Fermentative hydrogen production from sewage sludge

Abstract

ABSTRACTHydrogen production from organic wastes by dark fermentation is promising. Among a variety of organic wastes, sewage sludge has drawn extensive attention due to its large amount, high organic content, and stable source. This paper reviewed the characterization of sludge and the principles and potential of sludge hydrogen fermentation. Poor hydrolysis and low C/N ratio of sludge were two main limitations for sludge hydrogen fermentation. To improve hydrogen production, some pretreatment methods (heat, ultrasound, microwave, alkaline, acid, oxidation, enzyme, and bacteria) and the addition of cofermentation substrates have been applied for enhancing the hydrogen production from sludge fermentation. The effect of key factors (temperature, pH, retention time and organic loading rate (OLR), agitation intensity, nutrients, inhibitors, and inoculum) on hydrogen production and process stability was introduced and discussed. Furthermore, the kinetic models were briefly discussed. After sludge hydrogen fermentation, some end products, including acetate, propionate, butyrate, and ethanol, could be used for deducing the fermentation type and applied as substrates for the second-stage process (e.g., anaerobic digestion and photofermentation) for further energy recovery. The development of these two-stage processes was illustrated. Concluding remarks and perspectives for this process were also evaluated.