Urban organic waste valorization through an integrated pilot scale biorefinery for polyhydroxyalkanoates and biogas production

Abstract

The main three-year doctoral research activity is centered around the pilot scale implementation of a biorefinery aimed at the valorization of organic waste into polyhydroxyalkanoates (PHAs) and biogas. The whole production chain comprises the organic waste fermentation, the aerobic line for PHA production and the anaerobic co-digestion of the secondary waste streams produced within the biorefinery. A mixture of organic fraction of municipal solid waste and waste activated sludge from the municipal wastewater treatment was used as primary carbon source. The initial phases of the study focused on the fermentation process and the aerobic line, the most performing conditions corresponded to a fermentation yield (YVFA) equal to 0.40 g CODVFA/g VS and a storage yield in the accumulation phase (YP/VFAbatch) equal to 0.50 CODPHA/CODVFA. Then, the studies focused on the anaerobic line, i.e. the acidogenic fermentation and anaerobic co-digestion. Following studies aimed at the optimization of the fermentation process, the best obtained yields guaranteed a YVFA of 0.57 and 0.74 gCODVFA/g VS in batch and continuous tests respectively. The most performing conditions were then tested at pilot scale, the overall yield was considerably increased, reaching 76 g PHA/kg VS. In addition, legislative barriers and product social acceptance of waste derived bioplastics were preliminarily investigated. As final optimization, different operating conditions were investigated in the MMCs PHA selection process, that allowed to reach further improvement of the biorefinery overall yield, equal to 110 g PHA/kg VS. The results obtained in the present thesis shed a light on promising innovations in the field of organic waste valorization, proving the feasibility of the whole productive chain and its future industrial scale implementation.