The removal of arsenic(V) from acidic solutions

The residual concentrations of dissolved arsenic(V) in 1.5% sulphuric acid solutions treated with iron salts and alkaline earth metal compounds have been measured. The results are plotted on triangular composition diagrams covering the composition ranges As 0.2% to 1.2%, Fe 1.0% to 4.0%, alkaline earth metal 3.0% to 6.5%. The results indicate that ferrous iron and lime are the most effective in removing 99.9% of the arsenic over a wide composition range to give residual dissolved arsenic concentrations of ca. 0.5 ppm. Ferric iron is more effective when used in conjunction with mixed calcium and magnesium hydroxides than with lime alone. Ferric iron and dolomite offered the least effective treatment.The effect of lime particle size on the residual dissolved arsenic concentration following ferrous iron-lime treatment was studied. The optimum lime particle size range for arsenic removal was 50–100 μm.Leaching tests were carried out on samples of arsenic bearing sludge from the ferrous iron and lime treatment process mixed with sand chalk and clay soils. The presence of 5,000 ppm of acetic acid in the aqueous leachant did not appear to significantly affect the leaching test results and, after passage through contaminated and uncontaminated soils arsenic concentrations in the leachate were generally below 0.05 ppm. Ferrous iron and lime appeared to be suitable for treating the arsenic solutions and the resulting sludge seemed to be suitable for land disposal.     

膜混凝反应器除砷

用国产中空纤维膜组件,研究膜混凝反应器小试规模条件下的除砷效果.结果表明:膜混凝反应器的除砷效果良好,砷的去除率高达92.8%～98.2%,可使原水中As(V)的浓度从100 μg/L左右降至10μg/L以下,出水平均舍砷4.40μg/L,完全满足城市供水水质标准的要求;膜污染是导致膜比通量下降的主要原因,铁盐对膜污染的贡献较小,膜污染主要是有机物污染,占总量的67.2%;通过物理清洗和化学清洗可使膜比通量恢复到新膜的87.8%.     

Factors influencing arsenic and nitrate removal from drinking water in a continuous flow electrocoagulation (EC) process

An experimental study was conducted under continuous flow conditions to evaluate some of the factors influencing contaminant removal by electrocoagulation (EC). A bench-scale simulation of drinking water treatment was done by adding a filtration column after a rectangular EC reactor. Contaminant removal efficiency was determined for voltages ranging from 10 to 25 V and a comparative study was done with distilled water and tap water for two contaminants: nitrate and arsenic(V). Maximum removal efficiency was 84% for nitrate at 25 V and 75% for arsenic(V) at 20 V. No significant difference in contaminant removal was observed in tap water versus distilled water. Increase in initial As(V) concentration from 1 ppm to 2 ppm resulted in a 10% increase in removal efficiency. Turbidity in the EC reactor effluent was 52 NTU and had to be filtered to achieve acceptable levels of final turbidity (5 NTU) at steady-state. The flow regime in the continuous flow reactor was also evaluated in a tracer study to determine whether it is a plug flow reactor (PFR) or constantly stirred tank reactor (CSTR) and the results show that this reactor was close to an ideal CSTR, i.e., it was fairly well-mixed.     

Effect of competitive ions on the arsenic removal by mesoporous hydrous zirconium oxide from drinking water

Adsorption properties of 302-type commercially available hydrous zirconium oxide (302-HZO) towards arsenic and some competitive anions and cations have been studied under batch and column conditions. Due to amphoteric properties, anion exchange performance of hydrous zirconium oxide is pH dependent. Media exhibits high affinity towards arsenic in a broad pH range, with high adsorption capacity at pH < 8. It was shown that silicate and phosphate ions are arsenic's main competitors affecting media adsorption capacity. Presence of transition metal cations in <1 ppm does not affect 302-HZO capacity on arsenic, whereas alkaline-earth cations improve arsenic removal. The possibility for significant increase of 302-HZO adsorption capacity on arsenic at pH > 8 by using “solid acidifier” technique is discussed. Results of 302-HZO field trials are presented.     

