Effect of ligand interactions within modified granular activated carbon (GAC) on mixed perfluorooctanoic acid (PFOA) and perfluorooctanesulfonic acid (PFOS) adsorption.

A new adsorbent based on commercial granular activated carbon (GAC) and loaded with Cu(II) (GAC-Cu) was prepared to enhance the adsorption capacity of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonate (PFOS). The surface area (SA) and pore volume of GAC-Cu decreased by ∼15% compared to those of pristine GAC. The scanning electron microscopy-energy dispersive spectrometry (SEM-EDS) and leaching test results indicated that, compared with GAC, the Cu atomic ratio and Cu amount in GAC-Cu increased by 2.91 and 2.43 times, respectively. The point of zero charge (PZC) measured using a salt addition method obtained a pH of 6.0 (GAC) and 5.0 (GAC-Cu). According to the isotherm models obtaining highest coefficient of determination (R2), GAC-Cu exhibited a 20.4% and 35.2% increase for PFOA and PFOS in maximum uptake (qm), respectively, compared to those of GAC. In addition, the adsorption affinity (b) for GAC-Cu increased by 1045% and 175% for PFOA and PFOS, respectively. The pH effect on the adsorption capacity of GAC-Cu was investigated. The uptake of PFOA and PFOS decreased with an increase in pH for both GAC and GAC-Cu. GAC-Cu exhibited higher uptake than GAC at pH 6 and 7, but no enhanced uptake was observed at pH 4.0, 5.0, and 8.5. Therefore, ligand interaction was effective at weak acid or neutral pH.

Adsorption Characteristics for Cu(II) and Phosphate in Chitosan Beads under Single and Mixed Conditions.

Chitosan, a natural organic polymer, has shown bifunctional characteristics in the removal of cationic and anionic contaminants from water and wastewater treatment. In particular, cationic Cu(II) and anionic phosphate can simultaneously interact with chitosan owing to the presence of the amino group in the form of NH2 and NH3+ in chitosan. To gain greater insight into the bifunctional adsorption characteristics of chitosan, its adsorption capacity for Cu(II) and phosphate was tested under single and mixed (co-ion) conditions to investigate the interactions between four types of chitosan beads and NH2 and NH3+. In the single condition, Cu(II) uptake was reduced from 0.243 to 0.0197 mmol/g due to the crosslinking and drying processes, whereas no significant reduction in phosphate uptake was observed, indicating that the crosslinking agent only interacted with NH2 to decrease the number of available adsorption sites for Cu(II). Under the mixed condition, the simultaneous presence of the two ions clearly increased the uptake of each other, with the adsorption of phosphate being more influenced than that of Cu(II). The comparison of the rate constant, k1 or k2, using pseudo-first- and pseudo-second-order models confirmed that phosphate reached equilibrium faster than Cu(II), suggesting that electrostatic interaction was preferred over coordination. In addition, under mixed conditions, co-ion competition slowed down the adsorption kinetics for both Cu(II) and phosphate.

Removal of copper, nickel and chromium mixtures from metal plating wastewater by adsorption with modified carbon foam.

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.

Effect of nitrogen doping on titanium carbonitride-derived adsorbents used for arsenic removal.

Arsenic in water and wastewater is considered to be a critical contaminant as it poses harmful health risks. In this regard, to meet the stringent regulation of arsenic in aqueous solutions, nitrogen doped carbon-based materials (CN) were prepared as adsorbents and tested for the removal of arsenic ion from aqueous solutions. Nitrogen-doped carbon (CNs) synthesized by chlorination exhibited well-developed micro- and small meso-pores with uniform pore structures. The structure and characteristics of the adsorbents thus developed were confirmed by field-emission scanning electron microscopy, transmission electron microscopy, Brunauer-Emmett-Teller analysis, X-ray diffraction, X-ray photoelectron spectroscopy, and Fourier transform infrared spectroscopy. Among the CNs developed, CN700 exhibited high adsorption capacity for arsenic (31.08 mg/g). The adsorption efficiency for arsenic ion was confirmed to be affected by pyrrolic nitrogen and micro-pores. These results suggest that CNs are useful adsorbents for the treatment of arsenic, and in particular, CN700 demonstrates potential for application as an adsorbent for the removal of anionic heavy metals from wastewater and sewage.

