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Researchers are in continuous search of better strategies to minimize, if not prevent, the anthropogenic release of toxic heavy metals, such as Cu(II) and Pb(II), into drinking water resources and the natural environment. Herein, we report for the first time the low-temperature combustion synthesis of magnetic chitosan-manganese ferrite in the absence of toxic cross-linking agents and its removal of Cu(II) and Pb(II) from single-component metal solutions. The nonlinear Langmuir model best described the isotherm data, while the nonlinear pseudo-second order model best described the kinetic data, signifying monolayer Cu(II) or Pb(II) adsorption and chemisorption as the rate-determining step, respectively. Adsorption capacities by magnetic chitosan-manganese ferrite obtained for both metals were consistently higher than those by manganese ferrite, indicating that chitosan enhanced the performance of the magnetic adsorbent. The maximum adsorption capacities of magnetic chitosan-manganese ferrite for Cu(II) and Pb(II) were 14.86 and 15.36 mg g−1, while that of manganese ferrite were 2.59 and 13.52 mg g−1, respectively. Moreover, the adsorbents showed superior binding affinity and sorption for Pb(II) than Cu(II) owing to the stronger ability of the former to form inner-sphere complexes with manganese ferrite and magnetic chitosan-manganese ferrite. Finally, thermodynamic studies revealed that the uptake of either Pb(II) or Cu(II) by magnetic chitosan-manganese ferrite was spontaneous and endothermic. The as-prepared adsorbent was characterized for morphology, elemental composition, surface functional sites, and particle size using scanning electron microscopy, energy dispersive spectroscopy, Fourier transform infrared spectroscopy, and dynamic light scattering technique, respectively.

In this study, manganese dioxide (MnO2) derived from groundwater treatment sludge was used in the adsorption of nickel (Ni(II)) ions from aqueous solutions. The synthetic MnO2 was prepared via permanganate reduction using manganese extracted from the sludge by reductive acid leaching and hydroxide precipitation. Scanning electron microscopy images showed aggregated micron-sized MnO2 particles. Fourier transform infrared analysis of MnO2 revealed functional groups at 3,396 cm−1, 1,630 cm−1, 1,427 cm−1 and 468 cm−1 bands. Zeta potential measurements at the pH range of 2–8 confirmed the net negative surface charge of MnO2 particles. Moreover, Ni(II) adsorption by MnO2 was best described by the Langmuir isotherm model, as indicated by the high values for the coefficients of determination (R2> 0.9703). The separation factor (RL) for the range of pH values and initial Ni(II) concentrations considered in this study indicated that Ni(II) adsorption by MnO2 was favorable. The kinetic data of Ni(II) adsorption by MnO2 at pH 6.5 and initial Ni(II) concentrations from 10 to 200 mg L−1 conformed to the pseudo-second order adsorption kinetic model, with R2 > 0.9997. Chemisorption occurred through the complexation of Ni(II) ions with available MnO2 functional groups. The thermodynamic study at temperatures of 298.15, 308.15 and 318.15 K revealed that Ni(II) adsorption by MnO2 was spontaneous and thermodynamically favorable for initial Ni(II) concentrations ranging from 50 to 200 mg L−1. Overall, Ni(II) adsorption by MnO2 was endothermic, as indicated by the positive ΔH° values. In addition, MnO2 had good affinity towards the Ni(II) ions, as shown by the positive ΔS° values at all Ni(II) concentrations. Simple cost analysis revealed that the MnO2 production from groundwater sludge was economically viable and may be scaled up for commercial applications.

