The Optimization Of Rural Biogas Fermentation Parameters And Evaluation Of Its Residuals

The establishment of Biogas is important for constructing the socialism new village, improving agricutral productivity, optimizing the energy struction, protecting the agricutral environment. and raising the living standards of people in rural areas of China. In this work, the evaluation of the fermentation efficiency for raw materials, the technical parameters for the fermentation process, and the characteritists of fermentation residuals in nutrients and enviormental safety must be carry out previously, and the optimization of zymolytic parameters is considered as the keystone of this work. In this paper, a series of experiments were conducted in the laboratory, to simulate the principle of hydraulic pressure methane tank. Three factors, including ratio of muck and grass, the ratio of materials, inoculum, impacted on biogas production were determinated. Moreover, a group of orthogonal design experiments were done to optimize the parameters of stack retting processing mode, ratio of muck and grass, the ratio of materials and inoculum for biogas production. The main result was given as below.(1) By changing the ratio of muck and grass, a four treatments with a different carbon-nitrogen ratio showed that, under 8% of raw total solids, pH 6.8-7.4, the methane tank sludge, 20% of them inoculated, after 30 days of fermentation, the treatment by pure pig muck gave the best result. For this treatment, the total aerogenesis tolerance was 95644.5 mL, the day aerogenesis tolerance was 3188.2 mL, the pit held aerogenesis rate was 0.4875 m3/m3·d, the stuff held aerogenesis rate was .6108m3/m3·d, the raw material aerogenesis rate was 0.2290m3/ kg·TS. In comparison, under the carbon-nitrogen ratio 25:1, The total aerogenesis tolerance was 63311.8L, the day aerogenesis tolerance was 2110.4 mL, the pit held aerogenesis rate was 0.3227 m3/m3·d,the stuff held aerogenesis rate was 0.4043m3/m3·d, the raw material aerogenesis rate was 0.1518m3/ kg·TS.(2) Three processing modes, including the outside stack letting, pool inside stack retting and not stack netting, were used to determine the biogas fermentative efficency, and the best result was found in pool inside stack retting. It offered the total aerogenesis tolerance 59195.2mL, the day aerogenesis tolerance 1891.2 mL, the pit held aerogenesis rate 0.2892m3/m3·d,the stuff held aerogenesis rate. was 0.3617m3/m3·d, the raw material aerogenesis rate was0.1644 m3/ kg·TS.(3) By the inoculum of 10%, 20% and 30% methane tank sludge, the result showed that 30% of inoculum was the best one, it perfomed with 40567.3 mL of the total aerogenesis tolerance, 1352.2 mL of the day aerogenesis tolerance, 0.2068 m3/m3·d of the pit held aerogenesis rate, 0.2591 m3/m3·d of stuff held aerogenesis rate, 0.1127 m3/ kg·TS of the raw material aerogenesis rate.(4) Under the condition of 8% raw total solids, pH 6.8-7.4, the methane tank sludge, 20% of them inoculated, after 30 days of fermentation, Orthogonal design experiment was used the optimize the best control condition of biogas fermentation, which concluded the factors stack retting processing mode, ratio of muck and grass, the ratio of materials and inoculum. The results showed that the four factors' effect on biogas production were in the order of the ratio of materials>ratio of muck and grass>inoculum>stack retting processing mode. In theoretically, the optimized technical parameters were no stack retting, 10% of inoculum, 3:1 of ratio of muck and grass, pig muck+fresh grass. it perfomed with 98419.8mL mL of the total aerogenesis tolerance, 3280.7 mL of the day aerogenesis tolerance, 0.5016 m3/m3·d of the pit held aerogenesis rate, 0.5902 m3/m3·d of stuff held aerogenesis rate, 0.2213 m3/ kg·TS of the raw material aerogenesis rate.(5) The evaluation of nutrients and enviormental safety in biogas fermentation raffinate and leabvings showed that the residuals contained not only abundant organic matter, but also many nutrient elements such as, especially for available nitrogen, phosphor and potassium, they are benifical to promoting the growth of agro-plant and improving the quality of agricultural production. However, the higher heavy metal contents were also found in biogas fermentation raffinate, the pollution index for Cu,Zn,As,Hg,Cd,Pb and Cr were 0.90 ,0.63,1.19,0.66,0.82,0.04 and 0.57, respectively. The highest index was found in As. For biogas fermentation leavings, the of pollution index for Cu,Zn,As,Hg,Cd,Pb and Cr were 0.24,0.18 , 0.04, 0.01, 0.11, 0.01 and 0.01. The heavy metal bio-available must be evaluated before we use it as a kind of superior organic fertilizers.