Ex-situ biogas upgrading to methane and removal of VOCs in a system of zero valent iron and anaerobic granular sludge

Abstract

In the current study, a novel process of ex-situ biogas upgrading to biomethane is presented which is based on a system consisted of anaerobic sludge and zero valent iron (ZVI). The ZVI when is added in an aquatic system with anaerobic granular sludge generates H2 under anaerobic abiotic conditions. Then, the H2 and CO2 are converted by the hydrogenotrophic methanogens to CH4. Biogas upgrading to biomethane was achieved in 4 days in a system of anaerobic granular sludge, 50 g L1 ZVI initial pH 5 and 20 g L1 NaHCO3. In this system when zero valent scrap iron (ZVSI) was added instead of ZVI required longer period (21 days) to achieve biogas upgrading. Volatile organic compounds (VOCs) analysis in raw biogas (in system of anaerobic sludge and ZVI) showed mainly the reduction of low mass straight- and branched-chain alkanes (C6-C10); however, no other particular trend regarding the removal of other VOCs was observed. H2S and NH3 were found to be substantially reduced, when the anaerobic sludge was exposed to ZVI compared to no decrease in serum bottles free of ZVI.