Seong-Jik Park

The role of phosphate in bacterial interaction with iron-coated surfaces

This study investigated the role of phosphate in the adhesion of bacteria (Staphylococcus aureus ATCC 10537) to iron-coated surfaces. Column experiments were performed at phosphate concentrations ranging from 0.0 to 2.0 mM. Bacterial breakthrough curves were obtained by monitoring effluent, and mass recovery and sticking efficiency were quantified from these curves. At phosphate concentrations between 0 and 0.5 mM, bacterial attachment to iron-coated sand decreased with increasing phosphate concentration (mass recovery increased from 14.0 to 86.3%), possibly due to charge modification of the coated sand from positive to negative by adsorbed phosphate ions. Between 0.5 and 2.0 mM, however, bacterial attachment increased with increasing phosphate concentration (mass recovery decreased from 86.3 to 41.3%), possibly due to compression of the electrical double layer between bacteria and phosphate-adsorbed/negatively charged surfaces by free phosphate ions. This study demonstrates that phosphate can play different roles in bacterial interaction with iron-coated surfaces depending on its concentration.

Analysis of bacterial cell properties and transport in porous media

The cell properties of Escherichia coli ATCC 11105 (gram-negative rod and motile) and Staphylococcus aureus ATCC 10537 (gram-positive coccus and immotile) and their transport in porous media were investigated in this study. Bacterial cell properties such as cell geometry, zeta potential, and hydrophobicity were analyzed using surface measurement and bio-imaging techniques. Transport of both bacteria was examined using column experiments in quartz sand, iron-coated sand (ICS), iron-coated sand pretreated with humic acid (ICS-HA), glass bead, and field soil (sandy loam). Experimental results revealed that E. coli had a larger equivalent diameter and were more hydrophobic than S. aureus, while the difference in zeta potential was not statistically significant even though E. coli had a slightly more negative value than S. aureus. Column experimental results demonstrated that the mass recovery of S. aureus was higher than that of E. coli in all porous media used in this study. These results indicate that transport of S. aureus was greater than E. coli under the given experimental conditions. This study demonstrates that pathogenic bacteria with different characteristics from E. coli can have different transport in porous media.A multiresidue analytical method was developed for the determination of 9 endocrine disrupting chemicals (EDCs) and 19 pharmaceuticals and personal care products (PPCPs) including acidic and neutral pharmaceuticals in water and soil samples using rapid resolution liquid chromatography-tandem mass spectrometry (RRLC-MS/MS). Solid phase extraction (SPE), and ultrasonic extraction combined with silica gel purification were applied as pretreatment methods for water and soil samples, respectively. The extracts of the EDCs and PPCPs in water and soil samples were then analyzed by RRLC-MS/MS in electrospray ionization (ESI) mode in three independent runs. The chromatographic mobile phases consisted of Milli-Q water and acetonitrile for EDCs and neutral pharmaceuticals, and Milli-Q water containing 0.01 % acetic acid (v/v) and acetonitrile: methanol (1:1, v/v) for acidic pharmaceuticals at a flow rate of 0.3 mL/min. Most of the target compounds exhibited signal suppression due to matrix effects. Measures taken to reduce matrix effects included use of isotope-labeled internal standards, and application of matrix-match calibration curves in the RRLC-MS/MS analyses. The limits of quantitation ranged between 0.15 and 14.08 ng/L for water samples and between 0.06 and 10.64 ng/g for solid samples. The recoveries for the target analytes ranged from 62 to 208 % in water samples and 43 to 177 % in solid samples, with majority of the target compounds having recoveries ranging between 70–120 %. Precision, expressed as the relative standard deviation (RSD), was obtained less than 7.6 and 20.5 % for repeatability and reproducibility, respectively. The established method was successfully applied to the water and soil samples from four irrigated plots in Guangzhou. Six compounds namely bisphenol-A, 4-nonylphenol, triclosan, triclocarban, salicylic acid and clofibric acid were detected in the soils.

