Optimization of anaerobic co-digestion of sewage sludge with fruit and vegetable wastes (FVW): Methane production potential, process performance and stabilized sludge quality

Abstract

Anaerobic co-digestion performance and stabilized sludge quality were investigated with fruit and vegetable wastes in semi-continuous lab-scale reactors for primary (PS), secondary (SS) and mixed sludge (MS) fractions at organic loading rates (OLRs) of 1.65, 0.40 and 1.0 kg VS/m3.day, respectively, at 35°. Fruit waste (FW), vegetable waste (VW) or fruit+vegetable waste (FVW) fractions were added as co-substrates at different OLR combinations. Optimum OLR values were 0.84, 0.33-0.44 and 1.18 g VS/L.day at %51, 209 and 84% (w:w) respectively for FW, VW and FVW, resulting in increases at 50-75, 250-300 ve 44-66% in daily methane production. Increase in OLRs led to decrease in methane yield and hydrolysis degree in the FW receiving digester whereas a toxic effect took place in VW feeding, especially on methanation with an irreversible pattern in PS co-digestion. VW exhibited a higher biodegradegradability than FW with a higher methane yield while pH was lowered in FW co-digestion.The results showed that co-digestion at low OLRs was beneficial in obtaining higher methane recovery while stabilized sludge worsened in dewatering ability. Stabilized SS gained a suitable level of electrical conductivity and nutrient content for soil application through higher conversion to microbial biomass. © 2022 Gazi Universitesi Muhendislik-Mimarlik. All rights reserved.