Removal of Ni(II) ions from aqueous solutions using waste of tea factory: adsorption on a fixed-bed column

The removal efficiency of waste tea from nickel containing aqueous solutions was investigated. All experiments were conducted fixed-bed columns. Experiments were carried out as a function of liquid flow rate (5-20 mL/min), initial Ni(II) concentration (50-200 mg/L), bed height (10-30 cm), pH of feed solution (2.0-5.0) and particle size (0.15-0.25 to 1.0-3.0 mm) of adsorbent. The total adsorbed quantities, equilibrium uptakes and total removal percents of Ni(II) related to the effluent volumes were determined by evaluating the breakthrough curves obtained at different flow rates, different inlet Ni(II) concentrations, different pH value, different bed height and different particle size for waste tea. The longest breakthrough time and maximum of Ni(II) adsorption is obtained at pH 4.0. Decrease in the particle size from 1.0-3.0 to 0.15-0.25 mm resulted in significant increase in the treated volume, breakthrough time and bed capacity. The results show that the column performed well at lowest flow rate. Also, column bed capacity and exhaustion time increased with increasing bed height. When the initial Ni(II) concentration is increased from 50 to 200 mg/L, the corresponding adsorption bed capacity appears to increase from 7.31 to 11.17 mg/g. The bed depth service time (BDST) model and the Thomas model were used to analyze the experimental data and the model parameters were evaluated. Good agreement of the experimental breakthrough curves with the model predictions was observed.     

Effects of ferrous ions on the reductive dechlorination of trichloroethylene by zero-valent iron

The surface characteristics of zero-valent iron (ZVI) and the efficiency of reductive dechlorination of trichloroethylene (TCE) in the presence of ferrous ions were studied. The experimental results indicated that the acid-washing of a metallic iron sample enhanced the efficiency of TCE degradation by ZVI. This occurred because acid-washing changed the conformation of oxides on the surface of iron from maghemite (gamma-Fe(2)O(3)) to the more hydrated goethite (alpha-FeOOH), as was confirmed by XPS analysis. However, when ferrous ions were simultaneous with TCE in water, the TCE degradation rate decreased as the concentration of ferrous ion increased. This was due to the formation of passive precipitates of ferrous hydroxide, including maghemite and magnetite (Fe(3)O(4)), that coated on the surface of acid-washed ZVI, which as a result inhibited the electron transfer and catalytic hydrogenation mechanisms. On the other hand, in an Fe(0)-TCE system without the acid-washing pretreatment of ZVI, ferrous ions were adsorbed into the maghemite lattice which was then converted to semiconductive magnetite. Thus, the electrons were transferred from the iron surface and passed through the precipitates, allowing for the reductive dechlorination of TCE.     

Reactivity of Fe(II)/cement systems in dechlorinating chlorinated ethylenes

Ferrous iron (Fe(II)) in combination with Portland cement is effective in reductively dechlorinating chlorinated organics and can be used to achieve immobilization and degradation of contaminants simultaneously. Reactivities of chlorinated ethylenes (perchloroethylene (PCE), trichloroethylene (TCE), 1,1-dichloroethylene (1,1-DCE), vinyl chloride (VC)) in Fe(II)/cement systems were characterized using batch slurry reactors. Reduction kinetics of the chlorinated ethylenes were sufficiently fast to be utilized for the proposed treatment scheme, and were described by a pseudo-first-order rate law. The order of reactivity of the chlorinated ethylenes was TCE>1,1-DCE>PCE>VC. Reduction of TCE and PCE mainly yielded acetylene, implying that the transformation of the two compounds occurred principally via reductive beta-elimination pathways. Transformation of 1,1-DCE and VC gave rise to primarily ethylene, implying that major degradation pathways were a reductive alpha-elimination for the former and a hydrogenolysis for the latter. The reactivity of the Fe(II)/cement systems in dechlorinating TCE was proportional to Fe(II) dose when the Fe(II)/cement mass ratio varied between 5.6 and 22.3%. The Fe(II)/cement systems with a higher Fe(II) loading were less extensively affected by pH in reductive reactions for TCE than in the previous experiments with PCE or chlorinated methanes. Amendment of Fe(II)/cement systems with Fe(III) addition was found effective in increasing the reactivity in the previous study, but the current findings indicated that the extent to which the reaction rate increased by the amendment might be dependent on the source of the cement and/or the compounds tested.     

