As an environmentally friendly material, biochar has been widely used to remediate soil/water contaminants such as heavy metals and organic pollutants. The addition of biochar or modified biochar to porous media might affect the retention of plastic particles and thus influence their fate in natural environment. In this study, both biochar and magnetic biochar (Fe3O4-biochar) were synthesized via a facile precipitation method at room temperature. To determine the significance of biochar and Fe3O4-biochar amendment on the transport and deposition behaviors of plastic particles, the breakthrough curves and retained profiles of three different sized plastic particles (0.02 μm nano-plastic particles, and 0.2 μm and 2 μm micro-plastic particles) in quartz sand were compared with those obtained in quartz sand either with biochar or Fe3O4-biochar amendment in both 5 mM and 25 mM NaCl solutions. The results show that for all three different sized plastic particles under both examined solution conditions, the addition of biochar and Fe3O4-biochar in quartz sand decreases the transport and increases the retention of plastic particles in porous media. Fe3O4-biochar more effectively inhibits the transport of plastic particles than biochar. We found that the addition of biochar/Fe3O4-biochar could change the suspension property and increase the adsorption capacity of porous media (due to the increase of porous media surface roughness and negatively decrease the zeta potentials of porous media), contributing to the enhanced deposition of plastic particles. Moreover, we found that negligible amount of biochar and Fe3O4-biochar (<1%) were released from the columns following the plastic particle transport when the columns were eluted with very low ionic strength solution at high flow rate (to simulate a sudden rainstorm). Similarly, small amount of plastic particles were detached from the porous media under this extreme condition (16.5% for quartz sand, 14.6% for quartz sand with biochar amendment, and 7.5% for quartz sand with Fe3O4-biochar amendment). We found that over 74% of the Fe3O4-biochar can be recovered from the porous media after the retention of plastic particles by using a magnet and 87% plastic particles could be desorbed from Fe3O4-biochar by dispersing the Fe3O4-biochar into 10 mM NaOH solution. In addition, we found that the amendment of unsaturated porous media with biochar/Fe3O4-biochar also decreased the transport of plastic particles. When biochar/Fe3O4-biochar were added into porous media as one layer of permeable barrier near to column inlet, the decreased transport of plastic particles could be also obtained. The results of this study indicate that magnetic biochar can be potentially applied to immobilize plastic particles in terrestrial ecosystems such as in soil or groundwater. © 2019 Elsevier Ltd

The influence of dendrimer on the bacterial transport and deposition behaviors in saturated porous media (quartz sand) was investigated in both NaCl (10 and 25 mM) and CaCl2 solutions (1.2 and 5 mM). 3.5G and 4G poly (amido amine) (PAMAM) dendrimer was employed as negatively and positively charged dendrimer, respectively. Three dendrimer concentrations (10 μg/L, 1 and 10 mg/L) were considered in present study. We found that regardless of the solution chemistry (ionic strength and ion types) and dendrimer concentrations, the presence of negatively charged PAMAM 3.5G in suspensions enhanced bacterial transport and inhibited their deposition in quartz sand; while the presence of positive charged PAMAM 4G yet induced the opposite effects (decreased bacterial transport and increased their deposition in quartz sand). The increased repulsive force between cell and quartz sand due to the adsorption of PAMAM 3.5G onto both cell and sand surfaces, the competition deposition sites as well as the steric repulsion via the suspended PAMAM 3.5G drove to the increased bacterial transport with PAMAM 3.5G copresent in suspensions in quartz sand. While the reduced repulsive force between cell and quartz sand induced by the chemical heterogeneity on both cell and sand surfaces (due to the adsorption of positive charged PAMAM 4G) increased bacterial retention in quartz sand with copresence of PAMAM 4G (10 μg/L and 1 mg/L) in suspensions. Steric repulsion due to the presence of great amount of suspended PAMAM 4G yet lead to the enhanced bacterial transport with furthering increasing PAMAM 4G to 10 mg/L relative to the lower PAMAM 4G concentration. © 2019

