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Lecture 4: Biological Wastewater Treatment

Prepared by

Husam Al-Najar

The Islamic University of Gaza- Environmental Engineering Department

Environmental Microbiology (EENV-2321)

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Water Use Cycle

Water SourceWater Treatment

Plant

Water

Distribution

System

Water

UseWastewater

Collection

Wastewater

Treatment

Plant

Discharge

to Receiving

Water

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Wastewater: is simply that part of the water supply to the community or

to the industry which has been used for different purposes and has been

mixed with solids either suspended or dissolved.

Wastewater is 99.9% water and 0.1% solids. The main task in treating

the wastewater is simply to remove most or all of this 0.1% of solids.

People excrete 100- 150 grams wet weight of feces

And 1- 1.3 liters of urine per person per day.

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Type of Wastewater Source of wastewater

Gray water Washing water from the kitchen, bathroom,

laundry (without faeces and urine)

Black water Water from flush toilet (faeces and urine with flush

water)

Yellow water Urine from separated toilets and urinals

Brown water Black water without urine or yellow water

Type of wastewater from household

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The amount of organic matter in domestic wastewater determines the

degree of biological treatment required.

Three tests are used to assess the amount of organic matter:

• Biochemical Oxygen Demand (BOD)

• Chemical oxygen demand (COD)

• Total Organic Carbon (TOC)

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Measurements of organic matter

Many parameters have been used to measure the concentration of organic

matter in wastewater. The following are the most common used methods:

1. Biochemical oxygen demand (BOD)

BOD5 is the oxygen equivalent of organic matter. It is determined by measuring

the dissolved oxygen used by microorganisms during the biochemical oxidation

of organic matter in 5 days at 20oC

xDFDODOBOD fit

BODt = BOD at t days (mg/l)

DOi = initial dissolved oxygen (mg/l)

DOf = final dissolved oxygen (mg/l)

Vs= sample volume (ml)

Vb = bottle volume (ml)

DF = dilution factor

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10 mL of a wastewater sample are placed in a 300-mL BOD bottle. The initial DO of the sample is 8.5 mg/L. The DO is 3 mg/L after 5 days. What is the 5-day BOD?

Example 1

Solution

Oxygen consumed in 5 days= Initial DO – final DO = 8.5 - 3= 5.5 mg/l

Dilution Factor (DF) = 300/10= 30

BOD520 = (DOi – DOf) x DF = 5.5 X 30 = 165 mg/l

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2. Chemical oxygen demand (COD)

It is the amount of oxygen necessary to oxidize all the organic carbon

completely to CO2 and H2O.

Is measured by oxidation with potassium dichromate (K2Cr2O7) in the presence

of sulfuric acid and silver and expressed in milligram per liter.

3. Total organic carbon (TOC)

This method measures the organic carbon existing in the wastewater

by injecting a sample of the WW in special device in which the carbon

is oxidized to carbon dioxide then carbon dioxide is measured and

used to quantify the amount of organic matter in the WW. This method

is only used for small concentration of organic matter.

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4. Theoretical oxygen (ThOD)

If the chemical formula of the organic matter existing in the WW is known the

ThOD may be computed as the amount of oxygen needed to oxidize the

organic carbon to carbon dioxide and a other end products.

Periodic Table of Elements

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Example 2

Calculate the Theoretical Oxygen Demand (ThOD) for sugar C12 H22 O11

dissolved in water to a concentration of 100 mg/L. Calculate "TOC".

