State Key Laboratory of Pollution Control and Resources Reuse, School of Environmental Science and Engineering, Tongji University, 1239 Siping Road, Shanghai 200092, China.
Water Res. 2013 Sep 1;47(13):4576-84. doi: 10.1016/j.watres.2013.05.012. Epub 2013 May 16.
To improve short-chain fatty acids (SCFAs) production from waste activated sludge (WAS), studies that focus on pre-treatment methods, pH control or adding extra carbon like rice were reported. In this study, a kind of green waste (perennial ryegrass) was used as carbon source to adjust carbon to nitrogen ratio (C/N) in WAS to enhance SCFAs production. The effects of different C/N ratio ranging from 26/1 to 7/1 on SCFAs production and cellulose, hemicellulose, and lignin consumption were investigated in detail. It was observed that the maximal SCFAs yield was 368.71 g COD per kilogram of total solids (TS) at C/N 20/1 with fermentation time of 12 d, which was, respectively, over 4 and 12 times than that at C/N 26/1 (sole perennial ryegrass) and C/N 7/1 (sole WAS). Meanwhile, cellulose, hemicellulose and lignin consumptions were 109.12, 148.74, 20.90 g COD/kg TS, respectively, at C/N 20/1 with fermentation time of 12 d. The analysis of the composition of SCFAs showed that acetic acid ranked the first among other acids from C/N ratio of 26/1 to 18/1, whereas propionic acid was the dominant product from C/N ratio of 16/1 to 7/1. Because the results of this study were different from previous studies of SCFAs generation, the mechanism of improved SCFAs at C/N ratio of 20/1 by perennial ryegrass addition was investigated. Results showed that as soluble COD, soluble protein and soluble carbohydrate increased, more substrates were available for SCFAs production at C/N ratio of 20/1. In addition, with the drop of pH to 4.82, methane generating was inhabitant and the SCFAs production was therefore significantly enhanced. Additionally, the mechanism of improved SCFAs generation was analyzed from the view of enzyme activities and microbial community. The experiments revealed that at C/N ratio of 20/1 the activities of enzymes were the highest comparing with other C/N ratios and lignin was the rate-limiting steps in WAS anaerobic digestion by perennial ryegrass addition. The 16S rRNA gene clone library demonstrated that Clostridia, Spirochaetes, and Bacteroidetes were the dominant microbial community at C/N ratio of 20/1.
为了提高废活性污泥（WAS）中短链脂肪酸（SCFAs）的产量，已有研究聚焦于预处理方法、pH 值控制或添加额外的碳源（如水稻）。在本研究中，我们使用一种绿色废物（黑麦草）作为碳源来调节 WAS 中的碳氮比（C/N），以提高 SCFAs 的产量。详细研究了不同 C/N 比（26/1 至 7/1）对 SCFAs 产量以及纤维素、半纤维素和木质素消耗的影响。结果表明，在 C/N 比为 20/1 时，发酵时间为 12d 时，SCFAs 的最大产量为每公斤总固体（TS）368.71gCOD，分别比 C/N 比为 26/1（仅黑麦草）和 C/N 比为 7/1（仅 WAS）时高出 4 倍和 12 倍。同时，在 C/N 比为 20/1 时，纤维素、半纤维素和木质素的消耗量分别为 109.12、148.74 和 20.90gCOD/kgTS，发酵时间为 12d。SCFAs 组成分析表明，在 C/N 比从 26/1 到 18/1 的范围内，乙酸是各种酸中的第一，而丙酸是 C/N 比从 16/1 到 7/1 的范围内的主要产物。由于本研究的结果与之前关于 SCFAs 生成的研究结果不同，因此研究了通过添加黑麦草来提高 C/N 比为 20/1 时 SCFAs 的机制。结果表明，随着可溶 COD、可溶蛋白和可溶碳水化合物的增加，在 C/N 比为 20/1 时，更多的底物可用于 SCFAs 的生成。此外，随着 pH 值下降到 4.82，产甲烷菌受到抑制，因此 SCFAs 的生成显著增强。此外，还从酶活性和微生物群落的角度分析了提高 SCFAs 生成的机制。实验表明，在 C/N 比为 20/1 时，与其他 C/N 比相比，酶的活性最高，并且木质素是添加黑麦草后 WAS 厌氧消化的限速步骤。16S rRNA 基因克隆文库表明，在 C/N 比为 20/1 时，优势微生物群落为梭菌、螺旋体和拟杆菌。
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