leachate by yaoyufang


									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
     Stabilization Phases – Phase I:
                   Initial Adjustment

•   Initial waste placement
•   Preliminary moisture accumulation
•   Initial subsidence
•   Closure of landfill area
  Stabilization Phases – Phase II:

• Field capacity exceeded
• Leachate formed
• Electron acceptor shifts from oxygen to
  nitrates to sulfates
• Trend toward reducing conditions
• Volatile acids appear
 Stabilization Phases – Phase III:
                  Acid Formation

• Volatile fatty acids predominate in leachate
• pH declines
• Substrate conversion occurs
    Stabilization Phases – Phase IV:
              Methane Fermentation

•   Methane and carbon dioxide production
•   pH at minimum
•   Nutrient consumption
•   Precipitation of metals
•   Leachate BOD/COD declines
    Stabilization Phases – Phase V:
                   Final Maturation

•   Biological dormancy
•   Nutrients limiting
•   Gas production ceases
•   Oxygen slowly reappears
•   Humic substances produced
         Factors Affecting Leachate
    Quality and Quantity (Table 4-7)
•   Particle size       • Waste Age
•   Compaction          • Landfill
•   Waste composition     design/operation
•   Site Hydrology      • Sampling procedures
•   Cover Design        • Interaction of leachate
                          with environment
                       BOD/COD Ratio

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

     Low             < 0.5        <2

   Medium          0.5 – 0.75     2–3

     High            > 7.5        >3

•   Indication of nutrient availability
•   Phosphorus may be limiting nutrient
•   Ammonia important buffer
•   Nitrogen present for long periods of time
• Influence chemical and biological processes
  of precipitation, redox, sorption,
• Controlled by volatile acids during acid
• 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 concerns
No discernable chronological pattern
Leachate concentration controlled by sulfide,
  carbonate, chloride, and phosphate
     Leachate Quantity Estimation

• Percent of Precipitation
• Water Balance Technique (Figure 4-6)

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

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

•   Layout management scheme
•   Select leachate removal technique
•   Size pump
•   Select storage
•   Select treatment and disposal
     Leachate removal from LCS -

• Manhole in cell (sump pump)
• Penetration of liner/external sump (wet
  well/dry well, or sump pump)
• Side slope riser (slim sump pumps)
                        Leachate Storage

•   Underground storage tanks
•   Lagoons
•   Above ground tanks
•   three day’s storage at peak annual flow
       Leachate Treatment/Disposal

• On site
  –   biological
  –   chemical
  –   evaporative
  –   physical
• Off-site treatment

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