1. SOLID/ SLUDGE MANAGEMENT

2. Solid and Biosolids SOLIDS AND BIOSOLIDS
The largest waste (in volume)
Form:liquid or semisolid liquid ( % solid)
Term biosolid: WW solid are organic product that can be used beneficially after treatment (WEF 1998)
Term sludge: used only before achieve beneficial use criteria
Term solid: if uncertain criteria

3. Solids Sources

4. Schematics diagram of conventional activated sludge

5. Characteristics and quantities of waste sludge
To estimates the raw solids removed by plain sedimentation:
Where
Wp = raw primary sludge solids (g/d)
f = fraction of SS removed in primary settling
SS = suspended solids in unsettled ww (g/d)

6. Characteristics and quantities of waste sludge
To estimates the secondary treatment solids generated:
Where
Ws = biological sludge solids (g/d)
K = fraction of applied BOD that appears as excess biological solid. K depend on F/M ratio or bacteria growth rate.
BOD = BOD in applied ww after primary sedimentation(g/d)
Total sludge solids production in conventional treatment plant with primary and secondary treatment, Wps = Wp+Ws

7. Characteristics and quantities of waste sludge
Volume of wet sludge, V (Liter)
Where
W = weight of dry solids, kg
s = solids content
p = water content

8. Example
A ww with 200 mg/L BOD and 220 mg/L SS is processed in trickling filter plant. K=0.34. Assuming 50% SS removal and 35% BOD removal from primary clarifier:
Estimates the quantities of sludge solids from primary and secondary biological filtration per cubic meter of ww treated.
Calculate volume of wet sludge from final clarifier and combined with solid content 5%.

9. SLUDGE COMPOSITION Predominantly water Micro-organisms
Viruses, pathogens, germs in general
Organic particles, heavily bio-degradable
Organic compounds, inert, adsorpted to sludge flocs
Heavy metals
Micro-pollutants, pharmaceuticals, endocrine disrupters
All non-degraded compounds extracted from wastewater are found in the sludge

10. Sludge characteristics

11. SLUDGE TREATMENT GOAL Volume reduction Elimination of pathogenic germs
Thickening
Dewatering
Volume reduction
If used in agriculture as fertiliser or compost
Elimination of pathogenic germs
Gas production
Reduction of dry content and odour
Improvement of dewatering
Stabilization of organic substances
Nutrients, fertilizer
Humus
Biogas
Recycling of substances

12. Sludge treatment alternatives
Eckenfelder & Santhanam (1981)

13. Sludge processing

14. thickening

15. Sludge thickening Why is it important?
Used to increase solid content of sludge by removing removing a portion of liquid fraction
Usually accomplished by physical means; e.g settling, flotation, centrifugation, gravity belt and rotary drum.
Why is it important?
Beneficial to the subsequent treatment processes from the following stand points:
Capasity of tanks and equipment required
Quantity of chemical required for sludge conditioning
Amount of heat (in digester) and fuel required for heat drying and incineration

16. Sludge thickening
2. Cost reduction
-small pipe size and pumping cost
3. Liquid sludge can be transported easily
In designing thickening facility, it is important to:
Provide adequate capasity to meet peak demand
Prevent septicity, with its attendant odor problem.

17. Gravity belt thickener

18. Schematic diagram : CENTRIFUGAL THICKENING

19. Example
Estimate the sludge volume reduction when the sludge is thickened from 4% to 7% solids concentration. The daily sludge production is 100 m3.
Solution:
Calculate amount of dry sludge produced
Calculate volume in 7% solid content
Calculate percentage of sludge volume reduction
Ans: 42.9%

20. EXAMPLE:
Primary sludge containing trickling filter humus is gravity thickened in circular tank with 3.6m dia. and 3 m side water depth. The applied sludge is 10 m3/d with 4.5% solids and the thickened sludge withdrawn is 5 m3/d at 7.5% solids. The blanket of consolidating sludge in the tank has a depth of 1 m. For odour control, 170 m3/d of treated wastewater is pumped to the tank along with sludge to increase overflow rate. Calculate:
Solid loading
% solid captured
Overflow rate
Solid retention time

21. stabilization

22. STABILIZATION Not suitable for survival of microb
Stabilization process of sludges for  volume reduction, production of usable gas (methane), and improving the dewaterability of sludge
Solids and biosolids (sludge produced from primary or secondary treatment) are stabilized to:
- reduce pathogens
- eliminate offensive odors
- inhibit, reduce, or eliminate the potential for
putrefaction (decay, decompose of organic matters).
Therefore, stabilization involves the reduction of volatile content and addition of chemicals to solid and biosolid and…
Not suitable for survival of microb

23. Alkaline Stabilization
Aerobic digestion
Anaerobic digestion
Composting
Alkaline Stabilization

24. Gravity Thickener Inflow Scum scimmer Sludge liquor Picket fence
Thickened sludge

25. Thickening by Flotation

26. Flotation unit

27. Processes in digester Anaerobic degradation
Degradation of organic substances of app. 50%
Biogas production: 63% CH4 (Methane) 35% CO2 2% other gases (N2, H2, H2S)
 electricity and heating
Organic nitrogen is converged to NH4+
 N-loading of WWTP