In this study, the potential of groundwater treatment sludge reuse in the adsorption of nickel ions from aqueous solutions was evaluated. The effects of varying solution pH (4.5, 5.5, 6.5, 7.5), initial nickel concentrations (10, 50, 100, 200 mg L−1) and contact time (10, 30, 60 120 min) on Ni(II) removal were investigated. Results showed that the pH level had no significant effect on the Ni(II) removal. At all pH levels, the amount of nickel adsorbed increased from 1.3 mg g−1 to a maximum of 11.6 mg g−1 as the initial Ni(II) concentration was increased from 10 to 200 mg L−1. The nickel adsorption on the sludge at all pH levels was described by the Freundlich model, as implied by the high coefficient of determination (R2) values of 0.9890 to 0.9977 for this model. The adsorption affinity constant (n value) obtained from the Freundlich equation, which ranged from 2.98 to 3.10, suggests chemical adsorption of nickel on the sludge. The kinetic data of nickel adsorption on the sludge at pH 6.5 and initial Ni(II) concentrations of 50, 100 and 200 mg L−1 was best described by the pseudo-second order adsorption kinetic rate model, with coefficient of determination values ranging from 0.9945 to 0.9995, indicating that chemisorption between the sludge binding sites and Ni(II) governs the adsorption process. The results of the study confirm the applicability of the groundwater treatment sludge as a low-cost alternative for nickel removal from wastewater.

Groundwater treatment residuals are rich in nano-sized metal oxides which have the potential to remove various water contaminants. In this study, hexavalent chromium adsorbents were synthesized from the residuals of a 30,000 m 3 d -1 groundwater treatment plant in Taiwan. The effects of acid type and ratio, acid concentration, ultrasonication time, and heating duration on adsorption capacity were examined. Adsorbents synthesized using dual-acid solutions yielded lower adsorption capacities compared to those which used pure acid solutions. Adsorption capacity decreased with higher ultrasonication time and heating duration. Chromium removal was improved with higher ionic strength and lower pH of the solution. Results showed high correlation between experimental data and the Freundlich isotherm ( R 2 = 0.9607) and the pseudo-second order kinetic model ( R 2 = 0.9740) suggesting that the dominant mechanism in the adsorption process is chemisorption. The involvement of Fe and Mn species during chromium adsorption was confirmed by the results of energy dispersive X-ray spectroscopy and Fourier transform infrared (FTIR) spectroscopy analyses.

The ubiquitous occurrence of heavy metals in the aquatic environment remains a serious environmental and health issue. The recovery of metals from wastes and their use for the abatement of toxic heavy metals from contaminated waters appear to be practical approaches. In this study, manganese was recovered from groundwater treatment sludge via reductive acid leaching and converted into spherical aggregates of high-purity MnO2. The as-synthesized MnO2 was used to adsorb Cu(II) and Pb(II) from single-component metal solutions. High metal uptake of 119.90 mg g−1 for Cu(II) and 177.89 mg g−1 for Pb(II) was attained at initial metal ion concentration, solution pH, and temperature of 200 mg L−1, 5.0, and 25 °C, respectively. The Langmuir isotherm model best described the equilibrium metal adsorption, indicating that a single layer of Cu(II) or Pb(II) was formed on the surface of the MnO2 adsorbent. The pseudo-second-order model adequately fit the Cu(II) and Pb(II) kinetic data confirming that chemisorption was the rate-limiting step. Thermodynamic studies revealed that Cu(II) or Pb(II) adsorption onto MnO2 was spontaneous, endothermic, and had increased randomness. Overall, the use of MnO2 prepared from groundwater treatment sludge is an effective, economical, and environmentally sustainable substitute to expensive reagents for toxic metal ion removal from water matrices.

Chemical cleaning of membranes fouled by natural organic matter (NOM) generates secondary pollution. In this study, the effect of ultrasonic cleaning of polytetrafluoroethylene (PTFE) membrane fouled by pre-coagulated humic acid-bentonite mixture was investigated. Results show that chemical coagulation prior to microfiltration improved turbidity and TSS removals by 9.5% and 11.4%, respectively. Experimental data fitted to constant pressure filtration models determined the sequence of dominant fouling mechanism as follows: (i) membrane resistance-limited, (ii) pore blocking resistance-limited, and (iii) cake formation resistance-limited. Relative membrane permeability of 53 and flux recovery of 45% were achieved when continuous ultrasonic cleaning was done at a 2.0 cm probe distance, 25 min total cleaning time, 15 mg/L coagulant dose, and 15 W ultrasonic power. Ultrasonic cleaning was found to be more effective than hydraulic cleaning in terms of flux recovery. Compared to chemical cleaning, it is a competitive and safer alternative in mitigating NOM-induced fouling.

