Simultaneous production of 2,3-butanediol, ethanol and hydrogen with a Klebsiella sp. strain isolated from sewage sludge

A Klebsiella sp. HE1 strain isolated from hydrogen-producing sewage sludge was examined for its ability to produce H2 and other valuable soluble metabolites (e.g., ethanol and 2,3-butanediol) from sucrose-based medium. The effect of pH and carbon substrate concentration on the production of soluble and gaseous products was investigated. The major soluble metabolite produced from Klebsiella sp. HE1 was 2,3-butanediol, accounting for over 42–58% of soluble microbial products (SMP) and its production efficiency enhanced after increasing the initial culture pH to 7.3 (without pH control). The HE1 strain also produced ethanol (contributing to 29–42% of total SMP) and a small amount of lactic acid and acetic acid. The gaseous products consisted of H2 (25–36%) and CO2 (64–75%). The optimal cumulative hydrogen production (2.7 l) and hydrogen yield (0.92 mol H2 mol sucrose−1) were obtained at an initial sucrose concentration of 30 g COD l−1 (i.e., 26.7 g l−1), which also led to the highest production rate for H2 (3.26 mmol h−1 l−1), ethanol (6.75 mmol h−1 l−1) and 2,3-butanediol (7.14 mmol h−1 l−1). The highest yield for H2, ethanol and 2,3-butanediol was 0.92, 0.81 and 0.59 mol mol-sucrose−1, respectively. As for the overall energy production performance, the highest energy generation rate was 27.7 kJ h−1 l−1 and the best energy yield was 2.45 kJ mol sucrose−1, which was obtained at a sucrose concentration of 30 and 20 g COD l−1, respectively.