SLUDGE by LQu6N8tq

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									SLUDGE
   Screenings              •Substances responsible for
                            offensive character of
   Grit
                            wastewater
   Scum
                            •Highly organic in nature
   Solids
   Biosolids               •Pathogenic

                            •High water content

Reduce water content, organic content and render
solids suitable for reuse or final disposal
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
REGULATIONS
  40   CFR 503
   – Land application of sludge (Class A and Class
     B)
   – Surface disposal
   – Patogen and vector reduction
   – incineration
Volume Mass Relationships
    Specific gravity of solids

     Ws      Wf      Wv
                  
    S s  w  w S f Sv  w
          Specific gravity of solids

         1 Ws Wwater
               
         S s S s S water
THICKENING
          the solids content of sludge by
  Increase
   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
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
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.
Belt Filter Press (Komline-Sanderson)
Filter Press
 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
Aerobic Digestor




 12-20 days of aeration
 ~50% reduction in solids
Digester
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
Conventional standard
rate single-stage



High rate Completely
mixed single-stage




Two-stage Process
Process Microbiology
Lipids, Proteins, Nucleic Acids, Polysaccharides
                          Hydrolysis
Fatty Acids, Amino Acids, Monosaccharides etc          Acidogenesis


 Alcohols, hydrogen, CO2,formate, acetate



                                                   Methanogenesis
            Methane and Carbon Dioxide
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
Digester Design
   Mean Cell Residence Time
   Volumetric Loading Factor
   Observed Volume Reduction
   Loading Factors Based on Populations
Toxics in Municipal Sludge
                            Constituent   Range,    Typical,
                                          mg/dry    mg/dry
Problem with buildup of                     kg        kg
heavy metals in soil      Chromium           10-
receiving sludge                          99,000        500
                          Copper             84-        800
                                          17,000
                          Nickel          2-5300         80
                          Zinc              101-
                                          49,000       1700
                          Cadmium         1-3410         10
                          PCBs            1.5-9.3        3.8
                          Lindane                        0.8
                          Chlordane        0.6-19        4.8
                          Hexachloro-                    0.6
                          benzene
Ultimate Sludge Disposal

								
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