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Landfill Processes

Landfill Processes. Importance of Leachate Quality and Quantity Determination. Design leachate collection systems Design leachate treatment facilities Determine acceptability of offsite treatment Estimate offsite migration potential. Degradation pathways.

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Landfill Processes

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  1. Landfill Processes

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

  3. Degradation pathways

  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. 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 (Table 4-7)

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

  11. Biodegradability BOD/COD COD/TOC Low < 0.5 < 2 Medium 0.5 – 0.75 2 – 3 High > 7.5 > 3 Relative Biodegradability of Leachate

  12. Nitrogen/Phosphorus • Indication of nutrient availability • Phosphorus may be limiting nutrient • Ammonia important buffer • Nitrogen present for long periods of time

  13. 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

  14. 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

  15. Leachate Quantity Estimation • Percent of Precipitation • Water Balance Technique (Figure 4-6)

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

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

  18. 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

  19. Leachate Management steps • Layout management scheme • Select leachate removal technique • Size pump • Select storage • Select treatment and disposal

  20. Leachate removal from LCS - Options • Manhole in cell (sump pump) • Penetration of liner/external sump (wet well/dry well, or sump pump) • Side slope riser (slim sump pumps)

  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

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