Study On Influence Factors And Kinetics In Anaerobic Digestion Of Kitchen Wastes

Kitchen wastes is waste and food-scrap produced from the operation of restaurant, refectory, and from family life, ect. It is important constituent part of organic wastes in city, Which account for 40%～60% in all organic wastes. It's characters is Putrescible and smelly, but is high organic content, Which shows that kitchen wastes is an contamination as well as resource. In recent years, the amount of kitchen wastes produced from municipal increased rapidly in China, and that With frequent outbreak of public heathy affair such as SARS, AI, HIN1 etc. The treatment and disposal of kitchen wastes have become one of the urgent and complex problems in environmental science field. Now, anaerobic digestion technology is being used by more and more country because it's merit that energy consumption is lower, pollution is much less, reducing quantity is better, clean energy is produced etc. But the technology was in initial Stage in our country, some critical technical problems were still unresolved, so it is necessary that study on these problem.In view of the above-mentioned facts,the paper studied on different influence factors and kinetics process in anaerobic digestion of kitchen wastes. Investigated hydrolysis, acidification, operational characteristics and economical efficiency of Single-phase anaerobic digestion and Two-phase anaerobic digestion by experiment. Moreover, analyzed on kinetics of hydrolysis, acidification and gas production in theory. The results showed that:(1) In order to increasing speed and efficiency of hydrolysis, Pretreatment methods of crashing and lye marinating should be done before kitchen wastes was digested; Increasing of hydrolysis rate, VS removal rate and acidification rate synchronously could not be realized by rising system temperature. Furthermore, The experimental results showed that hydrolytic rate of big particle size organic wastes were mainly controlled by the diffusion resistance, Reducing particle size of organic wastes could increase hydrolytic rate; A new empirical model of the hydrolysis for kitchen wastes was formulated with including the coefficient of diffusion resistance, Expression form is: This model was verified with experimental data, it was showed that the model could predict the concentration of organic substances during the anaerobic digestion of kitchen wastes.(2) Experimental results showed that concentration of vaccinal sludge and temperature were not main factors that changed type of acidification. But controlling pH could induce the change of type trend of acidification. When pH of system was 4～5, type of acidification trended to acetic acid fermentation; When pH of system was 5～6, type of acidification trended to propionic acid fermentation; When pH of system was 8～9, type of acidification trended to butyric acid fermentation. Pretreatment method of thermo-alkaline could increase generating speed and accumulative quantity of acidified production. Result of kinetics analysis showed that acidification rate was faster than acidification rate of unpretreatment kitchen wastes. The outcome research of inhibition of ammonia nitrogen showed that when concentration of vaccinal sludge was higher, resistibility of system to ammonia nitrogen was stronger, high temperature condition could boost up inhibition of ammonia nitrogen, inhibition of ammonia nitrogen in acidic condition was lower than in alkaline condition.(3) Experimental result of Single-phase anaerobic digestion and Two-phase anaerobic digestion showed that gas production process of Single-phase anaerobic digestion could be divided as start-up stage, development stage, suitable load stage and overload stage, gas production process of two-phase anaerobic digestion could be divided as start-up period, growth period and stability period. In different stages, operational characteristics of Single-phase anaerobic digestion and Two-phase anaerobic digestion was different, so different control measures should be used in different stage. Compared Single-phase anaerobic digestion with Two-phase anaerobic digestion, it's start-up period was longer, accumulative methane production was lower, COD concentration of effluent water was lower, operational process was more unstable, methane production per unit VS was lower. But removal efficiency of organic matter and removal quantity of organic matter per unit reactor volum of Single-phase was higher than two-phase. Futhermore, economic efficiecncy of Single-phase anaerobic digestion was higher than Two-phase anaerobic digestion.(4) Gas production kinetics model base on carbon transition mechanism could make a description of process of anaerobic digestion, but it's expression and computational process is complex. A simplified gas production empirical kinetics model was established by analyzeing experimental data of single-phase and two-phase anaerobic digestion, the model is modified through inducing inhibition coefficients and load rate. This model was verified with experimental data, it showed that the model could predict accumulative methane production.