microbiology of water and waste water management

8/7/2019 Microbiology of Water and Waste Water Management

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MICROBIOLOGY OF WATER AND WASTE WATER MANAGEMENT

Microbial Communities in Natural Water

The three biological organisms present in wastewater are bacteria, viruses, and parasites. Sewage

consists of vast quantities of bacteria, most of which are harmless to man. However, pathogenic (disease-

causing) organisms such as typhoid, dysentery, and other intestinal disorders may be present in

wastewater. Bacteria are the most widely distributed life forms. Pathogenic bacteria range in length from

approximately 0.4 to 14 mm (a mm or micrometer equals one one-thousandth of a millimeter) and 0.2 to

1.2 mm in width. Key bacterial pathogens responsible for waterborne disease include Legionella,

Salmonella typhi, Shigella, and Vibrio cholerae. Viruses are inactive when outside of a living host cell.

Viruses linked to waterborne disease have protein coats that provide protection from environmental

hazards and range in size from 0.02 to 0.09 mm. Unlike bacteria and protozoa, they contain only one type

of nucleic acid (RNA or DNA). Key pathogens include hepatitis A. Protozoa, common in bodies of water,

are much larger than bacteria and viruses. To survive harsh environmental conditions, some species can

secrete a protective covering and form a resting stage called a cyst. Encystment can protect protozoa

from drinking water disinfection efforts and facilitate the spread of disease. Key protozoa being studied as

agents of waterborne disease include Giardia and Cryptosporidium.

Fecal pollution of water

Fecal pollution of water from a health point of view is the contamination of water with disease-

causing organisms (pathogens) that may inhabit the gastrointestinal tract of mammals, but with particular

attention to human fecal sources as the most relevant source of human illnesses globally. Ingestion of

water contaminated with feces is responsible for a variety of diseases important to humans via what is

known as the fecal-oral route of transmission. Food, air, soil, and all types of surfaces can also be

important in the transmission of fecal pathogens, and thereby implicated in disease outbreaks. Most fecal

microorganisms, however, are not pathogenic. Indeed, some are considered beneficial to the host as they

can out compete pathogens for space and nutrients, complement the biochemical potential of the hosts

gastrointestinal tract, and help in the development of the host immune system. Nonetheless, animal feces

can also carry a number of important frank and opportunistic pathogens, capable of inflicting debilitating

illnesses and, in some cases, death.

Indicators of Feacal Pollution

Traditionally, indicator micro-organisms have been used to suggest the presence of pathogens.

Today, however, we understand a many reasons for indicator presence and pathogen absence, or vice

versa. In short, there is no direct correlation between numbers of any indicator and enteric pathogens. To

eliminate the vagueness in the term microbial indicator, the following three groups are now recognized.


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1. Process indicator: A group of organisms that demonstrates the efficacy of a process.

2. Faecal indicator: A group of organisms that indicates the presence of faecal contamination.

Ex: E. coli.

3. Index and model organisms: A group/or species indicative of human pathogen.

Feacal Coliforms as index of water Pollution

The use of bacteria as indicators of the sanitary quality of water probably dates back to 1880 when Von

Fritsch described Klebsiella pneumoniae and K. rhinoscleromatis as micro-organisms characteristically

found in human faeces. In 1891, the Franklands came up with the concept that organisms characteristic of

sewage must be identified to provide evidence of potentially dangerous pollution. By 1893, the Wurtz

method of enumerating B. coli by direct plating of water samples on litmus lactose agar was being used

by sanitary bacteriologists, using the concept of acid from lactose as a diagnostic feature. This was

followed by gas production, with the introduction of the Durham tube (Durham 1893). The concept of

coliform bacteria, those bacteria resembling B. coli, was in use in Britain in 1901. The colony count for

bacteria in water, however, was not formally introduced until 1934. Therefore, the sanitary significance of

finding various coliforms along with streptococci and C. perfringens was recognised by bacteriologists by

the start of the twentieth century. It was not until 1905, however, that Mac Conkey (1905) described his

now famous Mac Conkeys broth, which was diagnostic for lactose-fermenting bacteria tolerant of bile

salts. Nonetheless, coli-forms were still considered to be a heterogeneous group of organisms, many of

which were not of faecal origin.

It is almost impossible to isolate from water the organisms responsible for water-borne diseases.

Few organisms are present and they do not multiply in water. The only safe method to prevent waterborne

disease is to condemn fecally polluted water as being unfit for human use, as it may contain harmful

organisms. Fecal pollution can be determined by examination of water for colon bacilli (E.coli). E.coli is

abundant in feces and not found outside intestinal tract in nature. The E.coli in water indicates the presence

of pathogenic microorganisms in water, which may be responsible for a number of water-borne diseases.

Hence, E.coli is known as indicator organism. Water also contains bacteria that resemble E.coli but may or

may not be of fecal origin. These bacteria also ferment lactose with formation of gas like E.coli. The other

indicator organisms are Streptococcus faecalis Streptococcus faecium, Streptococcus bovis, Streptococcus

equinus etc., and Clostridium perfringenes.

Significance of Feacal Coliforms

The group of coliform bacteria as an indicator of other pathogenic micro-organisms, specifically

organisms of faecal origin, has had much emphasis in all countries. This is due primarily to the fact that

the coliform bacteria groups meets many of the criteria for a suitable indicator organism, and are thus a

sensitive indicator of faecal pollution:


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They are abundant in faeces

They are generally found only in polluted waters,

They are easily detected by simple laboratory tests,

Can be detected in low concentrations in water

The number of indicator bacteria seems to be correlated with the extent of contamination.

It is important to remember, however, that not all coliforms originate from human faeces as they

can originate from other mammalian species or from other environmental sources (e.g., bird droppings).

When coliforms are discharged to the aquatic environment they will tend to die at a rate which depends,

amongst other things, on the temperature and turbidity of the water and the depth to which solar radiation

penetrates. Therefore, it is not safe to conclude that the lack of coliforms in a water means that it has not

been subject to faecal pollution. It is necessary to be familiar with a number of terms are as follows:

Total coliforms: The Total coliform group comprises several distinct types (genera) of bacteria. These

bacteria have been isolated from the faeces of humans and other warm-blooded animals, as well as

contaminated and non-contaminated soils. This group of bacteria is widely used as a measure of health

hazard from faecal contamination. The total coliform group comprises the aerobic and facultative, gram

negative, nonspore-forming, rod shaped bacteria that ferment lactose with gas formation within 48 hours at

35 C.

Faecal coliforms: The Faecal coliform group of bacteria are indicative of faeces of humans and other

warm blooded animals. The specific bacterium Escherichia coli is part of this group. The test for faecal

coliform is at an elevated temperature, 44.5C, where growth of other non-faecal bacteria is suppressed.

However, some non-faecal bacteria may be also be identified in the faecal coliform test, though a small

percentage ( 95%) are.

Escherichia coli (E. coli) This bacterium is a particular member of the faecal coliform group of bacteria;

this organism in water indicates the presence of faecal contamination. E. coli reside in human intestinal

tracts. They are excreted in large numbers in faeces, averaging about 50 million per gram. Untreated

domestic wastewater generally contains 5 to 10 million coliforms per 100 ml.

