| Considering the increasement of nanoparticle concentration in natural water andthe toxic effects of nanoparticles, much attention has been paid to the transformationand removal of nanoparticles in aqueous environment. As a kind of ubiquitous organicpollutant, the effects of sodium dodecylbenzene sulfonate (SDBS) on aggregationbehaviors and coagulation removal of titanium dioxide nanoparticles (TiO2NPs) wereinvestigated in simulate water and Songhua River samples to verify the influencingmechanisms of SDBS on aggregation and coagulation removal of TiO2NPs andascertain the differences of aggregation and coagulation in simulate and natural water.Firstly, the effects of pH (4.0~6.0), ionic strength (5~20mmol/L NaCl, CaCl2),SDBS concentration (0~1.0mg/L) on1.0mg/L TiO2NPs suspensions were explored indeionized water. It has been found that the influences of pH and ionic strength onaggregation were owed to the changes of electrical double-layer repulsions between twoparticles. As a result of the combination of the Derjaguin-Landau-Verwey-Overbeek(DLVO) and non-DLVO forces, the impacts of SDBS on aggregation were dependenton the pH values and the ionic strength of TiO2NPs suspensions. Aggregation was morelikely to occur for suspensions with a low SDBS concentration and a pH value less thanthe isoelectric point than the suspensions with a higher SDBS concentration. Then,aggregation behaviors of10mg/L TiO2NPs suspensions and the effects of pH (4.0~8.3)and SDBS concentration (0~2.500mmol/L) were investigated in Songhua Riversamples and deionized water, respectively. Affected by the inherent colloids and organiccomponents, aggregation behaviors of TiO2NPs were much more complicated inSonghua River samples. Aggregation occurred under all the conditions, and thehydrodynamic diameters of aggregates maintained at the nanoscale after three hoursaggregation in Songhua River samples. However, in deionized water, aggregates mightgrow up to micro size for the same aggregation time to lose the properties ofnanoparticles.With respect to the coagulation removal of TiO2NPs in Songhua River samplesand deionized water, poly aluminium chloride (PAC) was emoloyed as coagulant. Theeffects of pH (4.0~9.0), PAC dosage (10~60mg/L in Songhua River samples,0~0.20mg/L in deionized water), SDBS concentration (0~2.500mmol/L) and aggregation time(0~24h) were explored, respectively. The forms of aluminum hydrolysis products andthe surface charge of TiO2NPs relied on the pH values, and a proper pH value wasnecessary to obtain higher TiO2NPs removal efficiency. The coagulation removal ofTiO2NPs by PAC was mainly attributed to the charge neutralization, and there existed an optimum coagulant dosage for TiO2NPs removal. To ensure the coagulationefficiency, higher PAC dosage was needed because of the higher negative surfacecharges of TiO2NPs and non-DLVO forces between TiO2NPs in the presence of SDBS.Aggregation were favorable for the coagulation removal of TiO2NPs due to the changesof raw water conditions, improvement of the settleability and effective collision of TiO2NPs. In deionized water, thanks to the24hours aggregation, nanoparticle and turbidityremoval efficiency would be improved by4%~10%. In this study, the highest removalefficiency of TiO2NPs was79.61%and86.46%for Songhua River samples anddeionized water, respectively. Affected by the inherent colloids and organic components,much more PAC dosage was needed for coagulation in Songhua River samples, and themechanisms for coagulation removal of TiO2NPs were more complicated. In SonghuaRiver samples, the effects of SDBS and aggregation states on coagulation were not assignificant as that in deionized water.The mechanisms illustrated in this study about the effects of SDBS on aggregationand coagulation removal of TiO2NPs were applicable to other surfactant-nanoparticlesystems and theoretical significant for water plants to meet the challenges of thenanoparticle concentration raise in water sources. |
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