Development and evaluation of a trickle bed bioreactor for enhanced mass transfer and methanol production from biogas

Biological conversion of the biogas produced by landfills and anaerobic digestion systems (60-70% methane (CH4), 30-40% carbon dioxide (CO2)) to methanol using methanotrophs (aerobic CH4-oxidizing bacteria) is an emerging approach to convert waste-derived biogas to liquid chemicals and fuels. The purpose of this work was to develop a trickle-bed reactor (TBR) to improve mass transfer of CH4 and oxygen (O-2) to methanotroph growth media for enhanced CH4 oxidation and methanol production. Mass transport of O-2 in a TBR packed with ceramic balls was nearly two-fold higher than an unpacked TBR. CH4 oxidation in the TBR (0.4-0.6 mmol/h) was about four times higher than that in shake flasks that used similar inoculum and headspace:volume and biogas:air ratios. Using optimal operating parameters (biogas:air = 1:2.5, 12 mmol formate addition, 3.6 mmol phosphate), methanol productivity (0.9 g/L/d) from the non-sterile TBR was among the highest reported in the literature. Operation under non-sterile conditions caused differences in the microbial community composition between experiments, and the most predominant methanotrophs appeared to be members of the genus in which the inoculum is classified (Methylocaldum sp. 14B). (C) 2017 Elsevier B.V. All rights reserved.