Enrichment And Separation Of Micronand Nano-Particulate Contaminants From Waters Using Surface-Functionalized Microbubble Systems

With the unprecedented development and widespread application of micro-and nano-technology,concerns have been raised in relation to the potential risks that micron-and nano-particles may pose to the environment and organisms.Surface-functionalized microbubble technology is considered as an effective method for the enrichment and separation of micron-and nano-particle contaminants from water.In this study,surface-functionalized microbubbles had been generated by different chemical agents?surfactants and coagulants?with high-speed agitation.First,tracking technologies were used to analyze the fate and interface behavior of Ti O₂nanoparticles during the surface-functionalized microbubble process.Secondly,considering the transformation/dissolution characteristics of metallic engineered nanoparticles?MENPs?,during the enrichment of typical MENPs?Ag,Zn O,Ti O₂nanoparticles?with different degrees of lability by using surface-functionalized microbubbles,the impact of surfactant or coagulant dose,p H of MENP suspensions,and water matrix was investigated.Finally,adopting surface-functionalized microbubbles in separating microplastics?MPs?-the unsurfaced-modified polystyrene?PS?and the carboxyl functional group-coated poly-?methyl methacrylate??PMMA?-from waters in the presence of dissolved organic matter?DOM?,and DOM concentration,surface property of MPs and water matrix were investigated for their influences on the process performance;moreover,the interaction of MPs and DOM was investigated.The main results obtained are presented as follows:At the optimum SDS relative dosage of 0.78 mg/mg Ti O₂,the Ti O₂ nanoparticle number concentration was largely reduced by 2-4 orders of magnitude based on nanoparticle tracking analysis?NTA?whilst approximately 84.0%of particles were separated according to inductively coupled plasma-mass spectrometry?ICP-MS?.NTA shows the change of overall particle dispersion status in the water phase while ICP-MS provides the Ti-related separation effect.Micro-Raman,dynamic laser scattering and small angle laser light scattering exhibited advantages in obtaining the configuration and morphology of flocs.The large flocs with open structure were apt to form and be favorably separated at the appropriate chemical dosage.However,overdosing dosages weakened the capture capacity of bubbles and gave rise to small and dense aggregates.The surface-functionalized microbubbles were capable of enriching over 90.0%of ionic Ag?I?which ended up as Ag Br and Ag₂CO₃ in floats when the p H of suspension was 6.0.The polyaluminum chloride?PACl?-modified microbubbles with positive surface charges were good at capturing the particulate Zn O??84.8%?but failed to collect the ionic species.It should be noted that the total MENP enrichment efficiency was closely related to the content proportions of different species.In the river water,both of the DOM and the electrolytes might influence the enrichment process by affecting the species transformation of Ag and Zn O nanoparticles.For the stable Ti O₂ nanoparticles,97.1%of the nanoparticles were captured by bubbles.DOM apparently reinforced the enrichment performance since the molecules acted as bridge and facilitated the attachment between TNPs and bubbles.Humic acid?HA?promoted the separation of PS-MPs?the separation efficiency could reach more than 94.4%at the optimal dose?,but inhibited the separation of PMMA-MPs?HA competed with PMMA for bubbles?.This difference might be attributed to the surface property and charges of the particles.In the environmental waters-river water and influent of the wastewater treatment plant,the two types of MP particles were almost completely eliminated.The fluorescence quenching titration revealed that bubbles tended to preferably capture the free DOM molecules and the DOM-coated MP particles.Moreover,flocs generated by DOM might also capture and collect MPs by bubbles through sweeping.This study,for the first time,shows the change of nanoparticles in water and solid phases using surface-functional microbubble technology.It also provides a reference to other technologies for studying the nanoparticle fate and the process performance.It contributes to establishing the robust microbubble-induced enrichment method considering the characteristics of MENP contaminants.It provides a simpler and more environmentally friendly technology to separate MPs in water and lays the foundation for MP separation in environmental waters.