Adsorption of arsenic(V) into modified lamellar Kenyaite

The synthetic Kenyaite sample was used for organofunctionalization process with N-propyldiethylenetrimethoxysilane and bis[3-(triethoxysilyl)propyl]tetrasulfide. The resulted materials were submitted to process of adsorption with arsenic solution at pH 2.0 and 298+/-1K. The adsorption isotherms were adjusted using a modified Langmuir equation with regression non-linear; the net thermal effects obtained from calorimetric titration measurements were adjusted to a modified Langmuir equation. The adsorption process was exothermic (Delta(int)H=-4.08 to -5.94 kJ mol(-1)) accompanied by increase in entropy (Delta(int)S=41.29-62.09 J K(-1)mol(-1)) and Gibbs energy (Delta(int)G=-22.33 to -24.45 kJ mol(-1)). The energetic effect caused by metal cation adsorption was determined through calorimetric titration at the solid-liquid interface and gave a net thermal effect that enabled the calculation of the exothermic values and the equilibrium constant.     

Studies on the removal of arsenic (III) from water by a novel hybrid material

The present work provides a method for removal of the arsenic (III) from water. An ion-exchanger hybrid material zirconium (IV) oxide-ethanolamine (ZrO-EA) is synthesized and characterized which is subsequently used for the removal of selective arsenic (III) from water containing 10,50,100 mg/L of arsenic (III) solution. The probable practical application for arsenic removal from water by this material has also been studied. The various parameters affecting the removal process like initial concentration of As (III), adsorbent dose, contact time, temperature, ionic strength, and pH are investigated. From the data of results, it is indicated that, the adsorbent dose of 0.7 mg/L, contact time 50 min after which the adsorption process comes to equilibrium, temperature (25 ± 2), solution pH (5-7), which are the optimum conditions for adsorption. The typical adsorption isotherms are calculated to know the suitability of the process. The column studies showed 98% recovery of arsenic from water especially at low concentration of arsenic in water samples.     

Synthesis and characterization of a mesoporous hydrous zirconium oxide used for arsenic removal from drinking water

Powder (20-50 μm) mesoporous hydrous zirconium oxide was prepared from a zirconium salt granular precursor. The effect of some process parameters on product morphology, porous structure and adsorption performance has been studied. The use of hydrous zirconium oxide for selective arsenic removal from drinking water is discussed.     

A combined treatment approach using Fenton's reagent and zero valent iron for the removal of arsenic from drinking water

Studies on the development of an arsenic remediation approach using Fenton's reagent (H2O2 and Fe(II)) followed by passage through zero valent iron is reported. The efficiency of the process was investigated under various operating conditions. Potable municipal water and ground water samples spiked with arsenic(III) and (V) were used in the investigations. The arsenic content was determined by ICP-QMS. A HPLC-ICPMS procedure was used for the speciation and determination of both As(III) and (V) in the processed samples, to study the effectiveness of the oxidation step and the subsequent removal of the arsenic.The optimisation studies indicate that addition of 100 microl of H2O2 and 100 mg of Fe(II) (as ferrous ammonium sulphate) per litre of water for initial treatment followed by passing through zero valent iron, after a reaction time of 10 min, is capable of removing arsenic to lower than the US Environmental Protection Agency (EPA) guideline value of 10 microg/l, from a starting concentration of 2 mg/l of As(III). Using these suggested amounts, several experiments were carried out at different concentrations of As(III). Residual hydrogen peroxide in the processed samples can be eliminated by subsequent chlorination, making the water, thus, processed, suitable for drinking purposes. This approach is simple and cost effective for use at community levels.     

Characterization of arsenic (V) and arsenic (III) in water samples using ammonium molybdate and estimation by graphite furnace atomic absorption spectroscopy

Arsenic (V) is known to form heteropolyacid with ammonium molybdate in acidic aqueous solutions, which can be quantitatively extracted into certain organic solvents. In the present work, 12-molybdoarsenic acid extracted in butan-1-ol is used for quantification of As (V). Total arsenic is estimated by converting arsenic (III) to arsenic (V) by digesting samples with concentrated nitric acid before extraction. Concentration of As (III) in the sample solutions could be calculated by the difference in total arsenic and arsenic (V). The characterization of arsenic was carried out by GFAAS using Pd as modifier. Optimization of the experimental conditions and instrumental parameters was investigated in detail. Recoveries of (90-110%) were obtained in the spiked samples. The detection limit was 0.2 microg l(-1). The proposed method was successfully applied for the determination of trace amount of arsenic (III) and arsenic (V) in process water samples.     

