Arsenic adsorption on lignocellulosic substrate loaded with ferric ion

We loaded a lignocellulosic substrate extracted from wheat bran with ferric ions. This new low-cost adsorbent was prepared for the adsorption and removal of arsenate and arsenite ions from aqueous systems. The loading process of Fe in this biomaterial was done by hydrolization of a ferric salt while an alkaline solution was added dropwise. The new material obtained has a high sensivity to arsenite and arsenate species. Here, we investigated the effect of contact time, pH, and Fe content on the adsorption of both arsenic ions on the new material. This adsorption was found to be highly pH-dependent, which can be explained on the basis of electrostatic interactions between ionic species in solution and the ≡FeOH surface groups. The maximum adsorption capacity of arsenite and arsenate species vary linearly with the amount of Fe loaded on the lignocellulosic substrate.     

Leaching of arsenic from coal fly ashes 2. Arsenic pre‐leaching with sodium gluconate solution

The present study deals with the development of an efficient and reliable process for safe disposal of coal fly ash to remove arsenic that has been found to be the most easily leachable and hazardous heavy metal in coal fly ash. Pre‐leaching of fly ash prior to disposal by a natural chelating agent, sodium gluconate (SG), was proposed and studied. Several operational factors influencing arsenic leachability, such as concentration of SG solution, liquid to solid ratio, pH, length of leaching time and leaching temperature were examined. Arsenic was found to leach out substantially with SG, but almost no further release was observed from the ash pre‐leached by SG. After the pre‐leaching treatment, the desirable high buffering capacity of the ash was well sustained. SG solution was effectively regenerated by activated alumina adsorption so that it could be successfully reused for multiple leaching/adsorption cycles.     

Dedication

Elevated concentrations of arsenic (As) occurred during warm months in water from the outlet of Lake Mohawk in northwestern New Jersey. The shallow manmade lake is surrounded by residential development and used for recreation. Eutrophic conditions are addressed by alum and copper sulfate applications and aerators operating in the summer. In September 2005, arsenite was dominant in hypoxic to anoxic bottom water. Filterable As concentrations were about 1.6–2 times higher than those in the upper water column (23–25 μg/L, mostly arsenate). Hypoxic/anoxic and near-neutral bottom conditions formed during the summer, but became more oxic and alkaline as winter approached. Acid-leachable As concentrations in lake-bed sediments ranged up to 694 mg/kg in highly organic material from the tops of sediment cores but were <15 mg/kg in geologic substrate. During warm months, reduced As from the sediment diffuses into the water column and is oxidized; mixing by aerators, wind, and boat traffic spreads arsenate and metals, some in particulate form, throughout the water column. Similar levels of As in sediments of lakes treated with arsenic pesticides indicate that most of the As in Lake Mohawk probably derives from past use of arsenical pesticides, although records of applications are lacking. The annual loss of As at the lake outlet is only about 0.01% of the As calculated to be in the sediments, indicating that elevated levels of As in the lake will persist for decades.     

Assessment of Contamination By Percolation Of Septic Tank Effluent Through Natural and Amended Soils

Fly ash has been found to be a potential material for the treatment of municipal and industrial wastewater, and may be useful in the treatment of septic tank effluent. Laboratory columns (30 cm) were used to determine the sorption capacity and hydraulic properties of lagoon fly ash, loamy sand, sand, and sand amended by lagoon fly ash (30 and 60%) and red mud gypsum (20%). The removal of chemical oxygen demand (COD) was high in all column effluents (71–93%). Extent of nitrification was high in Spearwood sand, Merribrook loamy sand and 20% red mud gypsum amended Spearwood sand. However, actual removal of nitrogen (N) was high in columns containing lagoon fly ash. Unamended Spearwood sand possessed only minimal capacity for P sorption. Merribrook loamy sand and red mud gypsum amended sand affected complete P removal throughout the study period of 12 weeks. Significant P leakage occurred from lagoon fly ash amended sand columns following 6–10 weeks of operation. Neither lagoon fly ash nor red mud gypsum caused any studied heavy metal contamination including manganese (Mn), lead (Pb), zinc (Zn), cadmium (Cd) and chromium (Cr) of effluent. It can be concluded that Merribrook loamy sand is better natural soil than Spearwood sand as a filter medium. The addition of lagoon fly ash enhanced the removal of P in Spearwood sand but the efficiency was lower than with red mud gypsum amendment.     

