Effect of NOM on arsenic adsorption by TiO(2) in simulated As(III)-contaminated raw waters

The effect of natural organic matter (NOM) on arsenic adsorption by a commercial available TiO(2) (Degussa P25) in various simulated As(III)-contaminated raw waters was examined. Five types of NOM that represent different environmental origins were tested. Batch adsorption experiments were conducted under anaerobic conditions and in the absence of light. Either with or without the presence of NOM, the arsenic adsorption reached steady-state within 1h. The presence of 8 mg/L NOM as C in the simulated raw water, however, significantly reduced the amount of arsenic adsorbed at the steady-state. Without NOM, the arsenic adsorption increased with increasing solution pH within the pH range of 4.0-9.4. With four of the NOMs tested, the arsenic adsorption firstly increased with increasing pH and then decreased after the adsorption reached the maximum at pH 7.4-8.7. An appreciable amount of arsenate (As(V)) was detected in the filtrate after the TiO(2) adsorption in the simulated raw waters that contained NOM. The absolute amount of As(V) in the filtrate after TiO(2) adsorption was pH dependent: more As(V) was presented at pH>7 than that at pH<7. The arsenic adsorption in the simulated raw waters with and without NOM were modelled by both Langmuir and Frendlich adsorption equations, with Frendlich adsorption equation giving a better fit for the water without NOM and Langmuir adsorption equation giving a better fit for the waters with NOM. The modelling implies that NOM can occupy some available binding sites for arsenic adsorption on TiO(2) surface. This study suggests that in an As(III)-contaminated raw water, NOM can hinder the uptake of arsenic by TiO(2), but can facilitate the As(III) oxidation to As(V) at TiO(2) surface under alkaline conditions and in the absence of O(2) and light. TiO(2) thus can be used in situ to convert As(III) to the less toxic As(V) in NOM-rich groundwaters.     

Photochemical oxidation of As(III) by vacuum-UV lamp irradiation

In this study, vacuum-UV (VUV) lamp irradiation emitting both 185 and 254 nm lights has been investigated as a new oxidation method for As(III). Laboratory scale experiments were conducted with a batch reactor and a commercial VUV lamp. Under the experimental conditions of this study, the employed VUV lamp showed a higher performance for As(III) oxidation compared to other photochemical oxidation methods (UV-C/H(2)O(2), UV-A/Fe(III)/H(2)O(2), and UV-A/TiO2). The VUV lamp oxidized 100 microM As(III) almost completely in 10 min, and the reaction occurred mainly due to OH radicals which were produced by photo-splitting of water (H(2)O+hv (lambda=185 nm)-->OH.+H.). There was a little possibility that photo-generated H(2)O(2) acted as a minor oxidant of As(III) at alkaline pHs. The effects of Fe(III), H(2)O(2), and humic acid (HA) on the As(III) oxidation by VUV lamp irradiation were investigated. While Fe(III) and H(2)O(2) increased the As(III) oxidation efficiency, HA did not cause a significant effect. The employed VUV lamp was effective for oxidizing As(III) not only in a Milli-Q water but also in a real natural water, without significant decrease in the oxidation efficiency. Since the formed As(V) should be removed from water, activated alumina (AA) was added as an adsorbent during the As(III) oxidation by VUV lamp irradiation. The combined use of VUV lamp irradiation and AA was much more effective for the removal of total arsenic (As(tot)=As(III)+As(V)) than the single use of AA. The As(tot) removal seemed to occur as a result of the pre-oxidation of As(III) and the subsequent adsorption of As(V) on AA. Alternatively, the combination of VUV lamp irradiation and coagulation/precipitation with FeCl(3) was also an effective removal strategy for As(tot). This study shows that vacuum-UV (VUV) lamp irradiation emitting both 185 and 254 nm lights is a powerful and environmentally friendly method for As(III) oxidation which does not require additional oxidants or catalysts. The As(III) oxidation by VUV lamp irradiation was tested not only in a batch reactor but also in a flow-through quartz reactor. The As(III) oxidation rate became much faster in the latter reactor.     

