Improvement of activated sludge stabilisation and filterability during anaerobic digestion by fruit and vegetable waste addition

Anaerobic co-digestion of fruit and vegetable waste (FVW) and activated sludge (AS) was investigated using anaerobic sequencing batch reactors (ASBRs). The effects of AS:FVW ratio and the organic loading rate (OLR) on digesters performances were examined. The mixtures having AS:FVW ratios of 100:00, 65:35, 35:65, by a total solid (TS) basis were operated at an hydraulic retention time (HRT) of 20 d. However, 30:70, 20:80, 15:85, 10:90 and 0:100 ratios were tested at an HRT of 10 d. To investigate effects of aerobic and anaerobic digestion on the sludge filterability, specific resistance to filtration (R) was also determined. Increasing FVW proportions in the feedstock significantly improved the biogas production yield. The reactor that was fed with a 30:70 ratio showed the highest VS removal and biogas production yield of 88% and 0.57 L g−1 VS added, respectively. The filterability results showed that the anaerobic effluent was characterised by a slightly better filterability efficiency of 1.6 × 1016 m kg−1 than 1.74 × 1016 m kg−1 of aerobic effluent. However, FVW addition improved the anaerobic co-digestion effluent filterability (5.52 × 1014 m kg−1).