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Landfill Processes

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. Stabilization Phases – Phase I: Initial Adjustment.

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Landfill Processes

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  1. Landfill Processes

  2. Objectives • Describe the physical, chemical, and biological processes occurring in a landfill • Describe leachate quality (Table 4-3) • Describe leachate quantity • Discuss leachate management

  3. Anaerobic Pathway

  4. Stabilization Phases – Phase I: Initial Adjustment • Initial waste placement • Preliminary moisture accumulation • Initial subsidence • Closure of landfill area

  5. 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

  6. Stabilization Phases – Phase III:Acid Formation • Volatile fatty acids predominate in leachate • pH declines • Substrate conversion occurs

  7. Stabilization Phases – Phase IV:Methane Fermentation • Methane and carbon dioxide production • pH at minimum • Nutrient consumption • Precipitation of metals • Leachate BOD/COD declines

  8. Stabilization Phases – Phase V:Final Maturation • Biological dormancy • Nutrients limiting • Gas production ceases • Oxygen slowly reappears • Humic substances produced

  9. Importance of Leachate Quality and Quantity Determination • Design leachate collection systems • Design leachate treatment facilities • Determine acceptability of offsite treatment • Estimate offsite migration potential

  10. Particle size Compaction Waste composition Site Hydrology Cover Design Waste age Landfill design/operation Sampling procedures Interaction of leachate with environment Factors Affecting Leachate Quality and Quantity

  11. BOD/COD Ratio • Relative biodegradability of leachate • Present for as long as 100 years • Tends to decline following onset of methane formation

  12. Bio-degradability BOD/COD COD/TOC Low < 0.5 < 2 Medium 0.5 – 0.75 2 – 3 High > 0.75 > 3 Relative Biodegradability of Leachate

  13. 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

  14. 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

  15. 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

  16. Leachate Quantity Estimation • Percent of Precipitation • Water Balance Technique (Figure 4-4)

  17. HELP • Quasi 2-D deterministic computer-based water budget model • Performs daily sequential analyses to generate daily, monthly and annual estimates of water routing

  18. Purpose • To permit evaluators and landfill designers wit a tool to rapidly evaluate and compare the performance of alternative landfill designs

  19. 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

  20. Leachate Management Design Steps • Layout management scheme • Select leachate removal technique • Size pump • Select storage • Select treatment and disposal

  21. Leachate Storage • Underground storage tanks • Lagoons • Above ground tanks • three day’s storage at peak annual flow

  22. Storage

  23. Leachate Treatment/Disposal • On site • biological • chemical • evaporative • physical • Off-site treatment

  24. Return to Home Page Return to Home Page Last updated March 15, 2014 by Dr. Reinhart

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