Pathogenic bacteria and viruses causing enteric diseases in humans originate from faecal

discharges of diseased persons. Consequently, water containing coliform bacteria is identified as


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potentially dangerous. Coliform bacteria are, therefore, considered as an indicator of bacteriological

quality of water for the following reasons:

Coliform bacteria far outnumbers the pathogenic micro-organisms,

They do not multiply in natural waters,

The die-off rate of pathogenic bacteria is greater than the death rate of coliforms

Test for coliform bacteria is relatively simple and can be performed in water quality laboratories

The bacterium E.coli is exclusively of faecal origin. Some coliform bacteria are normal inhabitants

of soil and water. In testing for conforms, therefore, tests may be run in conjunction to verify their faecal

origin. However, unconfirmed testing, indeed, would provide a factor of safety. The degree to which

indicator organisms represent the presence of individual pathogens (such as Salmonella) has been the

subject of continuing investigation. There does seem to be a genera correlation between the concentration

of Faecal coliform bacteria and the occurrence of Salmonella. When faecal coliform numbers are about

1000 per 100 ml, Salmonella occurrence is about 95 % Relationships between total coliform and individual

pathogens is not so quantitative. Thus the test of total coliform is not so effective for an indicator. The total

coliform test is complicated by the presence of non-faecal bacteria. As a general rule, faecal coliform

levels are about 20% of total coliform concentrations, although a wide spread exists.

BACTERIOLOGICAL EXAMINATION OF WATER

The test for coliform bacteria is usually conducted using a liquid culture. Enumeration employing solid

culture media is not commonly done in India. The liquid culture multiple tube technique consists of

mainly 2 stages (third test is optional). These are 1. Presumptive test 2. Confirmed test 3.Completed test

(Optional)

1. Presumptive test

The first step in water examinations is known as the presumptive test. The presumptive test is based on gas

production during fermentation of lauryl tryptose broth which contains beef extract, peptone and lactose

within 48 hour of incubation at 35C. The confirmed test is used to accept or reject the presence of

coliforms in a positive presumptive test. A small inoculum from a positive lactose broth is transferred to a

tube containing brilliant green lactose bile broth. The green dye and bile salts in this broth inhibit non-

coliform growth. The presence of coliform is confirmed by growth and gas production within 48 hour at

35C. The Most Probable Number (MPN) of coliform can then be calculated from the number of

confirmed tubes.

False Positive Presumptive Tests: A positive, presumptive test does not necessarily mean that members of

the colon group are present. In most cases it is true, but there are exceptions. False, positive, presumptive

tests are caused by (1) the presence of other organisms capable of fermenting lactose with the production


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of acid and gas and (2) bacterial associations or synergism. The organisms most frequently responsible for

false presumptive test includeClostridium perfringens (welchii), Bacillus aerosporus, Streptococcus

faecalis, members of the Friedliinder group (Klebsiella), Pseudomonas aeruginosa, False, presumptive

tests are also caused by S. faecalis, C. perfringens, organisms of the genus Proteus, and B. coli

anaerogenes. Flase positive, presumptive tests are frequently caused by a type of bacterial association

known as synergism. Bacterial synergism may be defined as the joint action of two organisms on a

carbohydrate resulting in the production of gas that is not formed by either organism when grown

separately.

2. Confirmed Test

In order to be certain that gas-production is due to coliforms a confirmed test must be performed. Two

procedures are normally employed. In one method a drop of culture from a positive lactose broth tube is

transferred to brilliant green lactose bile fermentation broth, and is incubated for 24 to 48 hours at 35C.

The appearance of gas within 48 hrs constitutes a positive confirmed test. The dye inhibits gram positive

organisms and eliminates a false presumptive test and the synergistic reaction of gram positive and gram

negative organisms growing together. In the second method a drop of culture from the positive lactose

broth is streaked on a petriplate containing, Endo Agar, or Eosin-Methylene Blue Agar. The appearance of

nucleated colonies, with or without a metallic sheen, within 24 hours indicates a positive confirmed test.

3. Completed Test

Isolated colonies from petriplates are transferred into lactose fermentation broth and streaked on to an agar

slant. The presence of gas in the fermentation broth and the presence of gram negative non sporeforming

bacilli on the slant give evidence that coliform bacteria were present in the original water sample.

IMViC Reaction

E. coli and A. aerogenes are normally referred to as faecal and non-faecal contaminants of water,

respectively, and are the most important organisms of the coliform group. Since they closely resemble

each other in their morphological and cultural characteristics, biochemical tests, are, performed to

differentiate them. These tests are collectively designated as the IMViC reactions. The name was coined

by Parr from the first letters of the four tests, namely Indole, Methyl red, Voges Proskauer, and Citrate.

There are 16 possible combinations of positive and negative tests of these four characteristics. Most, of

these combinations have been found, but the reactions ofE. coli and A. aerogenes are commonly found.

The remaining 14 types are usually designated as "intermediates". Since E. coil is more indicative of fecal

pollution than the other genera and species noted (especially A. aerogenes), it is often desirable to

determine its incidence in a coliform population. The IMViC formula is the classical method used, where I

= indole production, M = methyl red reaction, V = Voges- Proskauer reaction (production of acetoin), and

C = citrate utilization. IMViC reactions are a set of four useful reactions that are commonly employed in


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the identification of members of family enterobacteriaceae. The four reactions are: Indole test, Methyl Red

test, Voges Proskauer test and Citrate utilization test. The letter i is only for rhyming purpose.

By this method, the two organisms noted have the following formulas:

I M V C

E.coli + + - -

A. aerogenes - - + +

PRINCIPLES OF THE IMViC REACTION

INDOLE TEST: Principle: Some bacteria can produce indole from amino acid tryptophan using the

enzyme typtophanase. Production of indole is detected using Ehrlichs reagent or Kovacs reagent. Indole

reacts with the aldehyde in the reagent to give a red color. An alcoholic layer concentrates the red color as

a ring at the top.

Procedure: Bacterium to be tested is inoculated in peptone water, which

contains amino acid tryptophan and incubated overnight at 37oC. Following

incubation few drops of Kovacs reagent are added. Kovacs reagent consists of

para-dimethyl aminobenzaldehyde, isoamyl alcohol and con. HCl. Ehrlichs

reagent is more sensitive in detecting indole production in anerobes and non-

fermenters. Formation of a red or pink coloured ring at the top is taken as

positive. Example: Escherichia coli: Positive; Klebsiella pneumoniae: Negative

METHYL RED (MR) TEST:

Principle: This is to detect the ability of an organism to produce and maintain stable acid end products

from glucose fermentation. Some bacteria produce large amounts of acids from glucose fermentation that

they overcome the buffering action of the system. Methyl Red is a pH indicator, which remains red in

color at a pH of 4.4 or less. Procedure: the bacterium to be tested in inoculated into glucose phosphate

broth, which contains glucose and a phosphate buffer and incubated at 37C for 48 hours. Over the 48

hours the mixed-acid producing organism must produce sufficient acid to overcome the phosphate buffer

and remain acid. The pH of the medium is tested by the addition of 5 drops of MR reagent. Development

of red color is taken as positive. MR negative organism produces yellow color. Example: Eschericihia

coli: Positive; Klebsiella pneumoniae: Negative


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VOGES PROSKAUER (VP) TEST:

Principle: While MR test is useful in detecting mixed acid producers, VP test detects butylene glycol

producers. Acetyl-methyl carbinol (acetoin) is an intermediate in the production of butylene glycol. In this

test two reagents, 40% KOH and alpha-naphthol are added to test broth after incubation and exposed to

atmospheric oxygen. If acetoin is present, it is oxidized in the presence of air and KOH to diacetyl.

Diacetyl then reacts with guanidine components of peptone, in the presence of alphanaphthol to produce

red color. Role of alpha-naphthol is that of a catalyst and a color intensifier.

CITRATE UTILIZATION TEST:

Principle: This test detects the ability of an organism to utilize citrate as the sole source of carbon and

energy. Bacteria are inoculated on a medium containing sodium citrate and a pH indicator bromothymol

blue. The medium also contains inorganic ammonium salts, which is utilized as sole source of nitrogen.

