Effect of mild hydrothermal pretreatment on characteristics of anaerobic digestion and physico-chemical properties of rice straw
DU Jing, CHEN Guang-yin, HUANG Hong-ying, JIN Hong-mei, XI Yong-lan, QIAN Yu-ting, XU Yue-ding, CHANG Zhi-zhou
East China Scientific Observing and Experimental Station of Development and Utilization of Rural Renewable Energy, Institute of Agricultural Resources and Environment, Jiangsu Academy of Agricultural Sciences, Nanjing 210014, China
In order to assess the feasibility of mild hydrothermal pretreatment for the increase biogas productivity, a bench-scale experiment was conducted using rice straw in 80℃ of hydrothermal pretreatment temperature and 60% of material water content. The changes of physico-chemical properties of rice straws and its biogas production during anaerobic digestion were analyzed to investigate the effect of pretreatment time on biogas productivity. The results indicated that mild hydrothermal pretreatment enhanced dissolution of organic matter in rice straws. After mild hydrothermal pretreatment, the value of pH with the aqueous extracts decreased drastically, while the contents of chemical oxygen demand, total volatile fatty acid and acetic acid were increased significantly (P<0.05). Compared with the control treatment, the content of COD in straw aqueous extract of T1, T2 and T3 treatments increased by 47.19%, 55.18% and 60.62%, respectively; whereas 22.34%, 33.98% and 50.12% for TVFA content and 19.52%, 34.02% and 49.37% for acetic acid concentration, respectively. Meanwhile, acetic acid ratio of TVFA was more than 85%. Statistical analysis showed that physico-chemical characteristics of aqueous extracts in T1 treatment were significantly different from those in control treatment. However, no significant difference was found between different mild hydrothermal pretreatments. The cellulose component of rice straw was decomposed obviously after mild hydrothermal pretreatment, but little difference of wood fiber was found between the mild hydrothermal pretreatments. The anaerobic digestion results showed that mild hydrothermal pretreatment significantly improved the gas productivity of rice straws. The volume of gas production rate and the cumulative biogas yield increased by 12.53% and 36.17%, respectively, after 20d anaerobic digestion of rice straws. Therefore the mild hydrothermal pretreatment is feasible in the enhancement of gas productivity. In view of the energy costs for pretreatment in engineering application, the appropriate time of mild hydrothermal pretreatment should be around 6h. In future, the functional mechanism of mild hydrothermal pretreatment, the moisture content of materials and optimization of combine pretreatments should be studied to provide technical support of pretreatment process for straw biogas project.
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