Removal of arsenic from water: Effects of competing anions on As(III) removal in KMnO4–Fe(II) process

Effects of sulfate, phosphate, silicate and humic acid (HA) on the removal of As(III) in the KMnO₄–Fe(II) process were investigated in the pH range of 4–9 with permanganate and ferrous sulfate applied at selected dosage. Sulfate decreased the removal of arsenic by 6.5–36.0% at pH 6–9 and the decrease in adsorption did not increase with increasing concentration of sulfate from 50 to 100 mg/L. In the presence of 1 mg/L phosphate, arsenic removal decreased gradually as pH increased from 4 to 6, and a sharp drop occurred at pH 7–9. The presence of 10 mg/L silicate had negligible effect on arsenic removal at pH 4–5 whereas decreased the arsenic removal at pH 6–9 and the decrease was more significant at higher pH. The presence of HA dramatically decreased the arsenic removal over the pH range of 6–9 and HA of higher concentration resulted in greater drop in arsenic removal. The effects of the competing anions on arsenic removal in the KMnO₄–Fe(II) process were highly dependent on pH and the degree of these four anions influencing As(III) removal decreased in the following order, phosphate > humic acid > silicate > sulfate. Sulfate differed from the other three anions because sulfate decreased the removal of arsenic mainly by competitive adsorption while phosphate, silicate and HA decreased the removal of As(III) by competitive adsorption and sequestering the formation of ferric hydroxide derived from Fe(II).     

Comparative study of arsenic removal by iron using electrocoagulation and chemical coagulation

This research studied As(III) and As(V) removal during electrocoagulation (EC) in comparison with FeCl₃ chemical coagulation (CC). The study also attempted to verify chlorine production and the reported oxidation of As(III) during EC. Results showed that As(V) removal during batch EC was erratic at pH 6.5 and the removal was higher-than-expected based on the generation of ferrous iron (Fe²⁺) during EC. As(V) removal by batch EC was equal to or better than CC at pH 7.5 and 8.5, however soluble Fe²⁺ was observed in the 0.2-μm membrane filtrate at pH 7.5 (10-45%), and is a cause for concern. Continuous steady-state operation of the EC unit confirmed the deleterious presence of soluble Fe²⁺ in the treated water. The higher-than-expected As(V) removals during batch mode were presumed due to As(V) adsorption onto the iron rod oxyhydroxides surfaces prior to the attainment of steady-state operation. As(V) removal increased with decreasing pH during both CC and EC, however EC at pH 6.5 was anomalous because of erratic Fe²⁺ oxidation. The best adsorption capacity was observed with CC at pH 6.5, while lower but similar adsorption capacities were observed at pH 7.5 and 8.5 with CC and EC. A comparison of As(III) adsorption showed better removals during EC compared with CC possibly due to a temporary pH increase during EC. In contrast to literature reports, As(III) oxidation was not observed during EC, and As(III) adsorption onto iron hydroxides during EC was only 5-30% that of As(V) adsorption. Also in contrast to literature, significant Cl₂ was not generated during EC, in fact, the rods actually produced a significant chlorine demand due to reduced iron oxides on the rod. Although Cl₂ generation and As(III) oxidation are possible using a graphite anode, a combination of graphite and iron rods in the same EC unit did not produce As(III) oxidation. However, a two-stage process (graphite anode followed by iron anode in separate chambers) was effective in As(III) oxidation and removal. The competing ions, silica and phosphate interfered with As(V) adsorption during both CC and EC. However, the degree of interference depends on the concentration and presence of other competing ions. In particular, the presence of silica lowered the effect of phosphate with increasing pH due to silica’s own significant effect at high pHs.     

