温和湿热预处理对稻秸理化特性及生物产沼气的影响

为考察温和湿热预处理提高秸秆产气速率的可行性,以水稻秸秆为原料,在湿热预处理温度80℃、物料含水率60%条件下,通过分析湿热处理前后稻秸理化特性及厌氧生物产气特性的变化,研究不同湿热预处理时间对秸秆预处理及产沼气效果的影响.结果表明,温和湿热预处理促进了稻秸有机物的溶出,预处理后稻秸水浸提液pH值有较大幅度下降,而COD、TVFA和乙酸含量均大幅度增加,与对照组相比,T1、T2和T3处理秸秆水浸提液COD浓度分别增加了47.19%、55.18%和60.62%,TVFA浓度分别增加了22.34%、33.98%和50.12%,乙酸浓度分别增加了19.52%、34.02%和49.37%,并且乙酸占TVFA百分比均超过85%以上,差异显著性分析表明,处理T1水浸提液各理化特性指标与对照组相比呈极显著差异,而不同温和湿热预处理之间无显著差异;对稻秸纤维素组分破坏效果明显,但不同预处理时间对秸秆木质纤维组分破坏效果影响不大;厌氧发酵产气的结果表明,温和湿热预处理可明显提高稻秸厌氧生物产沼气,发酵20 d平均容积产气率可提高12.53%以上,累积TS产气率可提高36.17%以上.可见,温和湿热预处理提高秸秆厌氧生物产沼气效果是可行的,考虑到工程应用中预处理能耗成本因素,湿热预处理时间以T1处理(即6 h)为宜.

Effect of mild hydrothermal pretreatment on characteristics of anaerobic digestion and physico-chemical properties of rice straw

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.