Masakazu Kanematsu

Extended Triple Layer Modeling of Arsenate and Phosphate Adsorption on a Goethite-based Granular Porous Adsorbent

The extended triple layer model (ETLM), which is consistent with spectroscopic and theoretical molecular evidence, is first systematically tested for its capability to model adsorption of arsenate and phosphate, a strong competitor, on a common goethite-based granular porous adsorptive media (Bayoxide E33 (E33)) in water treatment systems under a wide range of solution conditions. Deprotonated bidentate-binuclear, protonated bidentate-binuclear, and deprotonated monodentate complexes are chosen as surface species for both arsenate and phosphate. The estimated values of the ETLM parameters of arsenate for the adsorbent are close to those for pure goethite minerals previously determined by others. The ETLM predictions for arsenate and phosphate adsorption basically agree with experimental results over a wide range of pH, surface coverage, and solid concentrations. High background electrolyte concentration (i.e., I = 0.1 M), however, was found to strongly impact arsenate and phosphate adsorption on E33 probably because of the porous structure of the adsorbent, which cannot be observed for pure goethite minerals and could not be completely modeled by the ETLM. Prediction of phosphate adsorption isotherms at higher pH were relatively poor, and this may suggest searching for alternative surface species for phosphate. Since adsorption equilibrium constants of major coexisting ions encountered in water treatment systems for goethite minerals have been estimated by others, the application of ETLM theory to this common goethite-based adsorptive media will enable us to understand how those coexisting ions macroscopically and thermodynamically interact with arsenate and phosphate in the environment of adsorptive water treatment system in a way consistent with molecular and spectroscopic evidence.

Characterization and Potential Environmental Risks of Leachate from Shredded Rubber Mulches

In order to determine whether shredded rubber mulches (RM) pose water quality risks when used in stormwater best management practices (BMPs) such as bioretention basins, batch leaching tests were conducted to identify and quantify constituents in leachates from RM such as metal ions, nutrients, total organic carbon (TOC), and aryl hydrocarbon receptor (AhR) activity (determined by the chemically activated luciferase gene expression (CALUX) bioassay) at varied temperature and initial pH values. The results indicate that aqueous extracts of RM contain high concentrations of zinc (Zn) compared with wood mulches (WM), and its concentration increased at lower pH and higher temperature. Although methanol extracts of RM displayed high AhR activity, none of the aqueous extracts of RM had significant activity. Hence, while unknown constituents that have significant AhR activity are present in RM, they appear to be not measurably extracted by water under environmental conditions relevant for stormwater (5<pH<9, 10<T<40 degrees C). Our results suggest that organic constituents in water extracts of RM which have AhR activity may not be of significant concern while leaching of Zn from RM appears to be a potentially larger water quality issue for RM.

Quantification of the Effects of Organic and Carbonate Buffers on Arsenate and Phosphate Adsorption on a Goethite-Based Granular Porous Adsorbent

Interest in the development of oxide-based materials for arsenate removal has led to a variety of experimental methods and conditions for determining arsenate adsorption isotherms, which hinders comparative evaluation of their adsorptive capacities. Here, we systematically investigate the effects of buffer (HEPES or carbonate), adsorbent dose, and solution pH on arsenate and phosphate adsorption isotherms for a previously well characterized goethite-based adsorbent (Bayoxide E33 (E33)). All adsorption isotherms obtained at different adsorbate/adsorbent concentrations were identical when 1 mM of HEPES (96 mg C/L) was used as a buffer. At low aqueous arsenate and phosphate concentration (∼1.3 μM), however, adsorption isotherms obtained using 10 mM of NaHCO(3) buffer, which is a reasonable carbonate concentration in groundwater, are significantly different from those obtained without buffer or with HEPES. The carbonate competitive effects were analyzed using the extended triple layer model (ETLM) with the adsorption equilibrium constant of carbonate calibrated using independent published carbonate adsorption data for pure goethite taking into consideration the different surface properties. The successful ETLM calculations of arsenate adsorption isotherms for E33 under various conditions allowed quantitative comparison of the arsenate adsorption capacity between E33 and other major adsorbents initially tested under varied experimental conditions in the literature.

Arsenic removal from water using flame-synthesized iron oxide nanoparticles with variable oxidation states.

