Removal of arsenic(III) from water by magnetic binary oxide particles (MBOP): Experimental studies on fixed bed column

Removal of Arsenate by Fixed-Bed Columns Using Chitosan-Magnetite Hydrogel Beads and Chitosan Hydrogel Beads: Effect of the Operating Conditions on Column Efficiency

Fixed-bed columns packed with chitosan-magnetite (ChM) hydrogel and chitosan (Ch) hydrogel were used for the removal of arsenate ions from aqueous solutions at a pH of 7.0. The effect of flow rate (13, 20, and 25 mL/h), height of the columns (13 and 33 cm), and initial arsenate concentration (2, 5 and 10 mg/L) on the column's efficiency for the removal of As(V) is reported. The maximum adsorption capacity (qb), obtained before the allowed concentration of contaminant is exceeded, the adsorption capacity (qe) when the column is exhausted, and the mass transfer zone were determined. With this information, the efficiency of the column was calculated, which is given by the HL/HLUB ratio. The higher this ratio, the higher the efficiency of the column. The highest efficiency and the highest uptake capacity value at breakthrough point were obtained when using the lower flow rate, lower initial arsenate concentration, and longer bed length. When 33 cm-high columns were fed with a 10 mg As(V)/L solution at 13 mL/h, the maximum uptake capacity values at exhaustion obtained for Ch and ChM were 1.24 and 3.84 mg/g, respectively. A pH increase of the solution at the column's exit was observed and is attributed to the proton transfer from the aqueous solution to the amino and hydroxyl groups of chitosan. The incorporation of magnetite into Ch hydrogels significantly increases their capacity to remove As(V) due to the formation of complexes between arsenic and the magnetite surface. Experimental data were fitted to the Thomas model, the Yoon-Nelson model and the Bohart-Adams model using non-linear regression analysis.

Arsenic in drinking water: overview of removal strategies and role of chitosan biosorbent for its remediation

Accessibility to clean drinking water often remains a crucial task at times. Among other water pollutants, arsenic is considered a more lethal contaminant and has become a serious threat to human life globally. This review discussed the sources, chemistry, distribution, and toxicity of arsenic and various conventional technologies that are in option for its removal from the water system. Nowadays, biosorbents are considered the best option for arsenic-contaminated water treatment. We have mainly focused on the need and potential of biosorbents especially the role of chitosan-based composites for arsenic removal. The chitosan-based sorbents are economically more efficient in terms of their, low toxicity, cost-effectiveness, biodegradability, eco-friendly nature, and reusability. The role of various modification techniques, such as physical and chemical, has also been evaluated to improve the physicochemical properties of biosorbent. The importance of adsorption kinetic and isotherm models and the role of solution pH and pH_PZC for arsenic uptake from the polluted water have also been investigated. Some other potential applications of chitosan-based biosorbents have also been discussed along with its sustainability aspect. Finally, some suggestions have been highlighted for further improvements in this field.

Arsenite removal from drinking water by bark-based magnetic iron oxide particle (BMIOP): a column study

The removal of arsenite [As(III)] from drinking water was investigated in a column at flow rates of 2.0 and 5.0 mL/min (up-flow direction) using bark-based magnetic iron oxide particles (BMIOP) prepared by coating (Fe(NO₃)₃.9H₂O) over Tamarindus Indica bark. The BMIOP was compared with regenerated BMIOP, commercial activated carbon, commercial activated alumina (Al₂O₃). At 2.0 mL/min, empty bed contact time (EBCT), breakthrough time (BT), the volume of treated water and breakthrough capacity (BC) on fresh BMIOP were found to be 6.8 min, 33.15 h, 4.380 L and 0.742 mg/g, respectively, and at 5.0 mL/min, were found to be 4.1 min, 13 h, 3.675 L and 0.453 mg/g respectively. EBCT, BT and BC were increased by 65.85%, 155% and 63.79%, respectively, as the flow rate was reduced from 5.0 to 2.0 mL/min. After regeneration of BMIOP, EBCT, BT, saturated time, BC and saturation capacity (SC) were reduced by 21.95%, 15.38%, 55.15%, 16.78% and 29.71%, respectively. The BC of fresh BMIOP was increased by factors 4.15, 3.60 and 1.20 and SC by factors 9.51, 7.88 and 1.42 compared to commercial activated carbon, commercial activated Al₂O₃ and regenerated BMIOP, respectively. Logit model could be used for the design of the adsorption column. Thomas model and artificial neural network (ANN) were applied to predict the characteristic column parameters useful for process design. Quality of treated water meets BIS requirements. Toxicity Characteristic Leaching Procedure (TCLP) and semi-dynamic tests show that the exhausted BMIOP is safe for disposal in a secure landfill; hence, BMIOP has been proved to separate As(III) from water.

