Study On Nitrogen Removal In Integrated Vertical Flow Constructed Wetland Sewage Treating System

As a new kinds of ecological engineering for wastewater treatment and water quality management thrived at 1970's, constructed wetlands (CW) is popularized all around world with the advantages of low construction fee, easy to operate and manage.Aimed at a new CW-Integrated vertical flow constructed wetland (IVCW), whichwas created by the cooperation of Institute of Hydrobiology in Chinese Academy of Sciences and Cologne University in Germany and University of Agricultural Science in Vienna, the nitrogen removal and transforms were studied based on the small sale plots (SSP) and medium scale plot (MSP). Main contents of this paper was as follows:1. The contributes of each part of IVCW in nitrogen removal were analyzed. The experimental results showed that nitrification and denitrification were the main removal ways of total nitrogen; Volatilization and adsorption effects can be ignored; The amounts of TN that can be removal by harvesting Canna generalis and Acorus tartarinowii were about 150.93 kg N/hm~2·yr and 661.88kg N/hm~2·yr, Acorus tartarinowii was better Canna generalis. And for nitrogen removal of Canna generalis: infancy plant was best while old plant was lowest, leaf of Canna generalis was best while stem was lowest.2. By adding potassium nitrate, ammonium carbonate, and urea separately to the natural lake water, different artificial sewages were got. The treatment efficiency of different nitrogen sewage by integrated vertical constructed wetland(IVCW) was researched. The experiment result showed that (1) removal efficiency of TN NO3 increase and subsequently decrease by increasing the quantity of potassium nitrate while reduce efficiency of NO2 decrease; and (2) removal efficiency of TN NH3-N increase and subsequently decrease by increasing the quantity of ammonium carbonate, while reduce efficiency of NO3~- NO2~-decrease; and (3)removal efficiency of TN increase and subsequently decrease by increasing the quantity of urea, while reduce efficiency of inorganic nitrogen decrease. The transform theory of nitrogen and the change of Phys-chemical parameters change of CW system were also analyzed.3. The nitrogen and phys-chemical character changes of different layers in IVCW treating sewages were measured. The experiment results showed that nitrate nitrogen and nitrite nitrogen were decreased by 56.96% and 63.43% along the direction of water in the constructed wetland because they were deoxidized to N2O and N2 by denitrification; Dissolved oxygen were decreased along the direction of water because the oxygen consumed of nitrification and life function, and pH were decreased because acid release of organic compound decomposed and nitrification. The total nitrogen concentration of lake water and effluent water was 2.120 mg/L and 1.195mg/L respectively. IVCW was a well sewage treating system. The removal rate of total nitrogen achieved 43.63% and the index of total nitrogen in wetland was let down from beyond V to III of the environmental quality level of surface water in China. The nitrogen removal was mainlyhappened in down-flow system of constructed wetland. The denitrification efficiency in up-flow system was not remarkable because of the low dissolved oxygen(0.71-1.48 mg/L)and lack of organic carbon(CODcr varied from 20.96 mg/L to 28.10mg/L)and the organic nitrogen release of wetland system toward water. For low dissolve oxygen and oxidation-deoxidized status in IVCW the nitrogen aminated was dominant while nitration was lower. To improve the nitrogen removal efficiency of IVCW, we could conclude that it was important that increasing reply oxygen and organic carbon in up-flow system. Nitrification and denitrification were crucial function of nitrogen removal in wetland. Subsection in-pouring water or pretreatment to transform ammonia nitrogen to nitrate nitrogen were recommendatory means, it could advance denitrification efficiency in wetland.4. Comparative studies were made for wastewater treatment efficiency by using combination system consisting of plug-flow wetland, down-flow wetland, aerobic lagoon and facultative lagoon. The results indicated that the process of down-flow wetland + oxidation pond removal NH3—N best, but algae in the oxidation pond may increase TSS in the effluent. Nitrification is advantaged for NH3—N removal, but it increase NO3 at the same time .Up-flow wetland is beneficial to the removal of NO3 .