In the establishment of the groundwater management index of the Szuchung Hot-Spring Area, the sensitivity of the temperature change is much smaller than the sensitivity of the groundwater level change. Therefore, only the groundwater level can be used as the management index. According to the records of existing hot spring observations, the groundwater level of each observation well has changed significantly during the short period of time due to the influence of artificial utilization, and overall it is still affected by the abundance and dry season. In order to obtain a standard management basis, it is necessary to calculate the overall groundwater level change baseline first to deducte the human influence. But lacking the long-term development record of the measured hot spring well, so it can only use the existing data for data analysis. In order to obtain the threshold value of management indicators, thisstudy uses the mobile average and geometric average of Dashan Old Station and Public Bathroom Station to obtain the benchmark groundwater level of each station. Then, with the standard deviation of one standard deviation, two standard deviations, and the largest drop in history, the actual groundwater level, safe groundwater level, severe groundwater level, and bottom limit groundwater level can be obtained. After the comparison, it was learned that Dashan Old Station recorded the lower than the bottom limit groundwater level in about three days in March and April 2016, and the number of days was lower than the safe groundwater level. The actual groundwater level of the Public Bathroom Station was almost above the safe groundwater level.

In water treatment plants, oxidizing agents (e.g., NaOCl) are commonly added prior to coagulation. This reduces algae activity and enhances coagulation effectiveness. However, oxidants generate harmful by-products (e.g., trihalomethanes, THMs). Landfill sites are scarce and sludge treatment processes are costly. Therefore, effective utilization of wasted sludge will lower removal and treatment costs significantly. magnetic iron and manganese oxides (MIMO) recovered from water treatment plant sludge (WTP sludge) were utilized for algae removal. This reduces sludge handling costs and waste materials are effectively recycled and reused.

In this study, the removal of Cu(II), Ni(II), Pb(II), and Zn(II) from aqueous solution in single and multi-metal system using chitosan-coated montmorillonite (ChiMC) beads was investigated. The non-crosslinked and crosslinked ChiMC beads were characterized using SEM–EDX, Fourier transform infrared, and Brunauer, Emmett, and Teller analysis. The effect of ionic strength and pH on the adsorption capacity and percent (%) removal of ChiMC was examined. Kinetic studies revealed that adsorption using ChiMC follows the pseudo-second-order equation with high correlation coefficient values (R2 > 0.95). The equilibrium data were correlated with Langmuir and Freundlich isotherm models, where crosslinked ChiMC provided higher maximum adsorption capacity over ChiMC. The calculated Langmuir adsorption capacities for Cu(II), Ni(II), Pb(II), and Zn(II) using ChiMC in single-metal system are 13.04, 12.18, 29.85, and 13.50 mg/g, respectively. An increase in the calculated adsorption capacities derived from Langmuir...

In this study, Cu(II) removal using non-crosslinked and cross-linked chitosan-coated sand (CCS) from aqueous solution was investigated. To improve the mechanical and chemical stability, chitosan was coated onto sand (CCS) and cross-linked using epichlorohydrin (ECH) and ethylene glycol diglycidyl ether (EGDE). The effect of pH (2.0–5.0) on the adsorption capacity was examined. The maximum adsorption capacity of CCS, CCS–ECH, and CCS–EGDE occurred at an initial pH of 5.0, 4.0, and 5.0, respectively. The kinetic experimental data agreed well with pseudo-second order equation (R 2 > 0.988), which implies that chemisorption is the rate controlling step. Langmuir, Freundlich and Dubinin–Radushkevich were used to analyze the equilibrium data, where the Langmuir model provided the best fit for the isotherm data obtained using CCS, CCS–ECH, and CCS–EDGE (R 2 > 0.990). Adsorption-desorption was carried out using HCl solution (pH 1.0 and 3.0) and tap water (pH 7.0), where HCl solution (pH 1.0) provided t...

