Synergistic effect from combined use of scrap-recycling slag and hydrated lime to stabilize Pb and Zn in highly contaminated soil.

For the soil in an area which has been repeatedly chosen as one of the 10 most polluted places in the world, stabilization of Pb and Zn was assessed in batch, incubation, and column experiments. Single and combined amendment of scrap-recycling slag (Slag-R), charcoal, coal ash, hydrated lime, and basic oxygen furnace (BOF) slag were applied for the stabilization. Notably, the combined amendment of Slag-R and hydrated lime exhibited superior stabilization efficiencies than the individual use of all stabilizing agents and combined use of charcoal and hydrated lime. The combined amendment of Slag-R and hydrated lime decreased Pb levels by 92-99% and Zn levels by 63-88% in the incubation experiments and by 75% and 89-93%, respectively, in the column experiments. In particular, the combined amendment showed a synergistic effect for Pb stabilization because a higher pH enhanced sorption onto the slag and because sorption onto Fe (hydr)oxides of the sorbent possibly helped to remove Pb. Zinc had a relatively lower sorption tendency, so it was mainly controlled by the pH increase from hydrated lime. Although the addition of hydrated lime was very effective in stabilizing high concentrations of Pb and Zn, the dosage should be controlled carefully because excessively high pH redissolves Pb and Zn as anions.

Selenate removal by zero-valent iron in oxic condition: the role of Fe(II) and selenate removal mechanism.

In this study, batch experiments were conducted to investigate the effect of the concentration of ferrous [Fe(II)] ions on selenate [Se(VI)] removal using zero-valent iron (ZVI). The mechanism of removal was investigated using spectroscopic and image analyses of the ZVI-Fe(II)-Se(VI) system. The test to remove 50 mg/L of Se(VI) by 1 g/L of ZVI resulted in about 60% removal of Se(VI) in the case with absence of Fe(II), but other tests with the addition of 50 and 100 mg/L of the Fe(II) had increased the removal efficiencies about 93 and 100% of the Se(VI), respectively. In other batch tests with the absence of ZVI, there were little changes on the Se(VI) removal by the varied concentration of the Fe(II). From these results, we found that Fe(II) ion plays an accelerator for the reduction of Se(VI) by ZVI with the stoichiometric balance of 1.4 (=nFe(2+)/nSe(6+)). Under anoxic conditions, the batch test revealed about 10% removal of the Se(VI), indicating that the presence of dissolved oxygen increased the kinetics of Se(VI) removal due to the Fe(II)-containing oxides on the ZVI, as analyzed by scanning electron microscopy-energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray photoelectron spectroscopy (XPS). The X-ray absorption near edge spectroscopy (XANES) and extended X-ray absorption fine structure (EXAFS) spectra also showed that the reductive process of Se(VI) to Se(0)/Se(-II) occurred in the presence of the both ZVI and Fe(II). The final product of iron corrosion was lepidocrocite (γ-FeOOH), which acts as an electron transfer barrier from Fe(0) core to Se(VI). Therefore, the addition of Fe(II) enhanced the reactivity of ZVI through the formation of iron oxides (magnetite) favoring electron transfer during the removal of Se(VI), which was through the exhaustion of the Fe(0) core reacted with Se(VI).

Enhanced Arsenate Removal Performance in Aqueous Solution by Yttrium-Based Adsorbents.