Dechlorination of trichloroethylene in aqueous solution by noble metal-modified iron

Bimetallic particles are extremely interesting in accelerating the dechlorination of chlorinated organics. Four noble metals (Pd, Pt, Ru and Au), separately deposited onto the iron surface through a spontaneous redox process, promoted the TCE dechlorination rate, and the catalytic activity of the noble metal followed the order of Pd>Ru>Pt>Au. This order was found to be dependent on the concentrations of adsorbed atomic hydrogen, indicating that the initial reaction was cathodically controlled. Little difference in the distribution of the chlorinated products for the four catalysts (cis-DCE: 51%; 1,1-DCE: 27%; trans-DCE: 15% and VC: 7%) was observed. The chlorinated by-products accumulated in both Pt/Fe and Au/Fe (10.3% and 2.5% of the transformed TCE, respectively), but did not accumulate in Pd/Fe and Ru/Fe. Ru/Fe was further examined as an economical alternative to Pd/Fe. The 1.5% Ru/Fe was found to completely degrade TCE within 80 min. Considering the expense, the yield of chlorinated products and the lifetime of a reductive material, Ru provides a potential alternative to Pd as a catalyst in practical applications.     

Copper(II) and lead(II) removal from aqueous solution in fixed-bed columns by manganese oxide coated zeolite

The ability of manganese oxide coated zeolite (MOCZ) to adsorb copper and lead ions in single- (non-competitive) and binary- (competitive) component sorption systems was studied in fixed-bed column. The experiments were applied to quantify particle size, bed length, influent flow rate and influent metal concentration on breakthrough time during the removal of copper and lead ions from aqueous solutions using MOCZ column. Results of fixed-bed adsorption showed that the breakthrough time appeared to increase with increase of the bed length and decrease of influent metal concentration, but decreased with increase of the flow rate. The Thomas model was applied to adsorption of copper and lead ions at bed length, MOCZ particle size, different flow rate and different initial concentration to predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design. The model was found suitable for describing the adsorption process of the dynamic behavior of the MOCZ column. The total adsorbed quantities, equilibrium uptakes and total removal percents of Cu(II) and Pb(II) related to the effluent volumes were determined by evaluating the breakthrough curves obtained at different conditions. The results suggested that MOCZ could be used as an adsorbent for an efficient removal of copper and lead ions from aqueous solution. The removal of metal ion was decreased when other additional heavy metal ion was added, but the total saturation capacity of MOCZ for copper and lead ions was not significantly decreased. This competitive adsorption also showed that adsorption of lead ions was decreased insignificantly when copper ions was added to the influent, whereas a dramatic decrease was observed on the adsorption of copper ions by the presence of lead ions. The removal of copper and lead ion by MOCZ columns followed the descending order: Pb(II) > Cu(II). The adsorbed copper and lead ions were easily desorbed from MOCZ with 0.5 mol l(-1) HNO3 solution.     

The mechanism and applicability of in situ oxidation of trichloroethylene with Fenton's reagent

Fenton's reagent is the result of reaction between hydrogen peroxide (H(2)O(2)) and ferrous iron (Fe(2+)), producing the hydroxyl radical (-*OH). The hydroxyl radical is a strong oxidant capable of oxidizing various organic compounds. The mechanism of oxidizing trichloroethylene (TCE) in groundwater and soil slurries with Fenton's reagent and the feasibility of injecting Fenton's reagent into a sandy aquifer were examined with bench-scale soil column and batch experiment studies. Under batch experimental conditions and low pH values ( approximately 3), Fenton's reagent was able to oxidize 93-100% (by weight) of dissolved TCE in groundwater and 98-102% (by weight) of TCE in soil slurries. Hydrogen peroxide decomposed rapidly in the test soil medium in both batch and column experiments. Due to competition between H(2)O(2) and TCE for hydroxyl radicals in the aqueous solutions and soil slurries, the presence of TCE significantly decreased the degradation rate of H(2)O(2) and was preferentially degraded by hydroxyl radicals. In the batch experiments, Fenton's reagent was able to completely dechlorinate the aqueous-phase TCE with and without the presence of soil and no VOC intermediates or by-products were found in the oxidation process. In the soil column experiments, it was found that application of high concentrations of H(2)O(2) with addition of no Fe(2+) generated large quantities of gas in a short period of time, sparging about 70% of the dissolved TCE into the gaseous phase with little or no detectable oxidation taking place. Fenton's reagent completely oxidized the dissolved phase TCE in the soil column experiment when TCE and Fenton's regent were simultaneously fed into the column. The results of this study showed that the feasibility of injecting Fenton's reagent or H(2)O(2) as a Fenton-type oxidant into the subsurface is highly dependent on the soil oxidant demand (SOD), presence of sufficient quantities of ferrous iron in the application area, and the proximity of the injection area to the zone of high aqueous concentration of the target contaminant. Also, it was found that in situ application of H(2)O(2) could have a gas-sparging effect on the dissolved VOC in groundwater, requiring careful attention to the remedial system design.     

