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Santa Barbara Amorphous-15 (SBA) is a stable and mesoporous silica material. Quaternized SBA-15 with alkyl chains (QSBA) exhibits electrostatic attraction for anionic molecules via the N+ moiety of the ammonium group, whereas its alkyl chain length determines its hydrophobic interactions. In this study, QSBA with different alkyl chain lengths were synthesized using the trimethyl, dimethyloctyl, and dimethyoctadecyl groups (C1QSBA, C8QSBA, and C18QSBA, respectively). Carbamazepine (CBZ) is a widely prescribed pharmaceutical compound, but is difficult to remove using conventional water treatments. The CBZ adsorption characteristics of QSBA were examined to determine its adsorption mechanism by changing the alkyl chain length and solution conditions (pH and ionic strength). A longer alkyl chain resulted in slower adsorption (up to 120 min), while the amount of CBZ adsorbed was higher for longer alkyl chains per unit mass of QSBA at equilibrium. The maximum adsorption capacities of C1QSBA, C8QSBA, and C18QSBA, were 3.14, 6.56, and 24.5 mg/g, respectively, as obtained using the Langmuir model. For the tested initial CBZ concentrations (2–100 mg/L), the adsorption capacity increased with increasing alkyl chain length. Because CBZ does not dissociate readily (pKa = 13.9), stable hydrophobic adsorption was observed despite the changes in pH (0.41–0.92, 1.70–2.24, and 7.56–9.10 mg/g for C1QSBA, C8QSBA, and C18QSBA, respectively); the exception was pH 2. Increasing the ionic strength from 0.1 to 100 mM enhanced the adsorption capacity of C18QSBA from 9.27 ± 0.42 to 14.94 ± 0.17 mg/g because the hydrophobic interactions were increased while the electrostatic attraction of the N+ was reduced. Thus, the ionic strength was a stronger control factor determining hydrophobic adsorption of CBZ than the solution pH. Based on the changes in hydrophobicity, which depends on the alkyl chain length, it was possible to enhance CBZ adsorption and investigate the adsorption mechanism in detail. Thus, this study aids the development of adsorbents suitable for pharmaceuticals with controlling molecular structure of QSBA and solution conditions.

Ibuprofen (IPF) is one of the most prescribed nonsteroidal anti-inflammatory drugs in recent times, but it is not readily removed in conventional wastewater treatments. Here, we investigate the adsorption characteristics of IPF onto calcined spherical hydrochar (CSH), which was synthesized through hydrothermal carbonization of sucrose followed by calcination. The adsorption experiments show that the equilibration time for IPF was 360 min, and a pseudo-second-order model was best fitted to the kinetic data. The isotherm data were best described by the Liu model with a theoretical maximum adsorption capacity of 95.6 mg/g. The thermodynamic data indicate the endothermic nature of the adsorption at 10-40 °C. The CSH was favorably regenerated and reused using methanol. In pH experiments, the IPF adsorption capacity declined gradually as pH rose from 2 to 8, dropped rapidly at pH 10, and became negligible at pH 12. The IPF adsorption to the CSH could occur through various adsorption mechanisms. Hydrogen-bond formation, π-π interactions, n-π* interactions, and electrostatic repulsion were explored and visualized with molecular modeling using CHEM3D. The Raman, FTIR, and XPS spectra suggest that π-π interactions could take place between the CSH and IPF. Considering the pK

The aim of study was to analyze diclofenac (DCF) removal from aqueous solutions by metal-organic framework MIL-100(Fe) using multi-parameter batch experiments and artificial neural network (ANN) modeling. First, single-parameter experiments were performed in terms of initial solution pH, MIL-100(Fe) dosage, initial DCF concentration, and temperature. The DCF removal decreased with an increase in pH from 5 to 10 and became negligible at pH 12. The kinetic and equilibrium data showed that DCF removal reached an equilibrium at 12 h, with a maximum capacity of 414.6 mg/g from the Langmuir isotherm model. The DCF removal was enhanced with increasing temperature. Multi-parameter experiments (n = 56) conducted under 28 duplicate experimental conditions showed DCF removal rates between 70.8 – 90.8% with a final pH range of 4.5 – 5.4 for most of the experimental conditions. The ANN model was developed based on the multi-parameter experimental data. The optimal topology for the ANN model was determined to be 4:7:6:2 (4 input variables, 7 neurons in the first hidden layer, 6 neurons in the second hidden layer, and 2 output variables). Among the four input variables, temperature was the most important variable affecting DCF removal rate under the given experimental ranges.

In this study, quaternary ammonium functionalized-silica gel was synthesized for nitrate removal using dimethyl dodecyl[3-(trimethoxysilyl)propyl] ammonium chloride (DMDAC) as a quaternary ammonium silane coupling agent, which was grafted to silica gel to obtain the DMDAC-silica gel. Batch experiments showed that the DMDAC-silica gel could effectively remove nitrate in the pH range of 4 to 10. Kinetic and equilibrium experiments showed that nitrate removal by the DMDAC-silica gel reached equilibrium in 60 min with a maximum nitrate removal capacity of 56.4 mg/g. Fixed-bed column experiments (bed depth = 10–30 cm; inner diameter of column = 2.5 cm; flow rate = 0.06–0.18 L/h) in nitrate solution demonstrated the dynamic behaviors of nitrate removal by the DMDAC-silica gel under various experimental conditions of flow rate, bed depth, and influent nitrate concentration. The DMDAC-silica gels could be successfully used for nitrate removal and regenerated and reused with 10% NaCl solution in the column. In groundwater (nitrate = 140 mg/L, chloride = 63 mg/L, sulfate = 440 mg/L, and bicarbonate = 20–300 mg/L), the nitrate BTCs appeared behind the sulfate BTCs with α S N values of 5.7–11.3, indicating that the DMDAC-silica gel could selectively remove nitrate over sulfate in dynamic flow conditions.

On the use of UV light emitting diodes (UV-LEDs), emitting at 260–290 nm, has attracted attention for treating cyanotoxins, although most previous studies related with UV/H2O2 process have been used conventional mercury UV lamp (λ = 254 nm). Therefore, the aim of the study was to investigate the UV-LEDs, having a wavelength of 255 nm, coupled with H2O2 process for the removal of microcystin-LR (MC-LR), microcystin-RR (MC-RR), and anatoxin-a (ANTX) and to verify the degradation kinetics, mechanism and impact of water quality parameters in relation to their molecular properties. Among three UV-LEDs (λ = 255, 266, and 280 nm), the shortest one was the most effective to remove MC-LR coincided with its decadic molar absorption coefficient. The degradation rate constants of MC-LR, MC-RR, and ANTX were 0.0644, 0.0241, and 0.0076 cm2 mJ−1, respectively, during the UV-LED/H2O2 process. For MC-LR and MC-RR degradation, reaction with OH is a major mechanism along with direct photolysis as a minor factor. ANTX degradation is predominantly attributed to OH. The second-order rate constant for ANTX is one order of magnitude lower than others because ANTX is recalcitrant to oxidation. The MC-LR degradation occurred at the diene and aromatic ring of Adda, Mdha, and amide bond and the main reactive oxidation site of MC-RR was the Adda chain. In contrast, photo-oxidation transformed ANTX to higher molecular weight compounds via polymerization instead of degradation. When MC-LR, MC-RR, and ANTX were co-present, lower concentration of dissolved organic carbon and higher acidity with bicarbonate was favorable to remove MC-LR and MC-RR according to their scavenging factors and reaction with CO −3. However, ANTX is relatively resistant to degradation at pH 3.2.