Utilization of citrate involves the enzyme citritase, which breaks down citrate to oxaloacetate and acetate.

Oxaloacetate is further broken down to pyruvate and CO2. Production of Na2CO3 as well as NH3 from

utilization of sodium citrate and ammonium salt respectively results in alkaline pH. This results in change

of mediums color from green to blue.

Procedure: Bacterial colonies are picked up from a straight wire and inoculated into slope of Simmons

citrate agar and incubated overnight at 37C. If the organism has the ability to utilize citrate, the medium

changes its color from green to blue. A liquid medium (without agar) without a dye can also be used where

turbidity is observed visually after incubation, against a control. A turbid broth is indicative of bacterial

growth and hence a positive test. Examples: Escherichia coli: Negative; Klebsiella pneumoniae: Positive

Eijeckman test

Eijkman, Christian (1858-1930), Dutch physiologist. Eijkman introduced his test for coliform bacteria in a

1904 paper. This is a test for the identification of coliform bacteria from warm-blooded animals based on

the bacteria's ability to produce gas when grown in glucose media at a higher (elevated) temperature at

46C. Eijkman's test consists of introduction of samples of water into dextrose peptone broth (DPB) and

incubation at 46C. The test is usually complete in 16-24 hours, and in 92-75% of positive Eijkman

fermentation tests the presence ofE. coli can be confirmed.


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Methods of Analysis

There are two basic analyses which can be performed to determine the presence of coliform bacteria.

These are the multiple tube technique and the membrane filter method. A comparison of the two

methods is given below.

Table Comparison of coliform analysis methods

Multiple Tube Method (MPN)

As referred to above, the multiple tube technique is applicable to many different water samples including

those obtained from potable, fresh, brackish and salt waters. The test can also be used for the estimation of

coliform bacteria in muds, sediments and sludges. The method, which has been successfully used in many

countries for the analysis of drinking and other waters, reports coliform results in terms of the most

probable number (MPN) of organisms. That is, the test gives the most likely number of coliformbacteria rather than the actual number. The basis of the test is that multiple tubes of culture medium are

inoculated with various dilutions of a water sample and incubated at a constant temperature for a given

period of time. If coliforms are present in a tube this is detected by growth within the tube and the

production of gas. Any gas produced is collected in an inverted gas collection tube placed within a larger

test tube containing the culture medium. The result of the analysis, in terms of the most probable number

of coliforms, depends upon the number of tubes which show a positive reaction.

Typically, the MPN value is determined from the number of positive tests in a series of 5

replicates made from 3 different dilutions or inoculation amounts (15 samples altogether). For example,

sample inoculation amounts may be 10, 1 and 0.1 ml per test tube. The test method can be described as

follows:

For drinking water: High numbers of coliform bacteria are not expected, so there is no need to make

dilutions. Transfer a 10 ml sample into each of 10 test tubes containing a lactose culture medium and an

inverted gas collection tube. MPN results can be read from Mac CradeysTable.


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Fig: Multiple tube method after a series of dilution

For the combination of positive tubes not appearing in Mac Gradeys Table, or in case the table is not

available, the following formula is used:

MPN/100 mL = no. of positive tubes x 100

mL sample in negative tubes x mL sample in all tubes

Membrane filter technique (MF):

In this technique, a thin membrane filter-disc is used. The filter-disc consists of cellulose derivatives and

can retain on its surface all bacteria from the water sample. The water is filtered through filter-disc and the

disc is then transferred with a sterile forceps on to a thin absorbent pad that has previously been saturated

with the appropriate medium (generally Endo-broth medium) and accommodated within a Petri dish. The

Petri dish containing absorbent pad and filter-disc is incubated at 37C for 18-24 hours. The medium

diffuses through the pores of the filter-disc and provides nutrient to the bacteria. After the incubation is

over, pone can see colonies developing upon the filter-disc. The characteristic colonies of different bacteria

could now be studied to determine water potability.

Fig: 1 Fig: 2 Fig: 3 Fig: 4 Fig: 5


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Fig: 6 Fig: 7

WATER POLLUTION

Tests for total coliform and fecal coliform nonpathogenic bacteria are used to indicate the presence of

pathogenic bacteria. Because it is easier to test for coliforms, fecal coliform testing has been accepted as

the best indicator of fecal contamination. Fecal coliform counts of 100 million per 100 milliliters may be

found in raw domestic sewage. Detectable health effects have been found at levels of 2,300 to 2,400 total

coliforms per 100 milliliters in recreational waters. Disinfection, usually chlorination, is generally used to

reduce these pathogens. Breakdown or malfunctions of chlorination equipment will probably result in

excessive discharge of pathogenic organisms and can seriously affect public health. Bacteria can also be

classified according to their dissolved oxygen requirement. Aerobic bacteria are bacteria that require

dissolved oxygen to live. Anaerobic bacteria cannot live if dissolved oxygen is present. Facultative

bacteria can live with or without dissolved oxygen. Wastewater often contains viruses that may produce

diseases. Outbreaks of infectious hepatitis have been traced through water systems because of wastewater

entering the supply. Sedimentation, filtration, and disinfection, if used efficiently usually provide

acceptable virus removal. There are also many species ofparasites carried by wastewater. The life cycle

of each is peculiar to the given parasite. Some are dangerous to man and livestock, particularly during

certain stages of the life cycle. Amoebic dysentery is a common disease caused by amoebic parasites.

Chlorination, chemical precipitation, sedimentation, or sand filtration is used to ensure protection against

parasites.


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LIST OF HUMAN WATER BORNE DISEASES

The microbial composition of sewage varies depending upon the source of wastewater. This also causes

variation in the microbial flora of sewage. Almost all groups of microorganisms, algae, fungi, protozoa,

bacteria and viruses are present. Raw sewage may contain millions of bacteria per ml. The bacterial group

comprises mainly the soil borne organisms, intestinal origin and coliforms. During treatment process the

microbial flora may be dominated by the corresponding physiological groups. A detailed list of sources of

microorganisms in water and waterborne diseases is given below.

Table: Sources of Bacteria and diseases transmitted

Disease and

TransmissionMicrobial Agent

Sources of Agent

in Water SupplyGeneral Symptoms

Botulism Clostridium botulinum

Bacteria can enter a wound

from contaminated water

sources. Can enter the

gastrointestinal tract by

consuming contaminated

drinking water or (more

commonly) food

Dry mouth, blurred

and/or double vision,

difficulty swallowing,

muscle weakness,

difficulty breathing,

slurred speech, vomiting

and sometimes diarrhea.

Death is usually caused

by respiratory failure.

Campylobacteriosis

Most commonly

caused by

Campylobacter jejuni

Drinking water contaminated

with feces

Produces dysentery likesymptoms along with a

high fever. Usually lasts

2-10 days.

Cholera

Spread by the

bacterium Vibrio

cholerae


with the bacterium

In severe forms it is

known to be one of the

most rapidly fatal

illnesses known.

