Virgin Granular Activated Carbon Research Articles

Batch and dynamic acid regeneration evaluation of granular activated carbons used in water cleaning treatment system. A comparative study between advanced analytical methods and a new infra-red thermographic method

A new Infrared Thermography (IRT) technique was used for textural characterization of different granular activated carbons (GAC) samples. Virgin GAC was used in a water cleaning system. Upon GAC exhaustion, an HCl and HNO3 acid regeneration method was explored using different concentration and contact time. Thermographic parameters for evaluation were (1) average temperature of the sample and (2) surface thermal density which were both deduced after applying digital images processing from the obtained IRT thermograms by flooding water over the GAC sample. Linear correlations were found between IRT parameters with SBET and Vmic (obtained from N2 gas adsorption) for exhausted and regenerated samples, being for the temperature, 0.94 and 0.91 respectively and for the surface thermal density, 0.93 and 0.92 respectively. IRT measurement results have been correlated and assessed with TGA, XRF, gas adsorption (N2 at 77 K and CO2 at 273 K), SEM-EDX NMR, FTIR, TD-GC-MS, GC-MS, GAC stability and elemental analysis. Based on all these techniques, it was found that mainly metal ions were adsorbed on the GAC. Chemical regeneration using a 7.4 wt% HCl solution was the most successful approach in removing the adsorbed metal ions (Ca, Mn and Ba) in comparison with more diluted HCl solution and HNO3 solutions. Dynamic regeneration also demonstrated that HCl performs better with a breakthrough time of 249 min, much lower than HNO3 (337 min). The used experimental column and the industrial water filter behave quite similar. Finally, in order to confirm the performance of the regenerated sample, isothermal adsorption studies as a function of the total water hardness were done, which confirmed that the regenerated GAC sample using 7.4 wt% HCl offers the best results (58.3% removal) in comparison with HNO3.

Chemical Regeneration of Activated Carbon Used in A Water Treatment System for Medical Services

The chemical regeneration of exhausted granular activated carbon (GAC) from a water treatment plant to produce dialysis water used in hemodialysis treatments for chronic renal disease patients from a general Hospital of Ciego de Avila province, Cuba, was investigated. Activated carbon (AC) exhausted mainly by inorganics (Ca (Ca-chelates), Mg and Na) was regenerated using hydrochloric acid and acetic acid (one regeneration cycle). Solutions of 5%, 10%, 15% and 20%(v/v) as well as four contact times (2 h, 4 h, 6 h and 48 h) for hydrochloric acid and three contact times (2 h, 4 h and 6 h) for acetic acid at 25°C and 1 atm in a dosage of 1 g GAC/10 mL were used. Inductively Coupled Plasma-Atomic Emission Spectroscopy (ICP-AES), thermogravimetric analysis (TGA), X-ray absorption technique (XRA) and Scanning Electronic Microscopy (SEM) were used to evaluate the effect of the regeneration on exhausted GAC. Batch and scaled column experiments were developed. Breakthrough curves were obtained to assess the AC’s performances after chemical regeneration. The removal/adsorption capacity towards free chlorine (as disinfection agent) and hardness ions (expressed in mg CaCO<sub>3</sub>/L) was estimated using the area under the breakthrough curves from scaled columns experiments. The hydrochloric acid arises as the best acidic regenerator; using a concentration of 20%(v/v), regenerated GACs using hydrochloric acid showed the highest desorption rate of inorganics as well as a free chlorine removal performance of around 30% concerning the virgin GAC sample. A new GAC management scheme is proposed for GACs used in the medical industry to improve the sustainability and economics of the water treatment process.

Removal of Hydrogen Peroxide Residuals and By-Product Bromate from Advanced Oxidation Processes by Granular Activated Carbon

