Experimental Research And Engineering Demonstration Of Surface Flow Constructed Wetland To Lightly Polluted City River Purification

Lightly polluted rivers refer to rivers that the river water quality in the range ofⅤto slightly black and odor."City Guide rectification work of black-odor water body"pointed out that the light pollution of river water quality improvement will be one of the most important work for a long period of time.Constructed wetlands,especially surface flow constructed wetlands,are of great practical significance for improving the water quality of lightly polluted rivers because of their good coordination with urban landscapes,low operating costs,and low maintenance and management techniques.It has broad application prospects in improving the water quality of polluted rivers.With regard to the water quality of lightly polluted rivers,the effects of 4 hydraulic retention times（1d,2d,4d,and 6d）and 3 types of fillers（zeolite,artificial ceramsite,volcanic rock）on the purification of surface flow constructed wetland water are analyzed experimentally.The results show that the removal effect of wetland pollutants is the best when the HRT is 4d,and the removal rates of COD,NH₄⁺-N,NO_X-N,TN,and TP reach 31.4%～51.8%,46.4%～55.6%,25.8%～28.5%,33.9%～36.8%,20.0%～25.0%.The removal effect of filler is volcanic rock>artificial ceramsite>zeolite.The removal rate of COD,NH₄⁺-N,NO_X-N,TN,TP of volcanic rock filler wetland reach 40.5%～56.7%,46.5%～62.8%,29.0%～49.0%,40.9%～51.3%,31.4%～47.5%.The surface flow artificial wetland was constructed with volcanic rock gravel as filler and reed as wetland emergent plants.The effect of adding three submerged plants（bitter grass,hornwort,and black algae）on the purification of wetland water quality was experimentally analyzed.The results show that:after adding submerged plants,the removal rate of each pollutant in the wetland has increased significantly,and the order of the effect on the removal effect is Hornwort>Black algae>Bitter grass.The CW added with hornwort has the best removal effects of COD,NH₄⁺-N,TN,and the removal effect are 72.2%～85.7%,75.4%～86.0%,and 66.8%～68.9%.The CW added with bitter grass has the best removal effect on NO_X-N and TP,and the removal rate reaches 33.4%～44.9%and 33.4%～44.9%.Through high-throughput sequencing,the microbial diversity and community structure of the reed stalks are analyzed.The results show that the OTU numbers of microbial samples on reed stems ranged from 262 to 943 OTUs.The overall OTU level increases with increasing temperature and has a significant correlation with temperature（p<0.05）.Vertically,the microbial species on the stems of reeds near the roots are more abundant.At the phylum level,the higher abundance of microorganisms on the stalks of the reed were Proteobacteria,Cyanobacteria,Bacteroidetes,Verrucomicrobia,and Chloroflexi.The abundance of microorganisms related to nitrogen and phosphorus removal on reed stems is relatively high,mainly including Phormidium,Pseudomonas,Azospirillum,Dechloromonas,Bacillus and so on.The highest abundance levels of microorganisms related to nitrogen and phosphorus removal functions reach 7.76%and 18.87%.At the northern end of the Fotang River in Kunshan,Jiangsu,the theoretical results of the laboratory research are applied to the surface flow constructed wetland project.After 6 months of long-term monitoring,the COD,NH₄⁺-N,and TP concentrations in the wetland effluent are stable at 15.19±4.49mg/L,0.56±0.27mg/L,and 0.16±0.05mg/L.The water quality reaches the water standard of Class IV.The result verifies the feasibility of surface flow constructed wetland applied to light pollution river water quality improvement.