Sewage sludge treatment describes the processes used to manage and dispose of sewage sludge produced during sewage treatment. Sludge is mostly water with lesser amounts of solid material removed from liquid sewage. Primary sludge includes settleable solids removed during primary treatment in primary clarifiers. Secondary sludge separated in secondary clarifiers includes treated sewage sludge from secondary treatment bioreactors. Sludge treatment is focused on reducing sludge weight and volume to reduce disposal costs, and on reducing potential health risks of disposal options. Water removal is the primary means of weight and volume reduction, while pathogen destruction is frequently accomplished through heating during thermophilic digestion, composting, or incineration. The choice of a sludge treatment method depends on the volume of sludge generated, and comparison of treatment costs required for available disposal options. Air-drying and composting may be attractive to rural communities, while limited land availability may make aerobic digestion and mechanical dewatering preferable for cities, and economies of scale may encourage energy recovery alternatives in metropolitan areas. Energy may be recovered from sludge through methane gas production during anaerobic digestion or through incineration of dried sludge, but energy yield is often insufficient to evaporate sludge water content or to power blowers, pumps, or centrifuges required for dewatering. Coarse primary solids and secondary sewage sludge may include toxic chemicals removed from liquid sewage by sorption onto solid particles in clarifier sludge. Reducing sludge volume may increase the concentration of some of these toxic chemicals in the sludge.[1]

1. SLUDGE HANDLING & DISPOSAL
Presented by
Sohel R Sheikh
Roll no:- 31
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2. Sludge refers to the residual, semi-solid material left from
industrial wastewater, or sewage treatment processes.
&
Sustainable sludge handling may be defined as a socially
acceptable, cost-effective method that meets the requirement of
efficient recycling of resources while ensuring that harmful
substances are not transferred to humans or the environment.
2
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3. Sludge handling processes
1. Primary operations
2. Thickening
3. Stabilization
4. Conditioning
5. Dewatering
6. Heat drying
7. Incineration 3
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4. 1.Primary operations
• This process includes
▫ Grinding
-particle size reduction
▫ Screening
-removal of fibrous materials
▫ Degritting
-grit removal
▫ Blending
-homogenization
▫ Storage
-flow equalization
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5. Advanced Primary Treatment1
• Using higher dosage of chemical coagulant/flocculent to
remove not only suspended solids but also the soluble organic
matter
• APT will also provide
persistent sulfide
odor absorption
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6. • APT program requires addition of the Ferric
Chloride(3 to 15ppm ferric iron)at a point just
upstream of the primary clarifiers.
• In general the higher the dosage of coagulant the
more BOD will removed, but dosage will limited by
amount of alkalinity available and by economy
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7. 2. Thickening
• To increase solids content percentage of sludge by removing a
portion of liquid fraction
• volume reduction of approximately 30 – 80 % can be reached
with sludge thickening2
METHODS :-
• gravity thickening
• flotation thickening
• Centrifugation
• Rotatary drum thickening
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8. 3. Stabilization
• Objectives
▫ Reduce pathogens
▫ Eliminate offensive odors
▫ Reduce potential for putrefaction
▫ Production of usable gas (methane).
• Mechanisms
oBiological reduction of volatile content
oApplication of heat to disinfect sludge
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9. Methods of stabilization
Alkaline stabilization :
• lime is added to untreated sludge , to raise
the PH to 12 or higher .
• Retards microbial reaction .
• Materials such as cement kiln dust ,fly ash are used
instead of lime .
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10. Anaerobic digestion
• A biological process that uses
bacteria in an oxygen free
environment.
• These bacteria converts volatile
solids into carbon dioxide,
methane and ammonia .
• single stage digester
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11. Aerobic digestion
• Organic part decomposes in presence of oxygen by
micro organisms .
• Mostly used in plants with average flow less than 5
MGD .
• Bacteria converts organic matter into carbon dioxide
.
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12. Advantages and disadvantages of
aerobic digestion
Advantages Disadvantages
Lower capital cost High power cost
End product odourless and stable Digested solids have poorer dewatering
characteristics
Lower BOD concentrations in
supernatant liquor
Useful by product such as methane is not
recovered
More basic fertilizer values recovered
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13. 4.Conditioning
• In this process sludge solids are treated with
chemicals or other means to prepare sludge for
dewatering.
• It improves the drainability of digested
sludge. Sludge becomes more amenable to
dewatering.
