A Study On The Properties Of Magnetized Activated Sludge

The test was based on the activated sludge method.It aimed to produce magnetized activated sludge by adding strong magnetized powder materials（magnetic medium,Fe₃O₄）that can be combined with activated sludge flocs,and it could increase the proportion of the sludge which can lead to the activated sludge flocs having the characteristics of being induced by the magnetic field.Magnetized active sludge was also used in the SBR process to strengthen the precipitation performance of activated sludge,in order to increase the concentration of sludge and reduce the load of sludge,as well as enhance the sewage treatment effect in the reactor,which provides a new idea for strengthening the SBR process.In this paper,the characteristics and application prospects of the magnetized activated sludge were explored through the beaker-grading cylinder test and the small-scale test to treat high-concentration rice water.The main conclusions are as followed:（1）Through the beaker-grading cylinder test,this paper determined the settling performance of activated sludge and magnetized activated sludge within 10 minutes which based on the sludge concentration of each gradient.It analyzed the influence of magnetic powder concentration and different magnetic powder specifications on the sedimentation performance of the sludge,as well as the influence of the change of the sludge concentration on the sedimentation performance of the magnetized activated sludge.The results show that when the sludge concentration and the magnetic powder specification were constant,the settling performance of the magnetized activated sludge was getting better with the increase of the magnetic powder concentration,e.g.MLSS=2000mg/L,5μm magnetic powder concentration,when the magnetic powder concentration is 2000mg/L,the sludge volume after 10min in the blank was reduced by 32.81%.When the magnetic powder concentration and the magnetic powder specification were constant,the settling performance of the magnetized activated sludge becomes worse to settle with the increase of the sludge concentration,e.g.magnetic powder concentration of 2000mg/L,5μm magnetic powder,when the sludge concentration is 7000mg/L,the volume of sludge after 10min in the blank was only reduced by 7.14%.When the magnetic powder concentration and the sludge concentration were constant,as the size of the magnetic powder changes,which means as the increase of the particle size of the magnetic powder,it was beneficial to the settlement of the magnetized activated sludge that the settlement law corresponds to the Stokes settling velocity formula,e.g.MLSS=3000mg/L and magnetic powder concentration of 2500mg/L,the volume of sludge with magnetic particle size of 30μm was reduced by 16.28%compared to the sludge with a magnetic particle size of 5μm.（2）Determine the magnetic powder specifications and magnetic powder concentration by testing the removal rate of each index of the effluent water.The test results show that the average treatment rate of COD in the magnetic powder A₅test was 97.47%,the average treatment rate of NH₄⁺-N in the magnetic powder A₅test was 92.05%,and the average of the TP in the magnetic powder A₅test was 51.42%;the average treatment rate of COD in the magnetic powder B₃₀test was 97.80%,the average treatment rate of NH₄⁺-N in the magnetic powder B₃₀test was 95.18%,and the average treatment rate of the TP in the magnetic powder B₃₀test was 68.29%.The removal efficiency of COD and NH₄⁺-N in the magnetic powder A₅test and the magnetic powder B₃₀test was equivalent,and the TP removal efficiency of the magnetic powder B₃₀test is better than that of the magnetic powder A₅test.It was because that the particle size of the magnetic powder B was smaller than that of the magnetic powder A,which had larger specific surface area.This was more conducive to combine with bacterial micelles,and provided more beneficial areas to the exchange of microbial substances,thus the magnetized activated sludge had better effect of magnetization and better pollutants removal efficiency than the magnetic powder A₅test.Overall,the magnetic powder B of 30nm specification was a better choice.After four groups analysis,when the magnetic powder concentration is 4000mg/L,the removal efficiency of COD and NH₄⁺-N was slightly better than that when the magnetic powder concentration was 2000mg/L;the removal efficiency of TP was not as good as that of magnetic powder when the concentration is 2000mg/L,the TP removal rate of A₅test differs by 12.24%,and the TP removal rate of B₃₀test differs by 28.94%,indicating that under this concentration gradient,the magnetic powder inhibited the growth of microorganisms and the activity of activated sludge,and it also had the influence on removal rate of TP.Therefore,the magnetic powder dosage of the magnetized SBR process in this test is 8g,which means the magnetic powder concentration was 2000mg/L.（3）According to the comparison between traditional SBR process and magnetized SBR process,in terms of the removal effect of COD and NH₄⁺-N,the removal rate of magnetized SBR process was 93.96%and 93.52%,which is better than 88.97%and 88.80%of traditional SBR process.In terms of removal effect of TP,the removal rate of the traditional SBR process was 69.44%,which is better than the58.73%of the magnetized SBR process.In terms of removal effect of TN,the removal rate of the magnetized SBR process was equivalent to that of the traditional SBR process,which was 74.61%and 72.75%,respectively.After adding magnetic powder,it can promote the decomposition and absorption of organic matter by activated sludge,and increase the concentration of sludge.Magnetized activated sludge had higher MLSS and MLVSS,which reduced the sludge load,increased the proportion of sludge,and improved the settling performance,which means SV₃₀reaches more than 70%and MLSS reaches about 9500mg/L,the reactor can operate normally under the conditions of processing high-concentration canteen rice-washing sewage.（4）There are different sewage treatment effects under different operating conditions,and the influencing factors were various,conditions（1）:inlet water 2min→stirring and aeration 5h→static precipitation 30min→effluent water 30s;condition（2）:Inlet water 2min→stirring and aeration 4h→static precipitation 30min→effluent water 30s;condition（3）:2min water in the water→stirring 2h→stirring and aeration 4h→static precipitation 30min→effluent water 30s.The specific performance was COD removal efficiency:condition（1）>condition（3）>condition（2）;NH₄⁺-N removal efficiency:condition（3）>condition（1）>condition（2）;TP removal efficiency:condition（1）>condition（2）>condition（3）;TN removal efficiency:condition（3）>condition（2）,in which the removal rate of COD and NH₄⁺-N can be maintained at about 95%,and the removal rate of TP was relatively unstable.The final sludge concentration was also different under different operating conditions,which was specifically represented by MLSS and MLVSS:condition（1）>condition（3）>condition（2）,under the three conditions,the sludge concentration can reach about10000 mg/L.The different indicators of the mixed solution under different operating conditions were specifically expressed as DO:condition（3）>condition（2）>condition（1）;ORP:condition（1）>condition（3）>condition（2）;p H in the reactor:condition（1）>condition（2）>condition（3）;internal temperature:condition（1）>condition（2）>condition（3）.（5）After adding the magnetic powder,the activated sludge had a good magnetization state.Take the mixed liquid in the reactor and place it on a magnet for testing,and it can be found that the sedimentation effect was significantly different from that when there is no magnet adsorption.It was also applied to keep for 30min,compared with the case of no magnet,the sludge interface with magnet was reduced by 55.8%,and even the effect of standing on the magnet for 5min was better than the effect of free standing for 30min,so the clarification time of the standing sediment was shortened to 10min or even 5min.Therefore,the time required for each treatment cycle can be shortened under the condition that the aeration time remains unchanged,and the effect of increasing the treatment water volume or improving the treatment efficiency can be achieved.