainage, steel pickling,

alkalines systems disordering previous textiles, chemical manufacture, wool

ecological system scouring, laundries

Dismfectants: Cl2, Selective kills ofmicro- Bleaching ofpaper and textiles,

11202, formalin, organisms, bad taste, and rocketry, resin synthesis, penicillinphenol odours preparation, gas, coke, and coal-tar

making, dye and chemical

manufacture

Ionic forms: Fe, Changed water characteristics: Metallurgy, cement making, ceramics,

Ca, Mg, Mn, Cl, staining, hardness, salinity, oil-well pumpage

SO4 encrustations

Oxidizing and Altered chemical balances Gas and coke making, fertilizer plants,reducing agents: ranging from rapid oxygen explosive manufacture, dyeing and

NH3,NO2-,NO3-, depletion to ovemutrition, synthetic fibre making, wood pulping,

S.—, SO3-- odors, selective microbial bleaching

growthsEvident to sight Foaming, floating, and Detergent wastes, tanning, food and

and smell settleable solids, stinks, meat processing, beet sugar mills,

anaerobic bottom deposits, oils, woolen mills, poultry dressing,

fats, and grease, waterfowl and petroleum refining

fish injuries

Pathogenic Infections in humans, Abattoir wastes, wool processing,

organisms: B. reinfection of livestock, plant fungi growths in waste treatment

anthracis, diseases from fungi- works, poultry processing wastewaters

Leptospira, toxic contaminated irrigation water,

fungi, viruses risks to vision in humans

Source: Chanlett, 1979.


1) Control at the point of generationThe first method of dealing with an industrial waste, which should always be considered wherepossible, is the reductioh of waste by recuperating the materials in it. It is commonly found to bepracticable to extract useful chemicals from wastewater and thereby not only simplify thetreatment problem, but at the same time save on overall costs. Savings can also be realized bypreventing salvable material from gaining access to liquid wastes, and problems of treatment canbe reduced by altering methods of manufacture. If wastes are discharged to watercourses, theymust be purified so as to conform with normal standards (Escritt and Haworth, 1984,468).

2) PretreatmentOnce industrial wastes have been produced, thcy must be treated in varying degrees according towhether they are to be discharged to a sewer or to a watercourse. For discharge to public sewers,wastes need to be treated to ensure that they are not harmful to the structure of the sewer, thatthey are not liable to react with sewage causing deposition of sediment, that they will not causeorganic growth in the sewer, and that they will not interfere with the processes of sewagetreatment (Escritt and Haworth, 1984,468).

Figure .1 Separated and Combined Storm and Sewer SystemsSource: Miller, 1990, 540.


Pretreatment of large volumes of waste is done by the interception of screenables or settleables,or both, to reduce gross solids load on streams, sewers, and treatment. Examples are found inpoultry dressing and meat packing plants, tanneries, canneries, beet sugar mills, and orerefineries and mills. More elaborate means are needed to reduce BOD loads by recirculatingroughing filters. Milk processing, cannery, paper mill, and pharmaceutical waste are also treatedby roughing filters. Chemical precipitation has been used on textile and low-level radioactivewaste (Chanlett, 1979, 185).

3) Combined treatment at the municipal treatment worksCombined treatment of industrial and municipal wastewater becomes a special technique whenthe wastewater of a single plant or group of plants is a major fraction of the total municipalsewerage, or when it has unique characteristics of high BOD, acidity / alkalinity, colour,suspended solids or toxicants. Except for residential areas, all public sewers receive some wastesfrom commercial, service, and smaller manufacturing establishments. Even these operationsshould be subject to charges based on volume, BOD, a specified pH range, or acidity / alkalinitycontent, and to regulations for the exclusion ofmaterials which interfere with treatment.

There are have been several attempts at combined treatment in the United States, but some haveended in unsatisfactory experiences. At a treatment plant in Massachusetts, the city had to bearall costs of increased volumes and treatment changes, and at another plant in New Jersey, thewastes from mills were simply too strong for municipal plants to treat(Chanlett, 1979, 186-7).