Symptoms include very

watery diarrhea, nausea,

cramps, nosebleed, rapid

pulse, vomiting, and

hypovolemic shock (in

severe cases), at which
http://en.wikipedia.org/wiki/Botulismhttp://en.wikipedia.org/wiki/Clostridium_botulinumhttp://en.wikipedia.org/wiki/Drinking_waterhttp://en.wikipedia.org/wiki/Blurred_visionhttp://en.wikipedia.org/wiki/Double_visionhttp://en.wikipedia.org/wiki/Vomitinghttp://en.wikipedia.org/wiki/Diarrheahttp://en.wikipedia.org/wiki/Respiratory_failurehttp://en.wikipedia.org/wiki/Respiratory_failurehttp://en.wikipedia.org/wiki/Campylobacteriosishttp://en.wikipedia.org/wiki/Campylobacter_jejunihttp://en.wikipedia.org/wiki/Feceshttp://en.wikipedia.org/wiki/Dysenteryhttp://en.wikipedia.org/wiki/Dysenteryhttp://en.wikipedia.org/wiki/Feverhttp://en.wikipedia.org/wiki/Cholerahttp://en.wikipedia.org/wiki/Vibrio_choleraehttp://en.wikipedia.org/wiki/Vibrio_choleraehttp://en.wikipedia.org/wiki/Nauseahttp://en.wikipedia.org/wiki/Crampshttp://en.wikipedia.org/wiki/Nosebleedhttp://en.wikipedia.org/wiki/Nosebleedhttp://en.wikipedia.org/wiki/Nosebleedhttp://en.wikipedia.org/wiki/Pulsehttp://en.wikipedia.org/wiki/Hypovolemic_shockhttp://en.wikipedia.org/wiki/Hypovolemic_shockhttp://en.wikipedia.org/wiki/Hypovolemic_shockhttp://en.wikipedia.org/wiki/Pulsehttp://en.wikipedia.org/wiki/Nosebleedhttp://en.wikipedia.org/wiki/Crampshttp://en.wikipedia.org/wiki/Vibrio_choleraehttp://en.wikipedia.org/wiki/Nauseahttp://en.wikipedia.org/wiki/Vibrio_choleraehttp://en.wikipedia.org/wiki/Cholerahttp://en.wikipedia.org/wiki/Campylobacter_jejunihttp://en.wikipedia.org/wiki/Feverhttp://en.wikipedia.org/wiki/Feceshttp://en.wikipedia.org/wiki/Campylobacteriosishttp://en.wikipedia.org/wiki/Dysenteryhttp://en.wikipedia.org/wiki/Respiratory_failurehttp://en.wikipedia.org/wiki/Diarrheahttp://en.wikipedia.org/wiki/Drinking_waterhttp://en.wikipedia.org/wiki/Vomitinghttp://en.wikipedia.org/wiki/Clostridium_botulinumhttp://en.wikipedia.org/wiki/Botulismhttp://en.wikipedia.org/wiki/Double_visionhttp://en.wikipedia.org/wiki/Blurred_vision


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point death can occur in

12-18 hours.

E. coli Infection

Certain strains of

Escherichia coli

(commonly E. coli)

Water contaminated with the

bacteria

Mostly diarrhea. Can

cause death in immuno

compromised

individuals, the very

young, and the elderly

due to dehydration from

prolonged illness.

Dysentery

Caused by a number of

species in the genera

Shigella andSalmonella with the

most common being

Shigella dysenteriae

Water contaminated with thebacterium

Frequent passage of feces

with blood and/or mucusand in some cases

vomiting of blood.

Salmonellosis

Caused by many

bacteria of genus

Salmonella


with the bacteria. More

common as a food borne

illness.

Symptoms include

diarrhea, fever, vomiting,

and abdominal cramps

Typhoid fever Salmonella typhi

Ingestion of water

contaminated with feces of an

infected person

Characterized by

sustained fever up to

40C (104F), profuse

sweating, diarrhea, less

commonly a rash may

occur. Symptoms

progress to delirium and

the spleen and liver

enlarge if untreated. In

this case it can last up to

four weeks and cause

death.

Vibrio Illness Vibrio vulnificus, Can enter wounds from Symptoms include
http://en.wikipedia.org/wiki/E._colihttp://en.wikipedia.org/wiki/E._colihttp://en.wikipedia.org/wiki/Escherichia_colihttp://en.wikipedia.org/wiki/Immunocompromisedhttp://en.wikipedia.org/wiki/Immunocompromisedhttp://en.wikipedia.org/wiki/Dehydrationhttp://en.wikipedia.org/wiki/Dysenteryhttp://en.wikipedia.org/wiki/Shigellahttp://en.wikipedia.org/wiki/Salmonellahttp://en.wikipedia.org/wiki/Salmonellahttp://en.wikipedia.org/wiki/Shigella_dysenteriaehttp://en.wikipedia.org/wiki/Feceshttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Mucushttp://en.wikipedia.org/wiki/Mucushttp://en.wikipedia.org/wiki/Salmonellosishttp://en.wikipedia.org/wiki/Salmonellahttp://en.wikipedia.org/wiki/Salmonellahttp://en.wikipedia.org/wiki/Food_borne_illnesshttp://en.wikipedia.org/wiki/Food_borne_illnesshttp://en.wikipedia.org/wiki/Diarrheahttp://en.wikipedia.org/wiki/Diarrheahttp://en.wikipedia.org/wiki/Feverhttp://en.wikipedia.org/wiki/Typhoid_feverhttp://en.wikipedia.org/wiki/Typhoid_feverhttp://en.wikipedia.org/wiki/Salmonella_entericahttp://en.wikipedia.org/wiki/Salmonella_entericahttp://en.wikipedia.org/wiki/Feceshttp://en.wikipedia.org/wiki/Sweatinghttp://en.wikipedia.org/wiki/Sweatinghttp://en.wikipedia.org/wiki/Rashhttp://en.wikipedia.org/wiki/Deleriumhttp://en.wikipedia.org/wiki/Deleriumhttp://en.wikipedia.org/wiki/Spleenhttp://en.wikipedia.org/wiki/Spleenhttp://en.wikipedia.org/wiki/Spleenhttp://en.wikipedia.org/wiki/Liverhttp://en.wikipedia.org/wiki/Vibriohttp://en.wikipedia.org/wiki/Vibrio_vulnificushttp://en.wikipedia.org/wiki/Vibrio_vulnificushttp://en.wikipedia.org/wiki/Woundshttp://en.wikipedia.org/wiki/Woundshttp://en.wikipedia.org/wiki/Vibrio_vulnificushttp://en.wikipedia.org/wiki/Vibriohttp://en.wikipedia.org/wiki/Liverhttp://en.wikipedia.org/wiki/Spleenhttp://en.wikipedia.org/wiki/Deleriumhttp://en.wikipedia.org/wiki/Feceshttp://en.wikipedia.org/wiki/Salmonella_entericahttp://en.wikipedia.org/wiki/Typhoid_feverhttp://en.wikipedia.org/wiki/Rashhttp://en.wikipedia.org/wiki/Sweatinghttp://en.wikipedia.org/wiki/Food_borne_illnesshttp://en.wikipedia.org/wiki/Salmonellahttp://en.wikipedia.org/wiki/Food_borne_illnesshttp://en.wikipedia.org/wiki/Feverhttp://en.wikipedia.org/wiki/Diarrheahttp://en.wikipedia.org/wiki/Salmonellosishttp://en.wikipedia.org/wiki/Shigella_dysenteriaehttp://en.wikipedia.org/wiki/Salmonellahttp://en.wikipedia.org/wiki/Dysenteryhttp://en.wikipedia.org/wiki/Mucushttp://en.wikipedia.org/wiki/Bloodhttp://en.wikipedia.org/wiki/Shigellahttp://en.wikipedia.org/wiki/Feceshttp://en.wikipedia.org/wiki/Dehydrationhttp://en.wikipedia.org/wiki/Escherichia_colihttp://en.wikipedia.org/wiki/E._colihttp://en.wikipedia.org/wiki/Immunocompromisedhttp://en.wikipedia.org/wiki/Immunocompromised


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Vibrio alginolyticus,

and Vibrio

parahaemolyticus

contaminated water. Also got

by drinking contaminated

water or eating undercooked

oysters.

explosive, watery

diarrhea, nausea,

vomiting, abdominal

cramps, and occasionally

fever.

