Abstract
Production of methane from H2 and CO2 was carried out with acclimated-mixed methanogens, in a jar fermentor in continuous culture at pH 7.2 and 37°C. 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 (μ) and specific consumption rate of H2 (qH2) were found to be 0.064 (h-1) and 104.8 (mmol/h g), respectively, which were the same as the μmax and qmax obtained in the batch culture reported previously, indicating that the fermentations were carried out with μmax 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 with 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 maximum value was reached and recovered immediately as soon as 5mL of 0.1N 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.
