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The influence of ionic strength on the transport behaviors of natural or engineered colloids has been widely studied in recent years, and the explanatory classical Derjaguin–Landau–Verwey–Overbeek ...

Changes in solution chemistry and transport conditions can lead to the release of deposited MnO2 nanoparticles from a solid interface, allowing them to re-enter the aqueous environment. Understanding the release behavior of MnO2 nanoparticles from naturally occurring surfaces is critical for better prediction of the transport potential and environmental fate of MnO2 nanoparticles. In this study, the release of MnO2 nanoparticles was investigated using a quartz crystal microbalance with dissipation monitoring (QCM-D), and different environmental surface types, solution pH values and representative macromolecular organics were considered. MnO2 nanoparticles were first deposited on crystal sensors at elevated NaNO3 concentrations before being rinsed with double-deionized water to induce their remobilization. The results reveal that the release rate of MnO2 depends on the surface type, in the decreasing order: SiO2 > Fe3O4 > Al2O3, resulting from electrostatic interactions between the surface and particles. Moreover, differences in solution pH can lead to variance in the release behavior of MnO2 nanoparticles. The release rate from surfaces was significantly higher at pH 9.8 that at 4.5, indicating that alkaline conditions were more favorable for the mobilization of MnO2 in the aquatic environment. In the presence of macromolecular organics, bovine serum albumin (BSA) can inhibit the release of MnO2 from the surfaces due to attractive forces. In presence of humic acid (HA) and sodium alginate (SA), the MnO2 nanoparticles were more likely to be mobile, which may be associated with a large repulsive barrier imparted by steric effects.

Ion specific effects have been proved to be an important factor controlling the stability and dynamics of engineered colloidal systems; however, there has been limited research on the ion specific effects on the transport behaviors of engineered nanoparticles (ENPs). In the present study, the initial deposition kinetics of fullerene (C60) and ceria (CeO2) NPs in first-group monovalent cationic solutions (i.e., MNO3, M = Li+, Na+, K+ and Rb+) were quantitatively investigated, by employing a laboratory quartz crystal microbalance with the dissipation monitoring (QCM-D) technique. The influence of common model biomacromolecules, including a polysaccharide (alginate) and protein (bovine serum albumin (BSA)), was reported as well. The results demonstrated that the cations can decrease the deposition kinetics of different charged NPs with decreasing hydration degree of additive cations in the order Li+ > Na+ > K+ > Rb+. The variance in the deposition behaviors of NPs at fixed electrolyte concentration can be quantitatively explained by a modified DLVO theory that introduced hydration forces, which induced short range repulsion within the model that dominated the colloidal interactions of NPs with the surface and resulted in these specific effects. Moreover, the two biomacromolecules impacted the deposition of both NPs in an opposite manner: BSA could enhance the attachment of NPs on the silica surface, while alginate can decrease the deposition and enhance their mobility in aqueous solutions, dependent on the molecular complexity. These findings are helpful for understanding the deposition behavior of NPs under the effect of ionic specificity and giving quantitative evidence for the role of counterion hydration in the interactions between electrostatically charged ENPs and the environmental surface in aqueous media.

Exploring the transport behaviors of thallium (Tl) in porous media is crucial for predicting Tl pollution in natural soils and groundwater. In recent years, the misuse of plastics has led to plastic becoming an emerging pollutant in soil. In this work, the effects of plastic particles on Tl(I) transport in water-saturated sand columns were investigated under different ionic strengths (ISs), pH values, and plastic particle sizes. The two-site nonequilibrium model was selected to fit the breakthrough curves (BTCs) of Tl(I). The results demonstrated that nanoplastics (NPs) accelerated Tl(I) transport at pH 7, which might be attributed to the competitive adsorption of NPs and Tl(I) on sand surfaces. However, at pH 5, the deposited NPs might provide more adsorption sites for Tl(I), and thus enhance its retention in the columns. In addition, the "straining" process could intercept microplastics (MPs) with Tl(I) that was attached under unfavorable attachment conditions, which would result in the inhibited mobility of Tl(I). On the other hand, the migration of plastics was restrained to some extent when Tl(I) was present. Overall, the findings from this work provided a new perspective for understanding the transport of Tl(I) and plastics in subsurface environments.

