Simulation Study On Nitrogen And Phosphorus Removal During The Process Of Longhu Lake Water Transform Into Submerged Water

Water is the source of life,with the world’s environmental pollution problems are increasingly widespread concern,many countries have different degrees of surface water pollution by nitrogen and phosphorus.River bank filtration is a natural purification technology,which have higher removal rate for a variety of pollutants,including nitrogen and phosphorus pollution,many scholars at home and abroad are committed to this research.After years of monitoring,we found that nitrogen and phosphorus in Longhu water seasonal exceed,so this article relies on the "Study on the Longhu Lake River Bank Filtration Key Technology of Jinmen Water Supply Project " to carry out the study area hydrogeological research,summary analysis of the original Longhu water quality characteristics.On this basis,the indoor and outdoor simulation experiments are carried out to study the removal of nitrogen and phosphorus by the diafiltration layer,analyze the influencing factors in nitrogen and phosphorus removal process.And through the construction of hydrogeological concept model,as well as indoor and outdoor experimental to determine the hydrogeological parameters,the use of Visual Modflow4.2 software to establish groundwater flow model,the natural flow field is predicted by the Modflow 2000 module,and the three-dimensional numerical simulation of the groundwater pollutant reaction-migration is carried out by combining the PHT3 D module in the software.predict nitrogen and phosphorus concentrations to provide theoretical basis for the rational exploitation and utilization of water resources in Longhu.The main research results are as follows:(1)The study area is in the coastal plain,abundant rainfall,with marine deposits overlying Yanshan early mixed granite.The structure of natural infiltration layer mainly consists of six layers: plain fill,fine medium sand,medium coarse sand,silt,sandy clay and residual soil.The water permeability coefficient is 0.559~1.137 m/d,which belongs to the weak permeable layer.(2)The water quality characteristics of Longhu water quality analysis showed that Longhu was in space relative to the east west water quality better,seasonal variation of TP concentration: spring > summer > autumn > winter,seasonal variation of ammonia concentration: spring > summer > winter > autumn;source structure from the perspective of pollution,the main pollutants influence water source protection area is rural life pollution,farmland planting pollution and livestock pollution.The total discharge of wastewater in Longhu water source protection area is 57 thousand and 800 t,the total amount of COD emission is 15.74 t,the total ammonia nitrogen discharge is 3.59 t,the total nitrogen emission is 9.95 t,the total phosphorus discharge is 1.11 t.(3)The experimental results of nitrogen and phosphorus removal during the process of Longhu lake water transform into submerged water shows: the interaction process of ammonia nitrogen by adsorption and precipitation,ion exchange,nitrification and denitrification in the infiltration layer,phosphorus removal mainly depends on precipitation and adsorption.There are two reasons why the effluent concentration is higher than that in Longhu.The concentration of nitrogen and phosphorus in groundwater is higher,and the nitrogen and phosphorus concentration in the sludge is higher.(4)The experimental results show that the diffusion coefficient of soil column(percolation layer)is 6.6cm2/h.The soil column height,influent concentration,infiltration layer structure for nitrogen and phosphorus removal in the process of the most important factors,which influence the maximum infiltration layer structure,when it is added to the soil,nitrogen and phosphorus removal efficiency of soil column was good.(5)Through the establishment of hydrogeological conceptual model,the three-dimensional numerical simulation of nitrogen and phosphorus reaction and migration is carried out:1)In the next 20 years,the water level in the mainland has changed little,and it has remained stable.2)By simulation and prediction,the ammonia concentration decreased to 0.06mg/L after four months with a standard with the Longhu groundwater,surface water concentration is 0.01mg/L,TP in four months when the concentration is 0.158mg/L,meet the four criteria of surface water,and the water table in Longhu is 0.013mg/L and the filtration layer on nitrogen and phosphorus removal but,because of the high content of nitrogen and phosphorus silt layer,the whole of Longhu surface water nitrogen and phosphorus removal.3)Due to the common effect of hydrodynamic dispersion and wells,resulting in nitrogen and phosphorus transfer in each direction of the aquifer,with water and nitrogen and phosphorus in the aquifer,groundwater migration by orthogonal direction control,nitrogen and phosphorus migration and groundwater level on the whole line,the direction of transport in groundwater and groundwater movement direction.4)The effects of different lithology,permeability and different position on the nitrogen and phosphorus transport,resulting in the uneven distribution of nitrogen and phosphorus in the vertical direction.