Efficient removal of arsenic from aqueous solution by continuous adsorption onto iron-coated cork granulates

The search for low-cost technologies for arsenic removal from water is in high demand due to its human toxicity, even at low concentrations. Adsorption can be a cost-effective water treatment technique if applied with inexpensive materials. Arsenic continuous removal by adsorption onto an alternative modified biosorbent, iron-coated cork granulates (ICG), was investigated in this work. Results showed that most experimental parameters of breakthrough curves (BTC) depend on flow rate, bed height, pH, and initial arsenic concentration. The temperature did not significantly affect arsenate removal in continuous mode; however, the adsorption capacity was affected in batch mode. The thermodynamic parameters suggest that the adsorption process is spontaneous and endothermic. The maximum adsorption capacity of ICG for As(V) removal at pH 3 was 4.2 ± 0.3 mg g^-1, calculated by Yan model fit (R² = 0.981), and for As(III) at pH 9 was 1.6 ± 0.2 mg g^-1 (R² = 0.994). ICG were able to treat As(V) from 100 µg L^-1 to under 10 µg L^-1 and 50 µg L^-1 for 895 and 1633 bed volumes, and As(III) for 569 and 861 bed volumes, respectively, both at pH 7. The application of ICG in arsenic oxyanions remediation was found to be effective under various conditions.

Adsorption performance and its mechanism of aqueous As(III) on polyporous calcined oyster shell-supported Fe-Mn binary oxide

Fe-Mn binary oxide (FMBO) is a promising adsorbent for As(III) removal through combined adsorption and oxidation. The calcined oyster shell-supported Fe-Mn binary oxide (FMBO/OS) adsorbent was synthesized by the co-precipitation method. Results indicated that the calcined oyster shell, as a carrier, improved the stability of FMBO and its adsorption capacity for As(III). The maximum adsorption capacity of FMBO/OS on As(III) reached 140.5 mg·g^-1 . Under pH 5.0 and 25°C, the removal efficiency of FMBO/OS to As(III) solution (C₀  = 10 mg·L^-1 ) reached 87% within 12 h. Moreover, based on the characterization analyses, the removal mechanisms of As(III) were deduced to include the combined adsorption and oxidation process of FMBO and the synergistic effect of oyster shells. This work provides new insights into synthesizing efficient and green adsorbents to remove aqueous As(III). Meanwhile, it provides technical support for reusing waste biomass materials such as the oyster shell. PRACTITIONER POINTS: FMBO/OS was prepared by a simple hydrothermal co-precipitation method. The carrier alleviates the agglomeration of Fe-Mn oxides. The adsorbent shows a strong adsorption capacity of As(III) and good selectivity. The good results benefit from the synergistic effect of calcium arsenate generation. The prepared adsorbent can adsorb arsenic in real samples.

