Enhanced Coagulation with Mn(III) Pre-Oxidation for Treatment of Micro-Polluted Raw Water

Yan Yan,Sun Sun,Wu Wu,Liu Liu,Pan Pan,Wang Wang

doi:10.3390/w11112302

Abstract

Mn(III) oxidation technology has attracted increasing interest in recent years because of its fast decontamination kinetics and second-pollution-free characteristic. Whether it can be used as a pre-oxidation step to enhance conventional coagulation process remains to be evaluated. Herein, an Fe-coagulation/sedimentation process combined with Mn(III) pre-oxidation (Mn(III)+C/S), hypochlorite pre-oxidation (Cl2+C/S), and permanganate pre-oxidation (PM+C/S) was applied to treat simulated micro-polluted raw water. The removal performance of routine water quality indices (turbidity, dissolved organic carbon, total nitrogen, nitrate-nitrogen, ammonia-nitrogen, Pb(II), and Cr(VI)) and the emerging pollutants (acesulfame, carbamazepine, bisphenol S, and nano-ZnO) created by these three processes were researched. The mechanism of how Mn(III) pre-oxidation influences C/S was explored by identifying the transformation products of Mn(III), measuring the timely variation of flocs’ zeta potential and size, and scanning flocs’ micromorphology. Compared to Cl2+C/S and PM+C/S, Mn(III)+C/S exhibited its superiority in removing dissolved organic carbon (72.9%), total nitrogen (31.74%), and emerging pollutants (21.78%–93.49%). The enhanced removal of these contaminants by Mn(III)+C/S found its explanation in the strong oxidation power of Mn(III) and the multiple roles of in-situ formed MnO2 (e.g., flocculation core, adsorption co-precipitant, and densification agent). The acute toxicity tests confirmed that water treated by Mn(III)+C/S did not show a significant change in the associated toxicity. The findings of the present study indicate that Mn(III) oxidation technology shows great potential as an alternative to pre-oxidation technology of waterworks.

Highlights

In the past few decades, drinking water resources of many cities in China have been subject to varying degrees of pollution [1,2,3,4,5], which threatens the safety of drinking water
It is difficult to remove them by the traditional coagulation–sedimentation–filtration–disinfection process, which subsequently results in a lot of problems, including the occurrence of colors, tastes, and odors, formation of disinfection byproducts (DBPs), and the increase of coagulant/chlorine demands [6,7,8]
This study evaluated the advantages of combining Mn(III) oxidation and coagulation to remove conventional contaminants (turbidity, dissolved organic carbon (DOC), total nitrogen (TN), nitrate nitrogen (NO3 − –N), ammonia nitrogen (NH4 + –N), lead (Pb2+ ), hexavalent chromium (Cr(VI)), and emerging pollutants, and a comparison was made during enhanced coagulation with PM and chlorine

Summary

Introduction

In the past few decades, drinking water resources of many cities in China have been subject to varying degrees of pollution (micro-polluted raw water) [1,2,3,4,5], which threatens the safety of drinking water. It is difficult to remove them by the traditional coagulation–sedimentation–filtration–disinfection process, which subsequently results in a lot of problems, including the occurrence of colors, tastes, and odors, formation of disinfection byproducts (DBPs), and the increase of coagulant/chlorine demands [6,7,8]. These risks become more highlighted for low-temperature raw water because of the low coagulation kinetics under cold conditions [9]. Among these methods, pre-oxidation has attracted worldwide attentions because of its excellent effect on improving coagulation, easy operation, and low cost. In the pre-oxidation processes, oxidants such as chlorine are introduced at the beginning of the purification project to destroy hydrophilic organic compounds that stabilize dispersed colloids in the water and create favorable conditions for coagulation

Methods

Findings

Discussion

Conclusion