Implementing polyhydroxyalkanoates production to anaerobic digestion of organic fraction of municipal solid waste to diversify products and increase total energy recovery

Abstract

A simple biorefinery aimed at producing both biomethane (CH₄) and polyhydroxyalkanoates (PHAs), was proposed to valorize the organic fraction of municipal solid waste (OFMSW). Anaerobic digestion (AD) was tested at different organic loading rates (OLR-I-II-III) (i.e. 3, 4 and 6 g L^-1 d^-1, respectively), producing biomethane and volatile fatty acids (VFAs)-rich digestate, the VFAs were then used to produce PHAs. Specific biogas and CH₄ production remained similar when adopting different OLRs (biogas of 522-600 NL kg^-1 VS and CH₄ of 64-67% v/v). VFAs concentrated with OLR increases and their patterns were modified. PHA production was in the range of 117-199 g kg^-1 OFMSW_TS with the lowest production being associated to different polymer composition. The net energy recovery of this simple biorefinery accounted for 64% of OFMSW energy content, and the PHAs produced represented over 30% of the total energy.

Keywords: Anaerobic digestion; Organic fraction of municipal solid waste (OFMSW); Organic loading rate; Polyhydroxyalkanoates (PHAs); Volatile fatty acids (VFAs).