存储时间对玉米秸秆理化性状及产甲烷潜力的影响

收割后的秸秆需要经过时间不等的存储后进入到厌氧系统生产沼气,而秸秆的存储时间不同对产甲烷潜力有一定的影响。该文对收割后的玉米秸秆分别经过0、2、5、10、20、30和45 d自然堆放存储,分析不同存储时间秸秆的理化性质变化以及对产甲烷潜力的影响。通过分析不同存储时间秸秆的感官性状、总固体(totalsolid,TS)、挥发性固体(volatile solid,VS)、pH值、木质纤维素、叶绿素、挥发性脂肪酸(volatile fat acid,VFA)等理化性质,发现秸秆存储20 d后各个性状趋于稳定。对不同存储时间处理的秸秆进行产甲烷潜力(biochemical methane potential,BMP)测试,结果显示,存储0、2、5、10、20、30、45 d的BMP分别为325.49、315.35、297.85、296.71、295.25、287.83、291.01 mL/g(以VS计)),随着存储时间的增加,BMP总体上呈下降趋势,且存储0～5 d的下降较快,存储大于5 d的秸秆BMP结果相近。试验得出,秸秆存储时间不同对产甲烷潜力有明显影响,主要由于受到多种原料性质的影响,尤其是木质纤维素、可溶性化学需氧量、还原糖、挥发性脂肪酸。研究结果可为工程化秸秆沼气项目和生物天然气项目的运行提供参考。

Effect of storage time on physiochemical properties and methanogenesis potential of maize straw

Abstract: China is a large agricultural country, and crop straw is one of the main components of the agricultural waste. Anaerobic digestion (AD) to produce biogas is an efficient way for straw utilization. Utilizing straws as raw materials in biogas projects are usually need to be stored for a period of time after harvesting. Different storage time has effects on the biochemical methane potential (BMP) of straws. In this paper, we analyzed the change of physical & chemical properties and effects on the BMP of maize (Zea mays) straw under the circumstances of storage time for 0, 2, 5, 10, 20, 30 and 45 days piled naturally with room temperature. Physicochemical properties, such as sensory properties, total solid (TS), volatile solids (VS), pH, lignocellulose, chlorophyll, volatile fat acid (VFA), ammonia nitrogen, etc., were analyzed under different storage time. The results indicate that the properties of straws tended to be stable after 20 days of storage. As the storage time increased, the water content decreased, and the straw looked like hay after 20 days of storage. The soluble characteristics extracts, such as soluble chemical oxygen demand (SCOD), reducing sugar and VFA, decreased rapidly during storage for 0 - 5 days, and then were stable after around the 5th days. The content of lignocellulose in the storage process was generally increasing. The BMP tests on straws with different storage time showed that the BMP value with different storage time for 0, 2, 5, 10, 20, 30 and 45 days were 325.49, 315.35, 297.85, 296.71, 295.25, 287.83 and 291.01 mL/g (in VS), respectively. As the storage time increased, the BMP showed an overall downward trend, and the methane production rate of storage time for 0 - 5 d was decreased significantly, while the rate tend was stable after storage for 10 days. The BMP with storage for more than 5 days (10 d, 20 d, 30 d and 45 d) were roughly similar. During the whole AD period, the cumulative methane production trends of the respective experimental group were similar, while the daily methane production showed a higher peak (AD period at 1.25 - 6 d) and a lower peak (AD period at 6 - 10 d). After the two peaks, the daily methane production tended to be stable. The biodegradability of each group showed that the fresh straw (without storage) had the highest biodegradability, and the biodegradability decreased with the storage time lasting. With the reducing of moisture content and sugar content during the storage, the metabolism of plant cells and microorganisms were weakened or even die. Thereby, extending the storage time had slight effect on each property and BMP of straw. There was a significant TS loss during the storage procedure because of the plant cell respiration and the microbial biochemistry. Considering the TS loss, the methane potential loss reached to 36.48%. We concluded that maize straw storage for different lengths of time had a significant effect on the BMP, mainly due to the influence of various chemical components, especially moisture lignocellulose, SCOD, reducing sugar and volatile fat acid. The results can provide reliable references for the straw biogas projects operation.