Effect Of Total Solid Concentration And Proportion Of Maize Straw And Cow Mane On Biogas Fermentation

An experiment using constant temperature anaerobic fermentation equipment was conducted. Cow manure and corn stalk were used in this experiment, and the inoculum was biogas slurry from regular methane tank. This test included the ratio of the weight of cow manure and maize straw was 2:1(A), pure cow manure(B), pure maize straw(C) and the ratio of the weight of cow manure and maize straw was 1:2(D). The total solid concentration was at 4%, 8% and 12%, and the temperature was at(30±1)℃. Analysis of biogas production,methane content and fermentation residue was aims to explore the relationship among proportion of cow manure and maize straw, total solid concentration and biogas production,and it could clear up nutrients in the fermentation as well. Main conclusions are as follows:Total biogas yield of A was 9.8%, 19.3% and 4.7% higher than B, C and D. Methane content of A was 6.2%, 27.6% and 3.8% higher than B, C and D. Biogas production rate per material weight of A was 7%, 19.3% and 4.5% higher than B, C and D. Total biogas yield,biogas production rate per material weight and methane content of different treatments were all ranked by an order: A>D>B>C, total solid concentration of 8% and 12%: A>D>B>C.Total biogas yield was lowest at total solid concentration of 4%, and it was merely 4754 ml.It was obviously that cow manure was more important than corn stalk in biogas production at anaerobic co-digestion of cow manure and corn stalk. Ph minimum of fermentation fluid were respectively ranked by orders: B>A=D>C(4%), A>D>B>C(8%) and B>A>D>C(12%). At three total solid concentration, the change of pH of anaerobic co-digestion was relatively stable which was beneficial to generate appropriate amount of VFAs, and it also can adjust C/N of fermentation fluid. C/N of A was 28.9:1 and it was beneficial to microbes. Anaerobic co-digestion was good for reducing ORP of fermentation fluid, then it was beneficial to methane bacteria. At last, it improved the biogas fermentation.The optimum proportion of cow manure and maize straw was 2:1.Total solid concentration too high and too low was harmful to biogas fermentation. pHof different total solid concentration descended in the early, ascended in the middle, and tended towards stability in the late of anaerobic fermentation. The content of VFAs tended to first increase and then decrease. The content of VFAs increased with the increase of total solid concentration. The content of VFAs was too little to translate into methane at the total solid concentration of 4%. Then the content of VFAs up to 7264 mg/L of C was seriously acidic at 12%. At the same time, PH of fermentation fluid was only 6.14. It decreased the rate of producing biogas and the process of producing biogas was unstable. Alkalinity of fermentation fluid was higher and beneficial to conversion of VFAs. Biogas bacteria lacked available substrate with low solid concentration, and producing biogas was damaged as well.ORP was lower at 8%, it was good for producing methane in good anaerobic fermentation environment. The optimum solid concentration was 8% in this test.The residue of biogas fermentation contained large amount of N, P, K, OM, and the different content of them suggested that fermentation conditions was different too. The content of N, P and K respectively was 0.272%, 0.042% and 0.129% when solid concentration was 8%, and the proportion of cow manure and maize straw was 2:1. It was120%, 60% and 45% higher than solid concentration of 4%, and it was 11%, 14% and 9%higher than solid concentration of 12%. The content of N and P in biogas residue at solid concentration of 4% was 59% and 52% higher than 8%, and it was 47% and 54% higher than12%. There were no significant differences noted among three solid concentration. The content of HA and OM increased with the increase of solid concentration. At same solid concentration, the content of OM of B in biogas slurry was averagely up to 0.43%. It was36.8%, 34.1% and 47.1% higher than A, C and D. The content of OM of C in biogas residue was up to 59.8% at solid concentration of 4%, meanwhile, the content of CF was up to 64.7%which was highest in all treatments. The content of HA trends was not pronounced in this test.Too high or too low total solid concentration leaded to little mineral elements in biogas slurry but more in biogas residue. The content of CF was too high to decomposing of the fermentation material. The release of mineral elements was restrained as well.