Application of H2O2 lifetime as an indicator of TCE Fenton-like oxidation in soils

Hydrogen peroxide decomposition and trichloroethylene (TCE) oxidation kinetics were studied through batch slurry experiments, performed on two TCE contaminated soils (a sandy soil and a clay soil), characterized by different texture and organic fraction; besides, experiments were also performed on sandy soil columns, in order to more closely reproduce the typical conditions of an in situ treatment. The results of the batch tests indicated that hydrogen peroxide lifetime was correlated to the oxidation efficiency; namely, complete TCE oxidation was achieved only for the conditions characterized by longer hydrogen peroxide lifetime, that was obtained by addition of a proper stabilizer (KH(2)PO(4)). The soil properties were also observed to influence both hydrogen peroxide decomposition and TCE oxidation kinetics, probably as a consequence of the different TOC content. The soil column experiments, performed on 10, 20, and 30 cm long columns, indicated that hydrogen peroxide decomposition, which was almost complete at 30 cm depth, was on the contrary negligible when the stabilizer was added. In agreement with this observation, the performance of TCE oxidation were greatly improved in the latter case. Based upon the collected results, it can be concluded that hydrogen peroxide experiments may be useful, at least in the first screening phase of the design activity, for selecting, among the different operating conditions, those that may be potentially more effective for the oxidation treatment.     

Comparison of Pb(II) uptake by coir and dye loaded coir fibres in a fixed bed column

The possibility of adsorbing Pb(II) from solution using coir, a cheap lignocellulosic fibre, was assessed in a fixed bed column. The coir fibres were also chemically modified by covalent loading of a reactive dye, C.I. Reactive Orange 13, and used as adsorbent. Column adsorption studies were carried out at different initial Pb(II) concentrations and it was observed that the breakthrough time decreased with increase in the initial Pb(II) concentration. The column packed with dye loaded coir fibres was operated for longer duration than the one packed with unmodified coir fibres. The total Pb(II) adsorbed was also higher in a column packed with dye loaded coir fibres. The desorption level in the fixed bed column packed with coir fibres was of the order of 85%, whereas the one packed with dye loaded coir fibres was more than 90%. Both the columns were regenerated and used upto five cycles.     

A comparative study for the ion exchange of Fe(III) and Zn(II) on zeolite NaY

The uptake capacity of Fe(III) and Zn(II) ions in NaY zeolite was investigated. Experiments were carried out in a fixed bed column at 30 degrees C, pH 3.5 and 4.5 for Fe(III) and Zn(II), respectively, and an average particle size of 0.180 mm. In order to minimize the diffusional resistances the influence of flow rate on the breakthrough curves at feed concentrations of 1.56 meq/L for Fe(III) and 0.844 meq/L for Zn(II) was investigated. Flow rate of the minimal resistance in the bed according to mass transfer parameter were 2.0 mL/min for iron and 8.0 mL/min for zinc ions. Freundlich and Langmuir isotherm models have been used to represent the column equilibrium data. The iron dynamic isotherm was successfully modeled by the Langmuir equation and this mathematical model described well the experimental breakthrough curves for feed concentrations from 0.1 up to 3.5 meq/L. The zinc dynamic isotherm was successfully modeled by the Freundlich equation. This equilibrium model was applied to mathematical model. Experimental breakthrough curves could be predicted. Experiments were also carried out in a batch reactor to investigate the kinetics adsorption of the ions Fe(III) and Zn(II). Langmuir kinetic model fit well both experimental data.     