The present study was designed to investigate the cotransport and deposition of different-sized plastic particle from nano- (0.02 μm) to micrometer-scale (0.2 and 2 μm) with goethite and hematite (two types of representative iron oxides abundant in natural environment) in porous media at both low (5 mM) and high ionic strength (25 mM) in NaCl solutions. We found that through different mechanisms (i.e., modification of surface properties of iron oxides, steric repulsion, or alteration in deposition sites on quartz sand), different-sized plastic particles induced different effects on the transport and deposition behaviors of iron oxides in quartz sand. Likewise, via different mechanisms such as change of surface properties or alteration in deposition sites on quartz sand, different transport behaviors for different sized plastic particles induced by the copresence of iron oxides were also observed. The results of this study suggested that cotransport of iron oxides and plastic particles in porous media is far more complex than those of individual colloid transport. Since both plastic particles and iron oxides are ubiquitous presence in natural environment, it is expected that they would interact with each other and thus alter the surface properties, leading to the change of transport behaviors in porous media. Copyright © 2019 American Chemical Society.

Plastic particles are widely present in the natural environment and are highly likely to interact with bacteria (the ubiquitous microbes in the natural environment), which might affect the transport and deposition of bacteria in porous media. In this study, the significance of plastic particles from nanoscale to micrometer-scale (0.02-2 μm) on the transport and deposition behaviors of bacteria (Escherichia coli) in quartz sand was examined under environmentally relevant conditions in both NaCl and CaCl2 solutions at pH 6. The results showed that the presence of different-sized plastic particles did not affect bacterial transport behaviors at low ionic strength (10 mM NaCl and 1 mM CaCl2), whereas, at high ionic strength conditions (50 mM NaCl and 5 mM in CaCl2), plastic particles increased bacterial transport in quartz sand. At low ionic strength conditions, the mobility of both plastic particles and bacteria was high, which might drive the negligible effects of plastic particles on bacterial transport behaviors. The mechanisms driving the enhanced cell transport at high ionic strength were different for different-sized plastic particles. Specifically, for 0.02 μm nanoplastic particles, the adsorption of plastic particles onto cell surfaces and the repel effect induced by suspended plastic particles contributed to the increased cell transport. As for 0.2 μm microplastics (MPs), the suspended plastic particles induced repel effect contributed to the increased cell transport, whereas, for 2 μm MPs, the competition deposition sites by the plastic particles were the contributor to the increased cell transport. © 2018 American Chemical Society.

Magnetic Fe3O4@BiOI@AgI (FBA) spheres were synthesized through a multi-step process. The fabricated photocatalysts were characterized by different techniques. To testify the visible light driven photocatalytic activity of FBA, Rhodamine B and Bisphenol A were chosen as model common and emerging organic contaminants, respectively. While, gram-negative strain Escherichia coli was selected as model waterborne bacteria. The results showed that under visible light irradiation, FBA contained strong photocatalytic degradation capacity towards both RhB and BPA. Moreover, FBA was also found to exhibit excellent disinfection activity towards E. coli. The photocatalytic mechanisms for different pollutants by FBA were determined and found to vary for different pollutants. Specifically, scavenger experiments, degradation intermediates determination, as well as theoretical density functional theory (DFT) analysis showed that RhB and BPA were degraded via photosensitization (dominated by e- and ·O2−) and direct photocatalytic oxidation (contributed by h+, e- and ·O2−), respectively. Whereas, E. coli cells yet were found to be inactivated by the generation of e- and ·O2− rather than by the released Ag+. Since it contained superparamagnetic property, FBA could be easily separated from the reaction suspension after use. Due to the excellent photo stability, FBA exhibited strong photocatalytic activity in the fourth reused recycle. Therefore, FBA could serve as a promising alternative for water purification. © 2018 Elsevier Ltd

