Biopolymers made from methane in bioreactors

Methane (CH4) is a potent greenhouse gas and mitigation is important to reduce global warming impacts. In this study, we aimed to convert CH4 to polyhydroxybutyrate (PHB; a biopolymer) by enrichment of methanotrophic consortia in bioreactors. Two different methanotrophic consortia were established form landfill top‐cover (landfill biomass [LB]) and compost soils (compost biomass [CB]), through cultivation under CH4:CO2:air (30:10:60) in batch systems. The established cultures were then used as inoculi (0.5 g LB or CB⋅L−1) in continuous stirred tank reactors (CSTRs) aerated with CH4:CO2:air at 0.25 L⋅min−1. Under stable CSTRs operating conditions, the effect of spiking with 1:1 copper:iron (final concentrations of 5μM) was tested. Methane oxidation capacity (MOC), biomass dry weight (DWbiomass), PHB, and fatty acid methyl esters (FAMEs) contents were used as effect parameters. A maximum MOC of 481.9 ± 8.9 and 279.6 ± 11.3 mg CH4⋅g−1 DWbiomass⋅h−1 was recorded in LB‐CSTR and CB‐CSTR, respectively, but PHB production was similar for both systems, that is 37.7 mg⋅g−1 DWbiomass. Treatment with copper and iron improved PHB production (22.5% of DWbiomass) in LB‐CSTR, but a reduction of 13.6% was observed in CB‐CSTR. The results indicated that CH4 to PHB conversion is feasible using LB‐CSTRs and addition of copper and iron is beneficial.