Removal of lead (II) ions from synthetic and real effluents using immobilized Pinus sylvestris sawdust: adsorption on a fixed-bed column

The purpose of this work was to evaluate the potential of Pinus sylvestris sawdust, in a continuous flow removal of lead (II) ions from synthetic and industrial aqueous effluents. The kinetic parameters obtained in a batch process were used to scale-up the process on a mini-column and to choose the breakthrough model. The column experimental data concerning the volumes treated were correlated using the bed depth service time model. These experimental data closely fitted the bed depth service time model at 10% of the breakthrough curve. The results from the bed depth service time model on the mini-column were then used to design a pilot plant adsorption unit. The performance of the pilot plant column accurately agreed with that obtained from the mini-column. The experiments carried out in a dynamic reactor allowed to bring out the influence of various parameters on the efficiency of the P. sylvestris sawdust. In addition, the process was checked for the treatment of industrial aqueous effluents on a pilot plant scale and the results were in accordance with those obtained from synthetic effluents.     

Use of carbon stable isotope to investigate chloromethane formation in the electrolytic dechlorination of trichloroethylene

Carbon stable isotope trichloroethylene ((13)C TCE) was used to investigate the formation of chloromethane (CM) during the electrolytic dechlorination of trichloroethylene (TCE) at a granular-graphite packed cathode. A method was developed to use a conventional GC/MS to analyze and quantify regular and (13)C TCE and their dechlorination products. The concentration of a (13)C compound can be calculated, based on the concentration of its regular counterpart, from the response ratio of two fragments of different mass per charge values from the compounds in a sample and two characteristic MS spectrum ratios: one is the response ratio of the two fragments of the regular compound, and the other is the response ratio of the corresponding fragments of the regular and (13)C compounds at the same concentrations. The method was used to analyze the regular and (13)C compounds observed in an experiment of dechlorination in an ammonium acetate solution that contained both regular TCE and (13)C TCE. Results of analysis confirmed that CM was not a direct product of TCE dechlorination at the granular graphite cathode that cis-DCE was an intermediate product of TCE dechlorination, and that 1,1-DCE was not a dechlorination product.     

Synthesis of granular activated carbon/zero valent iron composites for simultaneous adsorption/dechlorination of trichloroethylene

The coupling adsorption and degradation of trichloroethylene (TCE) through dechlorination using synthetic granular activated carbon and zerovalent iron (GAC-ZVI) composites was studied. The GAC-ZVI composites were prepared from aqueous Fe²⁺ solutions by impregnation with and without the use of a PEG dispersant and then heated at 105 °C or 700 °C under a stream of N₂. Pseudo-first-order rate constant data on the removal of TCE demonstrates that the adsorption kinetics of GAC is similar to those of GAC-ZVI composites. However, the usage of GAC-ZVI composites liberated a greater amount of Cl than when ZVI was used alone. The highest degree of reductive dechlorination of TCE was achieved using a GAC-ZVI700P composite (synthesized using PEG under 700 °C). A modified Langmuir-Hinshelwood rate law was employed to depict the behavior of Cl liberation. As a result, a zero-order Cl liberation reaction was observed and the desorption limited TCE degradation rate constant decreased as the composite dosage was increased. The GAC-ZVI composites can be employed as a reactive GAC that is not subject to the limitations of using GAC and ZVI separately.     