Arsenate Removal from Aqueous Media Using Chitosan-Magnetite Hydrogel by Batch and Fixed-Bed Columns

The removal of arsenate ions from aqueous solutions at near-neutral pH was carried out using chitosan-magnetite (ChM) hydrogel beads in batch systems. Equilibrium isotherms and kinetic studies are reported. Obtained equilibrium and kinetic data were fitted to mathematical models, estimating model parameters by non-linear regression analysis. Langmuir model was found to best fit equilibrium data; a maximum adsorption capacity of 66.9 mg As/g was estimated at pH 7.0. Pseudo-first order kinetic model was observed to best fit kinetic data. The pH of the solution was observed to increase with increasing contact time, which is attributed to protonation of amine groups present in the hydrogel. Protonation of functional groups in the ChM sorbent yields a higher number of active sites for arsenate removal, being as this a process that can’t be overlooked in future applications of ChM hydrogel for the removal or arsenate ions. Chitosan-magnetite and ChM-arsenate interactions were determined by XPS. Arsenate removal using fixed-bed column packed with ChM was carried out, reporting a non-ideal behavior attributed to pH increase of the effluent caused by proton transfer to ChM hydrogels.

Testing of Chemically Activated Cellulose Fibers as Adsorbents for Treatment of Arsenic Contaminated Water

Exposure to different arsenic concentrations (higher than 10 μg/L), either due to the direct consumption of contaminated drinking water or indirectly by using contaminated food is harmful for human health. Therefore, it is important to remove arsenic from aqueous solutions. Among many arsenic removal technologies, adsorption offers a promising solution with a good efficiency, however the material used as adsorbent play a very vital role. The present investigation evaluated the behavior of two cellulose-based adsorbent materials, i.e., viscose fibers (V) and its TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) derivative, obtained by using the well-established TEMPO-mediated protocol (VF). Due to the known arsenic affinity for Fe ions the two materials were later doped with it. This was done after a preliminary functionalization with di-2-ethylhexyl phosphoric acid (DEHPA), to obtain two materials: V-DEHPA-Fe and VF-DEHPA-Fe. Arsenic adsorption is known to be pH dependent (between 6 and 8); therefore, the optimal pH range for As(V) adsorption has been established. In order to evaluate the adsorption mechanism for both the synthesized materials, the influence of contact time, temperature and initial concentration was evaluated. Langmuir, Freundlich and Sips equilibrium isotherm models were used in order to determine the ability of the model to describe As(V) adsorption process. The maximum adsorption capacity of the material V-DEHPA-Fe was 247.5 µg As(V)/g with an As(V) initial concentration of 5 mg/L and for the material VF-DEHPA-Fe it was 171.2 µg As(V)/g with initial concentration of 5 mg/L.

Removal of arsenate using graphene oxide-iron modified clinoptilolite-based composites: adsorption kinetic and column study

In this study, graphene oxide (GO), iron modified clinoptilolite (FeZ), and composites of GO-FeZ (GOFeZA and GOFeZB) were synthesized and characterized using SEM, EDS, XRF, FTIR, and pHpzc. The arsenate uptake on composites of GOFeZA and GOFeZB was examined by both kinetic and column studies. The adsorption capacity increases with the increase of the initial arsenate concentration at equilibrium for both composites. At the initial arsenate concentration of 450 μg/L, the arsenate adsorption on GOFeZA and GOFeZB was 557.86 and 554.64 μg/g, respectively. Arsenate adsorption on both composites showed good compatibility with the pseudo second order kinetic model. The adsorption process was explained by the surface complexation or ion exchange and electrostatic attraction between GOFeZA or GOFeZB and arsenate ions in the aqueous solution due to the relatively low equilibrium time and fairly rapid adsorption of arsenate at the beginning of the process. The adsorption mechanism was confirmed by characterization studies performed after arsenate was loaded onto the composites. The fixed-bed column experiments showed that the increasing the flow rate of the arsenate solution through the column resulted in a decrease in empty bed contact time, breakthrough time, and volume of treated water. As a result of the continuous operation column study with regenerated GOFeZA, it was demonstrated that the regenerated GOFeZA has lower breakthrough time and volume of treated water compared to fresh GOFeZA.

