Operation of a Two-stage Continuous Fermentation Process Producing Hydrogen and Methane from Artificial Food Wastes

An anaerobic two-stage continuous fermentation process with combined thermophilic hydrogenogenic and methanogenic stages (two-stage fermentation process) was applied to artificial food wastes on a laboratory scale. In this report, organic loading rate (OLR) conditions for hydrogen fermentation were optimized before operating the two-stage fermentation process. The OLR was set at 11.2, 24.3, 35.2, 45.6, 56.1, and 67.3 g-CODcr L day with a temperature of 60C, pH5.5 and 5.0% total solids. As a result, approximately 1.8-2.0 mol–H2 mol-hexose was obtained at the OLR of 11.2-56.1 g-CODcr L day. In contrast, it was inferred that the hydrogen yield at the OLR of 67.3 g-CODcr L day decreased because of an increase in lactate concentration in the culture medium. The performance of the two-stage fermentation process was also evaluated over three months. The hydraulic retention time (HRT) of methane fermentation was able to be shortened 5.0 days (under OLR 12.4 g-CODcr L day conditions) when the OLR of hydrogen fermentation was 44.0 g-CODcr L day, and the average gasification efficiency of the two-stage fermentation process was 81% at the time.