State Key Laboratory of Pulp and Paper Engineering, School of Light Industry and Engineering, South China University of Technology, Guangzhou, 510640, China.
Environ Sci Pollut Res Int. 2022 Jul;29(32):48648-48660. doi: 10.1007/s11356-022-19075-4. Epub 2022 Feb 23.
The water in sludge is trapped within the extracellular polymeric substance (EPS) with gelatinous structure, greatly challenging the sludge deep dewatering. In this paper, the effect of the EPS viscoelasticity and the structural characteristics of sludge flocs on water distribution was revealed to provide a highly efficient approach in research on sludge dewatering. After biological, and physical method conditioning, the change of viscoelasticity and sludge network structure before/after EPS extraction was comprehensively explored, together with the sludge dewaterability and water distribution. The results suggested the proportion of capillary water and adsorption water carried in soluble EPS (S-EPS) was 59.17% and 40.83%, and that in tightly bound EPS (TB-EPS) was 54.77% and 45.23%, respectively. By contrast, the capillary water in loosely bound EPS (LB-EPS) accounted for as high as 99.99%. In comparison with raw sludge, adsorption water proportion in TB-EPS and S-EPS was reduced after lysozyme (LZM) or freezing-thaw conditioning, which was ascribed to reduction of EPS viscosity and the weakness of water adsorption capacity. Additionally, the sludge yield stress (τ) value first reduced and then increased with the extraction of EPS. Meanwhile, the consistency coefficient (k) also decreased from 4.23 Pa·s to 0.006 Pa·s and then slightly increased after LZM conditioning. This observation indicated the sludge system became sensitive to shearing, and its network structural strength as well as colloid elasticity first weakened and then slightly strengthened. In addition, after LZM or freezing-thaw conditioning, the sludge particle size significantly increased after TB-EPS extraction, while the sludge particle more easily absorbed water molecules, thereby increasing adsorption water and capillary water within the sludge flocs. This phenomenon also resulted in an increasing trend of capillary suction time (CST) after TB-EPS extraction, indicating the deterioration of sludge filtration performance.
污泥中的水分被困在具有凝胶状结构的胞外聚合物物质 (EPS) 中，这极大地增加了污泥深度脱水的难度。本文揭示了 EPS 粘性和污泥絮体结构对水分分布的影响，为污泥脱水研究提供了一种高效方法。通过生物和物理方法调理后，综合探讨了 EPS 提取前后粘性变化和污泥网络结构的变化，以及污泥的脱水性能和水分分布。结果表明，可溶性 EPS（S-EPS）中携带的毛细水和吸附水的比例分别为 59.17%和 40.83%，而紧密结合的 EPS（TB-EPS）中分别为 54.77%和 45.23%。相比之下，松散结合的 EPS（LB-EPS）中的毛细水比例高达 99.99%。与原污泥相比，溶菌酶（LZM）或冻融调理后 TB-EPS 和 S-EPS 中的吸附水比例降低，这归因于 EPS 粘度降低和水吸附能力减弱。此外，随着 EPS 的提取，污泥屈服应力（τ）值先降低后升高。同时，稠度系数（k）也从 4.23 Pa·s 降低到 0.006 Pa·s，然后在 LZM 调理后略有增加。这表明污泥体系对剪切变得敏感，其网络结构强度和胶体弹性先减弱后略有增强。此外，在 LZM 或冻融调理后，TB-EPS 提取后污泥粒径显著增大，而污泥颗粒更容易吸收水分子，从而增加了污泥絮体中的吸附水和毛细水。这一现象也导致 TB-EPS 提取后毛细吸水时间（CST）呈上升趋势，表明污泥过滤性能恶化。
