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.     

Arsenate removal by zero valent iron: Batch and column tests

This study investigates the efficiency of zero valent iron (ZVI) to remove arsenate from water. Batch experiments were carried out to study the removal kinetics of arsenate under different pH values and in the presence of low and high concentrations of various anions (chloride, carbonate, nitrate, phosphate, sulphate and borate), manganese and dissolved organic matter. Borate and organic matter, particularly at higher concentrations, inhibited the removal of arsenic. Column tests were carried out to investigate the removal of arsenate from tap water under dynamic conditions. The concentrations of arsenic and iron as well as the pH and Eh were measured in treated water. Efficient removal of arsenate was observed resulting at concentrations below the limit of 10 μg/L in treated waters.     

Biosorption of arsenic from contaminated water by anaerobic biomass

The potential of an anaerobic sludge from an anaerobic wastewater treatment plant to remediate (inorganic) arsenic contaminated water was evaluated. The granular biomass was chemically modified as PO(4)-biomass and Cl-biomass. The biomass was then investigated in equilibrium batch experiments and continuous flow fixed-bed column operation. Initial arsenic concentration, contact time and solution pH affected the biosorption capacity. Arsenate exhibited greater removal rates than arsenite. Adsorption data fitted better with the Langmuir than the Freundlich isotherm model. Kinetic data followed a pseudo-second-order model. In column operation, at pH 5, 90 and 220 bed volumes of water with the respective arsenate concentrations of 500 and 200 μg/L were treated. Desorption of almost 40% arsenate was achieved by using 0.5M NaCl solution. Protein/amino acid-arsenic interaction was proposed as the dominant mechanism in the biosorption process. The arsenic-laden biomass satisfied USEPA's Toxicity Characteristic Leaching Procedure (TCLP) test and can be safely disposed of as non-hazardous waste.     

Advanced treatment of coking wastewater by coagulation and zero-valent iron processes

Advanced treatment of coking wastewater was investigated experimentally with coagulation and zero-valent iron (ZVI) processes. Particular attention was paid to the effect of dosage and pH on the removal of chemical oxygen demand (COD) in the two processes. The results showed that ZVI was more effective than coagulation for advanced treatment of coking wastewater. The jar tests revealed that maximal COD removal efficiency of 27.5-31.8% could be achieved under the optimal condition of coagulation, i.e. 400mg/L of Fe(2)(SO(4))3 as coagulant at pH 3.0-5.0. On the other hand, the COD removal efficiency could be up to 43.6% under the idealized condition of ZVI upon 10 g/L active carbon and 30 g/L iron being dosed at pH 4.0. The mechanisms for COD removal in ZVI were dominated by coagulation, precipitation and oxidation-reduction. ZVI would also enhance the biodegradability of effluent by increasing BOD5/COD from 0.07 to 0.53. Moreover, some ester compounds could be produced in the reaction. Although ZVI was found more efficient than coagulation in eliminating low molecular weight (<2000 Da) compounds in the wastewater, there were still a few residual contaminants which could hardly be eliminated by either of the process.     

Removal of arsenic and humic substances (HSs) by electro-ultrafiltration (EUF)

A laboratory scale electro-ultrafiltration (EUF) system was developed and used to explore the removal of arsenic and humic substances (HSs) from water. As a negatively charged species, arsenate(V) was readily removed after applying voltage to the EUF cell. Arsenite(III) was removed via EUF after the pH of the water had been adjusted. Meanwhile, the rejection of HSs increased due to the presence of an electric field. This study also showed that the removal of arsenite(III) from water relies primarily on electrostatic and non-electrostatic mechanisms. In the presence of HSs, arsenate(V) complexed with the HSs and was then able to be removed by EUF. This study demonstrates that EUF is a highly promising means of removing arsenic from water.     

