Tuning dark fermentation operational conditions for improved biohydrogen yield during co-digestion of swine manure and food waste

Abstract

Large amounts of swine manure (SM) and livestock waste production in South Korea, leading to enormous environmental pollution and requiring extensive treatment before discharge. To address these issues, the upstream dark fermentation (DF) technique provides a sustainable solution to recover biohydrogen (bio-H2) using solubilized organics; however, the process parameters need to be optimized to boost the yield. The modulation of process variables, including input chemical oxygen demand (COD) doses (2, 6.4, 10, and 12 g/L), pH (5, 5.5, and 6), hydraulic retention time (HRT: 4.5 days, 2 days, and 1 day), and cosubstrate (SM: food waste (FW) = 8:2), was studied to improve the performance of DF. Mixing FW and SM maintains the feedstock pH in the range of 5.8–6.21 in DF, boosting hydrogen (H2) production to 0.5 L, which is considerably higher than that in DF fed with individual substrates. Similarly, a higher H2 generation and hydrogen yield (HY) of 1.32 L/L/day and 275.57 mL/gVSadded, respectively, were obtained for HRT of 1 day compared to HRT of 2 days (H2 production of 0.830 L/L/day and HY of 159.05 mL/gVSadded) and 4.5 days (H2 production of 0.403 L/L/day and HY of 80.6 mL/gVSadded) in 5 L DF. The produced H2 had a high purity of 83.21%. Thus, DF with operational variables of HRT of 1 day and pH of 5.5–6.2 with cosubstrate feeding was found to be effective for boosting the bio-H2 yield and treatment efficiency. Such optimized process parameters guide the operation of scalable DF to keep the stability and equilibrium of the process and maximize the HY.