Enhanced biogas production and in situ ammonia recovery from food waste using a gas-membrane absorption anaerobic reactor

A novel GAs-Membrane Absorption anaerobic Reactor (GAMAR) was developed by combining gas-membrane absorption system with anaerobic digestion. A gas-permeable expanded polytetrafluoroethylene (ePTFE) membrane was submerged in the anaerobic reactor. Free ammonia could transfer through the gas-permeable membrane and be recovered by acidic solution. The free ammonia concentration was lower than 40 mgN L-1 in GAMAR, which alleviated ammonia inhibition. Meanwhile free ammonia concentration up 70 mgN L-1 in the reference reactor inhibited methanogens and led to unstable operation. The volumetric biogas production rate of GAMAR was 2.83 m(3) m(-3) d(-1), and 58% higher than the reference reactor. Long term use of membrane led to membrane fouling and hydrophobicity loss. The contact angle of membrane decreased from 105.9 +/- 1.2 degrees to 97.6 +/- 6.3 degrees after 43 d. The abundance of methanogens in GAMAR was 1.8-2.1 times higher than that in the reference reactor, which was in accordance with the higher biogas production rate in GAMAR.