Research On Mn Oxidation Deposition And Control Technology In The Background Of "Yellow Water" Caused By Mn In Drinking Water Distribution System

Drinking water safety problems are closely related to people’s heath life.The problem of"yellow water"caused by the deposition and re-release of manganese particulate matter in drinking water distribute systems(DWDs)is one of the water quality problems strongly reflected by people.A series of studies have shown that even if the manganese concentration in the factory water is lower than the national standard,it can lead to the occurrence of manganese cause“yellow water”accidents.At present,there is still little research on the occurrence pattern,causes and corresponding treatment measures of manganese cause“yellow water”.The purpose of this paper is to investigate the pattern of“yellow water”in the period when“yellow water”occurs,and to identify the causes of“yellow water”accidents in the actual water supply area and propose countermeasures in the drinking water treatment process and the pattern of oxidation and deposition in the transmission and distribution network.Analyzing the pattern of yellow water occurrence in the water supply area of several water treatment plants(WTPs)would find that the concentration of Mn in the finished water exceeded0.02 mg/L,“yellow water”events would occur in DWDs very soon.“Yellow water”with Mn exceeding the standard limit of 0.1 mg/L reflects the problem of Mn deposition and re-release in DWDS.The Mn concentration was significantly and positively correlated with the chromaticity of“yellow water”samples.In conclusion,monitoring the concentration of Mn(Ⅱ)ions in source water,adopting efficient Mn removal measures,and maintaining the Mn concentration in the finished water of the WTPs below 0.02 mg/L are critical for controlling large scale Mn-caused“yellow water”events.To investigated Mn deposit formation mediated by microbes using 300-day pipe loop experiments constructed with corroded iron pipes harvested from construction site.The results show that Mn(Ⅱ)added every two days to PVC pipes could be completely oxidized since day50,due to the development of biofilms containing Mn(Ⅱ)-oxidizing bacteria(MOB).In contrast,about half of the added Mn(Ⅱ)remained unoxidized in iron pipes with a relatively low dissolved oxygen(DO)concentration in bulk water during the study period.Kinetic study indicated that Mn(Ⅱ)adsorption by iron corrosion products was one primary mechanism for Mn(Ⅱ)disappearance in iron pipes.When air aeration was performed to maintain DO above 8.0 mg/L,nearly complete Mn(Ⅱ)oxidation was observed in the aerated iron pipes.Microbial analysis reveals that potential MOB in the unaerated iron pipes was the least abundant than in the PVC and aerated iron pipes.Additionally,during the study period,Mn deposition onto the surface of corrosion scales did not affect iron release to bulk water.This study demonstrated that corroded iron pipes were less favorable for microbial Mn(Ⅱ)oxidation and Mn O_x accumulation than PVC pipes,presumably due to the limitation of dissolved oxygen in iron pipes.After the conversion pattern of Mn(Ⅱ)in the DWDs was investigated and the concentration of Mn(Ⅱ)in the finished water required to prevent“yellow water”,the effect of Mn(Ⅱ)removal by filtration with granular activated carbon(GAC)under different conditions was studied.The results showed that GAC filtration could reduce Mn(Ⅱ)from 400μg/L to 10μg/L,while sand filtration did not show evident Mn(Ⅱ)removal function during the study period.Water quality changes,pretreatment with Na Cl O and chemogenic Mn O_x coating on GAC media surface did not impair the Mn(Ⅱ)removal capacity of biological GAC filters.q PCR results indicated that GAC media colonized dramatically more biomass than sand media,potentially resulting in effective Mn(Ⅱ)removal by biological GAC filtration.Under chlorinated conditions,GAC filtration underperformed sand filtration in Mn(Ⅱ)removal.Much faster chlorine decay was observed in GAC filters than in sand filters,making it hard to sustain Mn(Ⅱ)oxidation and thus leading to less Mn(Ⅱ)removal.Chemogenic Mn O_x coating on sand media surface could not assist in abiotic or biotic Mn(Ⅱ)oxidation by dissolved oxygen,and chlorine dosing was necessary to maintain Mn(Ⅱ)removal in sand filters.