Preparation and evaluation of iron–chitosan composites for removal of As(III) and As(V) from arsenic contaminated real life groundwater

A study on the removal of arsenic from real life groundwater using iron–chitosan composites is presented. Removal of arsenic(III) and arsenic(V) was studied through adsorption at pH 7.0 under equilibrium and dynamic conditions. The equilibrium data were fitted to Langmuir adsorption models and the various model parameters were evaluated. The monolayer adsorption capacity from the Langmuir model for iron chitosan flakes (ICF) (22.47 ± 0.56 mg/g for As(V) and 16.15 ± 0.32 mg/g for As(III)) was found to be considerably higher than that obtained for iron chitosan granules (ICB) (2.24 ± 0.04 mg/g for As(V); 2.32 ± 0.05 mg/g for As(III)). Anions including sulfate, phosphate and silicate at the levels present in groundwater did not cause serious interference in the adsorption behavior of arsenate/arsenite. The column regeneration studies were carried out for two sorption–desorption cycles for both As(III) and As(V) using ICF and ICB as sorbents. One hundred and forty-seven bed volumes of As(III) and 112 bed volumes of As(V) spiked groundwater were treated in column experiments using ICB, reducing arsenic concentration from 500 to <10 μg/l. The eluent used for the regeneration of the spent sorbent was 0.1 M NaOH. The adsorbent was also successfully applied for the removal of total inorganic arsenic down to <10 μg/l from real life arsenic contaminated groundwater samples.     

Modeling As(V) removal by a iron oxide impregnated activated carbon using the surface complexation approach

The objective of this research was to model As(V) removal onto a iron oxide impregnated activated carbon (FeAC) using the surface complexation model (SCM) approach. As(V) removal by FeAC was due to the impregnated Fe oxide, not the base carbon material and was a strong function of pH. The two-monoprotic site-triple layer model adequately described As(V) removal using 2 fitting parameters compared with the 3 parameters needed for the diprotic site model. This, along with a better representation of the recognized As(V) removal mechanism (ligand exchange with -OH) as well as the acid-base behavior makes the two-monoprotic approach the better model for As(V) removal by the impregnated iron oxide although the diprotic model was able to describe the pH dependent removal of As(V). Both models were also able to predict As(V) removal at different adsorbent/adsorbate ratios using K(As) determined from a single FeAC adsorption experiment. Thus, fewer adsorption experiments are required in order to model As(V) removal in equilibrium and column systems. The results described in this work will be used as a foundation in developing a dynamic model to predict As(V) adsorption in a fixed-bed adsorber.     

Removal of As(III) and As(V) from water using a natural Fe and Mn enriched sample

The arsenic removal capacity of a natural oxide sample consisting basically of Mn-minerals (birnessite, cryptomelane, todorokite), and Fe-oxides (goethite, hematite), collected in the Iron Quadrangle mineral province in Minas Gerais, Brazil, has been investigated. As-spiked tap water and an As-rich mining effluent with As-concentrations from 100 μg L⁻¹ to 100 mg L⁻¹ were used for the experiments. Sorbent fractions of different particle sizes (<38 μm to 0.5 mm), including spherical material (diameter 2 mm), have been used. Batch and column experiments (pH values of 3.0, 5.5, and 8.5 for batch, and about pH 7.0 for column) demonstrated the high adsorption capacity of the material, with the sorption of As(III) being higher than that of As(V). At pH 3.0, the maximum uptake for As(V) and for As(III)-treated materials were 8.5 and 14.7 mg g⁻¹, respectively. The Mn-minerals promoted the oxidation of As(III) to As(V), for both sorbed and dissolved As-species. Column experiments with the cFeMn-c sample for an initial As-concentration of 100 μg L⁻¹ demonstrated a very efficient elimination of As(III), since the drinking water limit of 10 μg L⁻¹ was exceeded only after 7400 BV total throughput. The As-release from the loaded samples was below the limit established by the toxicity characteristic leaching procedure, thus making the spent material suitable for discharge in landfill deposits.     

