L4. Biological Wastewater Treatment2 PDF
L4. Biological Wastewater Treatment2 PDF
L4. Biological Wastewater Treatment2 PDF
Prepared by
Husam Al-Najar
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Water Use Cycle
Water
Water Treatment
Water Source Distribution
Plant
System
Wastewater Discharge
Water Wastewater Treatment to Receiving
Use Collection Plant 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.
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Type of wastewater from household
Black water Water from flush toilet (faeces and urine with flush
water)
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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
Solution
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2. Chemical oxygen demand (COD)
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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.
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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
12 32 gO2
ThOD = 1.123gO2 / g sugar
342 g sugar
100mg sugar 1.123gO2 10 3 mgO2 1g sugar
ThOD = 3
L g sugar 1gO2 10 mg sugar
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
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Concentration
Nitrites mg/l 0 0 0
Inorganic mg/l 3 5 10
Volatile organic compounds (VOCs) mg/l <100 100 - 400 > 400
Wastewater characteristics in Gaza Strip
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Types and numbers of microorganisms typically found in untreated
domestic wastewater
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
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Why do we need to treat wastewater ?
• 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
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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 19
Treatment Process
O2
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Bar Screens
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Anaerobic lagoon
Design Criteria:
• Depth 2.5 to 5m
• Hydraulic retention time 1-20 days
• Design Loading for BOD removals in anaerobic lagoon (Horan, 1990)
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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
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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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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
Influent
Aeration tank Treated flow
TTTTTTTTTTTTTT
Waste
Sludge
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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)
F Q * BOD
M MLSS *V
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)
V *1000
SVI Where, V= volume of settled sludge after 30 minutes
MLSS
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.
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Sludge Volume Index (SVI)
1000 ml 1000 ml
30 Minute
SV
Sludge
Volume: ml
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PSEUDOMONAS SP NITROBACTER SP CARCHESIUM SP