•Ti doped BiOI microspheres contained strong VLD disinfection property.•The electronic structure of BiOI was tuned by Ti doping.•Optimal Ti doping amount was determined.•h+, O2−, e− and H2O2 were found to play important roles.Ti doped BiOI microspheres were successfully synthesized through a solvothermal method. The photocatalysts were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), high-resolution transmission electron microscopy (HRTEM), X-ray photoelectron spectroscopy (XPS) and UV–vis diffuse reflectance spectra (DRS) spectroscopy, respectively. The as-synthesized microspheres had 3D hierarchical structures, and the morphologies and visible-light-driven (VLD) disinfection performances were found to be determined by the amount of loaded Ti. The incorporation of Ti in the lattice of BiOI broadened the band gap of BiOI and enhanced the VLD disinfection activity. Ti doped BiOI microspheres with the optimal Ti content exhibited excellent antibacterial performances against both representative Gram-negative and Gram-positive strains, which completely inactivated 3.0 × 107 CFU mL−1E. coli in 24 min and 3.0 × 106 CFU mL−1S. aureus in 45 min, respectively. Active species including h+, e−, O2− and H2O2 were found to play important roles in disinfection system. Moreover, the damage of cell membrane and emission of cytoplasm directly led to the inactivation.Higher conduction band energy induced better visible light driven disinfection activity of BiOI by Ti doping.

We report a novel process for the self-assembly of Fe3O4 nanoparticles (NPs) onto titanate nanotubes (TNTs), nanofibers (TNFs) and nanosheets (TNSs) to synthesize magnetic titanate nanocomposites. Both coulombic and van der Waals forces made important contributions to control the assembly process, in which the Fe3O4 NPs were uniformly dispersed onto the surfaces of the titanate nanostructures by a facile acid-induced method. The Fe3O4 NPs possessed unique magnetic properties for adsorbent separation, while the structures of the titanates determined the efficiency of Pb2+ removal. Interestingly, it was found that Pb2+ can be completely and quickly removed by the TNTs/Fe3O4 and TNSs/Fe3O4 nanocomposites. It is worth noting that the TNTs/Fe3O4 nanocomposite possessed the maximum adsorption capacity of 382.3 mg g−1, displaying a high efficiency for Pb2+ removal. The effects of pH value and contact time at different initial Pb2+ concentrations have been investigated. Based on the characterization results of X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, a possible removal mechanism was proposed. This work provides a facile and general approach to synthesize magnetic functional nanocomposites for water treatment.

This study investigated the influence of carbon nanotubes (CNTs) on the transport and retention behaviors of bacteria (E. coli) in packed porous media at both low and high ionic strength in NaCl and CaCl2 solutions. At low ionic strengths (5 mM NaCl and 0.3 mM CaCl2), both breakthrough curves and retained profiles of bacteria with CNTs (both 5 and 10 mg L–1) were equivalent to those without CNTs, indicating the presence of CNTs did not affect the transport and retention of E. coli at low ionic strengths. The results were supported by those from cell characterization tests (i.e., viability, surface properties, sizes), which showed no significant difference between with and without CNTs. In contrast, breakthrough curves of bacteria with CNTs were lower than those without CNTs at high ionic strengths (25 mM NaCl and 1.2 mM CaCl2), suggesting that the presence of CNTs decreased cell transport at high ionic strengths. The enhanced bacterial deposition in the presence of CNTs was mainly observed at segments near the column inlet, leading to much steeper retained profiles relative to those without CNTs. Additional transport experiments conducted with sand columns predeposited with CNTs revealed that the codeposition of bacteria with CNTs, as well as the deposition of the cell–CNTs cluster formed in cell suspension due to cell bridging effect, largely contributed to the increased deposition of bacteria at high ionic strengths in porous media.

