GAC Adsorption Research Articles

Sorption of Poly- and Perfluoroalkyl Substances (PFASs) Relevant to Aqueous Film-Forming Foam (AFFF)-Impacted Groundwater by Biochars and Activated Carbon

Despite growing concerns about human exposure to perfluorooctanoate (PFOA) and perfluorooctanesulfonate (PFOS), other poly- and perfluoroalkyl substances (PFASs) derived from aqueous film-forming foams (AFFFs) have garnered little attention. While these other PFASs may also be present in AFFF-impacted drinking water, their removal by conventional drinking-water treatment is poorly understood. This study compared the removal of 30 PFASs, including 13 recently discovered PFASs, from an AFFF-impacted drinking water using carbonaceous sorbents (i.e., granular activated carbon, GAC). The approach combined laboratory batch experiments and modeling: batch sorption data were used to determine partition coefficients (Kd) and calibrate a transport model based on intraparticle diffusion-limited sorption kinetics, which was used to make forward predictions of PFAS breakthrough during GAC adsorption. While strong retention was predicted for PFOS and PFOA, nearly all of the recently discovered polyfluorinated chemicals and PFOS-like PFASs detected in the AFFF-impacted drinking water were predicted to break through GAC systems before both PFOS and PFOA. These model breakthrough results were used to evaluate a simplified approach to predicting PFAS removal by GAC using compound-specific retention times on a C18 column (RTC18). Overall, this study reveals that GAC systems for the treatment of AFFF-impacted sources of water for PFOA and PFOS likely achieve poor removal, when operated only for the treatment of PFOS and PFOA, of many unmonitored PFASs of unknown toxicity.

Adsorption characteristics and kinetics of organic airborne contamination for the chemical filters used in the fan-filter unit (FFU) of a cleanroom

Abstract In the cleanrooms of the semiconductor factories removed airborne molecular contamination (AMC) are utilized expansively by Chemical filters. Adsorption by activated carbons (AC) as filter media within the chemical filter is one of the useful methods for removal of organic airborne contamination in a cleanroom. The objective of this study is to judge coconut shell activated carbon adsorbent-loaded nonwoven fabric filter performance by deciding adsorption characteristics, breakthrough curves, and pressure drop. The testing conditions were kept at 25 ± 1 °C, and relative humidity at 44 ± 1% with face velocities of 0.3, 0.5 and 0.7 m/s for capacity decision. The challenge gas concentrations of isopropanol (IPA) were adjusted at 10, 35, and 50 ppm to promote the breakthrough of filter adsorption. The concentrations were monitored by a real-time photo-ionization detector. Results presented that breakthrough curves related to the challenge vapor concentration and the face velocity. Adsorption capacity was increased with increased challenge gas concentration and raised face velocity significantly. Results were analyzed by the Freundlich and Langmuir equation at different face velocity and determined the characteristic parameters for each adsorption isotherm. The results show that the Langmuir model is better fit compared to Freundlich model. In order to examine the adsorption mechanisms, three simplified kinetic models, i.e., the pseudo-first-order, second-order kinetic models and intraparticle diffusion model were utilized to present the kinetic data and the rate constants were computed. The rate parameter for the pseudo-first-order mechanism, k1, rate parameter for the pseudo-second-order mechanism, k2, and rate parameter, ki, of intraparticle diffusion were compared. It was detected that the pseudo-second-order adsorption mechanism is superior and the overall rate of the GAC adsorption process appears to be influenced by more than one step that is both the external mass transfer and intraparticle diffusion mechanisms.

입상활성탄흡착과 막여과공정을 이용한 고도정수처리특성

입상활성탄흡착과 막여과공정을 이용한 고도정수처리특성

Nitrogen removal from coal gasification wastewater by activated carbon technologies combined with short-cut nitrogen removal process

