Arsenic removal by reverse osmosis

Arsenic is widely distributed in nature in air, water and soil. Acute and chronic arsenic exposure via drinking water has been reported in many countries, especially Argentina, Bangladesh, India, Mexico, Mongolia, Thailand and Taiwan, where a large proportion of ground water is contaminated with arsenic at levels from 100 to over 2,000 micrograms per liter (ppb). Public health standards of maximum of 50 ppb have been adopted by the US and World Health Organization in the 1970s and the 80s. Carcinogenicity and genotoxicity led to the WHO recommendation of 10 ppb maximum level in 1993, followed by the US adoption of the same in 2001, with the US estimate that 5% of all US community water systems will have to take corrective actions to lower the current levels of arsenic in their drinking water. In high arsenic areas of the world, the need for better water treatment and resulting economic impact would be even greater. In this article, we briefly review the geochemistry, natural distribution, regulation, anthropogenic sources and removal mechanisms of arsenic, pointing especially to the promise of reverse osmosis (RO) as a practical means of purification. We conclude that arsenic in the commonly high oxidation states of (V) is very effectively removed by RO. With further attention to the removal of the weakly acidic arsenic (III) species in waters by the operation of RO at sufficiently high pHs made possible by the newer antiscalants, practical processes can be developed with RO to remove all major species of arsenic from water. Further studies are needed in the characterization of the arsenic species being treated and in the design of the RO process to match the demands.     

Nanofiltration Membrane Process for the Removal of Arsenic from Drinking Water

The removal of arsenic from drinking water by nanofiltration membranes was investigated. Experiments were conducted with tap water to which arsenate and arsenite were added. Two types of nanofiltration membranes, i.e., NF‐90 and NF‐200, have been tested. The effect of various operating conditions, e.g., applied pressure, feed concentration, pH and temperature, were also investigated. The pH and arsenic concentration in the feed and the operating temperature are found to be decisive factors in determining the arsenic concentration remaining in the permeate. The level of removal of As(V) was higher than 98 % for both membranes, but that of As(III) was much lower. It can be concluded that by controlling the operating parameters, source water containing As(V) may be recovered as drinking water to EPA maximum contaminant level quality standards, but that water containing As(III) must undergo a pre‐oxidation treatment before passing through the nanofiltration membrane in order to maintain drinking water quality.     

Quality of groundwater in eastern Croatia. The problem of arsenic pollution

Groundwater in the area of eastern Croatia contains high concentrations of iron, manganese, ammonia, organic substances and arsenic. The appearance of inorganic arsenic in groundwater is mainly caused by arsenic from natural geological sources. Since the groundwater is the main source of drinking water for the population in this area, almost 200,000 people are daily drinking water with arsenic concentration ranging from 10 to 610 μg/L. The Croatian legislation recently revised the maximum concentration limit (MCL) for arsenic in drinking water to 10 μg/L. The population in the two towns (Osijek and Vinkovci) of this region is supplied with groundwater processed by coagulation-filtration method, but in the other towns and villages water treatment implies only rapid sand filtration. Both methods for water treatment have resulted with higher arsenic concentration than MCL, so the main goal of this study was determination of population exposure to arsenic via drinking water and possible improvement of drinking water quality. Population exposure to arsenic via drinking water is determined with hair analysis, since the hair arsenic concentration is one of three most commonly employed biomarkers used to identify or quantify overall arsenic exposure. During this study the preliminary analyses of hair arsenic concentrations in several towns and villages in eastern Croatia were provided. The positive correlation between heightened arsenic concentration in drinking water and hair arsenic concentration was determined. In order to improve drinking water quality e.g. arsenic removal from contaminated drinking water, different modified adsorbents were used and compared (zeolite–clinoptilolite, manganese greensand and cationic exchange resin). Adsorbents were chemically modified and saturated with Fe(III) ions, while the arsenic solutions were prepared by processed groundwater.     

