Assessing the capabiblity of CH4 biodegradation under varied concentrations: kinetics and polydroxybutyrate production

Abstract

CH4 concentrations are likely to influence the biodiversity of methanotrophs and, consequently, their kinetic characteristics. In the present study, microbial cultures of methane-oxidizing bacteria were enriched in three stirred tank reactors under different CH4 concentrations in order to assess the kinetic parameters qmax and KS, and their capability to couple CH4 biodegradation with the production of polyhydroxyalkanoates (PHA) under sequential N limitations. Culture enrichment at CH4 concentrations of 20 (R1), 2 (R2) and 0.2 (R3) g m-3 supported biomass concentrations of 9, 1.7 and 0.26 g L-1 by day 120, respectively. The microorganisms enriched in R2 presented the highest qmax values (4.76 × 10-4 gCH4 gbiomass-1 h-1) at week 14, while the microorganisms enriched in R1 and R3 exhibited at week 19 the lowest KS values (5.2 × 10-6 and 4.75 × 10-6 M, respectively). Culture aging resulted in a gradual decrease in qmax. Furthermore, culture enrichment under periodic N limitation episodes resulted in increasing levels of PHB, thus reaching percentages of up to 0.36% and 9.46% (w/w) in R1 and R2, respectively. Polyhydroxybutyrate and polyhydroxyvalerate accumulation during CH4 abatement, as here recorded, could significantly contribute to improve the economic viability of the treatment process.