Granular Activated Carbon Bed Research Articles

Application of a three-component competitive adsorption model to evaluate and optimize granular activated carbon systems

A recently developed kinetic model for granular activated carbon (GAC) adsorbers (COMPSORB-GAC) that quantitatively describes the adsorption of trace organic contaminant in the presence of competing natural organic matter (NOM) was applied to evaluate the performance of different GAC system configurations: conventional fixed-bed adsorbers, layered upflow carbon adsorbers (LUCA), and moving-bed adsorbers (with few or many bed sections). COMPSORB-GAC separately tracks the adsorption of three components: a trace compound, a strongly competing NOM fraction that reduces trace compound equilibrium capacity, and a pore-blocking NOM fraction that reduces kinetics. Performance was simulated for various design criteria and with model parameters derived for two natural waters with significantly different NOM concentrations. For the range of simulated conditions and with baseline performance defined by a fixed-bed adsorber, LUCA generally reduced carbon usage rates (CURs) by 15–35%. A 2-section and a 16-section moving-bed reactor reduced baseline CURs by 20–30% and 45–55%, respectively. Projected CURs for the water source with a relatively high NOM concentration were 2–3 times higher for all reactor configurations and indicated that NOM preloading would cause performance deterioration in deep GAC beds, which highlights the importance of source water quality. These results show how COMPSORB-GAC can be used in a comprehensive, site-specific optimization of GAC systems to ensure robust system performance and to balance capital and operating costs.

Granular activated carbon for the recovery of the main pear aroma compound: Viability and kinetic modelling of ethyl-2,4-decadienoate adsorption

Methyl and ethyl esters of 2,4-decadienoic acids are considered the main responsible compounds for the typical flavour impact of pears. In this work, the adsorption on granular activated carbon (GAC) was the selected method for extracting ethyl-2,4-decadienoate from an aqueous phase, examining the possibility of recovery of this valuable aroma component from the aqueous fruit juice. Equilibrium and kinetic data were obtained in fixed-bed column experiments. The experimental variables under study were the concentration of the ethyl-2,4-decadienoate in the feed solution, in the range 0.20–0.39 mol m −3 and the length of the GAC bed. Equilibrium data were fitted to the Freundlich isotherm, obtaining the characteristic parameters. For the analysis of the kinetic data, a mathematical model accounting for effective pore diffusion was proposed. The value of the intraparticle diffusivity was obtained using an estimation procedure to give D p ∗ = 2.47 × 10 - 9 m 2 s −1. This value, higher than the molecular diffusion coefficient indicates an important contribution of surface diffusion to the effective pore diffusivity parameter. Finally, the application of the adsorption model using the estimated value of D p ∗ simulated satisfactorily well the breakthrough curves under the operation conditions.

Removing low ppb level perchlorate, RDX, and HMX from groundwater with cetyltrimethylammonium chloride (CTAC) pre-loaded activated carbon

Perchlorate contaminates vast amounts of groundwater throughout the United States which could potentially be used as potable water. Activated carbon pre-loaded with cetyltrimethylammonium chloride has been shown in this research to be an effective adsorbent for removing perchlorate from three low conductivity (50–66 μS/cm) groundwaters containing perchlorate (ClO 4 −) concentrations of 0.85, 1.0, and 5.6 parts per billion (ppb), respectively. In rapid small-scale column tests (RSSCTs), the virgin granular activated carbon (GAC) (used as a control) treated between 20,000 and 40,000 bed volumes (BV) of water. In contrast, the activated carbon that was pre-loaded with CTAC processed 170,000–270,000 BV before perchlorate was detected above 0.25 ppb in the effluent. Though this pre-loading significantly increased the capacity for perchlorate, it also diminished the GAC's capacity to remove organics. The groundwater containing 1 ppb ClO 4 − also contained the nitro-organics HMX (0.6 ppb) and RDX (5.5–6.6 ppb). RDX was detected in the effluent from the CTAC-pre-loaded bed after only 8000 BV had been processed whereas 308,000 BV could be processed through the virgin bed before RDX was detected. Likewise, HMX breakthrough was observed after 116,000 BV in the CTAC-pre-loaded bed while the virgin RSSCT exhibited no breakthrough of HMX during a test that was operated for 309,000 BV. However, by combining a CTAC-pre-loaded bed followed by a virgin GAC bed in series, both perchlorate and RDX could be removed for the same length of time.

