Post on 25-Dec-2015
transcript
Landfill Processes
Objectives
Describe the physical, chemical, and biological processes occurring in a landfill
Describe leachate quality (Table 4-3)
Describe leachate quantity Discuss leachate management
Anaerobic Pathway
Degradable particulate organic material (Proteins Carbohydrates and Lipids)
Inert Soluble
Amino Acids & Sugars Long chain fattyacids
Valerate, Butyrate,& Propionate
Acetate Hydrogen
Methane
Hydrolysis
Fermentation ofAmino acids &
Sugars
AnaerobicOxidation of
LCFA
Acetotrophicmethanogenesis
Hydrogenotrophicmethanogenesis
AnaerobicOxidation of
Acids
Stabilization Phases – Phase I: Initial AdjustmentInitial waste placementPreliminary moisture accumulationInitial subsidenceClosure of landfill area
Stabilization Phases – Phase II: TransitionField capacity exceededLeachate formedElectron acceptor shifts from
oxygen to nitrates to sulfatesTrend toward reducing conditionsVolatile acids appear
Stabilization Phases – Phase III:Acid FormationVolatile fatty acids predominate in
leachatepH declinesSubstrate conversion occurs
Stabilization Phases – Phase IV:Methane FermentationMethane and carbon dioxide
productionpH at minimumNutrient consumptionPrecipitation of metalsLeachate BOD/COD declines
Stabilization Phases – Phase V:Final MaturationBiological dormancyNutrients limitingGas production ceasesOxygen slowly reappearsHumic substances produced
Importance of Leachate Quality and Quantity DeterminationDesign leachate collection systemsDesign leachate treatment
facilitiesDetermine acceptability of offsite
treatmentEstimate offsite migration potential
Factors Affecting Leachate Quality and QuantityParticle sizeCompactionWaste
compositionSite HydrologyCover Design
Waste age Landfill
design/operationSampling
procedures Interaction of
leachate with environment
BOD/COD Ratio
Relative biodegradability of leachate
Present for as long as 100 yearsTends to decline following onset of
methane formation
Relative Biodegradability of Leachate
Bio-degradability
BOD/COD COD/TOC
Low < 0.5 < 2
Medium 0.5 – 0.75 2 – 3
High > 0.75 > 3
Nitrogen/Phosphorus
Indication of nutrient availabilityPhosphorus may be limiting nutrientAmmonia important bufferNitrogen present for long periods of
timeMay control length of post closure
care period
pH
Influence chemical and biological processes of precipitation, redox, sorption, methanogenesis
Controlled by volatile acids during acid phase
After methanogenesis begins, controlled by carbonates and ammonia
Major factor in controlling metal solubility
Heavy Metals
May act as inhibitors of biological stabilization process
Water quality concernsNo discernable chronological
patternLeachate concentration controlled
by sulfide, carbonate, chloride, and phosphate
Leachate Quantity EstimationPercent of PrecipitationWater Balance Technique (Figure
4-4)
HELP
Quasi 2-D deterministic computer-based water budget model
Performs daily sequential analyses to generate daily, monthly and annual estimates of water routing
Purpose
To permit evaluators and landfill designers wit a tool to rapidly evaluate and compare the performance of alternative landfill designs
Limitations
Model does not account for surface water run on from outside landfill area
Model does not account for cracks in soil Model does not account for vegetative
species other than grass Model considers a wetting front Does not model aging of liner Requires extensive use of default
parameters
Leachate Management Design StepsLayout management schemeSelect leachate removal techniqueSize pumpSelect storageSelect treatment and disposal
Leachate Storage
Underground storage tanksLagoonsAbove ground tanksthree day’s storage at peak annual
flow
Storage
Leachate Treatment/DisposalOn site
– biological– chemical– evaporative– physical
Off-site treatment
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Last updated April 19, 2023 by Dr. Reinhart