The initial deposition kinetics of colloidal MnO2 on three representative surfaces in aquatic systems (i.e., silica, magnetite, and alumina) in NaNO3 solution were investigated in the presence of model constituents, including humic acid (HA), a polysaccharide (alginate), and a protein (bovine serum albumin (BSA), using laboratory quartz crystal microbalance with dissipation monitoring equipment (QCM-D). The results indicated that the deposition behaviors of MnO2 colloids on three surfaces were in good agreement with classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. Critical deposition concentrations (CDC) were determined to be 15.5 mM NaNO3 and 9.0 mM NaNO3 when colloidal MnO2 was deposited onto silica and magnetite, respectively. Both HA and alginate could largely retard the deposition of MnO2 colloids onto three selected surfaces due to steric repulsion, and HA was more effective in decreasing the deposition rate relative to alginate. However, the presence of BSA can provide more attractive depo...

Engineered nanoparticles (ENPs) will inevitably enter wastewater treatment plants (WWTPs) due to their widespread application; thus, it is necessary to study the migration and transformation of nanoparticles in sewage treatment systems. Extracellular polymeric substances (EPSs) such as polysaccharides, proteins, nucleic acids, humic acids and other polymers are polymers released by microorganisms under certain conditions. Intracellular polymeric substances (IPSs) are microbial substances contained in the body with compositions similar to those of extracellular polymers. In this review, we summarize the characteristics of EPSs and IPSs from sewage-collecting microbial aggregates containing pure bacteria, activated sludge, granular sludge and biofilms. We also further investigate the dissolution, adsorption, aggregation, deposition, oxidation and other chemical transformation processes of nanoparticles, such as metals, metal oxides, and nonmetallic oxides. In particular, the review deeply analyzes the migration and transformation mechanisms of nanoparticles in EPS and IPS matrices, including physical, chemical, biological interactions mechanisms. Moreover, various factors, such as ionic strength, ionic valence, pH, light, oxidation-reduction potential and dissolved oxygen, influencing the interaction mechanisms are discussed. In recent years, studies on the interactions between EPSs/IPSs and nanoparticles have gradually increased, but the mechanisms of these interactions are seldom explored. Therefore, developing a systematic understanding of the migration and transformation mechanisms of ENPs is significant.

Thallium (Tl) has drawn wide concern due to its high toxicity even at extremely low concentrations, as well as its tendency for significant accumulation in the human body and other organisms. The need to develop effective strategies for trace Tl removal from drinking water is urgent. In this study, the removal of trace Tl (0.5 μg L −1 ) by conventional quartz sand filtration enhanced by nanosized manganese dioxide (nMnO 2 ) has been investigated using typical surface water obtained from northeast China. The results indicate that nMnO 2 enhanced quartz sand filtration could remove trace Tl(I) and Tl(III) efficiently through the adsorption of Tl onto nMnO 2 added to a water matrix and onto nMnO 2 attached on quartz sand surfaces. Tl(III)-HA complexes might be responsible for higher residual Tl(III) in the effluent compared to residual Tl(I). Competitive Ca 2+ cations inhibit Tl removal to a certain extent because the Ca 2+ ions will occupy the Tl adsorption site on nMnO 2 . Moreover, high concentrations of HA (10 mgTOC L −1 ), which notably complexes with and dissolves nMnO 2 (more than 78%), resulted in higher residual Tl(I) and Tl(III). Tl(III)-HA complexes might also enhance Tl(III) penetration to a certain extent. Additionally, a higher pH level could enhance the removal of trace Tl from surface water. Finally, a slight increase of residual Tl was observed after backwash, followed by the reduction of the Tl concentration in the effluent to a “steady” state again. The knowledge obtained here may provide a potential strategy for drinking water treatment plants threatened by trace Tl.

In the present study, nano-sized TiO2/Al2O3 modified polyvinylidene fluoride (PVDF) membranes (MM) were fabricated and then utilized for oil/water emulsion separation. The results showed that, compared with PVDF membrane (OM), the contact angle of MM decreased and hydrophilicity increased. The ultrafiltration (UF) of oil in water emulsions with transmembrane pressure (TMP) increasing results in a sharp fall in relative flux with time. The cake filtration models did not always predict the performance over the complete range of filtration times very well. In the initial 30 min, all the four cake models can simulate this UF process to a certain extent, and the suitability was: cake filtration > intermediate pore blocking > standard pore blocking > complete pore blocking models. However, they were no longer adapted well with UF time extent to 60 min, but only cake filtration (R2 = 0.9535) maintained a high adaptability. Surface and cross-sectional morphology of the membrane was investigated by SEM to make an advanced certificate of this UF mechanism.