4) On-site treatmentIndustrial wastewater is always treated on-site. Treatment waste is discharged to receivingwaters, or reused by the same facilities or others, or treated further to meet special requirements.A wide variety of industrial wastes are treated by conventional sewage treatment methods.However, in the complete treatment of wastewater, special treatment techniques are needed, aswill be shown in the next section.

6.2.2. Special treatment techniques for industrial wastewaters

As for the technical aspect of industrial wastewater treatment, methods include bacteriologicaltreatment similar to domestic sewage treatment, with additional special treatment as shown inTable 6.5 (dependent on the nature of the waste)


Table 6.5 Major Industrial Treatment Methods

Method ResultsUnderground It has been successfully used in the US for disposal ofwaste water fromdisposal chemical industries. Suitable geological conditions include a deep porous

layer underneath impervious rock.Screening, It has been used for removing solids from the efflñents of many food andMechanical textile industries. The type of screen varies according to the size offiltration particle.Sedimentation One of the most commonly applied methods ofremoving suspended

solids. Quiescent sedimentation is more common than continuous-flowmethods used mainly in domestic sewage.

Chemical Much of the content oftrade wastes can be removed with the aid ofprecipitation I precipitants. Chemicals, for the purpose of neutralizing acid or ailcaline,neutralization are also used at the same time.Adsorption It plays an important role in the widely used process of chemical

precipitation. Activated carbon, bauxite etc. are used for absorbents.Grease separation Grease can be removed by chemical treatment, which causes it to be

precipitated in sedimentation tanksFlotation It provides a method for removing suspended solids and pseudocolloidal

suspension, or fatty, greasy, tarry, and oily matter.Dialysis, Dialysis separates inorganic acids and salts from organic materials.Electrolysis Electrolysis applies for recovering copper.Storage and These methods are applicable to radioactive waste. Radioactive isotopesdisposal in sealed deteriorate at a reducing rate with time, and those which have a short half-capsules in deep life may be rendered harmless if stored for a sufficient time.sea

Source: Escritt and Haworth, 1984.

7. CONTROL AND REGULATION OF WASTEWATER

For the purposes of control and regulation, it is useful to distinguish between point source andnonpoint source ofwater pollution from human activities. What follows is a brief explanation ofthese two types, their control and regulation (Miller, 1990, 520-521).

7.1. Point source and nonpoint source wastewater

Point source wastewater involves the discharge ofpollutants at specific locations through pipes,ditches, or sewers into bodies of surface water. Examples include factories, sewage treatmentplants (which remove some but not all pollutants), and active and abandoned underground coalmines.

Phani, Rowe-Evans, andShigehisa 51

-----------

r_

__

Nonpoint source wastewater involves discharge over big land areas into surface andunderground water and into parts of the atmosphere from which pollutants are deposited onsurface waters. Examples include runoff into surface water and into groundwater fromcroplands, livestock feedlots, logged forests, urban and suburban land septic tanks, constructionareas, parking lots, roadways, and acid deposition.

Sewage treme pacd

ed

Figure 7.1 Point and Nonpoint Sources ofWater PollutionSource. Miller, 1990, 521.

7.2. Control of nonpoint.and point source wastewater

1) Control of nonpoint source wastewaterLittle progress has beeitmade in the control of nonpoint water pollution because ofthe difficultyand expense of identifying and controlling discharges from so many diffuse sources. Controllingthese inputs requires emphasis on prevention by better land use, soil conservation,, reducingresource waste, controlling air pollution, and regulating population growth. In the United States,nonpoint pollution in agriculture is responsible for an estimated 64% of the total mass ofpollutants entering rivers and 57% of those entering lakes (Miller, 1990,520).

2) Control of point source wastewaterIn the United States, water pollution control laws were enacted in the 1 970s. These efforts haveenabled the US to hold the line against increased pollution of most of its rivers and streams bydisease-causing agents and oxygen-demanding waste. National water quality surveys indicatethat by 1985 about 73% of monitored stream miles fully supported their designated uses, mainlyfishing, boating and swimming.