Field based speciation of arsenic in UK and Argentinean water samples

A field method is reported for the speciation of arsenic in water samples that is simple, rapid, safe to use beyond laboratory environments, and cost effective. The method utilises solid-phase extraction cartridges (SPE) in series for selective retention of arsenic species, followed by elution and measurement of eluted fractions by inductively coupled plasma mass spectrometry (ICP-MS) for “total” arsenic. The method is suitable for on-site separation and preservation of arsenic species from water. Mean percentage accuracies (n = 25) for synthetic solutions of arsenite (As^III), arsenate (As^V), monomethylarsonic acid (MA), and dimethylarsinic acid (DMA) containing 10 μg l⁻¹ As, were 98, 101, 94, and 105%, respectively. Data are presented to demonstrate the effect of pH and competing anions on the retention of the arsenic species. The cartridges were tested in the UK and Argentina at sites where arsenic was known to be present in surface and groundwaters, respectively, at elevated concentrations and under challenging matrix conditions. In Argentinean groundwater, 4–20% of speciated arsenic was present as MA and 20–73% as As^III. In UK surface waters, speciated arsenic was measured as 7–49% MA and 12–42% DMA. Comparative data from the field method using SPE cartridges and the laboratory method using liquid chromatography coupled to ICP-MS for all water samples provided a correlation of greater than 0.999 for As^III and DMA, 0.991 for MA, and 0.982 for As^V (P < 0.01).     

Characterization of boron tolerant bacteria isolated from a fly ash dumping site for bacterial boron remediation

Boron is an essential micronutrient for plants, but can above certain concentrations be toxic to living organisms. A major environmental concern is the removal of boron from contaminated water and fly ash. For this purpose, the samples were collected from a fly ash dumping site, Nagasaki prefecture, Japan. The chemical characteristics and heavy metal concentration of the samples were performed by X-ray fluorescent analysis and leaching test. For bacterial analysis, samples were collected in sterile plastic sheets and isolation was carried out by serial dilution method. The boron tolerant isolates that showed values of maximum inhibitory concentration toward boron ranging from 100 to 260 mM level were screened. Based on 16S rRNA sequencing and phylogenetic analysis, the isolates were most closely related to the genera Bacillus, Lysinibacillus, Microbacterium and Ralstonia. The boron tolerance of these strains was also associated with resistant to several heavy metals, such as As (III), Cr (VI), Cd, Cu, Pb, Ni, Se (III) and Zn. Indeed, these strains were arsenic oxidizing bacteria confirmed by silver nitrate test. These strains exhibited their salt resistances ranging from 4 to 15 % were determined in Trypticase soy agar medium. The boron tolerant strains were capable of removing 0.1–2.0 and 2.7–3.7 mg l^?1 boron from the medium and fly ash at 168 h. Thus, we have successfully identified the boron tolerant and removal bacteria from a fly ash dumping site for boron remediation.     

