Controlling methane and hydrogen production from cheese whey in an EGSB reactor by changing the HRT

This study assessed the effects of hydraulic retention time (HRT; 8 h–0.25 h) on simultaneous hydrogen and methane production from cheese whey (5000 mg carbohydrates/L) in a mesophilic (30 °C) expanded granular sludge bed (EGSB) reactor. Methane production was observed at HRTs from 4 to 0.25 h. The maximum methane yield (9.8 ± 1.9 mL CH4/g CODap, reported as milliliter CH4 per gram of COD applied) and methane production rate (461 ± 75 mL CH4/day Lreactor) occurred at HRTs of 4 h and 2 h, respectively. Hydrogen production increased as methane production decreased with decreasing HRT from 8 to 0.25 h. The maximum hydrogen yield of 3.2 ± 0.3 mL H2/g CODap (reported as mL H2 per gram of COD applied) and hydrogen production rate of 1951 ± 171 mL H2/day Lreactor were observed at the HRT of 0.25 h. The decrease in HRT from 8 to 0.25 h caused larger changes in the bacterial populations than the archaea populations. With the decrease in HRT (6 h–0.25 h), the Shannon diversity index decreased (3.02–2.87) for bacteria and increased (1.49–1.83) for archaea. The bacterial dominance increased (0.059–0.066) as the archaea dominance decreased (0.292–0.201) with the HRT decrease from 6 to 0.25 h.