This study investigated the cotransport of titanium dioxide nanoparticles (nTiO2) and fullerene nanoparticles (nC60), two of the most widely utilized nanoparticles, in saturated quartz sand under a series of ionic strengths in NaCl solutions (0.1–10 mM) at both pH 5 and 7. Under all examined ionic strengths at pH 5, both breakthrough curves and retained profiles of nTiO2 in the copresence of nC60 were similar to those without nC60, indicating that nC60 nanoparticles copresent in suspensions did not significantly affect the transport and retention of nTiO2 in quartz sand at pH 5. In contrast, under all examined ionic strengths at pH 7, the breakthrough curves of nTiO2 in the copresence of nC60 in suspensions were higher and the retained profiles were lower than those without nC60, which demonstrated that the presence of nC60 in suspensions increased the rate of transport (decreased retention) of nTiO2 in quartz sand at pH 7. Competition of deposition sites on quartz sand surfaces by the copresence of nC60 was found to contribute to the increased nTiO2 transport at pH 7. Under all examined ionic strength conditions at both pH 5 and 7, the breakthrough curves of nC60 were reduced in the copresence of nTiO2, and the corresponding retained profiles were higher than those without nTiO2, indicating that the presence of nTiO2 decreased the transport of nC60 in quartz sand. Co-deposition of nC60 with nTiO2 in the form of nTiO2-nC60 clusters as well as the deposition of nC60 onto previously deposited nTiO2 were responsible for the increased nC60 deposition in the presence of nTiO2 at pH 5, whereas deposition of nC60 onto surfaces of predeposited nTiO2 was found to be responsible for the increased nC60 deposition at pH 7.

The objective of this study was to determine the bactericidal mechanisms of Ag-doped multi-walled carbon nanotube (MWCNT) nanoparticles (Ag0/MWCNTs) to Escherichia coli DH5α. The contributions of silver ion dissolution, reactive species, and direct contact on bacteria inactivation were systematically determined. The relatively higher survival rate of bacteria exposed to 0.02 mg L−1 Ag+ ions (the maximum concentration of Ag+ ions dissolved from Ag0/MWCNTs) suggested that the antibacterial property of Ag0/MWCNTs was not caused by silver ion dissolution. The effects of each reactive species (OH, H2O2, O2−, h+, and e−) on the disinfection process were investigated by using multiple scavengers, and the results showed that OHb, OHs, and h+ play important roles in bactericidal actions. The significance of OHb, OHs, and h+ in the disinfection process was further confirmed in the partition systems combined with scavenger. The antibacterial effects of these reactive species mainly arose through direct contact of the nanocomposites with the bacteria. The effects of extracellular polymeric substances (EPS) and natural organic matter (NOM) on the inactivation of bacteria were also investigated. The lower antibacterial effect observed for EPS-rich bacteria relative to EPS-poor bacteria demonstrated the protective effects of EPS in the disinfection system. The decreased bacterial toxicity effect acquired by the addition of humic acid (as the model NOM) in the disinfection system demonstrated the influence of NOM on the bacterial toxicity of nanocomposites, where the sorption of NOM onto the surface of the nanocomposites contributed to the decreased antibacterial effects.Graphical abstractHighlights► Ag0/MWCNTs exhibit a stronger antibacterial effect on E. coli than MWCNTs and Ag NPs. ► OHb, OHs, and h+ contribute to the antibacterial effect of Ag0/MWCNTs. ► Inactivation effects of reactive species are achieved by direct contact with cells. ► Removal of EPS induces greater bactericidal effect. ► SRHA mitigates bactericidal effects due to sorption on the surfaces of Ag0/MWCNTs.

The significance of clay particles on the transport and deposition kinetics of bacteria in irregular quartz sand was examined by direct comparison of both breakthrough curves and retained profiles with clay particles in bacteria suspension versus those without clay particles. Two representative cell types, Gram-negative strain E. coli DH5α and Gram-positive strain Bacillus subtilis were utilized to systematically determine the influence of clay particles (bentonite) on cell transport behavior. Packed column experiments for both cell types were conducted in both NaCl (5 and 25 mM ionic strengths) and CaCl2 (5 mM ionic strength) solutions at pH 6.0. The breakthrough plateaus with bentonite in solutions (30 mg L–1 and 50 mg L–1) were lower than those without bentonite for both cell types under all examined conditions, indicating that bentonite in solutions decreased cell transport in porous media regardless of cell types (Gram-negative or Gram-positive) and solution chemistry (ionic strength and ion valence). The enhanced cell deposition with bentonite particles was mainly observed at segments near to column inlet, retained profiles for both cell types with bentonite particles were therefore steeper relative to those without bentonite. The increased cell deposition with bentonite observed in NaCl solutions was attributed to the codeposition of bacteria with bentonite particles whereas, in addition to codeposition of bacteria with bentonite, the bacteria–bentonite–bacteria cluster formed in suspensions also contributed to the increased deposition of bacteria with bentonite in CaCl2 solution.

