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

Abstract

Our previous work demonstrated that an acclimated mixed bacterial consortium was able to produce H 2 from sugar substrates. To reduce the medium cost for more commercially viable H 2 production, cassava starch was used as the feedstock to produce H 2 via dark fermentation. Three factors, namely, temperature, pH and starch concentration ( C starch ) , were intensively examined for their effects on H 2 production activity. The H 2 production kinetics was determined using a Monod-type kinetic model. The results show that mesophilic temperature ( 37 ∘ C ) is preferable for H 2 production with the H 2 -producing sludge used. The H 2 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 H 2 production performance. In a non-pH-controlled culture (initial pH = 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 H 2 production rate occurred when the initial starch concentration was 24 g COD/l. The dependence of H 2 production rate on starch concentration could be described by using Monod-type model and the predicted kinetic constants, namely, maximum H 2 production rate ( v max , H 2 ) and Monod constant ( K s ) , were 1741 ml/h/l and 16.28 g COD/l, respectively. Under the optimal conditions ( 37 ∘ C , pH 6.0, C starch = 24 g COD / l ), the H 2 production rate increased to 1119 ml/h/l, while a high H 2 yield of 9.47 mmol H 2 /g starch was obtained. This performance appeared to be superior to that obtained from other starch-to-bio H 2 systems reported in the literature.