The influence of proteins on bacterial transport and deposition behaviors in quartz sand was examined in both NaCl (10 and 25 mM) and CaCl2 solutions (1.2 and 5 mM). Bovine Serum Albumin (BSA) and bovine trypsin were used to represent negatively and positively charged proteins in natural aquatic systems, respectively. The presence of negatively charged BSA in suspensions increased the transport and decreased bacterial deposition in quartz sand, regardless of the ionic strength and ion types. Whereas, positively charged trypsin inhibited the transport and enhanced bacterial deposition under all experimental conditions. The potential mechanisms controlling the changes of bacterial transport behaviors varied for different charged proteins. The steric repulsion resulting from BSA adsorption onto both bacteria and quartz sand was found to play a dominant role in the transport and deposition of bacteria in porous media with BSA copresent in suspension. BSA adsorption onto bacterial surfaces and competition for deposition sites onto sand surfaces (adsorption of quartz sand surfaces) contributed to the increased cell transport with BSA in suspension. In contrast, the attractive patch-charged interaction induced by the adsorption of trypsin onto both bacteria and quartz sand had great contribution to the decreased bacterial transport in porous media with trypsin copresent in suspension. The increase in bacteria size, and the adsorption of trypsin onto cell surfaces (resulting in less negative cell surface charge) and quartz sand surfaces (providing extra deposition sites) were found to be the main contributors to the decreased transport and increased deposition of bacteria in quartz sand with trypsin in suspension. © 2018

A novel Z-scheme AgI/Bi2MoO6 hybrid photocatalyst was fabricated via a solvothermal-precipitation approach to disinfect bacteria in water. Powder X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopic (SEM) equipped with energy-dispersive X-ray spectroscopy (EDX), high resolution transmission electron microscope (HRTEM), UV-vis diffuse reflectance spectra (DRS), as well as photoluminescence spectra (PL) were employed to characterize the fabricated photocatalyst. Due to the stronger redox potential and better separation of charge carriers induced by the Z-scheme structure, the optimal synthesized AgI/Bi2MoO6 exhibited excellent disinfection activity towards both Gram-negative strain Escherichia coli (E. coli) and Gram-positive strain Staphylococcus aureus (S. aureus) under visible light irradiation. 5.0 × 107 CFU mL−1 of E. coli and S. aureus cells were completely disinfected within 30 min and 90 min, respectively. Ag+ ions did not contribute to the disinfection activity, while active species including h+, ·O2−, e-, and H2O2 contributed to the cell inactivation. By changing the interaction force and being involved in the photocatalytic reactions, the common anions (Cl−, NO3−, SO42−, and H2PO4−) would affect the disinfection activity. Moreover, AgI/Bi2MoO6 exhibited effective disinfection activity in four consecutive reused cycles. Thus, AgI/Bi2MoO6 could be used as a promising photocatalyst for water disinfection.

The influence of Bisphenol A (BPA) on the transport and deposition behaviors of bacteria in quartz sand was examined in both NaCl (10 and 25 mM) and CaCl2 solutions (1.2 and 5 mM) by comparing the breakthrough curves and retained profiles of cell with BPA in suspensions versus those without BPA. Gram-negative Escherichia coli and Gram-positive Bacillus subtilis were employed as model cells in the present study. The extended Derjaguin-Landau-Verwey-Overbeek interaction energy calculation revealed that the presence of BPA in cell suspensions led to a lower repulsive interaction between the cells and the quartz sand. This suggests that, theoretically, increased cell deposition on quartz sand would be expected in the presence of BPA. However, under all examined solution conditions, the presence of BPA in cell suspensions increased transport and decreased deposition of bacteria in porous media regardless of cell type, ionic strength, ion valence, the presence or absence of extracellular polymeric substances. We found that competition by BPA through hydrophobicity for deposition sites on the quartz sand surfaces was the sole contributor to the enhanced transport and decreased deposition of bacteria in the presence of BPA. © 2017

