Life cycle assessment on the treatment of organic waste streams by anaerobic digestion, hydrothermal carbonization and incineration

By means of source-segregation, organic waste streams are deterred from mass-burning and more sustainable treatment paths may be enabled. This study analyzed the environmental and economic performance of custom treatment paths for organic waste streams in Germany towards energy generation. The reference quantity was the production and export of 1 kWh of exergy, while treating a certain amount of waste. The methodologies of environmental life cycle assessment (eLCA) and levelized costs of exergy (LCOE) were applied. The considered treatment systems were (i) anaerobic digestion, (ii) hydrothermal carbonization (HTC) and (iii) incineration. The technologies were considered individually or in a cascade. The analyzed waste streams were the organic fraction of municipal solid waste (OFMSW), food waste and waste wood. For food waste and OFMSW, anaerobic digestion followed by the spreading of the digestate was characterized by overall beneficial environmental and economic properties. As the preferable treatment system was the same for both substrates, a separate collection of food waste was not considered worthwhile. For waste wood, the most environmentally friendly and economic option was direct incineration - either in a waste incinerator or in a lignite power plant. The implementation of an HTC process appeared viable for the treatment of OFMSW and food waste, both from an environmental and economic point of view. However, the energy intensive system must be outlined towards an environmentally friendly heat source. In this context, a cascading of anaerobic digestion with the HTC-process proofed to be an acceptable alternative.