Determining the selectivity of divalent metal cations for the carboxyl group of alginate hydrogel beads during competitive sorption.

To investigate the competitive sorption of divalent metal ions such as Ca(2+), Cu(2+), Ni(2+), and Pb(2+) on alginate hydrogel beads, batch and column tests were conducted. The concentration of carboxyl group was found to be limited in the preparation of spherical hydrogel beads. From kinetic test results, 80% of sorption was observed within 4h, and equilibrium was attained in 48 h. According to the comparison of the total uptake and release, divalent metal ions were found to stoichiometrically interact with the carboxyl group in the alginate polymer chain. From the Langmuir equation, the maximum capacities of Pb(2+), Cu(2+), and Ni(2+) were calculated to be 1.1, 0.48, and 0.13 mmol/g, respectively. The separation factor (α) values for αPb/Cu, αPb/Ni, and αCu/Ni were 14.0, 98.9, and 7.1, respectively. The sorption capacity of Pb(2+) was not affected by the solution pH; however, the sorption capacities of Cu(2+) and Ni(2+) decreased with increasing solution pH, caused by competition with hydrogen. According to the result from the fixed column test, Pb(2+) exhibited the highest affinity, followed by Cu(2+) and Ni(2+), which is in exact agreement with those of kinetic and isotherm tests. The sorbent could be regenerated using 4% HCl, and the regenerated sorbent exhibited 90% capacity upto 9 cycles.

Preparation and characterization of an organic/inorganic hybrid sorbent (PLE) to enhance selectivity for As(V).

For the selective removal of arsenate (As(V)) a hybrid sorbent was prepared using a non-toxic natural organic material, chitosan, by loading a transition metal, nickel. The immobilization of nickel was achieved by coordination with a deprotonated amino group (NH2) in the chitosan polymer chain. The amount of nickel was directly correlated to the presence of the amino group and was calculated to be 62 mg/g. FTIR spectra showed a peak shift from 1656 to 1637 cm(-1) after Ni(2+) loading, indicating the complexation between the amino group and nickel, and a peak of As(V) was observed at 834 cm(-1). An increase of sulfate concentration from 100 mg/L to 200 mg/L did not significantly affect As(V) sorption, and an increase in the concentration of bicarbonate reduced the As(V) uptake by 33%. The optimal pH of the solution was determined at pH 10, which is in accordance with the fraction of HAsO4(2-) and AsO4(-3). According to a fixed column test, a break through behavior of As(V) revealed that selectivity for As(V) was over sulfate. Regeneration using 5% NaCl extended the use of sorbent to up to uses without big loss of sorption capacity.

Modified composites based on mesostructured iron oxyhydroxide and synthetic minerals: a potential material for the treatment of various toxic heavy metals and its toxicity.

The composites of mesostructured iron oxyhydroxide and/or commercial synthetic zeolite were investigated for use in the removal of toxic heavy metals, such as cadmium, copper, lead and arsenic, from aqueous solution. Four types of adsorbents, dried alginate beads (DABs), synthetic-zeolite impregnated beads (SZIBs), meso-iron-oxyhydroxide impregnated beads (MIOIBs) and synthetic-zeolite/meso-iron-oxyhydroxide composite beads (SZMIOIBs), were prepared for heavy metal adsorption tests. Laboratory experiments were conducted to investigate the removal efficiencies of cations and anions of heavy metals and the possibility of regenerating the adsorbents. Among these adsorbents, the MIOIBs can simultaneously remove cations and anions of heavy metals; they have high adsorption capacities for lead (60.1mgg(-1)) and arsenic (71.9mgg(-1)) compared with other adsorbents, such as DABs (158.1 and 0.0mgg(-1)), SZIB (42.9 and 0.0mgg(-1)) and SZMIOIB (54.0 and 5.9mgg(-1)) for lead and arsenic, respectively. Additionally, the removal efficiency was consistent at approximately 90%, notwithstanding repetitive regeneration. The characteristics of meso-iron-oxyhydroxide powder were confirmed by X-ray diffraction, Brunauer-Emmett-Teller and transmission electron microscopy. We also performed a comparative toxicity study that indicated that much lower concentrations of the powdered form of mesostructured iron oxyhydroxide had stronger cytotoxicity than the granular form. These results suggest that the granular form of meso iron oxyhydroxide is a more useful and safer adsorbent for heavy metal treatment than the powdered form. This research provides promising results for the application of MIOIBs as an adsorbent for various heavy metals from wastewater and sewage.