The aim of this study was to synthesize and consider an oxidized mesoporous carbon-based magnetic composite (M-O-MC) for heavy metal removal from aqueous solutions. The M-O-MC used was a black powdery particle that was attracted to external magnets and thus separated from aqueous solutions. The M-O-MC had an average particle size of 232 ± 63 nm, with a BET specific surface area of 179 m2/g and a total pore volume of 0.18 cm3/g. The X-ray diffractometer pattern of the M-O-MC showed characteristic peaks related to maghemite due to the impregnation of iron oxide nanoparticles. Fourier-transform infrared spectra showed that carboxylic and Fe-O bonds were assigned on the M-O-MC due to surface functionalization. The X-ray photoelectron spectra showed that carboxyl functional groups on the surface of the M-O-MC were involved in the adsorption of Cu(II). Batch tests were performed using Cu(II) as a target heavy metal. The Cu(II) adsorption to the M-O-MC was influenced by solution pH and other cations. In the four cycles of adsorption–desorption testing, the M-O-MC was successfully regenerated and reused, maintaining its magnetic property. The equilibrium time for the Cu(II) adsorption was 3 h, whereas the maximum adsorption capacity was 51.4 mg/g. The Cu(II) adsorption was endothermic, increasing with a rise in temperature from 15 °C to 45 °C. In batch tests with plating wastewater containing various metal ions (Cu(II), total Cr, Ni(II), Zn(II), etc.), the M-O-MC was applied as an adsorbent for the removal of heavy metal ions.

The aim of this study was to synthesize dual-functionalized poly(vinyl alcohol) (PVA)/poly(acrylic acid) (PAA) electrospun nanofibers with enzyme and copper ion (Cu(II)) for enhancing anti-biofouling activities. The PVA/PAA nanofibers were successfully synthesized by co-electrospinning (voltage = 17 kV; tip-to-collector distance = 15 cm) and cross-linked by heat treatment. The PVA/PAA nanofibers were functionalized through adsorbing Cu(II) onto the nanofibers to prepare the PVA/PAA-Cu(II) nanofibers. Three proteases (proteinase K, trypsin, and α-chymotrypsin) and a quorum quenching enzyme (acylase I) were tested for biofilm reduction that α-chymotrypsin effectively inhibited the biofilm formation and removed biofilms of Pseudomonas aeruginosa and Staphylococcus aureus. The PVA/PAA nanofibers were dual-functionalized with α-chymotrypsin and Cu(II) to obtain PVA/PAA-Cu(II)-α nanofibers. Degradation tests for extracellular polymeric substances (EPS) extracted from P. aeruginosa indicated that the PVA/PAA-Cu(II)-α nanofibers could degrade the EPS proteins up to 0.26 mg mL−1 for 300 min, which was higher than that of free α-chymotrypsin. For anti-biofouling tests, the log number of planktonic and sessile cells of P. aeruginosa was the lowest in the PVA/PAA-Cu(II)-α nanofibers. The anti-biofouling activities of the PVA/PAA-Cu(II)-α nanofibers could be attributed to the effects of both Cu(II) (killing planktonic and sessile cells) and α-chymotrypsin (degrading the EPS protein in biofilm).

Layered double hydroxide (LDH) has been widely used as an adsorbent to remove contaminants from aqueous solutions. However, LDH in powder form might not be suitable in water and wastewater treatment systems due to low hydraulic conductivity and sludge production. Therefore, it is necessary to synthesize bead-type adsorbents for application in treatment systems. In this study, LDH beads were prepared through immobilization of powdered Mg Fe LDH in polymer matrices, composed of poly(vinylidene fluoride) and poly(vinyl alcohol). The LDH beads had an average size of 2.4 ± 0.6 mm with a Brunauer-Emmett-Teller (BET) specific surface area of 30.41 m2/g and total pore volume of 0.12 cm3/g. Batch experiments were conducted on the use of the LDH beads for phosphate sorption in stream water (pH = 6.9, ionic strength = 613 μS/cm) collected from the Seoho stream located in Suwon, Korea. Fourier-transform infrared (FTIR) spectrometer and X-ray photoelectron spectroscopy (XPS) were used to analyze the chemical characteristics of the LDH beads before and after phosphate sorption. Phosphate sorption to the LDH beads remained relatively constant at initial pH values of 5–9. The LDH beads could be used repeatedly for phosphate sorption through desorption with a NaOH solution. The equilibrium time for the phosphate sorption was 3 h, whereas the maximum sorption capacity was 2.050 mgP/g. In addition, the phosphate sorption increased with a rise in temperature from 15 to 45 °C. Under dynamic flow conditions (flow rate = 4.9 and 9.8 mL/min; bed depth = 10, 20, and 30 cm; inner diameter of column = 2.5 cm), fixed-bed column experiments were performed to test the applicability of the LDH beads in the phosphate removal from the stream water. The phosphate sorption capacity of the column was quantified to be 1.175 mgP/g at given experimental conditions (bed depth = 30 cm; flow rate = 4.9 mL/min). The performance of fixed-bed columns was quantified by analyzing phosphate breakthrough curves with fixed-bed kinetic sorption models (Bohart-Adams and modified dose-response models). This study demonstrated that the LDH beads could be successfully applied as adsorbents for phosphate removal from natural water.

Thermal treatment of mercury (Hg)-contaminated soil was studied to investigate the desorption behavior of Hg at different temperatures. The soil samples were collected from two locations with different land uses around the mine and industrial site. The effect of soil properties such as inorganic carbonate minerals and organic matter content on Hg desorption was investigated to understand the thermal desorption process. The effect of soil composition on Hg desorption showed that behavior at 100 °C was similar, but a different behavior could be found at 300 °C. The thermal desorption efficiency at 300 °C is affected by the thermal properties of soils and the Hg desorption capacity of the soils. The Hg from both soil types was removed above 300 °C, and Hg was effectively removed from mine soil due to the partial decomposition of carbonate in the soil composition, while industrial soil showed that desorption would be restrained by Hg organic matter complexes due to organic matter content. Despite a relatively higher concentration of Hg in the mine soil, Hg removal efficiency was greater than that in the industrial soil. Sequential extraction results showed that only the Hg fractions (residual fractions, step 6) in mine soil changed, while the industrial soil was affected by changes in Hg fractions (step 3 to step 6) at 300 °C. Changes in soil pH during thermal desorption are also influenced by heating time and temperature. Therefore, the mechanisms of Hg desorption during thermal treatment were observed by soil properties. The volatilization of Hg in the soil is induced by organic carbon, while soil Hg release is controlled by organic matter complexes. Supplementary Information The online version contains supplementary material available at 10.1007/s11356-021-14024-z.

In this study, indigenous acidophilic bacteria living in mine drainage and hot acidic spring were collected and used for bioleaching experiments. The incubated indigenous acidophilic bacteria were inoculated on various minerals. The changes in pH, Eh, and heavy metal concentrations were examined with uninoculated controls to study bioleaching over time. As a result, the aspects of bioleaching varied greatly depending on the origin of microorganisms, the type of minerals, the temperature conditions, etc. We applied an ANN model to express and predict these complex bioleaching trends. Through the application of an ANN model, we developed the ANN models that can predict the changes in concentration of pH, Eh, and heavy metal ion concentrations and further evaluated predictability. Through this, the predictability of bioleaching using the ANN models can be confirmed. However, we also identified limitations, showing that further testing and application of the ANN models in more diverse experimental conditions are needed to improve the predictability of the ANN models.

In this study, a metal organic framework MIL-100(Fe) was synthesized for rhodamine B (RB) removal from aqueous solutions. An experimental design was conducted using a central composite design (CCD) method to obtain the RB adsorption data (n = 30) from batch experiments. In the CCD approach, solution pH, adsorbent dose, and initial RB concentration were included as input variables, whereas RB removal rate was employed as an output variable. Response surface methodology (RSM) and artificial neural network (ANN) modeling were performed using the adsorption data. In RSM modeling, the cubic regression model was developed, which was adequate to describe the RB adsorption according to analysis of variance. Meanwhile, the ANN model with the topology of 3:8:1 (three input variables, eight neurons in one hidden layer, and one output variable) was developed. In order to further compare the performance between the RSM and ANN models, additional adsorption data (n = 8) were produced under experimental conditions, which were randomly selected in the range of the input variables employed in the CCD matrix. The analysis showed that the ANN model (R2 = 0.821) had better predictability than the RSM model (R2 = 0.733) for the RB removal rate. Based on the ANN model, the optimum RB removal rate (>99.9%) was predicted at pH 5.3, adsorbent dose 2.0 g L − 1 , and initial RB concentration 73 mg L − 1 . In addition, pH was determined to be the most important input variable affecting the RB removal rate. This study demonstrated that the ANN model could be successfully employed to model and optimize RB adsorption to the MIL-100(Fe).

