Powdered Activated Carbon Concentration Research Articles

Adsorptive removal of chromium (VI) from aqueous solution over powdered activated carbon: Optimisation through response surface methodology

This paper investigates the adsorptive removal of Cr (VI) from aqueous solution over commercial powdered activated carbon (PAC) and carries optimisation of removal efficiency for the process using response surface methodology (RSM). The effects of different parameters such as pH, initial Cr (VI) concentration, adsorbent dose, contact time and temperature on adsorption were studied to find the best operating conditions. This study showed that when initial concentration was 50 ppm, 100% Cr (VI) removal was possible with pH 2 and 2 g L −1 PAC concentration. Different adsorption kinetic models and isotherms were compared respectively with the proposed kinetic model based on liquid phase adsorbate concentration and the developed new three-parameter isotherm. The new isotherm supported the experimental results with a better accuracy. The main process parameters considered for optimisation were pH, adsorbent dose and adsorption time. The experimental was designed according to central composite rotatable design (CCRD) and second order regression model was developed for regression analysis and ANOVA study. The optimum pH, PAC dose and time were found to be 2.32, 1.79 g L −1 and 25.76 min. Pareto analysis established that PAC dose was the most influential parameter.

Simultaneous activated carbon adsorption within a membrane bioreactor for an enhanced micropollutant removal

Significant adsorption of sulfamethoxazole and carbamazepine to powdered activated carbon (PAC) was confirmed by a series of adsorption tests. In contrast, adsorption of these micropollutants to the sludge was negligible. The removal of these compounds in membrane bioreactor (MBR) was dependent on their hydrophobicity and loading as well as the PAC dosage. Sulfamethoxazole exhibited better removal rate during operation under no or low (0.1 g/L) PAC dosage. When the PAC concentration in MBR was raised to 1.0 g/L, a sustainable and significantly improved performance in the removal of both compounds was observed – the removal efficiencies of sulfamethoxazole and carbamazepine increased to 82 ± 11% and 92 ± 15% from the levels of 64 ± 7%, and negligible removal, respectively. The higher removal efficiency of carbamazepine at high (1.0 g/L) PAC dosage could be attributed to the fact that carbamazepine is relatively more hydrophobic than sulfmethoxazole, which subsequently resulted in its higher adsorption affinity toward PAC.

Effects of combining biological treatment and activated carbon on hexavalent chromium reduction

The objectives of the present work were: (a) to analyze the Cr(VI) removal by combining activated sludge (AS) with powdered activated carbon (PAC), (b) to analyze the effect of PAC and Cr(VI) on the growth kinetics of activated sludge, and (c) to determine if the combined method (AS-PAC) for Cr(VI) removal can be considered additive or synergistic with respect to the individual processes. Chromate removal was improved by increasing PAC concentrations in both PAC and AS-PAC systems. Cr(VI) removal using the AS-PAC system was higher than using AS or PAC. The increase of Cr(VI) caused longer lag phase and lower observed specific growth rate (μ(obs)), biomass yield (Y(X/S)), and specific growth substrate consumption rate (q(S)) of activated sludge; additionally, PAC did not enhance the growth kinetic parameters (μ(obs), Y(X/S), q(S)). Cr(VI) reduction in AS-PAC system was the result of the additive effect of each individual Cr(VI) removal process.

Hybrid membrane process: Performance evaluation of biological PAC

This study investigated the use of biological powdered activated carbon (PAC) for the removal of natural organic matter (NOM) and ammonia from drinking water. The impact of solids retention time (SRT), hydraulic retention time (HRT), PAC diameter and PAC concentration on the process efficiency was evaluated. Five bioreactors were filled with a slurry using two PAC concentrations (5 or 25 g l−1), two PAC mean diameters (25 or 200 μm) and two SRTs (30 or 100–160 days). The bioreactors were operated during 161 days using post-ozonated water as influent. It was determined that the PAC concentration in the bioreactors was a key parameter for the improvement of biological removal. The higher PAC concentration (25 g l−1) was more efficient for the removal of ammonia, dissolved organic carbon (DOC) and biodegradable dissolved organic carbon (BDOC). Full nitrification was observed after 90 days in bioreactors with 25 g l− of PAC. The PAC diameter (25 vs. 200 μm) did not significantly influence BDOC, DOC and N-NH4 removals under stable conditions, although nitrification was initiated faster using a 25-μm diameter PAC. Increasing HRT from 15 to 30 minutes improved NOM and ammonia removals. Reducing SRT from 100–161 to 30 days improved DOC removals but reduced BDOC and ammonia removals. The overall performances observed during this study demonstrate the efficiency of biological PAC. Its combination with ultrafiltration in a hybrid membrane process appears promising but the feasibility from an operational standpoint still has to be demonstrated

