Mechanism And Technology Of Urban Wastewater Advanced Purification Based On Magnetic Anion Exchange Resin Adsorption

Water shortage has gradually become prominent with socio-economic rapidly growth and inreasingly serious water pollution problems. However, urban wastewater treatment can effectively alleviate this situation. As a totally new solid-liquid separation technology, magnetic reisn can remove most of effluent organic matters(EfOM) combined with coagulation. And it makes the large-scale application of advanced treatment become possible. Although extensive literatures have reported DOM remove mechanism and enhanced coagulation by magnetic resin, there did not get a broad consensus, and specialized research must be done.This paper selected three effluent from different municipal wastewater treatment plant as experimental water, and a series of characterization for each DOM have been done, such as hydrophobic and hydrophilic, EEM, molecular weight(membrane cutting and GPC), FT-IR, ultraviolet-visible scan and acid-base titration. The results show that there were not obviously differences in FT-IR spectrum. However, we can find some characteristics of municipal secondary effluent DOM. Hydrophilic material content is higher, the lower humic content, the smaller the molecular weight and the higher charge density, mainly as a protein-like substances in the three-dimensional fluorescence spectra. In contrast, the higher the content of hydrophobic substances, the higher humic content, relatively large molecular weight and the lower charge density, mainly humic substances in the three-dimensional fluorescence spectra. The polydispersity coefficient caculated from GPC showed JCZ had a complex molecular weight distribution.In order to investigate the factors that impact of magnetic resin on DOM removal, NDMP was chosen as experimental resin, and the nature of each DOM were compared before and after treating by resin. Experimental found that the hydrophilicity, SUVA, molecular weight of DOM were not attractive for NDMP resin. Comparative changes before and after resin treated in acidity, we found NDMP primarily removed the acidity provided by carboxyl group, weaker by hydroxy group. Zeta potential of desorption solution also indicated NDMP removed negative charged DOM. The kinetic results showed NDMP could removed WLK, JXZ, DC 82%,71%, 63% of UV254 at balance, respectively, indicating that more charge density, more removal efficient. However, high charge density of DOM caused cumulative effect of resin. And high charge density of water required more resin dosage to carry out reaction.Enhanced coagulation mechanism pre-treated by NDMP was also explored. Fe salt was chosen as a coagulant, and examined the best coagulant dosage before and after resin treated. The result showed that there were high correlation between best coagulant dosage and electro-negativity of each DOM, which indicated acidity was an important factor to coagulant dosage. The flocs potential also showed that coagulation mainly removed negative charged NOM, just like NDMP. The enhanced coagulation mechanism also could be explained. That because NDMP removed a portion of negative charged DOM or high negative charged DOM, caused static electricity weakened between flocs, accordingly to bridge and netting been enhanced, so that floc size, strength and removal for electrically neutral DOM were improved. The microscope result also confirmed this mechanism. Compared with coagulation alone, NDMP combined with coagulation process could improve organic matter removal, also reduce by 50% to 70% coagulant dosage, greatly reducing the cost.