Arsenic contamination in drinking water has become an increasingly important issue due to its high toxicity to humans. The present study focuses on the development of the yttrium-based adsorbents, with basic yttrium carbonate (BYC), Ti-loaded basic yttrium carbonate (Ti-loaded BYC) and yttrium hydroxide prepared using a co-precipitation method. The Langmuir isotherm results confirmed the maximum adsorption capacity of Ti-loaded BYC (348.5 mg/g) was 25% higher than either BYC (289.6 mg/g) or yttrium hydroxide (206.5 mg/g) due to its increased specific surface area (82 m²/g) and surface charge (PZC: 8.4). Pseudo first- and second-order kinetic models further confirmed that the arsenate removal rate of Ti-loaded BYC was faster than for BYC and yttrium hydroxide. It was subsequently posited that the dominant removal mechanism of BYC and Ti-loaded BYC was the carbonate-arsenate ion exchange process, whereas yttrium hydroxide was regarded to be a co-precipitation process. The Ti-loaded BYC also displayed the highest adsorption affinity for a wide pH range (3-11) and in the presence of coexisting anionic species such as phosphate, silicate, and bicarbonate. Therefore, it is expected that Ti-loaded BYC can be used as an effective and practical adsorbent for arsenate remediation in drinking water.

Community exposure to arsenic in the Mekong river delta, Southern Vietnam.

We examined the daily inorganic arsenic (i-As) intake from drinking water and rice in 45 households (75 individuals) in the An Giang province, Southern Vietnam. The daily i-As intake ranged from 28-102 µg d(-1), equivalent to the daily dose of 0.6-1.9 µg d(-1) kg((body wt))(-1). Increased As concentrations were observed in human hair in the study location. Approximately 67% (n = 44), 42% (n = 28), and 15% (n = 10) of the hair samples had As levels exceeding 1, 3, and 10 µg g(-1), respectively. The total As concentrations in female and male hair correlated well with the total daily i-As intake. Measurement of As concentrations in the hair of people who were consuming or had previously consumed As from contaminated sources may help predict the onset of negative health effects. We suggested an application of the Bayes's theorem to calculate the probability that an individual in a population will acquire a negative health effect, given that the concentration of arsenic in the subject's hair has been determined.

Effects of pH and dissolved oxygen on Cr(VI) removal in Fe(0)/H2O systems.

The effects of pH and dissolved oxygen (DO) on aqueous Cr(VI) removal by micro-scale zero-valent iron (Fe(0)/H(2)O system) were investigated. Batch experiments were conducted at pH 4.0, 5.0 and 6.0 under oxic and anoxic conditions. Column experiments were performed at pH 5.0 and 7.5 under oxic condition. Spectroscopic analyses were applied to explain the mechanism of Cr(VI) removal using X-ray absorption near-edge structure (XANES), X-ray diffraction (XRD), and scanning electron microscopy (SEM). Results showed that the kinetics of Cr(VI) removal were fastest at pH 5 under both oxic and anoxic conditions. As a rule, Cr(VI) removal were faster under oxic conditions than under anoxic conditions. Column experiments showed that Cr(VI) removal was about 1.7-fold higher at pH 5 than at pH 7.5. XANES (X-ray absorption near edge structures) results showed that Fe(0) reduced Cr(VI) to Cr(III) under both oxic and anoxic conditions. X-ray diffraction patterns of the Cr(VI)-Fe(0) reaction products suggested partial formation of chromite (FeCr(2)O(4)) at pH 5 and 6 under oxic conditions. However, nano-sized clusters of Cr(III)/Fe(III) hydroxide/oxyhydroxide were formed on the surface of Fe(0) under anoxic conditions. These results indicate that the presence of oxygen in solution plays an important role in control of the kinetic of Cr(VI) removal and in development of various Cr(VI) reduction products.

Removal of arsenate from water by adsorbents: a comparative case study.

