Operational Characteristic Of Near Natural Wetland Treating Polluted River Water

Nansi Lake suffered from structured pollution and destruction of lakeshore wetland ecosystem was serious. The economic and effective projects of constructed wetlands for treatment of polluted river water are necessary because of time arrival of South-to-North Water Transfer. The constructed wetland for treatment of Xinxue River water in Nansi Lake aera was studied in terms of aqutic plants screen,hydraulic characteristic and pollution removal through laboratory and field pilot experiments, and developed a new type of constructed wetland for treatment of polluted river and ecosystem restoration.Aquatic plants screen was studied in terms of the removal efficiencies of pollutants containing COD_Cr,TN,NH₄⁺-N and TP in wetland. The capacity of aquatic plants' oxygen diffusion was analyzed first. Of all the plants tested, the oxygen diffusion capacity of Phragmites australis is the highest, followed by those with Ceratophyllum demersum L, Typha orientalis, Scirpus crassipes, Lythrun salicaria, and the lowest was Lythrun salicaria., the capacity of aquatic plants' oxygen diffusion was interrelated markedly to reduction of intensity of illumination. The static test results showed that removal loads of COD_Cr,TN,NH₄⁺-N and TP in aquatic systems were 2.33g/(m²Â·d),0.15g/(m²Â·d),0.08g/(m²Â·d) and 0.05 g/(m²Â·d) respectively in the condition of inlet concentrations of COD_Cr,with 80mg/L,TN with 8mg/L,NH₄⁺-N with 4mg/L and TP with 2.5mg/L, respectively. The capacity of decontamination with Ceratophyllum demersum L. and Phragmites australis were better. The capacity of aquatic plants' oxygen diffusion was interrelated markedly to reduction of COD_Cr and NH₄⁺-N, while not interrelated markedly to reduction of TN and TP.The hydraulic characteristic of near natural wetland was studied based on theories open channel uniform flow and reactor residence time distribution curve. The analysis of open channel uniform flow indicated that the constructed wetland can resist shock load effectively. The analysis of flow pattern indicated that there were shortcut and dead zones in the surface flow wetlands, the longitudinal dispersion was existed to mixture sectional flow uniformly, and improved the pollutants removal efficiencies of wetland system. The factors containing plant,water distribution and topography had effects on the flow pattern in the wetland system, and dead zones rate with 15.4% decreased to 6.1% by optimizing of water distribution and plants.The pilot wetland systems were developed by selecting Phragmites australis and Ceratophyllum demersum L. and optimizing water distribution. The operation results indicated that the optimum hydraulic load was 5cm/d, the removal efficiencies of COD_Cr,NH₄⁺-N and TP in surface wetland system were 84.4%,46.5%å’Œ82.6%, respectively. The pollutants removal loads of COD_Cr,NH₄⁺-N and TP in surface wetland system were 3.09 g/(m²Â·d),0.53 g/(m²Â·d) and 0.14 g/(m²Â·d), respectively. The COD_Cr removal loads in wetland system were 3.75g/(m²Â·d),3.37 g/(m²Â·d) and 3.26 g/(m²Â·d) in summer, autumn and winner, respectively. And the NH₄⁺-N removal loads in wetland system were 1.12g/(m²Â·d),0.68 g/(m²Â·d) and 0.59 g/(m²Â·d) in summer,autumn and winner, the removal efficiency in summer was higher than those in autumn and winner. The removal efficiencies of COD_Cr,NH₄⁺-N and TP were 84.4%,46.5% and 82.6% with the planting style of Phragmites australis and Ceratophyllum demersum L, higher than those without plants and with single Phragmites australis. The influence of the heat preservation technology on the pollutant removal effect of surface flow wetland in winter was studied. The results showed that covering plastic film avoided the froze in winter, and the average removal rates of COD_Cr,TN and NH₄⁺-N in the covered wetland were higher 11.6%,5.5% and 14.8% respectively than those in the natural condition.Based on the study mentioned above, the demonstrate project of Xinxue River near natural wetland was designed and built in Nansi lake for the treatment of polluted river water to make sure the water quality of lake inlet reaching to classâ…¢of environmental quality standard for surface water, and the project displayed good economic benifits, ecology benifits and society benifits preliminarily.