Use of lyophilized and acclimated digestate dominated by Methanobrevibacter as a start-up inoculum in anaerobic digester led to higher methane production in biochemical methane potential assays

Abstract

Transporting wet inoculum for full-scale anaerobic digester (AD) start-up is usually infeasible and costly, especially, for remote locations. To overcome these burdens lyophilized AD inoculum is thought to be used after on-site acclimation. For this reason, in this study, the impact of three different acclimated lyophilized AD inoculums collected from full-scale mesophilic AD installations treating different feedstocks was tested for 20 days to monitor AD start-up and methane production by using biochemical methane potential (BMP) assays. The lyophilized inoculums after acclimation were fed to corresponding triplicate digesters treating similar feedstocks as digestate (DG), waste activated sludge (WAS) plus landfill leachate (LL) and WAS, LL plus food waste from municipal solid waste (FWMSW). As a control, no inoculum added digesters with three different feedstocks collected freshly from full-scale mesophilic AD installations treating DG, WAS + LL and WAS + LL + FWMSW were also run in triplicates. All the digesters displayed enhanced methane production in two days of the incubation, the digesters fed with DG as an inoculum displayed shortened start-up and the highest methane production with 42.77 % comparing to control. BMP assays of the other two inoculums tested also displayed 4.73 % enhanced methane production for WAS plus LL and 4.51 % enhanced methane production for WAS, LL plus FWMSW comparing to their corresponding controls. Metagenome analyses of the inoculums used revealed that the dominant methanogens were Methanobacteriaceae (100 % Methanobrevibacter) for DG, %33 Methanosaetaceae (%100 Methanothrix) and %27 Methanobacteriaceae (%71 Methanobrevibacter and %29 Methanosphaera) for WAS + LL, %35 Methanosaetaceae (%100 Methanothrix) and %30 Methanobacteriaceae (%91 Methanobrevibacter and %9 Methanosphaera) for WAS + LL + FWMSW. The lyophilized DG dominated by hydrogenotrophic genus Methanobrevibacter seems to be promising inoculum after acclimation, however, its efficiency needs to be further analysed for the ADs treating various feedstocks.