Current Trends of Arsenic Adsorption in Continuous Mode: Literature Review and Future Perspectives

Arsenic is a toxic element for humans and a major pollutant in drinking water. Natural and anthropogenic sources can release As into water bodies. The countries with the greatest arsenic contamination issues lack the affordable technology to attain the maximum permitted concentrations. Adsorption can be a highly efficient and low-cost option for advanced water treatment, and the development of new cheap adsorbents is essential to expand access to water with a safe concentration of arsenic. This paper aims to review the state of the art of arsenic adsorption from water in continuous mode and the latest progress in the regeneration and recovery of arsenic. The disposal of the exhausted bed is also discussed. Fixed-bed column tests conducted with novel adsorbents like binary metal oxides and biosorbents achieved the highest adsorption capacities of 28.95 mg/g and 74.8 mg/g, respectively. Iron-coated materials presented the best results compared to adsorbents under other treatments. High recovery rates of 99% and several cycles of bed regeneration were achieved, which can aggregate economic value for the process. Overall, further pilot-scale research is recommended to evaluate the feasibility of novel adsorbents for industrial purposes.

Removal of Cu(II) by Fixed-Bed Columns Using Alg-Ch and Alg-ChS Hydrogel Beads: Effect of Operating Conditions on the Mass Transfer Zone

The removal of Cu(II) ions from aqueous solutions at a pH of 5.0 was carried out using fixed-bed columns packed with alginate-chitosan (Alg-Ch) or alginate-chitosan sulfate (Alg-ChS) hydrogel beads. The effect of the initial Cu(II) concentration, flow rate, pH, and height of the column on the amount of Cu removed by the column at the breakpoint and at the exhaustion point is reported. The pH of the solution at the column's exit was initially higher than that at the entrance, and then decreased slowly. This pH increase was attributed to proton transfer from the aqueous solution to the amino and COO^- groups of the hydrogel. The effect of operating conditions on the mass transfer zone (MTZ) and the length of the unused bed (H_LUB) is reported. At the lower flow rate and lower Cu(II) concentration used, the MTZ was completely developed and the column operated efficiently; by increasing column height, the MTZ has a better opportunity to develop fully. Experimental data were fitted to the fixed-bed Thomas model using a non-linear regression analysis and a good correspondence between experimental and Thomas model curves was observed.

Characterization and Arsenic Adsorption Behaviors of Water Treatment Residuals from Waterworks for Iron and Manganese Removal

Water treatment residuals (WTRs), obtained from a groundwater treatment plant for biological iron and manganese removal, were investigated and used as adsorbents for arsenic removal. The surface morphology and structural features of the WTRs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction (XRD), and Brunauner–Emmett–Teller analysis (BET). Laboratory experiments were also carried out to test the adsorption capability and adaptability of WTRs on both As (III) and As (V) removal from the water. The results showed that the WTRs were mainly amorphous and had a large specific surface area of 253.152 m²/g. The maximum adsorption capacities, evaluated using the Langmuir isotherm equation, were 36.53 mg/g and 40.37 mg/g for As (III) and As (V), respectively. The pseudo-second-order model fitted the kinetic data better, with R² more than 0.99 for both As (III) and As (V). The removal of As (V) decreased with the increase in pH, especially when the pH was above 9, whereas for As (III), the removal effectiveness almost remained constant at both acidic and neutral pHs. H₂PO₄⁻ and SiO₃²⁻ could strongly inhibit arsenic adsorption onto the WTRs, and the effect of other ions was little.

Optimization of hybrid polymer preparation by ex situ embedding of waste Fe/Mn oxides into chitosan matrix as an effective As(III) and As(V) sorbent

