Sewage and liquid waste management involves treating sewage through various stages. Sewage first undergoes pre-treatment which includes screening to remove large debris and grit removal to allow sand and gravel to settle. It then undergoes primary treatment which uses sedimentation to remove 50-70% of solids. Secondary treatment uses biological processes like activated sludge or trickling filters to reduce organic material using oxygen and bacteria. The treated effluent undergoes disinfection before being disposed of safely while sludge is digested and disposed of through methods like land application or sea disposal. Various treatment stages aim to purify sewage to acceptable standards before disposal.

1. Sewage and liquid waste management
Dr. N. Bayapa Reddy
Associate professor
Dept. of Community Medicine
The Apollo Medical College

2. Definitions
Sewage: Waste water consisting of liquid & solid human
excreta together with Liquid from houses, cow-shed,
stables, & factories.
Sullage: waste water without human excreta
Dry weather flow: the average amount of sewage which
flows through the sewerage system in 24 hours
Sewage Treatment
• Wastewater treatment consists of applying known
technology to improve or upgrade the quality of a
wastewater

3. Urban Waste Water
• Sources:
Wastewater produced by residential and commercial
establishments and discharged into sewers
• What is in it?
– Domestic waste
– Industry
– Rainwater run-off

4. STP
• Sewage can be treated close to where it is created in
septic tanks, Biofilters or aerobic treatment systems, or
collected and transported to a municipal treatment plant
• The principal objective of wastewater treatment is
generally to allow human and industrial effluents to be
disposed off without danger to human health or
unacceptable damage to the natural environment

5. Health aspects
• Creation of nuisance, unsightliness and unpleasant
odours
• Breeding of flies and mosquitoes
• Pollution of soil and water supplies
• Contamination of food
• Increase in the incidence of disease especially enteric
and helmenthic diseases

6. Aim of sewage purification
• Raw sewage or inadequately treated sewage should
not be discharged into rivers, sea or other source of
water supply
• The Oxygen in the water is consumed by aerobic
bacteria
• Stabilize the organic matter so that it can be disposed
off safely
• Convert the sewage water into an effluent of an
acceptable standards

7. The strength of sewage is expressed
• Biological oxygen demand (BOD):- the amount of
oxygen absorbed by a sample of sewage during
specific period (5days) at specific temperature (200
C)
– Normal 300 mg/l
– if its more than that it is strong
– If it is 100 mg/L it is weak
• Chemical Oxygen Demand (COD)
• Suspended solids 100-500 ppm
– SPM 100 ppm it is waek
– SPM 500 ppm it is strong

8. Treatment
• Pre-treatment
• Primary treatment
• Secondary treatment
• Tertiary treatment
• Sludge treatment
• Sludge disposal

9. Conventional wastewater treatment
processes

10. Conventional wastewater treatment consists of a
combination of physical, chemical and biological
processes and operations to remove solids, organic
matter and sometimes, nutrients from wastewater.
General terms used to describe different degrees of
treatment, in order of increasing treatment level, are
preliminary, primary, secondary, and tertiary and/or
advanced wastewater treatment.
In some countries, disinfection to remove pathogens
sometimes follows the last treatment step

11. Pre-treatment
• Screens
– Remove large debris (large organic matter)
– Remove suspended solids
• Grit traps
– Slow down flow rate to allow coarse grit to settle
out
• Mechanical
• Landfill or recycled

12. A. screening
screening Metal screen which intercepts
large floating objects to prevent clogging
of treatment plant.

13. B. Removal of grit
• This chamber is approximately
– 10 to 20 mts in length;
– it is so designed as to maintain a constant velocity of
about 1 foot per second,
– with a detention period of 30 seconds to 1 minute
• Grit chamber is to allow the settlement of heavier solids
such as sand and gravel, while permitting the organic
matter to pass through.
• The grit which collects at the bottom of the chamber
is removed periodically or continuously.

14. Grit chamber
Aerated grit chamber :
diffused air keeps organic
solids in suspension as grit
settles
Vortex - Type Grit Chambers
Vortex is created
-Grit move to the outside
of the unit and gets collected

15. Primary Sedimentation or primary clarifiers
• The tanks are large enough to hold from 1/4 to 1/3 the
dry weather flow
• Sewage is made to flow very slowly across the tank at
a velocity of 1-2 feet per minute.
• spends about 6-8 hours in the tank
• Nearly 50-70 per cent of the solids settle down under
the influence of gravity
• that sludge can settle and floating material such as
grease and oils can rise to the surface and be
skimmed off.

16. Primary treatment
The objective of primary treatment is the removal of settle-
able organic and inorganic solids by sedimentation, and
the removal of materials that will float (scum) by skimming
Approximately 25 to 50% of the incoming biochemical
oxygen demand (BOD5), 50 to 70% of the total suspended
solids (SS), and 65% of the oil and grease are removed
during primary treatment
Some organic nitrogen, organic phosphorus, and heavy
metals associated with solids are also removed during
primary sedimentation

17. Primary Sedimentation Tank

18. Secondary Treatment
The treatment processes used to reduce
the BOD of sewage waste are secondary
treatment processes.