Bifunctional resin-ZVI composites for effective removal of arsenite through simultaneous adsorption and oxidation

Bifunctional resin-supported nanosized zero-valent iron (N–S-ZVI) composite was developed by combining the oxidation properties of nZVI/O₂ with adsorption features of iron oxides and anion-exchange resin N–S. In batch culture experiments, N–S and the N–S-ZVI composite were examined for As(III) and As(V). The results reveal that ZVI in the composite played a key role in enhancing As(III) removal. The N–S-ZVI composites could oxidize more toxic As(III) to less toxic As(V) with high efficiency under ambient conditions without the need of noble metals. At the same time, the oxidized As(V) could be effectively removed by adsorption onto the surface of composites. The mechanisms for the oxidation of As(III) to As(V) and the simultaneous removal of As(V) are proposed. In order to investigate the potential performance of N–S-ZVI in practical use, the effects of solution pH and coexisting anions on arsenite removal and on fixed-bed column treatment of simulated waters were studied. All the results indicated that the bifunctional composites have a great potential for As(III) removal from contaminated waters.     

Preparation and evaluation of a novel Fe-Mn binary oxide adsorbent for effective arsenite removal

Arsenite (As(III)) is more toxic and more difficult to remove from water than arsenate (As(V)). As there is no simple treatment for the efficient removal of As(III), an oxidation step is always necessary to achieve higher removal. However, this leads to a complicated operation and is not cost-effective. To overcome these disadvantage, a novel Fe-Mn binary oxide material which combined the oxidation property of manganese dioxide and the high adsorption features to As(V) of iron oxides, were developed from low cost materials using a simultaneous oxidation and coprecipitation method. The adsorbent was characterized by BET surface areas measurement, powder XRD, SEM, and XPS. The results showed that prepared Fe-Mn binary oxide with a high surface area (265 m2 g(-1)) was amorphous. Iron and manganese existed mainly in the oxidation state +III and IV, respectively. Laboratory experiments were carried out to investigate adsorption kinetics, adsorption capacity of the adsorbent and the effect of solution pH values on arsenic removal. Batch experimental results showed that the adsorbent could completely oxidize As(III) to As(V) and was effective for both As(V) and As(III) removal, particularly the As(III). The maximal adsorption capacities of As(V) and As(III) were 0.93 mmol g(-1) and 1.77 mmol g(-1), respectively. The results compare favorably with those obtained using other adsorbent. The effects of anions such as SO4(2-), PO4(3-), SiO3(2-), CO3(2-) and humic acid (HA), which possibly exist in natural water, on As(III) removal were also investigated. The results indicated that phosphate was the greatest competitor with arsenic for adsorptive sites on the adsorbent. The presence of sulfate and HA had no significant effect on arsenic removal. The high uptake capability of the Fe-Mn binary oxide makes it potentially attractive adsorbent for the removal of As(III) from aqueous solution.     

Arsenic attenuation by oxidized aquifer sediments in Bangladesh

Recognition of arsenic (As) contamination of shallow fluvio-deltaic aquifers in the Bengal Basin has resulted in increasing exploitation of groundwater from deeper aquifers that generally contain low concentrations of dissolved As. Pumping-induced infiltration of high-As groundwater could eventually cause As concentrations in these aquifers to increase. This study investigates the adsorption capacity for As of sediment from a low-As aquifer near Dhaka, Bangladesh. A shallow, chemically-reducing aquifer at this site extends to a depth of 50 m and has maximum As concentrations in groundwater of 900 microg/L. At depths greater than 50 m, geochemical conditions are more oxidizing and groundwater has <5 microg/L As. There is no thick layer of clay at this site to inhibit vertical transport of groundwater. Arsenite [As(III)] is the dominant oxidation state in contaminated groundwater; however, data from laboratory batch experiments show that As(III) is oxidized to arsenate [As(V)] by manganese (Mn) minerals that are present in the oxidized sediment. Thus, the long-term viability of the deeper aquifers as a source of water supply is likely to depend on As(V) adsorption. The adsorption capacity of these sediments is a function of the oxidation state of As and the concentration of other solutes that compete for adsorption sites. Arsenite that was not oxidized did adsorb, but to a much lesser extent than As(V). Phosphate (P) caused a substantial decrease in As(V) adsorption. Increasing pH and concentrations of silica (Si) had lesser effects on As(V) adsorption. The effect of bicarbonate (HCO(3)) on As(V) adsorption was negligible. Equilibrium constants for adsorption of As(V), As(III), P, Si, HCO(3), and H were determined from the experimental data and a quantitative model developed. Oxidation of As(III) was modeled with a first-order rate constant. This model was used to successfully simulate As(V) adsorption in the presence of multiple competing solutes. Results from these experiments show that oxidized sediments have a substantial but limited capacity for removal of As from groundwater.     

