Studies On Pollution Mechanism And Repair Methods In The Small Enclosed Urban Water

In recent years, the quality of people’s life made steady progress and the ecological city is very popular in the field of construction. An increasing number of small closed landscape water bodies were constructed in order to improve the living environment. The small closed landscape water mainly exists in the urban green space, parks, buildings and other places. This kind of water has the characteristics of low environmental capacity, self-purification ability and easily affected by human activities, etc. For landscape water body, the good apparent traits are the most basic requirement. But due to the characteristics of the landscape water body itself, the serious apparent pollution phenomena such as the malignant proliferation of algae, the anomaly of color and turbidity, and even the black-odor phenomenon appeared constantly.In this study, the enclosed water located in Shitao Garden which lived on the campus was regarded as the research object. About one and a half year’s observation and water quality monitoring were conducted and a field test was carried to study the pollution mechanism and quantify the pollution sources. The course of apparent pollution was described by Sensation Pollution Index (SPI). This paper tried to evaluate the restorative effects of emergency repair methods of renew water and adding lime and to study the growth characteristic of duckweed by the hydraulic disturbance test. The following conclusions were got through a series of studies.(1) With the rise of temperature, the apparent pollution of closed landscape water was worse gradually. SPI had a significant positive correlation with temperature, turbidity, UV254, Chl-a and a negative correlation with DO. The correlation coefficients respectively were0.786,0.951,0.595,0.849,-0.699. These findings indicated that the decomposition of plant residues and the competitive growth of algae and duckweed would result in the serious apparent pollution.(2) The decomposition of green waste, rain and surface runoff, and the atmospheric deposition were the major source of closed landscape water. The amount of COD, PO43--P, and NH4+-N from the litters was33.98kg,0.06kg,1.01kg, from the confluence of rainwater was15.4kg,0.047kg,1.05kg, from the atmospheric precipitation was5.25kg,0.003kg and0.43kg every year. The contribution rates of three primary pollutants were40.56%-62.2%,28.9%-42.17%, and9.61%-21.9%.(3) The emergency repair methods of renew water and adding lime which just need one-time investment showed a certain effect on water restoration, while it had no effect on the restoration of apparent pollution. The duckweed and algae would still be malignant proliferation and the accumulation of pollutants in the water still exists, although the water quality could reach standard for around eight months. The disturbance test confirmed that the hydraulic disturbance when the outer linear velocity was0.045m/s could inhibit the growth of duckweed.This conclusion can provide theoretical basis for the scientific management and engineering remediation of enclosed landscape water, which has a strong theoretical significance and engineering significance.