Case study of landfill leachate recirculation using small-diameter vertical wells

Area of Science:

• Environmental Engineering
• Waste Management
• Geotechnical Engineering

Background:

• Landfill leachate recirculation is a strategy to enhance waste decomposition and biogas production.
• Vertical wells offer a method for distributing liquids within landfills.
• Understanding liquid distribution and its impact on waste is crucial for optimizing landfill operations.

Purpose of the Study:

• To investigate the performance of small-diameter vertical wells for landfill leachate addition.
• To quantify the impact of leachate recirculation on waste moisture content and decomposition.
• To assess factors limiting liquid addition rates in landfills.

Main Methods:

• A case study involving the addition of over 25,000 m³ of leachate via 134 vertical wells (5 cm diameter) at depths of 3, 12, and 18 m over five years.
• Monitoring of liquid addition performance, including flow rates and hydraulic conductivity.
• Measurement of lateral moisture movement using sensors and assessment of waste decomposition via biochemical methane potential tests.

Main Results:

• Liquids addition performance varied, with estimated radial hydraulic conductivity ranging from 3.5×10⁻⁶ to 4.2×10⁻⁴ m s⁻¹.
• Lateral moisture movement extended 8 to 10 m from the wells.
• Average waste moisture content increased from 23% to 45% (wet weight basis), and significant decomposition was observed (p<0.025).

Conclusions:

• Small-diameter vertical wells can effectively distribute leachate in landfills, increasing moisture content and promoting waste decomposition.
• Surface seeps and pressurized addition scenarios can limit liquid addition rates.
• Leachate recirculation via vertical wells is a viable method for accelerating landfill waste stabilization.