Hydrogen production from sewage sludge using mixed microflora inoculum: Effect of pH and enzymatic pretreatment

Hydrogen was successfully produced by fermenting primary sewage sludge which had been both heat treated and digested with a commercially available enzyme preparation. When either heat treatment or enzymatic digestion were not used, no hydrogen was produced during fermentation. Heat treated mesophilic anaerobic sludge was used as an inoculum rather than a pure microbial culture. Fermentation was conducted at pH levels ranging from of 4.5 to 7.0. When fermentation took place at pH 5.5 a peak hydrogen production rate of 3.75 ml min−1 was observed. At this pH the hydrogen yield was 0.37 mol H2 mol−1 carbohydrate, equivalent to 18.14 L H2 kg−1 dry solids.