During drinking water treatment, advanced oxidation process (AOP) with O3 and H2O2 may result in by-products, residual H2O2 and BrO3−. The water containing H2O2 and BrO3− often flows into subsequent granular activated carbon (GAC) filters. A concentrated H2O2 solution can be used as GAC modification reagent at 60 °C to improve its adsorption ability. However, whether low concentrations of H2O2 residuals from AOP can modify GAC, and the impact of H2O2 residuals on BrO3− removal by the subsequent GAC filter at ambient temperature, is unknown. This study evaluated the modification of GAC surface functional groups by residual H2O2 and its effect on BrO3− removal by GAC. Results showed that both H2O2 and BrO3− were effectively removed by virgin GAC, while pre-loaded and regenerated GACs removed H2O2 but not BrO3− anymore. At the ambient temperature 150 µmol/L H2O2 residuals consumed large amounts of functional groups, which resulted in the decrease of BrO3− removal by virgin GAC in the presence of H2O2 residuals. Redox reactions between BrO3− and surface functional groups played a dominant role in BrO3− removal by GAC, and only a small amount of BrO3− was removed by GAC adsorption. The higher the pH, the less BrO3− removal and the more H2O2 removal was observed.

Effect of Changes in Physical Properties of Granular Activated Carbon (GAC) on the Adsorption of Natural Organic Matter (NOM) with Increasing the Number of Thermal Regeneration: Pore Size and NOM Molecular Weight

Objectives : The purpose of this study was to evaluate the effect of increasing the number of regeneration of granular activated carbon (GAC) on the adsorption capacity of natural organic matter (NOM), and to suggest the technical process options associated the limit number of regeneration and the efficient use of regenerated GAC.Methods : The physicochemical properties of virgin and thermally regenerated GAC were analyzed. To evaluate the NOM adsorption capacity of virgin- and regenerated-GAC, five laboratory-scale columns packed with virgin- and regenerated-GAC were used for treating effluent from pilot-scale drinking water treatment facility. The NOM concentration in the influent and the effluent treated by each column was analyzed by LC-OCD (liquid chromatography-organic carbon detector) to evaluate the adsorption capacity of each NOM fractions (humic substances (HS), building blocks (BB), low molecular weight organics (LMWs)).Results and Discussion : Due to the change in the pore structure of GAC by thermal regeneration, the volume of micropores (< 2 nm) decreased, while the volume of mesopores (> 2 nm) increased. The volume ratio of micropore in virgin-GAC was about 60%, but it gradually decreased as the number of regenerations increased, resulting that the volume ratio of micropore in the 5th-regenerated (5th-Re) GAC decreased to 23%. On the other hand, the volume ratio of mesopore increased in proportion to the number of regenerations from 40% of the virgin GAC to 77% of the 5th-Re-GAC. The DOC adsorption capacities of the regenerated GACs were higher than that of virgin GAC, and the DOC adsorption capacity increased as the number of regenerations increased. As a result of comparing the adsorption capacity of virgin- and regenerated-GAC by NOM fractions, the adsorption capacity of high molecular weight NOM, such as HS, increased by 1.5 to 1.7 times as the number of regenerations increased. In contrast, the adsorption capacity of low molecular weight NOM, such as BB and LMWs, decreased by 78% and 48% as the number of regeneration increased. The limit number of regeneration was evaluated based on that the adsorption capacity (qe) of each NOM fractions keep over than 70% relative to its virgin GAC. As a result, the adsorption capacity for low molecular weight NOM was greatly reduced in GAC regenerated over than 3rd time, so that the 2nd-Re-GAC was valid to keep 70% removal of whole NOM fractions. Low adsorption of low molecular weight NOM (BB and LMWs) by 3rd-Re-GAC could be complemented by using together with virgin-GAC, and low adsorption of high molecular NOMs (HS) could be compensated as well.Conclusions : Due to the change in the pore structure of GAC by thermal regeneration, the DOC adsorption capacity was higher in regenerated GAC than its virgin-GAC, and the adsorption capacity of DOC and high molecular weight NOM (HS) was enhanced as the number of regenerations increased. On the other hand, the pore volume of micropore was reduced by regenerations, and in more than 3rd times regenerations, the adsorption capacity of low molecular weight NOMs (BB and LMWs) was reduced by less than 70% compared to its virgin GAC, so that 2nd-Re-GAC was suggested for suitable GAC. When using a mixture of virgin- and 3rd-Re-GAC, low adsorption of low molecular weight NOM (BB and LMWs) by 3rd-Re-GAC could be complemented by using together with virgin-GAC, and low adsorption of high molecular NOMs (HS) could be compensated as well.

