Study On Purification Of Rainwater By Compound Vertical-flow Constructed Wetland-microfiltration Composite System

With the rapid development of urbanization in our country,in recent years,many cities have experienced problems such as lack of water resources,serious water pollution,and urban internal problems.In particular,karst mountainous areas in southwestern China are rich in rainwater resources,but their spatial and temporal distributions are uneven,and water and soil erosion is serious.This has caused typical seasonal water shortages.In the past 20 years,the country has built a large number of water cellars in karst mountainous regions in southwestern China.However,large numbers of water cellars have water quality problems caused by turbidity and microbiological contamination,causing difficulties for people and livestock to drink water.In this context,in order to make full use of rainwater resources and simulate rainwater in Wuhan,a rainwater collection-composite vertical-flow artificial wetland-microfiltration membrane?RC-IVCW-MF?composite system was constructed to conduct a pilot study on the deep purification of rainwater.The treatment performance of the composite vertical-flow constructed wetland and the advanced treatment performance of the microfiltration membrane were studied,and the sterilization effect of the composite system was discussed in order to provide strong support for its practical engineering applications.This article through the experimental study,the following conclusions are obtained:?1?It was more appropriate for the simulation system to use the rain water after 30minutes in Wuhan as the system water intake.And the average values of COD_cr,total phosphorus,total nitrogen,and ammonia nitrogen in rainwater were 21.12mg/L,0.11mg/L,6.53mg/L,and 1.24mg/L,respectively.And total phosphorus reached Class III of the“Standard of Surface Water Environmental Quality?GB 3828-2002?”,the total nitrogen is inferior to Class V,the ammonia nitrogen and COD_cr could meet Class IV of water quality standards.?2?Based on the study of ammonia nitrogen,total nitrogen,total phosphorus and COD_cr in the rainwater under different hydraulic retention time?HRT?conditions of IVCW unit.It was found that the optimal hydraulic retention time was 12h.At this time,the removal rates of ammonia nitrogen,total nitrogen,total phosphorus,and COD_crr were 62.16%,69.60%,46.52%,and 21.85%,respectively.The effluent quality of ammonia nitrogen,total phosphorus,and COD_cr could meet Class III of the“Standard of Surface Water Environmental Quality?GB 3828-2002?”.The removal rate of ammonia nitrogen and COD_cr in the composite vertical flow man-made has a significant correlation with the influent concentration.?3?By studying the effect of pretreatment on membrane flux,it was found that the trend of changes in membrane flux could be effectively alleviated after IVCW pretreatment.It was found that the cleaning way of NaClO and 1%HCl alternately backwash was better by comparing the effect of three cleaning methods of NaClO,1%HCl,NaClO and 1%HCl on the recovery of membrane flux?4?In order to investigate the treatment performance of microfiltration membrane,the effects of different membrane fluxes and different connection methods on the general water quality indicators of drinking water were studied.The results showed that with the increase of membrane flux,CODMn and turbidity removal rate showed a downward trend,there was no significant change in sulfide,chloride,hardness and total dissolved solids concentration.And the removal rates of aluminum,iron,copper,manganese,and zinc were downward trend.it could increase the removal rate of CODMn and turbidity by tandem microfiltration membrane units,it have less effect on sulfides,chlorides,hardness,and total dissolved solids concentration.At the same time,it could improve the performance of aluminum,iron,copper,manganese,and zinc.The removal rate and effluent water quality could reached the“Standards for Drinking Water Quality?GB 5749-2006?.?5?The microfiltration membrane unit could effectively remove bacteria and Escherichia coli.The UV sterilizer has a 100%removal rate of bacteria and Escherichia coli in the effluent of the microfiltration membrane unit.