Effect Of PH On Bio-hydrogen Production By Sequential Dark-photo Fermentation From Waste Activated Sludge

By-product from biological treatment of wastewater treatment plant sludge contains a large number of proteins, carbohydrates, etc organic resources that can be utilized by microorganisms, is a legal system for clean energy-hydrogen good biological substrates. In order to maximize the implementation of the hydrogen production, the most optimal pH value for dark-photo was studied, and waste activated sludge (WAS) from sewage plant was investigated as the substrate in this paper. Paper first studied the effect of pH value on WAS dark fermentation hydrogen production, the results showed that the alkaline condition is advantageous to the WAS fermentation hydrogen production. The accumulated H2yield reached23.7mL/g-VSS after132h after dark fermentation under the condition of pH10.0. After analyzed the stages of hydrogen production, it found that the WAS hydrolysis degree and VFAs production is higher, and the activity of methanogens is restrained under the condition of pH10.0. Thus the higher H2accumulation production was get. In addition the study also found that alkaline conditions was more conducive to realize the aim of WAS reduction. Total suspended solids (SS) and volatile suspended solids (VSS) reduction is reach51.83%and51.83%under the condition of pH11.0.In order to improve the utilization rate of the WAS and hydrogen production, this paper studied the condition of the photo-fermentation with the WAS dark fermentation liquid as the substrate and Rhodobacter sphaeroides as hydrogen production microbes. The results showed that NH4+-N concentration can inhibit photo-fermentation to produce hydrogen, The cumulative H2yield reached a maximum38.0mL when the concentration of NH4+-N is0.005g/L; both too high and too low concentration of Volatile Fatty Acids (VFAs) will have an effect to photo-fermentation hydrogen production. The stagnation of hydrogen production period is short and the H2conversion rate is higher when the VFAs concentration is1.88gCOD/L, and it can get the maximum cumulative H2yield in a shorter reaction time, and so it is the optimal VFAs concentration for photo-fermentation to produce hydrogen.70001ux is the optimal light intensity for photo-fermentation hydrogen production. The photo-fermentation accumulative H2yield reached34.2mL at pH7.0condition after240h.Combined with the research results of WAS dark and photo-fermentation, investigate the hydrogen production conditions of sequential dark-photo fermentation. The results found pH10.0is the best dark fermentation condition. Higher hydrogen production(1331.9mL) was get under photo-fermentation with1L pH9.0WAS dark fermentation liquid, and the hydrogen production rate is117.8mL/g-VSS. The photo-fermentation hydrogen production rate is117.5mL/g-VSS with pH10.0dark fermentation liquid as the photo-fermentation substrate. The two kinds of hydrogen production rate were similar under the these two conditions, at the same time under the condition of considering the cost, dark fermentation conditions in pH9as is the best condition for WAS combined dark-photo fermentation hydrogen production.Finally, the Gompertz model is used to describe the pH influence on excess sludge dark fermentation and the fermentation kinetics, the results under the condition of dark fermentation, the fit of the pH value under the condition of R2is greater than0.95, better fitting degree, and under the condition of pH10.0, obtained the largest Pmax is27.4mL/gVSS and Rm is0.26mL/(gVSS·h). Under the condition of light fermentation, the fit of the pH value under the condition of R2is greater than0.99, the maximum Pmax under neutral condition (pH7.0) is46.8ml, it is concluded that the biggest Rm0.197mL/h, got the same conclusion with the test.