The significance of natural organic matter (NOM, both humic acid and alginate) on the transport and deposition kinetics of ZnO nanoparticles (NPs) in irregular quartz sand was examined by direct comparison of both breakthrough curves and retained profiles with NOM present in NPs suspension versus those obtained without NOM. Packed column experiments were conducted in both NaCl and CaCl2 solutions under a series of environmentally relevant ionic strengths. Under all examined conditions, breakthrough plateaus with NOM even at concentration as low as 1 mg L−1 of total organic carbon (TOC) were higher than those without NOM, indicating that presence of NOM in NPs suspensions enhanced ZnO NPs transport. Although hyper-exponential retained profiles were observed both in the presence and absence of NOM, the amount of retained ZnO NPs acquired in the presence of NOM decreased slowly as the transport distance increased. Straining induced by concurrent aggregation is found to cause the hyper-exponential decrease. In the presence of NOM, electrosteric interaction effectively reduced the ZnO NPs deposition on collector surfaces and NPs–NPs aggregation. Subsequently, the amount of NPs that jammed in the column inlet in the absence of NOM were markedly decreased, which therefore exhibited as flatter retained profiles.Graphical abstractHighlights► Distinct effects of NOM on ZnO NPs transport and spacial distribution was observed. ► Both SRHA and Alg markedly increased the mobility of ZnO NPs in porous media. ► The retained profiles with NOM exhibited more flat than those without NOM. ► Electrostatic force and steric repulsion contributed to less retention with NOM. ► Decreased concurrent aggregation induced more flat retained profiles with NOM.

Ceramic foams with different relative densities (i.e., different extension ratios) were successfully prepared from stone powder sludge (SPS) via a foaming and gelcasting method. Ceramic foams with various relative densities were characterized in terms of porosity, specific surface area, and water absorption capacity. The porosity of the ceramic foams ranged from 35% to 78%, depending on the extension ratio. The specific surface area and water absorption capacity increased as the relative density decreased (i.e., increasing extension ratio), resulting in enhanced pore connectivity. The feasibility of the SPS foams as microorganism-immobilized carriers and the effect of inner pores on simultaneous nitrification/denitrification were tested through wastewater treatment experiments. The results from fixed-bed reactors packed by SPS carriers with different relative densities revealed that the organic removal efficiency for all reactors was greater than 90%. In addition, the nitrification/denitrification experimental results suggested that the increase of the NH4+-N loading rate resulted in the improvement of nitrification efficiency and the decrease of nitrogen loss in all reactors. However, no significant correlation between relative density (i.e., extent of inner pore development) and nitrification/denitrification efficiency was found.Highlights► Ceramic foams are fabricated from waste stone powder sludge. ► The inner pore structure of SPS foams is successfully controlled. ► SPS foams are feasible to be utilized as biocatalytic carriers.

The impact of ionic strength and cation valence on the transport and deposition kinetics of ZnO nanoparticles in saturated porous media was systematically investigated in this research. Packed column experiments were performed over a series of environmentally relevant ionic strength in both NaCl (ranging from 1 to 20 mM) and CaCl2 (ranging from 0.1 to 1 mM) solutions. Solution chemistries (ionic strength and ion types) greatly affected the transport of ZnO nanoparticles in saturated quartz sand. Flat breakthrough plateaus were observed at relatively low ionic strength in both NaCl (1 and 5 mM) and CaCl2 (0.1–0.5 mM) solutions, whereas, ripening was observed at high ionic strength (10 and 20 mM in NaCl, and 1 mM CaCl2) conditions. Deposition of nanoparticle increased with increasing solution ionic strength in both monovalent and divalent salt solutions. The presence of divalent ions in solutions increased nanoparticle deposition in quartz sand. Under all examined conditions, nanoparticles mainly retained at segments near the column inlet. The retained ZnO nanoparticle concentrations versus transport distance decreased faster than the theory prediction of log-linear decrease under all examined conditions. Our study found that concurrent aggregation of ZnO nanoparticles occurred during the transport process, which contributed to the hyper-exponential retained profiles.Graphical abstractHighlights► Solution chemistries greatly affected the transport behavior of ZnO nanoparticles. ► Transport of ZnO nanoparticles in quartz sand is controlled by DLVO theory. ► Retained profiles deviated from theory predicted log-linear decreases. ► Nanoparticle aggregation during travel led to hyper-exponential retained profiles.

