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Wastewater Treatment
Bülent Mertoğlu
Wastewater Contaminants
Suspended solids
Priority pollutants: metals (Cd, Hg), benzene compounds, and
chlorinated compounds
Microorganisms: pathogenic and nonpathogenic
Organics: refractory and biodegradable
Nutrients:
– Phosphorus, Nitrogen (ammonia, nitrites, nitrates)
Typical Composition of Untreated Wastewater
Constituent Weak (mg/l) Strong (mg/l)
Alkalinity 50 200
BOD5 100 300
COD 250 1000
Suspended Solids 100 350
TDS 200 1000
Total Nitrogen 20 80
Total Organic Carbon 75 300
Total Phosphorous 5 20
7
The amount of organic carbon present determines:
the amount of O2 needed for biological treatment
the size of waste treatment facility needed
the efficiency of the treatment process
biochemical oxygen demand
total organic carbon
chemical oxygen demand
Objective 1 - Reduce organic content (reduction of BOD)
There are three methods to determine carbon present:
Biochemical Oxygen Demand (BOD)
Definition: The amount of dissolved oxygen utilized by microbes for
the biochemical oxidation of organic (carbonaceous BOD) and
inorganic (autotrophic or nitrogenous BOD)
The BOD test was developed in 1930’s. This is a five day test that
measures the amount of O2 consumed in a wastewater sample by a
mixed population of heterotrophic bacteria in the dark at 20oC
BOD of wastewater is typically 110-440 mg/L and must be reduced
to 20 mg/L for discharge
BOD = Di – Df
P
where:
Di = initial dissolved O2 concentration
Df = final or 5-day dissolved O2 concentration
P = volumetric fraction of wastewater
Example: 5 ml wastewater is added to a 300 ml BOD flask
P = 5 = 0.0167 Di = 8 mg/L Df = 2 mg/L300
BOD = 8 – 2 = 359 mg/L0.0167
Oxidation is usually 60-70% complete after 5 days
Total Organic Carbon (TOC)
TOC is measured using a TOC analyzer. The sample is combusted
and organic carbon quantified using infrared detection.
Chemical Oxygen Demand (COD)
COD is measured following digestion at high temperature with
strong oxidant such as chromic acid, or sulfuric acid/potassium
dichromate. The chromate ion reacts with the COD producing a
color that is measured.
If COD >> than BOD what does this mean?
Total Kjeldahl Nitrogen
TKNOrg-N (Amino Acids, Urea)
NH4-N
N2: Nitrogen gas (79 % of air)NH3: ammoniaNH4- : ammonium ionNO2- : nitrite ionNO3- : nitrate ionOrg N: organic nitrogenTKN: Total Kjeldahl Nitrogen(% 40 org N -- %60 NH4H )
Nitrogen Removal:
Activated Sludge Process
Introduction
Biological wastewater treatment systems, microorganisms are the main players.
19
Applications
1. Carbonaceous removal - aerobic
- anaerobic
2. Nitrogen removal - nitrification
- denitrification
3. Phosphate removal - anaerobic/aerobic
20
Microbial Group Electron Donor Electron Acceptor Carbon Source
Aerobic Heterotrophs
Org. Carbon O2 Org. Carbon
NitrifiersNH4
+
NO2-
O2
O2
CO2
CO2
Denitrifiers Org. Carbon NO3- Org. Carbon
MethanogensAcetate
H2
AcetateCO2
AcetateCO2
Activated Sludge Principles
• The microorganisms are “activated” for rapid uptake of new
substrate, thus the term activated sludge
• Bacteria are encouraged to grow by providing
− Oxygen
− Food (Organic compounds - BOD)
− Nutrients
− Correct temperature
− Time
• As bacteria consume BOD, they grow and multiply
• The basis of the activated sludge process is the growth of floc
forming bacteria on wastewater organics
22
Bacterial Growth Curve
• Lag-phase During this phase bacteria become acclimated to their
new surroundings. They are digesting food, developing enzymes
and other things required for growth.
• Accelerated Growth-phase The bacteria are growing as fast as
they can, since there is an excess of food. The cells are mostly
dispersed, not sticking together.
• Declining Growth-phase Reproduction slows down because there
is not an excess of food. A lot of food has been eaten and there are
now a large number of bacteria to compete for remaining food, so
the bacteria do not have enough remaining food to keep the growth
rate at a maximum.
Bacterial Growth Curve
• Stationary-phase The number of bacteria is the highest possible,
but not much food is left, so the bacteria cannot increase in number.
There is some reproduction, but some cells are also dying, so the
numbers of bacteria remain relatively constant. The bacteria have
now lost their flagella and have a sticky substance covering the
outside of the cell, allowing them to agglomerate into floc. In fact,
the floc gets big enough that if aeration and mixing were stopped,
the floc could settle to the bottom.
• Death-phase The death rate increases with very little if any growth
occurring. Therefore, the total number of living bacteria keeps
reducing. The bacteria are just trying to keep alive.
Activated Sludge
Activated sludge process consists of an aerated tank and a settler.
Monod Equation
Oxidation Ditch
Treatment Plants in Istanbul
Paşaköy Wastewater TreatmentPlant
Anoxic Tank
Oxic Tank
Aeration Tank
Overflow
Mechanical Aerators
Fixed aerator Floating aerator
Turbine aerator
Diffusers
Air Pipe Header Diffusers
Recycle Pipe
Aeration Tank