Aneerobic fermentation of refuse

An overview is given of the anaerobic treatment of concentrated organic municipal wastes under spontaneous conditions in -landfills and under controlled reactor conditions. Biogas capture in landfills offers a potential to recover energy and furthermore to reduce the extent of air, water and soil pollution by the landfill. The technology is quite simple to install and apply and can be economically interesting if a convenient consumer of the gas is located in the vicinity of the landfill. Yet, optimisation of this in-situ fermentation is urgently needed. With regard to the in-reactor technology, particular attention is given to a newly developed dry anaerobic composting process. This concerns a solid state fermentation process for the stabilization of the organic fraction of solid household refuse. The process consists of an intensive anaerobic fermentation at 30–35 X total solids and a temperature of 35 °C (mesophilic) or 55 °C (thermophilic), followed by a post digestion. It produces both biogas and a commercial humus-like endproduct. The results obtained over a 1 year period in a pilot plant of 56 m3 have demonstrated the feasibility of the process for large scale application. Gas production rates of 6 to 8 m³ per m³ reactor per day were obtained at a retention time of 12 to 18 days under thermophilic conditions. The gas yield per ton of raw organic fraction amounted to 180 m³ of biogas with a methane content of 55 %.