The deposition of bacteriophage MS2 on bare and clay-coated silica surfaces was examined in both monovalent (NaCl) and divalent (CaCl2 and MgCl2) solutions under a wide range of environmentally relevant ionic strength and pH conditions by utilizing a quartz crystal microbalance with dissipation (QCM-D). Two types of clay, bentonite and kaolinite, were concerned in this study. To better understand MS2 deposition mechanisms, QCM-D data were complemented by zeta potentials measurements and Derjaguin–Landau–Verwey–Overbeek (DLVO) interaction forces calculation. In both monovalent and divalent solutions, deposition efficiencies of MS2 increased with increasing ionic strength both on bare and clay-coated surfaces, which agreed with the trends of interaction forces between MS2 and solid surface and thus was consistent with DLVO theory. The presence of divalent ions (Ca2+ and Mg2+) in solutions greatly increased virus deposition on both silica and clay deposited surfaces. Coating silica surfaces with clay minerals, either kaolinite or bentonite, could significantly increase MS2 deposition.Graphical abstract. Coating silica surfaces with clay minerals, either kaolinite or bentonite, could significantly increase MS2 deposition.Highlights► Solution chemistry affects MS2 deposition on silica and clay-coated surfaces. ► Deposition of MS2 on silica and clay-coated surfaces is controlled by DLVO forces. ► Presence of divalent ions (Ca2+ and Mg2+) in solutions increases MS2 deposition. ► Coating silica surfaces with clay minerals increases MS2 deposition.

The significance of natural organic matter (NOM) on the transport of bacteria in packed porous media (quartz sand) was examined in both NaCl and CaCl2–NaCl mixing solutions at pH 6.0. Three representative cell types (with EPS), Rhodococcus sp. QL2 (Gram-positive, non-motile), Escherichia coli BL21 (Gram-negative, non-motile), and E. coli C3000 (Gram-negative, motile), were utilized to systematically determine the influence of NOM (Suwannee River humic acid (SRHA)) on cell transport behavior. To investigate the significance of SRHA on transport of bacteria without EPS on cell surfaces, experiments for treated cells with the removal of EPS from cell surfaces were also performed. The breakthrough plateaus for all examined bacteria with the presence of SRHA (1 mg L−1) in solutions were higher than those with the absence of SRHA under all examined conditions, indicating that the presence of SRHA in solutions enhanced cell transport regardless of cell types (Gram-negative or Gram-positive), motility (non-motile or motile), presence or absence of EPS on cell surfaces, and solution chemistry (ionic strength and ion valence). Zeta potentials for bacteria and quartz sand with the presence of SRHA were similar as those without SRHA present in solutions, suggesting that SRHA did not alter the surface charge of bacteria or sand, thus the enhanced cell transport by SRHA was not likely driven by alteration in the surface charge of either cell or quartz sand. SRHA pre-equilibration experiments demonstrated that the site competition by a portion of SRHA and the repelling deposition by suspended SRHA contributed to the decreased cell deposition observed with the presence of SRHA in bacteria suspension.Graphical abstractHighlights► Transport of bacteria in porous media is significantly influenced by SRHA. ► SRHA enhances cell transport regardless of cell type, motility, and w/ or w/o EPS. ► Site competition by a portion of SRHA contributes to decreased cell deposition. ► Repelling deposition by suspended SRHA also contributes to reduced cell deposition.

