Effects of leachate recycle and anaerobic digester sludge recycle on the methane production from solid wastes

Performances of lab-scale lysimeters were evaluated to develop a new landfill system for the recovery of CH₄ from solid wastes. Lysimeters were operated at three different conditions: control (L-control), leachate recycle (L-recycle), and sludge recycle (L-sludge). For L-sludge, sludge from the leachate-treating anaerobic digester was recycled, whereas the produced leachate was recycled for L-recycle. After 430 days of operation, the amounts of COD recovered by CH₄ were 0.13, 0.29, and 22.5 kg for L-control, L-recycle, and L-sludge, respectively. For L-sludge, 77% of total COD outflow was recovered by CH₄, and the remaining COD was washed out by leachate. However, less than 5% of total COD outflow was recovered as CH₄ from L-control and L-recycle. Stabilization of organics in L-sludge approached completion within 430 days, while other lysimeters still produced leachate with high COD. Results indicated that the continuous addition of active methanogenic population from the anaerobic digester rather than simple leachate recycle was effective for the rapid and significant CH₄ recovery from solid wastes.