19. Secondary Treatment
• Removes dissolved organic material
– Activated sludge
– Trickling filter beds
• Using aerobic biological processes to consume soluble organic
contaminants
– Oxygen
– Bacteria

20. A. Trickling Filters / Percolating filter
The trickling filter or percolating filter is a bed of
crushed stones or cinker, 1 to 2 m (4-8 ft.) deep
and 2 to 30 m (6-100 ft.) in diameter
The effluent from the primary sedimentation tank
is sprinkled uniformly on the surface of the bed
by a revolving device.
The device consists of hollow pipes each of which
have a row of holes.

21. zoogleallayer
• Over the surface and down through the
filter
– a very complex biological growth consisting of
algae, fungi, protozoa and bacteria of many
kinds occurs. This is known as the
"zoogleallayer".
– zoogleal layer lives, grows and dies. The
dead matter sloughs off, It is a light green,
flocculent material and is called "humus".

22. Trickling Filter Beds
• Sewage sprinkled over porous
material
• Contains micro-organisms
– Breaks down organic matter
– Reduces BOD
• Rotating ars
• Beds of:
– Coke
– Limestone
– Plastic
• Large surface area
• Drains collect water and provide
oxygen
• May need recirculation

23. B. Activated sludge process
• Activated Sludge is a widely used aerobic method of
sewage treatment.
• After primary settling, the waste stream is brought to
an aeration tank.
• The effluent from the primary sedimentation tank is
mixed with sludge drawn from the final settling tank
(also known as activated sludge or return sludge; this
sludge is a rich culture of aerobic bacteria).
• The "heart" of the activated sludge process is the
aeration tank.
• The mixture is subjected to aeration in the aeration
chamber for about 6 to 8 hours

24. Activated Sludge and Aeration
• Addition of solids
rich in micro-
organisms and
dissolved oxygen
• Promotes the
growth of
biological flocs
• Helps decompose
organic matter

25. • The typhoid and cholera organisms are definitely
destroyed, and the coliforms greatly reduced.
• Activated sludge plants occupy less space, require
skilled operations.
• One acre of activated sludge plant does the work of
10 acres of percolating filter.

26. Secondary sedimentation
• The oxidized sewage from the trickling filter or aeration
chamber is led into the secondary sedimentation tank
where it is detained for 2-3 hours.
• The sludge that collects in the secondary sedimentation
tank is called 'aerated sludge' or activated sludge,
because it is fully aerated.
• Part of the activated sludge is pumped back into the
"aeration tanks" in the activated sludge process and the
rest pumped into the sludge digestion tanks for
treatment and disposal

27. Sludge digestion
• One of greatest problems associated with sewage
treatment is the treatment and disposal of the
resulting sludge.
• One million gallons of sewage produces 15-20 tons of
sludge.
• The sludge is a thick, black mass containing 95 per
cent of water, and it has a revolting odour.

28. Sludge disposal
• Digestion: If sludge is incubated under favourable
conditions of temperature and pH, it undergoes
anaerobic auto-digestion in which complex solids are
broken down into water, carbon dioxide, methane and
ammonia.
• The volume of sludge is also considerably reduced. It
takes 3-4 weeks or longer for complete sludge
digestion.
• Sea Disposal: Sea coast towns and cities can dispose of
sludge by pumping it into the sea
• Land: Sludge can be disposed of by composting with
town refuse.

30. Disposal of Effluent
• Disposal by dilution: Disposal into water courses
such as rivers and streams is called 'disposal by
dilution‘
– Recommended that an effluent from a sewage
treatment plant should not have more than SPM 30
mg/litre
– B.O.D. should not exceed 20 mg/ l of 5 days .
• Disposal on Land : effluent can be used for irrigation
purposes

31. • Disinfection is the final step in the sewage treatment
process
• Designed to kill entero pathogenic bacteria and
viruses that were not eliminated during the previous
stages of treatment.
• Disinfect ion is commonly done by chlorination with
chlorine gas or hypo chlorite Dose 5-25 mg / L 99.9
% reduction of coliform
Chlorination

32. 32
Stabilization Ponds for
Wastewater Treatment

33. oxidation pond
• The organic matter contained in the sewage is oxidized
by bacteria (hence oxidation pond) to simple chemical
compounds such as carbon dioxide, ammonia and water.
• A cheap method of sewage treatment is the oxidation
pond
• there must be the presence of
– (1) algae
– (2) certain types of bacteria which feed on decaying
organic matter, and
– (3) sun-light.

34. 34
Stabilization Ponds
• The algae, with the help of sunlight, utilize the carbon
dioxide, water and inorganic minerals for their
growth
• Oxygen that is needed for oxidation is derived
– small extent from the atmosphere
– mostly from the algae which liberates oxygen
under the influence of sunlight.
– The oxidation ponds are predominantly aerobic
during sunshine hours as well as some hours of the
night.
– In the remaining hours of the night, the bottom
layers are generally anaerobic

35. oxidation pond
• The effluent may be used for growing vegetable crops
(land irrigation) or may be discharged into a river or
other water courses after appropriate treatment.
• Oxidation ponds have become an established method
of purifying sewage for small communities.

36. 36
Pretreatment Classifications
• None – receives raw untreated WW
• Screening – receives screened raw
untreated WW
• Primary – pond acts as a form of
secondary treatment
• Secondary-pond acts as a tertiary
(polishing) treatment

37. Example---Milo, Maine
http://www.mwwca.org/milo.htm

39. Summery of Oxidation pond