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.     

Magnetic binary oxide particles (MBOP): a promising adsorbent for removal of As (III) in water

Magnetic binary oxide particles (MBOP) synthesized using chitosan template has been investigated for uptake capacity of arsenic (III). Batch experiments were performed to determine the rate of adsorption and equilibrium isotherm and also effect of various rate limiting factors including adsorbent dose, pH, optimum contact time, initial adsorbate concentration and influence of presence cations and anions. It was observed that uptake of arsenic (III) was independent of pH of the solution. Maximum adsorption of arsenic (III) was ∼99% at pH 7.0 with dose of adsorbent 1 g/L and initial As (III) concentration of 1.0 mg/L at optimal contact time of 14 h. The adsorption equilibrium data fitted well to Langmuir and Freundlich isotherm. The maximum adsorption capacity of adsorbent was 16.94 mg/g. With increase in concentration of Ca²⁺, Mg²⁺ from 50 mg/L to 600 mg/L, adsorption of As (III) was significantly reduced while for Fe³⁺ the adsorption of arsenic (III) was increased with increase in concentration. Temperature study was carried out at 293 K, 303 K and 313 K reveals that the adsorption process is exothermic nature. A distinct advantage of this adsorbent is that adsorbent can readily be isolated from sample solutions by application of an external magnetic field. Saturation magnetization is a key factor for successful magnetic separation was observed to be 18.78 emu/g which is sufficient for separation by conventional magnate.     

Removal of arsenic (III) and arsenic (V) from aqueous medium using chitosan-coated biosorbent

A biosorbent was prepared by coating ceramic alumina with the natural biopolymer, chitosan, using a dip-coating process. Removal of arsenic (III) (As(III)) and arsenic (V) (As(V)) was studied through adsorption on the biosorbent at pH 4.0 under equilibrium and dynamic conditions. The equilibrium adsorption data were fitted to Langmuir, Freundlich, and Redlich-Peterson adsorption models, and the model parameters were evaluated. All three models represented the experimental data well. The monolayer adsorption capacity of the sorbent, as obtained from the Langmuir isotherm, is 56.50 and 96.46 mg/g of chitosan for As(III) and As(V), respectively. The difference in adsorption capacity for As(III) and As(V) was explained on the basis of speciation of arsenic at pH 4.0. Column adsorption results indicated that no arsenic was found in the effluent solution up to about 40 and 120 bed volumes of As(III) and As(V), respectively. Sodium hydroxide solution (0.1M) was found to be capable of regenerating the column bed.     