Solution

C12 H22 O11 + 12O2 12 CO2 + 11 H2O

ThOD = sugar

sugar

ggOg

gO/123.1

342

32122

2

ThOD = sugar

sugar

sugar

sugar

mg

g

gO

mgO

g

gO

L

mg3

2

2

3

2

10

1

1

10123.1100

ThOD = 112.3 mg O2 / L

TOC = 144 g carbon/ 342g sugar = 0.42 gc/ gs

TOC = 0.42 x 100 = 42 mg carbon/L

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Typical Wastewater Composition

Concentration

Contaminants Unit Weak Medium Strong

Total Solids (TS) mg/l 350 720 1200

Total Dissolved Solids (TDS) mg/l 250 500 850

Fixed mg/l 145 300 525

Volatile mg/l 105 200 325

Settle able solids (SS) mg/l 100 220 350

Fixed mg/l 20 55 75

Volatile mg/l 80 165 275

Settle able Solids mg/l 5 10 20

Biochemical Oxygen Demand (BOD) mg/l 110 220 400

Total Organic Carbon (TOC) mg/l 80 160 290

Chemical Oxygen Demand (COD) mg/l 250 500 1000

Nitrogen (total as N) mg/l 20 40 85

Organic mg/l 8 15 35

Free ammonia mg/l 12 25 50

Nitrites mg/l 0 0 0

Phosphorus (total as P) mg/l 4 8 15

Organic mg/l 1 3 5

Inorganic mg/l 3 5 10

Chlorides mg/l 30 50 100

Sulfatea mg/l 20 30 50

Alkalinity (as CaCO3) mg/l 50 100 200

Grease mg/l 50 100 150

Total coliform no/100 ml 106 - 107 107 – 108 107 – 109

Volatile organic compounds (VOCs) mg/l <100 100 - 400 > 400

Concentration

Contaminants Unit Weak Medium Strong

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Parameter

(mg/l)

Wastewater characteristics

North area Gaza Rafah

BOD 728 667 777

COD 1385 1306 1399

SS 663 617 540

Wastewater characteristics in Gaza Strip

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Organism Concentration (per ml)

Total coliform 105 - 106

Fecal coliform 104 - 105

Fecal streptococci 103 - 104

Enterococci 102 - 103

Shigella present

Salmonella 100 - 102

Clostridium perfringens 101 - 103

Giardia cysts 10-1 - 102

Cryptosporidium cysts 10-1 - 101

Helminth ova 10-2 - 101

Enteric virus 101 - 102

Types and numbers of microorganisms typically found in untreated

domestic wastewater

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• To prevent groundwater pollution

• To prevent sea shore

• To prevent soil

• To prevent marine life

• Protection of public health

• To reuse the treated effluent

For agriculture

For groundwater recharge

For industrial recycle

Why do we need to treat wastewater ?

• Solving social problems caused by the accumulation of wastewater

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Fishing opposite to Al-Shati camp

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Raw wastewater from Al-Shati Camp (discharge to the sea)

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Sheikh Ejleen partially treated effluent

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• Protecting the public health:

Wastewater contains pathogenic microorganisms lead to dangerous

diseases to humans and animals

Hazardous matter such as heavy metals that are toxic

Produces odorous gases and bad smell

• Protecting the environment:

Raw Wastewater leads to septic conditions in the environment and

consequently leads to the deterioration of surface and groundwater quality

and pollutes the soil.

Raw wastewater is rich with nitrogen and phosphorus (N, P) and leads to

the phenomena of EUTROPHICATION.

EUTROPHICATION is the growth of huge amounts of algae and other

aquatic plants leading to the deterioration of the water quality.

Raw wastewater is rich with organic matter which consumes oxygen in

aquatic environment.

Raw wastewater may contains toxic gases and volatile organic matter

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Treatment Process

Primary

treatment

• screening

• grit removal

• removal of oil

• sedimentation

Secondary treatment

• Aerobic, anaerobic lagoons

• Trickling filter- activated

sludge-oxidation ditch

• Mostly BOD removal

technology

Tertiary treatment

• Nitrate removal

• Phosphorus removal

• Disinfection

O2

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Bar Screens

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Design Criteria:

• Depth 2.5 to 5m

• Hydraulic retention time 1-20 days

• Design Loading for BOD removals in anaerobic lagoon (Horan, 1990)

Anaerobic lagoon

Design

Temperature (oC)

Volumetric Loading (VL)

(g BOD/m3/day)

BOD Removal

(%)

< 10 100 40

10-20 20T-100 2T+20

> 20 300 60

Depth *V

Flow *influent BOD

L

Area

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Anaerobic lagoon

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Aerobic lagoon

Design Criteria:

• Depth 2 to 5m

• The European standard is considered (>5KW/103m3)

• Hydraulic retention time R = 3-5 days

• Considering the kinetic and rate of cell synthesis equation:

Le and Li are the effluent and influent BOD respectively.

