VALORISATION OF WASTEWATER TREATMENT SEWAGE SCUM THROUGH THE PRODUCTION OF BIOFUELS

The ReFil project (PRIN MUR, Italy) aims to valorise sewage scum separated by flotation in the primary stage of municipal wastewater treatment plants (WWTP). Due to its origin and composition (45% grease and 26% cellulose-hemicellulose), it could represent a raw material for producing biofuels. While the grease is employable for biodiesel production, the cellulose/hemicellulose fraction could be used for producing sugar-rich liquor via enzymatic saccharification. Despite these sugars may serve as substrate for bioethanol production, new alternative valorisation approaches are being investigated due to the high energy consumption of ethanol distillation (spending 22% of its combustion energy) whose feasibility relies only on an economy of scale. In such a scenario, transporting sugar-rich liquor to large centralized ethanol production plants would be necessary. However, this approach may not be economically sustainable, especially when considering the multitude of WWTP spread across large territories. Therefore, this work investigates the feasibility of fermenting a sugar-rich liquor for hexanoic acid production by employing an anaerobic mixed culture system. A pseudo-continuous bioreactor (8-L) was used for producing carboxylic acids (CAs) under acidogenic fermentation conditions (12 days of HRT, 37°C). It was inoculated (10% v/v) with a digestate arising from a commercial anaerobic digester and is being fed with a laboratory prepared glucose-rich solution mimicking the actual liquor. After achieving process stability with high CAs and no methane productions, the bioreactor will be fed with the actual liquor. Moreover, experiments will be dedicated to screening best operational conditions for maximising hexanoic acid production.