H2 addition through a submerged membrane for in-situ biogas upgrading in the anaerobic digestion of sewage sludge

Abstract In-situ upgrading of biogas in a mesophilic anaerobic digester of sewage sludge by sparging H 2 through a membrane was studied. Large gas recirculation rates were required to facilitate H 2 transfer to the bulk liquid phase; at  ∼200 L L reactor −1  d −1 , H 2 utilization efficiency averaged 94% and the specific CH 4 production increased from 0.38 L L reactor −1  d −1 , during conventional digestion, to 0.54 L L reactor −1  d −1 . Sludge digestion was not compromised by elevated H 2 partial pressure nor by the associated rise in the pH (8.1) because of CO 2 removal. In this regard, VFA accumulation was not detected and the performance of VS removal was similar to the observed without H 2 supply. Microbial analysis revealed that homoacetogens were outcompeted by hydrogenotrophic methanogens. Methanoculleus sp., Methanospirillum sp., Methanolinea sp. and Methanobacterium sp. were the hydrogenotrophic archaea present over the experiment.