We synthesized and characterized surface-imprinted poly (ethyleneimine) (PEI)-grafted mesoporous silica SBA-15 (Cu-imprinted PEI-SBA-15) for selective Cu(II) sorption from aqueous solutions. To enhance the Cu(II) selectivity of Cu-imprinted PEI-SBA-15, Cu(II) loading on PEI-SBA-15 was increased via Cu(II) sorption under high-molar-concentration ratios of chloride (Cl) and Cu(II) ions. Then, selective Cu(II) sorption sites were increased through imprinting processes (crosslinking and elution) on Cu-loaded PEI-SBA-15. Selective experiments were performed using Cu-imprinted PEI-SBA-15 prepared at various [Cl−]/[Cu(II)] ratios, ranging from 2 to 1000. In multinary solutions containing divalent ions, such as Cu(II), Pb(II), Zn(II), Ni(II), and Co(II), Cu(II) selectivity was highest (79.62) at a [Cl−]/[Cu(II)] ratio of 500; the relative Cu(II) selectivity for Cu-imprinted PEI-SBA-15 over PEI-SBA-15 was 29.24. In multinary solutions containing Cu(II) along with trivalent and tetravalent ions, such as Al(III), Cr(III), and Zr(IV), the Cu(II) selectivity was also highest (3.40) at a ratio of 500; the relative Cu(II) selectivity was 3.96. In this study, we demonstrated that the Cu(II) selectivity of surface-imprinted SBA-15 could be enhanced through its preparation under high [Cl−]/[Cu(II)] ratios.

The stability of carbon black nanoparticles (CB-NPs) was investigated in five different ecotoxicity test media for fish, daphnia, and algae (i.e., ISO Test water, Elendt M4 medium, OECD TG 201 medium, AAP medium, and Bold’s Basal Medium) in the presence and absence of Suwannee River Humic Acid (SRHA) as a function of time. Hydrodynamic size, particle sedimentation rate, and visual images of suspensions were analyzed for 96 h, and the SRHA concentration was varied from 0 to 10 mg/L. Zeta potential and water contact angle of CB-NP, and SRHA sorption to CB-NPs were also examined to complement stability analyses. CB-NPs always exhibited negative zeta potential regardless of media type and SRHA concentration, and became more negative in the presence of SRHA due to SRHA sorption. Moreover, CB-NPs were found to be hydrophobic in the absence of SRHA, whereas they became hydrophilic when SRHA was adsorbed. Stability test results showed that regardless of test media, the hydrodynamic size increased fast and the sedimentation rate was high in the absence of SRHA, indicating poor stability of the CB-NPs. Conversely, the presence of SRHA substantially increased the stability of CB-NPs over 96 h, regardless of the SRHA concentration and test media type. Stability trends in the presence and absence of SRHA were not consistent with predictions from classical Derjaguin–Landau–Verwey–Overbeek (DLVO) theory. However, extended and modified DLVO theories, that also accounted for hydrophobic-attractive forces due to the inherent nature of CB-NPs and steric repulsive forces associated with the brush-like conformation of SRHA adsorbed to CB-NPs, better described CB-NPs’ stability in the absence and presence of SRHA, respectively.

In this study, both powdered and granular N-(3-trimethoxysilylpropyl)diethylenetriamine (DAEAPTS)-grafted mesoporous silica SBA-15 were synthesized for hexavalent chromium (Cr(VI)) removal from industrial wastewater. The powdered adsorbents were synthesized via grafting DAEAPTS onto SBA-15. The Cr(VI) sorption characteristics of the adsorbents were examined under batch conditions in synthetic Cr(VI) solutions. Batch experiments revealed that the Cr(VI) sorption was favorable at acidic pH conditions with the greatest sorption at pH 3. The Cr(VI) sorption was a fast process, reaching equilibrium within 10 min. The maximum Cr(VI) sorption capacity was 330.88 mg/g. To overcome limitations of the powdered adsorbents for large-scale application (hydraulic and separation problems), the spherical granular adsorbents (average size = 1.13 ± 0.09 mm) were prepared through immobilizing the powdered DAEAPTS-grafted SBA-15 into a polymer blend (poly(vinyl alcohol) and sodium alginate). The granular adsorbents were applied for Cr(VI) removal from two industrial plating wastewaters in flow-through column experiments. In the experiment with wastewater 1 (Cr(VI) concentration = 328.7 mg/L), the Cr(VI) sorption capacity of the granular adsorbents was 158.8 mg/g. In the experiment with wastewater 2 (Cr(VI) concentration = 2671.6 mg/L), the pristine and regenerated adsorbents were tested to demonstrate that the granular adsorbents could be successfully regenerated and reused for Cr(VI) removal.

Diclofenac (DCF) is a nonsteroidal anti-inflammatory drug commonly found in wastewater and drinking water. The potential of carbon spheres (CSs) to serve as adsorbents in removal of DCF from water has been explored recently. However, glucose-derived CSs and cellulose-derived CSs reportedly have very low DCF adsorption capacities. Here, we describe the synthesis of sucrose-derived carbon spheres (SDCSs) for adsorption of DCF from aqueous solutions. The physicochemical properties of the SDCSs were characterized using various instrumental techniques. The SDCSs were spherical particles with an average size of 224.2 ± 19.5 nm, a point of zero charge (pHpzc) of 3.14, a Brunauer–Emmett–Teller specific surface area of 239.3 m2/g, a total pore volume of 0.142 cm3/g, and an average pore diameter of 2.38 nm. The adsorption characteristics of the SDCSs were investigated under batch conditions by varying the solution pH, reaction time, initial DCF concentration, and temperature. Adsorption experiments demonstrated that the DCF adsorption capacity was highest at an initial pH of 5 and decreased gradually as the pH was increased to 11. X-ray photoelectron spectroscopy spectra of the SDCSs before and after DCF adsorption indicate that DCF adsorption to the SDCSs occurred through hydrogen-bond formation and π-π interactions. According to the pHpzc value and experimental pH data, repulsive electrostatic interactions between the negatively charged SDCSs and negatively charged DCF resulted in a decrease of DCF adsorption capacity as pH increased. Kinetic and equilibrium data showed that DCF adsorption to the SDCSs reached equilibrium at 6 h, with a maximum adsorption capacity of 531.5 mg/g, which was far higher than glucose-derived CSs and cellulose-derived CSs. DCF adsorption to the SDCSs was endothermic, increasing with increasing temperature from 10 ℃ to 40 ℃. Five adsorption-desorption cycles demonstrated that the SDCSs can be regenerated with methanol and reused in DCF adsorption. This study demonstrates that SDCSs have a high adsorption capacity and reusability for adsorption of DCF from aqueous solutions.

