Yu Guang-Hui, He Pin-Jing, Shao Li-Ming, Zhu Yi-Shu
State Key Laboratory of Pollution Control and Resource Reuse, Key Laboratory of Yangtze River Water Environment, College of Environmental Science and Engineering, Tongji University, Shanghai, PR China.
Water Res. 2008 Apr;42(8-9):1925-34. doi: 10.1016/j.watres.2007.11.022. Epub 2007 Nov 24.
Ultrasonic pretreatment of excess sludge can improve its aerobic digestibility, leading to enhanced sludge reduction. In order to understand the mechanisms of this improvement, sludge flocs were divided into four layers, i.e. (1) slime, (2) loosely bound extracellular polymeric substances (LB-EPS), (3) tightly bound EPS (TB-EPS) and (4) pellet. Extracellular proteins, polysaccharides and five types of hydrolytic enzymes (protease, alpha-amylase, alpha-glucosidase, alkaline-phosphatase and acid-phosphatase) from sludge flocs were investigated to determine their influence on sludge aerobic digestion after ultrasonic pretreatment. Results suggested that most of the extracellular enzymes (except alpha-amylase) were present in pellet and TB-EPS layers, with minor quantities detected in LB-EPS and slime layers, and almost none detected in bulk solution. As for alpha-amylase in sludge flocs, most of it (52.6%) was also mainly bound with pellet; however, the rest of it was dispersed nearly uniformly throughout the sludge flocs. Ultrasonic pretreatment enhances enzymatic activities and promotes the shifts of extracellular proteins, polysaccharides and enzymes from inner layers of sludge flocs, i.e., pellet and TB-EPS, to outer layers, i.e., slime, to increase the contact and interaction among extracellular proteins, polysaccharides and enzymes that were originally embedded in the sludge flocs, resulting in improved efficiency in aerobic digestion. The optimum ultrasonic pretreatment conditions had a lasting time of 10min and density of 3 kWL(-1) at the frequency of 20 kHz. With the optimum ultrasonic pretreatment, the sludge reduction for TSS in aerobic digestion was 42.7% in which the part of 11.8% was removed by the ultrasonic pretreatment, compared with 20.9% for control, after an aerobic digestion time of 10.5d.
剩余污泥的超声预处理可提高其好氧消化性，从而增强污泥减量效果。为了解这种改善的机制，将污泥絮体分为四层，即：(1) 黏液层，(2) 松散结合的胞外聚合物 (LB-EPS)，(3) 紧密结合的EPS (TB-EPS) 和 (4) 颗粒。研究了污泥絮体中的胞外蛋白质、多糖和五种水解酶（蛋白酶、α-淀粉酶、α-葡萄糖苷酶、碱性磷酸酶和酸性磷酸酶），以确定它们在超声预处理后对污泥好氧消化的影响。结果表明，大多数胞外酶（α-淀粉酶除外）存在于颗粒层和TB-EPS层中，在LB-EPS层和黏液层中检测到少量，在本体溶液中几乎未检测到。至于污泥絮体中的α-淀粉酶，大部分（52.6%）也主要与颗粒结合；然而，其余部分几乎均匀地分散在整个污泥絮体中。超声预处理增强了酶活性，促进了胞外蛋白质、多糖和酶从污泥絮体的内层（即颗粒和TB-EPS）向外层（即黏液层）的转移，增加了原本嵌入污泥絮体中的胞外蛋白质、多糖和酶之间的接触和相互作用，从而提高了好氧消化效率。最佳超声预处理条件为：在20 kHz频率下，持续时间10分钟，密度3 kW·L⁻¹。采用最佳超声预处理后，好氧消化10.5天后，TSS的污泥减量率为42.7%，其中11.8%的部分通过超声预处理去除，而对照为20.9%。