A study on arsenic adsorption on polymetallic sea nodule in aqueous medium

A detailed study on As(III) and As(V) adsorption on polymetallic sea nodule in aqueous medium has been reported. Elemental composition of sea nodule comprises primarily, iron, manganese and silicon with trace quantities of aluminium, copper, cobalt and nickel. As(V) adsorption on sea nodule is dependent on pH while As(III) is insensitive to it. Adsorption data broadly follow Langmuir isotherm. Kinetic data follow a pseudo-second-order model for both As(III) and As(V). Arsenic loading on sea nodule is dependent on initial arsenic concentration. Optimum As(III) loading is 0.74 mg/g at 0.34 mg/L and for As(V) it is 0.74 mg/g at 0.78mg/L. As(III) adsorption is broadly independent of ionic environment. Except for PO(4)(3-), As(III) adsorption is not influenced by anions but cations influence it significantly. As(V) adsorption, on the other hand, is influenced by anions and not by cations. Experimental evidence indicates an inner sphere complex for As(III) and partial inner and partial outer sphere complex for As(V). Both As(III) and As(V) adsorptions are marked with very little desorption in the pH range of 2-10. Sea nodule can speciate As(III) and As(V) in groundwater at or above pH 6. Sea nodule was successfully tested as an adsorbent for the removal of arsenic from six contaminated groundwater samples of West Bengal, India, containing arsenic in the range 0.04-0.18mg/L.     

As(V) retention and As(III) simultaneous oxidation and removal on a MnO2-loaded polystyrene resin

Based on KMnO4 oxidative capacity, a polystyrene matrix loaded with manganese dioxide was synthesized from an anionic commercial resin in chloride form. This medium, called R-MnO2, was tested for As(V) retention and for As(III) simultaneous oxidation and removal. Equilibrium was reached in 2 h and isotherms showed that R-MnO2 maximal capacities towards As(III) and As(V) are, respectively, 0.7 and 0.3 mmol/g. Various mechanisms were involved in As(III) retention: oxidation of H3AsO3(0) by MnO2(s) leading to the formation of HAsO4(2)- and Mn2+, fixation of As(V) formed on the resin beads and precipitation of Mn3(AsO4)2 with Mn2+ released. Successive arsenic desorption and retention steps were performed and showed that the quantity desorbed was low compared to the quantity removed during the first stage of the process. A second removal step, carried out under the same conditions as the first one, proved that the matrix second-removal capacity was weak. This solid sorbent, although not reusable, can be considered in field application as arsenic retention is really strong.     

Chemical reactions between arsenic and zero-valent iron in water

Batch experiments and X-ray photoelectron spectroscopic (XPS) analyses were performed to study the reactions between arsenate [As(V)], arsenite [As(III)] and zero-valent iron [Fe(0)]. The As(III) removal rate was higher than that for As(V) when iron filings (80-120 mesh) were mixed with arsenic solutions purged with nitrogen gas in the pH range of 4-7. XPS spectra of the reacted iron coupons showed the reduction of As(III) to As(0). Soluble As(III) was formed when As(V) reacted with Fe(0) under anoxic conditions. However, no As(0) was detected on the iron coupons after 5 days of reaction in the As(V)-Fe(0) system. The removal of the arsenic species by Fe(0) was attributed to electrochemical reduction of As(III) to sparsely soluble As(0) and adsorption of As(III) and As(V) to iron hydroxides formed on the Fe(0) surface under anoxic conditions. When the solutions were open to atmospheric air, the removal rates of As(V) and As(III) were much higher than under the anoxic conditions, and As(V) removal was faster than As(III). The rapid removal of As(III) and As(V) was caused by adsorption on ferric hydroxides formed readily through oxidation of Fe(0) by dissolved oxygen.     

