Reduction-retention Effect Of Farmland Pollutants Of Artificial Ecological Ponds In Dianchi Watershed

The agricultural non-point pollution have become the key reason that causes the eutrophication of Dian Lake, and the farmland sewage is the primary pollution source. This study focuses on the reduction of farmland sewage. Based on the survey of water retention ponds in Chai River catchment within Dianchi watershed, it’s necessary to conduct the eco-renovation to improve the pollutants removal efficiency of water ponds. In order to find out the optimal combination which had the best pollutants removal effect, we studied the effect of different influent concentration, hydraulic retention time, filler type and thickness of permeable reactive barriers on pollutants removal in the laboratory experiment. Finally the water retention ponds were revamped by the optimal simulation combination and the pollutants reduction effect were monitored. The main results are as follows:(1) The interception of different water retention pond for each pollutant in different month existed differences. The results showed that the interception range of total phosphorus, total nitrogen, nitrate nitrogen, ammonia nitrogen, chemical oxygen demand and suspended solid for each time were4.75g-766.43g,0.13kg-6.19kg,0.12kg-2.84kg,0.68g-542.17g,0.64kg-10.57kg and13.13kg-157.75kg, respectively. The water retention ponds had the ability of self-purification (hydraulic retention time for2days), and the results showed that the average self-purification rate of total phosphorus, total nitrogen, nitrate nitrogen, ammonia nitrogen, chemical oxygen demand and suspended solid were15.02%,11.66%,11.75%,11.51%,10.60%and12.02%, respectively.(2) The ability of pollutant reduction for four kinds of combination (A, B, C, D) in laboratory experiment were as follows:the best combination of reducing total phosphorus was A, and the highest removal rate was40.29%; the best combination of reducing total nitrogen was A, and the highest removal rate was85.89%; the best combination of reducing nitrate nitrogen was D, and the highest removal rate was67.89%; the best combination of reducing ammonia nitrogen was A, and the highest removal rate was85.77%; the best combination of reducing chemical oxygen demand was B, and the highest removal rate was66.92%. Taken together, the best simulation combination for all pollutants was A, considering saving the water space and intercepting more pollutants, thickness of50cm for permeable reactive barriers was chosen in the field.(3) The average removal rate of all pollutants for artificial ecological ponds (hydraulic retention time for2days) were markedly significantly improved than water retention ponds’s.The results showed that the average removal rate of total phosphorus, total nitrogen, nitrate nitrogen, ammonia nitrogen, chemical oxygen demand and suspended solid were35.19%,36.91%,35.01%,40.61%,30.25%and32.17%, respectively. The permeable reactive barriers played an obvious role in pollutant reduction, and the average removal rate of total phosphorus, total nitrogen, nitrate nitrogen, ammonia nitrogen, chemical oxygen demand and suspended solid were13.72%,18.88%,17.63%,18.66%,15.91%and16.40%, respectively.(4) The research on the stability of the artificial ecological ponds showed that as the extension of the test cycle, the average removal rate of total phosphorus, total nitrogen, ammonia nitrogen, chemical oxygen demand and suspended solid became getting slow down, while the average removal rate of nitrate nitrogen remained relatively stable.