Research On The Key Technology Of Nitrogen And Phosphorus Interception In Farmland Ecological Ditch

The interception technology of nitrogen and phosphorus in farmland ecological ditch is one of the agricultural non-point source pollution control technologies.It can effectively intercepts nitrogen and phosphorus in farmland sewage flowing through ditches by artificially transforming the original farmland ditches and installing plants and other auxiliary measures on the ditch bottom and slope protection.Although the current farmland ecological ditch has achieved good nitrogen and phosphorus interception effect,the common farmland ecological ditch slope protection plants are mostly plants growing in summer,which often wither in autumn and winter,resulting in the poor decontamination effect of the farmland ecological ditch anniversary.In addition,the sediment of farmland ecological ditches is an important way to remove phosphorus,but it has been saturated by long-term adsorption,so it is difficult to effectively intercept and remove the high load phosphorus formed by the runoff in the early stage of rainfall,resulting in the phased excessive phosphorus sewage discharge.In this study,Phragmites australis and Phalaris arundinacea were selected to construct the slope protection composite plant community of farmland ecological ditch due to they were separated in time niche(i.e.growth cycle)to explore the complementary decontamination characteristics of the two plants on an annual basis.In addition,aerated concrete with strong phosphorus adsorption capacity is selected as the filling material of farmland ecological ditch to explore its adsorption characteristics in high phosphorus water at the beginning of rainfall and desorption characteristics in low phosphorus water at the end of rainfall,namely "sponge effect".In addition,the above two key technology demonstrations are applied to the farmland ecological ditch,and the effect in practical application is tested by comparing with the conventional ecological ditch.Through the above research,the aim is to solve the problem of poor annual decondution effect in the former farmland ecological ditches and the problem that phosphorus often appears in the farmland ecological ditches in the early period of rainfall is difficult to meet the discharge standards,so as to realize some key technological breakthroughs of nitrogen and phosphorus interception in the farmland ecological ditches to a certain extent.The main research results of this paper are as follows:(1)The annual dynamics of ammonia nitrogen,total nitrogen and total phosphorus removal were significantly different between Phragmites australis and Phalaris arundinacea.Among them,the annual dynamic of removal effect of ammonia nitrogen,total nitrogen and total phosphorus in Phragmites australi presented a symmetrical unimodal curve,and the peak appeared in July;the annual dynamics of removal effects of ammonia nitrogen,total nitrogen and total phosphorus of Phalaris arundinacea were asymmetrically bimodal curve,with the main peak and secondary peak appearing in April and November respectively.At the same time,the removal efficiency of ammonia nitrogen and total nitrogen of Phragmites australis was better than that of Phalaris arundinacea from June to October,while that of Phalaris arundinacea from January to May and from November to December was better than that of Phragmites australis;the total phosphorus removal efficiency of Phragmites australis was better than that of Phalaris arundinacea to December,while Phalaris arundinacea was better than Phragmites australis only in January to May.To sum up,Phragmites australis and Phalaris arundinacea have strong annual complementary decontamination.The introduction of Phalaris arundinacea and Phragmites australis to construct complex plant community can make up for the defect of single Phragmites australis in the annual removal effect of nitrogen and phosphorus,which is shown as Phalaris arundinacea in January to May and November to December to make up for the removal effect of ammonia nitrogen and total nitrogen in Phragmites australis,and in January to may to make up for the removal effect of total phosphorus in Phragmites australis.(2)In high phosphorus concentration water,aerated concrete has obvious adsorption effect on phosphorus,and the adsorption amount of aerated concrete is highly positively correlated with the concentration of phosphorus in water.And in low phosphorus concentration water,aerated concrete has obvious desorption effect on phosphorus,and the desorption amount of aerated concrete is negatively correlated with phosphorus concentration in water.At the same time,with the continuation of the experiment,the adsorption rate and desorption rate of aerated concrete both decreased continuously,and the initial adsorption and desorption played a dominant role in the whole adsorption and desorption process.In addition,aerated concrete has a good continuous adsorption and desorption effect.In the three continuous 120 h adsorption cycles,the adsorption amount of aerated concrete decreases slightly with the increase of the adsorption period,but there is no significant difference between the three continuous 120 h adsorption cycles.In the treatment of three continuous 48 h desorption cycles,the desorption amount of aerated concrete decreases gradually with the increase of desorption period,and the desorption amount of three continuous 48 h desorption cycles is significantly different.(3)By comparing the demonstration ditch with the control ditch,it is found that there is indeed an annual complementary characteristic of the Phragmites australis-Phalaris arundinacea composite plant community for the decontamination of the ecological ditch.At the same time,using the sponge effect of phosphorus adsorption desorption of aerated concrete can also effectively reduce the instantaneous peak of phosphorus load at the beginning of rainfall.Therefore,the two key technologies proposed in this study are not only scientific and reasonable in static test,but also effective in practical application.