52 Sanitadon Infrastructure

These pollution control laws require the Environmental Protection Agency to establish nationaleffluent standards and to set up a nationwide system for monitoring water quality. These effluentstandards limit the amounts of certain conventional and toxic waters from factories, sewagetreatment plants, and other point sources. Each point source discharger must get a permitspecifying the amount of each pollutant that facility can discharge (Miller, 1990, 545).

Despite such efforts, inputs of nitrates, phosphates, pesticides, and other toxic chemicals haveincreased in many rivers since the 1970s and still contaminate drinking water and cause largefish kills. According to studies by the General Accounting Office in 1988, about 80% of allindustrial dischargers were officially in compliance with their discharge permits. But studieshave shown that most industries periodically violate their permits. Also, some 500 cities havefailed to meet federal standards for sewage treatment plants. 34 East Coast cities, includingBoston and two sections of New York, were still not doing anything more to their sewage thanscreening out large floating objects before discharging the rest into coastal waters (Miller, 1990,545).

Wastewater coming from factories or commercial facilities that cannot match the environmentalstandard as well as from facilities that discharge in lower specific rates of substances, haveserious environmental impacts (United Nations, 1982,48).

Effluent charge systems impose fees on industrial facilities according to the quality or quantitiesofpollutants discharged. These systems are often more economical than regulatory mechanisms

to induce firms to reduce pollution load. The Netherlands has an effective water pollution chargesystem that provides a strong incentive for industries to reduce pollution. From 1969 to 1980, it

is estimated that 50 to 70% of the pollution reduction in 14 industrial sectors was due to effluentcharges (Douglass, 1996, 111).

In developing countries, strict environmental standards were mainly set by Western engineers asa string attached to official economic assistance. However, these standards are not usually

observed by industrial sectors for several reasons: first, it is too costly to do so in the context ofglobal market competition; second, monitoring cannot be effectively implemented with the

present technical capacity of local governments; third, corruption within local governments

becomes an important obstacle for carrying out these standards properly.

8. CONCLUSION

From an examination of history we can see how much technology in the area of sanitation has

contributed to better health and living conditions of people; “by eliminating vector and

waterborne diseases, sanitary engineering, the forerunner of modern day environmental

engineering, set a precedent of serving civilization through technology...” (Gloyna, 1986, 814).

The industrial age, or the age of Enlightenment, with its many technological innovations moved

us out of the Dark Ages into the modern era. But in this modern era there are still a great many

people, at least 30% of the world’s population, living as though in the Dark Ages under

deplorable sanitary conditions. In India, for example, there are 3 child deaths per minute from


dirty water, and globally, 20 million people suffer from dysentery ailments and intestinalparasites (Lean, 1990, 29). Clearly, technology in and of itself will only improve the world’shealth and sanitation problems marginally unless its appropriateness and distribution are alsoconsidered.

In terms of appropriateness, the transfer of technology, no matter how innovative, will fail indeveloping countries unless other factors are taken into consideration; namely, environmentaland geological conditions; density of settlements; social factors; existing technology; and mostimportantly, cost factors. In terms of distribution, the provision of sanitation geographically andsectorally is grossly imbalanced. In developing countries, urban-biased policies have resulted inthe cities being relatively better serviced than rural areas, despite the fact that 50 to 80 per cent ofthe population reside beyond the urban fringe. Sectorally, the provision, of sanitation isnoticeably less compared with the provision of potable water. From the donors as well asrecipients perspective, getting rid of human waste and other household wastes is not as attractiveas “providing water to the thirsty” (Pickford, 1995, 38). Consequently, sanitation often comeslow in the priority lists of donors and beneficiaries. Yet, sanitation and water are clearly of equalimportance in terms of the objectives ofhealth, convenience, and the environment.

In the developed world, the issue of sanitation has a slightly different focus. The problem here isnot so much a lack of sanitation, but rather too much of it. We have engineering and hygienicstandards that are excessively high. Our current standard of living as well as our obsession withcleanliness promote rather than curtail the production of waste. We extract and consume somuch water, and in turn produce so much waste, that nature does not have sufficient time torejuvenate and replenish our supply. Consequently, we turn to technology to solve our problems,relying on it to do one of two things: 1) fmd new sources of water, or 2) accelerate or replacenature’s treatment process in an extremely energy and capital intensive manner. This wouldappear to be the future of wastewater technology in developed nations -- finding solutions thatare remedial but impermanent, and treating symptoms rather than causes. We must, however,remember that futures are there for us to shape as we see fit, and only an intense and concertedeffort to change tracks will result in a better future for sanitation around the world.


