| The straw stalk resources in China are rich. Straw production is about 700 million t a year, and 42% of them were returned to the field directly or indirectly, 30% of them were used as agricultural fuel, and 8 % were applied on industry or others. So that 20% of them, about 120 million tons, were burned or abandoned, this caused environmental pollution and resources waste. Therefore, the technology of comprehensive utilization of crop stalks was urgently required. The development of biogas technology using straw as substrate not only can transform crop straw by microbial fermentation into high-quality fuel and alleviate energy pressure of supply and demand but also solve shortage of raw materials in the rural digesters, adjusted energy structure, improve home sanitary conditions and rural health standards. So, energy technology of straw dry fermentation is an important way for crop straw utilization.The quick start of straw dry fermentation was researched using L9 (33) orthogonal test and the impact of trace elements on gas production were also studied. According to anaerobic characteristics of straw dry fermentation, a household-type gas fermentation device was designed, and pilot test was conducted using the device with straw dry fermentation. Meanwhile the running condition of a large-scale biogas project was also monitored. The results showed that:Under the condition of at 35℃, total solid density is 25%, the ration of C/N is 25 and with the same pH value, the optimum condition was: rice haystack was composted for six days , the ratio of manure and straw is 1:1.86 , and the sludge inoculum is 40% (W/W). The daily biogas production was significantly effected by Ni2+ and Co2+. Maximum daily biogas production was obtained when the concentration of Ni2+ and Co2+ was 2μmol/L respectively.Based on the above optimized conditions, acid production characteristics of the fermentation startup procedure were studied. In acetate and propionate is mainly production in start-up period of normal fermentation. The concentration of acetate is high and up to 4000 mg·L-1 at the beginning of fermentation then decreased gradually to 1000 mg·L-1 then even below after 14 days of fermentation, then stayed at 500 mg·L-1 around, which means that the acetate was decomposed easily. The propionate content was first increased and latter decreased, from 2000 mgL-1 gradually increased to 4000 mg·L-1 after 14 days of fermentation then decreased to 2000 mg·L-1 , which maybe be determined by metabolite pathways of propionate.Biogas also can be produced at room temperature in pilot test of straw dry fermentation. The sustainable time of straw dry fermentation can last 3 to 6 months at room temperature, the average volume of gas produced was 0.08 m3/m3·d, the maxiumum volume was 0.23 m3/m3·d. Gas production decreased when fluctuation of temperature exceed 10℃and microbial activity was inhibited. If insulation measures was carried out and amount of inoculation were increased, the volume of gas production can be increased. So, the dry fermentation of straw is feasible in household digesters, there are still many problems to be resolved.In this paper the data collected from the sampling Yixing City in one month were analyzed. Pig sludge was used as raw materials for the fermentation of highly efficient anaerobic reactor technology of UBF. The results showed: Average removal ratios of CODCr was more than 85% and BOD5 is more than 93.1%; The concentration of TN in inleting water was 730～1550 mg·L-1 and was 502～620 mg·L-1 in outleting water; The concentration of TP in inleting water was 87～197 mg·L-1, and was 53～98 mg·L-1 in biogas slurry . About 7500 m3 of biogas was produced each month, the average rate of biogas production was 0.25m3/ m3·d. The system can be operated stably.
|
PDF Full Text Request