Anaerobic co-digestion of sewage sludge and food waste: Effect of pre-fermentation of food waste in bench- and pilot-scale digesters

Abstract

The effect of pre-fermentation of food waste (FW) for 48 h at 24 °C in anaerobic co-digestion with sewage sludge (SS) was studied in bench and pilot digesters (30 °C, HRT 30 d). The digesters fed with a mixture of SS and fresh or pre-fermented food waste (FW) (80:20% v/v) presented better performance (53% VSS reduction and 186–223 NmL biogas/g VSSadd) than the digester fed with only sludge (35% VSS reduction and 41 NmL biogas/g VSSadd). In both digesters, the pH quickly dropped in the first weeks of operation. However, the digester fed with SS and pre-fermented FW achieved 1.5 times faster pH recovery and relatively stable biogas production throughout the operation (186 ± 23 NmL biogas/g VSSadd). The pilot-scale results confirmed those obtained in bench-scale. Therefore, the pre-fermentation of FW did not affect long-term co-digestion but contributed to a better performance in the starting phase of the digesters.