IMPROVED GROWTH AND METHANE PRODUCTION CONDITIONS FOR METHANOBACTERIUM-THERMOAUTOTROPHICUM

Methanobacterium thermoautotrophicum was grown on a defined mineral sa lts medium under strictly anaerobic conditions with H-2 and CO2 as the sole energy and carbon sources, respectively. The cultivation medium was optimized with respect to non-organic components including Se(IV), W(VI), N, Ni(II), Fe(II), Co(II) and Mo(VI). Sulphide concentration i n the medium was maintained constant using an on-line regulatory syste m by the addition of 0.5 M Na2S. A maximum supply rate of 0.6 vvm of a mixture of 80% H-2 and 20% CO2 was achieved for the gaseous substrate s. Under these conditions a specific growth rate of 0.30 h(-1) and a c ell concentration of 4.8 g cell dry weight (DW) 1(-1), representing a 140% increase over previously published results, were obtained. The gr owth yield of 2.3 g DW mol(-1) CH4 was similar to published values. Ho wever, the overall specific productivity was enhanced from 11 mmol CH4 g(-1) DW h(-1) to 24 mmol CH4 g(-1) DW h(-1), corresponding to an imp rovement of 120%.