Investigation Of Food Wastes And Optimization In Anaerobic Fermentation Process

In recent years, with the improvement of Chinese urban living standards, the production of food waste increased rapidly. Recently, most of large municipal cities of China, food wastes production are above1000t/d. The characters of it had high moisture content and rich in pathogenic microorganisms, but also had high organic content, which showed that food waste is a contamination as well as resource. Due to lack of appropriate treatment and disposal technologies, serious food waste pollution problems have been increasing. On the other hand, anaerobic fermentation technology is being used by more and more country because of it’s merit of lower energy consumption, less pollution, better reducing quantity and is also an ideal source for biogas production, which is very important for the increasingly serious energy crisis in our country. The technology of anaerobic fermentation technology was still in initial stage, some critical technical problems were still unresolved, so it is very necessary for study on these problems.In this paper, to find out a suitable way for food waste treatment, the waste characteristics in4seasons have been investigated, and based on the characteristics of the waste, anaerobic fermentation was considered to be a suitable way for food waste treatment. As food waste had high salt and fat content, which may not conducive to anaerobic fermentation, we breeded salt-tolerant methanogenic bacteria and sought appropriate pretreatment to reduce each impact. Two-phase anaerobic fermentation operating characteristics of different proportions of fruit and vegetable waste with food waste were also disscussed in this paper, the results showed following conclusions:(1) Investigated on the waste characteristics from Chinese restaurant, Chinese canteen and western-style canteen in4seasons, the results showed the average moisture content of the food waste was more than60%, with more than87%of VS/TS and a pH range of4.64-6.98. The contents of organic components were high, the contents of fat and protein and carbohydrate being16.98%-38.92%,6.58%-11.65%and46.27%-68.28%, respectively. It is implied the food waste could be bio-degraded easily. The salt content was0.69%-2.44%, with total P content of0.13%-0.30%. It is suggested high content of salt and fat could limit the efficiency of bio-degradation. Based on all above characteristics, separated collection and two-phase anaerobic digestion was considered to be a suitable way for food waste treatment.(2) Acclimated salt concentration on granular sludge, after126days to success in increasing concentration to3%, we isolated a strain of methanogen (M-1) from this salt-tolerant anaerobic sludge. The strain was spherical or ellipsoidal, single or groups appeared, G+, non-motile, and didn’t form bud-spore.The colony was circular, translucent, smooth, and emits cyancolor fluorescence under the ultraviolet fluorescence microscope. The best optimum growth temperature was35℃, adapt in the range of30-40℃; the best optimum growth pH was7.0, adapt in the range of7.0-7.5; the best optimum growth salinity was1%, adapt in the range of0%-2%, when the salinity was more than4%the strain could not grow any more.The strain also has penicillin and tetracycline tolerance.(3) In the anaerobic fermentation test, through the different salt content waste inoculated ordinary granular sludge and salt-tolerant anaerobic sludge either, to explore the usefulness of salt sludge by TS, VS, pH, BDM, phosphate activity and gas production rate, the results showed that the salt-tolerant anaerobic sludge was significantly better than the ordinary granular sludge in all indicators, thus, the salt-tolerant anaerobic sludge can be used as the efficient sludge for degradated food waste, to relieve the inhibition of anaerobic fermentation.(4) Analysis the impact of different fat concentrations of food waste on anaerobic fermentation, obtained the largest fat-resistant concentration was6%, excessive fat concentration was inhibited the biogas producing, reduced the degradation rate and made low phosphate activity. With different levels of alkaline treatment, heat treatment, microwave treatment, and mixed fruit and vegetable waste to pretreat high fat food waste, combinated the factors of economic and efficiency, selected microwave treatment (650W,6min) as the best pretreatment for the merit of fast and effective.(5) Analysis in different proportions of food waste and vegetable waste in two-phase anerobic fermentation, we got the best HRT of acidogenic reactor in25%,50%,75%and100%food waste was10d,15d,15d and20d either, and the best solid rate was10%, when the food waste compare to the vegetable waste was1:3as the best ratio for acidogenic reactor fermentation. As to the methane-phase reactor, the best HRT of25%and50%food waste was3d, and75%and100%food waste was4d, when the food waste compared to the vegetable waste was1:1as the best ratio for methane-phase reactor fermentation.