Sources of Viruses and diseases transmitted

Disease and

TransmissionMicrobial Agent

Sources of

Agent in

Water Supply

General Symptoms

Gastroenteritis

Astrovirus,

Calicivirus,

Enteric

Adenovirus, and

Parvovirus

Manifests itself

in improperly

treated water

Symptoms include diarrhea, nausea, vomiting,

fever, malaise, and abdominal pain

SARS (Severe

Acute Respiratory

Syndrome)

Coronavirus

Manifests itself

in improperly

treated water

Symptoms include fever, myalgia, lethargy,

gastrointestinal symptoms, cough, and sore

throat

Hepatitis AHepatitis A virus

(HAV)

Can manifest

itself in water

(and food)

Symptoms are only acute (no chronic stage to

the virus) and include Fatigue, fever, abdominal

pain, nausea, diarrhea, weight loss, itching,

jaundice and depression.

Poliomyelitis

(Polio)Poliovirus

Enters water

through the

feces of

infected

individuals

90-95% of patients show no symptoms, 4-8%

have minor symptoms (comparatively) with

delirium, headache, fever, and occasional

seizures, and spastic paralysis, 1% have

symptoms of non-paralytic aseptic meningitis.

The rest have serious symptoms resulting in

paralysis or death
http://en.wikipedia.org/wiki/Vibrio_alginolyticushttp://en.wikipedia.org/wiki/Vibrio_alginolyticushttp://en.wikipedia.org/wiki/Vibrio_parahaemolyticushttp://en.wikipedia.org/wiki/Vibrio_parahaemolyticushttp://en.wikipedia.org/wiki/Oystershttp://en.wikipedia.org/wiki/Oystershttp://en.wikipedia.org/wiki/Vibrio_parahaemolyticushttp://en.wikipedia.org/wiki/Vibrio_parahaemolyticushttp://en.wikipedia.org/wiki/Vibrio_alginolyticus


14/27

WATER POLLUTANTS

Pollutants can originate from either a point source or a dispersed source. A point source is a channel, pipe,

or any other confined source such as a pipe discharging wastewater treatment plant effluent or untreated

wastewater into a stream. A dispersed source is an unconfined area from which pollutants enter a body of

water. For example, surface runoff from agricultural and urban areas carrying such pollutants as silt,

fertilizers, animal wastes, pesticides, and oil drips do not enter at one particular point. These materials can

enter a body of water as it flows through the area. Also, acidic runoff from mining areas is a dispersed

pollutant. Water pollutants from both point and dispersed sources can be classified into groups of

materials, based mainly on their environmental or health effects. The following list indicates common

types of pollutants of concern:

1. Pathogenic organisms

2. Oxygen-demanding materials

3. Plant nutrients

4. Suspended solids and sediments

5. Toxic chemicals and metals

6. Radioactive substances

7. Oil

8. Thermal (heat) pollution

Municipal and industrial wastewaters and runoff from farms and other open areas are sources of the first

five types of pollutants.

COMPOSITION OF MUNICIPAL WASTE WATER (SEWAGE)

When human feces and urine are diluted with flushing water or other gray water (such as from washing,

bathing, and cleansing activities), it becomes sewage, domestic wastewater, or sanitary wastewater. In

other words, from the standpoint of sources of generation, sewage or domestic wastewater may be defined

as a combination of the liquid- or water-carried wastes from residences, institutions, and commercial and

industrial establishments, together with such groundwater, surface water, and stormwater as may be

present. Sewage can be classified into two types.

Domestic sewage or domestic wastewater: human excrement, waterborne human excretion, or

watercarried wastes from liquid or nonliquid culinary purposes, washing, cleansing, laundering, food

processing, or ice production;

Municipal sewage or municipal wastewater: municipal liquid waste originating primarily from

residences, but may include contributions from Commercial, institutional, and industrial sources; and

Inflow and infiltration.


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Sewage Composition and Contaminants

Body wastes, food waste, paper, rags,

and biological cells form the bulk of

suspended solids in sewage. Even inert

materials such as soil particles become

fouled by adsorbing organics to their

surfaces. Although suspended solids

are biodegradable by hydrolysis,

biodegradable material in sewage is

usually considered soluble organics.

Soluble organics in sewage are

composed chiefly of proteins (40

60%), carbohydrate (2550%), and

lipids (approximately 10%). Proteins

are chiefly amino acids; carbohydrates

are compounds such as sugars,

starches, and cellulose. Lipids include

fats, oil, and grease. All of these

materials contain carbon that can be

converted to carbon dioxide biologically, thus exerting oxygen demand. Proteins also contain nitrogen, and

thus a nitrogenous oxygen demand is also exerted. The biochemical oxygen demand (BOD) test is

therefore used to quantify biodegradable organics. All forms of waterborne pathogens may be found in

sewage wastewater. These include bacteria, viruses, protozoa, and helminthes. These organisms are

discharged by persons who are infected with disease. A list of contaminants commonly found in sewage,

along with their sources and environmental consequences, is given in Table .

The quantity and composition of sewage vary widely from location to location depending on, for example,

food diet, socioeconomic factors, weather, and water availability. Quantitatively, constituents of sewage

may vary significantly, depending on the other kinds of wastewater and the amount of dilution from the

infiltration/inflow into the collection system. The results of analyzing a typical municipal wastewater or

sewage from a municipal collection system are given in Table .The composition of wastewater from a

given collection system may change slightly on a seasonal basis, reflecting different water uses.

Additionally, daily fluctuations in quality are also observable and correlate well with flow conditions.


16/27

Generally, smaller systems with more homogenous uses produce greater fluctuations in wastewater

composition.

MUNCIPAL SEWGAE TREATMENT PROCESSES

These can be divided basically

into three stages which are as

follows.

Physical: Physical processes

were some of the earliest methods

to remove solids from

wastewater, usually by passing

wastewater through screens to

remove debris and solids. In

addition, solids that are heavier

than water will settle out from

wastewater by gravity. Particles

with entrapped air float to the top

of water and can also be

removed. These physical

processes are employed in many

modern wastewater treatment

facilities today.

Biological: In nature, bacteria

and other small organisms in

water consume organic matter in

sewage, turning it into new

bacterial cells, carbon dioxide,

and other by-products. The

bacteria normally present in

water must have oxygen to do their part in breaking down the sewage. In the 1920s, scientists observed

that these natural processes could be contained and accelerated in systems to remove organic material from

wastewater. With the addition of oxygen to wastewater, masses of microorganisms grew and rapidly

metabolized organic pollutants. Any excess microbiological growth could be removed from the wastewater

by physical processes.


17/27

Chemical: Chemicals can be used to create changes in pollutants that increase the removal of these new

forms by physical processes. Simple chemicals such as alum, lime or iron salts can be added to wastewater

to cause certain pollutants, such as phosphorus, to floc or bunch together into large, heavier masses which

can be removed faster through physical processes. Over the past 30 years, the chemical industry has

developed synthetic inert chemicals know as polymers to further improve the physical separation step in

wastewater treatment. Polymers are often used at the later stages of treatment to improve the settling of

excess microbiological growth or bio-solids.

Preliminary Treatment Processes

Preliminary treatment is a physical process intended to remove large objects and grit from sewage. The

removal of these materials is necessary because they could reduce the efficiency or increase the

maintenance of downstream processes. Preliminary treatment may include the following processes:

screening, grit removal, comminution (activities such as cutting, crushing, powder metallurgy, grinding

and rasping which will reduce the particle size), and flow equalization.

