| The significance of ultrafiltration (UF) technology applied in water treatment has been gradually recognized in recent years. However, when UF membrane is employed in the water purification process, it will be inevitably fouled. On the premise of water quality insurance, how to mitigate the membrane fouling effectively is a technical difficulty in membrane technologies. In this study, a charged TiO2 pre-coating progress has been developed to reduce the membrane fouling.The pre-coat formed by charged particles on the membrane surface can keep colloids、 organic macromolecules and other pollutants from contacting with membrane surface,and mitigate the membrane fouling obviously.Using SDBS to modified TiO2 at pH=5-6,the charging performance and dispersion property of TiO2 were improved significantly.After modified,the average particle size of TiO2 increased from 6.43μm to 7.579μm. The ratio of particles size that smaller than ultrafiltration membrane pore size is zero, so TiO2 particles could not enter membrane pores to lead to blockage of membrane pores.Adsorption experiments showed that TiO2 particles had good effect on organics adsorption, but had little effect on ammonia adsorption.Charged TiO2 was pre-coated on the UF membrane by electric field.The effect of charged TiO2 pre-coating process on improving UF membrane flux was studied.The results showed that charged TiO2 precoating could aviod the direct contact of pollutants and membrane, decreasing membrane fouling speed and maintaining relative high membrane flux. Running to the fifth period under the condition of electric field intensity 30v/cm, coating time 10min, pre-coating dosage of 2g/l, membrane flux was recovered to 76.5% of the initial flux and was 18.5% higher than membrane without pre-coating process. Meanwhile, TiO2 with charged particle modification precoating may exist a’Best Precoating Thickness’, when the precoating thickness was the’Best Precoating Thickness’, the filtration performance of ultrafiltration membrane was the best.Overall, the charged TiO2 pre-coating progress can develop UF membrane treatment water quality. The turbidity of pre-coating membrane treatment water was always less than 0.6NTU,but the turbidity was always more than 0.6NTU in the control group at the same time, moreover the turbidity more than 1NTU sometimes during 20 recordedly running days. It showed that pre-coat can adsorb and intercept turbidity substance effectively. The concentration of ammonia in the pre-coating membrane treatment water was 0.86mg/L,and it was 0.83mg/L in the control group. TiO2 has little effect on the ammonia adsorption, but it could reduce the area of membrane surface to adsorb the ammonia, so the removal of the ammonia was reduced. The removal efficiency of CODMn on the pro-coating process was 63.6%, that was 10.7% more than the control group. TiO2 particle has very small diameter and very large special surface area, so it has good effect on removing pollutants.On the whole operation progress, both cake filtration coefficient (Kc) and pore narrowing coefficient (Kp) of the pre-coat membrane were smaller than the control group.It showed that pre-coat could improve cake fouling and pore adsorption fouling at the same time. The Kc keeped falling on the two progresses because of the cake formation. By analysis of membrane foulants, it could be seen that the colloid was most (66%) but the solution was least (19%) on the control group, and the SS was most (50%) but the colloid was less (45%) on the pre-coat membrane.The increase of large particles in the cake components could make cake harsher and reduce special membrane resistance. Compared to the control group, the pore adsorption resistance Rp decreased from 6×1011m"- to 3×1011 m-1,and the special membrane resistance decreased from 2.29×1011 m/g to 1.30x1011m/g. It showed that the cake was looser and irreversible fouling decreased on the pre-coating progress, and this was why membrane flux resumed better after backwash. |
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