Research On Purification Effect Of Fe Layered Double Hydroxides Film Modified Substrate For Sewage Treatment

Constructed wetland technology is a new type of ecological treatment technology,which has low operation cost and simple operation,and is more suitable for the treatment of domestic sewage in rural areas.But in the process of constructed wetland,the substrate is easy to saturate.In order to solve the problem of matrix saturation,4 kinds of Fe LDHs（layered double hydroxides）were used to modify the sintered porous brick and zeolite.The adsorption kinetics model was used to explore the adsorption rate and adsorption equilibrium ability of the matrix,and the best modified matrix was selected to operate simulated vertical flow artificial wetting it is order to find the influence of LDHs modified matrix on the purification efficiency of domestic sewage.On this basis,experiment designs five groups of different hydraulic load simulation constructed wetland.So as to optimize the operation parameters of hydraulic load,and provide a theoretical basis for the construction of vertical flow constructed wetland system for rural domestic sewage.The results show that:（1）Through the LDHs film modification,change the surface roughness and internal structure of the matrix.The SEM spectra showed that the surface adherent materials of Ca-Fe sintered porous brick and Mg-Fe zeolite were more obvious.（2）The adsorption capacity of ammonia nitrogen is in turn:Mg-Fe zeolite>Ca-Fe zeolite>Co-Fe zeolite>Zn-Fe zeolite>zeolite>Ca-Fe sintered porous brick>Co-Fe sintered porous brick>Mg-Fe sintered porous brick>Zn-Fe sintered porous brick>sintered porous brick and the removal rate is at 73.36%⁹8.27%.Through the Langergren dynamic model,Ca-Fe sintered porous brick’s adsorption rate is the fastest and the actual equilibrium is balanced.The adsorption capacity is 0.2261 mg/g.The maximum equilibrium adsorption capacity of Mg-Fe zeolite is 0.2948 mg/g.（3）The adsorption amount of total phosphorus before and after the matrix modification is as follows:Ca-Fe sintered porous brick>Co-Fe sintered porous brick>Mg-Fe sintered porous brick>Zn-Fe sintered porous brick>sintered porous brick>Zn-Fe zeolite>Mg-Fe zeolite>Co-Fe zeolite>Ca-Fe zeolite>zeolite.The removal rate of sintered porous bricks before and after modification was 93.12%⁹8.06%,and the removal rate of zeolite before and after modification was 27.80%⁴2.02%.Through the Langergren dynamic model,the Ca-Fe sintered porous brick reaches the adsorption equilibrium in the shortest time,the adsorption rate is the fastest,and the actual equilibrium adsorption capacity is 0.0735 mg/g.The equilibrium adsorption capacity of Mg-Fe zeolite was the highest.（4）4 groups of simulated vertical flow constructed wetland systems were designed,which were R1（sintered porous brick loading）,R2（Ca-Fe sintered porous brick loading）,R3（sintered porous brick and zeolite 1:1 loading）,R4（Ca-Fe sintered porous brick and Mg-Fe zeolite 1:1 loading）.No blockage occurred during the operation,and TP,NH₄⁺-N,NO₃^--N,TN and COD all achieved a certain purification effect.R2 and R1,R4 and R3,the modified substrate composed of vertical flow constructed wetland for the removal of the above pollutants has been improved.Among them,the R4 system has the best removal effect on pollutants.The average effluent concentration of TP,NH₄⁺-N,TN and COD is0.50 mg/L,1.4 mg/L,17.44 mg/L and 57.63 mg/L respectively.The effluent concentration of TP and NH₄⁺-N meet the first grade standard of the pollutant discharge standard（mg/L）of the urban sewage treatment plant.COD and TN meet the first level B standard,which generally reaches the first level B standard.（5）Five groups of Ca-Fe sintered porous brick and Mg-Fe zeolite 1:1 loaded vertical flow constructed wetland system were SW1,SW2,SW3,SW4 and SW5 respectively.The hydraulic loads were 0.05 m/d,0.11 m/d,0.21 m/d,0.32 m/d and 0.42 m/d.The result showed that the smaller the hydraulic load,the better the removal effect.In order to meet the urban sewage discharge standard,the hydraulic load reaches 0.11m/d can meet the first class A standard,the hydraulic load is 0.21 m/d can reach the first grade B,the hydraulic load is 0.32 m/d sewage discharge meet the two grade standard.（6）According to the situation of the rural population and each family is calculated by4 people,each person produces a 50 L of sewage per day.According to the requirements of the sewage discharge,if you want to reach the two level of discharge standard,you need to select the 0.32 m/d operating load.The area of the vertical flow constructed wetland system should be set to 0.625 m2;if you want to reach the first grade B standard you need to elect the 0.21 m/d running load,which needs to set the vertical flow constructed wetland system area to 0.95 m2;if you want to reach the first level A standard,select the 0.11 m/d running load,which needs to set the vertical flow constructed wetland system area to 1.82m2.To sum up,modification of Fe LDHs film improves the adsorption saturation of the original matrix itself,thus improving the purification efficiency of the pollutants in the sewage.By screening the optimal matrix ratio,the ability of the artificial wetland system to treat sewage is enhanced,which is suitable for the treatment of rural domestic sewage.