The Current Situation Of Microcystins Pollution In Surface Water Of Central And Western Of Jilin And Studying On Microcystins Purification Efficiency Of Constructed Wetlands

With the rapid economic and social development,large amount of untreated wastewater has been discharged into natural water bodies,which causes serious eutrophication in surface water.The eutrophication and climate change result in cyanobacteria harmful algae blooms（cyano-HABs）,which has been an increasing trend worldwide.Some genera of cyanobacteria can produce toxic secondary metabolites.Among all the cyanotoxins,microcystins（MCs）was considered as the most harmful cyanotoxins.Non-point source pollution was serious in Northeast China.The average temperature of Northeast China was lower than other area of China.Data on the current situation of MCs pollution in this region are seriously lacking,and ecological purification technologies for MCs pollution control are also relatively lacking.Therefore,field investigation and greenhouse simulation experiment were carried out in this research for investigating on MCs pollution status in river and lakes of central and western of Jilin province and studying on MCs purification efficiency of constructed wetlands（CWs）.In greenhouse simulation experiment,we selected nitrogen and phosphorus nutrients and a typical MCs variant（i.e.,MC-LR）as our research object to prepare synthetic wastewater.Key processes and removal mechanisms from synthetic wastewater in CWs were explored,and appropriate substrate materials were screened out.The possibility of microbial fuel cell and biochar addition to enhance the treatment efficiency of utilizing the constructed wetlands was explored and verified.The main conclusions of this study are as follows:（1）According to field investigation of central and western of Jilin province,the main pollutants in this area were TN and TP.The water quality of most sampling sites（63%）was worse than Class V of Environmental Quality Standard for Surface Water（GB3838-2002）in China.MCs could be detected in all the surface water bodies and detectable rate was attained 97%.The highest MCs concentration was up to 2.411μg/L in one sampling site of YS Reservoir.In the beaker simulation experiment,the typical freeze-thaw process in Northeast China could inhibit the natural MCs degradation.Once the natural water melts,the risk of MCs still exists.（2）Planted and unplanted CWs filled with four substrates（i.e.,gravel（G-CWs）,ceramsite（C-CWs）,iron-carbon（I-CWs）and slag（S-CWs））were established to evaluate nutrients and MC-LR removal efficiency from eutrophic water affected by the presence of plant and different substrate.Except for I-CWs,the presence of plants can promote the removal efficiency of nutrients and MC-LR of CWs to varying degrees.The presence of plants and the different types of substrates affected the microbial community structure of CWs.All types of CWs showed good nitrogen removal efficiency,and the removal percentage was more than 90%.C-CWs and I-CWs showed better removal performance for TP and MC-LR.However,at the high influent load of MC-LR（15.00μg/L）,the effluent MC-LR concentration of other CWs was higher than provisional guidance of WHO and China（1μg/L）,except for the C-CWs.According to microbial community analysis,the presence of plants improves the richness and diversity of microbial community and the relative abundance of various functional microorganisms.The abundance and diversity of microorganisms in the C-CWs were the richest,while the composition of microbial community in I-CWs was simplified.（3）Microbial fuel cell（MFC）is an emerging wastewater treatment technology developed in recent years.It has attracted extensive attention for its good removal efficiency of refractory organic matter and ability to convert organic matter energy into electric energy.It has reported that microbial fuel cell coupled CWs（MFC-CWs）can enhance nutrients and MC-LR removal efficiencies.In this study,nutrients and MC-LR removal performance of closed-circuit MFC-CWs were superior to the open-circuit MFC-CWs.The addition of sponge iron into anode can significantly improve the electricity generation performance of MFC-CWs and reduce the internal resistance of the system.However,the addition of sponge iron can reduce the adsorption capacity of anode,which leads to the reduction of adsorption performance of TP and MC-LR.In addition,based on microbial community analysis,there were significant differences in microbial community structure of anode among all treatment groups.The relative abundance of microcystin-degrading bacteria in conventional MFC-CWs was higher than that in other treatment groups,while the addition of sponge iron promoted the growth and reproduction of electrochemically active bacteria（EAB）in the system.（4）Due to the large specific surface area and large number of functional groups on the surface,biochar was commonly applied in various pollutants removal.In this study,adding biochar into CWs not only improves the nutrients and MC-LR removal efficiency,but also reduces the generation of extracellular polymers（EPS）in CWs.Compared with the control group without biochar,NO₃^--N,TP and MC-LR removal performance was significantly（p<0.05）improved by biochar addition.The removal efficiency increased with the biochar addition ratio increased.In addition,the content of EPS in biochar addition CWs was also significantly（p<0.05）decreased,and the main difference was observed in the content of LB-EPS and TB-EPS.The results of microbial community analysis were presented that the relative abundance of functional microorganisms related to the nutrients and MCs degradation was increased in biochar addition CWs.In conclusion,biochar addition into CWs can improve the removal efficiency of nutrients and MC-LR and reduce the risk of system clogging.Considering the pollutants removal efficiency and cost,CWs with 20%biochar addition ratio can be considered as proper choice for eutrophication and MCs pollution control in this study.