New method for enhancement of bioenergy production from municipal organic wastes via regulation of anaerobic fermentation process

Abstract

Although biological recovery of energy (such as hydrogen and methane) from municipal organic wastes (MOW) is a hot topic, the bio-energy production yield is usually unsatisfied due to the low efficiency of anaerobic fermentation process regulation. In this paper, a new method for increasing the production yields of hydrogen and methane from MOW via efficiently regulating the anaerobic fermentation process was reported. It was found that by firstly fermenting the MOW under alkaline conditions to produce hydrogen and volatile fatty acids (VFA)-enriched fermentation liquid (stage I), and then anaerobically treating the fermentation liquid at neutral pH value for methane production (stage II), the yields of both hydrogen and methane were significantly increased. The highest yields of H2 and VFAs were obtained at C/N of 25.2 and pH of 8 in stage I, and the corresponding fermentation liquid generated the highest CH4 yield in stage II. The overall energy gain of this method was estimated as 4.54kWh/kg-COD. The mechanism study showed that the enzymatic activities with MOW hydrolysis (protease and amylase), acidification (phosphotransacetylase, phosphotransbutyrylase, acetate kinase, butyrate kinase, oxaloacetate transcarboxylase, and CoA transferase) and hydrogen generation (pyruvate-ferredoxin oxidoreductase) exhibited the greatest at alkaline pH, which resulted in the increase of hydrogen production together with remarkably high VFA (especially acetic acid) accumulation. When this VFA-enriched fermentation liquid was used to produce methane, the enhancement of methane yield was therefore observed.