Diclofenac (DCF) is a non-steroidal, anti-inflammatory drug commonly prescribed for humans and animals. DCF has been widely detected in aquatic environments and wastewater, and so various adsorbents have been applied for DCF removal from aqueous solutions. Here, we explored DCF removal by quaternary ammonium-functionalized mesoporous silica SBA-15 (q-SBA-15) in aqueous solutions using artificial neural network (ANN) and response surface methodology (RSM) modeling. For this purpose, SBA-15 was synthesized and quaternized with dimethyloctyl[3-(trimethoxysilyl)propyl] ammonium chloride to obtain q-SBA-15. The physicochemical characteristics of q-SBA-15 were examined using various instruments including field emission scanning electron microscopy, transmission electron microscopy, elemental analysis, nitrogen gas adsorption-desorption analysis, nuclear magnetic resonance spectroscopy, X-ray diffractometry, Fourier-transform infrared spectrometry (FTIR), and X-ray photoelectron spectrometry (XPS). N2 adsorption-desorption analysis indicated that q-SBA-15 had a BET surface area of 125.1 m2/g, an average pore diameter of 3.86 nm, and a mesopore volume of 0.121 cm3/g. In the FTIR spectra, several new peaks appeared after DCF removal, confirming DCF adsorption onto the surface of q-SBA-15. The XPS spectra illustrated that DCF was adsorbed onto N+ surface sites on the quaternary ammonium moiety of q-SBA-15 through anion exchange between anionic DCF− and chloride ion. Single-parameter experiments were conducted in terms of initial pH, adsorbent dosage, reaction time, and initial DCF concentration. DCF removal rate decreased gradually in the initial pH of 6.0–10.0. DCF removal reached equilibrium at 12 h with the maximum removal capacity of 593 mg/g. Multi-parameter experiments were designed using the central composite design method with four input parameters and two output parameters (DCF removal rate and final pH). Fifty-six experiments (28 experimental conditions in duplicate) were conducted to examine the simultaneous effects of the input parameters on the output parameters. Based on the experimental data, RSM and ANN models were developed to predict the DCF removal rate and final pH. The additional experimental data (4 experimental conditions in duplicate) demonstrated that the developed ANN model had better predictability than the RSM model for the output parameters.

In this study, benzyl triethylammonium chloride (BTEAC)-functionalized poly(vinyl alcohol) (PVA) nanofibers were fabricated via electrospinning and deposited on a commercial polycarbonate (PC) membrane (f-PVA/PC membrane) in order to enhance the anti-biofouling activity of the membrane. Permeation flux, biofilm formation, contact, and regeneration tests were performed to evaluate the anti-biofouling potential of the f-PVA/PC membrane against bacteria, including Klebsiella pneumoniae, Pseudomonas aeruginosa, Staphylococcus aureus, and Escherichia coli. The permeation flux test showed that the normalized flux of the f-PVA/PC membrane was retained at 1.0 after filtration of 500 mL of the bacterial solution (K. pneumoniae), whereas the fluxes of the PC and PVA/PC membranes decreased to 0.57 and 0.84, respectively. In the biofilm formation test, the number of biofilm cells on the f-PVA nanofibers (P. aeruginosa = 4.21–4.98 log colony-forming unit (CFU), S. aureus = 3.74–4.39 log CFU) was less than those on the PVA nanofibers (P. aeruginosa = 5.68–6.89 log CFU, S. aureus = 4.72–5.82 log CFU). The contact test demonstrated that mortality rates (contact time = 60 min) on the f-PVA/PC membrane (K. pneumoniae = 94.08%, S. aureus = 99.99%, E. coli = 92.30%) were greater than those on the PC membrane (K. pneumoniae = 73.75%, S. aureus = 62.41%, E. coli = 76.80%). Fluorescence microscopy images illustrated that the population of red (dead) bacterial cells on the f-PVA/PC membranes was greater than that on the PVA/PC membrane. The regeneration test indicated that the f-PVA/PC membrane retained its anti-biofouling activity during regeneration and reuse over six cycles with mortality rates of 93.82–96.29% (K. pneumoniae), 74.27–85.15% (S. aureus), 91.68–95.19% (E. coli), and 94.94–96.90% (mixed-strain bacteria). The results demonstrated that the f-PVA nanofibers could enhance the anti-biofouling potential of the membrane through both anti-adhesive and anti-bacterial surface modifications.

Ceramic membrane ultrafiltration experiments were performed with 7-channel tubular membrane (molecular weight cutoff = 300 kD) at a constant transmembrane pressure and crossflow rate under recirculation mode. In the experiments, the fouling characteristics of river water (RW, dissolved organic carbon (DOC) = 3.4 mg/L) were compared with humic acid solution (HA1, DOC = 3.7 mg/L). Also, the fouling behaviors of secondary effluent (SE, DOC = 7.9 mg/L) were compared with HA2 (DOC = 8.5 mg/L). Fluorescence excitation-emission matrix, modified Hermia’s model, and resistance-in-series model were used to analyze the fouling characteristics. Results demonstrated that RW and SE could cause ceramic membrane fouling more rapidly due to their hydrophilic organic compositions in comparison with hydrophobic HA.

Nanofibrous adsorbents were fabricated by electrospinning with a blend solution of poly(acrylic acid) (PAA) and poly(vinyl alcohol) (PVA) polymers and used for copper (Cu(II)) removal from industrial plating wastewater. Fourier-transform infrared spectrometry analysis demonstrated that a new peak appeared at 1617 cm−1 due to the interactions between Cu(II) and carboxyl oxygen on the surfaces of the PAA/PVA nanofibrous adsorbents during Cu(II) removal in the plating wastewater. X-ray photoelectron spectroscopy analysis showed that the Cu 2p peak at a binding energy of 932 eV appeared in a wide scan of the nanofibrous adsorbents after Cu(II) removal in the plating wastewater. The carboxyl groups on the surfaces of the nanofibrous adsorbents could provide sorption sites for Cu(II) removal. Laboratory experiments in synthetic solutions showed that the nanofibrous adsorbents were effective in Cu(II) removal. The nanofibrous adsorbents had a maximum Cu(II) removal capacity of 49.3 mg g−1 with a far higher selectivity for Cu(II) over Ni(II) in a binary system. Also, the nanofibrous adsorbents could be regenerated and reused for Cu(II) removal through successive adsorption–desorption processes. Batch experiments in industrial plating wastewater (Cu(II) concentration = 430.06 mg L−1) demonstrated that the nanofibrous adsorbents had Cu(II) removal capacity of 25.8–33.6 mg g−1 in the adsorbent dose of 0.4–2.0 g L−1. However, the removal of other heavy metal ions (Ni, Zn, etc.) in the wastewater by the nanofibrous adsorbents was negligible. The nanofibrous adsorbents were also applied through filtration tests for Cu(II) removal from the wastewater under dynamic flow conditions.

In this study, the characterizations and adsorption efficiencies for chromium, copper and nickel were evaluated using manufacture-grade Fe2O3-carbon foam. SEM, XRD, XRF and BET analyses were performed to determine the characteristics of the material. Various pore sizes (12–420 μm) and iron contents (3.62%) were found on the surface of the Fe2O3-carbon foam. Fe2O3-carbon foam was found to have excellent adsorption efficiency compared to carbon foam for mixed solutions of cationic and anionic heavy metals. The adsorption capacities for chromium, copper and nickel were 6.7, 3.8 and 6.4 mg/g, respectively, which were obtained using a dual exponential adsorption model. In experiments with varying dosages of the Fe2O3 powder, no notable differences were observed in the removal efficiency. In a fixed-bed column test, Fe2O3-carbon foam achieved adsorption capacities for chromium, copper and nickel of 33.0, 12.0 and 9.5 mg/g, respectively, after 104 h. Based on these results, Fe2O3-carbon foam was observed to be a promising material for treatment of plating wastewater.

Microcystin-LR (MC-LR) is the most common cyanotoxin released from algal-blooms. The study investigated the MC-LR adsorption mechanisms by comparing adsorption performance of protonated mesoporous carbon/silica (MC-H, MS-H) and their amino-functionalized forms (MC-NH2 and MS-NH2) considering surface chemistry and pore characteristics. The maximum MC-LR adsorption capacity (Langmuir model) of MC-H (37.87 mg/g) was the highest followed by MC-NH2 (29.25 mg/g) and MS-NH2 (23.03 mg/g), because pore structure is partly damaged during amino-functionalization. However, MC-NH2 (k2 = 0.042 g/mg/min) reacted faster with MC-LR than MC-H during early-stage adsorption due to enhancing electrostatic interactions. Intra-particle diffusion model fit indicated Kp,1 of MC-H (2.11 mg/g/min1/2) was greater than MC-NH2 due to its greater surface area and pore volume. Also, large mesopore diameters are favorable to MC-LR adsorption by pore diffusion. The effect of adsorbate molecular size on adsorption trend against MC-H, MC-NH2 and MS-NH2 was determined by kinetic experiments using two dyes, reactive blue and acid orange: MS-NH2 achieved the highest adsorption for both dyes due to the large number of amino groups on its surface (41.2 NH2/nm2). Overall, it was demonstrated that adsorption of MC-LR on mesoporous materials is governed by (meso-)pore diffusion and π – π (and hydrophobic) interactions induced by carbon materials; in addition, positively-charged grafted amino groups enhance initial MC-LR adsorption rate.