Screening: Screening removes large objects that could clog or damage downstream equipment. Screens

typically consist of inclined steel bars spaced at equal intervals in a sewage channel. Common practice is

to use a mechanically cleaned bar screen that has an emergency bypass channel containing a manually

cleaned screen. Design parameters for bar screens include bar size, bar spacing, angle of inclination,

channel width, and sewage approach velocity.

Grit Removal: Grit consists of sand, gravel, and other high specific gravity material that may abrade and

wear mechanical equipment or may accumulate in treatment tanks. A common method for grit removal

involves using aerated grit chambers, in which diffused air is introduced

to the sewage along the bottom of one side of a rectangular chamber. This creates a rolling motion that

keeps the lighter organic materials in suspension but allows the heavier grit particles to settle to the bottom

of the tank, where they are removed.

Primary Treatment Processes

Sedimentation: Primary sedimentation is the oldest and most widely used process in treating sewage. It is

a physical process whose goal is to achieve solids separation. Solids removal by sedimentation is a

function of retention time and surface settling rate. The surface settling rate is defined as the volumetric

flow rate over the surface area of the clarifier in units of velocity. Particles whose settling velocity is

greater than the surface settling rate are removed from the sewage stream. However, if the detention time

is too long, the sewage turns septic, and gas bubbles formed in the sewage reduce the efficiency of the

process. A typical minimum side water depth for primary clarifiers is 10 feet. To allow for adequate

settling, a minimum distance of 10 feet should separate the inlet and the outlet. Clarifier design is typically


18/27

based on two flows, the average design flow and the peak hourly flow. The calculated size of the clarifier

is based on both flows, and the larger clarifier is selected.

Secondary Treatment Processes

Oxidation Ponds: Oxidation Ponds are also known as stabilization ponds or lagoons. They are used for

simple secondary treatment of sewage effluents. Within an oxidation pond heterotrophic bacteria degrade

organic matter in the sewage which results in production of cellular material and minerals. The production

of these supports the growth of algae in the oxidation pond. Growth of algal populations allows further

decomposition of the organic matter by producing oxygen. The production of this oxygen replenishes the

oxygen used by the heterotrophic bacteria. Typically oxidation ponds need to be less than 10 feet deep inorder to support the algal growth. In addition, the use of oxidation ponds is largely restricted to warmer

climate regions because they are strongly influenced by seasonal temperature changes. Oxidation ponds

also tend to fill, due to the settling of the bacterial and algal cells formed during the decomposition of the

sewage. Overall, oxidation ponds tend to be inefficient and require large holding capacities and long

retention times. The degradation is relatively slow and the effluents containing the oxidized products need

to be periodically removed from the ponds. An oxidation pond can be seen in the figure below.


19/27

Activated Sludge Processes: Activating sludge is a biological treatment process using a suspension of

microorganisms to treat sewage in an aerobic environment. The microorganisms are allowed to flocculate

and settle under quiescent conditions, and treated sewage then flows over weirs for further treatment or

discharge. Solids from the bottom of the clarifier are recycled to the reactor to provide an adequate

concentration of microorganisms for treatment. The contents of the reactor, called mixed liquor, must be

aerated and mixed by using either mechanical aerators or diffused air. There are several variations of the

conventional activated sludge process. These include plug flow reactors, including step feed, tapered

aeration, extended aeration, and complete mix reactors, including sequencing batch reactors. A plug flow

reactor has a configuration in which the sewage flows through a long, narrow channel for treatment. It

approximates flow through a pipe. In an ideal plug flow reactor, there is no longitudinal mixing of the

sewage. A step feed reactor is a variation of the plug flow reactor in which the sewage is introduced into

the reactor at several places. This allows more equal distribution of the organic load. Tapered aeration is

another variation of the plug flow reactor. In tapered aeration, the majority of the aeration capacity is

provided at the head of the reactor, where the organic load is the highest, and less aeration is provided

where the organic load is lower. Extended aeration is a treatment process requiring long detention times

(typically greater than 24 hours) and low organic loadings. Extended aeration is commonly available in

package-type treatment plants and is economical for small treatment plants. A complete mix reactor is the

opposite of a plug flow reactor. All of the sewage is completely mixed in a short, wide reactor. Due to

rapid and complete mixing of the reactor contents, complete mix reactors can tolerate shock loads better

than plug flow reactors. A sequencing batch reactor (SBR) is a variation of the complete mix reactor;

stabilization, settling, and equalization take place in the same tank, eliminating the need for a clarifier.

Aeration Requirements. The dissolved oxygen concentration in aeration tanks should be greater than 2

mg/L at all times. These aeration requirements do not include the aeration capacity needed for nitrification.

If nitrification is required, an additional oxygen per gram of ammonia nitrogen is required.

Trickling Filters: Trickling filters are a fixed film process where the microorganisms are attached to a

stone or plastic medium. The sewage flows through a rotating arm, which distributes it over the medium.

As the sewage flows over the medium, the microorganisms absorb organics from the sewage. When the

sewage is not being applied to that specific section of the medium, air flows through the filter, providing

the oxygen that the microorganisms need for respiration. Sewage is recirculated back to the filter to

maintain a proper application rate for efficient operation of the filter, to equalize the organic loading to the

filter, and to prevent the microorganisms from drying out.


20/27

Rotating Biological Contactors: Rotating biological contactors (RBCs) are another version of the fixed

film process. The microorganisms are attached to a plastic disk, which is partially submerged and rotated

through the sewage. When the microorganisms are submerged, they absorb organics. During the time the

microorganisms are exposed to the air, they receive the oxygen that is required for treatment. Treatment

efficiency is a function of the surface area of the disks,more surface area provides greater treatment.

Unlike trickling filters, no recirculation is required for rotating biological contactors.

Stabilization Ponds: Stabilization ponds are large, lined basins that may be aerobic, facultative, or

anaerobic. Ponds use detention time measured in days, rather than hours, and are typically relatively

shallow compared with other biological treatment processes. Thus, a large land area is required for ponds,

and they are usually used only in small communities. Their advantages include low construction and

operating costs. Aerobic ponds may be aerated mechanically or naturally. Natural aeration is by

atmospheric diffusion and production of

oxygen by algae. Facultative ponds have

several stratified layersan upper, aerated

section; a lower, anaerobic section; and an

intermediate section consisting of both

aerobic and anaerobic processes. Anaerobicponds may be up to 30 feet deep and are

used for treating high strength (typically

industrial) waste. Deep ponds maximize

anaerobic conditions. An anaerobic pond is

shown in the figure.


21/27

Tertiary Treatment Processes

Nitrification: Ammonia nitrogen is converted to nitrate in a two-step process, in which ammonia is first

converted to nitrites and the nitrites are then converted to nitrates. The rate-limiting step is the conversion

of ammonia to nitrite. Nitrification can co-occur with carbon oxidation, or it may take place in a separate

nitrification tank. The reaction rate is slower and, therefore, requires a

longer detention time than carbon oxidation. Nitrifying organisms have a slower growth rate than the

organisms for carbon oxidation, and the process requires a longer mean cell residence time (sludge age).

Biological Phosphorus Removal: Biological phosphorus removal can be enhanced in a two-step process.