Infrared thermography: A new approach for the characterization and management of activated carbons applied in water treatment

A new non-invasive methodology based on infrared thermography (IRT) to evaluate the exhaustion level of granular activated carbon (GAC) at different depths of a target industrial water treatment filter is studied. IRT results are discussed in terms of adsorption capacity and correlated with dedicated analytical methods: N2 gas adsorption, TGA, TD-GC/MS and NMR. Findings revealed that the surface temperature and surface thermal density parameters are contingent with the exhaustion level as well as the surface area and pore volumes of the GAC samples. Surface temperature decreased with 80% and the surface thermal density with 35% comparing exhausted Top-GAC and virgin GAC. Linear correlation was found between IRT parameters and the exhaustion profile of 98%. During GAC exploitation the surface area was reduced to 85% and the total volume of pore to 80%. The IRT method demonstrated to be simple and accurate and suitable for GAC management of water treatment.

Regeneration of per- and polyfluoroalkyl substance-laden granular activated carbon using a solvent based technology

Per- and polyfluoroalkyl substances (PFAS) are a large class of chemicals widely used for many commercial and industrial applications and have resulted in contamination at sites across globally. Pump-and-treat systems, groundwater extraction, and ex situ treatment using granular activated carbon (GAC) are being implemented, either in full or pilot scale, to treat PFAS-impacted groundwater and drinking water. The only current method of regenerating spent GAC is to reactivate it at temperatures greater than 1000 °C, which requires large amounts of energy and is quite expensive. This research focused on development and demonstration of an effective GAC regeneration technology using a solvent-based method for PFAS-laden GAC used in water treatment. Two different organic solvents (ethanol and isopropyl alcohol) with 0.5% and 1.0% ammonium hydroxide (NH4OH) as a base additive were tested to determine the most effective regenerant solution to remove PFAS from the contaminated GAC. Based on column tests using laboratory-contaminated GAC with perfluorooctanoic acid (PFOA) and perfluorooctanoic sulfonate (PFOS), the solvent-base mix (SBM) of ethanol with 0.5% NH4OH was found to be the optimum performing regenerant solution. The GAC life span assessment showed that solvent-regenerated GAC performed similar to virgin GAC without losing its optimal performance of PFAS sorption. Further, the solvent-regenerated GAC showed optimal performance even after four cycles of solvent regenerations tested using the optimum SBM. Average percent removal in laboratory-contaminated GAC using the optimum SBM was 65% and 93% for PFOS and PFOA, respectively. Four field-spent GAC samples were also regenerated using the optimum SBM. Percent removal from these samples was found to be in range of 55%–68%. The type of GAC used, level of contamination and type of PFAS present, water type and quality, and the presence of co-contaminants may have influenced the removal capacity. Distillation experiments have shown that it is feasible to concentrate the spent solvent prior to disposal, which reduces the amount of PFAS-contaminated solvent waste produced in regeneration cycles.

Effects of sodium hypochlorite concentration on the methanogenic activity in an anaerobic fluidized membrane bioreactor

The effect of membrane cleaning chemical, NaOCl on specific acetoclastic methanogenic activity (SAMA) of biomass in the anaerobic fluidized membrane bioreactors (AFMBRs) was assessed. Granular activated carbon (GAC) was used as a fluidizing media in the AFMBR to provide membrane scouring effect and surface for biofilm attachment. Effect of NaOCl on methane production was negligible for GAC with biofilm (bGAC) samples up to 150 mg NaOCl/g VSS, but was significant for the bulk liquid samples with noticeable lag period over 300 h even at the dosage of 50 mg NaOCl/g VSS. The toxicity of NaOCl on methane production was reduced in samples with virgin GAC (vGAC) by allowing 14 days of biomass buildup period prior to NaOCl addition, although the vGAC alone did not alleviate the toxicity. The results revealed that NaOCl concentrations beyond 100 mg/L within the reactor inhibited methanogenic activity and the effects were more pronounced on suspended biomass than the immobilized biomass on GAC.