Influence of (bi)carbonate on bacterial interaction with quartz and metal oxide-coated surfaces

This study investigated the influence of (bi)carbonate on the adhesion of bacteria (Bacillus subtilis ATCC 6633) to quartz, aluminum oxide-coated, and iron oxide-coated surfaces. Column experiments were conducted at various NaHCO(3) concentrations. Bacterial breakthrough curves were obtained by monitoring effluent, and mass recoveries were quantified from these curves. With NaHCO(3) concentrations varying from 0 to 200mM, the corresponding effective ionic strength varied from 0 to 149.0mM and solution pH from 6.2 to 8.7. Results show that at low and intermediate NaHCO(3) concentrations (1 and 10mM), bacterial adhesion to negatively charged quartz sand increased with increasing NaHCO(3) concentration, due to compression of the electrical double layers. At high NaHCO(3) concentrations (100 and 200mM), however, bacterial attachment to quartz sand decreased compared to the case of 10mM, possibly due to formation of short-range forces (steric repulsion/hydration force) by high ionic strength. In aluminum-coated sand, bacterial adhesion decreased gradually with increasing NaHCO(3) concentrations, due to charge modification from positive to negative by adsorbed (bi)carbonate ions. At low concentrations of 0.1 and 1mM, bacterial attachment to iron-coated sand surfaces decreased with increasing NaHCO(3) concentration, due to charge modification of coated sand surfaces from positive to negative. At intermediate concentration of 10mM, iron-coated sand surfaces were negatively charged like quartz sand, and so the presence of (bi)carbonate ions resulted in the increment of bacterial adhesion due to compression of the electrical double layers. At high concentrations of 100 and 200mM (pH 8.5-8.6), where iron-coated surfaces were negatively charged, bacterial deposition decreased compared to the case of 10mM, possibly due to the same phenomenon observed in quartz sand (short-range forces). This study demonstrates that bacterial adhesions to quartz and metal oxide-coated surfaces in the presence of (bi)carbonate ions show different responses depending on the NaHCO(3) concentration and surface charges of porous media.

Bacterial attachment to iron-impregnated granular activated carbon

Bacterial attachment to iron-impregnated granular activated carbon (Fe-GAC) was investigated in this study using Enterococcus faecalis ATCC 10100 and charcoal-based GAC. Two sets of column experiments were performed under different ionic strengths and pH conditions. Breakthrough curves of bacteria were obtained by monitoring effluent. Mass recoveries and attachment rate coefficients were quantified from these curves. In addition, characteristics of Fe-GAC were analyzed using field emission scanning electron microscopy (FESEM) and X-ray spectrometry (EDS). Results show that Fe-GAC was characterized by mosaic-like deposition layers of iron oxides with about 2 microm in thickness. Color mapping with FESEM visualized the spatial distribution of carbon (yellow-green) and iron (red) on Fe-GAC. EDS indicates that iron was distinctly found from Fe-GAC at three peak positions. Results also reveal that bacterial attachment to Fe-GAC was affected by ionic strength and pH. Bacterial mass recoveries decreased from 62.9 to 41.7% with increasing ionic strength from 1 to 50 mM. This indicates that bacterial attachment to the surfaces of Fe-GAC was enhanced with increasing ionic strength. With increasing pH from 6.46 to 9.19, mass recoveries increased from 50.5 to 84.2%, indicating that bacterial attachment to Fe-GAC was reduced with increasing pH. This study demonstrates that iron oxides offer favorable attachment sites for bacteria on the surfaces of Fe-GAC and further improves the knowledge of bacterial removal in Fe-GAC.

Determination of bacterial mass recovery in iron-coated sand: influence of ionic strength.