Laboratory and field filtration experiments were conducted to study the effectiveness of As(V) removal for five types of adsorbent media. The media included activated alumina (AA), modified activated alumina (MAA), granular ferric hydroxide (GFH), granular ferric oxide (GFO), and granular titanium dioxide (TiO2). In laboratory batch and column experiments, the synthetic challenge water was used to evaluate the effectiveness for five adsorbents. The results of the batch experiments showed that the As(V) adsorption decreased as follows at pH 6.5: TiO2 > GFO > GFH > MAA > AA. At pH 8.5, however, As(V) removal decreased in the following order: GFO = TiO2 > GFH > MAA > AA. In column experiments, at pH 6.5, the adsorbed As(V) for adsorbents followed the order: TiO2 > GFO > GFH, whereas at pH 8.5 the order became: GFO = TiO2 > GFH when the challenge water containing 50 µg/L of As(V) was used. Field filtration experiments were carried out in parallel at a wellhead in New Jersey. Before the effluent arsenic concentration increased to 10 µg/L, approximately 58,000 and 41,500 bed volumes of groundwater containing an average of 47 µg/L of As(V) were treated by the filter system packed with GFO and TiO2, respectively. The As(V) adsorption decreased in the following sequence: GFO > TiO2 > GFH > MAA > AA. Filtration results demonstrated that GFO and TiO2 adsorbents could be used as media in small community filtration systems for As(V) removal.

Arsenic in groundwater and sediment in the Mekong River delta, Vietnam.

A study of groundwater and sediment during 2007-2008 in the Mekong River delta in Vietnam (MDVN) revealed that 26%, 74%, and 50% of groundwater samples were above the US EPA drinking water guidelines for As (10 microg/L), Mn (0.05 mg/L), and Fe (0.3 mg/L). The range of As, Fe, and Mn concentrations in the MDVN were <0.1-1351 microg/L, <0.01-38 mg/L, and <0.01-14 mg/L, respectively. Elevated levels of As were found in groundwater at sampling sites close to the Mekong River and in wells less than 60-70 m deep. An inverse relationship was found between As and Mn concentrations in groundwater. Sediment samples from An Giang and Dong Thap had the highest As concentrations (18 mg/kg and 38 mg/kg, respectively). Arsenic sediment occurred mainly in the poorly crystalline Fe oxide phases. Reductive dissolution of the Fe oxide phase is not necessarily the dominant mechanism of As release to groundwater.

Arsenic removal from Vietnamese groundwater using the arsenic-binding DNA aptamer.

Single-stranded DNA aptamers were generated from a random library to remove arsenic from Vietnamese groundwater. On the basis of significant arsenic contamination levels, three areas in Ha Nam province (Vinh Tru, Bo De, and Hoa Hau) and five areas near the Mekong River Delta (MR1-5) were selected as study areas. The aptamers were in vitro selected using an arsenic aptamer affinity column created by immobilizing arsenic on Affi-gel 10 resin. Quantitative analyses of the aptamer candidates Ars-1 to Ars-8 by surface plasmon resonance (SPR) revealed the Ars-3 aptamer to have the highest affinity to arsenate [(As(V)] and arsenite [As(III)] with a dissociation constant (K(d)) of 4.95 +/- 0.31 and 7.05 +/- 0.91 nM, respectively. The specific affinity interactions of the Ars-3 aptamer to arsenic were verified against other heavy metals. After obtaining successful removal results with a laboratory-prepared aqueous arsenic solution, Ars-3 was applied for removal of any arsenic present in the groundwater samples collected from the studied areas in Vietnam. Field results were also successful: various arsenic concentrations ranging from 28.1 to 739.2 microg/L were completely removed after 5 min of incubation with the arsenic-binding aptamer Ars-3.

Contamination of groundwater and risk assessment for arsenic exposure in Ha Nam province, Vietnam.

The characteristics of arsenic-contaminated groundwater and the potential risks from the groundwater were investigated. Arsenic contamination in groundwater was found in four villages (Vinh Tru, Bo De, Hoa Hau, Nhan Dao) in Ha Nam province in northern Vietnam. Since the groundwater had been used as one of the main drinking water sources in these regions, groundwater and hair samples were collected in the villages. The concentrations of arsenic in the three villages (Vinh Tru, Bo De, Hoa Hau) significantly exceeded the Vietnamese drinking water standard for arsenic (10 microg/L) with average concentrations of 348, 211, and 325 microg/L, respectively. According to the results of the arsenic speciation testing, the predominant arsenic species in the groundwater existed as arsenite [As(III)]. Elevated concentrations of iron, manganese, and ammonium were also found in the groundwater. Although more than 90% of the arsenic was removed by sand filtration systems used in this region, arsenic concentrations of most treated groundwater were still higher than the drinking water standard. A significant positive correlation was found between the arsenic concentrations in the treated groundwater and in female human hair. The risk assessment for arsenic through drinking water pathways shows both potential chronic and carcinogenic risks to the local community. More than 40% of the people consuming treated groundwater are at chronic risk for arsenic exposure.

