| With the rural economic and living standards improving, the kitchen waste is growing continually. Among different kinds of treatment of kitchen waste, anaerobic digestion technology is worth to be promoted in rural areas because it can achieve high efficient treatment of kitchen waste and could avoid the secondary pollution. During organic wastes anaerobic ferment process, people used to mixed kitchen waste with other common organic wastes in rural areas,such as straw and manure, to avoid the acidification and improve the stability of anaerobic digestion system. On the other hand, single feedstock digestion of straw can result in degradation slowly and low biogas yield due to floating on the surface; Single feedstock digestion of manure also has the weakness such as greatly influenced by seasonal and regional, lack of raw material and so on. Anaerobic co-digestion could compensate for the lack of single feedstock anaerobic digestion and improve the efficiency of gas production and the utilization of organic wastes.In this study, three kinds of rural common organic solid wastes:kitchen waste, cow dung and wheat straw were used as feedstocks of anaerobic digestion. Study on the biogas production effect of different feedstocks and their mixed ratio under the same temperature and the reaction conditions (35 ℃, TS is 8%, inoculum size is 25%). The influence of biogas slurry pretreatment and NaOH pretreatment of wheat straw on the gas production efficiency was studied at the same time. The main results are as followings:(1) The influence of different mixed ratio of feedstocks on the results of anaerobic digestionUnder the experimental conditions, single feedstock digestion of kitchen waste presented the acidified phenomenon, its biogas production was 3428 mL and the biogas generation rate of TS was 54 mL/g. And when kitchen waste was co-digestion with cow dung and wheat straw, most of the combinations could improve the gas production efficiency with different levels, and maximum yield of biogas was obtained at different mixed ratio:kitchen waste mixed with cow dung when the ratio of TS was 1:1, the maximum cumulative biogas production was 6960 mL and the biogas production rate of TS was 109 mL/g; when kitchen waste mixed with wheat straw which was pretreated with biogas slurry and the ratio of TS was 1:2, the maximum cumulative biogas production was 9380 mL and the biogas production rate of TS was 147 mL/g. However, when the wheat straw was pretreated with NaOH and the proportion of TS was 1:1, the maximum cumulative biogas production was 9470 mL and the biogas production rate of TS was 152 mL/g; when the kitchen waste mixed with cow dung and wheat straw which was pretreated with biogas slurry, the proportion of TS was 0.8:0.2:1, its maximum cumulative biogas production was 11461 mL and the biogas production rate of TS was 179 mL/g. However, when the straw was preprocessed by NaOH solution and the proportion of TS was 0.5:0.5:1, its came to 8128 mL and 127 mL/g.(2) The influence of different wheat straw pretreatment method on the result of anaerobic digestionBoth of the two pretreatments of wheat straw:NaOH and biogas slurry could reduce the purity of TS and could lower the carbon nitrogen ratio from 85:1 to 27-35:1 and make the straw more suitable for anaerobic digestion. The digestion results showed that when wheat straw mixed with other feedstocks, biogas slurry pretreatment became higher than NaOH pretreatment, So we could use the biogas slurry pretreatment method to pretreat straw in practical production because of its easy, lower cost and small environment impact.(3) The nutritional content of biogas slurryBiogas slurry contained a certain amount of nitrogen, phosphorus and potassium, especially the content of available potassium was very abundant, it could reach to 881.91-1424.32 mg/L. |
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