REFERENCES

Arceivala, S.J. (1981). Wastewater Treatment and Disposal: Engineering and Ecology inPollution Control. New York, NY: Marcel Dekker Inc.

Berry, Brian 3. L. and Frank E. Horton (1974). Urban Environmental Management: Planning forpollution control. Englewood Cliffs, New Jersey: Prentice-hall Inc. -

Bhanñclimarri, R., A. Shilton, I. Armstrong, P. Jacobson, and D. Scarlet. Constructed Wetlandsfor Wasewater Treatment: The New Zealand Experience. Water Science andTechnology. v.24(5), 247-253.

Cairncross, Sandy and Richard G. Feachem (1983). Environmental Health Engineering in theTropics: An Introductory Text. London: John Wiley and Sons Ltd.

Chanlett, Emil T. (1979). Environmental Protection. NewYork, NY: McGraw-Hill BookCompany.

Dixo, N. 0., M. P. Gambrill, and P. F. Catunda (1995). Removal ofPathogenic Organismsfromthe Effluent ofan Upflow Anaerobic Digester Using Waste Stabilization Ponds. WaterScience and Technology. v.31(12), 275-284.

Douglas, I. (1983). The Urban Environment. London, England: Edward Arnold.

Douglass, Mike (1996). World Resources 1996-1997: The Urban Environment. New York,NY: Oxford University Press.

Edwards, Peter (1985). Aguaculture: A Component of Low Cost Sanitation Technology. WorldBank Technical Paper No. 36. Washington, DC: World Bank.

Ehlers, Victor M. and Ernest W. Steel (1965). Municipal and Rural Sanitation. New York, NY:McGraw-Hill Book Company.

Ellis, Derek (1989). Environments at Risk: Case Histories of Impact Assessment. New York,NY: Springer-Verlag.

Enger, Eldon D. (1992). Environmental Science: A Study of Interrelationships. Dubuque,Iowa: W.C. Brown Publishers.

Escritt, Leonard B. and William D. Haworth (1984). Sewerage and Sewage Treatment:International Practice. New York, NY: John Wiley and Sons Limited.

Fish, H. (1972). Water Pollution - Types, Causes And Effects. Effluent and Water TreatmentJournal (December).


Gloyna, Earnest (1986). Environmental Engineering-Historical, Current, and FuturePerspective. Journal of Environmental Engineering. October, v.112(5), 812-835.

Graham, Judith (1990). Ghana Experiments With Low-Cost Latrines. Source. September,v.2(3), 12-15.

Hammer, M.3. and M.J. Hammer Jr. (1996). Water and Wastewater Technology. EnglewoodCliffs, NJ: Prentice Hall. -

Hodges, Laurent (1973). Environmental Pollution: A Survey Emphasizing Physical & ChemicalPrinciples. New York, NY: Litolt, Rinehart & Winstan Inc.

Kaoma, J. (1980). Zambia’s Experience with Aqua Privies. In Sanitation in DevelopingCountries: Proceedings of a workshop on training held in Lobatse, Botswana, 14-20August. 41-47. Ottawa: International Development Research Centre.

Kumar, Pradeep and R. J. Garde (1990). Upgrading Wastewater Treatment by Water Hyacinthin Developing Countries. Water Science and Technology. v.22(7/8), 153-160.

Lean, Geoffrey (1990). Atlas of the Environment. London, England: Random Century GroupLtd.

Maarsschalkerweerd, Jan, Rory Murphy and Gail Sakamoto (1990). UVDisinfection inMunicipal Wastewater Treatment Plants. Water Science and Technology. v.22(7/8),145-152.

