This document outlines the key aspects of sludge management in wastewater treatment plants. It discusses the different types of sludge generated, including primary, secondary, and chemical sludge. Treatment processes like thickening, stabilization, conditioning, and dewatering are explained. Common thickening methods include gravity thickeners and belt thickeners. Stabilization is achieved through anaerobic digestion. Dewatering options compared are centrifuges, belt filter presses, and drying beds. The document concludes by proposing designs for sludge treatment units based on calculated sludge quantities and disposal of dewatered sludge to landfill.

1. FACULTYOF CIVILENGINEERING
MSc. CIVIL ENGINEERING
29 MARCH 2010

2. PRESENTATION OUTLINE

3. INTRODUCTION
The sludge is
• also commonly known as biosolids
• removed from the sewage treatment processes
• a critical biologically active mix of water, organic
matter , inorganic solids, dead and alive micro-
organisms, and trace contaminants.
The importance of sludge management increases
with the increase in amount of sewage treated.
Related sludge treatment facilities should be
provided within the area of sewage treatment
plant to accommodate sludge treatment, handling
and storage facilities.

4. TYPE OF SLUDGE
The majority of sludge generated is the material which
accumulated at the bottom of the settling tanks or
clarifiers.
Wastewater sludge can be classified generally as primary,
secondary also called biological and chemical
(Turovskiy and Mathai, 2006).
• The treated sludge can be classified by the treatment
such as:
• Aerobically digested
• Anaerobic digested (mesophilic and thermophilic)
• Alkaline stabilised
• Composted
• Thermally dried
• The treated sludge can be only primary, secondary or
chemical or a mixture of any two or three of the
sludges.

5. PRIMARY SLUDGE
• Most wastewater treatment plants remove
settleable solids from raw wastewater by the
physical processes of primary settling.
• The primary sludge solid is about 50% of the total
sludge solid
• The primary sludge solid production can vary
typically from 0.1 to 0.3 kg/m3 of wastewater
• The removal rate of suspended solids at primary
treatment is usually in the range of 50 – 60 %.
Primary sludge generally gives off foul or
unpleasant odors.
The water from sludge or supernatant is turbid and
smelly.

6. SECONDARY SLUDGE
• Secondary sludge also known as biological sludge is produced by
biological treatment processes.
• Activated sludge, trickling filters, rotary biological contactors etc
are typical processes that produce biological sludges or biomass.
• Quantities and properties vary with the metabolic growth rate of
the microorganisms present.
• Concentration and volumes of biological sludges are
determined by the operation of clarifiers and sedimentation and
generally more difficult to thicken and dewater than primary and
most of chemical sludge.
• Activated sludge and trickling filter sludge generally contain
solids concentrations of 0.4 to 1.5 % and 1 to 4 % respectively in
dry solid weight
• Biological sludge is more difficult to dewater than primary sludge
because of the light biological flocs inherent in biological sludge.

7. CHEMICAL SLUDGE
• Chemicals are used to improve suspended solids
removal, increase sludge production and amounts
depending on the chemical used.
• Chemicals are used in wastewater treatment for
removing a substances in chemical precipitation of
phosphorus.
• The chemicals used for phosphorus removal include
lime, alum and ‘pickle liquors’ such as ferrous chloride,
ferric chloride, ferrous sulphate and ferric sulphate
• Some treatment plants add the chemicals to the
biological process, chemical precipitates are mixed
with the biological sludge.
• Most plants apply chemical to secondary effluent and
use tertiary clarifiers or tertiary filters to remove
chemical precipitates.

8. OTHER WASTEWATER
RESIDUAL/SOLIDS
• Other than sludge, there are other residual
removed in wastewater treatment processes
especially at preliminary treatment :
• Screening
• Grit and grease
• Scum
• Septage sludge

9. SLUDGE TREATMENT
• The sludge as removed from sedimentation tank
or clarifiers contains a high proportion of water
more than 95 % and can be unstable, odorous
and unhygienic.
• The sludge have to be further treated before it
can be disposed to environment.
• The sludge treatment processes can be classified
as:
1) Thickening
2) Stabilization
3) Conditioning
4) Dewatering
5) Final Disposal

10. THICKENING
• Thickening is a process to increase the solid
concentration of sludge and decrease its volume by
removing a portion of the water from the sludge.
• The thickened sludge remains in the liquid state and is
capable of being pump without difficulty.
• The purpose of reducing volume by thickening is to
increase the efficiency and decrease the costs of
subsequent sludge processing steps.
• Thickening of waste activated sludge is important
because of its high volume and low solids concentration.
• Thickening from 1% solid concentration to 2% can
reduce the sludge volume by one-half. If it is
concentrated to 5% solids, the volume is reduce by one
fifth of its original volume. (Turovskiy and Mathai, 2006).