Removal of copper(II) from aqueous phase by Purolite C100-MB cation exchange resin in fixed bed columns: modeling

The dynamic removal of copper by Purolite C100-MB cation exchange resin was studied in packed bed columns. The values of column parameters are predicted as a function of flow rate and bed height. Batch experiments were performed using the Na-form resin to determine equilibrium and kinetics of copper removal. The uptake of Cu(II) by this resin follows first-order kinetics. The effect of stirring speed and temperature on the removal kinetics was studied. The activation energy for the exchange reaction is 13.58kJmol(-1). The equilibrium data obtained in this study have been found to fit both the Langmuir and Freundlich isotherm equations. A series of column tests were performed to determine the breakthrough curves with varying bed heights and flow rates. To predict the breakthrough curves and to determine the characteristic parameters of the column useful for process design, four kinetic models; Bohart-Adams, Bed Depth Service Time (BDST), Clark and Wolborska models are applied to experimental data. All models are found suitable for describing the whole or a definite part of the dynamic behavior of the column with respect to flow rate and bed height. The simulation of the whole breakthrough curve is effective with the Bohart-Adams and the Clark models, but the Bohart-Adams model is better. The breakthrough is best predicted by the Wolborska model. The breakthrough data gave a good fit to the BDST model, resulting in a bed exchange capacity very close to the value determined in the batch process.     

Fixed bed column study for heavy metal removal using phosphate treated rice husk

This paper reports the results of the study on the performance of low-cost adsorbent such as raw rice husk (RRH) and phosphate treated rice husk (PRH) in removing the heavy metals such as lead, copper, zinc and manganese. The adsorbent materials adopted were found to be an efficient media for the removal of heavy metals in continuous mode using fixed bed column. The column studies were conducted with 10 mg/l of individual and combined metal solution with a flow rate of 20 ml/min with different bed depths such as 10, 20 and 30 cm. The breakthrough time was also found to increase from 1.3 to 3.5 h for Pb(II), 4.0 to 9.0 h for Cu(II), 12.5 to 25.4h for Zn(II) and 3.0 to 11.3 h for Mn(II) with increase in bed height from 10 to 30 cm for PRH. Different column design parameters like depth of exchange zone, adsorption rate, adsorption capacity, etc. were calculated. It is found that the adsorption capacity and adsorption rate constant were increased and the minimum column bed depth required was reduced when the rice husk is treated with phosphate, when compared with that of RRH.     

Fixed bed column study for Cd(II) removal from wastewater using treated rice husk

A fixed bed of sodium carbonate treated rice husk was used for the removal of Cd(II) from water environment. The material as adopted was found to be an efficient media for the removal of Cd(II) in continuous mode using fixed bed column. The column having a diameter of 2 cm, with different bed depths such as 10, 20 and 30 cm could treat 2.96, 5.70 and 8.55 l of Cd(II) bearing wastewater with Cd(II) concentration 10 mg/l and flow rate 9.5 ml/min. Different column design parameters like depth of exchange zone, adsorption rate, adsorption capacity, etc. was calculated. Effect of flow rate and initial concentration was studied. Theoretical breakthrough curve was drawn from the batch isotherm data and it was compared with experimental breakthrough curve. An amount of 0.01 mol/l HCl solution was used for desorption of adsorption column. Column regeneration and reuse studies were conducted for two cycles of adsorption-desorption.     

Remediation of TCE-contaminated groundwater using nanocatalyst and bacteria

The objective of this study was to develop and evaluate the remediation of trichloroethene (TCE)-contaminated groundwater using both a nanocatalyst (bio-Zn-magnetite) and bacterium (similar to Clostridium quinii) in anoxic environments. Of the 7 nanocatalysts tested, bio-Zn-magnetite showed the highest TCE dechlorination efficiency, with an average of ca. 90% within 8 days in a batch experiment. The column tests confirmed that the application of bio-Zn-magnetite in combination with the bacterium achieved high degradation efficiency (ca. 90%) of TCE within 5 days compared to the nanocatalyst only, which degraded only 30% of the TCE. These results suggest that the application of a nanocatalyst and the bacterium have potential for the remediation of TCE-contaminated groundwater in subsurface environments.     