• It can be achieved by various methods such as
elutriation, chemical conditioning, heat
treatment, freezing etc.
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14. 5.Dewatering
• A physical unit operation used to reduce the moisture
content of sludge
• Difficulty due to fact that particles are very fine,
colloidal in nature and possess a gel-like structure
due to polymeric flocculation
• Compared to thermal (evaporative processes) for
water reduction, mechanical dewatering is often
selected due to its low energy requirement3
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15. Methods of dewatering
1. Centrifugation – for separating liquids of different
densities, thickening slurries .
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16. 2. Belt filter press
• Uses principle of gravity drainage and mechanically
applied pressure.
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17. 6. Heat drying
• It involves the application of heat to evaporate water
and to reduce the moisture content of biosolids
through conduction, convection or radiation .
• Advantage of this method is to reduce product
transportation costs, improve storage capability, and
marketability.
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18. Methods of heat drying
i] Direct drying- the wastewater solids come into
contact with hot gases, which cause evaporation of
moisture.
Dryers such as rotary dryer and fluidized bed dryer
are used.
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19. ii] Indirect drying- Moisture evaporates when the
wastewater solids contact the metal surface heated by
the hot medium. Dryers such as paddle dryers ,hollow
flight and disc dryers are used.
Paddle dryer
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20. Volume reduction
•
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21. 7.Incineration
• Involves total conversion of organic solids to
oxidized end products
• Sludge stabilization is not necessary before
incineration .
• Water, carbon-dioxide and ash are primarily end
products .
• The sludge generally has calorific values
ranging from11 to 17 MJ/kg
(reference :Werle and Wilk,2010)4
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22. Methods of incineration
1. multiple hearth incinerator
• Dewatered sludge
to dry ash.
• used in large plants.
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23. 2. FLUIDIZED BED
INCINERATION
• wastes are quickly
and uniformly
incinerated with
utilizing
thermal capacity
of hot fluidizing
sand
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24. Advantages of incineration
• Energy recovery potential 5
• Pathogens would be reduced by a pasteurization
process
• Waste volume reduction
• Destruction of combustible toxins
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25. Disadvantages
• Emission of mercury & NOx leading to air
pollution
• High capital and operational costs
• Ash must be landfilled and may be hazardous
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26. Sludge disposal
• Sewage sludge contains both compounds of
agricultural value and pollutants.
• Agriculture value- organic matter, nitrogen,
phosphorus and potassium.
• Pollutants- heavy metals, organic pollutants and
pathogens
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27. Methods of Sludge disposal
1.Land fill
2.Agricultural use
3.Other methods
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28. Landfill
• A site for the disposal of waste materials by burial and is
the oldest form of waste disposal.
• Some landfills are also used for waste management
purposes, such as the temporary storage, consolidation
and transfer, or processing of waste material (sorting,
treatment, or recycling).
• Problem with this method is that many landfills are filling
up, and towns are having trouble finding places to put
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29. 29/35

30. Agricultural use
• The purpose of using sludge in agriculture is
partly to utilize nutrients such as phosphorus
and nitrogen and partly to utilize organic
substances for soil improvement.
• All types of sludge can be spread on farmland if they
fulfill the quality requirements (heavy metals,
pathogens, pre- treatment)
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31. Advantages
• Utilization of nutrients contained in the sludge, i.e.
phosphorus and nitrogen.
• Utilization of organic substances contained
in the sludge for improvement of the humus layer of
the soil (i.e. soil improvement).
• The cheapest disposal route
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32. Disadvantages
• Major investments in storage facilities as sludge can only
be spread on farmland a few times a year.
• Dependency on the individual farmers and considerable
administration of agreements
• Lack of knowledge as to the content of organic micro-
pollutants and pathogenic organisms in sludge and their
impact on the food chains
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33. Other methods
• Ocean Disposal – Dumping or controlled release
of sewage sludge from a barge or other vessel into
marine water.
• Distribution and Marketing – The give-away,
transfer, or sale of sewage sludge or sewage
sludge product in either bagged or bulk form.
• Surface Disposal – A controlled area of land
where only sewage sludge is placed for a period of
one year or longer. Sludge placed in this area is
not provided with a daily or final cover.
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34. References
a. Vaxelaire J, Bongiovanni JM, Puiggali JR (1999) Mechanical
dewatering and thermal drying of residual sludge. Environ
Technol 20:29–36
b. Werle and Wilk,2010
c. Wastewater Treatment By Metcalf & Eddy, TMH
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