Disinfection by-products and microbial contamination in the treatment of pool water with granular activated carbon

For swimming pools, it is generally agreed that free chlorine levels have to be maintained to guarantee adequate disinfection. Recommended free chlorine levels can vary between 0.3 and 0.6 mg/L in Germany and up to 3 mg/L in other countries. Bathers introduce considerable amounts of organic matter, mainly in the form of such as urine and sweat, into the pool water. As a consequence, disinfection byproducts (DBPs) are formed. Regulations in Germany recommend levels of combined chlorine of less than 0.2 mg/L and levels of trihalomethanes (THMs) of less than 20 microg/L. Haloacetic acids (HAAs), haloacetonitriles (HANs), chloropicrin and chloral hydrate are also detected in considerable amounts. However, these compounds are not regulated yet. Swimming pool staff and swimmers, especially athletes, are primarily exposed to these byproducts by inhalation and/or dermal uptake. In Germany, new regulations for swimming pool water treatment generally require the use of activated carbon. In this project, three different types of granular activated carbon (GAC) (one standard GAC, two catalytic GACs) are compared for their long time behaviour in pool water treatment. In a pilot plant operated with real swimming pool water, production and removal of disinfection byproducts (THMs, HAAs, AOXs), of biodegradable substances (AOC), of bacteria (Pseudomonas aeruginosa, Legionella, coliforms, HPC) as well as the removal of chlorine and chloramines are monitored as function of GAC bed depth. Combined chlorine penetrates deeper in the filter bed than free chlorine does. However, both, free and combined chlorine removal efficiencies decrease over the time of filter operation. The decreases of removal efficiencies are also observed for parameters such as dissolved organic carbon, spectral absorption coefficient, adsorbable organic carbon and most of the disinfection byproducts. However, THMs, especially chloroform are produced in the filter bed. The GAC beds were contaminated microbially, especially with P. aeruginosa. The contamination was not removable by backwashing with chlorine concentrations up to 2 mg/l free chlorine.

Changes of the porous structure of activated carbons applied in a filter bed pilot operation

The paper investigates the changes in porosity (i.e., in the accessible adsorption capacity of carbonaceous adsorbents for pollutants during filter bed maturation) of three activated carbons applied in a filter bed pilot operation. The results of this investigation may help to reduce operating costs, increase granular activated carbon bed life, maximize the useful life of biofilters, and understand the mechanism of water purification by carbon adsorbents. The analysis of the pore structure was limited to the first year of service of the beds, since this was when the largest decrease in the available pore capacity occurred. Low-temperature nitrogen adsorption isotherms were used to evaluate the structural parameters and pore size distributions (PSDs) of carbon samples (virgin (reference) and mature adsorbents for different periods of water treatment) on the basis of the Nguyen and Do (ND) method and density functional theory (DFT). These results were compared with small-angle X-ray scattering (SAXS) investigations (PSDs calculated by Glatter's indirect transformation method (ITP)). The results show that in general, the ND and ITP methods lead to almost the same qualitative distribution curve behavior. Moreover, the enthalpy of immersion in water, mercury porosimetry, densities (true and apparent), and the analysis of ash are reported and compared to explain the decrease in adsorptive capacity of the carbons investigated. On the other hand, the efficacy of TOC (total organic carbon, i.e., a quantity describing the complex matrix of organic material present in natural waters) removal and the bacteria count were analyzed to explain the role of adsorption in the elimination of contaminants from water. Finally, a mechanism of organic matter removal was suggested on the basis of the above-mentioned experimental data and compared with mechanisms reported by other authors.

Macrostructural characterization of granular activated carbon beds

Scale-up and prediction of performance of granular activated carbon (GAC) fixed bed adsorbers require the knowledge of the structural parameters of the particles and of the corresponding beds. A set of suitable and relatively simple methods including alumina and helium pycnometry, image analysis and water permeametry are therefore proposed and validated in this paper. These methods allow determination of particle parameters like internal porosity, particle density, solid density and size distribution. The bed characteristics obtained by applying the proposed approach are bed porosity, bed dynamic specific surface area and tortuosity. Experimental results obtained with this approach and concerning two kinds of GAC particle shape are given in this paper.