Removal of As(V) and As(III) by reclaimed iron-oxide coated sands

This paper aims at the feasibility of arsenate and arsenite removal by reclaimed iron-oxide coated sands (IOCS). Batch experiments were performed to examine the adsorption isotherm and removal performance of arsenic systems by using the IOCS. The results show that the pH(zpc) of IOCS was about 7.0 +/- 0.4, favoring the adsorption of As(V) of anion form onto the IOCS surface. As the adsorbent dosage and initial arsenic concentration were fixed, both the As(V) and As(III) removals decrease with increasing initial solution pH. Under the same initial solution pH and adsorbent dosage, the removal efficiencies of total arsenic (As(V) and As(III)) were in the order as follows: As(V)>As(V)+As(III)>As(III). Moreover, adsorption isotherms of As(V) and As(III) fit the Langmuir model satisfactorily for the four different initial pH conditions as well as for the studied range of initial arsenic concentrations. It is concluded that the reclaimed IOCS can be considered as a feasible and economical adsorbent for arsenic removal.     

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.     

Confirming Pseudomonas putida as a reliable bioassay for demonstrating biocompatibility enhancement by solar photo-oxidative processes of a biorecalcitrant effluent

The performance of a sequencing batch reactor (SBR) seeded with aerobic granular sludge was studied. The lab-scale SBR treating domestic wastewater operated at a volumetric loading rate (VLR) of 0.75-3.41 kg COD/(m(3)d). The granule stability was related to the organic loading, and high loading would be favorable for granule stability. Analysis of typical cycle showed that granular sludge had good ability to simultaneously remove nitrogen and phosphorus. Most organic substances were removed at the anaerobic stage. At the aerobic stage, simultaneous nitrification and denitrification (SND) happened with phosphorus absorption. The SBR had good removal performance for organic matter and phosphate. However, the total nitrogen (TN) removal performance was ordinary, with average removal efficiency of about 52%. Batch experiments indicated that increases of influent C/N ratio and a large percentage of granule in the sludge were conducive for SND in SBR.     

Removal of sulfide in integrated anaerobic–aerobic wastewater treatment system

In recent years, the stipulations fixed by regulatory bodies have become stringent to keep environmental pollution under control. Normally COD and BOD are the parameters monitored to determine the efficiency of any treatment system. But in many cases, industrial wastewater may contain sulfate along with other organic constituents. Sulfate, if present in the wastewater, will be converted to H₂S under anaerobic conditions and this is hazardous. Subsequently, if the same wastewater is treated under aerobic conditions, a part of the air supplied will be utilized for oxidation of sulfide back to sulfate which leads to reduced efficiency of the aerobic treatment. The released wastewater with high sulfate levels will be going into the environment, which is undesirable. Methods are reported in the literature for the removal of sulfate and sulfide before and after anaerobic treatment respectively. Most of these methods are chemical which are either costly or impracticable. Therefore, a novel approach for removing sulfate or sulfide in the treatment scheme is required. In the present communication, studies are undertaken by designing an innovative stripper system where sulfide is removed to the extent of 60 to 70% before aerobic treatment. The parameters involved in design and operation of the stripper, such as airflow rate, liquid flow rate, liquid to air ratio, and pH profile, are optimized. It is a physical system in which air and waste water are passed as counter currents. The treated wastewater from the stripper, which contains less sulfide, may be post-treated in the aerobic system before final discharge. Hydrogen sulfide can be efficiently removed by coupling this type of stripper to existing anaerobic systems. The system can be efficiently used in existing treatment plants or in new designs to control sulfide (free sulfide generated in an anaerobic reactor in the case of wastewaters having high sulfate inhibits methanogenesis, resulting in reduced performance of the anaerobic process) generated in anaerobic reactors and to optimize the air and oxygen requirements in the aerobic system.     

Effect of spatial distribution and aging of ZVI on the reactivity of resin–ZVI composites for arsenite removal

A zero-valent iron (ZVI)–resin composite (D201–ZVI) has been proven as an effective arsenic removal material. Here, the effect of ZVI distribution and aging on the reactivity of the hybrid composite was investigated by comparing the As(III) removal performances of freshly synthesized and aged D201–ZVI composites. The ZVI distribution and structures of these composites were characterized using X-ray diffraction, X-ray photoelectron spectrometry, and scanning electron microscope equipped with an energy-dispersive X-ray analyzer (SEM-EDX). After aging in aerated water for 96 h, the ZVI distribution in the aged composites did not change significantly, which was confirmed by SEM-EDX. However, the Fe⁰ content decreased as the aging time increased. Among the as-prepared composites with variant ZVI distributions, the hybrids with more uniform ZVI distribution exhibited higher removal efficiency and faster reaction rate. Experimental results show that the D201–ZVI gradually lost reactivity with an increase in aging time from 24 to 96 h. The effects of aging time on the speciation of As suggest that the reduced As(III) removal efficiency was attributable to the decrease of the Fe⁰ content. Furthermore, the importance of the ZVI distribution is proposed to explain the aging effect.     