The removal of Mn2+ and Fe2+ from synthetic groundwater via oxidation using potassium permanganate was investigated. Batch jar tests were carried out under a constant pH of 8.0, where the effect of parameters such as the oxidant dose, presence of co-ions (Ca2+, Mg2+) and alum addition on the removal of Mn2+ and Fe2+ was examined. The partial removal of Mn2+ using aeration in single and dual metal system was 30.6% and 37.2%, respectively. The oxidant dose of 0.603 mg/L KMnO4 was the minimum amount needed to reduce Mn2+ below its maximum contaminant level. The presence of Fe2+ improved the removal of Mn2+ due to the autocatalytic effect of hydrous manganese-iron oxide, where its presence was confirmed by digital microscopy and EDX. The presence of Ca2+ and Mg2+ as well as the alum addition after oxidation has a negative effect on the removal of Mn2+. The removal mechanism of Mn2+ and Fe2+ was a combination of oxidation and adsorption or co-precipitation between the hydrous oxide and the dissolved me...

The adsorption of Mn2+ onto immobilized Mn-oxide and Fe-oxide adsorbent such as manganese oxide-coated sandl (MOCS1), manganese oxide-coated sand2 (MOCS2), iron oxide-coated sand2 (IOCS2), and manganese and iron oxide-coated sand (MIOCS) was investigated. The effects of pH (5.5 to 8.0) and temperature (25 to 45 degrees C) on the equilibrium capacity were examined. Equilibrium studies showed that there is a good fit with both Freundlich and Langmuir isotherm, which indicates surface heterogeneity and monolayer adsorption of the adsorbents. Kinetic data showed high correlation with the pseudo second-order model, which signifies a chemisorption-controlled mechanism. The activation energies, activation parameters (deltaG, deltaH, deltaS), and thermodynamic parameters (deltaG0, deltaH0, deltaS0) confirmed that adsorption with MIOCS was endothermic and more spontaneous at higher temperature while an opposite trend was observed for the other adsorbents. Thermodynamic studies showed that adsorption involved formation of activated complex, where MOCS 1 and MIOCS follow a physical-chemical mechanism, while MOCS2 and IOCS2 follows purely chemical mechanism.

In this study, quartz sand coated with water-treatment residuals was tested for its effectiveness as an arsenic adsorbent. The surface characteristics of the quartz sand before and after modification were analyzed. Different amounts of modified quartz sand were then tested for their adsorption capacity, using raw water with an arsenic concentration of 500 ppb. Analysis showed that the surface area and average pore diameter of the quartz sand had increased significantly after modification, as did the amounts of iron, manganese, and aluminum found as surface elements. Using both Freundlich and Langmuir isotherm models to measure the effectiveness of arsenic adsorption by the modified quartz sand, it was found that the latter model, for monolayer adsorption, was more appropriate.

In this study, the nano-silver impregnated media (NAg-ball) was proposed to inactive E. coli in water. After 24 h of contact with NAg-ball, about 99 % removal of E. coli from the water sample with an initial bacteria loading oItalic textf 103 - 105 CFU/ml was observed. According 32 day repetitive use, periodical surface cleaning would be suggested to maintain the high inactivation lasting of NAg-ball. The dosing of 1: 20 (Nag-ball: water) was found to be the best and most suitable in a 500 L pilot scale. This result confirmed the existence of synergistic effect lower dose shall be expected to treat the same loading of bacteria for further larger scale. Toxicity Characteristic Leaching Procedure (TCLP) test revealed trace amount of Ag, Cu, Cr and Zn released from NAg-ball into the treated water sample. In conclusion, nano-silver impregnated media has very good inactivation performance on E. coli. This NAg-ball provides a safe, convenient and effective solution in drinking water treatment, especially in the mountain area.