Effect of Advanced Oxidants Generated Via Ultraviolet Light on a Sequentially Loaded and Regenerated Granular Activated Carbon Biofilter

The objective of this research was to investigate a sequentially loaded and regenerated granular activated carbon (GAC) biofilter system and to determine whether regenerative ozonation/advanced oxidation could improve the removal and biodegradation of a volatile organic compound from a contaminated airstream. Bench-scale reactors were constructed to operate in a manner analogous to a commercially available system manufactured by Terr-Aqua Environmental Systems (only with longer contact time). The GAC system consisted of two GAC biofilter beds that operated in a cyclical manner. On a given day, the first GAC bed adsorbed methyl isobutyl ketone from a simulated waste airstream, while the second bed underwent regeneration; then on the next day, the second bed was in the adsorption mode while the first was regenerated. Three bench-scale systems were used to compare the performance under three operating conditions: (1) ozone/ associated oxidant regeneration of a GAC biofilter system that was seeded with microorganisms from a field site, (2) a humid air regeneration of a seeded GAC biofilter, and (3) a humid air regeneration of an unseeded GAC biofilter. For the advanced oxidant regenerated GAC biofilter, a maximum removal efficiency of >95% was achieved with an empty bed contact time of 148 sec and an influent concentration of 125 ppm methyl isobutyl ketone, and 90–95% was achieved at 148-sec empty bed contact time and a 1150-ppm influent.

Adsorption and catalytic oxidation of phenol in a new ozone reactor

Phenolic wastewater treatment in a new ozone reactor was investigated. The reactor was designed in such a fashion that gas induction was created in the reactor headspace by the high‐speed action of an impeller turbine inside a draft tube to maximize the ozone utilization. Another important feature of the present reactor design was incorporation of granular activated carbon bed in a circular compartment between the reactor wall and the shaft tube. The fixed granular activated carbon bed was observed to significantly enhance the phenol decomposition and the chemical oxygen demand removal when compared to gas‐induced ozonation alone, providing evidence of the synergistic effects of adsorption, catalytic reaction and ozonation. In addition to the enhanced phenol decomposition and chemical oxygen demand, ozonation was found to provide in‐situ regeneration of granular activated carbon which was considered crucial in the present reaction system. Kinetic investigations were also made using a proposed complex kinetic model in an attempt to elucidate the possible decomposition reaction mechanisms of the present gas‐induced ozonation system.

Ozonation of Phenolic Wastewater in a Gas-Induced Reactor with a Fixed Granular Activated Carbon Bed

Treatment of phenolic wastewater by ozonation in a new gas-induced reactor was investigated. The reactor was designed in such a fashion that gas induction was created on the liquid surface by the high-speed action of an impeller turbine inside a draft tube to maximize the ozone usage. Another important feature of the present reactor design was the granular activated carbon (GAC) bed packed in a circular compartment between the reactor wall and the shaft tube. Because of the adsorption and possible catalytic reaction by GAC, enhanced phenol decomposition and chemical oxygen demand (COD) were observed in the experimental tests, providing the evidences of the synergistic effects of adsorption, catalytic reaction, and ozonation. In addition to enhanced phenol and COD removal, ozonation was found to provide in situ GAC regeneration, which was considered highly beneficial in the industrial GAC adsorption process.

Industrial wastewater treatment in a new gas-induced ozone reactor

The present work was to investigate industrial wastewater treatment by ozonation in a new gas-induced reactor in conjunction with chemical coagulation pretreatment. The reactor was specifically designed in a fashion that gas induction was created on the liquid surface by the high-speed action of an impeller turbine inside a draft tube to maximize the ozone gas utilization. A new design feature of the present reactor system was a fixed granular activated carbon (GAC) bed packed in a circular compartment between the reactor wall and the shaft tube. The fixed GAC bed provided additional adsorption and catalytic degradation of organic pollutants. Combination of the fixed GAC bed and ozonation results in enhanced oxidation of organic pollutants. In addition to enhanced pollutant oxidation, ozonation was found to provide in situ GAC regeneration that was considered crucial in the present reaction system. Kinetic investigations were also made using a proposed complex kinetic model to elucidate the possible oxidation reaction mechanisms of the present gas-induced ozonation system. As a complementary measure, chemical coagulation pretreatment was found able to achieve up to 50% COD and 85% ADMI removal. Experimental tests were conducted to identify its optimum operating conditions.

