Medium-chain fatty acid production from thermal hydrolysed sludge without external electron donor supplementation

medium-chain fatty acid (MCFA) generation from mixed sludge (including primary sludge and waste activated sludge) was investigated without additional electron donors (EDs). Thermal hydrolysis process (THP) as sludge pretreatment increased the MCFA yield by ca. 128% in the anaerobic fermentation. During 102 days of operation, the fermentation of THP pre-treated mixed sludge stably generated 2.87 g COD/L MCFAs. Ethanol addition improved MCFA yield, suggesting that the self-generated EDs were not sufficient for MCFA production. Caproiciproducens was the dominant chain-elongating bacteria. Accordingly, THP-assisted sludge fermentation could be a promising external ED-free biotechnology to recover valuable MCFAs.