The significance of perfluorooctanoic acid (PFOA) on the transport and deposition behaviors of bacteria (Gram-negative Escherichia coli and Gram-positive Bacillus subtilis) in quartz sand is examined in both NaCl and CaCl2 solutions at pH 5.6 by comparing both breakthrough curves and retained profiles with PFOA in solutions versus those without PFOA. All test conditions are found to be highly unfavorable for cell deposition regardless of the presence of PFOA; however, 7%-46% cell deposition is observed depending on the conditions. The cell deposition may be attributed to micro- or nanoscale roughness and/or to chemical heterogeneity of the sand surface. The results show that, under all examined conditions, PFOA in suspensions increases cell transport and decreases cell deposition in porous media regardless of cell type, presence or absence of extracellular polymeric substances, ionic strength, and ion valence. We find that the additional repulsion between bacteria and quartz sand caused by both acid-base interaction and steric repulsion as well as the competition for deposition sites on quartz sand surfaces by PFOA are responsible for the enhanced transport and decreased deposition of bacteria with PFOA in solutions. © 2016 American Chemical Society.

This study investigated the influence of multiple colloids (hematite and humic acid) on the transport and deposition of bacteria (Escherichia coli) in packed porous media in both NaCl (5 mM) and CaCl2 (1 mM) solutions at pH 6. Due to the alteration of cell physicochemical properties, the presence of hematite and humic acid in cell suspensions significantly affected bacterial transport and deposition in quartz sand. Specifically, the presence of hematite (5 mg/L) decreased cell transport (increased cell deposition) in quartz sand in both NaCl and CaCl2 solutions, which could be attributed to the less negative overall zeta potentials of bacteria induced by the adsorption of positively charged hematite onto cell surfaces. The presence of a low concentration (0.1 mg/L) of humic acid in bacteria and hematite mixed suspensions reduced the adsorption of hematite onto cell surfaces, leading to increased cell transport in quartz sand in NaCl solutions, whereas, in CaCl2 solutions, the presence of 0.1 mg/L humic acid increased the formation of hematite-cell aggregates and thus decreased cell transport in quartz sand. When the concentration of humic acid was increased to 1 mg/L, enhanced cell transport was observed in both NaCl and CaCl2 solutions. The decreased adsorption of hematite onto cell surfaces as well as the competition of deposition sites on quartz sand with bacteria by the suspended humic acid contributed to the increased cell transport. © 2015 Elsevier Ltd.

Fe3O4@SiO2 magnetic nanoparticles modified by grafting poly(1-vinylimidazole) oligomer (FSPV) was fabricated as a novel adsorbent to remove Hg(II) from water. Fourier transform infra-red spectroscopy confirmed the successful grafting of oligomer, and thermogravimetric analysis showed FSPV had a high grafting yield with organic content of 22.8%. Transmission electron microscopy image displayed that FSPV particles were polymer-coated spheres with size of 10–20 nm. With saturation magnetization of 44.7 emu/g, FSPV particles could be easily separated from water with a simple magnetic process in 5 min. The Hg(II) adsorption capacity of FSPV was found to be 346 mg/g at pH 7 and 25 °C in 10 mM NaCl. Moreover, the removal of Hg(II) by FSPV was not obviously affected by solution pH (from 4 to 10) or humic acid (up to 8 mg/L as TOC). The presence of seven common ions including Na+, K+, Ca2+, Mg2+, Cl−, NO3−, and SO42− (up to 100 mM ionic strength) slightly increased the adsorption of Hg(II) by FSPV. X-ray photoelectron spectroscopy analysis revealed that the N atom of the imidazole ring was responsible for the bonding with Hg(II), whereas the bonding of Hg with N did not result in cleavage of Hg–Cl bond in HgCl2 and HgClOH. The regeneration of Hg(II)-loaded FSPV could be achieved with 0.5 M HCl rapidly in 10 min, and the removal of Hg(II) maintained above 94% in five consecutive adsorption–desorption cycles. Therefore, FSPV could serve as a promising adsorbent for Hg(II) removal from water.