The deposition kinetics of RNA extracted from both virus and bacteria on silica surfaces were examined in both monovalent (NaCl) and divalent (CaCl2) solutions under a wide range of environmentally relevant ionic strength and pH conditions by utilizing a quartz crystal microbalance with dissipation (QCM-D). To better understand the RNA deposition mechanisms, QCM-D data were complemented by diffusion coefficients and zeta potentials of RNA as a function of examined solution chemistry conditions. Favorable deposition of RNA on poly-l-lysine-coated (positively charged) silica surfaces was governed by the convective–diffusive transport of RNA to the surfaces. The deposition kinetics of RNA on bare silica surfaces were controlled by classic Derjaguin–Landau–Verwey–Overbeek (DLVO) interactions. The presence of divalent cations (Ca2+) in solutions greatly enhanced the deposition kinetics of RNA on silica surfaces. Solution pH also affected the deposition behavior of RNA on silica surfaces. Release experiments showed that detachment of RNA from silica surfaces was significant in NaCl solutions, whereas, the deposited RNA on silica surfaces in CaCl2 solutions was more likely to be irreversible.

The influence of humic acid and alginate, two major components of natural organic matter (NOM), on deposition kinetics of extracellular polymeric substances (EPS) on silica was examined in both NaCl and CaCl2 solutions over a wide range of environmentally relevant ionic strengths utilizing a quartz crystal microbalance with dissipation. Deposition kinetics of both soluble EPS and bound EPS extracted from four bacterial strains with different characteristics was investigated. EPS deposition on humic acid-coated silica surfaces was found to be much lower than that on bare silica surfaces under all examined conditions. In contrast, pre-coating the silica surfaces with alginate enhanced EPS deposition in both NaCl and CaCl2 solutions. More repulsive electrostatic interaction between EPS and surface contributed to the reduced EPS deposition on humic acid-coated silica surface. The trapping effect induced by the rough alginate layer resulted in the greater EPS deposition on alginate-coated surfaces in NaCl solutions, whereas surface heterogeneities on alginate layer facilitated favorable interactions with EPS in CaCl2 solutions. The presence of dissolved background humic acid and alginate in solutions both significantly retarded EPS deposition on silica surfaces due to the greater steric and electrostatics repulsion.Graphical abstractDeposition of EPS on silica could be significantly influenced by NOM (humic acid and alginate) either dissolved in solutions or adsorbed on silica surfaces in both monovalent and divalent solutions.Highlights► Deposition of EPS on silica surfaces is significantly influenced by NOM. ► Pre-coating silica surfaces with SRHA hinders the deposition kinetics of EPS. ► Pre-coating the silica surfaces with alginate enhances EPS deposition. ► NOM present in solutions decreases the deposition of EPS on silica.

The significance of extracellular polymeric substances (EPS) on cell transport and retained bacteria profiles in packed porous media (quartz sand) was examined by direct comparison of the overall deposition kinetics and retained profiles of untreated bacteria (with EPS) versus those of treated cells (without EPS) from the same cell type. Four representative cell types, Pseudomonas sp. QG6 (gram-negative, motile), mutant Escherichia coli BL21 (gram-negative, nonmotile), Bacillus subtilis (gram-positive, motile), and Rhodococcus sp. QL2 (gram-positive, nonmotile), were employed to systematically determine the influence of EPS on cell transport and deposition behavior. Packed column experiments were conducted for the untreated and treated cells in both NaCl (four ionic strength ranging from 2.5 mM to 20 mM) and CaCl2 (5 mM) solutions at pH 6.0. The breakthrough plateaus of untreated bacteria were lower than those of treated bacteria for all four cell types under all examined conditions (in both NaCl and CaCl2 solutions), indicating that the presence of EPS on cell surfaces enhanced cell deposition in porous media regardless of cell type and motility. Retained profiles of both untreated and treated cells for all four cell types deviated from classic filtration theory (log−linear decreases). However, the degree of deviation was greater for all four untreated cells, indicating that the presence of EPS on cell surfaces increased the deviation of retained profiles from classic filtration theory. Elution experiments demonstrated that neither untreated nor treated cells preferentially deposited in secondary energy minima. Furthermore, the release of previously deposited cells in the secondary energy minima did not change the shape of retained cell profiles, indicating that deposition in secondary energy minima did not produce the observed deviations of retained profiles from classic filtration theory.