11. THICKENING
• The thickening is employed prior to subsequent sludge
processing steps such as digestion and dewatering to
reduce the volumetric loading and increase the
efficiency of subsequent processes.
• The selection of a particular thickening process
sometimes depends on the size of the wastewater
treatment plant.
• The main design variables of any thickening process
are:
a) Solids concentration and flow rate of the feed stream
b) Chemical demand and cost if the chemicals are used for
conditioning
c) Suspended and dissolved solids concentrations and flow
rate of the clarified stream.
d) Solids concentration and flow rate of the thickened
sludge

12. THICKENING
• The most commonly used sludge thickening
processes are:
The gravity thickener
Dissolved air floatation thickening
Gravity belt thickening
Rotary drum thickening

13. GRAVITY THICKENING

14. GRAVITY BELT THICKENER

15. DRUM THICKENER

16. DISSOLVED AIR FLOATING SYSTEM

17. COMPARISON OF THICKENING METHODS

18. SLUDGE STABILIZATION
• Sludge stabilization processes are used to convert raw
wastewater sludges to inoffensive forms by decreasing the
organic content in the sludge.
• The thickened sludge contain high concentration of organic
materials and high concentration of pathogens.
• This is required when the sludge is to be disposed to land.
• The major sludge stabilization processes are:
– Biological stabilization
• Anaerobic Digestion
• Aerobic Digester
– Chemical stabilization - Lime stabilization
– Thermal stabilization - Heat treatment
• The sludge stabilization process must be viewed as an integral
component of the overall sludge-handling and treatment
system.
• The selection and design of each of the components within
this system are interdependent.

19. THE ANAEROBIC DIGESTION PROCESS

20. CONDITIONING
• Sludge conditioning refers the process of improving
solid-liquid separation.
• Conditioning is an important part of mechanical
thickening and dewatering of sludge.
• Conditioning can be performed by inorganic or organic
chemical, power plant or incinerator ash or by physical
processes such as heating.
• Sludge characteristics that affect thickening or
dewatering and for which conditioning is employed
include:
i. Source
ii. Solid concentration
iii. Particle size and distribution
iv. pH and Alkalinity
v. Surface charge and degree of hydration
vi. Other physical factors

21. DEWATERING
• Dewatering is the physical operation of reducing the moisture content of
sludge and biosolids to achieve reduction greater than that achieved by
thickening.
• The capital and operation cost can be reduced due to the substantial
reduction of sludge volume after dewatering.
• The main variable in any dewatering process are solid concentration and
flow rate of the feed stream, chemical demand and solids concentration
of dewatered sludge cake.
• The selection of particular process is determined by the type and volume
of sludge to be dewatered, characteristics such as dryness required of
the dewatered product and space available.
• Recommended design for sludge stabilization and dewatering for
minimum dry solids content after dewatering 20% dry solids.
• The dewatering processes that are commonly used in Malaysia include
mechanical processes such as ;
 Belt filter press
 Filter press
 Centrifuge
 Natural processes include :
 Drying beds
 Sludge lagoon

22. 22
BELT FILTER PRESS

23. 23
FILTER PRESS

24. 24
Cutaway illustration showing the main parts of a decanter.
A. Eddy Current Brake E. Conveyor
B. Planetary gear box F. Casing
C. Pillow block bearing G. Feed tube
D.Centrifugal cast bowl H. Adjustable plate dams
CENTRIFUGE DECANTER

25. 1. Sludge Treatment Facilities
Sludge Dewatering Unit Outline flow

26. COMPARISON OF DEWATERING PROCESSES

27. DEWATERED SLUDGE PRODUCTION

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ULTIMATE/FINAL DISPOSAL
Sludge from STP
Transport
from STP
Retain in STP
Co-disposal -
landfill
Minor Uses -
gardening,
landscaping
Forestry
Agriculture
Dedicated
sites -
trenching
Sea
Disposal
Land
Reclamation

29. 29
Egg Shape Sludge digesters
Sludge from the Sewage Treatment Plant
after thickening and dewatering.
Sludge pellets ready for market as fertilizer.
Trenching System Drying Beds Lagoon System
Bricks from
sludge
Gift products,
flower vases, etc

30. 30
Incineration Ash
Reclamation asphalt filler.
Eco cement

31. DESIGN AND CALCULATION

32. CONCLUSION
• primary sludge from primary clarifier and secondary sludge or
waste activated sludge (WAS) from secondary or final clarifier.
• Based on calculation, quantity primary sludge generated from
primary sludge is 6.04 m3/day which 5% dry solid and quantity
sludge secondary sludge is 19.3 m3/day ( 0.75% dry solids).
• total volume of sludge is 25 m3/day and combined dry solid is
2%.
• There are 2 alternative proposals evaluated for sludge
thickening, gravity sludge thickener and gravity belt thickener.
Both methods are expected to achieve about 4% dry solid.
• From calculation, circular gravity sludge thickener to be provided
with the size of 8m diameter, 3.5 m height and 0.3 m conical and
designed for sludge age of 5 days.
• Gravity belt thickener based on manufacturer’s specification,
the area to be provided is 1.5m x 5.1m x 1.1 m height with the
weight of 980 kg.

33. CONCLUSION
• The dewatering machine evaluated is centrifuge
decanter. Based on manufacturer’s specification the
centrifuge decanter can achieve about 25% dry solids.
The minimum requirement of dry solids content after
dewatering by SPAN is only 20% dry solids (SPAN, 2009).
• The proposed centrifuge decanter’s size is 3.34 x 0.97m x
1.3 m height. The use of drying beds also evaluated, but
the requirement of SPAN, the drying beds only to be
designed to support mechanical lift for more than 10,000
PE. Covered storage area to be provided for 1 month
sludge holding.
• It was estimated that 23.11 m3/day of filtrate or
supernatant from dewatering processes to be channeled
to lowest point either pump sump or reactor tank.
• The proposed ultimate disposal of treated sludge is to be
disposed to Kuala Selangor District Council (MDKS) land
fill at Jeram near Kuala Selangor.

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