A system combining granular activated carbon and powdered activated carbon technologies along with shortcut biological nitrogen removal (GAC-PACT-SBNR) was developed to enhance total nitrogen (TN) removal for anaerobically treated coal gasification wastewater with less need for external carbon resources. The TN removal efficiency in SBNR was significantly improved by introducing the effluent from the GAC process into SBNR during the anoxic stage, with removal percentage increasing from 43.8%–49.6% to 68.8%–75.8%. However, the TN removal rate decreased with the progressive deterioration of GAC adsorption. After adding activated sludge to the GAC compartment, the granular carbon had a longer service-life and the demand for external carbon resources became lower. Eventually, the TN removal rate in SBNR was almost constant at approx. 43.3%, as compared to approx. 20.0% before seeding with sludge. In addition, the production of some alkalinity during the denitrification resulted in a net savings in alkalinity requirements for the nitrification reaction and refractory chemical oxygen demand (COD) degradation by autotrophic bacteria in SBNR under oxic conditions. PACT showed excellent resilience to increasing organic loadings. The microbial community analysis revealed that the PACT had a greater variety of bacterial taxons and the dominant species associated with the three compartments were in good agreement with the removal of typical pollutants. The study demonstrated that pre-adsorption by the GAC-sludge process could be a technically and economically feasible method to enhance TN removal in coal gasification wastewater (CGW).

Catalytic Ozonation with Activated Carbon for Treatment of Humic Substances in Water

Ozonation of the ubiquitous and poorly biodegradable humic acid in aquatic system was conducted in the presence of activated carbon with the aim of catalyst. The optimum operating parameters deduced from this study was GAC amount of 16.5 v/v% (GAC column volume per reactor volume) in the humic acid solution of initial pH 9. DOC removal rate in Ozone/GAC process was higher than the sum of Ozone alone and GAC adsorption process. Formaldehyde formation in Ozone/GAC process was less than in Ozone alone and GAC adsorption process. The part of molecular size distribution under 10 k Dalton were increased in the Ozone/GAC process.

Pilot study of the removal of individual trihalomethanes (THMs) from chlorinated drinking water by GAC adsorption - Galatsi water treatment plant, Athens, Greece

<p>The objective of this pilot study was to evaluate the performance of Powdered Activated Carbon (PAC) for the removal of individual trihalomethanes (THMs) from chlorinated drinking water, Athens, Greece. The pilot treatment facility was located at the Water Treatment Plant of EYDAP (Athens Water Supply and Sewerage Company) in Galatsi, Athens, and consisted of two mixing tanks operating as open batch reactors, which were fed with chlorinated water from the overflow of the sedimentation tanks. Experimental cycles were performed, with different PAC doses ranging from 5 to 50 mg L-1 and with contact times 30 and 60 min for each cycle. Water samples taken at the start of each cycle and after contact with PAC, were analysed for individual THMs and Dissolved Organic Carbon (DOC). Bromide, free residual chlorine, pH and temperature were also measured. From the experimental results, it was shown that all THMs concentrations were decreased after PAC contact, the decrease being higher for higher PAC dose and higher contact time, with few exceptions. This fact probably indicates that adsorption rate plus volatilisation rate of THMs overcame formation rate, in most cases. It was also concluded that volatilisation and possible formation reactions of THMs had probably a more apparent effect to the total removal of most THMs at low PAC doses and low contact time. At higher PAC doses and higher contact time, PAC adsorption probably had an increased contribution to THMs removal, because of the larger carbon surface area and the longer contact time, resulting in higher adsorbed mass according to adsorption theory. By using isotherm results of individual THMs on activated carbon by other researchers, the theoretically adsorbed mass of THMs per g of PAC was roughly estimated and compared with the measured removed mass of THMs per g of PAC at PAC dose 50 mg L-1 and contact time 60 min for most THMs, on the assumption of equilibrium achievement. The removed mass of THMs by PAC appeared much higher than the theoretically adsorbed, especially for the most volatile members. The difference was attributed to volatilisation taking place in the open mixing tanks. In conclusion, the practical results from the application of PAC for the removal of THMs are much better than expected from single adsorption by PAC. Volatility of THMs, especially of chloroform (TCM), substitutes for weak adsorbability and gives increased removal. The influent DOC was almost constant in all experiments. The removal of DOC was generally higher for increased PAC dose and contact time. Although equilibration cannot have happened for DOC, the mass removal of DOC per g of PAC was higher by more than two orders of size than that of the smaller and in lower concentration THMs, as expected.</p>

Simultaneous removal of cadmium ions and phenol from water solution by pulsed corona discharge plasma combined with activated carbon