Batch experiments were performed to investigate the adsorption of Cu(II) from aqueous solution using noncrosslinked and crosslinked chitosan immobilized on bentonite (CIB). Crosslinking agents such as epichlorohydrin (ECH), glutaraldehyde (GLA), and ethylene glycol diglycidyl ether (EDGE) were utilized to improve the chemical and mechanical properties of the adsorbent. The effect of contact time, pH, and initial concentration on the adsorption capacity was determined. The adsorption capacities of the adsorbents are arranged in the following order: CIB-EDGE > CIB-ECH > CIB >> CIB-GLA. Langmuir and Freundlich equations were used to analyze the isotherm data. Equilibrium studies showed that CIB, CIB-EDGE, and CIB-ECH correlated well with the Langmuir model while CIB-GLA fits well with the Freundlich model. Kinetics of Cu(II) adsorption was best described by the pseudosecond-order equation, which indicates that chemisorption is the rate-limiting step. In the desorption study, more than 92 and 75% of Cu(II) could be recovered from CIB-EDGE and CIB-ECH beads using HCl solution (pH 1) agitated for 120 min. © 2012 Wiley Periodicals, Inc. J Appl Polym Sci, 2012

Precoagulation is one of the effective pretreatments in membrane filtration. This process mitigates membrane fouling, which is the major drawback of membrane technology in drinking water and wastewater treatment. This study investigated the effects of precoagulation under different coagulation mechanisms on membrane fouling. Use of ultrasound in polytetrafluoroethylene (PTFE) membrane cleaning was also evaluated. In precoagulation, synthetic raw water was precoagulated using aluminum sulfate at different coagulation mechanisms, named electrostatic patch effect (EPE), charge neutralization (CN), and sweep flocculation (SW). Flocs produced from different coagulation mech- anisms exhibited different sizes, structures, and strengths. Likewise, the fouling type generated from each mechanism was demonstrated as pore blocking for EPE, cake formation for SW, and combination phenomenon for CN. Moreover, this study indicated that the membrane flux was enhanced in the sequence of EPE > CN > SW. The flux recovery rate after ultrasonic cleaning was in the sequence of SW > CN > EPE. Finally, this study evidenced that the floc characteristics from various coagulation mechanisms affected membrane per- formance, fouling types, and ultrasonic cleaning efficiency. DOI: 10.1061/(ASCE)EE.1943-7870.0000406. © 2012 American Society of Civil Engineers.

The aim of this research was to investigate the removal of iron and manganese from groundwater by aeration, chlorine oxidation and microfiltration (MF). Pilot-scale experiments were performed at the Chang-Hua Water Treatment Plant in Taiwan. The raw waters contained soluble iron (0.4 mg/L) and manganese (0.5 mg/L) which were oxidized by chlorine and then filtered by hollow-fiber PTFE-MF. The oxidized particles on membranes under appropriate backwash were also investigated. The particle size and quality of treated water were examined. The experimental results indicated that the concentration of the residual manganese remained greater than 0.1 mg/L in treated water during the initial operation period. However, it decreased to below 0.01 mg/L after 2 weeks processing time. The scanning electron microscopy (SEM) energy dispersive spectroscopy analysis of oxidized metal particles under each process illustrated that the particles accumulated on membrane enhanced removal of iron and manganese, through autocatalytic activity in the accumulated layer on membrane. Moreover, the membrane operation pressure over 120 kPa was suggested for the active backwash process, where no structural damage on membrane was confirmed by SEM analysis.