Kinetic Modeling of Arsenic Removal from Water by Ferric Ion Loaded Red Mud

A laboratory study was conducted to investigate the ability of ferric ion loaded red mud (FRM) for the removal of arsenic species from water. The adsorbent material was characterized by scanning electron microscopy, X-ray diffraction, and Fourier transform infrared spectroscopy. For an initial arsenic concentration lower than 0.3 mg/L, the FRM with a dosage of 1 g/L was able to reduce As(III) at pH 7 below 10 µg/L, the maximum contaminant level (MCL) of arsenic in drinking water set by the World Health Organization. In the case of As(V) removal, FRM was also particularly effective in reducing the initial arsenic concentration value of 1 mg/L at pH 2, below the MCL requirement of arsenic for drinking water. According to kinetic sorption data, the initial stage of adsorptions of As(III) and As(V) onto FRM were mainly governed by the external diffusion mechanism; however, upon saturation of the external adsorbent surface, the arsenic species were eventually adsorbed by intraparticle diffusion mechanism. The present results are promising for using the very inexpensive FRM as a low-cost material that is effective in remediating drinking waters contaminated with low concentrations of arsenic species. We report here the sorption kinetics and adsorption mechanisms of As(III) and As(V) on the FRM that has not been decsribed previously.     

Use of ArsenXnp,a hybrid anion exchanger,for arsenic removal in remote villages in the Indian subcontinent

Many of the arsenic removal units operating in remote villages of West Bengal, India now use a hybrid anion exchanger (HAIX) which are essentially spherical anion exchange resin beads containing dispersed nanoparticles of hydrated ferric oxide (HFO). HAIX, now commercially available as ArsenX^np, offers a very high selectivity for sorption of oxyanions of arsenic due to the Donnan membrane effect. The sorption columns used in the field for removal of arsenic are either single column or split-column design. The sorption columns allow flow of atmospheric oxygen, thereby promoting oxidation of dissolved Fe(II) species of arsenic-contaminated raw water to insoluble Fe(III) oxides or HFO particulates. Apart from the usual role played by the sorbents like ArsenX^np or activated alumina towards arsenic removal, HFO particulates also aid in the treatment process. Each unit is attached to a hand-pump driven well and capable of providing arsenic-safe water to three hundred (300) households or approximately one thousand villagers. No chemical addition, pH adjustment or electricity is required to run these units. On average, every unit runs for more than 20,000 bed volumes before a breakthrough of 50 μg/L of arsenic, the maximum contaminant level in drinking water in India, is reached. In addition to arsenic removal, significant iron removal is also achieved throughout the run. Upon exhaustion, the media is withdrawn and taken to a central regeneration facility where 2% NaCl and 2% NaOH solution are used for regeneration. Subsequently, the regenerated resin is reloaded into the well-head sorption column. Following regeneration, the spent solutions, containing high arsenic concentration, are transformed into solids residuals and contained in a way to avoid any significant arsenic leaching. Laboratory investigations confirmed that the regenerated ArsenX^np is amenable to reuse for multiple cycles without any significant loss in capacity.     

Development of an Electrochemical Device for Removal of Arsenic from Drinking Water

The forthcoming introduction of lower standards for arsenic in drinking water requires new technologies for arsenic removal. We report the development of an electrochemical unit for remediating domestic water supplies for homes without municipally treated water. Electrolysis in a two‐anode system provides oxidants to convert As(III) to As(V) in situ, and a sacrificial anode to deliver iron into solution. Conditioning tanks after each electrolysis step ensure completion of the chemical reactions. At the pH of domestic water, As(V) co‐precipitates with Fe(OH)₃; subsequent filtration leaves <10 ppb of inorganic arsenic in solution.     