In this paper, an integrated approach, the pulsed corona discharge plasma combined with granular activated carbon (PCDP/GAC), is used for the simultaneous removal of cadmium ions (Cd2+) and phenol in wastewater. Experimental results show that 69.0% Cd2+ and 87.3% phenol can be simultaneously removed from the PCDP/GAC treatment system after 60min. This removal efficiency is 27.2% and 11.4% higher than in the GAC adsorption system, respectively, and 65.8% and 60.6% higher than in the PCDP treatment system, respectively. An increasing pulsed voltage is favorable for removal of Cd2+ and phenol. The removal efficiency of Cd2+ and phenol is the highest with oxygen as the feeding gas. At the same input power and an increasing initial phenol concentration, the removal efficiency of Cd2+ and phenol decreases. Scanning electron microscopy and energy-dispersive X-ray spectroscopy show that Cd2+ amount produced on GAC by the discharge treatment in the PCDP/GAC system is higher than that in the GAC adsorption system. Fourier transform infrared spectroscopy shows that OH, CH, and CC bonds on GAC are cleaved, whereas ArOC and CO groups increase during the PCDP treatment. A possible removal mechanism of Cd2+ and phenol in such a system is proposed.

Pilot - Plant Experiments For The Removal of Thms, Haas and Doc from Drinking Water by Gac Adsorption- Galatsi Water Treatment Plant, Athens

A pilot-plant study was carried out with the water supply to Athens water works filtered through a granular activated carbon (GAC) filter- adsorber. The objective of this study was to evaluate the performance of GAC for the removal from drinking water of the two main groups of disinfection by -products (DBPs), trihalomethanes (THMs) and haloacetic acids (HAAs), as well as of dissolved organic matter. The pilot treatment facility is located at the Water Treatment Plant of EYDAP in Galatsi, Athens, and was operated as a rapid gravity filter - adsorber. It was fed with chlorinated water, coming from the overflow of the sedimentation tanks, and operated continuously in parallel with a full-scale sand filter. At regular time intervals water samples were taken from both filters and analysed for THMs, HAAs and DOC. Other parameters were measured too. The operation of the GAC filter-adsorber continued until the GAC adsorption capacity for THMs and HAAs was almost exhausted. The results of the analyses showed that GAC was more effective in removing the dissolved organic matter than the smaller molecules of THMs and HAAs, fact which is in agreement with the relevant literature. GAC was also proved more effective in removing HAAs than removing THMs. The removal of THMs and the most part of the removal of HAAs and DOC must be attributed to adsorption by GAC, while that of a smaller part of DOC and HAAs may be attributed to biological activity in the filter bed, where chlorine had been totally removed by the catalytic action of the activated carbon surface.

Effect of Ozonation and Hydrogen Peroxide Oxidation on the Structure of Humic Acids and their Removal

Using pyrolysis-GC-MS and HPLC techniques, a series of studies were conducted on the effect of pre-oxidation on the structure of natural humic acids (HA) by ozone and hydrogen peroxide (H2O2). Both ozone and H2O2 could more or less result in direct removal of organic matter, but the removal of UV254 was much higher than that of TOC, implying that an important function of the oxidants is to change the structure of the organic molecules rather than to decompose them into inorganic matters. The result of pyrolysis-GC-MS analysis showed that in the process of oxidation, the organic functional groups on the HA molecules underwent a significant change in their structure, mostly from cyclic to chain hydrocarbons and/or from aromatics to aliphatics. This process was also accompanied by a decrease in the molecular weight of the HA. With an apparent change in the structure and molecular weight of the HA molecules after pre-oxidation, a great improvement was seen on the overall removal of TOC as coagulation or GAC adsorption was subsequently applied. Additionally, in the case of H2O2, a small dose of O3 showed much better catalysing effect than Mn2+, Cu2+ or Fe2+ ions.

