Enhanced Removal Of Triclosan And Nutrients In Constructed Wetlands With Manganese Mineral

Triclosan(TCS)is a broad-spectrum antibacterial and antifungal agent which was used more and more widely.However,TCS is harmful to the algae,aquatic organisms,mammals and even human.Because conventional wastewater treatment plants lackspecific technology for TCS,concentrations of TCS in the effluent is still high.In order to reduce the environmental pollution caused by residual TCS in the effluent,it is necessary to find an efficient and environmentally friendly water treatment technology.Constructed wetlands(CWs)have outstanding technical advantages in removal of organic contaminants for its low investment and operating cost,convenient management and the ability to beautify the environment,etc.However,there are still some problems for CWs.One is that the concentration of organic contaminantsis too low to be used by microorganism and the other is that CWs lack oxygen,which lead to the low removal efficiencies for contaminants.Manganese oxides are powerful oxidants that are capable of oxidizing a variety of contaminants and may be appropriate for being applied in CWs.Therefore,in order to provide scientific basis on the application of manganese oxides in CWs,there is an essential need to study the enhanced removal efficiency and the removal mechanisms of pollutants in CWs with manganese oxides.In the present study,we selected the optimal type of manganese oxides through an experiment and built theCWs with the manganese oxide to assess the removal efficiencies and enhanced removal mechanisms of TCS and nutrients.Then,to explore the practical application of manganese oxides,highly pure manganese oxide was used in CWs(Birnessite-coated sand CWs)to assess the removal efficiencies and enhanced removal mechanisms of TCS and nutrients.Main conclusions are as follows:(1)According to the study of selecting the optimal type of manganese oxides,the manganese ores had the highest removal efficiency for TCS.The removal efficiency for TCS following the order:manganese ores>Birnessite-coated sand>MnO2>manganese slag.Overall,manganese ores and Birnessite-coated sand had favorable removal effect for nutrients.Taking into the economic effectiveness account,we chosed the manganese ores for further study in CWs.(2)During experimental period,the removal efficiecy for TCS in the manganese ores CWs was up to 93.3%and that in the control CWs was only 83.8%.Results showed that the removal efficiencies of common pollutants in manganese ores CWs was better than control.The concentration of TCS in influent was mostly removed(29.96%)by manganese ores CWs in the region that filled with manganese ores and the concentration of Mn2+was also high in that region.(3)The manganese ores CWs had the higher microbial abundance and diversity than control.Based on our results,Proteobacteria were the most abundant phylum in CWs.The most abundant group of microorganisms in the manganese ores CWs could be assigned to the gamma-Proteobacteria,distinguishing from the communities present in control in which the most abundant group of microorganisms was beta-Proteobacteria.Therefore,we deduced that gamma-Proteobacteria was probably responsible for the oxidation and reduction of manganese in manganese ores CWs.(4)During experimental period,birnessite-coated sand CWs has the higher removal efficiency for TCS than the control.The removal efficiency for TCS in the birnessite-coated sand CWs was up to 91,8±2.1%and the control was only 83.8±1.9%.Besides,the Mn2+ was detected in the water samples and its concentration ranged from 0.016 mg/L to 0.033 mg/L in manganese CWs,The concentration of TCS was mostly removed in the 10-20 cm region of the highly pure manganese CWs and the concentration of Mn2+increased in the section,which suggested a microbial reduction of bimessite to dissolved Mn2+.The removal trend of NO3--N,NH4+-N,TP,COD declined more drasticly in the segment of the birnessite-coated sand CWs than control.(5)The birnessite-coated sand CWs had the higher microbial abundance and diversity than control.Proteobacteria which have been shown to correlate with TCS disappearance in stream sediments were the most abundant phylum in CWs.The most abundant group of microorganisms in the birnessite-coated sand CWs could be assigned to the gamma-Proteobacteria(B-20:31.08%,B-50:36.63%),distinguishing from the communities present in control in which the most abundant group of microorganisms was beta-Proteobacteria(C-20:65.9%,C-50:37.66%).From the study of microbial cultivation experiments,we found that the group of microorganisms which drove the oxidation of manganese may exist,but it still need further research.