Advanced oxidation processes have gained significant attention for treating tetracycline (TC) and oxytetracycline (OTC), however, their oxidation using the photo-Fenton process has not been sufficiently studied. Although degradations of TC and OTC were enhanced by increasing H2O2 and Fe2+ within the ranges investigated (H2O2 = 20–50 mg/L and Fe = 1–10 mg/L) under UV irradiation, further experiments for the photo-Fenton process were conducted with 20 mg/L of H2O2 and 5 mg/L of Fe2+ to balance efficiency and cost. The photo-Fenton process (UV/H2O2/Fe2+) was shown to be more effective to remove TC and OTC than H2O2, ultraviolet (UV), and UV/H2O2 at the same doses of oxidants. Inorganic anions and cations were shown to inhibit the degradation of TC and OTC during the photo-Fenton process, in the following order: HPO42- > HCO3− ≫ SO42- > Cl− and Cu2+ ≫ Ca2+ > Na+. The TC and OTC degradation are generally improved by increasing pH, which is opposite to the kpCBA,obs values, caused by increasing the deprotonation degree of TC and OTC. Four and nine transformation products of TC and OTC, respectively, were detected over the treatment period. Among the transformation products, m/z 443.14 (C22H22N2O8) formed during TC degradation, and m/z 433.16 (C20H20N2O9) and m/z 415.15 (C20H18N2O8) formed during OTC degradation, were reported for the first time. Vibrio fischeri toxicity assessment indicated that the inhibition ratio was decreased with a decreasing TC concentration, while, OTC transformation lead to higher toxicity. The product (m/z 477.15b) was determined to be the compound causing toxicity during degradation of OTC by using the quantitative structure activity relationship (QSAR). This toxic transformation product caused higher inhibition ratios than its parental compound (OTC), but its further oxidization resulted in decreasing the inhibition ratios.

The aim of this study was to examine nitrate removal by quaternized silica gel (q-SG) in ternary solutions of nitrate, phosphate, and sulfate under flow-through column conditions. q-SG was synthesized by grafting dimethyloctyl[3-(trimethoxysilyl)propyl] ammonium chloride on silica gel. Fixed-bed column experimental conditions (N = 15) were designed using central composite design to examine dynamic removal behaviors of competing anions in columns containing q-SG. During the experiments, influent solution containing ternary anions of nitrate, phosphate, and sulfate was injected into flow-through columns. In the effluent, the ternary anions along with chloride were monitored to obtain competitive breakthrough curves. Column experiments demonstrated the dynamic and competitive removal behaviors of anions during adsorption and leaching in the columns. Artificial neural network (ANN) model was developed based on the column experimental data to predict the removal rates of anions in the column experiments. In the model development, influent concentrations of nitrate, phosphate, and sulfate were selected as three variables in the input layer, whereas removal rates of nitrate, phosphate, and sulfate were chosen as three variables in the output layer. The developed ANN model with topology 3:8:9:3 (three input variables, eight neurons in the first hidden layer, nine neurons in the second hidden layer, and three output variables) could simultaneously predict the removal rates of anions in column experiments.

Polyethyleneimine (PEI)-functionalized mesoporous silica gel (SG) was synthesized through dual loading (d-PEI-SG) of copper (Cu) as a host ion for Cu(II)-PEI complex and crosslinking with glutaraldehyde in the synthesis pathway to enhance deposition of PEI on the SG. For comparison, the PEI-functionalized SG was also prepared through single loading (s-PEI-SG) of the host ion and crosslinking with glutaraldehyde. In thermogravimetric analysis, the weight loss of d-PEI-SG at 110–500 °C (7.8%) was greater than that of s-PEI-SG (2.8%), indicating the enhanced deposition of PEI on the silica gel surface of d-PEI-SG. The elemental composition from X-ray photoelectron spectroscopy analysis demonstrated that relative quantities of carbon and nitrogen in d-PEI-SG were larger than those of s-PEI-SG. In batch tests, the maximum Cu(II) adsorption capacity of d-PEI-SG was determined to 170.4 μmol g−1, which was four times larger than that (41.8 μmol g−1) of s-PEI-SG. In a multinary solution of divalent metal ions (Cu(II), Pb(II), Zn(II), Ni(II), and Co(II)) and trivalent/tetravalent metal ions (Cu(II), Al(III), Cr(III), and Zr(IV)), d-PEI-SG had a higher Cu(II) adsorption capacity and selectivity than s-PEI-SG. Column experiments were also conducted in the multinary solution of Cu(II), Pb(II), Zn(II), Ni(II), and Co(II), demonstrating that d-PEI-SG could remove more Cu(II) than s-PEI-SG in flow-through conditions.

The aim of this study was to quantify the interactions between graphene oxide (GO) and quartz sand by conducting experimental and modeling analyses. The results show that both GO and quartz sand were negatively charged in the presence of 0–50 mM NaCl and 5 mM CaCl2 (GO = −43.10 to −17.60 mV, quartz sand = −40.97 to −8.44 mV). In the Derjaguin-Landau-Verwey-Overbeek (DLVO) energy profiles, the adhesion of GO to quartz sand becomes more favorable with increasing NaCl concentration from 0 to 10 mM because the interaction energy profile was compressed and the primary maximum energy barrier was lowered. At 50 mM NaCl and 5 mM CaCl2, the primary maximum energy barrier even disappeared, resulting in highly favorable conditions for GO retention to quartz sand. In the Maxwell model analysis, the probability of GO adhesion to quartz sand (αm) increased from 2.46 × 10−4 to 9.98 × 10−1 at ionic strengths of 0–10 mM NaCl. In the column experiments (column length = 10 cm, inner diameter = 2.5 cm, flow rate = 0....

The removal of arsenic (As(III), As(V)) and selenium (Se(IV), Se(VI)) from aqueous solutions was examined in batch systems using magnetic iron oxide nanoparticles/multi-walled carbon nanotubes (MIO–MWCNTs) as adsorbents. The effects of reaction time, temperature, solution pH, initial contaminant concentration, and interfering anions were investigated. Kinetic model analyses demonstrate that the Elovich model was the most suitable for describing the As(III) and As(V) data, whereas the pseudo-second-order model provided the best fit for the Se(IV) and Se(VI) data. Thermodynamic analyses indicate that As(III) adsorption was endothermic, while As(V) adsorption was exothermic (As(III): ΔH° = 56.930 kJ/mol; As(V): ΔH° = −78.501 kJ/mol). Meanwhile, the adsorption of Se(IV) and Se(VI) was exothermic (Se(IV): ΔH° = −6.921 kJ/mol; Se(VI): ΔH° = −1.599 kJ/mol). The adsorption capacity of As(III) increased gradually from 4.25 to 6.95 mg/g between pH 1.6 and 6.8, while the adsorption capacity of As(V) decrease...