Coupling of adsorption, coagulation, and ultrafiltration processes for the removal of emerging contaminants in a secondary effluent

The removal of eleven emerging contaminants (acetaminophen, metoprolol, caffeine, antipyrine, sulfamethoxazole, flumequine, ketorolac, atrazine, isoproturon, 2-hydroxybiphenyl and diclofenac) present in a WWTP effluent by applying several combined treatments has been investigated. These combinations were constituted by PAC adsorption and/or coagulation pre-treatments followed by UF, as well as by an UF treatment followed by GAC adsorption post-treatment. PAC pre-treatment decreased membrane fouling, with the advantage that PAC was separated from the final effluent in the UF step. Low PAC dose in the range 10–50mgL−1 in the adsorption pre-treatment was enough in order to remove most of the emerging contaminants and to partially improve water quality parameters. However, if the goal is to reach a high improvement of water quality parameters in the pre-treatment step, a PAC dose above 500mgL−1 was required. Although coagulation pre-treatment did not increase appreciably the permeate flux in the UF step, the final quality of the permeate was improved, especially when the combination Fe(III)/UF was applied. Finally, a significant positive effect of the GAC post-treatment after the UF treatment was appreciated, which led to an increase in the removal of the water quality parameters and a significant elimination of emerging contaminants.

Pilot scale experiments on surface water treatment sequence including ozonation and adsorption processes

The paper presents results of the experimental studies on combined ozonation and activated carbon adsorption processes at the Water Treatment Plant (WTP) at Cracow (Poland). The study focused on the selection of an appropriate location of an ozonation process within the treatment scheme and on the choice of activated carbon grade for adsorption. Analysis of process efficiency in the proposed technological configuration was performed based on some specific physico-chemical parameters, monitored in the effluents from the unit processes. It was found that introduction of ozonation resulted in better reduction of parameters describing organic contaminants. The authors proposed the process sequence: ozonation – sand filtration – GAC adsorption, based on previous laboratory results. The selected activated carbon demonstrated a better reduction of organic contaminants, expressed as: permanganate COD, dissolved organic carbon (DOC), UV absorbance and SUVA 254 .

마이크로파조사를 위한 개질화 활성탄의 톨루엔 탈착

Toluene desorption of modified activated carbon for microwave irradiation was evaluated. As a virgin GAC reacted from microwave energy, it created an "arcing" between GAC particles in desorption process. The arcing became more and more vigorous and achieved a red flame of GAC. The silica coated GAC(Si/GAC) was developed to prevent arcing phenomenon and temperature control problem. The result shows virgin GAC with 5wt%, 10wt% and 20wt% silica had no arcing and could control temperature very well. However, the adsorption rate of Si/GAC was decreased by coated silica amount due to decreasing surface area of GAC. The 5wt% Si/GAC adsorption rate was quite similar to virgin GAC adsorption rate. After adsorption, the toluene-loaded GAC and Si/GAC was reactivated by 2450MHz MW irradiation with 300W for 5 min. Quantitative desorption of the toluene was achieved at MW irradiation at 300W with desorption efficiencies as high as 98.59% to 84.65%% after four cycles.

Leading the City of Baltimore into the 21st Century: Flexible Treatment Solutions and Integrated Raw Water Management

The City of Baltimore, Maryland is one of many US cities faced with challenges related to increasing potable water demands, diminishing fresh water supplies, and aging infrastructure. To address these challenges, the City recently undertook a $7M study to evaluate water supply and treatment alternatives and develop the conceptual design for a new 120 million gallon per day (MGD) water treatment plant. As part of this study, an innovative raw water management tool was constructed to help model source water availability and predicted water quality based on integration of a new and more challenging surface water supply. A rigorous decision-making approach was then used to screen and select appropriate treatment processes. Short-listed treatment strategies were demonstrated through a year-long pilot study, and process design criteria were collected in order to assess capital and operational costs for the full-scale plant. Ultimately the City chose a treatment scheme that includes low-pressure membrane filtration and post-filter GAC adsorption, allowing for consistent finished water quality irrespective of which raw water supply is being used. The conceptual design includes several progressive concepts, which will: 1) alleviate treatment limitations at the City's existing plants by providing additional pre-clarification facilities at the new plant; and 2) take advantage of site conditions to design and operate the submerged membrane system by gravity-induced siphon, saving the City significant capital and operations and maintenance (O&M) costs. Once completed, the new Fullerton Water Filtration Plant (WFP) will be the largest low-pressure membrane plant in North America, and the largest gravity-siphon design in the world.

