The physiology of trace elements in biological methane production

Abstract

Trace element (TE) requirements of Methanothermobacter okinawensis and Methanothermobacter marburgensis were examined in silico, and using closed batch and fed-batch cultivation experiments. In silico analysis revealed genomic differences among the transport systems and enzymes related to the archaeal Wood-Ljungdahl pathway of these two methanogens. M. okinawensis responded to rising concentrations of TE by increasing specific growth rate (µ) and volumetric productivity (MER) during closed batch cultivation, and can grow and produce methane (CH₄) during fed-batch cultivation. M. marburgensis showed higher µ and MER during fed-batch cultivation and was therefore prioritized for subsequent optimization of CO₂-based biological CH₄ production. Multiple-parameter cultivation dependency on growth and productivity of M. marburgensis was finally examined using exponential fed-batch cultivation at different medium-, TE- and sulphide dilution rates, and different gas inflow rates. MER of 476mmolL^-1h^-1 and µ of 0.69h^-1 were eventually obtained during exponential fed-batch cultivations employing M. marburgensis.

Keywords: Autotrophic and hydrogenotrophic methanogens; Bioreactor; Closed batch; Fed-batch; Methanothermobacter marburgensis; Methanothermococcus okinawensis.