We utilized gas-phase diffusion flame (DF) synthesis, which has potential for large-scale production of metal oxide nanoparticles, to produce iron oxide nanoparticles (IONPs) with variable oxidation states. The efficacy of these materials in removal of arsenate (As(V)) from water was assessed. Two different flame configurations, a DF and an inverse diffusion flame (IDF), were employed to synthesize six different IONPs by controlling flame conditions. The IONPs produced in the IDF configuration (IDF-IONPs) had smaller particle diameters (4.8–8.2 nm) and larger surface areas (141–213 m2/g) than the IONPs produced in the DF configuration (29 nm, 36 m2/g), which resulted in their higher adsorption capacities. As(V) adsorption capacities of the IDF-IONPs increased when the IONPs were synthesized in more oxidizing conditions. The fully oxidized IDF-IONPs, maghemite (γ-Fe2O3), showed the highest As(V) adsorption capacity, comparable to that of magnetite nanocrystals synthesized by thermal decomposition of iron pentacarbonyl and equivalent to three to four times higher capacity than that of a commonly used goethite-based adsorbent. All IONPs were magnetically responsive, which is of great importance for solid−liquid separation. This study demonstrates that the IONPs synthesized in gas-phase flame, particularly IDF-IONPs, are excellent adsorbents because of their high As(V) sorption capacity, potential for large-scale production, and useful magnetic property. Copyright 2013 American Association for Aerosol Research

Individual and combined effects of water quality and empty bed contact time on As(V) removal by a fixed-bed iron oxide adsorber: Implication for silicate precoating

The individual and combined effects of changes in water quality (i.e. pH, initial concentrations of arsenate (As(V)) and competing ions) and empty bed contact time (EBCT) on As(V) removal performance of a fixed-bed adsorber (FBA) packed with a nanostructured goethite-based granular porous adsorbent were systematically studied under environmentally relevant conditions. Rapid small scale column tests (RSSCTs) were extensively conducted at different EBCTs with synthetic waters in which pH and the concentrations of competing ions (phosphate, silicate, and vanadate) were controlled. In the absence of the competing ions, the effects of initial As(V) concentration, pH, and EBCT on As(V) breakthrough curves were successfully predicted by the homogeneous surface diffusion model (HSDM) with adsorption isotherms predicted by the extended triple layer model (ETLM). The interference effects of silicate and phosphate on As(V) removal were strongly influenced by pH, their concentrations, and EBCT. In the presence of silicate (≤21 mg/L as Si), a longer EBCT surprisingly resulted in worse As(V) removal performance. We suggest this is because silicate, which normally exists at much higher concentration and moves more quickly through the bed than As(V), occupies or blocks adsorption sites on the media and interferes with later As(V) adsorption. Here, an alternative operating scheme of a FBA for As(V) removal is proposed to mitigate the silicate preloading. Silicate showed a strong competing effect to As(V) under the tested conditions. However, as the phosphate concentration increased, its interference effect dominated that of silicate. High phosphate concentration (>100 μg/L as P), as experienced in some regions, resulted in immediate As(V) breakthrough. In contrast to the observation in the presence of silicate, longer EBCT resulted in improved As(V) removal performance in the presence of phosphate. Vanadate was found to compete with As(V) as strongly as phosphate. This study reveals the competitive interactions of As(V) with the competing ions in actual adsorptive treatment systems and the dependence of optimal operation scheme and EBCT on water quality in seeking improved As(V) removal in a FBA.

Disposal of Arsenic-Laden Adsorptive Media: Economic Analysis for California

Due to California’s stringent hazardous waste (HW) classification regulations, high-capacity adsorptive media (AM) used for the removal of arsenic from potable water are likely to be classified as HW if operated to breakthrough. An alternative is to prematurely retire the AM, avoiding generation of HW. The impact of waste classification of spent AM on annual costs for arsenic systems was investigated. For a typical small water system (SWS), the media replacement cost alone was predicted to range from

Distribution and fluxes of fluorescent whitening agents discharged from domestic wastewater into small rivers with seasonal changes of flow rates

0.80 to

Arsenic(III, V) adsorption on a goethite-based adsorbent in the presence of major co-existing ions: Modeling competitive adsorption consistent with spectroscopic and molecular evidence

2.00 per 1,000 L treated, in comparison to the average cost of tap water in the U.S. of

Distribution of dioxins in surface soils and river-mouth sediments and their relevance to watershed properties

0.53 per 1,000 L treated, highlighting the financial burden for SWS. The costs of media replacement dominated over costs for transport and disposal regardless of whether spent media were designated as HW or non-HW. Media costs and influent arsenic concentration were more significant factors than transport distance or disposal fees. Under typical conditions for SWS, it was found to be cost effective to load the m...

Origins and transport of aquatic dioxins in the Japanese watershed: soil contamination, land use, and soil runoff events.

Distributions of fluorescent whitening agents (FWAs) in the waters of a small river system in Japan were surveyed in summer when the water volume rose following high precipitation and in winter when it subsided as precipitation declined. The main source of FWAs in the river system was domestic wastewater, and fluxes in the tributaries depended on the size of the residential population and the elimination rates of sewage treatment systems in their catchments, although FWA concentrations in the river itself fluctuated, largely as a consequence of dilution by heavy precipitation and unstable water flows in the small-sized river system. The FWA concentrations in the river waterduring summer decreased not only by the dilution of river water but also by photodegradation because of more prolonged exposure to sunlight.