Improving the production of gas in landfills by methanogenic sand layer

Landfills provide a potential source of methane as a fuel source for energy generation. Results of a research on the production of methane gas from lab scale landfill bioreactor under saturated conditions have been presented in this paper. A landfill cell having thickness of 2.5 m was epitomized by a fabricated bioreactor. The diameter and height of the bioreactor were 0.2 m and 4 m respectively. Pebbles and loose sand grains filled the base of the bioreactor to a one meter height on top of which the solid waste layer of 2.5 m was placed and sand layer of 0.4 m as cover soil. The solid waste degradation remained mostly at acidification phase as inferred by the leachate condition containing NH3 and COD reaching 1,480 and 55,511 mg/L and pH of 5.1 respectively. Gas production did not occur at the centre of the solid waste matrix, which was likely for the inhibition of methanogenesis as a result of the low pH of the leachate. However methanogenesis was entrenched at the underlying sand matrix. Accelerated decomposition occurred as the leachate percolated through the sand matrix at an infiltration of 1.6 cm/day thereby, resulting in increased rate of gas production averaging 77 mL/day/kg with 55 to 65% being methane. The rate was about double the amount of gas collection reported from landfills. Harvesting gas from landfills can be improved by introducing in-situ degradation of leachate in the underlying sand matrix of the landfill.