The role of dry anaerobic digestion in the treatment of the organic fraction of municipal solid waste: A systematic review

Abstract

Anaerobic digestion (AD) has been seen as an attractive alternative for the treatment of the organic fraction of municipal solid waste (OFMSW), with the potential to provide useful products such as bio-methane, bio-hydrogen, and a highly concentrated compost. Among the different AD technological routes, dry AD stands out because it makes better use of resources and can handle higher solids concentration, being more robust and flexible as compared to wet AD systems. In this contribution, a systematic review was carried out on the evolution of AD systems, giving emphasis to the role of the dry AD route for OFMSW treatment throughout the last 15 years. As it has been seen as a current trend in the field, the opportunities for technological development of dry AD systems and the challenges to be faced for their implementation in large-scale settings were assessed. Furthermore, aspects associated with input substrates and biodigesters operating conditions were addressed, along with the most important dry AD reactor configurations and commercial technologies. The research studies show that dry AD is most implemented under mesophilic conditions in continuous processes. Furthermore, apart from being influenced by many operational factors (temperature, pH, total solids content, substrate to inoculum ratio, organic loading rate and hydraulic/solids retention time), the performance of dry AD systems in terms of biogas productivity depends on the characteristics of the substrates, co-substrates and inoculum. Laboratory-scale tests are found to be essential to overcome the operational obstacles in full-scale plants, allowing for better system performance, stability and process control.