Perchlorate removal via IRON‐PRELOADED GAC and BOROHYDRIDE REGENERATION

Tailored granular activated carbon (GAC) can reduce groundwater perchlorate levels from 60–80 μg/L to below detection. Specifically, rapid small‐scale column tests, also called RSSCTs, showed that by preloading GAC with iron–oxalic acid, the GAC adsorption capacity could be improved up to 42%. When the preloaded GAC became saturated with perchlorate, 65–74% of the GAC's original adsorption capacity could be restored by chemically regenerating the GAC with sodium borohydride. This chemical regeneration could be achieved with the use of a small fraction of the water that had been processed during the water treatment cycle. The waste stream from chemical regeneration contained concentrated perchlorate levels as high as 7,000–15,000 μg/L. With this approach, the simulations described in this article indicated that when two tailored GAC beds were operated in series with a 40‐min empty‐bed contact time, they could provide water treatment service for 60–75 days during the first operations cycle; following chemical regeneration, the GAC beds could provide about an additional 30–40 days of water service for several successive treatment and regeneration cycles.

Treatment of MTBE-Contaminated Water in Fluidized Bed Bioreactor

Methyl \Itertiary\N-butyl ether (MTBE) biodegradation was evaluated in a laboratory-scale granular activated carbon (GAC)-based fluidized bed bioreactor system. The reactor was operated in seven distinct phases during which the MTBE loading rate, hydraulic retention time, cocontaminant loading [butyl, toluene, ethylbenzene, and xylene (BTEX) and \Itertiary\N-butyl alcohol (TBA)] and temperature were varied. The reactor was able to treat MTBE to less than 20 ug/L at 25°C and total organic carbon (TOC) loading rates between 0.01 and 1.1 kg/m³ of expanded GAC bed per day (kg/m³ day). Net biomass yield in the reactor under high loading conditions was approximately 0.55 g of total suspended solids (TSS) per gram of TOC consumed. This high yield under the high loading rates necessitated that biomass be removed from the reactor to control bed expansion. At a loading rate of 1.5 kg/m³ day, MTBE effluents exceeded 20 ug/L. Reactor performance decreased as the reactor temperature was reduced from 25 to 15°C, but even at the lower temperatures MTBE removal efficiency exceede 99%. Methyl \Itertiary\N-butyl ether treatment efficiency was not effected by the addition of TBA or BTEX under the conditions evaluated. Results of this study demonstrate that fluid bed bioreactors inoculated with an appropriate microbial culture can efficiently treat MTBE-contaminated water.

Anaerobic treatment of pinkwater in a fluidized bed reactor containing GAC

Pinkwater is generated during the handling and demilitarization of conventional explosives. This listed hazardous waste contains dissolved trinitrotoluene (TNT) and cyclo trimethylene trinitramine (RDX), as well as some by-products. It represents the largest quantity of hazardous waste generated by the operations support command, and its treatment produces a by-product hazardous waste—spent granular activated carbon (GAC). Anaerobic treatment in a fluidized bed reactor (FBR) containing GAC is an emerging technology for organic compounds resistant to aerobic biological treatment. Bench scale batch studies using an anaerobic consortium of bacteria fed ethanol as the sole electron donor demonstrated the transformation of TNT to triaminotoluene (TAT), which then degrades to undetectable end products. RDX is sequentially degraded to nitroso-, dinitroso-, trinitroso- and hydroxylaminodinitroso-RDX before the triazine ring is presumably cleaved, forming methanol and formaldehyde as major end products. The bacterial members of the anaerobic consortia are typically found in sludge digesters at municipal or industrial wastewater treatment plants. The results of a pilot scale evaluation of this process that was conducted at McAlester Army Ammunition Plant (MCAAP, OK) over a 1 year period are reported in this paper. The pilot test experienced wide fluctuations in influent concentrations, representative of true field conditions. The FBR was a 20 in. (51 cm) diameter column with an overall height of 15 ft (4.9 m) and a bed of GAC occupying 11 ft (3.4 m). Water was recirculated through the column continuously at 30 gpm (114 l/min) to keep the GAC fluidized, and pinkwater for treatment was pumped into the recirculation line. Several flowrates were evaluated to determine the proper mass loading rate (mass of TNT and RDX per reactor volume per time, kg/m 3 per day) which the reactor could handle while meeting the discharge limitations. Based on the tests performed, a 1 gpm (3.785 l/min) rate in the 188 gal (710 l) volume of the fluidized GAC bed was determined to consistently meet the discharge requirements. This information was used to develop a cost estimate for a system capable of treating the total effluent currently produced at MCAAP. The cost of installing and operating this system was compared to the cost of GAC adsorption for MCAAP at current pinkwater generation rates. The GAC–FBR system had an annual operating cost of approximately US$ 19K, compared to US$ 71K annually for GAC adsorption. When including the amortization of the capital equipment required for the GAC–FBR, the payback period for installation of this new process was estimated at 3.7 years.

