Directional enhancement of fermentative coproduction of hydrogen and acetic acid from glucose via control of headspace pressure

Headspace pressure is a critical factor affecting hydrogen and acetic acid (HAc) generation. However, few studies have determined how to improve the coproduction of biohydrogen and HAc to increase the utilization efficiency from glucose by controlling headspace pressure. Here, we examined hydrogen and HAc coproduction by mesophilic fermentation with decreasing headspace pressures in a half-continuously running reactor. At 20 kPa, the glucose degradation rate was above 90%. HAc was the main soluble metabolite products (SMPs), with productivities of 1.74 mol/mol glucosedegraded, accounting for 93.95% of total SMPs, respectively. Maximum hydrogen productivity was 13.39 mM/d, and 70.11% of added glucose was converted into hydrogen and HAc with a total productivity of 133.72 g chemical oxygen demand/mol glucoseadded L d. Thus, hydrogen and HAc coproduction was achieved; however, homoacetogenesis was not completely inhibited by low headspace pressure, and the ratio of actual to theoretical hydrogen productivity was only 43.99%.