The first step takes place anaerobically. The microorganisms release phosphorus to generate energy for the

uptake of organics. The second step is aerobic. In this step, the microorganisms absorb large amounts of

phosphorus to replace the phosphorus that was lost in the anaerobic step, as well as to store additional

energy for the next feast or famine feeding cycle. There are two major biological phosphorus removal

methodologiesthe Anaerobic/Oxic (A/O) process, and the sequencing batch reactor. The A/O process is

proprietary. Phosphorus removal in the A/O process is dependent on the BOD:P ratio. The sequencing

batch reactor may be cycled to achieve biological phosphorus removal but usually is used for smaller flows

and with more limited design data.

Denitrification: Denitrification is the removal of the inorganic nitrogen from sewage. Several species of

bacteria can use nitrates, rather than oxygen, as their energy source. These bacteria convert the nitrates into

nitrogen gas. In the denitrification process, raw sewage flows into an anoxic zone with return sludge and

return mixed liquor from an aerobic zone. The anoxic zone denitrifies by using the nitrates in the mixed

liquor. Following the anoxic zone, the sewage flows to an aerobic zone where nitrates are created. The

nitrates are then recycled to the anoxic zone for removal. Denitrification is normally done in a plug flow

type system or in an oxidation ditch, although a sequencing batch reactor may be programmed for

denitrification.

Biological Dual Nutrient Removal: Biological dual nutrient removal is the reduction of both nitrogen and

phosphorus from sewage by microorganisms. The processes are a combination of the denitrification

process and the biological phosphorus removal process. The systems may use from three to five stages to

achieve the desired nutrient removal, but all have the use of an anaerobic zone in common, followed by an

anoxic zone, followed by an aerobic zone. Some of the processes may use two anoxic zones and/or two

anaerobic zones with different recycle streams to achieve greater nutrient removal, but the treatment

principles are the same.

SLUDGE TREATMENT

Following Methods are employed for treating the residual sludge after sewage treatment.


22/27

Coagulation/Sedimentation: Coagulation/sedimentation requires chemical addition to enhance the

sedimentation of solids, precipitate pollutants, or remove phosphorus. The chemicals most commonly used

are lime, aluminum salts, ferric salts, and polymers. Chemical phosphorus removal occurs by the addition

of chemicals to the sewage, which create an insoluble phosphate precipitate. Alum is frequently used in the

chemical precipitation of phosphorus, although iron salts may also be used. Alum also reacts with

hydroxyl radicals in the water, forming aluminum hydroxide, in addition to aluminum phosphate. Iron (III)

reacts in the same manner.

Filtration: Filtration is the removal of solids by passing the sewage through a bed of granular media.

Although the most commonly used filters are composed of sand, filters may also consist of multiple types

of media, such as coal over sand or coal over silica sand over garnet sand. Filters may be classified as slow

filters, rapid filters, or pressure filters. Slow filters require a buildup of a biological mat on the upper

surface of the filter, which provides greater treatment, but requires a low application rate, and therefore

requires a larger area. Rapid filters and pressure filters depend on the entire depth of the media for

filtration and may be operated at higher loading rates than slow filters, although backwashing of the media

is required.

Activated Carbon Adsorption: Adsorption is a process by which a compound adheres to a solid surface. In

sewage treatment, activated carbon is the most commonly used adsorbent. Activated carbon comes in two

forms, powdered and granular. Powdered activated carbon (PAC) is applied in slurry form at the head of

the aeration tanks and is removed in the final clarifiers. Granular activated carbon (GAC) is used in a filter

bed. Carbon adsorption is used only where highly treated effluent is required.

Membrane Systems: Membrane processes involve the use of a semipermeable barrier. The membrane

allows the water to flow through and retains the contaminants. There are several types of membrane

systems in sewage treatment, including reverse osmosis, nanofiltration, microfiltration, and ultrafiltration.

All of these processes require pressure to force water through the membrane. Ultrafiltration requires the

least pressure, whereas reverse osmosis requires the greatest pressure.Membrane processes are subject to

fouling of the membranes. These processes should be pilot tested to determine which process and

membrane will work best. Like carbon adsorption, membrane processes are used when only high-quality

effluent is required.

Chemical Disinfection Processes

Chlorination/Dechlorination: Chlorine has been used as a disinfectant for sewage for several

reasons, including inactivation of awide range of pathogens, maintenance of a residual, and economy.

There are several forms of chlorine that may be used: gaseous chlorine, sodium hypochlorite, and calcium

hypochlorite. Chlorine is toxic to aquatic life, so the recent trend has been to dechlorinate the sewage

before discharge to the receiving stream, which is usually done by using sulfur dioxide to reduce the


23/27

chlorine to chlorides. Sodium metabisulfite or bisulfite may be used as a substitute for sulfur dioxide in

small facilities. Reaction times are nearly instantaneous, and detention times are usually less than 2

minutes.

Ozonation: Ozone is a very powerful oxidant. It can inactivate sewage pathogens with less contact

time and a lower dosage than other disinfection methods. It is effective against a wide range of organisms,

and it does not leave a toxic residual. Ozone must be generated on-site because it is unstable. Ozone is

generated by corona discharge, which consists of passing clean, dry air or oxygen through electrodes,

which are separated by a dielectric and a gap.

Physical Disinfection Processes

Ultraviolet Light Disinfection: Ultraviolet radiations whose wavelengths are in the range of 240

280 nm inactivate microorganisms by causing damage to theirDNA. Ultraviolet lamps operate in the same

way as fluorescent lampsthe radiation is generated by passing an electrical current through ionized

mercury vapor. The mercury lamps may operate at low or medium pressures. Low-pressure lamps emit the

majority of their energy at 253.7 nm, which is in the optimal range for inactivation. Medium-pressure

lamps generate a smaller portion of their energy in the 240280 nm range, but the intensity of their light is

much greater. Therefore, fewer mediumintensity lamps are required for the same amount of disinfection.

The key to understanding how and why some wastewater treatment systems work well and others

don't, is the need to understand what these microbes need to function. As microbes are living organisms,

they require certain nutrients and environments to survive, multiply and perform. In any wastewater

treatment system there is a vast array of microbes present, i.e. aerobic, anaerobic and facultative, each

performing specific functions in their respective parts of the system. Each species has a tolerance of

ecological minimums and maximums with regard to various conditions; pH, temperature, dissolved

oxygen levels and nutrient levels. All microbes require optimal conditions in order to proliferate and infuse

the system with sufficient numbers of microbes to maximize the efficiency of the wastewater treatment

plant.

Dissolved Oxygen

Knowledge about dissolved oxygen in the sewage is essential from the point of view of aquatic

life. Oxygen in water is available to the plants and animals that live there only if it dissolved. Oxygen or

DO can range in concentration from 0 to 14.6 parts per million (ppm) in water. This is also equivalent to a

weight-based measure, milligrams per litre (or mg/1). The amount of oxygen that can be dissolved in water

is inversely related to temperature, i.e. as the water temperature gets higher, the amount of oxygen that can

be dissolved in the water goes down. It is also possible under some circumstances to have oxygen levels

above 14.6 mg/1. The more oxygen that is in the water, the more diversity can be expected in the plants

and animals found in the water. Pollutants that make DO go down (besides heat) are organic wastes such


24/27

as animal or human sewage or any chemicals that will be decomposed by bacteria in the water. The

growing bacteria that break down either the organic or chemical wastes consume oxygen for their

reproduction and thus deplete oxygen in the water.