ADSORPTION AND STEAM REGENERATION OF n-HEXANE, MEK, AND TOLUENE ON ACTIVATED CARBON FIBER

The adsorption and steam regeneration of n-hexane, MEK, and toluene on an activated carbon fiber (ACF) were conducted for single, binary, and ternary systems and were compared with those on a granular activated carbon (GAC). An ACF bed showed not only larger adsorption capacity but also faster steam regeneration than the GAC bed. Also, the tailing effect of desorption on a GAC loaded with polar MEK was significant compared with the result on an ACF. Especially, after several adsorption-desorption cycles, there was a significant drop in the adsorption capacity of the GAC within 20% whereas the adsorption capacity of the ACF dropped within 5%. Because adsorption affinity on the ACF became stronger for toluene, MEK, and n-hexane in sequence, roll-up phenomena appeared for binary and ternary systems. Because the roll-up phenomenon was affected by the molar ratio (MR), the magnitude of roll-up increased with a decrease of MR. Therefore, the adsorption step in a TSA process could be determined largely by the behavior of a weak adsorbate in the adsorption bed, whereas a strong adsorbate could play a key role in the steam regeneration step. However, under a high MR, both the high concentration component and strongest adsorbed component played an important role in steam regeneration.

BIOAUGMENTATION AND ANAEROBIC TREATMENT OF PHARMACEUTICAL EFFLUENT IN FLUIDIZED BED REACTOR

The start-up of an anaerobic fluidized bed reactor was carried out using a single inoculum (supernatant of anaerobic digester) and later on with multiple inoculum (a mixture of supernatant of anaerobic digester and volatile fatty acid (VFA)) to achieve a faster start-up. Then regular experiments were carried out to study the effect of hydraulic retention time (HRT) on COD removal (%) and biogas production. The pharmaceutical effluent with COD of 2000 to 4000 mg/L was treated in a fluidized bed reactor using an enricher-reactor concept with a hydraulic retention times of 3 (Uf=6Umf) to 24 (Uf=1.5Umf) hr. The maximum COD removal (%) of 91.2 and a maximum biogas production of 5.62 L/d were obtained at 24 hr HRT for a maximum COD concentration of 4000 mg/L corresponding to a fluidization velocity (Uf) of 20m/hr (1.5Umf) using a granular activated carbon bed of average size 700 μm.

Removal of Taste and Odour Compounds by Conventional Granular Activated Carbon Filtration

Abstract In recent years, musty-earthy tastes in drinking water have become a seasonal problem (September to November) for communities that draw their water from the upper St. Lawrence River. The source of the problem is attributed to the presence of geosmin and 2-methylisoborneol (MIB) at concentrations ranging from 5 to 60 ng/L. In 1997 and 1998, the Cornwall Water Purification Plant added granular activated carbon (GAC) to conventional gravity filters to control taste and odour compounds. We report on a study to test the efficiency of these conventional GAC-capped filters to reduce geosmin and MIB concentrations in finished water as a function of filter age, initial chlorine residual and contact time. GAC–capped filters removed on average 60% of the MIB and 80% of the geosmin from the source water after 2 and 12 months of filter operation. However, testing after 24 months operation showed reduced efficiency. Amounts removed ranged between 13 and 20% (15% average) for MIB and 50 to 57% (54% average) for geosmin in these filters. Testing also suggested that filter efficiency was greater with longer contact times and with higher chlorine residuals (in the range 0.1 to 0.6 mg free Cl2/L). In addition to carbon age, chlorine residual and contact time, flow channelization and slow release of the taste and odour compound load (particularly MIB) from the GAC bed may affect apparent filter efficiency.