Thallium (Tl) is an element of high toxicity and significant accumulation in human body. There is an urgent need for the development of appropriate strategies for trace Tl removal in drinking water treatment plants. In this study, the efficiency and mechanism of trace Tl (0.5 μg/L) removal by conventional coagulation enhanced by nanosized manganese dioxide (nMnO2) were explored in simulated water and two representative surface waters (a river water and a reservoir water obtained from Northeast China). Experimental results showed that nMnO2 significantly improve Tl(I) removal from selected waters. The removal efficiency was dramatically higher in the simulated water, demonstrating by less than 0.1 μg/L Tl residual. The enhancement of trace Tl removal in the surface waters decreased to a certain extent. Both adjusting water pH to alkaline condition and preoxidation of Tl(I) to Tl(III) benefit trace Tl removal from surface waters. Data also indicated that competitive cation of Ca2+ decreased the efficiency of trace Tl removal, resulting from the reduction of Tl adsorption on nMnO2. Humic acid could largely low Tl removal efficiency during nMnO2 enhanced coagulation processes. Trace elemental Tl firstly adsorbed on nMnO2 and then removed accompanying with nMnO2 settling. The information obtained in the present study may provide a potential strategy for drinking water treatment plants threatened by trace Tl.

A novel composite nanofiltration membrane incorporated with silica nanoparticles was prepared by interfacial polymerization on polysulfone (PSF) ultrafiltration membrane. The silica nanoparticles (∼15 nm) were homogeneously dispersed in poly(amidoamine) (PAMAM) dendrimer aqueous monomers and incorporated in situ into the polyamide films. Series of tests including FTIR–ATR, AFM, XPS, etc. were performed to characterize the polyamide (PA)-SiO 2 membrane's morphologies, structure, physical and chemical characteristics, separation properties and permeability, etc. The results showed that silica loading into the PA membrane resulted in roughness and hydrophilicity promotion. The permeation performance for PA-SiO 2 membrane increased nearly 50% without loss of salt rejection rate by adding 1.0% (wt.) nano-SiO 2 nanoparticles in aqueous solution. The order of rejection to inorganic salts is Na 2 SO 4 > MgSO 4 > MgCl 2 > NaCl revealed both PA and PA-SiO 2 membrane were nagatively charged. The zeta potentials testing results indicated addition of SiO 2 will increase the negative charge quantities on the surface of PA-SiO 2 membrane for negatively charged hydroxyl groups and silanol-covered nano-SiO 2 surface. The value of molecular weight cutoff (MWCO) for PA-SiO 2 membrane was about 1000 g/mol and the additive of SiO 2 nanoparticles to PA membrane enlarges the pore size slightly. The PA-SiO 2 membrane had a higher stable flux and could remove nearly 50% salts when treated with oily wastewater in one-cycle filtration. Desalination of oily wastewater using the nacomposite PA-SiO 2 membrane is feasible.

This paper studies the cumulative effect of various parameters, namely anionic polyacrylamide (APAM) concentration, oil concentration, pH, trans-membrane pressure (TMP), and total dissolved solid (TDS), and obtains optimal parameters for the minimum relative flux (J/J(0)) declining in aqueous solutions with response surface methodology (RSM). In order to analyze the mutual interaction and optimal values of parameters affecting ultrafiltration, a central composite rotatable design (CCRD), one method of RSM, was employed. The analysis of variance (ANOVA) of the cubic polynomial model demonstrated that this model was highly significant and reliable. The results show that the effect of APAM and oil on J/J(0) has an inverse trend with pH value increasing. Moreover, the mutual interaction of initial APAM (oil) concentration (C(APAM(oil))) and pH (TMP) were negligible, while the mutual interaction of C(APAM) and C(oil) has an obvious effect, i.e. the effect of initial feed C(APAM) became more important at higher values of initial feed C(oil), and the J/J(0) was only about 4%. The favorable operate conditions in this ultrafiltration process were at low C(APAM), C(oil), pH, and TMP, which agreed with the conclusions of many authors, while considering water production, C(APAM) and C(oil) < 50 mg/L, pH < 4, and TMP < 0.075 MPa could be accepted.