| At present,in most magnetic coagulation experiments,magnetic field is only used to strengthen the magnetism of magnetic powder or to separate magnetic powder from residual sludge by magnetic attraction in the process of separation and recovery of magnetic powder.In this study,the magnetic field will be used in the process of magnetic coagulation reaction to explore the influence of the existence of external magnetic field on magnetic coagulation effect.It is mainly divided into two stages of investigation,namely,adding external magnetic field in the stirring stage of magnetic coagulation and adding external magnetic field in the sedimentation process of flocs.By taking turbidity removal rate as the main reference standard,the influence of external magnetic field on the effect of magnetic coagulation treatment is compared.In this thesis,the sewage wastewater collected by the secondary water station of a university in Z city was taken as the experimental raw water,and the differences between conventional coagulation treatment and magnetic coagulation treatment were compared to explore the optimal reaction conditions under different conditions.The influence of hydraulic conditions,coagulant,flocculant,dosage order,particle size of magnetic powder,dosage of magnetic powder,standing time and other influencing factors on the removal rate with turbidity as the main index was investigated.On this basis,external magnetic field conditions are set to accelerate the sedimentation rate of the flocs with magnetic powder as the core,so as to improve the overall treatment efficiency.The specific research results are as follows(1)Compared with conventional coagulation,magnetic coagulation can effectively reduce the residual rate of pollutants in water after coagulation treatment,reduce the use of drugs,shorten the time of coagulation treatment,and improve the efficiency of the overall process.(2)For the treatment of sewage wastewater with turbidity around 220 NTU,the optimal reaction hydraulic conditions for coagulation are fast stirring strength of300r/min for 2min,slow stirring strength of 60r/min for 8min,using PAC as coagulant and PAM as flocculant.In magnetic coagulation,when the turbidity of raw water is about 220 NTU,the optimal dosage of magnetic particle is 75mg/L,and the particle size of magnetic particle is about 300 mesh.The best additive order was magnetic particle + coagulant polyaluminum chloride + flocculant polyacrylamide,that is,adding magnetic seed at 300r/min fast stirring condition for 2min,adding PAC at 300r/min fast stirring condition for 1min,and then adding PAM at 300r/min fast stirring condition for 1min.Finally,it was changed to slow stirring at 60r/min for8 min.(3)The existence of external magnetic field effectively improves the efficiency of magnetic coagulation treatment.When the external magnetic field intensity reaches0.004 t and the settling time is 8min,the effect of settling time is 10 min without the external magnetic field,which effectively reduces the time consumption of the whole magnetic loading coagulation treatment and improves the treatment efficiency.In the sedimentation process of flocs,the external magnetic field accelerates the sedimentation of flocs,shorts the time of the whole treatment process,and improves the efficiency of the whole process.(4)The external magnetic field(gravity downward)has different effects on the coagulation effect of magnetic particle particles with different particle sizes.Compared with magnetic particle particles with smaller particle sizes,magnetic particle particles with larger particle sizes are more significantly affected by the external magnetic field,and magnetic particle particles with larger particle sizes receive greater attraction in the magnetic field.Therefore,the flocs with magnetic powder particles as the core of flocculation can settle at a faster speed,and it is easier to cause the rupture of flocs and the rise of turbidity of effluent water due to the rapid sedimentation speed.Adding external magnetic field(gravity downward)and changing the size of magnetic field during the stirring process of magnetic coagulation treatment has no significant influence on the effect of magnetic coagulation treatment.(5)When the gravity of the external magnetic field up to the processing effect of particle size larger magnetic powder particles by certain ascension,this is due to the gravity and magnetic powder itself part of the upward gravity offset each other,not easy to make size larger magnetic particles because of its large proportion in when it did not fully to collide with the suspended particles sink to the bottom of the beaker,To a certain extent,the utilization rate of magnetic powder is improved and the effect of magnetic coagulation is improved.However,the external magnetic field in the upward direction of gravity has little influence on the coagulation effect of magnetic particles with smaller particle size,which can be ignored. |
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