Removal of manganese from water supplies intended for human consumption: a case study

In the Volcano Etna area (Sicily) a substantial part of groundwater, used for potable purpose, has concentrations of metals (vanadium, iron and manganese) higher than the maximum contaminant levels (MCLs) set by European and National regulations (European Directive 98/83 and D.Lgs. 31/2001). Specifically, high levels of manganese, up to 1810 μg/l, significantly exceeding the maximum contaminant level (MCL = 50 μg/l), were detected in groundwaters currently used as drinking water supply upwelled from the Etna Volcano aquifer. The paper presents the results of the manganese removal process by potassium permanganate oxidation followed by flocculation, settling and filtration. Batch tests were carried out varying pH, oxidant doses and polyelectrolytes. Two different filters (35 μm and 0.45 μm mesh) were tested as a final step of the treatment. Significant removal (up to 95%) was achieved by addition of polyelectrolytes at pH 8.5, with a 0.5 stoichiometric dose of oxidant and final filtration through 35 μm mesh filter.     

MIEX-DOC~离子交换树脂的饮用水除砷研究

对新型阴离子交换树脂MIEX-DOC的除砷性能进行了研究,考察了该树脂除砷容量、对三价砷[As(Ⅲ)]和五价砷[As(Ⅴ)]的去除能力、不同离子和水体pH值对树脂除砷[包括As(Ⅲ)和As(Ⅴ)]效率的影响。结果表明,MIEX-DOC树脂对人工配制高砷水(0.1mg.L-1)的除砷容量约为0.0051mg.mL-1;对As(Ⅲ)和As(Ⅴ)的去除能力相当;常见的共存离子对树脂除砷效率有抑制或促进影响;不同pH值下,MIEX-DOC树脂除砷效率不同,但对0.1mg.L-1的高砷水的除砷效率均达到50%以上。对农村高砷水的实地中试研究表明,当源水砷浓度约为0.1mg.L-1时,出水砷浓度低于0.05mg.L-1,达到《生活饮用水卫生标准》(GB 5749-2006)的农村小型集中式供水和分散式供水水质指标。成本分析结果表明,采用国产MIEX-DOC净水设备的除砷效果与进口设备相当,但除砷成本较低(0.56元.t-1),在我国农村高砷饮用水处理中有一定应用潜力。     

Arsenic removal from drinking water by electrocoagulation using iron electrodes

Arsenic removal from drinking water was investigated using electrocoagulation (EC) followed by filtration. A sand filter was used to remove flocs generated in the EC process. Experiments were performed in a batch electrochemical reactor using iron electrodes with monopolar parallel electrode connection mode to assess their efficiency. The effects of several operating parameters on arsenic removal such as current density (1.5–9.0 mA cm^?2), initial arsenic concentration (50–500 μg L^?1), operating time (0–15 min), electrode surface area (266–665 cm²), and sodium chloride concentrations (0.01 and 0.02M) were examined. The EC process was able to decrease the residual arsenic concentration to less than 10 μg L^?1. Optimum operating conditions were determined as an operating time of 5 min and current density of 4.5 mA cm^?2 at pH of 7. The optimum electrode surface area for arsenic removal was found to be 266 cm² taking into consideration cost effectiveness. The residual iron concentration increased with increasing residence time, and maximum residual iron value was measured as 287 μg L^?1 for electrode surface area of 266 cm². The addition of sodium chloride had no significant effect on residual arsenic concentration, but an increase in current density was observed.     

MIEX—DOC离子交换树脂的饮用水除砷研究

对新型阴离子交换树脂MIEX—DOC@的除砷性能进行了研究,考察了该树脂除砷容量、对三价砷[As（m）]和五价砷[As（V）]的去除能力、不同离子和水体pH值对树脂除砷[包括As（Ⅲ）和As（V）]效率的影响。结果表明,MIEX-DOC~树脂对人工配制高砷水（O．1mg·L-1）的除砷容量约为0．0051mg·mL-1;对As（Ⅲ）和As（V）的去除能力相当;常见的共存离子对树脂除砷效率有抑制或促进影响;不同pH值下,MIEX—DOC@树脂除砷效率不同,但对0．1mg·L-1的高砷水的除砷效率均达到50％以上。对农村高砷水的实地中试研究表明,当源水砷浓度约为0．1mg·L-1时,出水砷浓度低于0．05mg·L-1达到《生活饮用水卫生标准》（GB5749—2006）的农村小型集中式供水和分散式供水水质指标。成本分析结果表明,采用国产MIEX-DOC净水设备的除砷效果与进口设备相当,但除砷成本较低（0．56元·t-1）,在我国农村高砷饮用水处理中有一定应用潜力。     

