J.of Soc of Agri Struc, Japan.
Vol.24,No.4 March 1994,207-214
Original:
Language: English

    Production of methane from H₂ and CO₂ was carried out with acclimated-mixed methanogens, in a jarfermentor in continuous culture at pH 7.2 and 37 centigrade. Kinetic parameters for the growth of methanogens and for the conversion rate of H₂ and CO₂ to CH₄ were determined utilizing a non-steady-state procedure over 3 hours. The specific growth rate ($\mu$) and specific consumption rate of H₂ (q_H2) were found to be 0.064 (h^-l) and 104.8 (mmol/h g), respectively, which were the same as the $\mu$_max, and q_max obtained in the batch culture reported previously, indicating that the fermentations were carried out with p_max under non-rate-limited mass transfer conditions. The fermentation was also performed at various CO₂/H₂(20/80, %v/v) gas flow rates. At a gas flow rate of 177(mL/min), the cell concentration and the methane production rate reached 1879(mg/L) and 35.15(mmol/L h), respectively, with a CO₂ conversion rate of 80%. The results obtained in this study are higher by contrast with that of a pure culture or a mixed culture in a CSTR as reported elsewhere.
Also we obtained short time steady methane fermentation urith a higher gas flow rate range of 148-177(mL/min), then the rate of H₂ uptake and methane production suddenly dropped to a low level when the maxinium value was reached and recovered immediately as soon as 5 mL of 0.1 N Na₂S solution was added to the culture. This indicates that sulfide was gradually flushed out to the atmosphere from the liquid medium in the form of H₂S as the culture was continuously sparged with H₂ and CO₂. A source of sulfur is then neccessary for the methanogens to grow satisfactorily and sulfide must be added to the medium to prevent stoppage of growth on the continuous feed substrate gas of CO₂/H₂.

Keywords: Methane production, CO₂ fixation, sulfide-containing compound, Acclimated methanogens, Fermentation kinetics

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