Batch experiments were executed to investigate the removal of Cu(II) from aqueous solutions using non-crosslinked (CCB) and crosslinked chitosan-coated (CCB-ECH) bentonite beads. CCB and CCB-ECH beads were characterized by BET surface area and pore diameter analysis and X-ray diffraction (XRD). The percentage removal and adsorption capacity of Cu(II) ions were examined as a function of initial concentration and pH. The equilibrium data of CCB agreed well with the Langmuir model while CCB-ECH beads showed a better fit with the Freundlich model. Based on the isotherm study, CCB is a homogenous adsorbent, whereas CCB-ECH is a heterogeneous adsorbent. The adsorption capacities of CCB and CCB-ECH at pH 4 are 12.21 and 9.43 mg/g, respectively. The kinetic data correlated well with the pseudo-second order equation, which implies that chemisorption is the rate-limiting step. The desorption study was performed using eluent solutions, tap water (pH 7) and HCl solution (pH 1 and pH 3). The best Cu(II) recovery was obtained using HCl solution (pH 1).

The comparative and competitive adsorption of Cu(II), Ni(II), and Pb(II) from aqueous solution using chitosan immobilized on bentonite (CHB) was investigated. The adsorption data of single and binary systems indicated that Cu(II) and Pb(II) best fits Freundlich isotherm while Ni(II) follows Langmuir. In binary systems, a decrease in adsorption capacities and isotherm constants was observed, showing preference of adsorption in the order of Pb(II) > Cu(II) > Ni(II). Kinetic studies of single system indicated that the pseudo-second order is the best fit with high correlation coefficients (R2 > 0.99) and low sum of error values (SE = 0.13–0.46%). Thermodynamic studies illustrated that adsorption of CHB are exothermic and causes a decrease in the entropy. The adsorption of Pb(II) is spontaneous while Ni(II) is non-spontaneous at 25–55 °C. Cu(II) adsorption is only spontaneous at 25 °C.

The use of chitosan immobilized on bentonite (CHB) in the removal of Cu(II) from aqueous solutions was investigated using a column system. The effect on the time of breakthrough and uptake capacity of the column was examined. The dynamics of the adsorption process were evaluated by using bed depth service time (BDST) model and Thomas model. The adsorption capacity of 14.92 mg Cu(II)/g CHB with 24 h breakthrough was achieved at 500 mg/L of initial concentration, bed height of 4.3 cm, and flow rate of 0.20 mL/min. The time of breakthrough decreases while breakthrough curves become sharper with increase in flow rate and influent concentration, and a decrease in bed height of the adsorbent. Moreover, Thomas model was an acceptable kinetic model. The BDST model was utilized to compute dynamic bed capacity ( N 0 ), adsorption rate constant ( k ads ), and critical bed depth ( Z 0 ) at 29.94 g/L, 0.000857 L/(mg h) and 0.9187 cm respectively.

The aim of this study is to investigate the conditions for the removal of manganese ions from synthetic groundwater by oxidation using KMnO(4) to keep the concentration below the allowed level (0.05 mg/L). The process includes low-level aeration and addition of KMnO(4) in a Jar test system with Mn(2 + ) concentration of 0.50 mg/L, similar to that of natural groundwater in Taiwan. Different parameters such us aeration-pH, oxidant dose, and stirring speed were studied. Aeration alone was not sufficient to remove Mn(2 + ) ions completely even when the pH was increased. When a stoichiometric amount of KMnO(4) (0.96 mg/L) was used, a complete Mn(2 + ) removal was achieved within 15 min at an optimum pH of 8.0. As the amount of KMnO(4) was doubled, lower removal efficiency was obtained because the oxidant also generated manganese ions. The removal of Mn(2 + ) ions could be completed at pH 9.0 using an oxidant dose of 0.48 mg/L because Mn(2 + ) could be sorbed onto the MnO(2) particles. Finally, The MnO(2) particles were characterized using scanning electron microscopy (SEM) and energy dispersive X-ray analysis (EDX).

