Experimental Research On Removal Of Nitrogen And Phosphorus In Fanmland Drainage Based On Ecological Aerated Filter

This experiment focuses on the phenomenon that nitrogen and phosphorus in agricultural non-point source pollution enter rivers through farmland drainage ditches,causing water pollution.Two kinds of fillers with good adsorption performance for nitrogen and phosphorus were independently developed,and a new type of aeration ecology was build combined with the indigenous vegetative species with good nitrogen and phosphorus purification effect from farmland drainage ditches and the sponge iron filler developed in the previous research group.The effects and mechanism for the remove of nitrogen and phosphorus in farmland drainage under the new aeration ecological filter also were researched.The system combined the ecological filter,biological aerated filter,and AO process.In this system,through the synergistic action of adsorbent fillers,microorganisms,and plants,the reduce of nitrogen and phosphorus,prevented the migration of nitrogen and phosphorus into water bodies were achieved,so that control the agricultural surface pollution from the intermediate process.The two new types of fillers developed were water-supply sludge-fly ash ceramsite（SLA）and impregnation-calcination modified attapulgite（MA）,respectively.Through the nitrogen and phosphorus adsorption effect experiments on two new types of filters,it was found that the static and dynamic adsorption properties of phosphorus for new SLA were stronger than ordinary ceramsites and zeolites purchased in the market.At the same time,MA had good adsorption properties for nitrogen and phosphorus.Among,the fitting curve of SLA pairs to phosphate adsorption model was in line with Langmuir equation;Phosphorus adsorption by MA was Multi-layer non-uniform adsorption.Characterization of two filler matrices were researched by SEM,XRD,BET,XRF and FTIR.It was found that a dense,glazed structure exists on the outer surface of the SLA.At the same time the surface of SLA was rough,which had many tunnels that penetrate deep into the ceramsite.New phase 3Al₂O₃·2SiO₂ and Ca₃Fe₂（SiO4）₃ were generated during sintering.The part of crystal water in the attapulgite crystals were removed by MA and some of the attapulgite transformed into calcium zeolite.Modification would increase the specific surface area of attapulgite from 70.652 m²/g to 99.273 m²/g.In the test area,farmland drainage ditches of common indigenous plants such as fork tiller,iris,ryegrass,solanum nigrum were relatively well developed.The average removal efficiency of TN from plants at high,medium and low concentrations was iris（78.73%）>ryegrass（72.14%）>solanum nigrum（68.79%）>fork delivery（66.11%）>blank（61.21%）;The removal effect of plants on TP was as follows:ryegrass（88.86%）>iris（84.93%）>solanum nigra（79.70%）>fork delivery（76.73%）>blank（76.13%）.The aerated ecological filter was constructed by the selected fillers and indigenous plants.The plant was completed biofilm cultivation after 19 days of operation,under high dissolved oxygen operating conditions.When the HRT droped from 24 h to 6 h,the effluent water quality of the installation TP could still meet the Class II standard of Surface Water Environmental Quality Standard（GB3838-2002）.When the HRT was 24 h,the average water quality of TN was 8.26 mg/L.When the HRT was 12 h,the average water quality of TN was14.13 mg/L.When the HRT was 6 h,the average water quality of TN was 18.31 mg/L.Based on above results,hydraulic retention time could highly influence the removal efficiency of TN.The research on root microbial populations of plant species introduced in aeration eco-filters was made.It could be found that the most abundant species in plant roots microbial was iris root system,next was ryegrass and solanum nigrum was the least.Besides,the predominant in the root systems of iris and sorrel were high..Aeration biological filter biofilm anaerobic environment of the microbial community richness in general was higher than in aerobic environment,and microbial richness of sponge iron filler in anaerobic environment was higher than SLA.At the same time,the microbial abundance of biofilm on the surface of each filler was more than of naturally occurring microorganisms in natural water bodies.Finally,the predominance of dominant bacteria in sponge iron biofilm in natural water samples and aerobic environment also was high..