| In order to study the purification effects of composite vertical subsurface flow constructed wetland systems on heavy metals in pond aquaculture waters as well as indicator and pathogenic microorganisms,This study carried out the determination of water quality and heavy metals at the inlet and outlet,and the detection of indicator and pathogenic microorganisms,the differences in the enrichment effect of heavy metals between different plant roots and their substrates near roots,and the correlation between different environmental factors and the enrichment rate of heavy metals were analyzed.Differences in the distribution and attenuation of various indicators and pathogenic microbial organisms in water bodies and substrates,and their major removal pathways.The main findings are as follows:Through the measurement and analysis of the water quality indicators and heavy metals,the removal efficiency of lead and copper in the constructed wetland was 77.2%and 41.7%,respectively.Compared with other types of wetlands,the composite vertical subsurface flow constructed wetlands had some advantages for the removal of Pb and Cu;the As was released in wetland with an average release rate of 8.40%.The roots of Polygonum hydropiper and Thalia dealbata Fraser have enrichment effect on Cr,As,Pb and Cu,and the roots of Pontederia cordata L.have only enrichment of Cr and As.The substrates near the roots of Polygonum hydropiper,Pontederia cordata L.,and Thalia dealbata Fraser have a good enrichment effect on chromium,among them,the maximum rate of the concentration of the Pontederia cordata L.to chromium is 0.987mg.kg-1.d-1.The enrichment rate of Pb and Cu in Polygonum hydropiper root was negatively correlated with temperature and the enrichment rate of Cr and Cu was negatively correlated with pH;the enrichment rate of Cr and As in Pontederia cordata L.root was negatively correlated with temperature;the enrichment rate of Pb in Thalia dealbata Fraser root was negatively correlated with temperature and pH,the enrichment rate of Cu was negatively correlated with temperature.Through the detection and analysis of indicators and pathogenic microorganisms in water bodies and substrates in constructed wetlands,the removal efficiency of the indicator microorganisms from fecal coliforms,total coliforms and E.coli in constructed wetlands was better than that of Salmonella,and a higher amount of Salmonella was still detected in the effluent.The average removal rate was only 23.2%,the average removal rate of fecal macroflora,total coliform bacteria,and E.coli was 65.7%,50.9%,and 43.4%,while the average removal rate of Streptococcus faecalis was negative.The contamination of the body,substrate and effluent in the pool of constructed wetland cells originates mainly from excretion of faeces from animals.Overall,the indicators and pathogenic microorganisms in the cell pool of the wetland were higher than those in the cell pool,indicating that the retained sedimentation is a key role in removal of indicators and pathogenic microorganisms.The trend of the decay rate of each indicator and pathogenic microorganism in the substrate was the same as that of the water body,but both were lower than the attenuation rate in the water body,and the decay rates of Streptococcus faecalis in the water body and matrix were the highest,being 0.984 lg/d-1 and 0.4921g/d-1,respectively.In addition,the four species of indicating microorganisms,total coliforms,fecal coliforms,E.coli,and fecal streptococci,which were selected in this study,had higher decay rates in the water and in the substrate than in the pathogenic microorganisms.This study provides a theoretical basis and reference for the better input and production application of composite vertical subsurface flow constructed wetland and the selection of wetland plants from the perspectives of improving the aquaculture water environment,achieving the sustainable and healthy development of aquaculture,and ensuring the quality and safety of aquatic products. |
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