Conference article

Anaerobic digestion (AD) is a prominent green technology used for methane production from organic waste. Previous studies have shown that the amount of CH4 produced during anaerobic digestion can be increased by adding inorganic electron donors such as H2 and CO, both which can be produced as syngas from wood. Syngas inflow is implemented in the ADM1 model and simulations are carried out with different syngas additions to a well-documented case of wastewater treatment plant sludge AD. Three different compositions; (1) pure hydrogen, (2) 86 vol.% H2, 7 vol.% CO and 7 vol.% CO2, and (3) 44.4 vol.% H2, 33.3 vol.% CO and 22.2 vol.% CO2 were used for a first set of simulations testing process limitations. The second set of simulations were used to find out how much methane production can be increased for the given case if syngas composition is optimized. The CH4 production can be increased by 33 % by adding H2 (1) and was limited by pH going too high. Biogas CH4 content reached 92 % at this limit. The H2-rich syngas addition (2) reached 47 % CH4 production increase with 81 % CH4 content. The low H2 syngas case (3) produce more biogas but the CH4 content is reduced to 42 %. There is a narrow syngas composition range for which methane production can be increased by a factor >~ 2.7, limited by available nitrogen in the treated sludge.

Anaerobic digestion, ADM1, Syngas addition, CH4 production, CO degradation