Enhanced phosphate selectivity from wastewater using copper-loaded chelating resin functionalized with polyethylenimine.

In water and wastewater, phosphate is considered a critical contaminant due to cause algae blooms and eutrophication. To meet the stringent regulation of phosphate in water, a new commercial chelating resin functionalized with polyethylenimine was tested for phosphate removal by loading Cu(2+) and Fe(2+)/Fe(3+) to enhance selectivity for phosphate. Batch and column experiments showed that CR20-Cu exhibited high selectivity for phosphate over other strong anions such as sulfate. The average binary phosphate/nitrate and phosphate/sulfate factors for CR20-Cu were calculated to be 7.3 and 4.8, respectively, which were more than 0.97 and 0.22 for a commercial anion exchanger (AMP16). The optimal pH for the phosphate removal efficiency was determined to be 7. According to the fixed-bed column test, the breakthrough sequence for multiple ions was HPO4(2-)>SO4(2-)>NO3(-)>Cl(-). Saturated CR20-Cu can be regenerated using 4% NaCl at pH 7. More than 95% of the phosphate from CR20-Cu was recovered, and the phosphate uptake capacity for CR20-Cu was not reduced after 7 regeneration cycles.

Characterization of natural organic matter treated by iron oxide nanoparticle incorporated ceramic membrane-ozonation process.

In this study, changes in the physical and structural properties of natural organic matter (NOM) were observed during hybrid ceramic membrane processes that combined ozonation with ultrafiltration ceramic membrane (CM) or with a reactive ceramic membrane (RM), namely, an iron oxide nanoparticles (IONs) incorporated-CM. NOM from feed water and NOM from permeate treated with hybrid ceramic membrane processes were analyzed by employing several NOM characterization techniques. Specific ultraviolet absorbance (SUVA), high-performance size exclusion chromatography (HPSEC) and fractionation analyses showed that the hybrid ceramic membrane process effectively removed and transformed relatively high contents of aromatic, high molecular weight and hydrophobic NOM fractions. Fourier transform infrared spectroscopy (FTIR) and 3-dimensional excitation-emission matrix (EEM) fluorescence spectroscopy revealed that this process caused a significant decrease of the aromaticity of humic-like structures and an increase in electron withdrawing groups. The highest removal efficiency (46%) of hydroxyl radical probe compound (i.e., para-Chlorobenzoic acid (pCBA)) in RM-ozonation process compared with that in CM without ozonation process (8%) revealed the hydroxyl radical formation by the surface-catalyzed reaction between ozone and IONs on the surface of RM. In addition, experimental results on flux decline showed that fouling of RM-ozonation process (15%) was reduced compared with that of CM without ozonation process (30%). These results indicated that the RM-ozonation process enhanced the destruction of NOM and reduced the fouling by generating hydroxyl radicals from the catalytic ozonation in the RM-ozonation process.

Immobilization of As(III) in soil and groundwater using a new class of polysaccharide stabilized Fe-Mn oxide nanoparticles.

