三种湿地植物厌氧发酵产甲烷特性及产物稳定性研究

Methanogenesis and digestate stability of three wetland plants treated by anaerobic digestion

为研究湿地植物能源化利用潜力,采用全自动甲烷潜力测试系统对不同温度下三种湿地植物厌氧发酵产甲烷特性进行评价,并对产甲烷过程及发酵产物稳定性进行模拟和分析。结果表明:在30 d发酵周期内,中温(37℃)下三种湿地植物巨菌草、狐尾藻和水葫芦累积甲烷产量分别达166.5、159.4、236.9 m L·g^(-1)VS,分别比常温(25℃)提高了29.6%、18.3%和39.9%(P<0.01),且中温发酵产气速度更快,发酵周期更短,挥发性固体(VS)去除率更高;采用热重-示差扫描量热法(TG-DSC)对发酵产物稳定性进行分析,TG曲线呈现三个明显失重过程(100℃,250~350℃及400~600℃),全发酵周期总失重率逐渐降低,DSC曲线有两个明显的放热峰,低温区(300℃)放热强度逐渐降低,高温区(400~550℃)狐尾藻峰强度逐渐降低,巨菌草和水葫芦逐渐增加,且峰值右移,表明有机物逐步降解,发酵产物稳定性增加;采用Cheynoweth方程对巨菌草、狐尾藻和水葫芦中温发酵产气过程进行拟合,模型相关系数均大于0.95,产气预测值和实测值差异比分别为1.98%、0.82%和0.32%(P>0.05)。研究表明厌氧发酵制甲烷是湿地植物资源化利用的有效途径,有利于解决人工湿地技术二次污染问题。

To investigate the potential of wetland plants for energy utilization,the characteristics of methane production by anaerobic digestion of three wetland plants were evaluated using an automatic methane potential test system(AMPTS).The methanogenic process and stability of digestate were further simulated and analyzed.The results showed that cumulative methane production of three wetland plants,Pennisetum sp.,Myriophyllum verticillatum,and Eichhornia crassipes,reached 166.5 mL·g-1 VS,159.4 mL·g-1 VS,and 236.9 mL·g-1 VS under mesophilic conditions,respectively,which were 29.6%,18.3%,and 39.9%higher than their respective production obtained under room temperature within a 30-day digestion cycle(P<0.01).Moreover,a faster methane production rate,a shorter digestion cycle,and a higher volatile solids(VS)removal rate were achieved under mesophilic conditions.The characteristics of mesophilic digestate of the three wetland plants were investigated by thermogravimetry-differential scanning calorimetry(TG-DSC).Three weight losses were observed around 100℃,250~350℃,and 400~600℃,and the total weight loss rate decreased with digestion time.The DSC profiles for the three wetland plants were characterized by two exothermic peaks(300℃and 400~550℃).The peak intensity in the low temperature zone(300℃)for the three plants decreased across the entire digestion period.In the high temperature zone(400~550℃),the peak intensity of M.verticillatum decreased,whereas the intensity of Pennisetum sp.and E.crassipes increased across the entire digestion period.In addition,a right shift of high temperature exothermic peaks was observed in Pennisetum sp.and E.crassipes.These changes in profiles of TG-DSC implied a higher conversion of organic matter and a greater stability of digestate across the entire digestion period.The Cheynoweth equation was used to fit the methanogenic process of Pennisetum sp.,M.verticillatum,and E.crassipes.The correlation coefficients of the models proved to be more than 0.95,and the difference ratio was between the predicted and measured values at 1.98%,0.82%,and 0.32%,respectively(P>0.05).Our results indicated that production of methane by anaerobic digestion is an effective way to utilize wetland plants and is conducive to solving the secondary pollution of constructed wetland plants.