Organic fraction of municipal solid waste recovery by conversion into added-value polyhydroxyalkanoates and biogas

The integrated-multistage process proposed herein is a practical example of a biorefinery platform in which the organic fraction of municipal solid waste (OFMSW) is used as valued source for polyhydroxyalkanoates (PHA) and biogas production. Technical and economical feasibilities of this approach have been demonstrated at pilot-scale, providing a possible upgrade to traditional biowaste management practices, presently based on anaerobic digestion (AD). A pH-controlled OFMSW fermentation stage produced a liquid VFA-rich stream with high VFA/CODSOL ratio (0.90 COD/COD) that was easily used in the following aerobic stages for biomass and PHA production. The solid fraction was valorised into biogas through AD, obtaining energy and minimizing secondary flux waste generation. The reliable biomass enrichment was demonstrated by a stable feast-famine regime and supported by microbial community analysis. The selected consortium accumulated PHA up to 55% wt. Compared to the traditional AD process in an urban scenario of 900,000 AE, the integrated approach for OFMSW valorisation is preferable and it is characterized by an electrical energy production of 85.7 MWh/d and 1.976 t/d as PHA productivity. The proposed process was also evaluated as economically sustainable if the PHA is marketed from 0.90 €/kg as the minimum threshold to a higher market price.