Perchlorate adsorption and desorption on activated carbon and anion exchange resin.

The mechanisms of perchlorate adsorption on activated carbon (AC) and anion exchange resin (SR-7 resin) were investigated using Raman, FTIR, and zeta potential analyses. Batch adsorption and desorption results demonstrated that the adsorption of perchlorate by AC and SR-7 resin was reversible. The reversibility of perchlorate adsorption by the resin was also proved by column regeneration test. Solution pH significantly affected perchlorate adsorption and the zeta potential of AC, while it did not influence perchlorate adsorption and the zeta potential of resin. Zeta potential measurements showed that perchlorate was adsorbed on the negatively charged AC surface. Raman spectra indicated the adsorption resulted in an obvious position shift of the perchlorate peak, suggesting that perchlorate was associated with functional groups on AC at neutral pH through interactions stronger than electrostatic interaction. The adsorbed perchlorate on the resin exhibited a Raman peak at similar position as the aqueous perchlorate, indicating that perchlorate was adsorbed on the resin through electrostatic attraction between the anion and positively charged surface sites.

Monitoring of environmental phenolic endocrine disrupting compounds in treatment effluents and river waters, Korea.

The last two decades have witnessed growing scientific and public concerns over endocrine disrupting compounds (EDCs) that have the potential to alter the normal structure or functions of the endocrine system in wildlife and humans. In this study, the phenolic EDCs such as alkylphenol, chlorinated phenol and bisphenol A were considered. They are commonly found in wastewater discharges and in sewage treatment plant. In order to monitor the levels and seasonal variations of phenolic EDCs in various aquatic environments, a total of 15 water samples from the discharged effluent from sewage and wastewater treatment plants and river water were collected for 3 years. Ten environmental phenolic EDCs were determined by GC-MS and laser-induced fluorescence (LIF). GC-MS analysis revealed that most abundant phenolic EDCs were 4-n-heptylphenol, followed by nonlyphenol and bisphenol A during 2002-2003, while 4-t-butylphenol and 4-t-octylphenol were newly detected in aquatic environments in 2004. The category of phenolic EDCs showed similar fluorescence spectra and nearly equal fluorescence decay time. This makes it hard to distinguish each phenolic EDC from the EDCs mixture by LIF. Therefore, the results obtained from LIF analysis were expressed in terms of the fluorescence intensity of the total phenolic EDCs rather than that of the individual EDC. However, LIF monitoring and GC-MS analysis showed consistent result in that the river water samples had lower phenolic EDCs concentration compared to the effluent sample. This revealed a lower fluorescence intensity and the phenolic EDCs concentration in summer was lower than that in winter. For the validation of LIF monitoring for the phenolic EDCs, the correlation between EDCs concentration acquired from GC-MS and fluorescence intensity from LIF was obtained (R=0.7379). This study supports the feasibility of the application of LIF into EDCs monitoring in aquatic systems.

Removal of arsenic from groundwater by granular titanium dioxide adsorbent.

