Nitrogen And Phosphorus Discharging Patterns And Adsorption Measures Study On Farmland Drainage Ditch In Tianjin

In recent years,the agricultural nitrogen and phosphorus non-point pollution has become more and more terrible.Farmland drainage ditch as an important channel for the loss of nitrogen and phosphorus in agricultural land is an important way of agricultural non-point source pollution to spread.Tianjin has a long history of rice cultivation,and the problem of agricultural non-point source pollution is increasing terrible year by year.Therefore,it is necessary to master the migration and transformation of nitrogen and phosphorus in farmland drainage ditch and it is urgent to evaluate the water quality of farmland drainage ditch accuratly and objectively.On this basis,a composite adsorbent composed of modified zeolite and diatomite is proposed to provide theoretical support for agricultural non-point source pollution control.A typical farmland drainage ditch of Xiaozhan town of Jinnan district of Tianjin in the Haihe River Basin was chosen,the nitrogen and phosphorus concentration as well as the migration and transformation regulation of sediment-interstitial water-overlying water in the farmland drainage ditch was carried out.What's more,the water quality was evaluated by the identification index method which based on fuzzy logic;Finally,selecting one adsorbent material with a maximum adsorption of nitrogen from Zeolite,NaCl-modified zeolite and hot-modified zeolite by the indoor experiment,and the composite adsorbent material was obtained by the mixing of this adsorbent material and diatomite,and made a plan for the field application.The results suggested that:?1?The concentration of nitrogen and phosphorus decreased along the time and showed a slight decrease trend along the direction of the channel flow.The nitrogen was mainly in the form of NH₄⁺-N,which the NO₃^--N was less;?2?Under the condition without rainfall,the sediment adsorbed nitrogen and phosphorus in the early stage of rice growth,and released it through the interstitial water in the later stage of rice growth.The nitrogen and phosphorus concentration of the interstitial water was significantly higher than that of the overlying water,the nitrogen and phosphorus concentration of the interstitial water was about 3.1 and 6.5 times of that in overlying water;?3?In the condition of rainfall,the ditch sediment becomes the source of nitrogen and phosphorus,and the nitrogen and phosphorus in the sediment gradually migrate to overlying water in the form of NH₄⁺-N;the TN concentration in the overlying water is about 3.45 times of the PN?granular TN?,The concentration of TP is about 1.45 times of the PP?granular TP?,and granular nitrogen and phosphorus is the main loss of nitrogen and phosphorus in overlying water;?4?Based on the fuzzy logic identification index water quality evaluation method,it can be seen that the comprehensive water quality of the drainage is far lower than the water quality requirement of the farmland drainage;?5?The adsorption capacity of Natural zeolite,NaCl-modified zeolite and hot-modified zeolite were hot-modified zeolite?NaCl-modified zeolite?natural zeolite as followed;?6?The composite adsorbent was mixed by the hot-modified zeolite and diatomite according to 2:3.The removal rate of nitrogen and phosphorus for this compound adsorbent was 92.07%and 84.61%respectively.