This study investigated the influence of two representative suspended clay particles, bentonite and kaolinite, on the transport of titanium dioxide nanoparticles (nTiO2) in saturated quartz sand in both NaCl (1 and 10 mM ionic strength) and CaCl2 solutions (0.1 and 1 mM ionic strength) at pH 7. The breakthrough curves of nTiO2 with bentonite or kaolinite were higher than those without the presence of clay particles in NaCl solutions, indicating that both types of clay particles increased nTiO2 transport in NaCl solutions. Moreover, the enhancement of nTiO2 transport was more significant when bentonite was present in nTiO2 suspensions relative to kaolinite. Similar to NaCl solutions, in CaCl2 solutions, the breakthrough curves of nTiO2 with bentonite were also higher than those without clay particles, while the breakthrough curves of nTiO2 with kaolinite were lower than those without clay particles. Clearly, in CaCl2 solutions, the presence of bentonite in suspensions increased nTiO2 transport, whereas, kaolinite decreased nTiO2 transport in quartz sand. The attachment of nTiO2 onto clay particles (both bentonite and kaolinite) were observed under all experimental conditions. The increased transport of nTiO2 in most experimental conditions (except for kaolinite in CaCl2 solutions) was attributed mainly to the clay-facilitated nTiO2 transport. The straining of larger nTiO2-kaolinite clusters yet contributed to the decreased transport (enhanced retention) of nTiO2 in divalent CaCl2 solutions when kaolinite particles were copresent in suspensions.

Traditional chemical disinfectants are becoming increasingly defective due to the generation of carcinogenic disinfection byproducts and the emergence of antibiotic-resistant bacterial strains. Functionalized magnetic nanoparticles yet have shown great application potentials in water treatment processes especially for bacterial removal. In this study, three types of amino acids (arginine, lysine, and poly-l-lysine) functionalized Fe3O4 nanoparticles (Fe3O4@Arg, Fe3O4@Lys, and Fe3O4@PLL) were prepared through a facile and inexpensive two-step process. The amino acid modified Fe3O4 nanoparticles (Fe3O4@AA) showed rapid and efficient capture and removal properties for both Gram-positive Bacillus subtilis (B. subtilis) and Gram-negative Escherichia coli 15597 (E. coli). For both strains, more than 97% of bacteria (initial concentration of 1.5 × 107 CFU mL−1) could be captured by all three types of magnetic nanoparticles within 20 min. With E. coli as a model strain, Fe3O4@AA could remove more than 94% of cells from solutions over a broad pH range (from 4 to 10). Solution ionic strength did not affect cell capture efficiency. The co-presence of sulfate and nitrate in solutions did not affect the capture efficiency, whereas, the presence of phosphate and silicate slightly decreased the removal rate. However, around 90% and 80% of cells could be captured by Fe3O4@AA even at 10 mM of silicate and phosphate, respectively. Bacterial capture efficiencies were over 90% and 82% even in the present of 10 mg L−1 of humic acid and alginate, respectively. Moreover, Fe3O4@AA nanoparticles exhibited good reusability, and greater than 90% of E. coli cells could be captured even in the fifth regeneration cycle. The results showed Fe3O4@AA fabricated in this study have great application potential for bacteria removal from water.

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.