BOD Levels

Biochemical oxygen demand or BOD is a chemical procedure for determining the uptake rate of

dissolved oxygen by the biological organisms in a body of water. It is widely used as an indication of the

quality of water. BOD can be used as a gauge of the effectiveness of wastewater treatment plants. BOD

measures the rate of oxygen uptake by micro-organisms in a sample of water at a temperature of 20C and

over an elapsed period of five days in the dark. A knowledge about dissolved oxygen in the sewage is

essential from the point of view of aquatic life. Oxygen in water is available to the plants and animals that

live there only if it dissolved. oxygen or DO can range in concentration from 0 to 14.6 parts per million in

water. This is also equivalent to a weight-based measure, milligrams per litre (or mg/1). The amount of

oxygen that can be dissolved in water is inversely related to temperature, i.e. as the water temperature gets

higher, the amount of oxygen that can be dissolved in the water goes down. It is also possible under some

circumstances to have oxygen levels above 14.6 mg/1. This can happen where water goes over a dam or

other structures that causes unusual amounts of mixing. The more oxygen that is in the water, the more

diversity can be expected in the plants and animals found in the water. Pollutants that make DO go down

(besides heat) are organic wastes such as animal or human sewage or any chemicals that will be

decomposed by bacteria in the water. The growing bacteria that break down either the organic or chemical

wastes consume oxygen for their reproduction an thus deplete oxygen in the water.

Typical BOD values: Most rivers will have a 5-day carbonaceous BOD below 1 mg/L. Moderately

polluted rivers may have a BOD value in the range of 2 to 8 mg/L. Municipal sewage that is efficiently

treated by a three-stage process would have a value of about 20 mg/L or less. Untreated sewage varies, but

averages around 600 mg/L in Europe and as low as 200 mg/L in the U.S., or where there is severe

groundwater or surface water infiltration. The generally lower values in the U.S. derive from the much

greater water use per capita than in other parts of the world. In India Cooum River (Tamil Nadu) BOD

value is 36 mg/L. That is 80% more polluted than treated sewage. A common problem is the ability to

control high BOD (Biological Oxygen Demand) levels in a system. The first thought that there is not

enough oxygen in the system to do its job. This is usually based on suspicions that the mechanical

processes that generate air and oxygen - in relation to the volume capacity of the system, are not

functioning well enough or are inadequate. Traditional methods trend to either increase the oxygen levels

(dissolved oxygen) and or increase the retention capacity. This is typically the engineering solution and

does not always solve the problem.

Chemical Oxygen Demand


25/27

Chemical oxygen demand is another means of measuring the strength (in terms of pollution) of waste

water. By using this method, most oxidisable organic compounds present in the waste water sample may

be measured. COD measurements are preferred when a mixed domestic-industrial waste is entering a plant

or where a more rapid determination of the load is desired. COD is defined as the amount of oxygen

required for the chemical oxidation of organic matter with the help of strong chemical oxidants. The COD

test measures not only the oxygen equivalent of the waste organic matter but also that of the microbial

cells. The oxygen demand associated with the microbial cells is only partially exerted during a BOD test,

also some of the organic compounds measured by the COD determination may not be metabolised by the

microorganisms in either the BOD bottle or the biological treatment process. By performing a COD one

gets an idea about the total or entire organic matter and actually what one is interested to find out is the

biologically active matter which becomes the basis for further treatment. COD has certain advantages.

COD values for a given sample will be greater than BOD. The reason is that biochemical oxygen demand

measures only the quantity of organic material capable of being oxidised, while the chemical oxygen

demand represents a more complete oxidation. Results of COD can be obtained within 5 hours as

compared to 5 days of BOD. COD procedure is relatively easy and can give reproducible results. The

following ranges for COD results are given for general reference and apply primarily to average domestic

waste water. Significant amounts of industrial waste discharges may cause wide variations in these ranges.

Plant Influent 300-700 mg/l

Primary Effluent 200-400 mg/l

Trickling Filter Effluent 45-130 mg/l

Activated Sludge Effluent 30- 70 mg/l

Advanced Waste Treatment Effluent 5-15 mg

ANAEROBIC SEWAGE TREATMENT (SEPTIC TANK)

A septic tank is an underground vessel for treating wastewater from a single dwelling or building by a

combination of settling and anaerobic

digestion. Effluent is usually disposed

of by leaching. Settled solids are

pumped out periodically and hauled to

a treatment facility for disposal. When

properly sited, constructed, and

maintained, septic systems can provide

a low-cost environmentally responsible

method of waste disposal. Improperly


26/27

sited, constructed, operated, or maintained septic

systems can, however, lead to water quality

degradation and threats to public health. The basic

components of a septic tank system are shown in

Figs.

The septic tank is an enclosed receptacle designed to

collect wastewater, segregate floatable solids,

accumulate, consolidate, and store solids;

wastewater treatment is provided by septic tank

systems. The tank is the most important component

used in these systems. The waste enters the tank near

the top. There is a pair of baffles in the tank to keep

the solids in the tank, preventing them from flowing out of the tank with liquids. Bacteria in the tank break

down the solids as much as they can into a liquid form and this with the water leaves the tank on the other

side of the baffles. The liquid then flows to a leaching field where the liquid enters the soil and is absorbed.

If the bacteria cannot break the solids down, they will build up over time. If these solids are not removed

by periodic pumping, the tank will allow solids to be washed out to the leaching field and begin to clog the

soil. When the soil is clogged, the system stops working. A septic tank generally consists of a tank (or

sometimes more than one tank) of between 4000 - 7500 litres in size connected to an inlet wastewater pipe

at one end and a septic drain field at the other.

Bacterial and viral contamination from septic systems is the most common cause of drinking water

contamination. The liquid effluent from septic systems follows the same path as precipitation moving into

an unsaturated zone and aquifer. When the effluent reaches the water table, it moves down gradient to the

point of discharge (lake, stream, wetland, and well). The location of the septic system in relation to the

slope of the land surface is important because septic tank discharge follows the slope of the land surface.

Wells down-slope from septic tanks are subject to contamination. The septic tank effluent can contain

bacteria and also toxic materials and other contaminants. Some of the contaminants adhere to the soil and

aquifer material or travel with the water. A water sample from the well at a septic system site should be

obtained and analyzed for fecal coliform bacteria. Anaerobic decomposition is rapidly re-started when the

tank re-fills. A properly designed and normally operating septic system is odour free and, besides periodic

inspection and pumping of the septic tank, should last for decades with no maintenance. A well designed

and maintained concrete, fibreglass or plastic tank should last about 50 years.


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IMHOFF TANK

An Imhoff tank is a two-stage septic system where the sludge is digested in a separate tank. This avoids

mixing digested sludge with incoming sewage. The Imhoff tank, named for German engineer Karl Imhoff

(18761965), is a chamber suitable for the reception and processing of sewage. It may be used for the

clarification of sewage by simple settling and sedimentation, along with anaerobic digestion of the

extracted sludge. It consists of an upper

chamber in which sedimentation takes place,

from which collected solids slide down

inclined bottom slopes to an entrance into a

lower chamber in which the sludge is

collected and digested. The two chambers are

otherwise unconnected, with sewage flowing

only through the upper sedimentation

chamber and no flow of sewage in the lower

digestion chamber. The lower chamber

requires separate biogas vents and pipes for

the removal of digested sludge, typically after

6-9 months of digestion. The Imhoff tank is in

effect a two-story septic tank and retains the

septic tank's simplicity while eliminating

many of its drawbacks, which largely result from the mixing of fresh sewage and septic sludge in the same

chamber. Imhoff tanks are being superseded in sewage treatment by plain sedimentation tanks using

mechanical methods for continuously collecting the sludge, which is moved to separate digestion tanks.

This arrangement permits both improved sedimentation results and better temperature control in the

digestion process, leading to a more rapid and complete digestion of the sludge. This method of sediment

removal is also used in some drinking water treatment facilities, in which the tank is often called an Imhoff

cone. As in sewage treatment, the collected sludge must be properly disposed of.

microbiology of water and waste water management

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