In this study, five different quaternary ammonium functionalized-mesoporous silica SBA-15 adsorbents with different alkyl chain lengths (C1Q-, C4Q-, C8Q-, C12Q-, and C18Q-SBA-15) were synthesized. This study focused on the effect of alkyl chain length of quaternary ammonium silane coupling agent grafted to SBA-15 on the selective nitrate removal from aqueous solutions. Fourier-transform infrared (FTIR) and X-ray photoelectron spectroscopy (XPS) spectra confirmed that quaternary ammonium functional groups were successfully grafted onto the surface of SBA-15. In the FTIR spectra of C8Q-, C12Q-, and C18Q-SBA-15, peaks of CH2 asymmetric and CH2 symmetric stretching appeared at 2922–2944 cm−1 and 2852–2856 cm−1, respectively, which were getting stronger with an increase of alkyl chain length. In the N 1s spectra of the quaternized SBA-15, new peaks of NH4NO3 appeared at 405.8–406.2 eV after removal experiments, providing evidence of nitrate removal. The observed 13C solid-NMR spectra of the quaternized SBA-15 demonstrated that the quaternization occurred successfully on the adsorbents. Batch experiments demonstrated that the quaternized SBA-15 could effectively remove nitrate in the pH range from 4 to 10. The nitrate removal by the quaternized SBA-15 was fast process with equilibrium time of 10 min for C1Q- and C4Q-SBA-15 and of 30 min for C8Q-, C12Q-, and C18Q-SBA-15. The maximum nitrate removal capacities (mg/g) were in the order of C8Q-SBA-15 (136.4) > C4Q-SBA-15 (129.9) > C1Q-SBA-15 (89.4) > C12Q-SBA-15 (71.9) > C18Q-SBA-15 (30.7). In the presence of competing anions (chloride, phosphate, bicarbonate, and sulfate), C8Q-and C12Q-SBA-15 were more effective for nitrate removal than C1Q- and C4Q-SBA-15. In ground water (pH = 7.6, chloride = 47.7 mg/L, nitrate = 153.8 mg/L, sulfate = 445.4 mg/L; bicarbonate = 20.2 mg/L), C8Q- and C12Q-SBA-15 had nitrate-to-sulfate separation factors ( α S N ) of >3.7, whereas C1Q- and C4Q-SBA-15 had the α S N values of

In this study, phosphate (P) removal from aqueous solutions by hydrocalumite was investigated using batch experiments and model analyses. The maximum phosphate removal capacity was determined to be 127.53 mg P/g under the given experimental conditions (hydrocalumite dose = 0.05 g/L, initial P concentration = 2–20 mg P/L, reaction time = 24 h). Model analyses showed that the Elovich model was most suitable for describing the kinetic data, whereas the Redlich–Peterson model provided the best fits to the equilibrium data. Furthermore, phosphate removal by hydrocalumite was not sensitive to pH changes between 4.0 and 11.0. A thermodynamic analysis indicated that phosphate removal by hydrocalumite increased with a rise in temperature from 15 to 45°C, suggesting that the removal process was spontaneous and endothermic (ΔH° = 32.05 kJ/mol, ΔS° = 112.86 J/K/mol, ΔG° = −0.47 to −3.86 kJ/mol). The phosphate removal capacity in stream water (5.40–17.25 mg P/g) was also lower than that in a synthetic P soluti...

In this study, batch experiments were performed to examine the adhesion of bacteriophage MS2 to three iron oxide particles (IOP1, IOP2 and IOP3) with different particle properties. The characteristics of MS2 and iron oxides were analyzed using various techniques to construct the classical DLVO and XDLVO potential energy profiles between MS2 and iron oxides. X-ray diffractometry peaks indicated that IOP1 was mainly composed of maghemite (γ-Fe2O3), but also contained some goethite (α-FeOOH). IOP2 was composed of hematite (α-Fe2O3) and IOP3 was composed of iron (Fe), magnetite (Fe3O4) and iron oxide (FeO). Transmission electron microscope images showed that the primary particle size of IOP1 (γ-Fe2O3) was 12.3±4.1nm. IOP2 and IOP3 had primary particle sizes of 167±35nm and 484±192nm, respectively. A surface angle analyzer demonstrated that water contact angles of IOP1, IOP2, IOP3 and MS2 were 44.83, 64.00, 34.33 and 33.00°, respectively. A vibrating sample magnetometer showed that the magnetic saturations of IOP1, IOP2 and IOP3 were 176.87, 17.02 and 946.85kA/m, respectively. Surface potentials measured in artificial ground water (AGW; 0.075mM CaCl2, 0.082mM MgCl2, 0.051mM KCl, and 1.5mM NaHCO3; pH7.6) indicated that iron oxides and MS2 were negatively charged in AGW (IOP1=-0.0185V; IOP2=-0.0194V; IOP3=-0.0301V; MS2=-0.0245V). Batch experiments demonstrated that MS2 adhesion to iron oxides was favorable in the order of IOP1>IOP2>IOP3. This tendency was well predicted by the classical DLVO model. In the DLVO calculations, both the sphere-plate and sphere-sphere geometries predicted the same trend of MS2 adhesion to iron oxides. Additionally, noticeable differences were not found between the DLVO and XDLVO interaction energy profiles, indicating that hydrophobic interactions did not play a major role; electrostatic interactions, however, did influence MS2 adhesion to iron oxides. Furthermore, the aggregation of iron oxides was investigated with a modified XDLVO model. This model included magnetic interactions between the particles in order to predict the aggregation of iron oxides. Even though iron oxide particle aggregation could occur under experimental conditions, the DLVO model results using primary particle size were more suitable for the interactions between MS2 and the iron oxides because of fast sorption of MS2 onto the surfaces of iron oxides.

The removal of heavy metals from industrial wastewater is important, owing to its eco-toxicity in aqueous environment. In this study, the mechanism and efficiency of the removal of toxic heavy metals by an eco-friendly adsorbent was investigated. Various types of adsorbents made from jujube were synthesized by varying the drying temperature of gel-type beads and elution method for jujube constituents. The maximum adsorption capacity for lead and copper ions was determined using the Langmuir isotherm model, with DJB-A-S-F (freeze-dried jujube bead made from a solution of squeezed autoclaved jujube) having the highest values at 60.44 mg/g (lead) and 20.33 mg/g (copper). In addition, the characteristics of the various adsorbents were determined by the Brunauer–Emmett–Teller (BET) method, scanning electron microscopy (SEM), and energy dispersive X-ray analysis (EDX). Gas chromatography–mass spectrometry (GC–MS) was used to identify the constituents of DJB-A-S-F before and after adsorption of heavy metals (Pb- and Cu-DJB-A-S-F). Furthermore, in vitro cytotoxicity assay was performed to investigate whether the binding of heavy metals to DJB-A-S-F increases cellular toxicity. As a result, no differences in cell viability between DJB-A-S-F and the ones coupled to heavy metals were observed, indicating that the developed adsorbents are non-cytotoxic with good compatibility. Thus, DJB-A-S-F is a promising adsorbent for the removal of toxic heavy metal cations from wastewater.

The aim of this study was to characterize antimicrobial electrospun poly(vinyl alcohol) (PVA) nanofibers containing benzyl triethylammonium chloride (BTEAC) as an antimicrobial agent. The antimicrobial BTEAC-PVA nanofibers were prepared through electrospinning at the optimal conditions of 15 kV voltage and a 1.0 mL h − 1 flow rate. Based on the minimum inhibitory concentration (MIC) test results against Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli and Klebsiella pneumonia , BTEAC-PVA nanofibers containing 2.6% BTEAC were fabricated to test the antibacterial and antiviral activities. The average diameter of the BTEAC-PVA nanofibers increased from 175.7 to 464.7 nm with increasing BTEAC concentration from 0 to 2.6%. The antimicrobial activities of the BTEAC-PVA nanofibers were tested against bacteria. The antibacterial tests with 2.6% BTEAC-PVA nanofibers demonstrated that bacterial reduction in PVA nanofibers was similar to the control value, indicating that PVA had a minimal effect on bacteria death. For the BTEAC-PVA nanofibers, the bacterial reduction ratio increased with increasing contact time, demonstrating that BTEAC-PVA nanofibers successfully inhibited the growth of bacteria. In addition, the antiviral tests against viruses (bacteriophages MS2 and PhiX174) showed that the BTEAC-PVA nanofibers inactivated both MS2 and PhiX174.

