Effect Of Magnetic Flocculation-adsorption Combined Process To Remove Nitrogen And Phosphorus In Polluted River Water

In recent years,with the discharged of some domestic sewage and industrial wastewater,many rivers had suffered varying degrees of pollution.In order to solve the main nitrogen and phosphorus problems in river pollution,the adsorbent PAZ hydrogel beads were prepared to adsorb ammonia nitrogen,and the adsorption-magnetic flocculation combined process was used to remove the ammonia nitrogen and total phosphorus in the polluted river water,and the best adsorption conditions,the regeneration,dynamic adsorption and modification of adsorbents were studied.Finally,the magnetic flocculation products and adsorbents before and after adsorption were characterized,and the mechanism of adsorption and magnetic flocculation were discussed.The main conclusions of this research are as follows:（1）PAZ hydrogel were prepared by using polyvinyl alcohol,sodium alginate and micron zeolite,the main components of which are Si,O,Al,Ca and Na,the highest content is O and Si.The ratio of silica to aluminum of PAZ hydrogel and micron zeolite powder is basically the same The PAZ hydrogel contains a large number of pores,which provides convenient conditions for the adsorption of ammonia nitrogen.FTIR and XPS proved that PAZ hydrogel beads contained a large number of functional groups,and the micron zeolite was successfully encapsulated.PAZ-20 is a mesoporous material determined by BET,with a specific surface area of 9.8 m²·g^-1,a pore volume of 0.0593 cm³·g^-1,and an average pore diameter of 10.01 nm.XRD proved that the zeolite used in the experiment was mainly calcium clinoptilolite,and the addition of PVA/SA did not affect the crystal structure of micron zeolite.（2）When the adsorbent dosage of PAZ-20 is 10 and 20 g·L^-1,the ammonia nitrogen removal rate was 80.5%and 97.7%,respectively.When the p H increased from 3 to 8,the removal rate of ammonia nitrogen did not change significantly.The removal rate of ammonia nitrogen increased from 9 to 11,and the removal rate of ammonia nitrogen decreased with the increase of p H.When the water temperature increased from 5℃to 25℃,the removal rate of ammonia nitrogen increased significantly with the increase of water temperature;when the water temperature increased from 25℃to 35℃,the removal rate did not change much;when the temperature increased from 35℃to 40℃,the removal rate of ammonia nitrogen began to decline.The adsorption capacity of PAZ-20 for cations in water was K⁺>Mg²⁺>Na⁺>Ca²⁺.The degree of influence of coexisting cations on PAZ adsorption of ammonia nitrogen was K⁺>Na⁺>Ca²⁺>Mg²⁺.The permanganate index in the range of 50～300 mg·L^-1 had no significant effect on the adsorption of ammonia nitrogen by PAZ-20.PAZ-20 regenerated by Na OH once had a removal rate of 73.4%,70.2%after the second time,and 66.2%after the third time,which proved that PAZ-20 has a good regeneration capacity.The best conditions for dynamic adsorption of PAZ-20 were the inlet flow rate of 5 m L·min^-1 and the dosage of PAZ-20 of 300g.High temperature modification could increase the ammonia nitrogen removal rate of PAZ-20.The best modification conditions were the modification temperature of 400℃and the modification time of 2 h.（3）The best flocculant in this experiment was PAC.PAC had the highest total phosphorus removal rate and the volume of flocs is larger and more fluffy.The best conditions for the magnetic flocculation single factor experiment were PAC dosage of 90 mg·L^-1,PAM dosage of2 mg·L^-1,magnetic seed dosage of 80 mg·L^-1,and precipitation time of 8 min,fast stirring speed300 r·min^-1,slow stirring speed 100 r·min^-1,fast stirring time 2 min,slow stirring time 5 min and the order of dosage of flocculant+magnetic seed+coagulant.After orthogonal experiment optimization of the dosage of medicament,the best dosage of medicament was 105 mg·L^-1 PAC,2.5 mg·L^-1 PAM and 80 mg·L^-1 magnetic seed.Adsorption-magnetic flocculation combined process was used to treat simulated river water.The optimal conditions were 5 m L·min-1influent flow rate and 300 g PAZ-20 dosage.At this time,the penetration time of the adsorption column was 63 h and the total phosphorus removal rate all were above 90%.The adsorption-magnetic flocculation combined process was used to treat the actual river water,the penetration time of the adsorption column was 57 h,and the total phosphorus removal rate was greater than90%,which had a good ammonia nitrogen and total phosphorus removal rate for the actual river water.（4）The quasi-two-stage kinetic model and Langmuir adsorption isotherm model could better fit the process of PAZ hydrogel adsorption of ammonia nitrogen,and the theoretical maximum adsorption capacity was 4.44 mg·L^-1.The 1/n range was between 0.1 and 0.5,and the adsorption process of ammonia nitrogen was an easy adsorption process The results of adsorption thermodynamics showed that the adsorption of ammonia nitrogen by PAZ water beads was a spontaneous process,and the entropy of the adsorption process increased,and increasing the temperature is beneficial to the progress of the adsorption.The results of FTIR and XPS showed that PAZ-20 successfully adsorbed ammonia nitrogen,the content of Na decreased significantly after the adsorption of ammonia nitrogen,and the hydroxyl group participated in the process of adsorbing ammonia nitrogen.The results of SEM and FTIR showed that the flocs formed by PAC and PAM were encapsulated with magnetic seeds during the floc settling process,and the flocs contained a large number of functional groups,which was helpful for the process of magnetic flocculation and phosphorus removal.