Adsorption and heterogeneous oxidation of As(III) on ferrihydrite

Redox transformation of arsenic strongly influences its fate and transport in the environment. It is of interest to investigate heterogeneous oxidation of As(III) on the surface of major metal oxide in sediments. Whether As(III) can be oxidized on ferrihydrite and the role ferrihydrite plays as catalyst or oxidant are inconsistent in previous researches. In this work, oxidation of As(III) on ferrihydrite was studied by analysis of dissolved and adsorbed As(III) and As(V) quantitatively and qualitatively. X-ray absorption near edge spectroscopy (XANES) and pH_pznpc (point of zero net proton charge) of ferrihydrite with adsorbed As(III) showed clear evidence for partial oxidation on ferrihydrite. Oxidation of As(III) occurred when it was brought to contact with ferrihydrite at high Fe/As molar ratio (i.e. 50, 200). The concentration of As(V) in solid phase increased gradually while adsorbed As(III) concentration dropped. Fe(II) was not detectable during the oxidation of As(III). These results showed that ferrihydrite had the catalytic effect on oxidation of As(III). Only a fraction of As(III) was oxidized even when the system was exposed to air. The effects of ferrihydrite aging, media pH, coexistence of ions on As(III) oxidation were also investigated. The results suggest that catalytic oxidation of As(III) on ferrihydrite may play a role in geochemical cycling of arsenic in environment.     

Ozone and photocatalytic processes to remove the antibiotic sulfamethoxazole from water

In this study, water containing the pharmaceutical compound sulfamethoxazole (SMT) was subjected to the various treatments of different oxidation processes involving ozonation, and photolysis and catalysis under different experimental conditions. Removal rates of SMT and total organic carbon (TOC), from experiments of simple UVA radiation, ozonation (O(3)), catalytic ozonation (O(3)/TiO(2)), ozone photolysis (O(3)/UVA), photocatalytic oxidation (O(2)/TiO(2)/UVA) and photocatalytic ozonation (O(3)/UVA/TiO(2)), have been compared. Photocatalytic ozonation leads to the highest SMT removal rate (pH 7 in buffered systems, complete removal is achieved in less than 5min) and total organic carbon (in unbuffered systems, with initial pH=4, 93% TOC removal is reached). Also, lowest ozone consumption per TOC removed and toxicity was achieved with the O(3)/UVA/TiO(2) process. Direct ozone and free radical reactions were found to be the principal mechanisms for SMT and TOC removal, respectively. In photocatalytic ozonation, with buffered (pH 7) aqueous solutions phosphates (buffering salts) and accumulation of bicarbonate scavengers inhibit the reactions completely on the TiO(2) surface. As a consequence, TOC removal diminishes. In all cases, hydrogen peroxide plays a key role in TOC mineralization. According to the results obtained in this work the use of photocatalytic ozonation is recommended to achieve a high mineralization degree of water containing SMT type compounds.     

Kinetic and thermodynamic aspects of adsorption of arsenic onto granular ferric hydroxide (GFH)

Relatively limited information is available regarding the impacts of temperature on the adsorption kinetics and equilibrium capacities of granular ferric hydroxide (GFH) for arsenic (V) and arsenic (III) in an aqueous solution. In general, very little information is available on the kinetics and thermodynamic aspects of adsorption of arsenic compounds onto other iron oxide-based adsorbents as well. In order to gain an understanding of the adsorption process kinetics, a detailed study was conducted in a controlled batch system. The effects of temperature and pH on the adsorption rates of arsenic (V) and arsenic (III) were investigated. Reaction rate constants were calculated at pH levels of 6.5 and 7.5. Rate data are best described by a pseudo first-order kinetic model at each temperature and pH condition studied. At lower pH values, arsenic (V) exhibits greater removal rates than arsenic (III). An increase in temperature increases the overall adsorption reaction rate constant values for both arsenic (V) and arsenic (III). An examination of thermodynamic parameters shows that the adsorption of arsenic (V) as well as arsenic (III) by GFH is an endothermic process and is spontaneous at the specific temperatures investigated.     

The Impact of the Mg(II)/Fe(III) Ratio in the Composition of Layered Double Hydroxides for the Removal of Phosphate–Ions from Water Media

The results of the impact of the [Mg(II)]/[Fe(III)] as part of layered double hydroxides on their sorption capacity with respect to phosphate-ions are presented. It is shown that the most effective for the removal of the given anions from water media within the range pH 3–9 are calcined forms of sorbents being studied with the [Mg(II)]/Fe(III)] 2 : 1 and 3 : 1. Maximum values of adsorption constitute respectively 90.9 and 91.7 mg/g.