This document summarizes the multi-stage process of wastewater treatment. It begins with primary treatment which uses screens and sedimentation tanks to remove solids. Secondary treatment uses biological processes like activated sludge to break down organic matter. Tertiary treatment provides further purification through processes like filtration, nutrient removal, and disinfection. New developments include using nanostructured silica to remove heavy metals. Proper wastewater treatment is needed to safely discharge water back into the environment after removing contaminants.

1. By,
DAMARIS BENNY DANIEL
II MSc. Zoology

2. INTRODUCTION
• Physical, chemical or biological change in the water quality that
adversely affects the living organisms or makes water unsuitable for
desired uses is water pollution.
• Water pollution abatement technologies are used to reduce the
harmful effects of polluted water.
• It mainly includes wastewater treatment that uses physical, chemical
and biological methods to remove contaminants.
• The treatment of wastewater is mainly carried out in 3 stages
– Primary treatment
– Secondary treatment
– Tertiary treatment

3. PRIMARY TREATMENT
• Removes solids that are suspended in the waste water via physical
settling or filtration.
• The major steps are:
1. Wastewater is screened to remove larger objects
2. Then grit is removed
3. Rest of the solids are finally extracted using gravity in large
sedimentation tanks.

4. BAR SCREEN
• Wastewater first pass through bar screens (or bar racks).
• It removes coarse solids like sticks, stones and other large
objects.
• Screens of various size & shape are used depending on the
nature of solids to be removed.
• Bar screens consist of parallel metal bars, which have 20 –
60mm bars for coarse screens & 10 – 20mm bars for fine &
medium screens.
• It should be manually cleaned continuously to avoid clogging
problems.

5. GRIT CHAMBER
• Grit – small & dense materials like sand, dirt or broken glass.
• It is usually removed in grit chamber.
• It is a chamber in which the velocity of waste water flow is
reduced to a point where the denser grit will settle out, but the
organic solids will remain in suspension.
• Usually the velocity of flow will be b/w 0.15 – 0.3m/s

6. SEDIMENTATION TANK
• From grit chamber the effluent is passed into a primary settling tank
(Sedimentation tank).
• Here the suspended solids are removed by gravitational settling
under motionless conditions.
• Flocculants ( chemicals used to precipitate insoluble substances) are
added to water to promote sedimentation.
• The purpose of flocculation is to cause small pollutant particles to
aggregate and form large enough floc so that they settle down fast.
• Wastewater is let to stand for 2 – 3 hrs and it results in the removal
of 50% - 65% of suspended solids
• The settled solids is called primary sludge or raw sludge.

7. SEDIMENTATION TANK
• It usually have
– Inlet zone
– Settling zone
– Sludge zone
– Outlet zone

8. SECONDARY TREATMENT
• After primary treatment the effluent undergoes a secondary
treatment which degrades the biological content of the sewage.
• This usually uses biological processes.
• Microorganisms are introduced to the wastewater and consume the
organic matter, oxygen is delivered to the system ensuring
microorganism survival.
• This biological process occurs naturally in nature, but is accelerated
in secondary treatment systems.
• This is mainly done by activated sludge process, trickling filters,
aerated lagoons and oxidation ponds.

9. ACTIVATED SLUDGE PROCESS
• Activated Sludge Process uses micro organisms to feed on organic
contaminants in waste water.
• Basic principle
– When micro organisms grow, they form particles that clump
together
– These particles ( floc) are allowed to settle to the bottom of the
tank, leaving a relatively clear liquid free of organic material and
suspended solids.
• Thus, the settled organic matter that consist of several activated micro
organisms are called activated sludge.

10. ACTIVATED SLUDGE PROCESS
Process
• Waste water is aerated - forms floc with micro organism.
• These micro organism breaks down the suspended organic matter and
produce stable solids and multiplies to form more micro organisms.
• The wastewater from aeration tank is passed into the settling tank (clarifier)
and solids settle down – activated sludge.
• A part of the settled sludge is returned to the influent of the
aeration tank – returned activated sludge.
• Periodically, the excess solids and organisms
are removed from the system –
waste activated sludge – fed into the sludge digestor.

