INTENSIFICATION OF METHANE PRODUCTION FROM THE BIODEGRATION OF MSW IN LANDFILL BIOREACTORS USING MECHANICAL PRETRATEMENTS AND LEACHATE INJECTION: A PILOT-SCALE STUDY

摘要

Background and objectives: The anaerobic bioreactor landfill is developed in many countries as a long term Municipal Solid Waste (MSW) management option. The approach consists in the moisture control of the waste mass, usually via leachate circulation, in order to enhance methane production and thereby optimize energy recovery from the landfilled waste. Increasing the moisture content and the circulation of water through the landfill provides more favorable conditions for the microbiological processes of organic matter biodegradation from the waste. Mechanical pretreatments may also be implemented to further increase the bioavailability of the organic matter. However, leachate injection may also result in the inhibition of methanogenesis mainly due to the accumulation of volatile fatty acids (VFAs) and ammonia. The objective of this research was to identify at the pilot-scale the influence of mechanical pretreatment (crushing) on the initial stages of anaerobic digestion of domestic waste under bioreactor landfill simulated conditions. Methods: The experimental set-up consisted of 4 pilot-scale bioreactors of 1 m3 incubated at 35±2 ℃ and instrumented to monitor over time biogas and leachate productions and compositions along with the humidity and the settlement of the waste in each reactor. The reactors were filled with domestic waste taken from a landfill site located at ca. 100 km south of Lyon. Two modes of leachate injection (initial saturation followed by drainage, or weekly leachate injections) and two crushing levels (<150 mm for waste A and<70 mm for waste B) were tested. Results & main conclusions: Results showed that crushing logically increased the kinetics of biogas production regardless of the mode of leachate injection. The passive pre-aeration of the waste was found effective to promote rapidly and active methane production. Experimental data were very well simulated by Gompertz model, confirming the effect of particle size on biodegradation rate. Weekly leachate injections were found to be more efficient than the initial saturation of the waste, indicating that the percolation of water through the waste mass was an important factor to enhance biogas production and accelerate the degradation of solid waste.