Anaerobic digestion of the organic fraction of municipal solid waste for waste treatment and energy recovery

Abstract

The amount of municipal solid waste is continuously on the rise and increasing pressures exist to reduce the negative environmental impact of disposing of this waste. On the other hand, global energy demand is also on the rise. Anaerobic digestion has the potential of being part of an integral solution to manage waste sustainably and also of providing renewable energy through biogas formation, effectively contributing to the circular economy concept. Anaerobic digestion provides for the decomposition of organic waste, such as food waste, in a controlled environment producing a nutrient rich compost-like material and biogas. Biogas is made up of 50 to 65% methane which can be used as a renewable fuel. This study was carried out to understand the principles of anaerobic digestion and the main engineering concepts and variants, to establish the biomethane potential of the organic fraction of the municipal solid waste in Malta and finally to calculate its derived renewable energy potential. A test bench was developed to establish the methane potential of various substrates. The organic fraction of the municipal solid waste was characterised and resulted in an average organic matter of 23.8% of the wet feedstock. Through anaerobic digestion, the feedstock yielded 687 ±107 NL/kg(VS) of biogas with an average methane content of 59.1 ±3.2 %. Assuming a total household waste generation in 2015 of 190,000 tonnes, the potential energy content should all the organic waste from the municipal solid waste be treated through anaerobic digestion, would be in the region of 89GWh per annum. Excluding any ensuing renewable heat generation, a potential of 33GWh per annum of renewable electricity could be produced.