12. SLUDGE DIGESTION
• The sludge which settles in the sedimentation basin is pumped
to the sludge digestors where a temperature of 30–35ºC is
maintained.
• It is designed to encourage the growth of anaerobic bacteria
that decreases organic solids by reducing them to soluble
substances & gases (CO2 & CH4).
Complex organic
compounds
Acid forming
bacteria
organic acids
Methane forming
bacteria
CH4, CO2, H2S &
other
compounds
1st stage conversion 2nd stage conversion

13. OXIDATION POND
• Oxidation ponds are large, shallow ponds designed to treat waste water
through the interaction of sunlight, bacteria and algae.
• Algae grow within the pond and utilize sunlight to produce oxygen during
photosynthesis.
• This O2 is used by the aerobic bacteria in the oxidation pond to
breakdown the organic waste in the wastewater.
• The broken down solids
settle down in the
ponds, resulting in
effluent that is relatively
well treated.

14. AERATED LAGOON
• It is a treatment pond with artificial aeration to promote the
biological oxidation of waste water.
• Natural lagoons are made up of three layers an aerobic (layer with
oxygen), an anaerobic (layer with no oxygen) and a facultative
(mixed layer).
• In a constructed aerated lagoon air is pumped into the lagoon to turn
the whole pond into an aerobic zone.
• Adding air to the water speeds up the natural processes that break
down organic waste.
• Mechanical aeration device is present which supply the oxygen
needed by bacteria for stabilization

15. AERATED LAGOON

16. TRICKLING FILTERS
• Trickling Filter is an aerobic treatment system that utilizes
microorganisms attached to a medium to remove organic matter from
wastewater.
• It consist of a bed of packing material to which microbes are attached.
• This microbial growth on the filtering medium consists of bacteria, fungi,
algae etc and is called biological slime.

17. PROCESS
• Wastewater is sprayed into the air, then allowed to trickle through the
media.
• Microorganisms, attached to the media, break down organic material in
the wastewater.
• When more & more wastewater is passed, the slime layer thickens and
eventually gets detatched from the surface. This is called sloughing.
• A settling tank after the trickling filter, removes the detatched bacterial
film and some suspended matters.

18. TERTIARY TREATMENT
• It is the final treatment the waste water undergoes before it is
discharged into the environment.
• Also referred to as effluent polishing.
• The purpose of 30 treatment is to improve the 20 treated waste
by removing the nutrients and dissolved solids.
• The major processes done are:
– Filteration
– Nutrient removal
– Disinfection

19. • FILTERATION
• Either sand or activated charcoal is used to filter treated
effluent.
• NUTRIENT REMOVAL
• High levels of nutrients such as N2 & P must be removed –
otherwise eutrophication.
• Phosphorous removal
• Phosphorous can be removed by Polyphosphate accumulating
organisms (PAOs).
• It can also be removed by chemical precipitation, usually with
salts of Fe, Al or lime.

20. • Nitrogen removal
• In wastewaters, much of the nitrogen is found in the form of
ammonia.
• When secondary treatment is used, a great deal of this ammonia is
discharged in the effluent.
• Bacteria can utilize this ammonia as an energy source and convert
ammonia to nitrite and nitrate.
NH3 NO2 NO3
• DISINFECTION
• To kill micro – organisms present in water
• Chlorination is the most common method.
• UV light & ozone can also be used for disinfection.
Nitrosomonas Nitrobacter

22. RECENT DEVELOPMENTS
• New Wastewater Treatment System Removes Heavy
Metals
• Resulting from the combination of water
treatment investigations with the latest in
material science, a new type of nano material
called nano structured silica was found
to detect and eliminate heavy metals from wastewaters in
efficient and economically viable ways.
• This investigation has been published on the 2011 June release
of Journal of Separation Science and Journal of Colloid
Interface Science

23. CONCLUSION
• Waste water treatment is done to remove contaminants from
water.
• It is broadly classified into primary, secondary and tertiary
treatments.
• After going through all these processes, the water obtained
will be hygenic & safe for discharging into the environment.

24. BIBLIOGRAPHY
• Aloka Debi, Environmental Sience and Engineering (2008),
University Press, Hyderabad
• Chaudary D.S and Sundaravadivel M, Environmental management
(2004), Scitech Publications, Chennai.
• Madhab Chandra Dash and Satya Prakash Dash, Fundamentals of
Ecology, 3rd edition, McGraw Hill Companies, New Delhi.
• http://water.me.vccs.edu/courses/ENV108/lesson1_2.htm
• http://www.fao.org/docrep/t0551e/t0551e05.htm