Adsorptive removal of As(V) and As(III) from water by a Zr(IV)-loaded orange waste gel

Orange waste, produced during juicing has been loaded with zirconium(IV) so as to examine its adsorption behavior for both As(V) and As(III) from an aquatic environment. Immobilization of zirconium onto the orange waste creates a very good adsorbent for arsenic. Adsorption kinetics of As(V) at different concentrations are well described in terms of pseudo-second-order rate equation with respect to adsorption capacity and correlation coefficients. Arsenate was strongly adsorbed in the pH range from 2 to 6, while arsenite was strongly adsorbed between pH 9 and 10. Moreover, equimolar (0.27 mM) addition of other anionic species such as chloride, carbonate, and sulfate had no influence on the adsorption of arsenate and arsenite. The maximum adsorption capacity of the Zr(IV)-loaded SOW gel was evaluated as 88 mg/g and 130 mg/g for As(V) and As(III), respectively. Column adsorption tests suggested that complete removal of arsenic was achievable at up to 120 Bed Volumes (BV) for As(V) and 8 0BV for As(III). Elution of both arsenate and arsenite was accomplished using 1 M NaOH without any leakage of the loaded zirconium. Thus this efficient and abundant bio-waste could be successfully employed for the remediation of an aquatic environment polluted with arsenic.     

Ammonia and iron removal from drinking water with clinoptilolite tuff

Field experiments were carried out for removal of ammonium and iron ions from drinking water containing high amounts of humic acids and dissolved gases. Three ion exchange columns filled with sodium form clinoptilolite (particle size: 0.5–1.0 mm), were connected in series. The ammonia content of the influent drinking water was ∼10 mg dm⁻³ and the 0.5 mg NH₃-N/dm³ breakthrough concentration was kept. The iron content ranged between 0.70–0.90 mg dm⁻³ and 0.05 mg Fe/dm³ was chosen as a limit for good quality drinking water. In a 90 h continuous experiment about 3.24 m³ drinking water was purified by three 4 dm³ bed volume, 9.5 cm ID × 92 cm ion exchange columns. The ammonia ion exchange capacity was about 3 mg NH₃-N/g zeolite. The natural zeolite contained only 46% clinoptilolite. For regeneration, 50 dm³ (12.5 BV) regenerant was used. After backwashing with 10 BV ammonia-free water, the freshly regenerated column was placed to the end of the series in service. Design and construction of a pilot-plant unit, including a 50 m³/day capacity ion-exchange system, is suggested.     

Chlorination byproducts, their toxicodynamics and removal from drinking water

No doubt that chlorination has been successfully used for the control of water borne infections diseases for more than a century. However identification of chlorination byproducts (CBPs) and incidences of potential health hazards created a major issue on the balancing of the toxicodynamics of the chemical species and risk from pathogenic microbes in the supply of drinking water. There have been epidemiological evidences of close relationship between its exposure and adverse outcomes particularly the cancers of vital organs in human beings. Halogenated trihalomethanes (THMs) and haloacetic acids (HAAs) are two major classes of disinfection byproducts (DBPs) commonly found in waters disinfected with chlorine. The total concentration of trihalomethanes and the formation of individual THM species in chlorinated water strongly depend on the composition of the raw water, on operational parameters and on the occurrence of residual chlorine in the distribution system. Attempts have been made to develop predictive models to establish the production and kinetics of THM formations. These models may be useful for operational purposes during water treatment and water quality management. It is also suggested to explore some biomarkers for determination of DBP production. Various methods have been suggested which include adsorption on activated carbons, coagulation with polymer, alum, lime or iron, sulfates, ion exchange and membrane process for the removal of DBPs. Thus in order to reduce the public health risk from these toxic compounds regulation must be inforced for the implementation of guideline values to lower the allowable concentrations or exposure.     

The NitRem process for nitrate removal from drinking water

A. F. Miquel of Otto Oeko-Tech looks at potential water treatment technologies that are able to remove nitrates from drinking water and details the way in which the development of nitrate selective membranes has resulted in the adaptation of electrodialysis and the development of the Nitrem process.     

Combined electrocoagulation and electroflotation for removal of fluoride from drinking water

A combined electrocoagulation (EC) and electroflotation (EF) process was proposed to remove fluoride from drinking water. Its efficacy was investigated under different conditions. Experimental results showed that the combined process could remove fluoride effectively. The total hydraulic retention time required was only 30 min. After treatment, the fluoride concentration was reduced from initial 4.0-6.0mg/L to lower than 1.0mg/L. The influent pH value was found to be a very important variable that affected fluoride removal significantly. The optimal influent pH range is 6.0-7.0 at which not only can effective defluoridation be achieved, but also no pH readjustment is needed after treatment. In addition, it was found that SO(4)(2-) had negative effect; Ca(2+) had positive effect; while Cl(-) had little effect on the fluoride removal. The EC charge loading, EF charge loading and energy consumption were 3.0 Faradays/m(3), 1.5 Faradays/m(3), and 1.2 kWh/m(3), respectively, under typical conditions where fluoride was reduced from initial 4.0 to 0.87 mg/L.     