Mechanisms of Fouling Control in Membrane Bioreactors by the Addition of Powdered Activated Carbon

This paper describes the experiments and observations that examine the mechanisms by which the addition of powdered activated carbon (PAC), in the form of biologically activated carbon (BAC), improves the filtration performance of a submerged membrane bioreactor (MBR). The membrane performance was observed to increase significantly with steady state PAC concentration. It is necessary to steadily replenish the PAC, to match that which is lost in sludge wastage. The enhancement mechanisms identified are, first, the role of PAC as an adsorbent of organics and planktonic bacteria, second, the effect of PAC as a scouring agent that limits foulant deposition, and third, the effect of the combined adsorption and biodegradation of BAC on the foulant components. The effectiveness of each mechanism in decreasing the fouling rate has been carefully evaluated. All three mechanisms play a role and the most significant appears to be the combined adsorption and biodegradation effect. The properties and filtration characteristics of activated sludge, with and without BAC have been measured and compared in both short-term tests and long-term continuous operation runs. The results of the short-term (cross flow mode) tests are in qualitative agreement with long-term performance.

Treatment of reactive dye solutions by physicochemical combined process

Color and turbidity removal from solutions of two reactive dyes: brilliant blue Levafix EBRA and gold yellow Levafix EG were studied. Coagulation–flocculation by polyaluminium hydroxide (PAH) and bentonite, followed by adsorption on powdered activated carbon (PAC) techniques were used. Optimal parameters of coagulation-flocculation (jar tests) and adsorption (temperature, pH, contact time and PAC concentration) were determined under optimal conditions for maximal dye elimination. 99.89% and 99.02% of color removal were obtained from 100 mg/L of dye solutions, respectively. Bentonite and aluminum used concentrations were 0.50 g/L and 27.6 mg/L (blue EBRA); also 0.37 g/L and 15.0 mg/L (yellow EG), coupled with 1.0 g/L of PAC for each dye. At suitable conditions this combined process was able to efficiently remove color from solutions containing reactive dyes and produce easily settle-able sludge, using moderate amounts of reagents, and thereby the low-cost of treatment.

Dynamic response of combined activated sludge-powdered activated carbon batch systems

The objective of this study was to evaluate the effect of powdered activated carbon (PAC) on the growth kinetics of activated sludge; in addition, a kinetic model for this system was developed. Adsorption kinetic experiments of the growth substrate (cheese whey) in the absence of activated sludge were carried out in conical flasks (20 °C, pH 7). Substrate adsorption attained the equilibrium within the first hour. The Langmuir adsorption equation adequately fitted the specific adsorption capacity ( q C) as a function of the soluble COD (COD S). Activated sludge batch growth experiments in the presence of different PAC concentrations were also performed. Specific growth rate ( μ obs) and specific oxygen uptake rate ( q O 2 ) decreased as PAC concentration increased; however, stoichiometric coefficients Y X/S and Y O/S were almost constant. A mathematical model was developed to represent the effect of PAC on the microbial growth kinetics. The model combined biochemical processes (biomass growth, substrate consumption and product generation) with the adsorption kinetics of the substrate onto PAC. A good agreement between the proposed model and the experimental data was obtained. Simulations show that PAC acts as a buffer of substrate, yielding slower responses to changes of the substrate concentration.

Membrane hybrid processes for pretreatment before seawater reverse osmosis desalination

The objective of this work is to study at lab-scale the efficiency of a hybrid process coupling ultrafiltration (UF) and adsorption as a pretreatment before seawater reverse osmosis desalination (SWRO). Powdered activated carbon (PAC) and bentonite were used as adsorbents. Actual seawater from Mediterranean Sea was filtered by regenerated cellulose membrane of molecular weight cut-off 30 kDa. The PAC addition allows a decrease of UF fouling rate and an increase of the natural organic matter (NOM) removal, especially for a PAC concentration of 200 mg L-1. An increase of contact time between PAC and seawater induces a reduction of fouling rate. When the contact time increases, the contribution to NOM removal due to PAC adsorption becomes more signifi cant compared to that due to UF alone. Concerning studies with bentonite, the UF fouling rate depends on the bentonite concentration. Addition of more than 500 mg L-1 bentonite can decrease the fouling rate in comparison to ultrafiltration without bentonite. Bu...