饮用水除砷技术研究新进展

重点介绍了近年来各种除砷新技术的研究进展,内容包括:强化混凝、吸附、离子交换、膜法、预氧化除砷技术。评价了各除砷技术的优缺点与适用范围,并认为饮用水除砷技术的发展将呈现出以下特点:As(Ⅲ)和As(V)同步去除技术的开发;易于取得或制备、生物化学稳定性高、吸附容量大、选择性高、再生能力强的新型除砷吸附剂的开发;多种除砷技术联合,多重去除机理协同的除砷流程的开发;低能耗、低成本除砷技术的开发;生物除砷技术的开发。     

Arsenic Removal from High-Arsenic Water Sources by Coagulation and Electrocoagulation

In this work, the removal of arsenates from high-arsenic groundwaters, 20 mg As dm^?3, by using coagulation and electrocoagulation is compared. Results show that pH plays a key role in both processes, which allow us to explain the huge differences observed between both technologies and also between the use of iron and aluminum as coagulants. Electrocoagulation was found to be the best technology, being capable of removing arsenic down to 10 µg dm^?3, which is the limit fixed by most of health agencies around the world for drinking water. Regarding coagulation, the pH reduction caused by the dosage of chemicals during the coagulation process leads to a higher solubility of the arsenate compounds reducing the efficiency of the removal process and explaining the worse performance of coagulation, in comparison with electrocoagulation, in the removal of arsenic.     

Lead stabilized uPVC potable pipe: Extraction results under NSF standard number 61

Lead stabilized uPVC potable water pipe was successfully formulated and produced to comply with the health effects criteria established by the National Sanitation Foundation (NSF). The maximum allowable level (MAL) of lead extraction, from products that come in contact with drinking water, is specified in the new NSF Standard Number 61 as 5.0 µg/L (or, 5 parts per billion, ppb). Samples of uPVC pipe stabilized with 0.3 phr (parts per hundred parts of resin) of tribasic lead sulfate stabilizer were tested in accordance with the procedures of NSF Standard Number 61, and the extraction results were all below 2 ppb lead at both pH 5 and pH 10. Continued, daily extractions showed that the amount of lead released into drinking water fell below quantitation levels within one week, in agreement with previous findings reported in the scientific literature. Thus, lead stabilized uPVC potable water pipe has been shown to be safe and in compliance with established health effects criteria.     

Heavy metal removal by means of electrocoagulation using aluminum electrodes for drinking water purification

The present study has investigated the performance of electrocoagulation, to produce drinking water, using aluminum electrodes to remove nickel (Ni) and chromium (Cr) from two different water well samples from the north of Italy. Different experimental parameters, such as stirring and distance between the electrodes and current density, have been examined for both water samples. The series of experiments carried out on these two water samples has shown that the removal process of Ni is faster than that of Cr. In the case of water poisoned by Ni, a final concentration of 5 ppb was achieved starting from 41 ppb, while the Cr case showed a final concentration of 10 ppb compared to an initial 20 ppb. The electrocoagulation treatment presented in this study has shown very promising results and a high potential to remove very low amounts of heavy metals from water for drinking water production purposes.     

