H 2 addition through a submerged membrane for in-situ biogas upgrading in the anaerobic digestion of sewage sludge

In-situ upgrading of biogas in a mesophilic anaerobic digester of sewage sludge by sparging H through a membrane was studied. Large gas recirculation rates were required to facilitate H transfer to the bulk liquid phase; at ∼200 L L d , H utilization efficiency averaged 94% and the specific CH production increased from 0.38 L L d , during conventional digestion, to 0.54 L L d . Sludge digestion was not compromised by elevated H partial pressure nor by the associated rise in the pH (8.1) because of CO removal. In this regard, VFA accumulation was not detected and the performance of VS removal was similar to the observed without H 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.