Application of magnesite–bentonite clay composite as an alternative technology for removal of arsenic from industrial effluents

This study evaluated the feasibility of integrating amorphous magnesite and bentonite clay (composite) as an alternative technology for removing arsenic from industrial effluents. The removal of arsenic from industrial effluents by using magnesite–bentonite clay composite was carried out in batch mode. The effects of equilibration time, adsorbent dosage, adsorbate concentration, and pH on removal of arsenic were investigated. The experiments demonstrated that ≈100% arsenic removal is optimum at 30 minutes of agitation, 2 g of adsorbent dosage (2 g: 100 mL, S/L ratio), and 20 mg L^?1 of arsenic concentration. The adsorption data fitted well to both Langmuir and Freundlich adsorption models, hence proving monolayer and multilayer adsorption. The kinetic studies revealed that the data fitted better to a pseudo-second-order reaction than to a pseudo-first-order reaction, hence proving chemisorption. At optimized conditions, the composite was able to remove arsenic to below World Health Organization water quality guidelines, hence depicting that the composite is effective and efficient in removing arsenic from contaminated water. Based on that, this comparative study proves that the composite is a promising adsorbent with high adsorption capacity for arsenic and can be a suitable substitute for the conventional treatment methods.     

Investigation of As, Mn and Fe fixation inside the aquifer during groundwater exploitation in the experimental system imitated natural conditions

Water-dissolved oxygen was supplied into anaerobic aquifer , which oxidized Fe(II), Mn(II) and trivalent arsenic and changed them into undissolved solid matter through hydrolysis, precipitation, co-precipitation and adsorption processes. The experiment was carried out on the column imitated a bore core of anaerobic aquifer with water phase containing Fe(II), Mn(II), As(III) concentration of 45.12 mg/L, 14.52 mg/L, 219.4 μg/L, respectively and other ions similarly composition in groundwater. After 6 days of air supply, concentration of iron reduced to 0.38 mg/L, manganese to 0.4 mg/L, arsenic to 9.8 μg/L (equivalent 99.16% of iron, 97.25% of manganese and 95.53% of arsenic fixed), and for other ions, the concentration changed almost according to general principles. Ion phosphate and silicate strongly influenced on arsenic removal but supported iron and manganese precipitation from water phase. Based on the experimental results, new model of groundwater exploitation was proposed.     

Arsenic detoxification potential of <Emphasis Type="Italic">aox</Emphasis> genes in arsenite-oxidizing bacteria isolated from natural and constructed wetlands in the Republic of Korea

Arsenic is subject to microbial interactions, which support a wide range of biogeochemical transformations of elements in natural environments such as wetlands. The arsenic detoxification potential of the bacterial strains was investigated with the arsenite oxidation gene, aox genotype, which were isolated from the natural and constructed wetlands. The isolates were able to grow in the presence of 10 mM of sodium arsenite (As(III) as NaAsO₂) and 1 mM of d+glucose. Phylogenetic analysis based on 16S rRNA gene sequencing indicated that these isolated strains resembled members of the genus that have arsenic-resistant systems (Acinetobacter sp., Aeromonas sp., Agrobacterium sp., Comamonas sp., Enterobacter sp., Pantoea sp., and Pseudomonas sp.) with sequence similarities of 81–98%. One bacterial isolate identified as Pseudomonas stutzeri strain GIST-BDan2 (EF429003) showed the activity of arsenite oxidation and existence of aoxB and aoxR gene, which could play an important role in arsenite oxidation to arsenate. This reaction may be considered as arsenic detoxification process. The results of a batch test showed that P. stutzeri GIST-BDan2 (EF429003) completely oxidized in 1 mM of As(III) to As(V) within 25–30 h. In this study, microbial activity was evaluated to provide a better understanding of arsenic biogeochemical cycle in both natural and constructed wetlands, where ecological niches for microorganisms could be different, with a specific focus on arsenic oxidation/reduction and detoxification.     

A simple voltammetric procedure for speciation and evaluation of As removal from water

Here, we show a fast and sensitive method for the determination of inorganic arsenic in natural waters using differential pulse cathodic stripping voltammetry. All the arsenite determinations were done in 2.0 mol L⁻¹ HCl + 3.15 × 10⁻⁴ mol L⁻¹ Cu(II) supporting electrolyte. 1 × 10⁻³ mol L⁻¹ sodium thiosulphate was used as As(V) reducing agent. The detection limit was 0.5 μg L⁻¹ for both species. The method has been applied to water samples collected in an arsenic-contaminated region of Brazil, in particular, to verify the efficiency of the solar oxidation and removal of arsenic process applied to these waters.     

