Research On The Properties Of Removing Titanium Dioxide Nanoparticles By Coagulation And Optimizing The Coagulation System

Extensive application of nano-TiO₂brings economic benefits to society, butalso brings pollution. By discharge, leakage and natural circulation, the nano-TiO₂in air and soil will eventually enter into water. A number of studies haveconfirmed that TiO₂nanoparticles have toxicological effects on various organsand tissues, but also damage DNA. Therefore, this paper carried out the researchof removing TiO₂nanoparticles in water by coagulation, mainly investigated thestability of nano-TiO₂in water and the impact of water conditions on theremoval of nano-TiO₂by coagulation, in addition the system of coagulationremoving nano-TiO₂has been optimized, which may meet an emergency toguarantee the quality of water when the pollution of nano-TiO₂outbreaking.Two types of TiO₂nanoparticles were used in this study, one was withoutdispersant （NTs）, and another was stabilized by PBTCA （NPTs）.This review focuses on the impact of ultrasound conditions and ionicstrength (Na⁺, Ca²⁺, Al³⁺)on the stability of NTs and NPTs, aiming to providereferences of theoretical and experimental data for the subsequent experiments.The study found that in the investigated range, the ultrasound conditions of300W with20min led to the smallest average particle size of the NTs and NPTs,which were200.1nm and194.7nm respectively, and under low powerultrasound, prolonged time would be unfavorable to disperse NTs; to the criticalcoagulation concentration （CCC） values of the same metal ion, the CCC ofNPTs was always higher than that of NTs, and the relation betweenexperimental values of CCCs and the ionic valence was in accord with theSchulze-Hardy rule.Under a constant coagulant dosage: The dosing of to turbid material andhigh initial concentration of NTs will promote coagulation removal, but toturbid material was almost free from the influence on NPTs coagulation removalefficiency, and the increase of NPTs initial concentration made the removal ratesignificantly reduced; the increase of ionic strength and cation valence wouldpromote coagulation removal of NTs and NPTs; the existence of HA and H2PO4-would seriously hamper the coagulation of NTs and NPTs, but Cl^-, NO₃^-, SO₄^2-,and HCO₃^-had little effect on NTs and NPTs removal.This paper took mechanical flocculation tank as a prototype to optimize thesystem of nano-TiO₂coagulation removal aiming to provide reference values forthe engineering application. First, coagulation parameters were optimized with orthogonal test: For1mg/L and10mg/L of NTs and NPTs, the best coagulantwas aluminum sulfate （AS）, the optimal dosage was40mg/L; the optimumhydraulic conditions （G, GT） of NTs and1mg/L NPTs were first (98.8s^-1,5928.0) and then changing to (19.6s^-1,52968.0), and the optimum hydraulicconditions of10mg/L NPTs was first (98.8s^-1,5928.0) and then changing to(19.6s^-1,29448.0); the coagulation effect was influenced most greatly by thetype of coagulant,but least by the hydraulic conditions. During the inspection onthe influence of PAC dosage on10mg/L nano-TiO₂removal, PAC is not suitablefor NTs removal, while the NPTs were better removed, when the dosage of20mg/L, the NPTs removal rate reached93.7%. This paper also explored theremoval of nano-TiO₂of low concentration （1mg/L） affected by AS dosage.When AS dosage was15mg/L, NTs and NPTs removal rate could reach80%ormore, at the same time, the turbidity of effluent after sedimentation could reachthe standard. Finally, this paper also studied the influence of floc breakageprocess on coagulation effect, and found that floc breakage process had littleeffect on the removal rate.