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