Distribution And Survival Of Indicator And Pathogenic Microorganisms In Constructed Wetland

Constructed wetlands (CWs) which are simulating the ecosystems of natural wetlands utilize the cooperation of hydrophyte, soil and microorganisms to purify wastewater. The constructed wetland technology has the advantages of low investment and operation costs, high quality effluent with less dissipation of energy, high loading bearing, simple and convenient operation and management, as well as great value of ecological landscape. So constructed wetlands were widely used for wasterwater treatment, pollutant control and environment improvement.Compared with the traditional secondary wasterwater treatment process, the effects of constructed wetlands to public health and ecological secure should be taken more attention to. The key points of constructed wetland's environmental sanitary assessment are the selection of proper pathogenic and indicator microorganisms, and the study of their behaviors in constructed wetlands.In this study, indicator microorganisms such as total coliforms(TC), faecal coliforms(FC), Escherichia coli(EC), and fecal streptococci(FS), and pathogens such as Clostridium perfringens(CP) and salmonellae(SM) were analyzed from various components of a free water surface constructed wetland. Distribution and removal efficiency of indicator microorganisms and pathogens in free surface flow constructed wetland were investigated. And the die-off rates of the indicator and pathogenic microorganisms in the water and the sediment of the constructed wetland were determined. And indicator organisms and pathogens removal function performed by copepods in the constructed wetland was also investigated.The conclusions of the research were shown as follows:(1) The constructed wetland could effectively reduce Escherichia coli by 99.9%, fecal streptococci by 99.8%, total coliforms by 99.8% and fecal coliforms by 99.8%, the Salmonella spp. removal efficiency was relatively low by 97.5% and the C. perfringens removal was the least by 77.2%.(2) On a volume/dry weight basis the quantity of indicator and pathogenic organisms were two to three orders of magnitude higher in the sediment compared to the water column, which indicated the indicator and pathogenic organisms tend to concentrate in sediment of the constructed wetland. The quantity of Salmonella spp. in effluent and sediment and the C. perfringens in sediment were more greater than that of total coliforms, fecal coliforms, fecal streptococci and Escherichia coli.(3) The die-off rates of all the indicator and pathogenic microorganisms were greater in the water than in the sediment, and die-off rates of different kinds of indicator and pathogenic microorganisms were quite different. The die-off rate of fecal streptococci in water column was the highest among the six kinds of indicator and pathogenic microorganisms by 2.1021og₁₀ day^-1, the die-off rate of faecal coliforms in sediment was the highest by 0.470 log₁₀ day^-1 and the die-off rate of C. perfringens in water column and sediment were the lowest by 0.6631og₁₀ day^-1 and 0.0201og₁₀ day^-1, respectively.(4)Copepods have a high predation to indicator and pathogenic microorganisms. At the copepods concentrations of 3.0×10²/l and 6.0×10²/l, higher die-off rates were observed for indicator and pathogenic microorganisms compared to the control group, and indicator and pathogenic microorganisms in samples with higher concentration of copepods decreased much more rapidly than those in samples with lower concentration of copepods. The results suggest that the predation by copepods may be an important mechanism for the removal of bacteria from waster column in the constructed wetland.