What is wastewater treatment?
process of removing contaminants from wastewater,
both runoff and domestic and making it suitable to
discharge back into the environment.
Municipal wastewater treatment
Industrial wastewater treatment
How can we say water is pure?
a) Total solid (tested by boiling water)
a. Biological oxygen demand (BOD)
b. Chemical oxygen demand (COD)
Methods involved in wastewater
Mechanical (Physical) Treatment
Secondary (Biological) Treatment
Tertiary (Chemical) Treatment
The objective of preliminary treatment is the removal of
coarse solids and other large materials often found in raw
Removal of these materials is necessary to enhance the
operation and maintenance of subsequent treatment unit.
Removal of large non biodegradable and floating solids
(e.g. rags, clothes, woods, plastics, papers etc.)
Grit particles which are smaller than the aperture of the
coarse screen will pass through and may cause
abrasive problems to pipes and pumps.
In grit removal process, velocity is so controlled that grit
may settle but most of the organics are retained in
Objective is the removal of settelable organic and
inorganic solids by Sedimentation, and the removal of
the material that will float (scum) by skimming.
Around 25-50% of the incoming BODs, 50-70% of the
total suspended solids and 65% of oil and grease are
removed during primary treatment.
• Secondary treatment is designed to substantially degrade the biological content of the
sewage which are derived from the human waste, food waste, soaps and detergents etc.
• Aerobic bacteria and protozoa consume biodegradable soluble organic contaminants
(e.g. sugar, fats, short chain carbon molecules etc.) and binds much of the less soluble
fractions into floc.
• Microorganisms must be separated from the treated water by sedimentation to produce
clarified secondary effluent.
• Biological floc is settled out in secondary clarifier and the secondary sludge is then sent to
sludge treatment unit.
Wastewater may contain high level of nutrients (N or P
compounds) which excessive release to environment
may cause eutrophication.
Overgrowth of weeds, algae, blue-green algae
Toxins produced by some algae may contaminate
drinking water supply.
• Biological oxidation of nitrogen from ammonia to nitrate.
I. Ammonia to nitrite using Nitrosomonas
II. Nitrite to Nitrate using Nitrobacter ssp.
DE nitrification (anoxic condition)
• Nitrate is converted into nitrogen gas and released into air.
• Using Polyphosphate Accumulating Organism (PAOs)
• The process is called “Enhanced biological phosphorus
By chemical precipitation
• Using salts of irons (e.g. ferric chloride) or aluminium
(e.g. alum) or lime.
Purpose is to provide a final treatment stage to further improve the
effluent quality before it is discharged to the receiving environment.
• to reduce the number of microorganisms
Odor emitted by wastewater treatment are typically an
indication of anaerobic or septic condition.
Generally arises due to hydrogen sulfide.
Controlled by adding iron salts or hydrogen peroxide or
This process describes the management and disposal of
primary and secondary sludge.
processes involved are
Anaerobic bacteria acts on sludge and produces large
amount of waste solids and biogas ( high concentration
Methane can be used to generate electricity and run
Solid waste (containing water) is sent for composting.
An aerobic process that involves mixing of wastewater
solids with sources of carbons such as sawdust, straw or
Aerobic bacteria digests both wastewater solids and
carbon source and produce large amount of heat.
Resultant solid is then sent for dewatering.
Water is removed from solid waste for volume reduction.
Using drying beds
Mechanically filtering often through cloth screens.
The sludge is now ready to be used off sites as fertilizers.