Semi-artificial Wetland Purification Of Urban Sewage Effect And Its Mechanism

Wastewater treatment by constructed wetland has been developed in recent three decades and widely accepted by all nations for its properties of high efficiency, low cost,sustainable development and easy to manage. Researches on the efficiencies and mechanism of constructed wetland have got rapid development in our country, while few ones focus on the use of natural wetland for wastewater treatment. In this paper, taking the half-constructed wetland in the wastewater treatment system of a factory in north district of Changchun city as sample site, depending on the observation date of the fixed site, we got the quantitative analysis on the treatment efficiency of the natural wetland with man-made reconstruction which is used for purifying the wastewater from the factory. Based on the analysis, the determinate way on the function potential ,environment threshold value and the basic improvement methods and approaches were put forward.As it has been showed by the research, the treatment efficiency of the half-constructed wetland on COD,BOD,SS,NH etc as follows:29.3－44.4%,83－86%,33.3－47.4%,18.5－21.9% ,was lower than that of some constructed wetland, at the same time, the treatment effect on oil and six-valence chromium was not obvious. The purification mechanism mainly lies in the physical baffle, physiological absorption and microorganism action etc. The compact matrix structure and short hydrologic residence time result in the low treatment efficiency. The research shows that after man-made reconstruction and the input of wastewater, changes occur in the ecological structure and function of the natural wetland. The spatial spread of cattail community primarily was the result of the gradual accumulation of contaminations and nutrients in water and soil, and the important reason why the removal efficiency of contaminations declines can be found in the decrease of wetland area. There is high feasibility to use natural wetland for wastewater treatment,however, the structure of natural wetland needs to be further improved.