An overview of arsenic removal by pressure-drivenmembrane processes

Management of hazardous wastes, such as arsenic, is one of major public concern. Arsenic is a naturally occurring metalloid, which is widely distributed in nature. Recently, arsenic in drinking water attracted attention because some of the drinking water resources contain considerable concentrations of arsenic which cause acute; and chronic symptoms in many countries, especially in Bangladesh, China, Mongolia, and Taiwan. In 2001, the USEPA promulgated a rule lowering the arsenic MCL from 5 μgL⁻¹ to 10 μgL⁻¹. This paper offers an overview of geochemistry, distribution, sources, regulations, acute and chronic symptoms, and applications of membrane technologies in the water treatment research that have already been realized or that are suggested on the basis of bench or lab scale research. These membrane technologies include RO, NF, UF, and MF. Most of theses applications have proven to be reliable in removing arsenic from water. The possible influence of some source water parameters, membrane material, membrane types, membrane processes on arsenic removal efficiency by membrane technologies are also explored. This review paper also offers data relating to regulations of arsenic standard, acute and chronic symptoms that are caused by the exposure of arsenic to explain why water treatments need to use the membrane technology to meet the MCL standard.     

饮用水BDOC、AOC处理技术研究进展

围绕饮用水的生物稳定性，分析了常规水处理工艺对BDOC、AOC的影响，提出强化混凝和强化过滤的方法可改善出厂水的生物稳定性。讨论了生物氧化、臭氧氧化、活性炭吸附、臭氧-生物活性炭及膜过滤等工艺对饮用水中BDOC、AOC的去除效果，提出了提高出厂水生物稳定性的措施。     

Dissolved organic matter and arsenic removal with coupled chitosan/UF operation

Long time uptake arsenic will cause cancers and blackfoot disease. There are still several million people suffering from drinking arsenic contaminated water. This work studied the performance of coupled chitosan/UF for arsenic removal and the influence of dissolved organic matter on arsenic removal with UF operation. Humic acid representing dissolved organic matter was fractionated into five groups of molecular sizes by gel filtration chromatography. Arsenic rejection by UF under the experimental condition is only 10%. In the presence of humic compounds, the arsenic removal of 22% is obtained. DOM with apparent molecular weight > 35,000 Da is the principle component responsible for chelating arsenic and thereafter being rejected by UF membrane. The combined interactions of humic compounds, chitosan, and arsenic enable a 65% arsenic rejection by UF. The results presented here enable our understanding of the complicated mechanisms involved in chitosan/UF/DOM/arsenic system.     

Experimental and Numerical Modeling Studies of Arsenic Removal with Wood Ash from Aqueous Streams

Most of the arsenic removal processes are not cost‐effective and/or not efficient in removing As (III). In this research, it was found that Maple wood ash has the potential to adsorb both As (III) and As (V) from contaminated aqueous streams at low concentration levels without any chemical treatment. Static tests showed up to 80% arsenic removal and in various dynamic column tests the arsenic concentration was reduced from 500 ppb to lower than 5ppb. Finally, the ash column was modeled using the surface excess theory. The identified model significantly facilitates practical design of arsenic adsorption system.     

Removal of arsenic compounds from waste water by chemisorption filtration

The results of arsenic removal from water sources to a residual concentration of <10 μg/l are presented. The main physicochemical parameters were established for the As removal by polystyrene, modified granules of a poly VVFE polymer, and iron hydroxide-coated calcium alginate granules. It is shown that adsorptive filtration is the effective method for arsenic removal.     

改性麦饭石去除饮用水中的砷

饮用水中砷超标会严重危害人的身体健康。该文利用MnO：对麦饭石进行改性,制备了一种高效的吸附剂;同时研究了在不同pH值、接触时间、改性麦饭石的投加量及砷的初始浓度条件下,改性麦饭石对饮用水中As（V）的去除。研究结果表明：在以上不同条件下,改性麦饭石对水中As（V）均有一定的去除效果。当pH值为6、接触时间为60min、改性麦饭石投加量为1000mg／L、水中As（V）的初始浓度为100μg／L时,改性麦饭石对饮用水中的As（V）的去除率为91％,此时水中砷的含量低于国家生活饮用水卫生标准（10μg／L）。