Characteristics of Hydrogen and Methane Fermentation of Potato Processing Waste by Two-Phase Circulating Process without Dilution Water

A new type of two-phase process for producing hydrogen and methane from food waste was investigated using potato processing waste in this study. In this process a mixing tank, a thermophilic acidogenic reactor (55°C) and a mesophilic methanogenic reactor (36°C) were used in series. The methane-fermentation-mixed liquor was returned to the mixing tank for the dilution of influent food waste. A continuous experiment was conducted by changing the whole process hydraulic retention time (HRT) stepwise from 56 days to 30 days, then 20 days and 15 days. The process was successfully performed for over 290 days until the HRT was reduced to 15 days. A stable and high hydrogen production yield of 1.67 mol H2·mol-1 degraded hexose with a VFA concentration of 10000 to 25000 mgHAc·l-1 was obtained in the thermophilic acidogenic reactor, while a high efficiency of methane fermentation was achieved in the mesophilic methanogenic reactor. As a result, the high VS removal (92%) and total CODcr removal (85-90%) were achieved by the new process at HRTs of 20 to 56 days. The suggested new process was not only possible for the dilution-free treatment of potato processing waste, but also useful for continuous hydrogen fermentation at a high rate.