A novel granular titanium dioxide (TiO2) was evaluated for the removal of arsenic from groundwater. Laboratory experiments were carried out to investigate the adsorption capacity of the adsorbent and the effect of anions on arsenic removal. Batch experimental results showed that more arsenate [As(V)] was adsorbed on TiO2 than arsenite [As(III)] in US groundwater at pH 7.0. The adsorption capacities for As(V) and As(III) were 41.4 and 32.4 mgg(-1) TiO2, respectively. However, the adsorbent had a similar adsorption capacity for As(V) and As(III) (approximately 40 mgg(-1)) when simulated Bangladesh groundwater was used. Silica (20 mgl(-1)) and phosphate (5.8 mgl(-1)) had no obvious effect on the removal of As(V) and As(III) by TiO2 at neutral pH. Point-of-entry (POE) filters containing 3 l of the granular adsorbent were tested for the removal of arsenic from groundwater in central New Jersey, USA. Groundwater was continuously passed through the filters at an empty bed contact time (EBCT) of 3 min. Approximately 45,000 bed volumes of groundwater containing an average of 39 microgl(-1) of As(V) was treated by the POE filter before the effluent arsenic concentration increased to 10 microgl(-1). The total treated water volumes per weight of adsorbent were about 60,000 l per 1 kg of adsorbent. The field filtration results demonstrated that the granular TiO2 adsorbent was very effective for the removal of arsenic in groundwater.

Removal of arsenic from water by zero-valent iron.

Batch and column experiments were conducted to investigate the effect of dissolved oxygen (DO) and pH on arsenic removal with zero-valent iron [Fe(0)]. Arsenic removal was dramatically affected by the DO content and the pH of the solution. Under oxic conditions, arsenate [As(V)] removal by Fe(0) filings was faster than arsenite [As(III)]. Greater than 99.8% of the As(V) was removed whereas 82.6% of the As(III) was removed at pH 6 after 9h of mixing. When the solution was purged with nitrogen gas to remove DO, less than 10% of the As(III) and As(V) was removed. High DO content and low solution pH also increased the rate of iron corrosion. The removal of arsenic by Fe(0) was attributed to adsorption by iron hydroxides generated from the oxic corrosion of Fe(0). The column results indicated that a filtration system consisting of an iron column and a sand filter could be used for treatment of arsenic in drinking water.

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.

Removal of selenocyanate from water using elemental iron.

Batch experiments were conducted to investigate the removal of selenocyanate (SeCN-) from oil refinery wastewater and artificial wastewater with elemental iron [Fe(0)]. The chemical forms of selenium in the reacted solids were determined with X-ray photoelectron spectroscopy (XPS) and a sulfite extraction procedure. SeCN- was effectively removed from the wastewater with Fe(0) filings when the water pH was controlled at approximately 6. SeCN- was removed by Fe(0) through the formation of elemental selenium [Se(0)] and ferrous selenide. The possible chemical reactions between SeCN- and Fe(0) included deselenation of SeCN- and electrochemical reduction of Se(0) to selenide. A cost-effective process may be developed for the treatment of SeCN- in wastewater using Fe(0).

Combined effects of anions on arsenic removal by iron hydroxides.

Batch experiments were conducted to investigate the combined effects of phosphate, silicate, and bicarbonate on the removal of arsenic from Bangladesh groundwater (BGW) and simulated groundwater by iron hydroxides. The apparent adsorption constants indicated that the affinity of the anions for iron hydroxide sites decreased in the following order arsenate>phosphate>arsenite>silicate>bicarbonate. Phosphate, silicate, and bicarbonate decreased the removal of As(III) even at relatively low concentrations and low surface site coverage. Phosphate (0-0.08 mM), silicate (0-0.8 mM), and bicarbonate (0-14 mM) in separate solutions had none to moderate effects on As(V) removal in a solution containing 6.7 mg/l Fe and 0.3 ppm As(V). In the presence of bicarbonate and silicate the adverse effect of phosphate on As(V) adsorption was magnified. The residual As(V) concentration after iron hydroxide treatment increased from less than 13 microg/l in separate bicarbonate (2.2 mM) and phosphate (0.062 mM) solutions to 110 microg/l in the solution containing both anions. The results suggested the combined effects of phosphate, silicate, and bicarbonate caused the high mobility of arsenic in Bangladesh water.