The deposition kinetics of extracellular polymeric substances (EPS) on silica surfaces were examined in both monovalent and divalent solutions under a variety of environmentally relevant ionic strength and pH conditions by employing a quartz crystal microbalance with dissipation (QCM-D). Soluble EPS (SEPS) and bound EPS (BEPS) were extracted from four bacterial strains with different characteristics. Maximum favorable deposition rates (kfa) were observed for all EPS at low ionic strengths in both NaCl and CaCl2 solutions. With the increase of ionic strength, kfa decreased due to the simultaneous occurrence of EPS aggregation in solutions. Deposition efficiency (α; the ratio of deposition rates obtained under unfavorable versus corresponding favorable conditions) for all EPS increased with increasing ionic strength in both NaCl and CaCl2 solutions, which agreed with the trends of zeta potentials and was consistent with the classic Derjaguin−Landau−Verwey−Overbeek (DLVO) theory. Comparison of α for SEPS and BEPS extracted from the same strain showed that the trends of α did not totally agree with trends of zeta potentials, indicating the deposition kinetics of EPS on silica surfaces were not only controlled by DLVO interactions, but also non-DLVO forces. Close comparison of α for EPS extracted from different sources showed α increased with increasing proteins to polysaccharides ratio. Subsequent experiments for EPS extracted from the same strain but with different proteins to polysaccharides ratios and from activated sludge also showed that α were largest for EPS with greatest proteins to polysaccharides ratio. Additional experiments for pure protein and solutions with different pure proteins to pure saccharides ratios further corroborated that larger proteins to polysaccharides ratio resulted in greater EPS deposition.

The significance of extracellular polymer substances (EPS) on cell deposition on silica surfaces was examined by direct comparison of the deposition kinetics of untreated “intact” bacteria versus those from the same strain but with EPS removal via cation exchange resin (CER) treatment using a quartz crystal microbalance with dissipation (QCM-D). Four bacterial strains, mutant Escherichia coli BL21 (gram-negative, nonmotile), Pseudomonas sp QG6 (gram-negative, motile), Rhodococcus sp QL2 (gram-positive, nonmotile), and Bacillus subtilis (gram-positive, motile), were employed to determine the influence of EPS on cell deposition. Experiments were conducted in both monovalent (NaCl) and divalent (CaCl2) solutions under a variety of environmentally relevant ionic strength ranging from 1 to 100 mM at pH 6.0. The effectiveness of EPS removal via CER method was ensured by biochemical composition analysis of EPS solutions and further confirmed by FTIR analysis. Comparable zeta potentials were observed for untreated and CER treated bacterial cells in both NaCl and CaCl2 solutions, indicating that removal of EPS from cell surfaces via CER treatment did not affect the electrokinetic properties of the cell surfaces for all four strains. However, observed deposition efficiencies (α) were greater for untreated cells relative to those with CER treated cells across the entire ionic strength range examined in both NaCl and CaCl2 solutions for all four bacterial strains. These results strongly demonstrated that the removal of EPS from cell surfaces for all four strains decreased the deposition of bacteria on silica surfaces. This study clearly showed that the enhancement of cell deposition on silica surfaces due to the presence of EPS on cell surfaces was relevant to all bacterial strains examined regardless of cell types and motility.

We report a novel process for the self-assembly of Fe3O4 nanoparticles (NPs) onto titanate nanotubes (TNTs), nanofibers (TNFs) and nanosheets (TNSs) to synthesize magnetic titanate nanocomposites. Both coulombic and van der Waals forces made important contributions to control the assembly process, in which the Fe3O4 NPs were uniformly dispersed onto the surfaces of the titanate nanostructures by a facile acid-induced method. The Fe3O4 NPs possessed unique magnetic properties for adsorbent separation, while the structures of the titanates determined the efficiency of Pb2+ removal. Interestingly, it was found that Pb2+ can be completely and quickly removed by the TNTs/Fe3O4 and TNSs/Fe3O4 nanocomposites. It is worth noting that the TNTs/Fe3O4 nanocomposite possessed the maximum adsorption capacity of 382.3 mg g−1, displaying a high efficiency for Pb2+ removal. The effects of pH value and contact time at different initial Pb2+ concentrations have been investigated. Based on the characterization results of X-ray photoelectron spectroscopy (XPS) and Raman spectroscopy, a possible removal mechanism was proposed. This work provides a facile and general approach to synthesize magnetic functional nanocomposites for water treatment.