Impact of biofilter operation on microbial community structure and performance

The objectives of this pilot-scale study were to evaluate biological acclimation of virgin granular activated carbon (GAC), quantify the impact of nutrient (phosphorus and nitrogen) enhancement and to compare the performance of parallel biologically active carbon (BAC) filters operated continuously or cyclically (12 h/day), with respect to removal of dissolved organic carbon (DOC) and disinfection by-product (DBP) precursors. Virgin GAC media outperformed biologically active carbon for an initial 4-month period in terms of DOC reduction (30%), as expected based on the superior performance associated with adsorption compared to biodegradation. Once the adsorptive capacity was exhausted and the media was biologically acclimated, the performance of the new GAC was statistically similar in terms of organic carbon and disinfection by-product precursor removal to a filter containing media harvested from a filter operating biologically for 12 years. Phosphorus addition to the filter influent (0.3 mg PO4-P/L; C:N:P = 400:1:30) had a small impact on DOC (3 ± 2%) and THM formation potential (5 ± 3%) reduction when compared to biofiltration without nutrient enhancement. Ammonia nitrogen added to the filter influent (0.8 mg NH4-N/L; C:N:P = 200:40:1) was completely consumed through the biofilter; however, no impact on measured performance parameters was observed. Cyclical operation of full-scale biofilters resulted in a modest, but significant improvement in DOC removal (3 ± 2%) when compared to continuously operated pilot filters. Genotyping of both cyclically and continuously operated biofilters (with varying GAC ages) showed similar community composition; however, differences in the phylogenetic diversity of the samples were evident.

Evaluation of Water Treatment Efficiency according to Number of Regeneration of GACs For Efficient Operation of GAC Process

This study was conducted to evaluate the effect of increasing the number of regenerated granular activated carbon (GAC) on the adsorption efficiency of DOC and THMs from 2011 to 2016. As increase the number of regeneration times, the apparent density, hardness and I2 number were decreased, and the ash was increased. Average breakthrough period of virgin GAC for DOC (C/C0 = 0.8) was about 8 months and each GAC basin (300 m3) adsorbed about 4,246 kg of DOC. The regenerated GACs reached to breakthrough 7 to 10 months and these GACs have 3,514~4,656 kg/basin adsorption capacity. The average THMs breakthrough (C/C0 = 1.0) period of virgin GAC was about 7 months and each basin adsorbed 60.6 kg of THMs. 1st and 2nd and more regenerated GACs had 44.8 kg/basin, 21.6 kg/basin and 10.8 kg/basin adsorption capacity respectively. To determine the optimum regeneration times, 6th regenerated GAC has almost same degree of adsorbing DOC capacity of virgin GAC that means it is difficult to determine the appropriate regeneration times for DOC, on the other hands for THMs, 2nd regenerated GAC’s adsorption capacity has one thirds of virgin GAC of that and more 4th regenerated GAC has only one sixths of virgin of that, therefore, more two times of regenerated GAC needs to be considered for THMs removal. Key words: Granular Activated Carbon (GAC), Regeneration, Regeneration Times, Trihalomethanes (THMs), Dissolved Organic Carbon (DOC), Breakthrough

Synthesis and characterization of nano magnesium oxide impregnated granular activated carbon composite for H2S removal applications

In this study, a composite of nano‑magnesium oxide (MgO) and granular activated carbon (GAC) was synthesized and analyzed for its H2S adsorption capacity. The synthesis of composite involved a spray technique, which incorporates nano MgO even into micropores of GAC. The nanocomposite was characterized structurally and chemically, using scanning electron microscopy (SEM), X-ray diffraction (XRD), thermogravimetric analysis (TGA), N2-BET adsorption studies, ultra-violet photoelectron spectroscopy (UPS) and near edge X-ray absorption fine structure spectroscopy (NEXAFS) and inductively coupled plasma optical emission spectroscopy (ICP-OES). The composite described herein showed more than five times higher H2S adsorption capacity than the virgin GAC. The high adsorption capacity shown by the MgO-GAC composite could be attributed to the fact that the composite structure exploits both physical and chemical adsorption processes simultaneously. The physical adsorption was occured at the macro and mesoporous structure of GAC whereas as the chemical adsorption was at the nano-MgO site. The differential thermogravimetric (DTG) analysis evidenced that the main mode of chemical adsorption was the oxidation of H2S, whereas a secondary metal supported addition mechanism was also shown to exist.