Removal of metals from aqueous solution and sea water by functionalized graphite nanoplatelets based electrodes

In the present wok, we have demonstrated the simultaneous removal of sodium and arsenic (pentavalent and trivalent) from aqueous solution using functionalized graphite nanoplatelets (f-GNP) based electrodes. In addition, these electrodes based water filter was used for multiple metals removal from sea water. Graphite nanoplatelets (GNP) were prepared by acid intercalation and thermal exfoliation. Functionalization of GNP was done by further acid treatment. Material was characterized by different characterization techniques. Performance of supercapacitor based water filter was analyzed for the removal of high concentration of arsenic (trivalent and pentavalent) and sodium as well as for desalination of sea water, using cyclic voltametry (CV) and inductive coupled plasma-optical emission spectroscopy (ICP-OES) techniques. Adsorption isotherms and kinetic characteristics were studied for the simultaneous removal of sodium and arsenic (both trivalent and pentavalent). Maximum adsorption capacities of 27, 29 and 32 mg/g for arsenate, arsenite and sodium were achieved in addition to good removal efficiency for sodium, magnesium, calcium and potassium from sea water.     

Biosorption of palladium(II) from aqueous solution by moss (Racomitrium lanuginosum) biomass: equilibrium, kinetic and thermodynamic studies

Arsenite (As(III)) and arsenate (As(V)) removal by direct contact membrane distillation (DCMD) were investigated with self-made polyvinylidene fluoride (PVDF) membranes in the present work. Permeability and ion rejection efficiency of the membrane were tested before the arsenic removal experiments. A maximum permeate flux 20.90 kg/m(2)h was obtained, and due to the hydrophobic property, the PVDF membrane had high rejection of inorganic anions and cations which was independent of the solution pH and the temperature. The experimental results indicated that DCMD process had higher removal efficiency of arsenic than pressure-driven membrane processes, especially for high-concentration arsenic and arsenite removal. The experimental results indicated that the permeate As(III) and As(V) were under the maximum contaminant limit (10 microg/L) until the feed As(III) and As(V) achieved 40 and 2000 mg/L, respectively. The 250 h simultaneous DCMD performance of 0.5mg/L As(III) and As(V) solution was carried out, respectively. The permeate arsenic was not detected during the process which showed the PVDF membrane had stable arsenic removal efficiency. Membrane morphology changed slightly after the experiments, however, the permeability and the ion rejection of the membrane did not change.     

膨胀石墨负载零价铁的合成及其对水中Pb(II)去除效果与机制

以网络状孔型结构发达的膨胀石墨(EG)为载体, 采用化学沉积法制备负载零价铁(ZVI)的膨胀石墨(EG-ZVI)。利用SEM、XRD、FT-IR及XPS等对负载及反应前后的EG-ZVI进行表征, 探索了EG-ZVI对铅离子(Pb(II))的处理效果并对其反应产物及机理进行了分析。结果表明: 亚微米级ZVI成功负载到EG表面; 相比ZVI, EG-ZVI对Pb(II)的去除能力提升明显; EG-ZVI去除Pb(II)主要是吸附和还原作用的共同结果, 该过程符合一级动力学模型, 且控制步骤为化学反应过程。其还原过程是由负载在EG表面的ZVI腐蚀提供电子还原Pb(II)生成铅单质, 并进一步生成铅氧化物与氢氧化物; EG-ZVI能弥补ZVI在反应过程中生成惰性层导致去除效率低的不足, 使其在Pb(II)废水的实际修复中具有较高的应用前景。     

The role of functionalised multiwalled carbon nanotubes based supercapacitor for arsenic removal and desalination of sea water

