New concept for valorization of OFMSW: coupling steam explosion pre-treatment with PHA production by purple phototrophic bacteria, and anaerobic digestion

Introduction Currently a huge amount of municipal solid waste (MSW) is produced world-wide (2 billion tons annually), of which 34-53% is represented by organic fraction (OFMSW) (Abad et al., 2019). This biowaste typically contains organic residues like food and kitchen waste, discarded supermarket products, and pruning waste. Therefore, OFMSW represents an untapped source for energy and resource recovery (Fava et al., 2015). MSW is typically sent to landfill. Alternative methods include thermal treatment (pyrolysis and gasification) and biological technologies like composting and anaerobic digestion. The latter is a viable option for waste stabilization and energy recovery. However, the degradation rate is limited by the hydrolysis of solid substrates. The hydrolysis can be accelerated by thermal treatment like the steam explosion pretreatment, which allows deep disintegration of internal cell structures in biomass by a sharp pressure change. This process also increases the biodegradability of the resultant solid biomass (Cano et al., 2014a), and partially solubilizes the organic matter to a liquid fraction that can be furtherly processed. In recent years, the use of MSW to produce high-added value products such as polyhydroxyalkanoates (PHA) is gaining interest. A step forward in the attempt to reduce production costs is the use of mixed culture of phototrophic purple bacteria (PPB). PPB are highly metabolically diverse, allowing the assimilation of different carbon sources including sugars and organic acids in anaerobic conditions, which makes them perfect candidates for the treatment of heterogeneous materials as well as do not need equipment sterilization or aeration, two of the most expensive processes in the production of PHA (Koller et al., 2017). The current work aims to evaluate this new concept for the valorization of OFMSW. The effects of temperature and time on biodegradability of the streams generates from steam explosion (hydrolised and liquid fraction), were studied by biochemical methane potential (BMP) test and batch specific phototrophic activity (SPA).