Sludge Treatment and Disposal

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Sludge TypesPrimary sludge3 to 8% solidsAbout 70% organic materialSecondary sludgeConsists of wasted microorganisms and inert materialsAbout 90% organic material0.5 to 2% solids

Tipikal Karakteristik Sludge*

Sludge TreatmentThickeningSeparation of as much water as possible by gravity or floatation

StabilizationConversion of organic solids to more inert forms by digestion, (so that they do not create odor or cause oxygen demand)

ConditioningTreatment with heat or chemicals so that water can be more easily removed

*Ilustrasi Reduksi Volume akibat peningkatan Kadar Padatan

Sludge Treatment.De-wateringSeparation of as much water as possible by vacuum, pressure or drying

Volume ReductionConversion of organic solids to more inert forms by wet oxidation or incineration

Opsi Sludge Treatment

Sludge Treatment: ThickeningFlotationEspecially effective on activated sludgeIncreases solids content from 0.5 - 1% to 3-6%Gravity thickeningBest with primary sludgeIncreases solids content from 1-3% to 10%PrimarySludgeGravity ThickeningSecondarySludgeFlotationFurther processing

ThickeningGravity Belt Thickener(From: http://frontiertech.simplenet.com/FTIgravitybelt.htm) Gravity Thickener(From: http://www.thomasregister.com/olc/dorroliver/sedi.htm) Flotation

Sludge StabilizationAerobic DigestionExtension of activated sludgeAccomplished by aeration of sludge then followed by sedimentationSupernatant goes back to head of plant (high in BOD, TKN, total-P)Treated sludge is 3% solidsAnaerobic Digestion2 stage: acid fermentation followed by methane productionAdvantages:produce methanedo not add oxygenAs with aerobic digestion, supernatant goes to head of plant

Stabilization -- AerobicAerobic Digestion

Stabilization -- Anaerobic*CO2 + 4 H2 CH4 + 2 H2O*CH3COOH CH4 + CO2*Sludge transformed to H2 and CH3COOH by fermentation

Anaerobic digester microbiology

1. Extracellular hydrolysis (e.g. cellulase)2. Fermentation leading to organic acids (VFAs), acetate, CO2 and H23. Fermentation leading to acetic acid (CH3COOH), H2 and O24. Methanogenesis leading to CH4,CO2 and H2O

StabilizationReduce pathogen contentReduce odorsComplete VFA production and conversionVolatile solids reduction (about 60%)Gas production (70% CH4, 30% CO2) (anaerobic only)*

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Sludge Treatment: ConditioningChemical ConditioningAdd lime, ferric chloride, or alumCan also add polymersChemicals are added just prior to de-watering stage

Heat TreatmentHigh temperatures (175-230 oC)High pressures (10 to 20 atmospheres)Advantagesbound water is released and sludge is easily dewateredDisadvantagescomplex processhighly concentrated liquid stream

Sludge De-wateringSludge Drying BedsMost popular methodSimpleLow maintenanceEffected by climateVacuum FiltrationCylindrical drum covered by mesh or fabric - rotates into partially submerged vat containing conditioned sludgeApply vacuum to pull out waterAchieves 15-30 % solid content

Sludge De-wateringBelt Filter PressForces out water by essentially squeezing water between two moving filter beltsApply pressure to pull out waterAchieves ~19 % solid contentLower energy consumption than vacuum filtersDoes not have problems with sludge pickup like vacuum filters

Sludge Volume ReductionIncinerationComplete evaporation of water from sludgeRequires fuelSolid material is inertExhaust air must be treated prior to dischargeWet OxidationTreated sludge is wetRequires energySolid material is inertExhaust air must be treated prior to discharge

Volume Reduction: High Temperature Fluidized Bed Incineration(From: http://www.infilcodegremont.com/)(From: http://www.unep.or.jp/CTT_DATA/WATER/WATER_4/html/Water-173.html

Sludge DisposalMethod depends on regulationsLand Spreadinglawns, gardensagricultural landforest landgolf courses and other public recreational areasMunicipal Solid Waste LandfillUtilization in other materials

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