Research On Formation Characteristics And Mechanism Of Diatomite Dynamic Membrane And Application Of Dynamic Membrane

In recent years,dynamic membrane(DM)technolgy has attracted much attention due to the low-cost membrane material,low operating pressure,high filtration flux and easy backwashing.The diatomite paritcles were used as the formation materials to form DM layer on the micro-seive in this study.The filtration characteristics,particle removal efficiency and DM layer formaiton characteristics in the DM formaiton process were explored.The influence of particle size,supporting membrane pore size,operation condtions on the DM formation process were evaluated.The DM foramtion mechanism was analyzed with membrane blocking models and combined blocking models.At last,the diatomite enhanced DM technology was used for the backwashed wastewater recycling in biological aerated filter and the pre-dewataering of backwashed sludge.Firstly,the filtration characteristics in DM formaiton process were investigated in constant rate filtration and constant pressure filtraiton,in terms of filtration flux,trans-membrane pressure(TMP),effluent turbidity,and filtration resistance.At influent flow of 10 L/h,the TMP was increased from 0.8 k Pa to 0.9～1.23 k Pa in the DM formation process.Meanwhile,the effluent turbidity was reduced to 1 NTU with the formation of DM layer.Despite the filtration resistance was increased from 2.57×109 m-1 to 4.16×109 m-1,the formation of DM layer would not led to the increase of filtration resistance and operating cost.When the DM was formed under 200 mm water head,the reduction of filtration flux was not obvious in the DM formation process,ranging from 853.5 L/(m2·h)to 913 L/(m2·h).The effluent turbidity was kept below 1 NTU after the DM layer was formed.The variation of filtration resistance was not obvious in constant pressure filtraiton.Secondly,the formaiton particle size,supporting membrane pore size,and operating conditions would affect the DM formation process.With the increase of particle size(1～100 μm)in the DM formation process,the reduced TMP,quick effluent turbidity reduction and DM formation was observed at the same time,which was beneficial to the applciation of DM technology in wastewater treatment.With the increase of supporting membrane pore size(68～210 μm),late increase of TMP,slowly reduction of effluent turbidity,and long DM formation time was observed.With the increase of influent flow(9～21 L/h),the high increasing speed of TMP and filtration resistance was observed,and quick effluent turbidity reduction was also confirmed,suggesting the quick formation of DM layer.The increasement of influent particle concentration(0.1～1 g/L)will also accelerate the increase of TMP and filtration resistance,with qucik reduction of effluent turbidity,promoting the formaiton of DM layer.Besides,membrane blocking models were used to explain the DM foramtion process.Single cake filtration blocking model could explain the DM foramtion process reasonably on 68 μm and 90 μm meshes in constant rate filtration.When the supporting membrane pore size was increased to 158 μm,combined cake-standard blocking model performed much better with the DM formation process,accounting for the standard blocking and cake filtration process in the DM formation process with 158 μm.In constant pressure filtration process,single cake filtration process could fit well with the DM formation process with large diatomite particles.But DM formation prcess with small diatomite paritlces could only be explained well by the combined cake-complete blocking model.Finally,diatomite enhanced DM technology was used for the backwash wastewater treatment in biological aerated filter.At the diatomite dose of 0.4 g/L,the effluent COD could be reduced to 30 mg/L quickly,with TP reduced to 1 mg/L,which could meet the demand of the recycling of the treated backwashed wastewater.Meanwhile,the backwashed sludge was also pre-dewatered in the DM filtration process.With 0.6 g/L diatomite added,the water content of backwashed sludge could be reduced to 87.76% in DM filtraiton,much lower than that with sedimentation and coagulation-sedimentation process,which was close to the water content with sedimentaion-centrifugation process(84.45%).This confirmed the satisfactory dewatering of backwashed sludge in DM filtraiton.