A hybrid polymer for deep removal of arsenic from aqueous solutions was obtained by loading of waste Fe/Mn oxides into a chitosan matrix. The process was optimized by studying the influence of selected individual factors and their reciprocal combinations on the adsorptive and physical properties of the product. The influence of chitosan solution concentration, inorganic load amount, the ratio of Fe/Mn oxides to chitosan, and polymer cross-linking degree on kinetics of As(III) and As(V) adsorption was examined. The optimal values of the parameters were chitosan polymer concentration 1.5% w/w, inorganic load to chitosan ratio 1.67, and glutaraldehyde to chitosan amine groups molar ratio 3:1. The selected products were evaluated in terms of their morphology (scanning electron microscopy (SEM) with EDS analysis), porosity (N₂ and CO₂ adsorption isotherms), surface properties (Fourier-transform infrared spectroscopy (FTIR), isoelectric point determination) and durability in an acidic environment. The proposed process makes it possible to obtain a product combining beneficial adsorptive properties toward arsenic with the physical form and durability essential in fixed-bed adsorption systems.

Removal of Fluoride and Arsenic by a Hybrid Constructed Wetland System

A pilot-scale hybrid wetland system was constructed for the removal of fluoride and arsenic from synthetic wastewater. After five months of operation, the fluoride and arsenic removal rate were at the value of 65 % and 90 %, respectively. Through calculation, the accumulation of fluoride in plants only accounted for 1.63 % of the accumulation in substrates, and the accumulation of arsenic in plants accounted for 3.3 % of that in substrates. Both the accumulation of fluoride and arsenic in plants were much higher in roots than that in leaves. And for substrates, the accumulation in the first layer was higher than the second layer. The changes of microbial community in the substrate of the wetland during the operation were also analyzed to investigate the effects of operating condition on the microbial community and to study the role of microorganism on the removal of fluoride and arsenic. The results showed that the relative abundance of Firmicutes reduced, while the relative abundance of Proteobacteria increased, indicating that the fluoride and arsenic in solution had a great influence on the microbial community. Findings of this study suggest that the hybrid constructed wetland system may be a promising process for the removal of fluoride and arsenic from synthetic wastewater.

Adsorption of Trace Estrogens in Ultrapure and Wastewater Treatment Plant Effluent by Magnetic Graphene Oxide

In the current study, graphene oxide, Fe3+, and Fe2+ were used for the synthesis of magnetic graphene oxide (MGO) by an in situ chemical coprecipitation method. Scanning electron microscopy, transmission electron microscopy, Fourier transform infrared spectroscopy, and X-ray diffraction were used to characterize the well-prepared MGO. The prepared MGO was used as an adsorbent to remove five typical estrogens (estrone (E1), 17β-estradiol (E2), 17α-ethinylestradiol (17α-E2), estriol (E3), and synthetic estrogen (EE2)) at the ppb level from spiked ultrapure water and wastewater treatment plant effluent. The results indicated that the MGO can efficiently remove estrogens from both spiked ultrapure water and wastewater treatment plant effluent in 30 min at wide pH ranges from 3 to 11. The temperature could significantly affect removal performance. A removal efficiency of more than 90% was obtained at 35 °C in just 5 min, but at least 60 min was needed to get the same removal efficiency at 5 °C. In addition, an average of almost 80% of the estrogens can still be removed after 5 cycles of MGO regeneration but less than 40% can be reached after 10 cycles. These results indicate that MGO has potential for practical applications to remove lower levels of estrogens from real water matrixes and merits further evaluation.

Arsenic Removal Using "Green" Renewable Feedstock-Based Hydrogels: Current and Future Perspectives

In the recent times, scanty access to clean water has been one of the most prevalent problems, affecting humankind throughout the world. This calls for a tremendous amount of research to recognize new methods of purifying water at lower cost, minimizing the use of hazardous chemicals and impact on the environment. The interest of the scientific community in the potential applications of renewable feedstock-based hydrogels for heavy-metal adsorption for water remediation has been continuously increasing during the last few decades. This study is an effort to highlight the application of hydrogels for revolutionizing the present research on heavy-metal adsorption, particularly arsenic. Besides, the arsenic chemistry, health hazards of arsenic to human health, and adsorption of arsenic by natural polymer-based hydrogels have been reviewed in detail. In addition, challenges in taking the hydrogel technology forward and future prospectives like cost, handling, and disposal of the adsorbent have been discussed systematically.