Titanium dioxide (TiO₂) nanoparticles have been applied in membrane antifouling performance modification for years. However, the influence of TiO₂ nanoparticle dispersion status during the blending process on membrane properties and the inner mechanism has seldom been focused on. Herein, we investigated the influence of the various dispersing statuses of TiO₂ nanoparticles on membrane properties and antifouling performance by exploring various blending processes without changing the original recipe. Polyethylene glycol (PEG) was employed as a pore-forming agent during the membrane preparation process, and also as a pre-dispersing agent for the TiO₂ nanoparticles via the steric hindrance effect. Compared to the original preparation process of the PVDF/TiO₂ composite membrane, the pre-dispersing of TiO₂ via PEG ensured a modified membrane with uniform surface pores and structures on cross-sectional morphologies, larger porosity and water permeability, and more negative zeta potential. The contact angle was decreased by 6.0%, implying better hydrophilicity. The improved antifouling performance was corroborated by the increasing free energy of cohesion and adhesion, the interaction energy barrier (0.43 KT) between the membrane surfaces and approaching foulants assessed by classic XDLVO theory and the low flux decline in the filtration experiment. A kinetics mechanism analysis of the casting solutions, which found a low TSI value (<1.0), substantiated that the pre-dispersion of TiO₂ with PEG contributed to the high stability and ultimately favorable antifouling behaviors. This study provides an optimized approach to the preparation of excellent nano-TiO₂/polymeric composite membranes applied in the municipal sewage treatment field.

Herein, the influence of various contents of polyethylene glycol (PEG) on the dispersion of TiO₂ nanoparticles and the comprehensive properties of PVDF/TiO₂ composite membranes via the steric hindrance interaction was systematically explored. Hydrophilic PEG was employed as a dispersing surfactant of TiO₂ nanoparticles in the pre-dispersion process and as a pore-forming additive in the following membrane preparation process. The slight overlap shown in the TEM image and low TSI value (<1) of the composite casting solution indicated the effective dispersion and stabilization under the steric interaction with a PEG content of 6 wt.%. Properties such as the surface pore size, the development of finger-like structures, permeability, hydrophilicity and Zeta potential were obviously enhanced. The improved antifouling performance between the membrane surface and foulants was corroborated by less negative free energy of adhesion (about −42.87 mJ/m²), a higher interaction energy barrier (0.65 KT) and low flux declination during the filtration process. The high critical flux and low fouling rate both in winter and summer as well as the long-term running operation in A/O-MBR firmly supported the elevated antifouling performance, which implies a promising application in the municipal sewage treatment field.

The H₂-based membrane biofilm reactor (H₂-MBfR) has been acknowledged as a cost-effective microbial reduction technology for oxyanion removal from drinking water sources, but it remains unknown how the evolution of biofilm characteristics responds to the changing critical operating parameters of the H₂-MBfR for simultaneous bromate (BrO₃⁻) and nitrate (NO₃⁻) elimination. Therefore, an expanded multispecies model, applicable to mechanistically interpret the bromate-reducing bacteria (BRB)- and denitrifying bacteria (DNB)-dominated metabolic processes in the biofilm of the H₂-MBfR, was developed in this study. The model outputs indicate that (1) increased BrO₃⁻ loading facilitated the metabolism of BRB by increasing BRB fraction and BrO₃⁻ gradients in the biofilm, but had a marginal influence on NO₃⁻ reduction; (2) H₂ pressure of 0.04 MPa enabled the minimal loss of H₂ and the extension of the active region of BRB and DNB in the biofilm; (3) once the influent NO₃⁻ concentration was beyond 10 mg N/L, the fraction and activity of BRB significantly declined; (4) BRB was more tolerant than DNB for the acidic aquatic environment incurred by the CO₂ pressure over 0.02 MPa. The results corroborate that the degree of microbial competition for substrates and space in the biofilm was dependent on system operating parameters.

Hydrophilic modification of polymeric membranes by employing TiO₂ nanoparticles has attracted much attention in enhancing antifouling performance. Micelles of PVPylated-TiO₂ nanoparticles were designed to alleviate the agglomeration of TiO₂ nanoparticles via steric hindrance and electrostatic stabilization effect. Herein, Poly(vinyl pyrrolidone) (PVP) was used as a surfactant to mitigate the thorny agglomeration of nanoparticles in the casting solution and simultaneously as a pore-forming additive during the membrane preparation process. The lowest backscattering (BS) peak and turbiscan stability index (TSI) of the composite casting solution indicated the effective dispersion and stabilization under the steric interaction of 4 wt.% PVP. Properties such as the fully developed finger-like structure of cross-sectional morphologies, water permeability, negative Zeta potential, and hydrophilicity were enhanced evidently by the optimal modification of PVPylated-TiO₂ materials. High interaction energy indicated by classic extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory as well as the high relative flux during the filtration of various model foulants demonstrated the effective antifouling modification. The results of critical flux and fouling rate in 30 min also verified the enhancement of the antifouling performance of PVDF/PVPylated-TiO₂ composite membrane. This work provides a feasible strategy to construct composite membranes with high antifouling performance for wastewater treatment.

As a favorable hydrophilic additive for antifouling modification of polyvinylidene fluoride (PVDF) membrane, titanium dioxide (TiO₂) nanoparticles have been applied for years. Sodium dodecyl sulfonate (SDS), a representative anionic surfactant, has been proven to benefit the dispersion of nano-TiO₂ via an electro-spatial stabilizing mechanism. In this study, various proportionally SDS-functionalized TiO₂ nanoparticles were adopted to modify PVDF membrane. Dispersion and stability of SDS-functionalized TiO₂ nanoparticles in casting solutions were evaluated by multiple light scattering technology. The properties and antifouling performance of PVDF/SDS-TiO₂ composite membranes were assessed. The uniformity of surface pores as well as structures on cross-section morphologies was modified. The finger-like structure of PVDF/SDS-TiO₂ composite membrane was adequately developed at the SDS/TiO₂ mass ratio of 1:1. The improved antifouling performance was corroborated by the increasing free energy of cohesion and adhesion as well as the interaction energy barrier between membrane surfaces and approaching foulants assessed by classic extended Derjaguin–Landau–Verwey–Overbeek (XDLVO) theory, the low flux decline during bovine serum albumin (BSA) solution filtration process, and the high critical flux (38 L/(m²·h·kPa)) in membrane bioreactor. This study exploits a promising way to modify PVDF membrane applicable to the wastewater treatment field.