Column experiments were performed in this study to investigate the influence of ionic strength on the mass recovery of Escherichia coli in iron-coated sand. The first set of the experiments was performed in the coated sand under various NaCl concentrations. The second experiments were carried out in the coated sand under various NaCl concentrations with a fixed phosphate concentration. Bacterial mass recoveries were quantified from breakthrough curves. The mass recoveries were compared with those obtained from the experiments in quartz sand under the same ionic strength/composition. Experimental results show that the mass recovery in quartz sand decreased from 76.7 to 9.2% with increasing effective ionic strength (I e ) from 0 to 149.4 mM using NaCl. In the coated sand, however, the mass recovery remained constant in the range between 2.7 and 3.7% even though I e increased in the same range. This indicates that bacterial adhesion to the coated sand may not be affected by ionic strength in the presence of NaCl. Results also illustrate that the mass recovery in quartz sand decreased from 64.7 to 13.3% with increasing I e from 0.97 to 149.6 mM using NaCl under a fixed phosphate concentration (0.97 mM as I e ). In the coated sand, the mass recovery increased sharply to 58.5% in 0.97 mM phosphate concentration compared to the case in deionized water (3.0%). This indicates that in the coated sand bacterial mass recovery can increase due to the presence of phosphate. In addition, the mass recovery in the coated sand decreased from 58.5 to 6.7% with increasing I e from 0.97 to 149.6 mM using NaCl under a fixed phosphate concentration (0.97 mM as I e ). This demonstrates that bacterial adhesion to the coated sand may be influenced by ionic strength in the presence of phosphate.

Lab-scale experiments and model analyses for bacterial removal in flow-through columns containing dolomite

AbstractThe aim of this study was to investigate the removal of bacteria (Bacillus subtilis ATCC 6633) from aqueous solutions using dolomite as a filter medium. Column experiments were performed in step injection mode under various conditions of influent bacterial concentration (0.5–2.0u2009g/L), flow rate (0.5–1.5u2009mL/min), and column length (10–30u2009cm). The highest percentage bacterial removal (Re) of 75.2u2009±u20091.6% was obtained under the following conditions: influent bacterial concentrationu2009=u20091.0u2009g/L; flow rateu2009=u20090.5u2009mL/min; column lengthu2009=u200920u2009cm. The highest column capacity for bacterial removal (q0) of 2.126u2009±u20090.067u2009mg/g was achieved using an influent bacterial concentration of 2.0u2009g/L, flow rate of 1.0u2009mL/min, and column length of 20u2009cm. Increasing the bacterial concentration and flow rate had a negative effect on Re, whereas the q0 values were positively affected. Increasing the column length produced a positive effect on Re, whereas q0 declined. Simulation of the breakthrough curves (BTCs) using the Adams...

Analysis of Calculation Model for Specific Air-water Interface Area in Unsaturated Porous Media

In unsaturated porous media, the air-water interface (AWI) plays an important role in removing of biocolloids such as bacteria, viruses, and protozoan (oo)cysts. In this study, four models related to calculation of specific AWI area are analyzed to determine the appropriate model, and the selected models are verified using the previously reported experimental data. The results indicate that the modified model from Niemet et al. (2002) is the most appropriate tool for calculating the specific AWI area using the van Genuchten (1980) parameters obtained from the water retention curve. Hence, it is expected that this model could be used to quantitatively determine the attachment of biocolloids to AWI in the transport modeling of biocolloids in unsaturated porous media.

Evaluation of Bacterial Transport Models for Saturated Column Experiments

Bacterial transport models were evaluated in this study to determine the suitable model at describing bacterial transport in saturated column experiments. Four models used in the evaluation were: advective-dispersive equation (ADE) + equilibrium sorption/retardation (ER) + kinetic reversible sorption (KR) (Model I), ADE + two-site sorption (Model 2), ADE + ER + kinetic irreversible sorption (KI) (Model 3), ADE + KR + KI (Model 4). Firstly, analyses were performed with the first experimental data, showing that Model 4 is appropriate for describing bacterial transport. Even if Model 1 and 2 fit well to the observed data, they have a defect of not including the irreversible sorption, which is directly related to mass loss of bacteria. Model 3 can not properly describe the tailing observed in the data. However, further analysis with the second data indicates that Model 4 can not describe retardation of bacteria, even if the sorption-related parameters are varied. Therefore, Model 4 is modified by incorporating retardation factor into the model, resulting in the improved fitting to the data. It indicates that the transport model, into which retardation, kinetic reversible sorption, and kinetic irreversible sorption are incorporated, is suitable at describing bacterial transport in saturated column experiments. It is expected that the selected transport model could be applied to properly analyze the bacterial transport in saturated porous media.