The aim of this study was to investigate the bacteriophage removal in various clay minerals and clay-amended soils. Batch experiments in kaolinite, montmorillonite, and bentonite showed that kaolinite was far more effective at the MS2 removal than montmorillonite and bentonite. In kaolinite, the log removal increased from 0.046 to 2.18, with an increase in the adsorbent dose from 0.3 to 50 g L -1 , whereas the log removals in montmorillonite and bentonite increased from 0.007 to 0.40 and from 0.012 to 0.59, respectively. The MS2 removal in kaolinite-amended silt loam soils was examined at three different soil-to-solution (STS) ratios. Results indicated that the log removal of MS2 increased with an increase in the kaolinite content and the STS ratio. At the STS ratio of 1:10, the log removal of MS2 increased from 2.33 to 2.80 with an increase in the kaolinite content from 0% to 10% in kaolinite-amended soils. The log removals of MS2 at the STS ratios of 1:2 and 1:1 increased from 2.84 to 3.47 and from 3.46 to 4.76, respectively, with an increase in the kaolinite content from 0% to 10%. Results also indicated that the log removals of PhiX174 and Qβ in kaolinite-amended soils were similar to each other, but they were far lower than those of MS2 at all the kaolinite contents. The log removal of PhiX174 increased from 0.16 to 0.32, whereas the log removal of Qβ changed from 0.17 to 0.22 with an increase in the kaolinite content from 0% to 10%.

The aim of this study was to investigate the transport behavior of carboxyl-functionalized carbon black nanoparticles (CBNPs) in porous media including quartz sand, iron oxide-coated sand (IOCS), and aluminum oxide-coated sand (AOCS). Two sets of column experiments were performed under saturated flow conditions for potassium chloride (KCl), a conservative tracer, and CBNPs. Breakthrough curves were analyzed to obtain mass recovery and one-dimensional transport model parameters. The first set of experiments was conducted to examine the effects of metal (Fe, Al) oxides and flow rate (0.25 and 0.5 mL min − 1 ) on the transport of CBNPs suspended in deionized water. The results showed that the mass recovery of CBNPs in quartz sand (flow rate = 0.5 mL min − 1 ) was 83.1%, whereas no breakthrough of CBNPs (mass recovery = 0%) was observed in IOCS and AOCS at the same flow rate, indicating that metal (Fe, Al) oxides can play a significant role in the attachment of CBNPs to porous media. In addition, the mass recovery of CBNPs in quartz sand decreased to 76.1% as the flow rate decreased to 0.25 mL min − 1 . Interaction energy profiles for CBNP–porous media were calculated using DLVO theory for sphere–plate geometry, demonstrating that the interaction energy for CBNP–quartz sand was repulsive, whereas the interaction energies for CBNP–IOCS and CBNP–AOCS were attractive with no energy barriers. The second set of experiments was conducted in quartz sand to observe the effect of ionic strength (NaCl = 0.1 and 1.0 mM; CaCl 2 = 0.01 and 0.1 mM) and pH (pH = 4.5 and 5.4) on the transport of CBNPs suspended in electrolyte. The results showed that the mass recoveries of CBNPs in NaCl = 0.1 and 1.0 mM were 65.3 and 6.4%, respectively. The mass recoveries of CBNPs in CaCl 2 = 0.01 and 0.1 mM were 81.6 and 6.3%, respectively. These results demonstrated that CBNP attachment to quartz sand can be enhanced by increasing the electrolyte concentration. Interaction energy profiles demonstrated that the interaction energy profile for CBNP–quartz sand was compressed and that the energy barrier decreased as the electrolyte concentration increased. Furthermore, the mass recovery of CBNPs in the presence of divalent ions (CaCl 2 = 0.1 mM) was far lower than that in the presence of monovalent ions (NaCl = 0.1 mM), demonstrating a much stronger effect of Ca 2 + than Na + on CBNP transport. Mass recovery of CBNPs at pH 4.5 was 55.6%, which was lower than that (83.1%) at pH 5.4, indicating that CBNP attachment to quartz sand can be enhanced by decreasing the pH. The sticking efficiencies (α) calculated from the mass recovery by colloid filtration theory were in the range from 2.1 × 10 − 2 to 4.5 × 10 − 1 , which were far greater than the values (2.56 × 10 − 6 –3.33 × 10 − 2 ) of theoretical sticking efficiencies (α theory ) calculated from the DLVO energy by the Maxwell model.

The aim of this study was to investigate the removal of phosphate (P) using ammonium-functionalized MCM-41 (A-MCM-41). Batch experiments were performed with A-MCM-41 under various conditions including the adsorbent dose, reaction time, initial P concentration, and solution pH. The results showed that the phosphate removal in the MCM-41 (initial P conc. = 2 mgP L−1) was negligible with the percent removal of ≤1.0% at the adsorbent dosages between 0.5 and 2.0 g L−1. In the case of A-MCM-41, the percent removal increased from 73.6 to 100% as the adsorbent dose increased from 0.5 to 2.0 g L−1. This indicated an enhancement of the phosphate removal due to the surface modification of the MCM-41 through the functionalization of the ammonium group (NH3+). The results also demonstrated that the phosphate removal by the MCM-41 was minimal throughout the acidic and alkaline pH conditions (3.1% at pH 3.5; ≤1.0% at pH 5.4–10.7), whereas the phosphate removal by the A-MCM-41 was effective throughout the acidic ...

The aim of this study was to investigate the removal of As(V) from aqueous solutions using functionalized activated carbon fiber (ACF) as an adsorbent. The functionalized ACF was prepared through the impregnation of iron oxides on the surfaces of ACF. The X-ray fluorescence spectrometer analysis showed that carbon (C, 70.1%) and iron (Fe, 28.5%) were the major constituents of functionalized ACF. The N2 adsorption–desorption analysis showed that the Brunauer–Emmett–Teller surface area of functionalized ACF was determined to be 418.2 m2/g, which was 2.7 times smaller than that of raw ACF (1,123.0 m2/g) due to the impregnation of iron oxide. From the batch experiments, the maximum adsorption capacity of As(V) in functionalized ACF was determined to be 1.208 mg/g. The adsorption of As(V) to functionalized ACF was sensitive to solution pH changes, decreasing from 0.045 to 0.029 mg/g with increasing pH from 2.6 to 8.9. Kinetic model analysis showed that the pseudo-second-order model was most suitable at...

The aim of this study was to examine the phosphate (P) removal by quintinite from aqueous solutions. Batch experiments were performed to examine the effects of reaction time, temperature, initial phosphate concentration, initial solution pH and stream water on the phosphate adsorption to quintinite. Kinetic, thermodynamic and equilibrium isotherm models were used to analyze the experimental data. Results showed that the maximum P adsorption capacity was 4.77 mgP/g under given conditions (initial P concentration = 2-20 mgP/L; adsorbent dose = 1.2 g/L; reaction time = 4 hr). Kinetic model analysis showed that the pseudo second-order model was the most suitable for describing the kinetic data. Thermodynamic analysis indicated that phosphate sorption to quintinite increased with increasing temperature from 15 to 45˚C, indicating the spontaneous and endothermic nature of sorption process (ΔH 0 =487.08 kJ/mol; ΔS 0 =1,696.12 J/(K·mol); ΔG 0 =-1.67 to -52.56 kJ/mol). Equilibrium isotherm analysis demonstrated that both Freundlich and Redlich-Peterson models were suitable for describing the equilibrium data. In the pH experiments, the phosphate adsorption to quintinite was not varied at pH 3.0-7.1 (1.50-1.55 mgP/g) but decreased considerably at a highly alkaline solution (0.70 mgP/g at pH 11.0). Results also indicated that under given conditions (initial P concentration=2 mgP/L; adsorbent dose=0.8 g/L; reaction time=4 hr), phosphate removal in the stream water (1.88 mgP/g) was lower than that in the synthetic solution (2.07 mgP/g), possibly due to the presence of anions such as (bi)carbonate and sulfate in the stream water.

