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

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

6. 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

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

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

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

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

11. 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

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

13. Relative Biodegradability of Leachate Bio- degradability BOD/CODCOD/TOC Low < 0.5< 2 Medium0.5 – 0.752 – 3 High> 0.75> 3

14. 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

15. 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

16. 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

17. Leachate Quantity Estimation  Percent of Precipitation  Water Balance Technique (Figure 4-4)

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

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

20. 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

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

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

23. Storage

24. Leachate Treatment/Disposal  On site –biological –chemical –evaporative –physical  Off-site treatment

25. Return to Home Page Last updated August 27, 2015 by Dr. Reinhart