A pilot plant study using conventional and advanced water treatment processes: Evaluating removal efficiency of indicator compounds representative of pharmaceuticals and personal care products

With widespread occurrence of pharmaceuticals and personal care products (PPCPs) in the water cycle, their presence in source water has led to the need to better understand their treatability and removal efficiency in treatment processes. Fifteen indicator compounds were identified to represent the large number of PPCPs reported worldwide. Criteria applied to determine the indicator compounds included PPCPs widely used, observed at great frequency in aqueous systems, resistant to treatment, persistent in the environment, and representative of classes of organics. Through a pilot plant investigation to understand the optimal combination of unit process for treating PPCPs, 12 treatment trains with their additive and synergistic contributions were investigated; processes included dissolved air flotation (DAF), pre- and intermediate-ozonation with and without H2O2, intermediate chlorination, dual media filtration, granular activated carbon (GAC), and UV/H2O2. Treatment trains that achieved the greatest removals involved 1. DAF followed by intermediate ozonation, dual media filtration, and virgin GAC; 2. pre-ozonation followed by DAF, dual media filtration, and virgin GAC; and, 3. DAF (with either pre- or intermediate oxidation) followed by dual media filtration and UV/H2O2. Results revealed significant removal efficiencies for virgin GAC (preceded by DAF and intermediate ozonation) and UV/H2O2 with an intensity of 700 mJ/cm2, where more than 12 of the compounds were removed by greater than 90%. Reduced PPCP removals were observed with virgin GAC preceded by pre-ozonation and DAF. Intermediate ozonation was more effective than using pre-ozonation, demonstrating the importance of this process targeting PPCPs after treatment of natural organic matter. Removal efficiencies of indicator compounds through ozonation were found to be a function of the O3 rate constants (kO3). For compounds with low O3 rate constants (kO3 < 10 M−1s−1), H2O2 addition in the O3 reactor was required. Of the 15 indicator compounds, tri(2-chloroethyl) phosphate (TCEP) and cotinine were observed to be the most recalcitrant. Although UV/H2O2 with elevated intensity (700 mJ/cm2) was effective for PPCP removals, energy requirements far exceed intensities applied for disinfection.

Stratification of Granular Activated Carbon Filters for Advanced Wastewater Treatment

Advanced wastewater treatment with granular activated carbon (GAC) is a promising option to reduce emissions of organic micropollutants (OMP) into the aquatic environment. Frequent back-washes of the GAC filters are required due to high particle concentration in the treated wastewater but lead to stratification. Differences in adsorption capacities of individual strata are not known. The present study aimed at investigating physical and chemical differences at different filter depths of a stratified GAC filter. Two different commercial products were stratified during repeated filter bed expansions and sectioned into vertical fractions. Bulk densities, grain size distributions and ash contents of the individual fractions differed significantly. Adsorption tests with pulverized GAC from different levels showed great vertical differences in adsorption properties. OMP removals determined in the upper part of a GAC filter therefore cannot be extrapolated downwards. Both physical and chemical vertical heterogeneities with regard to adsorption capacities and residence times at different filter depths should be considered in the filter design, in the monitoring of a GAC filter, and in the interpretation of the GAC filter performance. Good correlations between abatements of UV light absorption and OMP removals were found for the virgin GAC throughout the non-uniform filter.

Effects of Dielectric Barrier Discharge Plasma Treatment on Pentachlorophenol Removal of Granular Activated Carbon

The pentachlorophenol (PCP) adsorbed granular activated carbon (GAC) was treated by dielectric barrier discharge (DBD) plasma. The effects of DBD plasma on the structure of GAC and PCP decomposition were analyzed by N2 adsorption, thermogravimetric, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and gas chromatography mass spectrometry (GC-MS). The experimental data of adsorption kinetics and thermodynamics of PCP on GAC were fitted with different kinetics and isotherm models, respectively. The results indicate that the types of N2 adsorption isotherm of GAC are not changed by DBD plasma, while the specific surface area and pore volume increase after DBD plasma treatment. It is found that the weight loss of the saturated GAC is the highest, on the contrary, the weight loss of DBD treated GAC is the least because of reduced PCP residue on the GAC. The XPS spectra and SEM image suggest that some PCP on the GAC is removed by DBD plasma, and the surface of GAC treated by DBD plasma presents irregular and heterogeneous morphology. The GC-MS identification of by-products shows that two main dechlorination intermediate products, tetrachlorophenol and trichlorophenol, are distinguished. The fitting results of experimental data of adsorption kinetics and thermodynamics indicate that the pseudo-first-order and pseudo-second order models can be used for the prediction of the kinetics of virgin GAC and DBD treated GAC for PCP adsorption, and the Langmuir isotherm model fits better with the data of adsorption isotherm than the Freundlich isotherm in the adsorption of PCP on virgin GAC and DBD treated GAC.