Magnetic nanoparticles (MNPs) modified simultaneously with amorphous Fe and Mn oxides (Mag-Fe-Mn) were synthesized to remove arsenite [As(III)] from water. Mag-Fe-Mn particles were fabricated through heterogeneous nucleation technique by employing the maghemite as the magnetic core and Fe Mn binary oxide (FMBO) as the coating materials. Powder X-ray diffraction, X-ray photoelectron spectroscopy (XPS), Raman spectroscopy, and transmission electron microscopy were utilized to characterize the hybrid material. With a saturation magnetization of 23.2 emu/g, Mag-Fe-Mn particles with size of 20 -50 nm could be easily separated from solutions with a simple magnetic process in short time (within 5 min). At pH 7.0, 200 mu g/L of As(III) could be easily decreased to below 10 mu g/L by Mag-Fe-Mn particles (0.1 g/L) within 20 min. As(III) could be effectively removed by Mag-Fe-Mn particles at initial pH range from 4 to 8 and the residual As was completely oxidized to less toxic arsenate [As(V)]. The co-occurring redox reactions between Mn oxide and As(III) was confirmed by XPS analysis. Chloride, sulfate, bicarbonate, and nitrate at common concentration range had negligible influence on As(III) removal, whereas, silicate and phosphate reduced the As(III) removal by competing with arsenic species for adsorption sites. As(M) removal was not obviously affected by natural organic matter (up to 8 mg/L as TOC). Mag-Fe-Mn could be regenerated with ternary solution of NaOH, NaCl, and NaClO. Throughout five consecutive cycles, the adsorption and desorption efficiencies maintained above 98% and 87%, respectively. Mag-Fe-Mn had a larger adsorption capacity for As(III) (47.76 mg/g) and could remove trace As(III) more thoroughly than MNPs modified solely with either Fe or Mn oxide due to the synergistic effect of the coating Fe and Mn oxides. This research extended the potential applicability of FMBO to a great extent and provided a convenient approach to efficiently remove trace As(III) from water. (C) 2013 Elsevier Ltd. All rights reserved.

This study investigated the cotransport of titanium dioxide nanoparticles (nTiO(2)) and fullerene nanoparticles (nC(60)), 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 h curves and retained profiles of nTiO(2) in the copresence of nC(60) were similar to those without nC(60), indicating that nC(60) nanoparticles copresent in suspensions did not significantly affect the transport and retention of nTiO(2) in quartz sand at pH 5. In contrast, under all examined ionic strengths at pH 7, the breakthrough curves of nTiO(2) in the copresence of nC(60) in suspensions were higher and the retained profiles were lower than those without nC(60), which demonstrated that the presence of nC(60) in suspensions increased the rate of transport (decreased retention) of nTiO(2) in quartz sand at pH 7 Competition of deposition sites on quartz sand surfaces by the copresence of nC(60) was found to contribute to the increased nTiO(2) transport at pH 7. Under all examined ionic strength conditions at both pH 5 and 7, the breakthrough curves of nC(60) were reduced in the copresence of nTiO(2), and the corresponding retained profiles were higher than those without nTiO(2), indicating that the presence of nTiO(2) decreased the transport of nC(60) in quartz sand. Co-deposition of nC(60) with nTiO(2) in the form of nTiO(2)-nC(60) clusters as well as the deposition of nC(60) onto previously deposited nTiO(2) were responsible for the increased nC(60) deposition in the presence of nTiO(2) at pH 5, whereas deposition of nC(60) onto surfaces of predeposited nTiO(2) was found to be responsible for the increased nC(60) deposition at pH 7.

Ag2O/TNBs were fabricated by depositing Ag2O nanoparticles on the surface of TiO2 nanobelts (TNBs). The disinfection activities of Ag2O/TNBs on two representative bacterial types: Gram-negative Escherichia coli ATCC15597 and Gram-positive Bacillus subtilis, were examined under both dark and visible light conditions. Ag2O/TNBs exhibited stronger bactericidal activities than Ag2O nanoparticles and TNBs under both dark and light conditions. For both cell types, disinfection effects of Ag2O/TNBs were greater under light conditions relative to those under dark conditions. The bactericidal mechanisms of Ag2O/TNBs under both dark and light conditions were explored. Ag+ ions released from Ag2O/TNBs did not contribute to the bactericidal activity of Ag2O/TNBs under dark conditions, whereas the released Ag+ ions showed bactericidal activity under visible light irradiation conditions. Active species (H2O2, O-center dot(2)-, and e(-)) generated by Ag2O/TNBs played important roles in the disinfection processes under both dark and visible light irradiation conditions. Without the presence of active species, the direct contact of Ag2O/TNBs with bacterial cells had no bactericidal effect. (C) 2013 Elsevier Ltd. All rights reserved.

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 DH5 alpha 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.