Process Stability And Biogas Efficiency Improve Technology In Anaerobic Digestion Of Kitchen Waste

Energy shortage has become an important problem facing by the world today; development and utilization of renewable energy are the basic way to solve the problem, especially anaerobic digestion. Municipal solid waste, especially the kitchen waste due to its rich nutrition, high yield has become the preferred raw material of anaerobic fermentation in cities. However, the fermentation process of kitchen waste prone to failure due to acidification. On the basis of analying promble of fermentation alone, co-digestion of kitchen waste was studied to select the best mixed material. The effect of interference fermented liquid p H value by adjusting initial pH was studied. And on these research results, the effect of approaches of adjusting pH were also studied. The primary aim of the study was to enhance the anaerobic digestion effect of kitchen waste and seek the theoretical basis of the application of anaerobic fermentation technology in our developed cities. The result of this study as follow:(1) The results of kitchen waste fermented separately in 25℃, 35℃, 55℃ found that kitchen waste fermentation in low temperature(25℃) was not possible and the process prone to ammonium nitrogen inhibition phenomena in under high temperature(55℃). Fermentation in thermophilic temperature was relatively stable. But on the whole, kitchen waste fermentation separately, acidification speed was fast(1-3 days) and biogas production was lower. Adjust pH level using Ca(oH)2 of liquor could improve acidification phenomenon.(2) The results of aanaerobic co-digestion of kitchen waste and common fermentation raw material with high alkalinity showed that the effect of co-digestion of kitchen waste with cow manure, sheep manure, chicken manure and sludge was better than separate fermentation. The fermentation effect becomes worse with the increase in proportion of kitchen waste. And when the proportion of kitchen waste exceeds 50%, the fermentation reaction would be difficult. Especially once the proportions of kitchen waste more than 10%, the buffering capacity of the fermentation system will be loss. The biogas production results showed that the highest total biogas production(17960mL) was obtained when the mixing ratio of kitchen waste and cow manure was 1:9, and the total biogas production(11848mL) of kitchen waste and chicken waste(1:9) was followed. The highest biogas production in the reactor of kitchen waste and sheep manure, kitchen waste and sludge was generated when the mixing ratio was 5:5 and 3:7, respectively, which were 8937 mL and 9611 mL. It could be concluded that cow manure was the most suitable mixed material with kitchen waste through analyzing and comparing indexes of the fermentation process.(3) The results of initial pH(on 6.0,6.5,7.0,7.5)on the co-digestion of kitchen waste and cow manure(1:1)showed that adjusting initial pH, except pH6.0, could significantly improve the stability and biogas production of fermentation system. Total biogas production increased 1.24-7.54 times comparing with the treatment without pH adjustment. The biogas production effect was the worst and biogas production potential is minimal when the initial pH was set to 6.0. On the contrary, when the initial pH was adjusted to7.5, the total biogas production and methane production were highest, about 14559 mL and 7043 mL, respectively.(4) The results of different pH adjustment strategies and pH levels of 6.5, 7.0, 7.5, and 8.0 reported that three different adjustment methods, that is, adjustment initial pH, adjust pH at the first biogas stagnation and adjust pH at both time, could improve biogas production. The highest biogas production and methane production can be up to 27447 mL and 13723 mL,respectively. When system p H was set to 7.0-7.5, methane production would get more than 13000 mL. If the p H adjusted to 6.5 and only adjusted once, the buffer capacity of co-digestion system was poor and the biogas production was lower.(5) Results of the effect of adjustment p H, adding approach of inoculum was introduced in the anaerobic co-digestion of kitchen waste and cow manure showed that combining pH adjustment with changing the adding approach of inoculum could further improving biogas production and shorten stagnation time. The highest biogas production could get 25626 mL. The average stagnation time which was predicted by the Gompertz model was 19.97 days which were 6.73 shorten than treatments only adjustment initial pH. The highest VS and COD reduction rate could get 44.97% and 99.84%, respectively. When acidified phenomenon has occurred in a fermentation system, add inoculum or adjustment pH can increase the pH of fermentation liquor and ease the phenomenon of acidification. In severe acidification period of the process of fermentation, fermentation liquor was replaced by fresh inoculum could soothe the inhibition phenomena of volatile fatty acid and rich microbial populations in the fermented liquid.