Study On Micro-aerated Vertical-flow Constructed Wetland Purifying Polluted River

Because urban river was impacted by industrial waste, municipal sewage and agricultural sources, water pollution and ecological damage were very serious. Therefore, it was necessary to strengthen urban polluted river treatment and improve the existing polluted river purification technology in the course of city development. Constructed wetland systems had been widely used in the treatment of polluted rivers, and it had good adaptability to water quality, large capacity and not subjected to the impact of flood or shipping. In addition, it had good nitrogen and phosphorus removal capacity and significant environmental benefits. At the same time it had a good landscape effects. Therefore, it had a good prospect.In this paper, micro-aeration was introduced in the integrated vertical flow constructed wetland, and a small test micro-aeration integrated vertical flow constructed wetland system was designed. The effect of aeration depth and position(expressed by aeration position), aeration intensity and aeration time on removal efficiency of nitrogen、phosphorus and organic pollutants in polluted river were investigated so as to analyzed the best micro aeration conditions. In addition, the effect of the best micro-aeration condition on some certain bacterial physiological groups quantity and enzyme activity were studied. The main results were as follow:1. The effect of aeration position on the removal efficiencies of nitrogen, phosphorus and ammonia were different under the same aeration intensity of2.55m3-h"’and same aeration time. When aeration time was20min, at aeration position7, which is at the height of12cm from the bottom of the first grid, the second grid, fourth and sixth grid, the removal efficiencies of nutrient were better than other aeration positions. When aeration time was40min, position1(the bottom of the first grid) was the aeration position which could achieve a good nutrient removal. When aeration time was60min, also in aeration position7, could achieve a good nutrient removal.The effect of aeration position on removal efficiency of contaminated river organics was different due to different aeration time. COD removal rate were changed obviously under different aeration positions when aeration time were20min and40min, respectively. Change of aeration position had little effect on wetland system organics degradation when aeration time was longer. Aeration time was not the longer the better, and removal efficiencies of pollutants were good when aeration time was40min.Aeration intensity had a certain effect on removal efficiencies of pollutants. Aeration intensity was not the higher the better, if it was too high, running costs were increased, but if it was too low, the effectiveness of wetland treatment was limited. Consider from the perspective of removal efficiencies and economic, selecting aeration intensity of2.55m3-h-1was best.The best micro-aeration conditions were that aeration intensity was2.55m3-h-1, aeration depth and position were at the bottom of most front-end down-flow chamber of IVCW and aeration time was40min. Under the best micro-aeration, the removal rates of TN, TP and COD were all above90%, and the removal rate of ammonium nitrogen reached more than70%. The effluent concentration of TN、COD and ammonium nitrogen were lower than the I class standard values of the surface water environment quality standard(GB3838-2002), and the effluent concentration of TP was between I and II class standard values. And oxygen condition of wetland system was improved. The best micro-aeration condition had little effect on pH changes of each grid’s effluent.Micro-aeration integrated vertical flow constructed wetland system’s structure of which consisted of three identical series downstream and upstream pools was good for improving removal efficiencies of nitrogen, phosphorus and organics.2. Micro-aeration treatment changed the matrix microorganisms quantity. Micro-aeration improved the matrix’s nitrifying bacteria quantity and enhanced the nitrification of system matrix, while decreased the number of denitrifying bacteria, making denitrification inhibited. Nitrifying bacteria quantity of closing to the water inlet was higher than denitrifying bacteria quantity1to2orders of magnitude because of aeration. Since denitrifying bacteria of closing to the water outlet had a large base of quantity, even if there was a certain amount of reduction, but it was still higher than the number of nitrifying bacteria in1order of magnitude.Micro-aeration reduced matrix dehydrogenase activity, while increased urease activity in the area of aeration position obviously, which was1.5times of urease activity without aeration.On the whole, micro-aeration improved distribution and activity of nitrifying bacteria and denitrifying bacteria, and improved removal rate of TN, thereby improving river water quality.