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Published byPhebe Carpenter Modified over 9 years ago
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Landfill Processes
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Objectives Describe the physical, chemical, and biological processes occurring in a landfill Describe leachate quality (Table 4-3) Describe leachate quantity Discuss leachate management
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Anaerobic Pathway
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Stabilization Phases – Phase I: Initial Adjustment Initial waste placement Preliminary moisture accumulation Initial subsidence Closure of landfill area
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Stabilization Phases – Phase II: Transition Field capacity exceeded Leachate formed Electron acceptor shifts from oxygen to nitrates to sulfates Trend toward reducing conditions Volatile acids appear
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Stabilization Phases – Phase III:Acid Formation Volatile fatty acids predominate in leachate pH declines Substrate conversion occurs
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Stabilization Phases – Phase IV:Methane Fermentation Methane and carbon dioxide production pH at minimum Nutrient consumption Precipitation of metals Leachate BOD/COD declines
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Stabilization Phases – Phase V:Final Maturation Biological dormancy Nutrients limiting Gas production ceases Oxygen slowly reappears Humic substances produced
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Importance of Leachate Quality and Quantity Determination Design leachate collection systems Design leachate treatment facilities Determine acceptability of offsite treatment Estimate offsite migration potential
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Factors Affecting Leachate Quality and Quantity Particle size Compaction Waste composition Site Hydrology Cover Design Waste age Landfill design/operation Sampling procedures Interaction of leachate with environment
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BOD/COD Ratio Relative biodegradability of leachate Present for as long as 100 years Tends to decline following onset of methane formation
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Relative Biodegradability of Leachate Bio- degradability BOD/CODCOD/TOC Low < 0.5< 2 Medium0.5 – 0.752 – 3 High> 0.75> 3
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Nitrogen/Phosphorus Indication of nutrient availability Phosphorus may be limiting nutrient Ammonia important buffer Nitrogen present for long periods of time May control length of post closure care period
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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
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Heavy Metals May act as inhibitors of biological stabilization process Water quality concerns No discernable chronological pattern Leachate concentration controlled by sulfide, carbonate, chloride, and phosphate
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Leachate Quantity Estimation Percent of Precipitation Water Balance Technique (Figure 4-4)
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HELP Quasi 2-D deterministic computer-based water budget model Performs daily sequential analyses to generate daily, monthly and annual estimates of water routing
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Purpose To permit evaluators and landfill designers wit a tool to rapidly evaluate and compare the performance of alternative landfill designs
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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
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Leachate Management Design Steps Layout management scheme Select leachate removal technique Size pump Select storage Select treatment and disposal
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Leachate Storage Underground storage tanks Lagoons Above ground tanks three day’s storage at peak annual flow
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Storage
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Leachate Treatment/Disposal On site –biological –chemical –evaporative –physical Off-site treatment
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Return to Home Page Last updated August 27, 2015 by Dr. Reinhart
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