Exploring optimal environmental factors for fermentative hydrogen production from starch using mixed anaerobic microflora

Our previous work demonstrated that an acclimated mixed bacterial consortium was able to produce H2H2 from sugar substrates. To reduce the medium cost for more commercially viable H2H2 production, cassava starch was used as the feedstock to produce H2H2 via dark fermentation. Three factors, namely, temperature, pH and starch concentration (Cstarch)(Cstarch), were intensively examined for their effects on H2H2 production activity. The H2H2 production kinetics was determined using a Monod-type kinetic model. The results show that mesophilic temperature (37∘C) is preferable for H2H2 production with the H2H2-producing sludge used. The H2H2 production efficiency and the composition of soluble metabolites were found to be highly sensitive to the change in pH, as pH 6.0 seemed to give the best overall H2H2 production performance. In a non-pH-controlled culture (initial pH=8.5pH=8.5), ethanol and butyrate were the major soluble metabolites, whereas the predominant metabolites switched to butyrate alone (accounting for 70–80% of total soluble microbial products) when the culture pH was controlled at a fixed level ranging from 5.5 to 7.0. Meanwhile, the maximum H2H2 production rate occurred when the initial starch concentration was 24 g COD/l. The dependence of H2H2 production rate on starch concentration could be described by using Monod-type model and the predicted kinetic constants, namely, maximum H2H2 production rate (vmax,H2)(vmax,H2) and Monod constant (Ks)(Ks), were 1741 ml/h/l and 16.28 g COD/l, respectively. Under the optimal conditions (37∘C, pH 6.0, Cstarch=24gCOD/l), the H2H2 production rate increased to 1119 ml/h/l, while a high H2H2 yield of 9.47 mmol H2H2/g starch was obtained. This performance appeared to be superior to that obtained from other starch-to-bioH2H2 systems reported in the literature.