Granular activated carbon promoted ozonation of a food-processing secondary effluent

This paper reports on the application of a simultaneous combination of ozone and a granular activated carbon (O 3/GAC) as a tertiary treatment of a wastewater generated from the activity of various food-processing industries. Prior to the O 3/GAC treatment, the wastewater was subjected to conventional primary and secondary treatments in a full-scale wastewater treatment plant (WWTP). The effluent from the WWTP presented high organic load (COD > 500 mg/l and TOC > 150 mg/l), which could be much reduced by the O 3/GAC treatment. Results from the O 3/GAC experiments were compared with those obtained in single ozonation, single adsorption onto GAC and sequential O 3–GAC adsorption experiments. While single processes and the sequential one showed limited capacity to remove organic matter for the food-processing effluent (COD removal <40%), the simultaneous O 3/GAC process led to decreases of COD up to 82% at the conditions here applied. The combined process also improved the ozone consumption, which decreased from about 19 g O 3/g TOC (single ozonation process) to 8.2–10.7 g O 3/g TOC (O 3/GAC process). The reusability of the GAC throughout a series of consecutive O 3/GAC experiments was studied with no apparent loss of activity for a neutral GAC (PZC = 6.7) but for a basic GAC (PZC = 9.1).

Behaviour of brominated and chlorinated flame retardants during drinking water treatment

Flame retardants are chemicals that are added to plastic materials in order to prevent them from catching fire and to slow down the burning process. Due to the widespread occurrence of flame retardants in the environment, it can be expected that especially the more hydrophilic compounds already contaminate raw water resources of water utilities. In this paper results of laboratory-scale experiments on the behaviour of ten brominated and chlorinated flame retardants during different steps of drinking water treatment will be presented. The target compounds were selected based on their production volumes and physical-chemical properties. The final list includes 1- and 2-bromostyrene, 2,4- and 2,6-dibromophenol, tetrabromophthalic acid, tetrachlorophthalic anhydride, chlorendic acid, tris(1,3-dichloro-2-propyl) phosphate, tris(2-chloroethyl) phosphate (TCEP), and tris(1-chloro-2-propyl) phosphate (TCPP). The results obtained from the laboratory-scale experiments clearly indicate that from the selected flame retardants only 1- and 2-bromostyrene are well biodegradable under aerobic conditions whereas the other flame retardants under investigation turned out to be persistent. Flocculation with either iron or aluminium salts is not an efficient option for removal of the selected flame retardants. For 1- and 2-bromostyrene removal rates of ca. 50% can be achieved whereas for the other compounds removal rates are in the range of 10 to 30% even when dosing 50 mg/L of flocculation agent. Oxidation with either ozone or ozone/hydrogen peroxide proved also to be rather inefficient for removal of the flame retardants under investigation, even at elevated doses of oxidant of 10 mg/L. However, results showed that the selected flame retardants adsorb well onto activated carbon and thus GAC adsorption seems to be a promising option for their removal.

Reuse of carwash wastewater with hollow fiber membrane aided by enhanced coagulation and activated carbon treatments

The particles from carwash wastewater were separated by a hollow fiber membrane aided by a enhanced coagulation and activated carbon. This study demonstrated that the addition of KMnO(4) to coagulant (PAC) could enhance the efficiency of coagulation, which helped reduce clogging of the ultrafiltration membrane and activated carbon. The existence of LAS can loosen the gel layer on the membrane and improve the flux. Adsorption of particles such as organic matter and oil is the main reason causing membrane flux decrease. When carwash wastewater was pretreated, the permeation flux of membrane showed a higher value. LAS, odour and colour are removed by GAC adsorption treatment at last. The COD, BOD, LAS and oil of reuse water was 33.4 mg/L, 4.8 mg/L, 0.06 mg/L and 0.95 mg/L, respectively.