Surface modification of a granular activated carbon by dielectric barrier discharge plasma and its effects on pentachlorophenol adsorption

Abstract The surface properties of a granular activated carbon (GAC) were modified by dielectric barrier discharge (DBD) plasma to enhance its adsorption capacity to pentachlorophenol (PCP). Surface characteristics and adsorption capacity of GAC before and after DBD plasma modification were investigated. Results showed that the surface of GAC after plasma modification, especially N 2 plasma, became smoother and the particulates on virgin GAC's surface were eliminated due to deposit effect of plasma. The N 2 plasma modification reduced the specific surface area and surface oxygen-containing functional groups of GAC. In contrast, O 2 plasma modification increased the specific surface area and introduced oxygen-containing groups.

Evaluation of physical properties and adsorption capacity of regenerated granular activated carbons (GACs)

The objectives of this study were to evaluate the variation in physical properties and investigate the adsorption capacity after regeneration of granular activated carbon (GAC). A correlation analysis was conducted to examine the relationship between the iodide number and loss rate. The experimental results showed that the loss rate of regenerated carbon should be related to the usage time of GAC. Physical properties including the effective size and uniformity coefficient were similar to those of virgin GAC. This result indicates that the function of GAC as an adsorption medium may be recovered completely. Although the iodine number and specific surface area of the regenerated GAC were smaller than those of virgin GAC, the cumulative pore volume of the former was larger. The removal efficiency of organic matter from the regenerated GAC column was equal to or slightly higher than that from the virgin GAC column. Consequently, regeneration may increase the number of mesopores which are responsible for the removal of organic matter.

Heterogeneous Oxidation of Methylene Blue with Surface-Modified Iron-Amended Activated Carbon

The present study aims to develop effective adsorption and oxidation of synthetic dye in wastewater by using the newly synthesized iron-amended activated carbon. Recently synthetic dye-containing wastewater has gained more attention due to its mass discharge, high toxicity and low biodegradation. For enhancing adsorption of dye and oxidative regeneration of dye-exhausted activated carbon, the novel amendment of iron-deposited granular activated carbon (GAC) was developed. It was to amend ferrous ion onto the acid-pretreated GAC when pH of iron solution was higher than the pH at point of zero charge (pH, pzc) of the GAC. Methylene blue (MB) in water was adsorbed onto the acid-treated iron- amended GAC (Fe-GAC) followed by single or multiple applications of H2O2. Batch experiments were carried out to study the adsorption isotherm and kinetics indicating adsorption of MB onto the Fe-GAC followed Langmuir isotherm and the pseudo-second order kinetics. The Fe-GACshowed the maximum adsorption capacity (qm) of 238.1 ± 0.78 mg/g which was higher than the virgin GAC with qm of 175.4 ± 13.6 mg/g at 20?C, pH 6 and the initial concentration of 20 - 200 mg/L. The heterogeneous Fenton oxidation of MB in the Fe-GAC revealedthat increasing the H2O2 loading from 7 to 140 mmol H2O2/mmol MB led to enhancing the oxidation efficiency of MB in the GAC from 62.6% to 100% due to the increased generation of hydroxyl radicals. Further enhancement of oxidation of MB in the Fe-GAC was made by the multiple application of H2O2 while minimizing OH radical scavenging often occurring at high concentration of H2O2. Therefore, the acid-treated iron-amended GAC would provide excellent adsorption capacity for MB and high oxidation efficiency of MB in the GAC with multiple applications of H2O2 and optimum iron loading.

