Philadelphia University
Faculty of Engineering
Department of Civil Engineering
First Semester, 2013/2014
ENVIRONMENTAL
ENGINEERING
343
Lecture 9:
Wastewater treatment 1
SOME PHYSICAL AND CHEMICAL PROPERTIES OF
WASTEWATER
1- INORGANIC SUBSTANCES
A -Nutrients: Two nutrients are essential for the
growth of organisms:
Nitrogen
 Phosphorus
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I- INORGANIC SUBSTANCES
Nitrogen; Exist in a form of “inorganic”, and “organic
nitrogen
Measured by TKN “total Kjeldahl Nitrogen; is a
measure of the total organic and ammonia nitrogen.
Phosphorus ; Exist in a form of “inorganic”, and
“organic phosphate
Total phosphorus (P)
Nitrogen & Phosphorus are essential for building cell
DISSOLVED OXYGEN
One of the most important measures of water quality
is dissolved oxygen. Oxygen, although poorly soluble in
water, is fundamental to aquatic life. Without free
dissolved oxygen, streams and lakes become
uninhabitable to aerobic organisms, including fish and
most invertebrates.
It is found that the concentration of DISSOLVED
OXYGEN in water is SMALL
Dissolved oxygen is inversely proportional to
temperature, and
the maximum amount of oxygen that can be dissolved
in water at 0°C is 14.6 mg/L to 7.6 at 30C.
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Dissolved oxygen in water is consumed by the oxidation
of dissolved ammonia (NH3)and ammonium ion (NH4+)to
form the nitrate ion (NO3⎯).
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NH3(aq) + 2O2(aq) + OH-----NO3-(aq) + 2H2O(aq)
The most common substance oxidized by oxygen in water
is ORGANIC MATTER OF BIOLOGICAL ORIGIN
Such organic matter (such as dead plant material
like polymerized carbohydrate below), is oxidised
by dissolved oxygen.
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e.g. CH2O+O2(aq) ------ CO2(g) + H2O(aq)
SOME PHYSICAL AND CHEMICAL PROPERTIES
OF WASTEWATER
II- ORGANIC SUBSTANCES
Various parameters are used as a measure of the
organic strength of wastewater:
BOD –Biochemical oxygen demand
 COD –Chemical oxygen demand
 TOC –Total organic carbon
 VSS –Volatile suspended solid
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II- ORGANIC SUBSTANCES
1- BIOCHEMICAL OXYGEN DEMAND- BOD
The quantity of oxygen utilized by a mixed population
of micro organisms to biologically degrade the
organic matter in the wastewater under aerobic
condition.
BOD is the most important parameter in water
pollution control.
it is used a measure of organic pollution as a basis
for estimating the oxygen
Needed for biological processes, as and indicator
of process performance
Expressed in milligrams of oxygen required per liter of
wastewater (mg/L).
BIOCHEMICAL OXYGEN DEMAND
BOD : BOD5: is the amount of dissolved oxygen
used up from the water by microorganisms as they
break down organic material at 20C over a 5-day
periods.
BOD5 for Rivers if > 5 mg/L, they considered polluted
 BOD For MWW range 150-1000mg/L
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II- ORGANIC SUBSTANCES
2- chemical oxygen demand -COD
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Determine the amount of oxygen needed to oxidize
the organics in a water or wastewater using a strong
oxidizing chemical agent- Potassium dichromate
rather than using micro-organisms as in BOD
It measures the total organic carbon with the
exception of some aromatics such as benzene which
are not oxidized in the reaction.
Indirectly measure amount of organic matter in the
water sample
Faster determination of oxygen demand in a water
sample, than BOD
It takes shorter time ( 2hrs) compared to 5 days for
BOD5
The EU upper limit of 125mg/L for treated
wastewaters prior to discharge to rivers
RELATION BETWEEN COD AND BOD
COD > BOD
 COD ~ ultimate BOD
 COD/BOD ~ 2, biodegradable organic
 COD >> BOD, non-biodegradable organic
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II- ORGANIC SUBSTANCES
3-TOTAL ORGANIC CARBON- TOC
TOC- : measures all carbon as CO2 in mg/L
 Inorganic carbon ( HCO3, CO2, CO3, etc) must be
removed prior test by acidifying and aerating the
sample.
 Theoretically the COD is 2.66 times greater than
TOC
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Composition of WW
Pathogens
Biodegradable Organics
Suspended
Solids
Soluble organics
Body waste, food
waste rags, paper,
biological cells
Protein (4060%) – amino
acids
Carbohydrates
25-50% - sugars
starch, cellulose
Bacteria, virus
etc.
Lipids (10%)fats, oils and
grease
Contain Carbon – exert an oxygen
demand
Wastewater Treatment Plants
Wastewater Characteristics –
Industrial
Municipal
If Industrial waste characteristics
are similar to municipal, the waste
is discharged into the municipal
sewers. If not, pre-treatment is
required
Note: although suspended organic
materials are biodegradable, In
wastewater we consider
biodegradable materials to be of the
Soluble type.
The
composition
of municipal
waste varies
seasonally as
well as daily.
Note: Unit
Operation –
contaminants are
removed via physical
forces
Unit Process –
contaminants are
removed via
chemical and or
biological processes
WASTEWATER
TREATMENT PLANTS
Municipal treatment is divided
into: Primary, Secondary and
Tertiary
Primary Treatment – removes
solid materials from streamLarge debris may be removed
by screens or reduced in size
by grinding device.
Inorganic solids are removed by
the grit chamber
Much of the organic suspended
solids are removed by
sedimentation
Primary treatment removes 60%
SS and 35% BOD
This treatment is still the only
treatment for used by many
cities around the world
WASTEWATER TREATMENT PLANTS
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Secondary Treatment: the major goal is to remove the
soluble BOD and SS that escape the primary treatment
Consist of the biological conversion of colloidal organics
into biomass – this is then removed by sedimentation
Designed to speed up these natural processes so that the
break down of degradable organic pollutants can be
achieved in relatively short time periods
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May remove > 85% BOD & SS;
Not removing N, P & heavy metals or pathogens
Contact is maintained between the MO and the organics
by:
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Suspending biomass in a reactor – Activated Sludge System
Passing the wastewater over a film of biomass attached to a
solid - Trickling Filter
WASTEWATER TREATMENT PLANTS
WASTEWATER TREATMENT PLANTS
 Trickling
Filter
 Stones are used to increase the surface area
for biofilm growth.
 Mature
biofilms become dislodge due to
friction and are washed out of the settling
basin with the liquid flow.
 Part
of the liquid effluent may be recycled to
the trickling filter for additional treatment or
to maintain hydraulic flow rates
TRICKLING FILTER
WASTEWATER TREATMENT PLANTS
Sludge Digestion
 Sludge from primary treatment as well as the
secondary clarifier are sent to the sludge
digestion unit where it is undergoes anaerobic
degradation.
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The results are:
Methane – Used for power generation
CO2
Liquid – contains high organic – recycled through
the plant
Inert solids – contains high minerals – soil
conditioner/ fertilizer on agricultural lands
CLARIFIER
SLUDGE DIGESTER