McGarry, Michael G. (1977). Waste Collection in Hot Climates: A Technical and EconomicAppraisal. In Water, Wastes and Health in Hot Climates. eds. Richard Feachem, MichaelMcGarry and Duncan Mara, 239-263. London: John Wiley and Sons.

Miller, G. Tyler (1990). Living in the Environment: An Introduction to Environmental Science.Belmont, California: Wadsworth Publishing Company.

Munyimbili, A.W.C. (1980). Pit Latrines in Malawi. In Sanitation in Developing Countries:Proceedings ofa workshop on training held in Lobatse. Botswana, 14-20 August. 16-20.Ottawa: International Development Research Centre.

Nardogan, Y. and W. J. Oswald (1995). Enhanced Nutrient Removal in High-Rate Ponds.Water Science and Technology. v.31(12), 33-43.

Njau, Frederick Z (1980). Sullage Disposal in Urban Centres. In Sanitation in DevelopingCountries: Proceedings ofa workshop on training held in Lobatse, Botswana, 14-20August. 59-60. Ottawa: International Development Research Centre.


Pathak, Bindeshwar (1991). Maintenance Management ofPublic Toilets: Experience ofa Non-Government Organization. Building and Environment v.266(3), 313-315.

Pickford, John (1995). Sustainable Water Supply and Improved Sanitationfor Low IncomeCommunities. In Technology and Developing Countries: Practical Applications,Theoretical Issues. ed. Richard Hecks. London, England: Frank Cass and Company Ltd.

Rajeswary, I. (1992). Mahalapye ‘s Latrines Sink No More. Source. July, v.4(l), 1Q43.

Roseland, Mark (1992). Toward Sustainable Communities. National Round Table Series onSustainable Development. Ottawa, Ontario: Government of Canada.

Salvato, Joseph A. (1992). Environmental Engineering and Sanitation. 4th ed. New York: JohnWiley and Sons.

Seabloom, Robert W. and Dale A. Carison (1986). Evolution ofLow Technology Waste WaterDisposal in the Developed Countries and Its Implicationsfor the Developing Nations.Water Science Technology. v.18, 59-62.

Sinnatamby, G. (1990) Low Cost Sanitation. In The Poor Die Young. eds. 3. Hardoy, S.Caimcross and D. Satterthwaite, 127-157. London: Earthscan.

Smith, L.J. (1987). Sewage Stabilization Ponds in Arabia and Kenya. Water Science andTechnology. v.19(12), 345-347.

Smith-Vargo, Linda (1991). New Possibilitiesfor Wastewater Treatment. Water Engineeringand Management. March, v.138(3), 27-29.

United Nations, Economic and Social Council (1995). UNICEF Strategies in Water andEnvironmental Sanitation. New York, NY: United Nations.

United Nations, General Assembly (1990). Achievements of the International Drinking WaterSupply and Sanitation Decade 198 1-1990, Report of the Secretary General. New York,NY: United Nations.

United Nations, Industry and Environment Office (1982). Guidelines for Assessing IndustrialEnvironmental Impact and Environmental Criteria for the Siting of Industry. Paris,France: United Nations.

Wilson, J.G. (1980a). Pit Latrines in Botswana. In Sanitation in Developing Countries:Proceedings of a workshop on training held in Lobatse. Botswana, 14-20 August. 13-15.Ottawa: International Development Research Centre.


Wilson, 3.G. (1 980b). The Botswana Aqua Privy. In Sanitation in Developing Countries:Proceedings of a workshop on training held in Lobatse, Botswana, 14-20 August. 48-49.Ottawa: International Development Research Centre.

Wolde-Gabriel, Beyene (1980). Septic Tanks. In Sanitation in Develoning Countries:Proceedings of a workshop on training held in Lobatse. Botswana, 14-20 August. 50-51.Ottawa: International Development Research Centre.

World Bank (1988). United Nations Development Program - World Bank, Water and SanitationProgram. Annual Report 1988. Washington D.C.: World Bank.

World Bank (1994). Surabaya Urban Development Project. Staff Appraisal Report No. 12516-END. Washington D.C.: World Bank.

‘-

asian urban research network - ubc scarp · 5.6. wastewater disposal: recover and reuse 38 5.6.1....

Documents