Dechlorination of chlorinated methanes by Pd/Fe bimetallic nanoparticles

This paper examined the potential of using Pd/Fe bimetallic nanoparticles to dechlorinate chlorinated methanes including dichloromethane (DCM), chloroform (CF) and carbon tetrachloride (CT). Pd/Fe bimetallic nanoparticles were prepared by chemical precipitation method in liquid phase and characterized in terms of specific surface area (BET), size (TEM), morphology (SEM), and structural feature (XRD). With diameters on the order of 30-50 nm, the Pd/Fe bimetallic nanoparticles presented obvious activity, and were suited to efficient catalytic dechlorination of chlorinated methanes. The effects of some important reaction parameters, such as Pd loading (weight ratio of Pd to Fe), Pd/Fe addition (Pd/Fe bimetallic nanoparticles to solution ratio) and initial pH value, on dechlorination efficiency were sequentially studied. It was found that the maximum dechlorination efficiency was obtained for 0.2 wt% Pd loading. The dechlorination efficiency was observed to increase with increasing Pd/Fe addition. The optimal pH value for dechlorination reaction of chlorinated methanes was about 7. Kinetics of chlorinated methane dechlorination in the catalytic reductive system of Pd/Fe bimetallic particles were investigated. The dechlorination reaction complied with pseudo-first-order kinetics.     

Electrically induced reduction of trichloroethene in clay

Chlorinated compounds such as trichloroethene (TCE) are recalcitrant contaminants commonly detected in soil and groundwater. Contemporary remedies such as electron donor amendment tend to be less or ineffective in treating chlorinated compounds in matrix of lower permeability, such as clay. In this study, electrically induced reduction (EIR) was tested by inserting electrodes in saturated clay containing 122.49–125.43 mg TCE kg^?1. Weak electric potentials (E) of 6, 9, and 12 V m^?1 were applied, and up to 97% of TCE were depleted during the study period. Corresponding increases in chloride concentrations was observed during TCE depletion, indicating a reductive dechlorination pathway. No migration of TCE was observed between the two electrodes, neither were intermediate compounds such as dichloroethene (DCE) or vinyl chloride (VC). Results were also tested against a mathematical equation we previously established for field applications. Electrically induced reduction may offer a novel method for in situ degradation of chlorinated contaminants, especially in low-permeable media such as clay.     

Enhanced dissolution of TCE in NAPL by TCE-degrading bacteria in wetland soils

The influence of trichloroethene (TCE) dechlorinating mixed cultures in dissolution of TCE in nonaqueous phase liquid (NAPL) via biodegradation was observed. Experiments were conducted in batch reactor system with and without marsh soils under 10 and 20 degrees C for 2 months. The dissolution phenomenon in biotic reactors containing mixed cultures was showed temporal increases compared to abiotic reactors treated with biocide. Effective NAPL-water transfer rate (K(m)) calculated in this study showed more than four times higher in biotic reactors than that in abiotic reactors. The results might be attributed to the biologically enhanced dissolution process via dechlorination in reactors. Temperature would be a factor to determine the dissolution rate by controlling bacterial activity. The TCE dechlorination occurred even in an interface of TCE-NAPL that demonstrated no previous TCE biodegradation, suggesting that microbes may be useful in developing source-zone bioremediation system. In conclusion, dechlorinating mixed culture could enhance dissolution in NAPL that may be useful in the application of source zone bioremediation.     

The effectiveness of ferrous iron and sodium dithionite for decreasing resin-extractable Cr(VI) in Cr(VI)-spiked alkaline soils

Ferrous iron, Na(2)S(2)O(4), and a mixture of Fe(II) and Na(2)S(2)O(4) (4:1 mol/mol) were tested for their effectiveness for decreasing resin-extractable Cr(VI) in alkaline Cr(VI)-spiked soils. The results indicated that adding those reductants greatly decreased the amount of resin-extractable Cr(VI) when the application rate of reductants equaled the number of equivalents of dichromate added to the Cr(VI)-spiked soils. This was mainly as a result of the Cr(VI) reduction into Cr(III), as supported by the XANES spectra. Among the tested reductants, a mixture of Fe(II) and Na(2)S(2)O(4) was the most effective to decrease resin-extractable Cr(VI). The extent to which resin-extractable Cr(VI) and soil pH were decreased was affected by the pH of the reductants. Among the tested reductants at various pH, FeSO(4) at pH below 1 was the most effective in decreasing resin-extractable Cr(VI) in alkaline soils. However, the soil pH was the most decreased as well. On the other hand, the mixtures of ferrous iron and dithionite at a wide range of pH were all efficient (>70% efficiency) in decreasing resin-extractable Cr(VI). Moreover, the extent of the decrease in soil pH was much smaller than that by FeSO(4) (pH<1) alone, and thus the possibility of the Cr(III) hazard can be avoided.