Effects of leachate recirculation on landfill gas production

Based on the typical MSW composition in Shanghai, lab-scale simulated landfill columns were used to study the effects of different leachate recirculation operations on landfill gas (LFG) production. Fresh leachate, pretreated leachate (anaerobic process or aerobic process), and leachate mixture (fresh leachate and leachate from a well-decomposed landfill) were recirculated to landfill columns respectively. The results indicated that the recirculation of leachate without any pretreatment inhibited methane fermentation, while the recirculation of leachate pretreated to some extent benefited to methane fermentation, in that it greatly improved the gas production rate, cumulative gas production Q_t, the ratio of Q_(eff)/Q_t (above 0.80, Q_(eff) means production of gas with methane concentration over 50%), and the ratio of Q_t/Q_p (above 0.40, Q_p means theoretic gas production), as well as shortened the gas production period into near one year. Different leachate pretreatment leaded to different effects, the descending sequence of effectiveness was anaerobic process, mixing with leachate with well-decomposed landfill, and aerobic process. Different leachate pretreatment processes and their treatment level were regarded to influence the methane fermentation and the amount of organic matter disposed ex situ, thus changing the production and quality of LFG.