牛粪厌氧发酵酸化处理条件的优化

Optimization of cattle manure hydrolysis and acidification for methane production

在牛粪厌氧发酵过程中,高含量的木质纤维素降低了厌氧发酵的水解酸化速度,水解酸化阶段成为牛粪厌氧发酵过程的限速步骤。为提高牛粪两相厌氧发酵甲烷的产量,对酸化处理条件进行优化。利用两相厌氧发酵工艺,在35℃发酵条件下,研究牛粪酸化处理时间、搅拌频率、料液浓度和尿素添加量对甲烷总产量的影响。单因素试验结果表明,最佳的酸化时间、搅拌频率、料液浓度、尿素添加量分别为96 h、3次.24 h 1(60 r·min-1,1 min·次-1)、8.0%、1.28 g·L-1。在单因素试验基础上,选取酸化时间、料液浓度、尿素添加量为自变量,以甲烷总产量为响应值,根据中心组合设计原理设计试验。采用3因素5水平的响应面分析法,建立酸化处理条件对甲烷产量影响的回归模型,进行显著性和交互作用分析。结果表明,在35℃、搅拌频率为3次.24 h 1(60 r·min-1,1 min·次-1)酸化条件下,酸化料液浓度对甲烷产量影响最大,尿素添加量次之,酸化时间影响最小;酸化最佳处理条件为:酸化时间93.7 h、料液浓度8.3%、尿素添加量1.26 g·L-1。经过优化,甲烷含量、总产气量、挥发性固体含量(VS)和化学需氧量(COD)去除率分别比未酸化处理提高了14.3%、44.7%、41.8%和33.9%,而酸化处理对纤维素、半纤维素和木质素含量影响不显著。由此可见,牛粪酸化处理有利于甲烷产生,可提高甲烷含量及VS和COD去除率。

Although high lignocellulose content decreases acidification rate of anaerobic fermentation of cattle manure, acidification phase is critical in anaerobic fermentation of cattle manure. Cattle manure acidification conditions were investigated with the aim of optimizing methane production in a two-phased anaerobic process of cattle manure. The effects of acidification time, stirring frequency, feed solution concentration and urea addition for cattle manure methane production were studied in a two-phased anaerobic fermentation at 35 ~C. Single factor experiments showed that 96 h of acidification, 3 times in every 24 h （60 r-rain-I, 1 min＇time-1） of stirring frequency, 8.0% feed solution concentration and 1.28 g.L-1 urea addition were the optimum conditions. Based on single factor experiments, a series of central composite design experiments were conducted for optimum synthesis. Response surface methodology （RSM） with central composite design （CCD） was used to explore optimum conditions for methane production. The effects of three variables （acidification time, feed solution concentration and urea addition） were subsequently appraised. A regression model for methane production under the acidification conditions was established for analysis of interactions and significance in accordance with central composite design. Results showed that methane production was greatly influenced by feed solution concentration, urea addition and acidification time under at 35 ~C and 3 times per every 24 h （60 r.min-1, 1 min＇time-1） stirring frequency. The optimum acidification conditions occurred at the acidification time of 93.7 h, feed solution concentration of 8.3% and urea addition of 1.26 g-L-1. Under the optimum condition, methane content and total production increase by 14.3% and 44.7%. Also the removal rates of volatile solid （VS） and chemical oxygen demand （COD） increased by 41.8% and 33.9%, respectively. However, the contents of cellulose, hemicellulose and lignin were not affected by cattle manure acidification. The findings indicated that cattle manure acidification improved methane production, methane content, and VS and COD removal rates.