A new class of stabilized Fe-Mn binary oxide nanoparticles was prepared with a water-soluble starch or carboxymethyl cellulose (CMC) as a stabilizer. The nanoparticles were characterized and tested with respect to sorption of As(III) and As(V) from water and for immobilization of As(III) in soil. While arsenic sorption capacities were comparable for bare, or stabilized Fe-Mn nanoparticles, particle stabilization enabled the nanoparticles to be delivered into soil for in situ immobilization of arsenite. High As(III) sorption capacity was observed over a broad pH range of 5-9. Column breakthrough tests demonstrated soil mobility of CMC-stabilized nanoparticles. Once delivered, the nanoparticles remain virtually immobile in soil under typical groundwater conditions, serving as a fixed sink for arsenic. When an As(III)-laden soil was treated with CMC-stabilized Fe-Mn at an Fe-to-As molar ratio of 6.5-39, the water leachable arsenic was reduced by 91-96%, and the TCLP leachability was reduced by 94-98%. Column elution tests of an As(III)-laden soil indicated that application of CMC-stabilized Fe-Mn transferred nearly all water-soluble As(III) to the nanoparticle phase. Consequently, As(III) is immobilized as the nanoparticles are immobilized in the soil. The nanoparticle amendment was able to reduce the TCLP leachability of As(III) remaining in the soil bed by 78%.

Removal of arsenic(V) from spent ion exchange brine using a new class of starch-bridged magnetite nanoparticles.

Ion exchange (IX) is considered by US EPA as one of the best available technologies for removing arsenic from drinking water. However, typical IX processes will generate large volumes of arsenic-laden regenerant brine that requires costly further handling and disposal. This study aimed to develop an engineered strategy to minimize the production and arsenic leachability of the process waste residual. We prepared and tested a new class of starch-bridged magnetite nanoparticles for removal of arsenate from spent IX brine. A low-cost, "green" starch at 0.049% (w/w) was used as a stabilizer to prevent the nanoparticles from agglomerating and as a bridging agent allowing the nanoparticles to flocculate and precipitate while maintaining their high arsenic sorption capacity. When applied to a simulated spent IX brine containing 300 mg/L As and 6% (w/w) NaCl, nearly 100% removal of arsenic was achieved within 1 h using the starch-bridged nanoparticles at an Fe-to-As molar ratio of 7.6, compared to only 20% removal when bare magnetite particles were used. Increasing NaCl in the brine from 0 to 10% (w/w) had little effect on the arsenic sorption capacity. Maximum uptake was observed within a pH range of 4-6. The Langmuir capacity coefficient was determined to be 248 mg/g at pH 5.0. The final treatment sludge was able to pass the TCLP (Toxicity Characteristic Leaching Procedure) based leachability of 5 mg/L as As.

Selective removal of arsenate from drinking water using a polymeric ligand exchanger.

The new maximum contaminant level (MCL) of 10 microg/L for arsenic in the US drinking water will take effect on January 22, 2006. The compliance cost is estimated to be approximately dollar 600 million per year using current treatment technologies. This research aims to develop an innovative ion exchange process that may help water utilities comply with the new MCL in a more cost-effective manner. A polymeric ligand exchanger (PLE) was prepared by loading Cu2+ to a commercially available chelating ion exchange resin. Results from batch and column experiments indicated that the PLE offered unusually high selectivity for arsenate over other ubiquitous anions such as sulfate, bicarbonate and chloride. The average binary arsenate/sulfate separation factor for the PLE was determined to be 12, which were over two orders of magnitude greater than that (0.1-0.2) for commercial strong-base anion (SBA) exchangers. Because of the enhanced arsenate selectivity, the PLE was able to treat approximately 10 times more bed volumes (BVs) of water than commonly used SBA resins. The PLE can operate optimally in the neutral pH range (6.0-8.0). The exhausted PLE can be regenerated highly efficiently. More than 95% arsenate capacity can be recovered using approximately 22 BVs of 4% (w/w) NaCl at pH 9.1, and the regenerated PLE can be reused without any capacity drop. Upon treatment using FeCl3, the spent brine was recovered and reused for regeneration, which may cut down the regenerant need and reduces the volume of process waste residuals. The PLE can be used as a highly selective and reusable sorbent for removal of arsenate from drinking water.