Exploiting olive oil mill effluents as a renewable resource for production of biodegradable polymers through an anaerobic-aerobic process

This study describes the performance of a three-stage process for the bioproduction of polyhydroxyalkanoates (PHAs) from olive oil mill wastewaters (OMWs). In the first stage OMWs were anaerobically fermented, in a packed bed biofilm reactor (PBBR), to a mixture of volatile fatty acids (VFAs) (up to 32 % of the overall COD), that are the most suitable substrates for PHAs production. This VFA-rich effluent was fed to the second stage of the process, performed in a fully-aerobic Sequencing Batch Reactor (SBR), in which mixed cultures able to store PHAs were selected. Rates and yields of PHA storage were similar to those obtained with a synthetic mixture of VFAs, indicating the non-inhibitory nature of the fermented OMWs. Finally, the storage response of the selected consortia was exploited in the third aerobic stage, which was operated, in batch conditions, at different loads (from 1 to about 9 times the usual SBR load) in order to maximize the polymer content in the biomass. The overall storage yield on the fermented OMWs was about 0.36 COD/COD, with about half of the PHAs being produced from substrates other than VFAs, such as alcohols. Overall, the proposed process is promising for the simultaneous treatment of OMWs and their valorization as a renewable resource for PHA production.