Biological hydrogen production from sterilized sewage sludge by anaerobic self-fermentation

Due to richness in proteins and carbohydrates, the sewage sludge produced from the wastewater treatment processes is becoming a potential substrate for biological hydrogen production. In this study, sterilized sludge was employed to produce hydrogen by batch anaerobic self-fermentation without any extra-feeds and extra-seeds. Sterilization can screen hydrogen-producing microorganisms from sludge microflora and release organic materials from microbial cells of sludge. Experimental results suggested that sterilization could accelerate and increase the hydrogen production of sewage sludge in the anaerobic self-fermentation, and the biogas did not contain methane. The hydrogen yield was increased from 0.35 mL H2/g VS (raw sludge) to 16.26 mL H2/g VS (sterilized sludge). Although sterilization could fully inhibit the activity of methanogens in the sludge, the hydrogen consumption still occurred in the anaerobic self-fermentation of sterilized sludge due to the existence of other hydrogen-consuming actions. The decrease of pH in the anaerobic self-fermentation of sterilized sludge was very lower (from 6.81 to 6.56) because NH4+ produced by degradation of proteins could neutralize organic acids produced in the process. The soluble chemical oxygen demand (SCOD) increase of sterilized sludge was higher than that of raw sludge. Volatile fatty acids (VFA) were the important by-products and acetate was the major composition. The hydrogen fermentation of carbohydrates was the major source of hydrogen production.