In order to investigate the simultaneous adsorption property of functionalised multiwalled carbon nanotubes (MWNTs) for sodium and arsenic, a new type of carbon fabric supported functionalised MWNTs (f-MWNTs) based supercapacitor was developed. In addition, this setup was tested for desalination of sea water. MWNTs were synthesised by chemical vapour deposition technique and purified, followed by functionalisation. MWNTs were characterised by different techniques. Performance of supercapacitor-based water filter was analysed for the adsorption of high concentration of arsenic (trivalent and pentavalent) and sodium as well as for desalination of sea water by using cyclic voltametry and inductively coupled plasma-optical emission spectroscopy techniques. Adsorption isotherms and kinetic characteristics were studied for the simultaneous removal of sodium and arsenic. High desalination (removal of sodium and magnesium) efficiency of sea water and cyclic repeatability for simultaneous removal of arsenic (arsenate and arsenite) and sodium have been demonstrated in this study. Easy handling and flexibility of this new type of electrodes-based setup provides a platform for the development of portable water filter.     

Arsenic removal from groundwater by MnO2-modified natural clinoptilolite zeolite: effects of pH and initial feed concentration

Adsorption of arsenic (As(5+)) on natural and MnO(2)-modified clinoptilolite-Ca zeolite adsorbents was investigated to explore the feasibility of removing arsenic from groundwater using natural zeolite adsorbents. The natural and MnO(2)-modified clinoptilolite-Ca zeolite adsorbents were characterized with nitrogen adsorption at 77K for pore textural properties, scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray fluorescence for morphology, elemental composition and distribution. Batch adsorption equilibrium experiments were conducted to study the effects of pH and initial feed concentration on arsenic removal efficiency. It was found that the amphoteric properties and arsenic removal efficiency of the natural clinoptilolite-Ca zeolite were significantly improved after modification with MnO(2). The MnO(2)-modified zeolite could effectively remove arsenic from water at a wide pH range, and the arsenic removal efficiency that is basically independent of the pH of feed solutions varies slightly with the initial arsenic concentration in the feed solutions. The removal efficiency obtained on the modified zeolite was doubled as compared to that obtained on the unmodified zeolite. The MnO(2)-modified clinoptilolite-Ca zeolite appears to be a promising adsorbent for removing trace arsenic amounts from water.     

Study on treatment of coking wastewater by biofilm reactors combined with zero-valent iron process

Experiments were conducted to investigate the behavior of the integrated system with biofilm reactors and zero-valent iron (ZVI) process for coking wastewater treatment. Particular attention was paid to the performance of the integrated system for removal of organic and inorganic nitrogen compounds. Maximal removal efficiencies of chemical oxygen demand (COD), ammonia nitrogen (NH(3)-N) and total inorganic nitrogen (TIN) were up to 96.1, 99.2 and 92.3%, respectively. Moreover, it was found that some phenolic compounds were effectively removed. The refractory organic compounds were primarily removed in ZVI process of the integrated system. These compounds, with molecular weights either ranged 10,000-30,000 Da or 0-2000 Da, were mainly the humic acid (HA) and hydrophilic (HyI) compounds. Oxidation-reduction and coagulation were the main removal mechanisms in ZVI process, which could enhance the biodegradability of the system effluent. Furthermore, the integrated system showed a rapid recovery performance against the sudden loading shock and remained high efficiencies for pollutants removal. Overall, the integrated system was proved feasible for coking wastewater treatment in practical applications.     

A method for preparing ferric activated carbon composites adsorbents to remove arsenic from drinking water

Iron oxide/activated carbon (FeO/AC) composite adsorbent material, which was used to modify the coal-based activated carbon (AC) 12 x 40, was prepared by the special ferric oxide microcrystal in this study. This composite can be used as the adsorbent to remove arsenic from drinking water, and Langmuir isotherm adsorption equation well describes the experimental adsorption isotherms. Then, the arsenic desorption can subsequently be separated from the medium by using a 1% aqueous NaOH solution. The apparent characters and physical chemistry performances of FeO/AC composite were investigated by X-ray diffraction (XRD), nitrogen adsorption, scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). Batch and column adsorption experiments were carried out to investigate and compare the arsenic removal capability of the prepared FeO/AC composite material and virgin activated carbon. It can be concluded that: (1) the main phase present in this composite are magnetite (Fe(3)O(4)), maghemite (gamma-Fe(2)O(3)), hematite (alpha-Fe(2)O(3)) and goethite (alpha-FeO(OH)); (2) the presence of iron oxides did not significantly affect the surface area or the pore structure of the activated carbon; (3) the comparisons between the adsorption isotherms of arsenic from aqueous solution onto the composite and virgin activated carbon showed that the FeO/AC composite behave an excellent capacity of adsorption arsenic than the virgin activated carbon; (4) column adsorption experiments with FeO/AC composite adsorbent showed that the arsenic could be removed to below 0.01 mg/L within 1250 mL empty bed volume when influent concentration was 0.5mg/L.     

