[Start-up and continuous operation of bio-hydrogen production reactor at pH 5]

A continuous stirred-tank reactor(CSTR)for bio-hydrogen production using molasses wastewater as substrate was investigated. Emphasis was placed on assessing the start-up and continuous operation characteristics when keeping pH value constant. It was found that at pH of 5, biomass of 6g/L, organic loading rate (OLR) of 7.0kg/(m3 x d) and a hydraulic retention time (HRT) of 6h, an equilibrial hydrogen-producing microbial community could be established within 30 days. Following that, oxidation redox potential (ORP) were kept within the ranges - 460mV - -480mV. Typical mixed acid type fermentation was exhibited in the reactor. Little difference was observed in the distribution of liquid end products. The liquid end products proportion of the total amount was 36% of acetic acid, 33% of ethanol, 18% of butyric acid, 13% of propionic acid and valeric acid, respectively. Hydrogen content in the biogas was about 30% - 35% . Maximal hydrogen production rate was 1.3m3/(m3 x d). The acid-producing fermentative bacteria were in the same preponderant status when the reactor showed mixed acid type fermentation. They are mostly cocci and bacilli.