State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, PR China.
State Key Laboratory of Pollution Control and Resource Reuse, School of the Environment, Nanjing University, Nanjing, 210023, PR China.
Chemosphere. 2019 Jul;227:269-276. doi: 10.1016/j.chemosphere.2019.04.020. Epub 2019 Apr 8.
Sludge acidification is a popular and efficient pretreatment method for improving sludge dewaterability. To explore the mechanisms of sludge acidification deeply and provide a theoretical basis for practical application, sewage sludge was repeatedly treated by acidification conditioning. The sludge pH was continuously adjusted from 7.0 to 3.0, then back to 7.0, and to 3.0 again in this study. When the sludge pH returned to a neutral condition, the sludge dewaterability was further deteriorated. However, after the second acidification conditioning, the sludge dewaterability was improved to the same level as that at the first conditioning. These experimental facts were due to two acidification effects. One was that acidification can efficiently destroy the structure of sludge flocs, thereby causing the degradation of extracellular polymeric substances (EPSs) and release of trapped water. Furthermore, some internal EPSs were released into the outer layer. The other was protonation effect, which can effectively compress the released EPSs, especially protein-like matters (PN) therein. These two combined effects caused a good sludge dewaterability. However, the former was irreversible, whereas the latter was reversible. When the pH of acidified sludge was readjusted to 7.0, the protonation effect weakened, thereby the original compressed EPS released into the outer layer of sludge and the PN content in soluble EPS fraction increased near five times, resulting in considerable deterioration of sludge dewaterability. The negative effects of released organic matters by acidification were often concealed and neglected due to protonation, thereby causing the reversal of dewatering performance in practice when the sludge pH was fluctuated.
污泥酸化是一种提高污泥脱水性能的常用且有效的预处理方法。为了深入探讨污泥酸化的机理，并为实际应用提供理论基础，本研究对污水污泥进行了反复的酸化调理。在该研究中，污泥 pH 从 7.0 连续调节至 3.0，然后再次调回 7.0，再调至 3.0。当污泥 pH 回到中性条件时，污泥脱水性能进一步恶化。然而，在第二次酸化调理后，污泥脱水性能提高到与第一次调理相同的水平。这些实验事实归因于两种酸化效应。一种是酸化可以有效地破坏污泥絮体的结构，从而导致细胞外聚合物物质（EPS）的降解和束缚水的释放。此外，一些内部 EPS 被释放到外层。另一种是质子化效应，它可以有效地压缩释放的 EPS，特别是其中的蛋白质样物质（PN）。这两种综合效应导致了良好的污泥脱水性能。然而，前者是不可逆的，而后者是可逆的。当酸化污泥的 pH 被重新调整至 7.0 时，质子化效应减弱，因此，原始压缩的 EPS 被释放到污泥的外层，并且可溶 EPS 部分中的 PN 含量增加近五倍，导致污泥脱水性能的显著恶化。由于质子化作用，酸化释放的有机物质的负面影响常常被掩盖和忽视，从而导致污泥 pH 波动时实际脱水性能的逆转。
