Biogas production from N-rich wastes: SAOB-HM enriched digester versus hydrophobic membrane assisted digester

Hydrophobic membranes (HMM) are common in water purification processes to separate volatile compounds. When such membranes are combined with anaerobic digesters (AD), inhibitory phenomena affecting methanogenesis due to ammonium nitrogen, would be overcome. In this work, four continuous AD were operated under high N level and similar conditions (feed composition and loading, temperature and inoculum). Two AD were coupled to HMM with different membrane surface area to digester volume ratio (Am/V), while the third AD had not membrane (control AD). A fourth reactor was operated at high retention time to prompt the syntrophic acetate oxidation (SAO) route. Despite the similar total N inlet content (3.5-4.3 gN L-1), reactor performances were completely different, depending on the Am/V ratio for low retention time values. Conversely, upon operation at a high retention time, the enrichment of acetate syntrophic oxidizing bacteria and hydrogenotrophic methanogens (SAOB-HM) prevented ammonia inhibition. A modified ADM1 model, which included ammonia extraction by HMM and the SAOB population, fitted to the experimental data and helped to understand the observed patterns. Peer Reviewed