Adsorptive separation of phosphate oxyanion from aqueous solution using an inorganic adsorbent

Phosphate removal from aqueous solution was explored using granular ferric hydroxide (GFH) as an inorganic adsorbent. Adsorption, desorption and kinetic studies were conducted on laboratory scale to evaluate the performance of GFH as an adsorbent for low concentrations of phosphate solution. The effect of pH on adsorption was investigated, and phosphate uptake was shown to decrease with an increase in solution pH, with maximum removal seen to occur at pH 3. The experimental data best fit the Temkin isotherm at both pH 3 and 4. Uptake of phosphate by GFH follows second-order kinetics, with the small particle range (76–200 μm) removing phosphate from the solution more rapidly than the larger particle range (710–850 μm). The kinetic results suggest that intra-particle diffusion is an important factor in phosphate adsorption onto GFH. Thermodynamic parameters (ΔG°, ΔH°, ΔS°) were evaluated, and the results indicated that the adsorption process was endothermic and spontaneous. This study demonstrates that GFH has potential to be used as a cost-effective adsorbent for phosphate removal from aqueous solution.     

In situ removal of arsenic from groundwater by using permeable reactive barriers of organic matter/limestone/zero-valent iron mixtures

In this study, two mixtures of municipal compost, limestone and, optionally, zero-valent iron were assessed in two column experiments on acid mine treatment. The effluent solution was systematically analysed throughout the experiment and precipitates from both columns were withdrawn for scanning electron microscopy, energy-dispersive X-ray spectroscopy, X-ray diffractometry analysis and, from the column containing zero-valent iron, solid digestion and sequential extraction analysis. The results showed that waters were cleaned of arsenic, metals and acidity, but chemical and morphological analysis suggested that metal removal was not due predominantly to biogenic sulphide generation but to pH increase, i.e. metal (oxy)hydroxide and carbonate precipitation. Retained arsenic and metal removal were clearly associated to co-precipitation with and/or sorption on iron and aluminum (oxy)hydroxides. An improvement on the arsenic removal efficiency was achieved when the filling mixture contained zero-valent iron. Values of arsenic concentrations were then always below 10 μg/L.     

Removal of arsenic in tailings by soil flushing and the remediation process monitoring

In order to investigate the optimum conditions for the application of soil flushing of arsenic, a batch test was carried out using EDTA at various concentration and pH levels. Based on the optimum condition derived from the batch test, a column test was conducted to examine the feasibility of the soil-flushing technology under field-equivalent conditions. In this column test, a low flushing solution flow rate showed a significantly higher As removal efficiency (71.6%) than a high flow rate (56.3%). TCLP (toxicity characteristic leaching procedure) and a seed germination test were carried out to monitor the toxicity both during and after the treatment. The finally treated tailings were shown to be significantly remediated, having a reduced toxicity by both the TCLP and seed germination tests.     

Removal of arsenic in tailings by soil flushing and the remediation process monitoring

In order to investigate the optimum conditions for the application of soil flushing of arsenic, a batch test was carried out using EDTA at various concentration and pH levels. Based on the optimum condition derived from the batch test, a column test was conducted to examine the feasibility of the soil-flushing technology under field-equivalent conditions. In this column test, a low flushing solution flow rate showed a significantly higher As removal efficiency (71.6%) than a high flow rate (56.3%). TCLP (toxicity characteristic leaching procedure) and a seed germination test were carried out to monitor the toxicity both during and after the treatment. The finally treated tailings were shown to be significantly remediated, having a reduced toxicity by both the TCLP and seed germination tests.     

