Ex-situ biological hydrogen methanation in trickle bed reactors : Integration into biogas production facilities

Abstract

Biological hydrogen methanation (BHM) is a biocatalytic process for biogas upgrading. Integrating ex-situ BHM processes into biogas facilities has the advantage of using inoculum, CO2, and nutrients directly from anaerobic digestion (AD) processes to enhance CH4 productivity. This study investigated the potential of biowaste digestate as an inoculum and digested biowaste reject water as the trickling liquid and nutrient source in thermophilic trickle bed reactors (TBRs). Use of reject water improved H2 conversion efficiency to up to 99 %, thus achieving a H2 loading rate of 10.8 LH2 L Rv-1 d-1 at a gas retention time (GRT) of 1.8 h and CH4 productivity of 2.6 L LRv-1 d-1 implying that reject water contains macronutrients beneficial to enriching hydrogenotrophic methanogens. However, at high H2 loading rates, a trace element supply was necessary to stabilize process performance. Hydrogenotrophic methanogens Methanothermobacter and Methanobacterium were selectively enriched, mainly due to the increased H2 loading rate.