Experiment On Removal Of Nitrogen From Agricultural Runoff By Multistage Constructed Wetland-pond System

Our country present water pollution problems have become increasingly serious, in Jiangxi, rural sewage, animal husbandry and aquaculture wastewater and agricultural runoff wastewater hardly treat effective, rural rivers,ponds and other pollution becomes more and more serious, These is the main pollution source of the Ganjiang River and Poyang Lake.This study combined with the status of the current rural sewage runoff was proposed using multistage constructed wetland pond combination system, the test device was constructed wetland and ecological pond through a series of model, the construction order is the ecological pond A- surface flow constructed wetland A- subsurface flow constructed wetland- surface flow constructed wetland B-ecological pond B. Which was grown in the ecological pond was Elodea nuttallii and surface flow constructed wetlands planted Canna, planted in subsurface flow constructed wetland is Canna, surface flow constructed wetland B planted reeds, planted in the ecological pond B was Myriophyllum spicatum.This study drawed the following results and conclusions:1) Analysis of influencing factor test. Orthogonal experiment results showed that in the TN removal process, the hydraulic retention time compared to the other two factors is more significant, the factors of combined nitrogen removal effect in order to: hydraulic retention time was greater than containing oxygen, containing oxygen was greater than carbon nitrogen ratio. In the NH₄⁺-N removal process and the hydraulic retention time compared to the other two factors was more significant, the factors of combined nitrogen removal effect was in the order of: hydraulic retention time was greater than containing oxygen, containing oxygen was larger than carbon nitrogen ratio. Single factor analysis showed that the highest removal rate of the conditions of the test results: the hydraulic retention time of 5 days, the carbon nitrogen ratio of 8, the oxygen content of 5.5mg/L. The orthogonal test was in the autumn to multistage constructed wetland pond system of nitrogen removal effect as a reference, effects of hydraulic retention time, with oxygen and carbon nitrogen ratio of the three factors of orthogonal test to optimize the conditions and each index significantly, and the test results were analyzed by orthogonal test assistant.2) Effect of hydraulic retention time on treatment. The results showed that the COD removal increased with hydraulic retention time removal rate gradually increased and finally reached 5 days after the removal rate of growth in hydraulic retention time began to flatten. The removal rate of TN increased with the hydraulic retention time and the corresponding increase, but when the hydraulic retention time reached 5 days after the start of decline, the highest removal rate reached 53.39%. NH₄⁺-N removal of hydraulic retention time is longer, the better removal effect, but when the hydraulic retention time arrived at 5 days, it declined, the test that NH₄⁺-N in the hydraulic retention time of 5 days, the effluent water quality was best.Establish the first order kinetic model, removal of COD model correlation coefficient greater than 0.9, indicating that the first-order kinetic model could better reaction combined system of COD degradation, the removal of TN correlation coefficient of the model was 0.8129. Removal of NH₄⁺-N model was 0.7891, used for mining the test is artificial wetland and ecological pond in series mode, although did not reach 0.9, but from the point of view of the correlation coefficient still had a good effect.3) Analysis of long-term and seasonal test. Selected the hydraulic retention time of 4 days for the removal of one year. Test results showed that the COD removal rate in the combined system was stable, that the test system in the treatment of COD could be maintained at a good level in the four seasons temperature changes, the minimum was at the turn of the spring and winter. In the summer is to reach the highest removal rate had been maintained more than 50%. TN in winter and spring is accompanied by decreased and the temperature of removal rate was gradually declining, spring after the temperature began to rise, removal rate began to steadily increase. To achieve the best removal effect in summer. In summer and autumn, the removal efficiency of TN was the best, which proved that the change of the seasons would directly affect the removal efficiency of the whole system to TN. In addition to the NH₄⁺-N also achieved satisfactory results, water quality is best close to surface water IV class water quality standards, in the winter cold season can also reach the surface water V class water quality standards.Study on the removal of pollutants from the combined system of 4. The results show that multi-stage artificial wetland pond combination system of COD removal capacity is greater than the wetland ecological pond, each construction material processing capacity is ecological pond A was greater than the ecological pond B was greater than the surface flow wetland was greater than a subsurface flow wetland was greater than the surface flow wetland B. TN removal ability of ponds and wetlands were basically the same, each construction material processing capacity was ecological pond A was greater than the ecological pond B was greater than surface flow wetland B was greater than the subsurface flow constructed wetland was greater than the surface flow wetlands a. Multistage constructed wetland pond system units of NH₄⁺-N removal capacity was subsurface flow constructed wetland was a bit poor, other fairly basic. Various structures processing capacity of the ecological pond B was greater than ecological pond A was greater than the surface flow wetland B was greater than the surface flow wetland was greater than a subsurface flow constructed wetland. The experimental results showed that the removal rate of constructed wetland in the ecological pond was enhanced, and the treatment effect of the multi stage constructed wetland pond system was better than that of the single constructed wetland system.