KT reaction rate where KT= K20 OTT-20 where K20=1.4/day

OT =1.056 when T ranges between 20-30oC

1.135 when T ranges between 4-20oC

R)K(1

L

T

i

eL

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Aerobic lagoon/ aerators

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Example:

The North Governorate (Jabalia, Beithanoun, Beit lahya) has a total

population of 115,000 inhabitants. Design the treatment

plant (anaerobic and aerobic ponds) to treat a wastewater

of 600 mg/L to 30 mg/L.

Knowing that:

1. The wastewater production is 100 L/C/d

2. The average wastewater temperature is 23 oC

3. The treatment process is anaerobic lagoons followed by

aerated lagoons.

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facultative ponds

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facultative ponds in Nature

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Influent Treated flow

Waste

Sludge

Aeration tank

TTTTTTTTTTTTTT

Conventional activated sludge system

The first version of activated sludge systems are called conventional

activated sludge system.

This system is composed of two parts:

a. Aeration tank:

b. Final sedimentation tank

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Conventional activated sludge process

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Effluent from primary treatment is pumped into a tank and mixed with a bacteria-

rich slurry known as activated sludge.

Air or pure oxygen pump through the mixture active bacterial growth and

decomposition of the organic material.

The material then goes to a secondary settling tank, where water at the top of the

tank and sludge is removed from the bottom.

The concentration of the pathogens is reduced in the activated sludge process by

antagonistic microorganisms as well as by adsorption to or incorporation in the

secondary sludge

An important characteristic of the activated sludge process is the recycling of a

large proportion of the biomass. This results in a large number of microorganisms

that oxidize organic matter in a relatively short time.

The content of the aeration tank is referred to as the mixed- liquor suspended

solids (MLSS).

The organic part of MLSS is called Mixed- liquor volatile suspended solids

(MLVSS), which is the nonmicrobial organic matter as well as dead and living

microorganisms and cell debris.

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The activated sludge process must be controlled to maintain a proper ratio of

substrate (organic load) to microorganisms or food to microorganisms ratio (F/M)

VMLSS

BODQ

M

F

*

*

Where,

Q = flow rate of sewage

BOD = biological oxygen demand

MLSS = mixed- liquor suspended solids

V= volume of the aeration tank

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PRIMARY AERATION TANK

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CRYOGENIC AIR SEPARATION FACILITY (HYPERION TREATMENT PLANT)

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The important parameters controlling the operation of the activated sludge process

are organic loading rate, oxygen supply, and control and operation of the final

settling tank.

For routine operation, sludge settleability is determined by use of the sludge

volume index (SVI)

MLSS

VSVI

1000*

The microbial biomass produced in the aeration tank must settle properly from

suspension so that it may be wasted or returned to the aeration tank.

Good settling occurs when the sludge microorganisms are in the endogenous

phase, which occurs when carbon and energy sources are limited.

A common problem in the activated sludge process is filamentous bulking, this

caused when excessive growth of filamentous microorganisms. The filaments

produced by these bacteria interfere with sludge settling and compaction.

Filamentous bacteria are able to predominate under conditions of low dissolved

oxygen, low nutrients and high sulfide levels.

Where, V= volume of settled sludge after 30 minutes

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1000 ml 1000 ml

30 Minute

SV

Sludge

Volume: ml

Sludge Volume Index (SVI)

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OPERCULARIA SP VORTICELLA CONVALLARIA ENTAMOEBA HISTOLYTICA

ESCHERICHIA COLI LECANE SP. (ROTIFER) POLIOVIRUS