Uptake of arsenate, trimethylarsine oxide, and arsenobetaine by the shrimp Crangon crangon

Common shrimp, Crangon crangon (L.), were exposed to inorganic arsenic (arsenate), trimethylarsine oxide, or arsenobetaine in sea water (100 μg As l⁻¹) or in food (1 mg As g⁻¹ wet wt) for up to 24 d, followed by 16 d depuration in clean sea water with undosed food, in order to determine the efficiency of uptake and retention of the compounds. Accumulation of arsenic in the tail muscle, gills, midgut gland, exoskeleton, and remaining tissues was found to depend on the chemical form of the arsenic and the route of exposure. No arsenic was accumulated by C. crangon exposed to arsenate or trimethylarsine oxide in sea water. Shrimps exposed to waterborne arsenobetaine initially accumulated a small amount of arsenic in their tail muscle and gills. After 16 d, C. crangon fed arsenate, trimethylarsine oxide, or arsenobetaine had accumulated arsenic in their tail muscle to levels ∼2-, 2-, or 40-times, respectively, that of the control group. A roughly linear rate of accumulation was shown by shrimps fed trimethylarsine oxide or arsenobetaine, but C. crangon fed arsenate accumulated arsenic for 16 d, then lost arsenic such that their concentration on Day 24 was not significantly different from that of the control group. Patterns of arsenic accumulation in the gills of shrimps fed the compounds were similar to those seen in the tail muscle. On a whole animal basis, C. crangon retained ∼1.2% of the arsenate, 1.6% of the trimethylarsine oxide, and 42% of the arsenobetaine consumed over the first 16 d of exposure, with roughly half present in the tail muscle in each case. Data obtained support the view that the direct uptake of arsenobetaine from sea water does not make a significant contribution to the relatively high concentrations of this compound in marine crustaceans, and that food is the primary source. Naturally occurring arsenic compounds in C. crangon and possible transformations of the administered arsenic compounds were examined by high performance liquid chromatography using an inductively coupled plasma mass spectrometer as the arsenic-specific detector. Control C. crangon contained arsenobetaine as the major arsenic compound (>95% of total arsenic); tetramethylarsonium ion (0.7%) and an unknown arsenic compound (1.7%) were also present as minor constituents. Shrimp ingesting arsenobetaine accumulated it unchanged. Shrimp ingesting arsenate did not form methylated arsenic compounds; they appeared to contain their accumulated arsenic as unchanged arsenate only, although the possibility that some of the arsenic was reduced to arsenite could not be excluded. C. crangon ingesting trimethylarsine oxide biotransformed the compound predominantly to dimethylarsinate. Received: 9 October 1997 / Accepted: 11 February 1998     

砷形态在湖水中垂直分布的研究

本文以天津水上公园湖泊作为研究现场，通过采样分析，研究了湖水中砷酸盐、亚砷酸盐、一甲基胂酸盐和二甲基胂酸盐的垂直分布及其影响因素。结果表明水上公园湖泊中砷酸盐是溶解态砷的主要存在形式，其垂直分布与悬浮物、叶绿素ａ、磷酸盐的浓度、水文等诸因素密切相关；一甲基胂酸盐含量保持相对稳定；光致转化是影响水中亚砷酸盐垂直分布差异的一个因素。     

Lung retention and bioavailability of arsenic after single intratracheal administration of sodium arsenite,sodium arsenate,fly ash and copper smelter dust in the hamster

Arsenic is present in airborne particulate material released by coal-fired power plants and non-ferrous metal smelters. We have assessed whether the physico-chemical properties of arsenic in such particles play a role in its lung retention and uptake by the body. Female hamsters were given a single intratracheal instillation of fly ash or copper smelter dust suspensions (at doses of 50 or 100 g As kg^–1) or identical amounts of soluble tri- and pentavalent arsenic, in the presence or absence of an inert dust material (tungsten carbide). The concentration of the element was measured in a 24 hour urine sample collected on the 1st, 2nd and 6th day after treatment and arsenic remaining in lung tissue was determined at the end of the same time periods. Both lung retention and urinary As excretion indicate a prolonged contact of the lung tissue with particulate As in contrast to soluble As salts. In addition to the effect of solubility described here, more research is needed to determine the effect of particle size and lung loading on retention, as well as the potential differences in the lung inflammatory response using arsenic-rich particulates from various sources.     

