Anaerobic co-digestion of food waste and bio flocculated sewage sludge towards bio-methane production

Abstract

The existing sewage treatment plants are energy consumers rather than producers and integration of anaerobic reactor can be a viable approach for enhancing their commercial viability. Therefore, anaerobic co-digestion of food waste and bio-flocculated sewage sludge was studied in a continuous stirred tank reactors (R1 and R2) having a working volume of 6.5 Litre at organic loading rates of 2.5 and 2.4 g VS L−1D−1. At mesophilic temperature, the stabilisation of inoculum was performed in batch mode for 60 days followed by continuous mode feeding for 120 days. The feeding ratio was decided based on availability of food waste and bio-flocculated sewage sludge from a typical domestic household for analysing the effect of volatile fatty acids accumulation on reactor performance. The R1 was fed with equal proportion of bio-flocculated sewage sludge and food waste while R2 was fed in 98:2 (v/v), respectively. To analyse the mixing and temperature distribution within the digester, the velocity and temperature profiles were obtained using Ansys Fluent. In R1, more biogas yield were observed than R2 due to 80% average VS reduction as compared to 55% in case of R2. The highest volatile fatty acids accumulation of 10951 mg L−1 was observed in R1 whereas R2 showed 2800 mg L−1, respectively. The more fluctuations in pH were observed in R1 as compared to R2 due to more food waste concentration and maximum bio-methane production was 133 and 233 mL CH4 g−1 VSadded in R1 and R2, respectively.