温度和紧实度对秸秆水解产酸的影响

Effects of temperature and compaction on hydrolysis and acidification of agricultural straw

为了解紧实度和温度对秸秆水解产酸过程的影响,以麦秸为原料,在不密封条件下,设置秸秆容重分别为0.03、0.05和0.08 t·m-3,水解温度为10、20和30℃,分析了实验过程中水解酸化液COD、SCOD、pH值、挥发性脂肪酸组成和含量的变化。结果表明:秸秆紧实度对秸秆有机物水解溶出速率影响明显,秸秆紧实度与秸秆有机物水解溶出速率成反比,与水解酸化液COD、SCOD和挥发性脂肪酸含量达到峰值的时间成正比,但在同等体积反应器内紧实度越大秸秆TS负荷越高,有利于提高水解酸化液COD、SCOD和VFAs浓度;秸秆紧实度对秸秆水解产酸产物的组成和含量影响明显,秸秆容重为0.03和0.05 t·m-3的处理水解产酸产物中乙酸占比达75%以上,丙酸、丁酸等含量较低,而秸秆容重为0.08 t·m-3的处理水解产酸产物中以丁酸和乙酸为主,为典型的丁酸型发酵,11 d后转变为丙酸型发酵;实验12 d后,不同紧实度处理水解酸化液中丙酸含量均逐渐增加;温度对秸秆有机物水解溶出的影响明显,水解酸化液COD、SCOD和pH值与温度成正比,温度高对秸秆有机物水解溶出有利,但同时也提高了可分解利用秸秆水解产酸产物的微生物活性,造成实验后期水解产酸产物大量损失。当温度为30℃时,水解产酸时间控制在5 d左右较合适,当温度为20℃时,水解产酸时间控制在2周左右较合适。

The effects of temperature and compaction on hydrolysis and acidification of agricultural straw were investigated under laboratory conditions. In this study,wheat straw was used as the material. The bulk densities of wheat straw were 0. 03,0. 05,and 0. 08 t · m- 3,while the fermentation temperatures were 10,20,and30 ℃. The contents of chemical oxygen demand（ COD）,soluble COD（ SCOD）,and volatile solid acids（ VFAs） and pH value were analyzed during the experiments. The results showed that a high bulk density of straw was unfavorable for the hydrolysis of wheat straw; a higher bulk density led to a lower hydrolysis rate of the organic matter of wheat straw and longer times required to reach the highest contents of COD,SCOD,and VFAs.However,a higher bulk density of straw means a larger mass of wheat straw in the same reactor volume,which leads to higher contents of COD,SCOD,and VFAs in the hydrolyzate. The composition and content of the hydrolyzate of wheat straw were also influenced by straw bulk density. In the treatments of wheat straw with bulk densities of 0. 03 and 0. 05 t·m- 3,acetic acid accounted for an absolute majority of the hydrolyzate,with low contents of propionic acid and butyric acid,while butyric acid and acetic acid were the main hydrolyzates in the treatment of wheat straw with a bulk density of 0. 08 t·m- 3. The treatment of wheat straw with a bulk density of0. 08 t · m- 3involved butyric-acid-type fermentation,which became propionic-acid-type fermentation after 11 days of reaction. The propionic acid content increased throughout the hydrolysis and acidification process. Temperature is one of the important factors in dissolution of wheat straw. COD and SCOD contents and pH value ofthe hydrolyzate were proportional to the temperature. A higher temperature was beneficial for dissolution of organic matter of straw. The activity of microbes that can decompose the hydrolyzate of wheat straw also increased,resulting in decreased hydrolyzate content after five days of reaction. Therefore,the appropriate hydrolysis and acidification time was five days.