College of Geography and Environmental Sciences, Zhejiang Normal University, Jinhua 321004, China.
Department of Chemical Engineering, Lakehead University, 955 Oliver Road, Thunder Bay, Ontario P7B 5E1, Canada.
Sci Total Environ. 2020 Feb 10;703:135540. doi: 10.1016/j.scitotenv.2019.135540. Epub 2019 Nov 15.
This study aims to investigate thermodynamic mechanisms of filtration behaviors of ultrafiltration (UF) process with polyacrylamide (PAM) flocculation for surface water treatment, which has not been investigated previously. It was interestingly found that, filtration of durably mixed sodium alginate (SA) solution corresponded to an extraordinarily high specific filtration resistance (SFR) (3.28 × 10 m·kg without polyacrylamide addition) and a V-shaped profile of SFR characterized by a sharp fall followed by a correspondingly sharp rise along with the increase in PAM addition concentration. Experimental characterizations suggested that, membrane fouling was mainly caused by the gel layer formation rather than the pore clogging and cake/floc formation. Rather than the chemical composition change, the changes of the solution physicochemical properties (pH and zeta potential) and foulant morphology are associated with above-mentioned interesting filtration behaviors. Accordingly, the thermodynamic mechanisms of the filtration behaviors were proposed. It was proposed that, the thermodynamics of polymeric network described by the Flory-Huggins lattice theory were responsible for the extraordinarily high SFR of SA gel layer. Low dosage of PAM addition decreased the negative zeta potential and homogeneity of the gel system, causing the reduced SFR. In contrast, further PAM addition increased the negative zeta potential and homogeneity of the gel system, and then increased the SFR of the gel layer. These results reasonably explained the V-shaped profile of SFR. This study provided significant insights into the effects of PAM addition on ultrafiltration behaviors of alginate solution.
本研究旨在探讨带聚丙烯酰胺 (PAM) 絮凝的超滤 (UF) 过程在地表水净化中的过滤行为的热力学机制，这在以前尚未被研究过。有趣的是，发现持久混合的海藻酸钠 (SA) 溶液的过滤对应于非常高的比过滤阻力 (SFR)（未添加聚丙烯酰胺时为 3.28×10 m·kg-1）和 SFR 的 V 形分布，其特征是随着 PAM 添加浓度的增加，SFR 急剧下降，然后相应地急剧上升。实验特性表明，膜污染主要是由凝胶层的形成引起的，而不是由孔堵塞和滤饼/絮体的形成引起的。与化学组成的变化不同，溶液物理化学性质（pH 和 ζ 电位）和污染物形态的变化与上述有趣的过滤行为有关。因此，提出了过滤行为的热力学机制。提出了由 Flory-Huggins 晶格理论描述的聚合物网络的热力学负责 SA 凝胶层的非常高的 SFR。低剂量的 PAM 添加降低了凝胶系统的负 ζ 电位和均一性，导致 SFR 降低。相比之下，进一步添加 PAM 增加了凝胶系统的负 ζ 电位和均一性，从而增加了凝胶层的 SFR。这些结果合理地解释了 SFR 的 V 形分布。本研究为了解 PAM 添加对海藻酸钠溶液超滤行为的影响提供了重要的见解。
