The Dispersion Stability Of TiO₂Nanoparticles In Water And Removal Effect By Conventional Process

TiO₂nanoparticles （NPs, nanoparticles） are widely used in many fields, due totheir unique photocatalytic, photovoltaic and excellent UV-absorbing function. However,NPs can release to multiple environmental media through direct or indirect way, TiO₂NPs also change through migration and transformation in various environmental media,and ultimately into the water environment, organic, ionic strength and pH or otherfactors will affect the dispersion of nanoparticles in water and further affect the stabilityof their toxicity, which may produce unpredictable potential hazards on human andecological environment. Therefore, the dissertation researches the dispersion stabilityand removal efficiency of TiO₂NPs in natural water by conventional water treatmentprocesses, it is important to study the influence of LAS, pH and sonication on TiO₂NPsdispersion stability in natural water, and investigates the impact on TiO₂NPs removalefficiency by coagulation factors, such as hydraulic conditions, settling time, coagulantdosage and water pH; additionally, explores the TiO₂NPs trapped effect throughadjusting filtration rate of filter unit. This study provide a foundation for removing TiO₂NPs in water environment and understanding the migration or transformation of TiO₂NPs, and also protecting the security of drinking water.TiO₂NPs characteristics of point of zero charge and morphology werecharacterized, to get the point of zero charge of TiO₂was5.6. Results of dispersionstability of nano-TiO₂in natural water confirmed that different-concentration of LASproduce different effects on the particle size distribution of TiO₂NPs, both showed asignificant negative correlation between each other; pH can change surface charge andquantity of TiO₂NPs and then affect the Zeta potential of TiO₂NPs, when pH is greaterthan or less than the point of zero and increases, the Zeta potential of TiO₂NPs wereboth increased. Appropriate ultrasonic treatment can enhance stability of TiO₂NPs inwater due to ultrasonic cavitation of ultrasound wave, but the longer ultrasound timeproduces TiO₂NPs reunit, because TiO₂NPs get extra ultrasonic energy, In this study,TiO₂reserves solution gets the best dispersion condition at250W,10min.The optimum coagultant dosage and hydraulic condition were both existed in theremoval of turbidity and TiO₂NPs in wate by coagulation unit of conventional watertreatment processes, both the removal efficiency were improved with the increaseconcentration of TiO₂NPs in water under a certain range respectively. In the samecoagulation conditions, the regularity of turbidity and TiO₂NPs removal laws were verysimilar, the maximum turbidity removal efficiency of different-concentration ofnano-TiO₂and turbidity were reached the range of95.0%⁹9.0%; hydraulic conditionshave a very big impact on agglomeration of TiO₂NPs, the best hydraulic condition wasobtained at the condition of rapid mixing of250r/min,1min, slowly stirring at100 r/min,20min. the removal rate of TiO₂NPs was enhanced with the increase of settlingtime, and when settling time reach a certain time, the removal rate will not increase. Theeffect of pH on turbidity removal was found not obvirously, but not on TiO₂NPs,adjusting the pH to where can get Zeta potential of TiO₂NPs at different-concentrationin the range of-5mV⁰mV can enhanc coagulation effect further.Filtration rate has a more significant effect on retention capacity of TiO₂NPs andturbidity, which increase with the decrease of filtration rate. Coagulation unit less orbetter effective effluent, the filter unit has a significant impact on TiO₂NPs andturbidity removal in both cases, filtered water are standard. For lower concentration ofnano-TiO₂removal, consider combining the depth of the water treatment process isimportant to ensure drinking water security.