28. Characteristic values of digester
Mean residence time of sludge
Small units, badly mixed
< 30 d
Medium size units with mixing
20 d
Large plants with mixing
12 – 16 d
Biogas production related to degradation of organic substances
0.9 m3 / kg VSSdegr.
Degradation of organic substances
40 – 55%

29. Simultaneous aerobic sludge stabilisation
No primary clarifier  no primary sludge
High sludge age SRT, app. 25 d
Activated sludge tank is larger than that combined with an anaerobic sludge stabilisation
No biogas production
Possibly combined with storage or thickener unit
Stable and simple operation

30. Comparison between anaerobic and aerobic processes
Anaerobic Aerobic
Organic loading rate
High loading rates:10-40 kg COD/m3-day
Low loading rates: kg COD/m3-day
(for high rate reactors, e.g. AF,UASB, E/FBR)
(for activated sludge process)
Biomass yield
Low biomass yield: kg VSS/kg COD
High biomass yield: kg VSS/kg COD
(biomass yield is not constant but depends
on types of substrates metabolized)
(biomass yield is fairly constant irrespective
of types of substrates metabolized)
Specific substrate utilization rate
High rate: kg COD/kg VSS-day
Low rate: kg COD/kg VSS-day
Start-up time
Long start-up: 1-2 months for mesophilic
: 2-3 months for thermophilic
Short start-up: 1-2 weeks

31. Comparison between anaerobic and aerobic processes
Anaerobic Aerobic
SRT
Longer SRT is essential to retain the slow
growing methanogens within the reactor
Microbiology
Anaerobic processes involve multi-step
chemical conversions and a diverse group of microorganisms degrade the organic matter in a sequential order
Aerobic process is mainly a one-species phenomenon, except for nutrient-removal processes
Environmental factors
The process is highly susceptible to
changes in environmental conditions
SRT of 4-10 days is enough for the activated sludge process
The process is more robust to changing environmental conditions

32. ANAEROBIC SLUDGE DIGESTION

33. Sludge
Digestion:
Anaerobic

37. Dewatering Drying

38. Volume reduction Water content in stabilised sludge > 95% !
 Reduction of water content and volume
Sludge volume
With water content 
 non-linear relation!

39. Volume reduction
12 Sludge treatment
Urban Water Systems

40. Dewatering Unit Operation Method W DS Decanter Continuous Centrifuge
Conditioning with flocculation agents (poly-electrolytes) for efficient dewatering
Unit
Operation
Method W
DS
Decanter
Continuous
Centrifuge
> 0.7
< 0.3
Chamber filter press (large plants)
Batch-wise
Hydraulic pressure through plates in water-tight chambers
> 0.6
≤ 0.4
Belt filter press (small plants)
continuous
Pressed between two filter belts around staggered rollers
> 0.7
≤ 0.3

41. Centrifuge

42. Filter Press

43. Filter Press

44. Drying bed Dimensioning  W  0.55 (Imhoff, 1990) Plant type
Thin sludge layer (< 20 cm)
Sand layer as drainage and filter layer
Sludge is
first dewatered by drainage
then air-dried through evaporation
Applicable for small plants
Dimensioning  W  0.55 (Imhoff, 1990)
Plant type
Specific surface
Only mechanical treatment
13 PE/m2
Trickling filter
6 PE/m2
Activated sludge plant
4 PE/m2

45. Filling the drying bed with sludge
Starting the drying process

46. Drying  Vaporisation of water content Partial drying  W 0.3 – 0.4
Full drying  W down to < 0.1
Contact drying over heated areas
Drying by convection through hot air counter-current inlet app. 600°C, outlet app. 300°C (Imhoff, 1999)
For large plants
Disposal is critical: fire, dust explosion
In granulate form as fertiliser

47. Sludge disposal/reuse

48. Use in agriculture Sludge treatment Fertiliser* Liquid sludge
 Recycling of nutrients, from stabilised sludge
Sludge treatment
Fertiliser*
Liquid sludge
P- and N-fertiliser
Dewatered sludge
P-fertiliser, N as storage product
Dried sludge
P-fertiliser
* Limit re. over-fertilisation
Problems
Acceptance
Heavy metals
Micro-pollutants, pharmaceuticals, endocrine disruptors

49. Composting  Aerobic biological degradation of organic substances
Prerequisites
Stabilisation
Dewatering
Hygienisation
Approach
Structure means: straw, wood, saw dust, wood chips
Mixture app. 1:1
Water content app. 0,65
 Requirements are more demanding than for sludge use as fertiliser!

50. Incineration Use of energy content, but not of nutrients
Mono incineration (sludge exclusively)
Calorific value of sludge high enough  no biogas use before, no stabilisation
Water content not minimised (no full drying)
Fluidised bed incinerator, incineration at 800 – 950°C in fluidised sand bed
Expensive!
Co- incineration
In coal power station
In solid waste incinerators
In cement production, ash is bounded to cement

51. Fluidized bed sludge incineration

52. Thank you