Biohydrogen and methane production from cheese whey in a two-stage anaerobic process

The aim of the present study was to investigate the potential of hydrogen and subsequent methane production from raw cheese whey at 35 °C. The fermentative hydrogen production process from raw cheese whey was conducted in a continuous-type stirred tank bioreactor, operated at low hydraulic retention time (HRT; 24 h). In this stage, the carbohydrates contained in cheese whey are fermented to a mixture of acids and a gaseous mixture rich in hydrogen. The continuous fermentative hydrogen production was sustained by the indigenous microflora already contained in the raw cheese whey because the bioreactor was not seeded with any source of inoculum. At a HRT of 24 h, the hydrogen production rate was 7.53 L of H2/day, while the yield of hydrogen produced was 0.041 m3of H2/kg of chemical oxygen demand (COD) added or 2.49 L of H2/L of cheese whey. The mixed liquor from this stage was further digested to biogas in a periodic anaerobic baffled reactor (PABR), a baffled-type bioreactor. The PABR was operated at HRTs of 20, 10, and 4.4 days. The highest biogas and methane production rates were 105.9 L of biogas/day and 75.6 L of CH4/day, respectively, and were obtained at an HRT of 4.4 days. During this stage, COD reduction reached 94%, obtained at an HRT of 4.4 days. Furthermore, the methane potential of the raw cheese whey was assessed by conducting a biochemical methane potential test. It was estimated to be 0.31 m3 of CH4/kg of COD added or 17.9 L of CH4/L of cheese whey. This work demonstrated that biohydrogen production from cheese whey can be very efficiently coupled with methane production in a subsequent step, exploiting the gaseous biofuel potential of this wastewater type