固态厌氧消化过程中有机质、有机酸和产气量空间异质性

Spatial heterogeneity of organic matter, organic acids and biogas production during solid-state anaerobic digestion process

研究反应器内发酵物料中有机质、有机酸和产气量在反应器中的空间差异对于有效提高混合物料的厌氧产气效率具有关键作用。该文以猪粪和秸秆混合物料为发酵原料,接种活性污泥,采用中温(35℃)筒式两相厌氧发酵工艺,对混合固态物料厌氧消化过程中不同区域料液的有机质、有机酸和产气速率进行监测,并主要分析其纵向的空间异质性变化。结果表明:固态厌氧发酵过程中,TS、VS、乙酸、丙酸、丁酸和戊酸的质量分数随着物料距反应器底面高度的增加而增大,越接近料液顶端,纵向差异越强,反之浓度降低越快,这5种关键物质在料液底部浓度较为均一,异质性明显降低;产气速率和单位VS累计产气量随着物料距反应器底面高度的增大而增加,皆为底层最低而顶层最高;反应过程中存在核心厌氧区,厌氧系统累计产气量和料液高度具有明显的幂增函数(R^2=0.9754)关系,该研究为固态厌氧高效发酵提供了数据参考。

Studies on the spatial heterogeneity of organic matter, organic acids, and biogas production play a key role in improving the efficiency of biogas production during solid-state anaerobic digestion. In this paper, based on the mixed materials of pig manure and straw inoculated with activated sludge, me sophilic digestion （37℃） in the laboratory was designed and conducted over a period of forty-six days in order to understand the spatial heterogeneity dynamics of organic matter, organic acid, and biogas production rates along with the depth of the fermentation materials. In this experiment, organic material, organic acids, and gas production rates from different reactor depths were monitored during a solid-state anaerobic digestion process, and the vertical dynamics of the heterogeneous environment were analyzed. The following results were obtained. 1） During a solid anaerobic fermentation process, both TS and VS have obvious longitudinal Variation; that is, the mass fractions of total solid （TS） and volatile solid （VS） increase with increasing height of the fermentation material （HFM） from the reactor bottom. Closer to the top of the fermentation material, longitudinal heterogeneity increased, whereas the concentration of TS and VS decreased more quickly. TS and VS of fermentation material in the top layer were highest and reached 17.41% and 12.16%, respectively. However, TS and VS in the E layer were lowest, reaching 6.72% and 4.30%, which differend little from the TS and VS of fermentation materials in the F layer. Furthermore, the TS and VS contents in the A layer were 2.59-fold and 2.83-fold greater than those in the E layer. 2） During the solid anaerobic fermentation process, low weight molecule organic acids also have significant longitudinal variation; that is, the mass fractions of acetic acid, propionic acid, butyric acid, and valeric acid increase with increasing HFM from reactor bottom. Closer to the top of the fermentation material, longitudinal heterogeneity increased, whereas the concentration of these short-chain organic acids decreased more quickly. The mass fraction of acetic acid, propionic acid, butyric acid, and valeric acid of the fermentation material in the A layer increased 17.08, 30.07, 62.79, and 54.54 times, respectively, those of F layer, and increased 1.11, 1.28, 1.29 and 1.03 times those of E layer. 3） The gas-production rate and cumulative gas production per unit of VS increased with the HFM from reactor bottom; the bottom had the lowest values but top had the highest values. The cumulative gas production per unit of VS from the A layer （1.36 L/g） was the maximum within the column, as compared to the minimum cumulative gas production per unit of VS from the E layer （0.36 L/g）, a reduction of 74%. 4） The correlation was markedly positive among main parameters, such as the cumulative gas production, the cumulative gas production per unit of VS, HFM, TS, VS, and organic acid content. Furthermore, a power function curve was fit between cumulative gas production and HFM, and the adjusted R square （0.9754） was statistically significant. All results showed that a core anaerobic zone existed in the reactor during the solid-state anaerobic digestion process, and a significant power function relationship existed between the cumulative gas production and HFM. Therefore, it suggested that locating the core anaerobic zone and monitoring it in the actual project can improve the efficiency of the entire anaerobic digestion system.