Arsenate removal by resin-supported ferric ions: Mechanism,modeling, and column study

Removal of 10 mg/dm³ of As(V) by resin-supported Fe(III) was investigated in batch and column studies. The best As(V) removal was achieved at pH 3, and a high sorption density of 0.40 mmol-As/mmol-Fe was obtained after 96 h in a batch study. This sorption density could not be explained only by As(V) surface complexation with ferrihydrite. X-ray absorption near edge structure (XANES) analysis at the As K-edge suggested that over 90% of the As(V) was removed by surface precipitation as poorly crystalline ferric arsenate and the remainder was removed by surface complexation with ferrihydrite. XANES analysis at Fe K-edge suggested that 14%–35% of Fe(III) in the resin was used in the ferrihydrite and ferric arsenate. Kinetic modeling of the precipitation of ferrihydrite and ferric arsenate combined with a surface complexation model for As(V) and ferrihydrite successfully reproduced the batch experiment results. The kinetic constant for precipitation of ferrihydrite and ferric arsenate obtained by fitting of the batch experiment results successfully reproduced the column experiment results. The ratio of surface precipitation of ferric arsenate and As(V) surface complexation with ferrihydrite obtained by the constructed model was the same as in the XANES results. In the column study, a slow flow was advantageous for As(V) removal because surface precipitation of ferric arsenate took a long time.     

Arsenic removal from real-life groundwater by adsorption on laterite soil

The adsorption characteristics of arsenic on laterite soil, a low-cost natural adsorbent, were studied in the laboratory scale using real-life sample. The studies were conducted by both batch and continuous mode. Laterite soil was found to be an efficient adsorbent for arsenic removal from the groundwater collected from arsenic affected area. The initial concentration of arsenic in the sample was 0.33 ppm. Under optimized conditions the laterite soil could remove up to 98% of total arsenic. The optimum adsorbent dose was 20 g/l and the equilibrium time was 30 min. Isotherm studies showed that the process is favorable and spontaneous. The kinetics showed that the removal of arsenic by laterite soil is a pseudo-second-order reaction. In the column study the flow rate was maintained at 1.49 m3/(m2 h). Using 10 cm column depth, the breakthrough and exhaust time found were 6.75 h and 19.0 h, respectively. Height of adsorption zone was 9.85 cm, the rate at which the adsorption zone was moving through the bed was 0.80 cm/h, and the percentage of the total column saturated at breakthrough was 47.12%. The value of adsorption rate coefficient (K) and the adsorption capacity coefficient (N) were 1.21 l/(mgh) and 69.22 mg/l, respectively. Aqueous NaOH (1 M) could regenerate the adsorbent, and the regenerated adsorbent showed higher efficiency.     

The management of arsenic wastes: problems and prospects

Arsenic has found widespread use in agriculture and industry to control a variety of insect and fungicidal pests. Most of these uses have been discontinued, but residues from such activities, together with the ongoing generation of arsenic wastes from the smelting of various ores, have left a legacy of a large number of arsenic-contaminated sites. The treatment and/or removal of arsenic is hindered by the fact that arsenic has a variety of valence states. Arsenic is most effectively removed or stabilized when it is present in the pentavalent arsenate form. For the removal of arsenic from wastewater, coagulation, normally using iron, is the preferred option. The solidification/stabilization of arsenic is not such a clear-cut process. Factors such as the waste's interaction with the additives (e.g. iron or lime), as well as any effect on the cement matrix, all impact on the efficacy of the fixation. Currently, differentiation between available solidification/stabilization processes is speculative, partly due to the large number of differing leaching tests that have been utilized. Differences in the leaching fluid, liquid-to-solid ratio, and agitation time and method all impact significantly on the arsenic leachate concentrations.This paper reviews options available for dealing with arsenic wastes, both solid and aqueous through an investigation of the methods available for the removal of arsenic from wastewater as well as possible solidification/stabilization options for a variety of waste streams.