Application Of Constructed Wetland In Deep Removal Of Nitrogen And Phosphorus From Tail Water,based On The Process Of Iron Migration And Transformation

The decrease of phosphorus adsorption capacity and the lack of denitrifying carbon source are the problems of the deep denitrification and phosphorus removal in artificial wetlands.Wetlands of iron rich matrix material under the action of fe oxides in iron reducing bacteria can be organic reduction and dissolution in the form of ferrous,ferrous in ferrous oxidation under the action of nitrate reducing bacteria can be used as electron donor to nitrate nitrogen reduction of nitrogen,and ferrous oxidation to form again ferric iron particles on phosphorus has strong adsorption,so the process has the potential of nitrogen and phosphorus.In this paper,based on the migration characteristics of iron matrix,trying to build new partition type constructed wetland system,use of iron rich matrix materials and wetland plant debris build iron reduction dissolution area,using conventional packing to build sewage treatment area,the ferrous iron reduction zone of anaerobic reaction and part of the soluble organic carbon by reflux input processing area,used for treatment of nitrogen and phosphorus,and thus realize the artificial wetland nitrogen phosphorus removal ability of continuously updated.The construction,operation parameters and processing mechanism were systematically studied by using small test system and artificial simulated wastewater.The main results are as follows:(1)In the partition type constructed wetland system,processing zone bed body A tail of phosphorus in water and nitrate nitrogen removal characteristics is shown as: run startup period,phosphorus removal rate is low,with increasing gradually achieve stability,after and nitrate nitrogen removal is the highest starting period,after gradually decline.In this study the experiment condition,the start-up water total phosphorus concentrations below 0.4 mg/L,can reach the surface water environment quality standard "Ⅴ class standard,stability stable discharging total phosphorus concentration can maintain below 0.3 mg/L,achieve the Ⅳ class standard of surface water environment quality standard.Nitrate nitrogen effluent concentration remained under 10 mg/L only within 60 days.(2)In the partition type constructed wetland system,reduction zone bed body B can dissolve out plenty of ferrous and organic compounds,including the dissolution of ferrous continuity,but the concentration of dissolution,fluctuated change characteristic,the start-up dissolution peak is the largest,followed by gradually reduce volatility,stripping concentration tends to be stable,this study under the experimental conditions,concentration of ferrous dissolution can be maintained for a long time in 40 mg/L.The dissolution process of organic matter is a single peak,in the start-up of stripping quickly achieve stripping peak,and then quickly fell sharply,maintain in low concentration,after this study under the experimental conditions,organic dissolution in the early 2500 mg/L,after 30 days down to 500 mg/L.(3)For processing area gravel substrate surface sediment flocs fe deposit and its valence variation analysis results show that the direct precipitation and its partially oxidized ferrous formed after the adsorption effect of ferric iron oxide particles is the mechanism of action of tail water phosphorus removed,iron oxides accumulated gradually long running system to make total phosphorus removal rate is increased to stable.Nitrate nitrogen efficient removal of tail water mainly depends on a lot of dissolution of heterotrophic denitrifying process of soluble organic matter,organic matter decreases,based on the input ferrous oxide denitrification process of nitrogen removal rate is low,mainly due to the low concentration of ferrous dissolution is not enough to support a high concentration of nitrate nitrogen reduction.Therefore,increasing the proportion of iron matrix in the fillers can obviously increase the dissolution of ferrous iron,thus improving the removal efficiency of nitrogen and phosphorus.At the same time,in the process of system operation,the addition of solid carbon source in b-bed dissolution area increases the dissolution of organic matter,and also promotes the removal of nitrate nitrogen.(4)In the long run of the system,the subiron dissolving load of the brick-red soil of rich iron matrix remained stable between 10 and 60 mg/(kg·d),and the lower the mixing ratio,the higher the dissolving load of ferrous metal.System running 150 days for a long time,total iron in the laterite dissolution rate is only about 4.86%,shows that laterite still has the very high utilization rate,with the rich in iron oxide laterite as matrix of artificial wetland system,the system can well run continuously.(5)The long running system has a higher removal rate for the low-concentration heavy metal Zn,Pb and Cd in the tail water,which can achieve the "surface water environmental quality standard".It indicates that the system has long run,and the large amount of iron oxide attached to the substrate surface has good adsorption and removal ability for heavy metals.