| At present,due to the construction of sewage treatment plants,urban drainage network transformation and comprehensive rivers regulation has lagged far behind in some cites in China,directly discharge of municipal wastewater into surface water lead to an increase of pollution indicators,even the drinking water source is polluted,which affects the safety of cities' drinking water.Sewage treatment should not be missed and should note be delayed.In this case,the emergency treatment of sewage is put on the stage,that is,to undertake the responsibilities of sewage treatment plant in a short time,which can temporarily guarantee the effective treatment of municipal domestic sewage.For the wastewater emergency treatment,the treatment process not only requires that it can effectively reduce most of the pollutants in the waster water,but also has the advantages of low cost and small floor area.Although the cost of conventional coagulation and sedimentation method can barely meet the requirements,the removal effect of main pollutant indexes and excessive floor area of sedimentation tank are often unsatisfactory.Magnetic coagulation and sedimentation technology has the advantages of strong removal effect,low cost,and reducing the floor area of sedimentation tank.It has a broad prospect in the emergency treatment of municipal domestic sewage.In this paper,through the mechanism analysis of particle collision efficiency and floc settling speed in the process of coagulation,the change of particle collision efficiency and floc settling speed after loading magnetic powder is investigated,and it is determined that magnetic loading coagulation can effectively improve the coagulation effect and settling performance compared with conventional coagulation,and it is demonstrated through the small-scale test.On this basis,the optimal dosage of coagulant,flocculant and magnetic powder,as well as the optimal particle size and optimal sequence of dosing are determined.Through the actual operation control of the magnetic loading coagulation and inclined plate precipitation facility,the above influencing factors are further optimized.At the same time,the turbidity of the inclined plate sedimentation tank at different depths under different load conditions is investigated,which provides theoretical basis for further optimization of sedimentation tank.The specific research results are as follows:(1)Through the analysis of the impact of the difference between magnetic loading force and settlement on the collision efficiency of particles,it was concluded that magnetic loading coagulation could improve the coagulation effect by improving the collision efficiency between particles.The results showed that the removal rates of turbidity,COD and TP were94.25%,58.67 and 88.24% respectively.Compared with conventional coagulation,the removal rates of the above three pollutants were increased by 6.13%,11.41% and 3.93%respectively.It was confirmed that magnetic loading coagulation could effectively improve the coagulation effect.(2)Through the analysis of the influence of the specific gravity,the conclusion that the magnetic loading coagulation could increase the settling speed of the flocs was obtained.The results showed that the average settling rate of conventional flocculation flocs was2.43×10-3m/s,and the average settling rate of magnetic loaded flocculation flocs was6.62×10-3m/s.Compared with conventional coagulation,the settling rate of magnetic loaded flocculation flocs was about 3 times of that of conventional coagulation flocs.(3)According to the laboratory test,the optimum dosage of PAC,PAM and magnetic powder were determined respectively were 250,1.5 and 200mg/L respectively,and the optimal particle size was 45?m,and the optimal sequence was “magnetic+ PAC+ PAM”.The removal of turbidity,TP and chroma by magnetic coagulation is the most obvious,the removal rates are over 94%,87% and 91% respectively,and the removal of COD are also effectively improved,reaching over 54%.However,magnetic coagulation can not be separated from the scope of physical and chemical treatment,the removal of total nitrogen and ammonia nitrogen was not satisfactory,only reached 43% and 20% respectively,even so,compared with conventional coagulation,it has been greatly improved;(4)Through the actual operation control of a set of “magnetic coagulation + inclined plate sedimentation tank” process equipment,the optimal dosage of PAC,PAM and magnetic powder was further optimized,which were 300,2 and 200mg/L respectively.The change of turbidity at different depth of sedimentation tank under different load was investigated,the maximum load of inclined plate sedimentation tank was 6.07m3/m2·h under the condition of ensuring the optimal effluent quality.This study further enriches the theory of magnetic coagulation and sedimentation technology,and provides a series of process optimal control parameters,which provides acertain reference and design basis for the subsequent application of magnetic coagulation and sedimentation technology in municipal domestic sewage treatment and sewage treatment with different components. |
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