Effect of granular activated carbon on degradation of methyl orange when applied in combination with high-voltage pulse discharge

The application of a gas–liquid series electrical discharge reactor for the degradation of methyl orange (MO) in the presence of granular activated carbon (GAC1V, GAC2V, and GAC3V) was investigated and the effect of these GACs in a combined treatment was evaluated, respectively. Under the experimental conditions used in this work, MO cannot be removed completely by GAC adsorption; the MO degradation is faster by pulse discharge, but satisfactory removal of chemical oxygen demand (COD) is never achieved. The MO degradation can be increased and COD can be removed effectively in the combined treatment through both the adsorption and the catalysis of GAC. The synergy intensity value indicates that a high correlation exists between the catalytic effect of GACs and the number of basic groups on their surface. Boehm titration and FTIR studies indicate that both acidic and basic groups on the GAC surface can be increased except that basic groups of GAC2V are slightly decreased by this process. This process can also slightly decrease their surface area and micropore and macropore volume. Furthermore, the virgin and saturated GAC samples can both be regenerated in situ after repeated use.

Pilot study of the removal of THMs, HAAs and DOC from drinking water by GAC adsorption

The objective of this pilot study was to evaluate the performance of a GAC postfilter-adsorber for the removal from the drinking water of Athens, Greece, of the two main groups of chlorination by-products, trihalomethanes (THMs) and haloacetic acids (HAAs), as well as of dissolved organic carbon (DOC). The analyses performed during the whole operation period (638 days) showed that the GAC breakthrough capacity for DOC was much higher than the capacity for total HAAs, which was higher than that for total THMs. The removal of THMs and the most part of the removal of HAAs and DOC should be attributed to adsorption by GAC, while that of a smaller part of HAAs and DOC may be attributed to biodegradation in the adsorber bed, where dechlorination, caused catalytically by the carbon surface, favoured microbial growth. Additionally, the GAC postfilter-adsorber showed a much higher adsorption efficiency than a GAC filter-adsorber, due to the smaller size of the carbon and the lower hydraulic loading rate. Also, observed desorption incidents of THMs (mainly) and HAAs, especially during the postfilteradsorber operation, were favoured by the same factors. Formation of THMs within the GAC bed was also indicated by the mass balance of total THMs during the whole cycle.

The treatment of algae-laden raw water with compact flofilter of dissolved air flotation and GAC deep bed filtration

Compact flofilter of dissolved air flotation and GAC deep bed filtration is a good integrated procedure, having the following characteristics: flotation and filtration are integrated in one tank, the flotation unit is above the filtration unit, filtration is GAC deep bed, and conventional and advanced treatments are integrated in one tank. During the treatment of algae-laden raw water with compact flofilter of dissolved air flotation and GAC deep bed filtration, the general performance was good: the outlet algae-count was 1.21×105–1.26×106 cell/l, the average removal of algae was 95.4%, the outlet chl-a was 0.68 μg/l, the removal of chl-a was 92.2%, the outlet turbidity was 0.16–0.20 NTU, the outlet had no odor, the outlet color was 3, the removal of color was 86.4%, the outlet Al-residual was 0.011 mg/l. Good removal of organics can be achieved: the average removal of UV254 was 54.3%, the outlet UV254 was 0.016–0.018 cm−1, the removal of DOC was 29.6%, the outlet DOC was 1.608 mg/l, the removal of BDOC was 42.6%, the outlet BDOC was 0.120 mg/l, the removal of AOC was 72.2%, the outlet AOC was 52 μg/l. Filter run period and UFRV were 36 h and 504 m3/m2. The results show that flofilter is a good alternative process for conventional treatment plus GAC adsorption.

NDMA Treatment by Sequential GAC Adsorption and Fenton-Driven Destruction

N-nitrosodimethylamine (NDMA) is a highly toxic environmental contaminant that was first detected in groundwater tainted by rocket fuel manufacturing wastes. NDMA is also a by-product of certain industrial processes including the chlorination of treated water and wastewater. Water treatment by carbon adsorption is costly because NDMA partitions only sparingly to carbon and frequent carbon replacement or regeneration is required. If activated carbon could be regenerated cheaply and quickly in place, NDMA adsorption on carbon, an easily implemented technology, could become attractive. In this study, the feasibility of adsorbing NDMA onto carbon followed by in-place carbon regeneration using Fenton's reagent was assessed. Batch and column tests indicated that the concentration of sorbed NDMA can be lowered to nondetectable levels in hours using reasonable hydrogen peroxide and iron concentrations. Three-log destruction of sorbed NDMA loaded to 1.04 mg NDMA/g carbon was achieved in approximately 12 h. Results...