Assessment of contamination by percolation of septic tank effluent through natural and amended soils

Fly ash has been found to be a potential material for the treatment of municipal and industrial wastewater, and may be useful in the treatment of septic tank effluent. Laboratory columns (30 cm) were used to determine the sorption capacity and hydraulic properties of lagoon fly ash, loamy sand, sand, and sand amended by lagoon fly ash (30 and 60%) and red mud gypsum (20%). The removal of chemical oxygen demand (COD) was high in all column effluents (71-93%). Extent of nitrification was high in Spearwood sand, Merribrook loamy sand and 20% red mud gypsum amended Spearwood sand. However, actual removal of nitrogen (N) was high in columns containing lagoon fly ash. Unamended Spearwood sand possessed only minimal capacity for P sorption. Merribrook loamy sand and red mud gypsum amended sand affected complete P removal throughout the study period of 12 weeks. Significant P leakage occurred from lagoon fly ash amended sand columns following 6-10 weeks of operation. Neither lagoon fly ash nor red mud gypsum caused any studied heavy metal contamination including manganese (Mn), lead (Pb), zinc (Zn), cadmium (Cd) and chromium (Cr) of effluent. It can be concluded that Merribrook loamy sand is better natural soil than Spearwood sand as a filter medium. The addition of lagoon fly ash enhanced the removal of P in Spearwood sand but the efficiency was lower than with red mud gypsum amendment.     

Evaluation of micro- and nano-carbon-based adsorbents for the removal of phenol from aqueous solutions

This work reports on the adsorption efficiency of two classes of adsorbents: nano-adsorbents including carbon nanotubes (CNTs) and carbon nanofibers (CNFs); and micro-adsorbents including activated carbon (AC) and fly ash (FA). The materials were characterized by thermogravimetric analysis, transmission electron microscopy, Brunauer–Emmett–Teller (BET) specific surface area, zeta potential, field emission scanning electron microscopy, and UV spectroscopy. The adsorption experimental conditions such as pH of the solution, agitation speed, contact time, initial concentration of phenol, and adsorbent dosage were optimized for their influence on the phenol. The removal efficiency of the studied adsorbents has the following order: AC > CNTs > FA > CNFs. The capacity obtained from Langmuir isotherm was found to be 1.348, 1.098, 1.007, and 0.842 mg/g of AC, CNTs, FA, and CNFs, respectively, at 2 hours of contact time, pH 7, an adsorbent dosage of 50 mg, and a speed of 150 rpm. The higher adsorption of phenol on AC can be attributed to its high surface area and its dispersion in water. The optimum values of these variables for maximum removal of phenol were also determined. The experimental data were fitted well to Langmuir than Freundlich isotherm models.     

HDTMAB改性粉煤灰对水体中磷的吸附特性

制备了十六烷基三甲基溴化铵(HDTMAB)改性粉煤灰,研究了该改性粉煤灰对水体中磷的吸附特性,结果表明:①当HDTMAB负载量为10%时,改性粉煤灰吸附磷酸盐的效果最佳;②改性粉煤灰对磷酸盐的吸附速度很快,20min可达吸附平衡;③改性粉煤灰对磷酸盐的吸附行为能较好地符合Langmuir等温吸附模型和Freundlich等温吸附模型,但在Freundlich模式下表现为两个线性区;④pH对改性粉煤灰吸附磷酸盐的性能有显著影响,随着pH的升高对磷酸盐的吸附能力逐渐增加。