Adsorption of arsenic species from water using activated siderite-hematite column filters

Arsenic is present at relatively high concentrations in surface water and groundwater as a result of both natural impacts and anthropogenic discharge, which requires proper treatment before use. The present study describes As adsorption on a siderite-hematite filter as a function of activating condition, empty bed contact time, and As species. Hydrogen peroxide activating increased As adsorption on siderite by 16.2 microg/g, and on hematite by 13.0 microg/g. The H2O2 conditioning enhanced adsorption efficiency of activated siderite-hematite filters up to throughput of 500 pore volumes of 500 microg/L As water. At values greater than 47 min, the empty bed contact time (EBCT) had only a weak influence on the removal capacity of pristine siderite-hematite filters. Due to the formation of fresh Fe(III)-oxide layer in the H2O2-conditioned filter and the pristine hematite-siderite filter, both of them may be utilized as a cost-effective reactor for treating As water. A toxicity characteristic leaching procedure (TCLP) test showed that the spent minerals were not hazardous and could be safely landfilled.     

Fluoride in drinking water and its removal

Excessive fluoride concentrations have been reported in groundwaters of more than 20 developed and developing countries including India where 19 states are facing acute fluorosis problems. Various technologies are being used to remove fluoride from water but still the problem has not been rooted out. In this paper, a broad overview of the available technologies for fluoride removal and advantages and limitations of each one have been presented based on literature survey and the experiments conducted in the laboratory with several processes. It has been concluded that the selection of treatment process should be site specific as per local needs and prevailing conditions as each technology has some limitations and no one process can serve the purpose in diverse conditions.     

Comparison of two methods for removal of arsenic from potable water

Arsenic, well known of its toxicity, is present in potable water in many areas in the world, as well as in underground water used for water supply in Vojvodina, a region in Serbia. Its removal from raw water is necessary before distribution. In this work two methods of arsenic removal from water are compared. First method is water ozonation by introducing ozone in water and then filtration. Second method is treatment of water in plasma reactor and then filtration. High efficiency of the second method was confirmed by low concentration of arsenic in filtrate (below detection limit).     

Bromate removal from water by granular ferric hydroxide (GFH)

The feasibility of granular ferric hydroxide (GFH) for bromate removal from water has been studied. Batch experiments were performed to study the influence of various experimental parameters such as effect of contact time, initial bromate concentration, temperature, pH and effect of competing anions on bromate removal by GFH. The adsorption kinetics indicates that uptake rate of bromate was rapid at the beginning and 75% adsorption was completed in 5 min and equilibrium was achieved within 20 min. The sorption process was well described by pseudo-second-order kinetics. The maximum adsorption potential of GFH for bromate removal was 16.5 mg g⁻¹ at 25 °C. The adsorption data fitted well to the Langmuir model. The increase in OH peak and absence of Br–O bonding in FTIR spectra indicate that ion-exchange was the main mechanism during bromate sorption on GFH. The effects of competing anions and solution pHs (3–9) were negligible. Results of the present study suggest that GFH can be effectively utilized for bromate removal from drinking water.     

Study of arsenic(V) adsorption on bone char from aqueous solution

Arsenic is a toxic element and may be found in natural waters as well as in industrial waters. Leaching of arsenic from industrial wastewater into groundwater may cause significant contamination, which requires proper treatment before its use as drinking water. The present study described the removal of As(V) on bone char in batch studies conducted as a function of pH, dosage of adsorbent, and contact time. Kinetics revealed that uptake of As(V) ion by bone char was very rapid in the first 30min and equilibrium time was independent of initial As(V) concentration. And the adsorption process followed a first-order kinetics equation. The arsenic removal was strongly dependent on pH and dosage of adsorbent. Fourier transform infrared spectra of bone char before and after As(V) adsorption demonstrated that Ca-OH functional group plays an important role for As(V) ions removal, and the mechanisms of the removal of As(V) on bone char was complex mechanism where both co-precipitation and ion exchange. The results suggested that bone char can be used effectively for the removal of As(V) ion from aqueous solution.