畜禽粪便与秸秆厌氧-好氧发酵气肥联产碳氮元素变化研究

Variations of carbon and nitrogen during anaerobic-aerobic fermentation for co-production of biogas and organic fertilizer using animal manure and straw

传统沼气工程的气肥联产工艺中,厌氧发酵产气与好氧发酵产肥互相独立,产气和产肥周期均较长、有机肥品质差,影响工程的高效运行。为缩短发酵周期、提高产气效率和有机肥品质,该研究将猪粪、鸡粪和秸秆混合进行15和30 d的干法厌氧发酵,将得到的沼渣添加秸秆辅料混合,分别设置65%和70%的发酵物料初始含水率进行15 d的高温好氧发酵,对比分析了不同厌氧-好氧发酵组合对产气和产肥的影响。结果表明:厌氧发酵阶段,混合物料的日产气率自发酵开始后逐渐上升,并在第8天达到最高峰,至第15天降至峰值的50%以下,此时累积产气量达到30 d发酵周期的71%,平均容积产气率达到1.91 m^3/(m^3?d),比发酵30 d平均容积产气率高41.5%。好氧发酵阶段,各处理组碳元素含量持续下降,氮元素含量先下降后增加,所得发酵产物均达到腐熟标准。采用15 d厌氧发酵所获得的沼渣进行好氧发酵,所得发酵产物的电导率、腐殖化程度和发芽指数均优于采用30 d厌氧发酵所获得的沼渣进行好氧发酵所得的发酵产物,同时总有机碳和总氮含量也较其分别提高了6.0%～21.7%和3.0%～10.2%,不同好氧发酵物料初始含水率对发酵产物的品质影响较不明显。因此,采用厌氧、好氧发酵周期均为15 d的组合,可缩短发酵周期、大幅提高产气效率和发酵产物的碳氮营养元素含量,有利于提高沼气工程运行效率和经济效益。

In the co-production of biogas and organic fertilizer in traditional biogas engineering, biogas production by anaerobic fermentation and organic fertilizer production by aerobic fermentation are normally separated. Over-consumption of nutrients in the fermented residue often occurs during the biogas production stage while higher biogas yield is required, which consequently influences the subsequent aerobic fermentation stage, resulting in long fermentation period and low qualities of the final products in treating the fermented residue. To shorten the production period of biogas and organic fertilizer and improve the efficiency and quality of biogas and organic fertilizer production, a series of dry anaerobic fermentation and aerobic fermentation tests with the mixed materials of pig manure, chicken manure and straw, were carried out in this study. During the anaerobic fermentation stage, tests of 15-day and 30-day fermentation periods were carried out. During the aerobic fermentation stage, tests of 65% and 70% moisture contents of the initial fermented staff, and 15-day fermentation period were set. The results showed that the daily biogas yield increased gradually from the 1^st day to 8^th day during the anaerobic fermentation stage, then decreased to less than 50% of the peak value on the 15^th day. On the 15^th day, the cumulative biogas yield reached 71% of 30-day anaerobic fermentation and the average daily volumetric gas yield reached 1.91 m^3/(m^3.d), which was 41.5% higher than that of 30-day anaerobic fermentation. During the aerobic fermentation stage, concentrations of total organic carbon (TOC) in each treatment decreased continuously, and concentrations of total nitrogen (TN) decreased firstly and then increased slightly. Based on electrical conductivities, humification degrees and germination indexes in the final fermented products, higher organic fertilizer qualities were gained when using 15-day anaerobic fermented biogas residues. Moreover, concentrations of TOC and TN were also higher in the final fermented products made from 15-day anaerobic fermented biogas residues than those made from 30-day anaerobic fermented biogas residues. Moisture contents of the initial aerobic fermented staff had little influences on the qualities of final fermented products. In conclusion, adjusting the periods of both anaerobic fermentation and aerobic fermentation for 15 days, can shorten the fermentation period, increase the biogas production efficiencies and the concentrations of carbon and nitrogen elements significantly in final fermented products, and improve the operation efficiency and cost-effectiveness of biogas industry.