SLUDGE

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SLUDGE

• Screenings
• Grit
• Scum
• Solids
• Biosolids

• Substances responsible for offensive character of
  wastewater
• Highly organic in nature
• Pathogenic
• High water content

Reduce water content, organic content and render
solids suitable for reuse or final disposal
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Sludge Management and Disposal

• Thickening, Conditioning
• gravity, flotation
• Dewatering, Drying
• Vacuum filtration, centrifugation, pressure
  filtr.
• Digestion, Composting, Stabilization
• aerobic, anaerobic, alkaline treatment
• Disposal
• land application, burial, incineration

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REGULATIONS

• 40 CFR 503
• Land application of sludge (Class A and Class B)
• Surface disposal
• Patogen and vector reduction
• incineration

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Volume Mass Relationships
Specific gravity of solids
Specific gravity of solids
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THICKENING

• Increase the solids content of sludge by removing
  a portion of the liquid fraction
• Activated sludge 0.8 to 4 results in fivefold
  decrease in sludge volume
• Settling, flotation, centrifugation, gravity
  belt, rotary drum

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Sludge Dewatering

• Sludge drying beds
• historically the most common
• sand bed, 15-30 days, evaporation seepage
• Vacuum Filtration
• cylindrical rotating drum covered with fabric
• submerged with applied vacuum
• Continuous belt filter presses (follows)
• Plate pressure filters
• vertical plates mounted on a frame

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Belt Filter Press Description
In the belt press process, chemical conditioned
sludge is resting on a gravity drainage section
so that it can be thicken. Water is able to fall
from the sludge by the force of gravity. Now
pressure is being applied in a low pressure
section, where the sludge is squeezed between
opposing porous cloth belts. Next it will travel
through a high pressure section, where the sludge
is subjected to a shear force as the belts pass
through a series of rollers. This shearing force
and squeezing process reduces additional
quantities of water from the sludge. Finally
dewatered sludge cake is removed from the belts
by scraper blades.
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Belt Filter Press (Komline-Sanderson)
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Filter Press
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Sludge Volume Reduction
A. Start with 1 liter of 1 by weight (i.e., 10
g/L) sludge. Mass of sludge (1 liter)(1000 g/L)
1000 g sludge Mass of solids (1 liter)(10
g/L) 10 g dry sludge solids Mass of water
1000 g - 10 g 990 g H2O
B. Gravity Thicken to 4 dry solids (i.e., 40
g/L). Mass of sludge (10 g)/(0.04) 250 g
sludge Mass of solids unchanged 10 g dry
sludge solids Volume Removed (1000 mL - 250
mL)/1000 mL 75 Mass of water 250 g - 10 g
240 g H2O
C. Vacuum Filter to 30 dry solids (i.e., 300
g/L). Mass of sludge (10 g)/(0.30) 33.3 g
sludge Mass of solids unchanged 10 g dry
sludge solids Volume Removed (1000 mL - 33.3
mL)/1000 mL 96.7 Mass of water 33.3 g - 10 g
23.3 g H2O
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Aerobic Digestor
12-20 days of aeration 50 reduction in solids
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Digester
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Anaerobic Digestion

• Sludge held without aeration for 10-90 days
• Process can be accelerated by heating to 35-40oC
• These are called High Rate Digestors (10-20 days)
• Advantages
• low solids production
• useable methane gas produced
• Disadvantages
• high capital costs
• susceptibility to shocks and overloads

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Conventional standard rate single-stage
High rate Completely mixed single-stage
Two-stage Process
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Process Microbiology
Lipids, Proteins, Nucleic Acids, Polysaccharides
Hydrolysis
Acidogenesis
Fatty Acids, Amino Acids, Monosaccharides etc
Alcohols, hydrogen, CO2,formate, acetate
Methanogenesis
Methane and Carbon Dioxide
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Process Microbiology

• Methanogens or Methane Formers
• 4H2 CO2 CH4 2H2O
• 4HCOOH CH4 2H2O 3CO2
• CH3COOH CH4 CO2
• CH3OH 3CH4 CO2 2H2O
• 4(CH3)3N H2O 9CH4 3 CO2 6H2O 4NH3

pH 6.6-7.6, alkalinity should be present slow
growth rates Y 0.06
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Digester Design

• Mean Cell Residence Time
• Volumetric Loading Factor
• Observed Volume Reduction
• Loading Factors Based on Populations

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Toxics in Municipal Sludge
Problem with buildup of heavy metals in soil
receiving sludge
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Ultimate Sludge Disposal