Effects of pretreatment on the surface chemistry and pore size properties of nitrogen functionalized and alkylated granular activated carbon

In this paper, granular activated carbon (GAC) from coconut shell was pretreated by HNO3, H2O2 and urea-formaldehyde resin, respectively. Then the obtained materials were functionalized in the same way for nitrogen group, and then alkylated. Effects of pretreatment on the surface chemistry and pore size of modified GACs were studied. Surface area and micropore volume of modified GAC which pretreated by HNO3 were 723.88m2/g and 0.229cm3/g, respectively, while virgin GAC were 742.34m2/g and 0.276cm3/g. Surface area and micropore volume decrease of the modified GACs which pretreated by the others two methods were more drastically. The types of groups presented were analyzed by electrophoresis, Fourier transform infrared spectroscopy (FTIR), and X-ray photoelectron spectroscopy (XPS). NCH3 group and CN group were detected on the surfaces of these three kinds of modified GACs. Results of XPS showed that the nitrogen functions of modified GAC which pretreated by H2O2 was 4.07%, it was more than that of the others two pretreatment methods. However, the modified GAC which pretreated by urea-formaldehyde resin was fixed more pyridine structure, which structure percentage was 45.88%, in addition, there were more basic groups or charge on the surface than the others.

Adsorption of bromate and competition from oxyanions on cationic surfactant-modified granular activated carbon (GAC)

A method of cationic surfactant loading was employed to modify granular activated carbon (GAC) so as to enhance GAC’s adsorption for bromate. Batch experiments of adsorption isotherms and kinetics studies indicated that cetyltrimethylammonium chloride (CTAC) greatly increased GAC’s adsorption capacity for bromate though CTAC loading had adverse effects on adsorption rates. The optimum CTAC loading was 0.18mmol/g. Adsorption isotherms were also carried out at different pHs. Bromate adsorption was more favorable at low pH. CTAC modified GAC showed higher resistance to pH changes than virgin GAC. Isotherm and kinetics data fitted well with Langmuir model and pseudo-second-order equation respectively. Competition from other anions was one of the factors that affected bromate adsorption by this modified GAC. Results showed that the strength of competition was dependent upon the valence. At the same molar ratio to bromate, competition followed the order of ClO4->NO3->SO42->PO43-.

Granular activated carbon/pyrite composites for environmental application: Synthesis and characterization

The goal of this study was to produce a reactive granular activated carbon (GAC) coated with pyrite (FeS2) for environmental remediation, which would combine both functions of GAC adsorption and FeS2 reduction reactions. GAC–FeS2 composite materials have been successfully prepared via sequential processes, i.e., incipient wetness iron impregnation, transformation into hematite (Fe2O3) by calcination at 300°C and sulfurization by calcination at 400°C. The point of zero charge (pHPZC) of GAC washed with nitric acid (HNO3) decreased to improve the drawing of iron ionic species into the pores of GAC and the results of FTIR confirmed the predominance of carboxylic acid groups which cause a negative charged GAC surface. XRD results indicated that the calcined composites are transitional GAC–Fe2O3 and final GAC–FeS2. The obtained FeS2 crystallite size calculated using Scherrer formulae was around 31–34nm and SEM/SEI showed FeS2 had an angular shape. The existence of FeS2 in GAC gave rise to a significant reduction of BET surface and pore volume. However, even though these reductions may result in the decrease of adsorption capacity when compared to the virgin GAC, the coated reactive FeS2 may result in the abiotic transformation of adsorbates such as trichloroethylene (TCE) and this would compensate for the loss of adsorption. Furthermore, the preliminary results of TCE experiments on GAC–FeS2 adsorption/dechlorination revealed that the composite initially accumulated and confined TCE on GAC and gradually dechlorinated TCE by embedded FeS2.

Rapid Small-Scale Column Tests on the Adsorption of Arsenate by Cationic Surfactant-Modified GAC

AbstractCationic surfactants were employed to modify granular activated carbon (GAC) for the purpose of improving GAC’s adsorption of arsenate from water. Rapid small-scale column tests (RSSCTs) were set up to test the adsorption capacities. Results indicated that surfactant cetyltrimethylammonium chloride (CTAC) modification manifested the highest improvement in GAC’s adsorption for arsenate. GAC modified by 2 mmol/L of CTAC was able to operate approximately 64,000 bed volumes before 10 μg/L of arsenate breakthrough as compared with 2,100 bed volumes for virgin GAC. GAC also performed much better than zeolite and bentonite both in surfactant retention and arsenic removal. Arsenate adsorption was affected by influent concentration, pH, and presence of other anions. The effect of competitive anions on arsenate adsorption was in the order of PO43->SO42->NO3-. Breakthrough tests on tap water spiked with arsenate indicated that the modified GAC had high selectivity for arsenate and considerable amount of ar...