Research On Anaerobic Fermentation Characteristics Of Peanut Shells And Swine Feces

With the rapid development of China's agriculture, every year there are a host of agricultural waste produced, which are randomly stacked or arbitrary incineration, causing serious environment pollution. Therefore, recycling anaerobic digestion process with low energy consumption and is demanded to deal with the agricultural waste. At present, studies on agricultural waste are mainly concentrated in livestock and poultry manure and crops straw, which include wheat straw, corn straw and rice straw. However, there are few studies on the recycling of peanut shells.Peanut shell is one kind of agricultural waste with crude fibre, which is helpless for anaerobic fermentation of microorganisms using the decomposition, therefore, the correspon- ding pretreatment is necessary. In order to resolve this problem, different methods were used to treat peanut shells before the anaerobic fermentation, and biogas yield, pH value and methane content were determined to study the influence of pretreatment on peanut shell . The orthogonal experiment was conducted based on single factor experiment to find the best pretreatment process. Finally, peanut shells after pretreatment and pig manure were mixed for anaerobic fermentation characteristics.Main research contents and conclusions include the following several aspects:(1) The effect of particle size on characteristics of the biogas yield of peanut shell. In this experiment, peanut shells were broken to pieces and screened into 6 kinds of particle sizes, which were <2 mm, 2～5 mm, 5～7 mm, 7～10 mm, >10 mm and unscreening, then used to fermented under strictly anaerobic conditions. The results showed that the total biogas yield of 7～10 mm was 27313ml, which was 30.24%, 21.14% and 23.06% higher than >10 mm,unscreening and <2 mm.The difference of methane content between different particle sizes was not significant (p>0.01).(2)The effect of pretreatment time on characteristics of the biogas yield of peanut shell. In this experiment, peanut shells were broken to pieces, but not screened. After pretreatment of different time, which were 0, 2, 4, 6, 8, 10, 12 days, peanut shell were used to fermented under strictly anaerobic conditions. The results showed that the total gas yield of 8 days was 20690 ml, which was 17.19% and 21.56% higher than 0 and 12 days. Besides, the average methane content was higher, and the differences of average methane content between it and 10 days, it and 12 days were not significant (p>0.01), but the differences between other treatments were significant (p<0.01).(3) The effect of NaOH pretreatment on characteristics of the biogas yield of peanut shell. NaOH pretreatment of peanut shell without fluid water were performed at normal temperature in different concentration, which were 0%, 2%, 4%, 6%, 8%. After the pretreatment, the experiments of peanut shell were conducted under strictly anaerobic conditions. The results showed that, the total biogas yield of peanut shell under 4% NaOH pretreatment was 28083 ml, which was 48.91% and 35.72% higher than 0% and 8% NaOH pretreatment, respectively. In addition, the average methane content was higher than 0%, 2% and 8%NaOH pretreatments. The differences of TS gas yield, VS gas yield and average methane content were significant between 4% and 0% NaOH pretreatment, 4% and 8% NaOH pretreatment(p<0.05), respectively. By contrast, the differences were not significant between 4% and 2%NaOH pretreatment, 4% and 6% NaOH pretreatment (p>0.05), respectively.(4) The study of pretreatment process of peanut shell for anaerobic fermentation. According to the previous experiments, orthogonal test of three factors and three levels was conducted. The results showed that, when the particle size was 5～7mm, the NaOH concentration was 6% and the pretreatment time was 8 days, the total biogas yield was 31030ml and the average methane content was 58.60%, which was the optimal anaerobic digestion process.(5) Make sure the best process of anaerobic fermentation of peanut shells and swine feces. The experiment was conducted by quadratic regression orthogonal rotation test of three factors on biogas yield and average methane contents, using TS density, C/N and inoculation volume as the index. The results showed that, according to the analysis of quadratic model, the influence of progression order of three factors on biogas yield and average methane contents were the same, TS density >C/N > inoculation amount. In order to to get better biogas yield of mixed raw materials (peanut shell and swine feces), which was to 64.127 L, TS density, C/N and inoculation volume should be 9.00%, 27.66:1 and 21.63%, respectively. Also, when the average methane content reached the highest 64.10%, TS density was 9.86%, C/N was 30.91:1, the inoculation volume was 20.01%.