Effects of Moisture on Warming of Activated Carbon Bed during VOC Adsorption

Thermal waves resulting from the dynamic adsorption of organic vapor present in air on a granular activated carbon (GAC) filter were studied. An experimental design was carried out to determine the influential factors among the relative humidity of air (0–60%), the initial water content of the activated carbon (0–9.8%), and the volatile organic compound (VOC) concentration (0–50 g⋅m−3, i.e., 0–20,700 ppmv for acetone). The temperature increase is a function of the initial VOC concentration as well as the energy flux released. The warming of the adsorber is shown to be important for the adsorption of high VOC concentrations on a dry carbon bed, but the thermal amplitude is distinctly reduced when the GAC is initially wet because of water desorption. The moisture content of the air in the range of 0–95% is not found to be a prominent factor affecting both the adsorption capacity and the warming of the GAC bed for the high VOC concentration tested (20,700 ppmv of acetone). Temperature monitoring provides interesting information about the adsorption process, and the mechanisms involved are discussed.

GAC-Amended UASB Reactor for the Stable Treatment of Toxic Textile Wastewater

A feasibility study was carried out in the laboratory for the sequential anaerobic/aerobic treatment of textile wastewater. The process units consisted of an anaerobic UASB (upflow anaerobic sludge blanket) reactor and a SCAS (semi-continuous activated sludge) reactor. A contact-sorption layer with GAC (granular activated carbon) was provided at the bottom of the conventional UASB reactor. The raw textile wastewater first passed through the GAC bed and then through the sludge bed. By means of the GAC bed, the top-layer granular sludge was protected from toxicants. Biological regeneration of GAC, which was enhanced via a recycle flow, was demonstrated. The combined GAC-UASB and SCAS treatments allowed a stable performance and a COD (chemical oxygen demand) and colour removal of 98 and 95 %, respectively.

Preliminary testing for control of DBPs in Cleveland

Pilot testing of chlorination and ozonation with regular and enhanced coagulation suggests ozonation is not the best choice for the Crown Water Treatment Plant in Cleveland, Ohio.Bench‐ and pilot‐scale studies of total organic carbon (TOC) removal in Lake Erie water using enhanced coagulation, ozonation, and granular activated carbon (GAC) were conducted to determine the applicability of these processes to the upgrade and expansion of the Crown Water Treatment Plant in Cleveland, Ohio. Alum–polymer blends, alum, and ferric chloride more effectively removed TOC than did polyaluminum sulfate–polymer blends. Ozone did not affect TOC concentrations, but it reduced bromochloroacetic acid. Bench‐scale tests showed an optimal dose of 10 mg/L powdered activated carbon with 25 mg/L alum–polymer blend was needed to achieve a 39 percent reduction in TOC. Rapid, small‐scale column tests with GAC beds of 5‐ and 10‐min empty‐bed contact time showed breakthrough at two and six days, respectively; they did not maintain 30 percent TOC reduction after 30 and 100 days, respectively. TOC removal for future control of disinfection by‐products could most effectively be achieved in Cleveland by enhanced coagulation.

WAVE FRONT ANALYSIS FOR DESIGN OF FIXED-BED ADSORBERS

Prevailing approaches utilize empty bed contact time (or EBCT) as the primary design parameter for fixed-bed adsorbers; this despite studies that demonstrate that wave front velocity analysis is a mathematically more straightforward approach for adsorber design and operation. There are a number of assumptions inherent in the wave front approach, however, that generate important design questions related to the timing and nature of the development of the constant pattern. These questions are addressed in a numerical study of the rate of movement of the fluid phase concentration wave front as the constant pattern is approached in a granular activated carbon bed. Analyses for two organic compounds of dissimilar adsorption characteristics, trichloroethylene and para-bromophenol, revealed highly variant approaches to the constant pattern condition. More importantly, the exercise demonstrates how dynamic model simulations can insure thai verification studies at the pilot scale are properly designed to obtain a correct quantitative description of the constant pattern mass transfer zone