Biodegradable material, known as chitosan-coated sand (CCS), was utilized for removal of copper (II) and lead (II) ions in water. Batch experiments were conducted to investigate the adsorption effect under different initial concentration (Co = 100, 500, 1000 and 2000 mg/L), solution pH (2, 3, 4, 5 and 6), and contact time (0.5, 1, 2, 4, 6, 12 and 24 h). Desorption studies were performed using diluted HCl solution (pH 1 and 3) and tap water (pH 7) on adsorbed metal ions. Langmuir and Freundlich adsorption models were used to describe static isotherms and constants. The data fitted well with Langmuir model at Qmax value of 8.18 and 12.32 mg/g CCS for Cu(II) and Pb(II) ions at 4 h contact time, respectively. Kinetic studies followed the pseudo second-order reaction, which indicated that the chemical sorption is the rate-limiting step. Results of desorption process signified potential for recovering metal ions from CCS.

In this study, an ultrasonic irradiation technique was utilized to mitigate the fouling of polyethersulfone (PES) and polyvinylidene fluoride (PVDF) membranes. The use of ultrasound at 20 kHz was applied to a dead-end microfiltration cell in order to mitigate fouling caused by the presence of colloidal bentonite particles. The effect of ultrasonic power and pulse duration on the permeate flux recovery was examined. Measurements indicate that an increase in ultrasonic power and longer pulse duration results to a higher permeate flux recovery. In order to reduce power consumption, a low to high power shift (LHPS) and pulsation method, were investigated. Methods of cleaning such as ultrasonic irradiation, ultrasonic cleaning with forward flushing and ultrasonic cleaning with backwashing were utilized and their cleaning efficiencies were examined. The cleaning performance was assessed using the clean water flux method and scanning electron microscope analysis of the cleaned membranes. Results showed that LHPS and pulsation method both improve the permeate flux recovery but were not able to attain the 93.97 and 74.88% flux recovery for PES and PVDF that was achieved by constant-15 W ultrasonic cleaning. In addition, forward flushing and backwashing may enhance the performance of ultrasonic cleaning at 9 W but could become disadvantageous at 15 W.

The effectiveness of electrodialysis (ED) in removing inorganic arsenic (As) from aqueous solution was investigated. A tailor-made ED stack was used to perform current-voltage and optimization experiments in a recirculating batch mode. Samples were pre-oxidized with NaClO using 1:2 sample to oxidant weight ratio (RS:O) to transform 100% of As(III) to As(V) in 180 seconds. A high feed water conductivity of 1500 μS/cm and a low feed water conductivity of 800μS/cm had limiting currents of 595 mA and 525 mA, respectively. Optimum experimental conditions that provided maximum As separation were applied potential (E) of 12 V, feed flow rate (Q) of 0.033 L/s, feed concentration (C) of 662.0 μg L(-1), and operating time (t) of 45 min, the most significant ones were applied potential, feed concentration and operating time. Model confirmation experiments showed a good agreement with experimental results with only 0.031% error. The total As in the diluate stream was 4.0 μg L(-1), consisting of an average of 3.0 μg L(-1) As(V) and 1.0 μg L(-1) As(III).

Batch adsorption study was utilized in evaluating the potential suitability of chitosan-coated bentonite (CCB) as an adsorbent in the removal of indium ions from aqueous solution. The percentage (%) removal and adsorption capacity of indium(III) were examined as a function of solution pH, initial concentration, adsorbent dosage and temperature. The experimental data were fitted with several isotherm models, where the equilibrium data was best described by Langmuir isotherm. The mean energy (E) value was found in the range of 1-8kJ/mol, indicating that the governing type of adsorption of indium(III) onto CCB is essentially physical. Thermodynamic parameters, including Gibbs free energy, enthalpy, and entropy indicated that the indium(III) ions adsorption onto CCB was feasible, spontaneous and endothermic in the temperature range of 278-318K. The kinetics was evaluated utilizing the pseudo-first order and pseudo-second order model. The adsorption kinetics of indium(III) best fits the pseudo-second order (R(2)>0.99), which implies that chemical sorption as the rate-limiting step.