Mesoporous silica MCM-41 was synthesized and functionalized with a silane coupling agent (3-aminopropyltrimethoxysilane, APTMS) for the removal of Acid Blue 25 (AB25, anionic dye) and Methylene Blue (MB, cationic dye) from aqueous solutions as adsorbents. The synthesized (MCM-41) and functionalized (f-MCM-41) materials were characterized using field emission scanning electron microscopy, energy-dispersive X-ray spectrometry, transmission electron microscopy, particle size analysis, nitrogen gas adsorption-desorption analysis, X-ray diffraction spectrometry, and Fourier transform infrared spectrometry. The results indicate that the surface modification of MCM-41 with APTMS was successfully carried out. Batch experiments were performed to examine AB25 and MB removal by MCM-41 and f-MCM-41 under various experimental conditions. The results show that f-MCM-41 was a good adsorbent for anionic AB25, but not for cationic MB. This could be attributed to the presence of amine groups on the surfaces of f-MC...

The aim of this study was to investigate Cr(VI) removal from chromium-plating rinse water using modacrylic anion-exchange fibers (KaracaronTM KC31). Batch experiments were performed with synthetic Cr(VI) solutions to characterize the KC31 fibers in Cr(VI) removal. Cr(VI) removal by the fibers was affected by solution pH; the Cr(VI) removal capacity was the highest at pH 2 and decreased gradually with a pH increase from 2 to 12. In regeneration and reuse experiments, the Cr(VI) removal capacity remained above 37.0 mg g-1 over five adsorption-desorption cycles, demonstrating that the fibers could be successfully regenerated with NaCl solution and reused. The maximum Cr(VI) removal capacity was determined to be 250.3 mg g-1 from the Langmuir model. In Fourier-transform infrared spectra, a Cr = O peak newly appeared at 897 cm-1 after Cr(VI) removal, whereas a Cr-O peak was detected at 772 cm-1 due to the association of Cr(VI) ions with ion-exchange sites. X-ray photoelectron spectroscopy analyses demonstrated that Cr(VI) was partially reduced to Cr(III) after the ion exchange on the surfaces of the fibers. Batch experiments with chromium-plating rinse water (Cr(VI) concentration = 1178.8 mg L-1) showed that the fibers had a Cr(VI) removal capacity of 28.1-186.4 mg g-1 under the given conditions (fiber dose = 1-10 g L-1). Column experiments (column length = 10 cm, inner diameter = 2.5 cm) were conducted to examine Cr(VI) removal from chromium-plating rinse water by the fibers under flow-through column conditions. The Cr(VI) removal capacities for the fibers at flow rates of 0.5 and 1.0 mL min-1 were 214.8 and 171.5 mg g-1, respectively. This study demonstrates that KC31 fibers are effective in the removal of Cr(VI) ions from chromium-plating rinse water.

The aim of this study was to investigate the Cr(VI) adsorption to magnetic iron oxide(MIO) nanoparticle- multi-walled carbon nanotubes (MWCNTs) in aqueous solutions using batch experiments. Results show that the maximum adsorption capacity of Cr(VI) to MIO-MWCNTs was 11.256 mg/g. Kinetic model analysis demonstrates that the pseudo-second-order model and Elovich model are suitable for describing the kinetic data. Thermodynamic analysis indicates that Cr(VI) adsorption to MIO-MWCNTs decreased with increasing temperature from 5-60 °C, indicating the spontaneous and exothermic nature of the sorption process. Equilibrium isotherm analysis demonstrates that the Redlich-Peterson model suitably describes the equilibrium data. In the pH experiments, Cr(VI) adsorption to MIO-MWCNTs decreased gradually from 5.70-2.13 mg/g with increasing pH from 3.0-7.3. Sequential extraction indicates that, among the five binding forms of Cr(VI) associated with MIO-MWCNTs, the predominant contributions are the fraction bound to Fe-Mn oxides (57.82%) and the residual (23.38%).

The aim of this study was to apply iron oxide nanoparticle-chitosan (ION-chitosan) composites to phosphate removal from natural water collected from the Seoho Stream in Suwon, Republic of Korea. Laboratory batch experiments showed that phosphate removal by the ION-chitosan composites was not sensitive to pH changes between pH values of 5.0 and 9.0. During six cycles of adsorption–desorption, the composites could be successfully regenerated with 5 mM NaOH solution and reused for phosphate removal. Laboratory fixed-bed column experiments (column height = 10 and 20 cm, inner diameter = 2.5 cm, flow rate = 8.18 and 16.36 mL/min) demonstrated that the composites could be successfully applied for phosphate removal under dynamic flow conditions. A pilot-scale field experiment was performed in a pilot plant, which was mainly composed of chemical reactor/dissolved air flotation and an adsorption tower, built nearby the Seoho Stream. The natural water was pumped from the Seoho Stream into the pilot plant, passed through the chemical reactor/dissolved air flotation process, and then introduced into the adsorption tower (height = 100 cm, inner diameter = 45 cm, flow rate = 7.05 ± 0.18 L/min) for phosphate removal via the composites (composite volume = 80 L, composite weight = 85.74 kg). During monitoring of the adsorption tower (33 days), the influent total phosphorus (T-P) concentration was in the range of 0.020–0.046 mgP/L, whereas the effluent T-P concentration was in the range of 0.010–0.028 mgP/L. The percent removal of T-P in the adsorption tower was 52.3% with a phosphate removal capacity of 0.059 mgP/g.

The objective of the present study was to investigate the transport and removal of Escherichia coli, Bacillus subtilis, Staphylococcus aureus, bacteriophage MS2, and bacteriophage Phix174 in the soils and pyrophyllite-amended soils. Laboratory columns experiments were performed under saturated flow conditions. Our results showed that bacteriophages passed through the soils more easily than bacteria under the given experimental conditions (pulse injection = 15 min, flow rate = 0.5 mL/min, column length = 20 cm, inner diameter = 2.5 cm, pH = 7.6, electrical conductivity (EC) = 150.1 μS/cm); the log removals of bacteria were in the range of 0.44 to 1.72, whereas the log removals of bacteriophages were between 0.01 and 0.13. Our results also demonstrated that the transport of bacteria and bacteriophages in the soil columns could be reduced considerably in the presence of pyrophyllite. Under the same column experimental conditions above, the log removals for MS2 and Phix174 in 50% soil + 50% pyrophyllite were 2.64 and 3.05, respectively, whereas the log removals in 100% pyrophyllite were 5.70 for MS2 and 5.10 for Phix174; those values were far greater than the log removals in 100% soil (MS2 = 0.063, Phix174 = 0.128). Additional column experiments (step injection, flow rate = 0.3 mL/min, column length = 30 cm, inner diameter = 2.5 cm, solution pH = 8.4, EC = 39.8 mS/cm) showed that the log removals for B. subtilis (1.72) and Phix174 (1.48) in the pyrophyllite were greater than those in the soil (B. subtilis = 1.41; Phix174 = 0.39). This study demonstrated that the pyrophyllite amendment method could be used for protecting groundwater from microbial contamination by animal carcass burial soils.

The aim of this study was to determine optimum kinetic and isotherm models for phosphate (P) sorption onto iron oxide nanoparticles through nonlinear regression analysis. Equilibrium batch experiments were conducted at the experimental conditions of initial P concentration = 0.5–20 mg/L, adsorbent doses = 0.1, 0.2, 0.3, 0.4, 0.5, and 0.6 g/L, and shaking time = 24 h. Kinetic batch experiments were also performed at the experimental conditions of initial P concentrations = 1, 2, 4, 6, 8, and 10 mg/L, adsorbent dose = 0.6 g/L, and shaking time = 10 min–24 h. Six isotherm models (Langmuir, Freundlich, Temkin, Redlich–Peterson, Khan, and Sips) were used to analyze the equilibrium data through nonlinear regression analysis. Three kinetic models (pseudo-first-order, pseudo-second-order, and Elovich) were used to analyze the kinetic data through nonlinear regression. Error functions including the sum of the squared errors, hybrid fractional error function (HYBRID), average relative error, Marquardt’s per...