Equilibrium and kinetics study on the adsorption of perfluorooctanoic acid from aqueous solution onto powdered activated carbon

Powdered activated carbon (PAC) was applied to remove perfluorooctanoic acid (PFOA) from the aqueous PFOA solution in this study. Contact time, adsorbent dose and temperature were analyzed as the effect factors in the adsorption reaction. The contact time of maximum PFOA uptake was around 1 h while the sorption removal efficiency increased with the PAC concentrations. And the process of adsorption increased from 303 K to 313 K and then decreased from 313 K to 323 K. Among four applied models, the experimental isotherm data were discovered to follow Langmuir isotherm model more closely. Thermodynamically, adsorption was endothermic because enthalpy, entropy and Gibbs constants were 198.5 kJ/mol, 0.709 kJ/mol/K and negative, respectively, which also indicated that the adsorption process was spontaneous and feasible. From kinetic analysis, the adsorption was suggested to be pseudo-second-order model. The adsorption of PFOA on the PAC was mainly controlled by particle diffusion.

Nickel Removal from Waters Using a Surfactant-Enhanced Hybrid Powdered Activated Carbon/Microfiltration Process. II. The Influence of Process Variables

This study focused on the removal of nickel ions from aqueous solution using a surfactant-enhanced (SE) powdered activated carbon (PAC)/microfiltration (MF) hybrid membrane process. The main objective of the research is to investigate the technical performance of the process under the influences of all relevant process variables namely process time, recycling time, pH, temperature, PAC concentration, surfactant concentration, nickel concentration, cross-flow velocity, and transmembrane pressure, thus to reveal its applicability to water problems involved in heavy metal pollution. The concentrations of PAC, surfactant, metal, and H+ ion were determined as significant process stream variables, while transmembrane pressure and temperature came into prominence as significant operating variables. ANOVA calculations indicated that the total influences of these six variables on process performance realized in a range of about 93−98%. Nickel concentration and PAC amount in the feed were established as the most influential variables for nickel rejection, and surfactant rejection and permeate flux, respectively. The increase of PAC from 0.1 to 4 g/L led to a flux decline of about 60%. The most critical parameter for process performance was the mass ratio of PAC to surfactant (PAC/surfactant) per unit mass of metal removed. The process which may be effectively operated in continuous cross-flow filtration mode within a short filtration time of 30 min has crucial advantages compared to high pressure driven membrane processes and offers a promising alternative to remove heavy metal pollutants from drinking waters and metal bearing wastewaters.

Effect of activated carbon on BOD and COD removal in a dissolved air flotation unit treating refinery wastewater

The effects of powdered activated carbon (PAC) on the performance of a pilot-scale laboratory dissolved air flotation (DAF) unit were investigated. Refinery wastewater of different pollutant concentrations was treated and the effects of different operating parameters on the removal efficiency of pollutants in terms of biological oxygen demand (BOD) and chemical oxygen demand (COD) were studied. A circular pilot-scale DAF unit with conical bottom was used and the operating parameters investigated included flow rate, recycle ratio, saturation pressure and the concentration of PAC added. It was found that for dosages of activated carbon in the range of 50–150 mg/l, the removal efficiencies for BOD increased from 27–70% to 76–94% while those for COD increased from 16–64% to 72–92.5% for inlet values of 45–95 mg/l and 110–200 mg/l for BOD and COD respectively. Such findings represent considerable improvement in the performance of the dissolved air flotation unit.

Determination of bromacil transport as a function of water and carbon content in soils

This study was conducted to determine the significance of bromacil transport as a function of water and carbon content in soils and to explore the implications of neglecting sorption when making assessments of travel time of bromacil through the vadose zone. Equilibrium batch sorption tests were performed for loamy sand and sandy soil added with four different levels of powdered activated carbon (PAC) content (0, 0.01, 0.05, and 0.1%). Column experiments were also conducted at various water and carbon contents under steady-state flow conditions. The first set of column experiments was conducted in loamy sand containing 1.5% organic carbon under three different water contents (0.23, 0.32, and 0.41) to measure breakthrough curves (BTCs) of bromide and bromacil injected as a square pulse. In the second set of column experiments, BTCs of bromide and bromacil injected as a front were measured in saturated sandy columns at the four different PAC levels given above. Column breakthrough data were analyzed with both equilibrium and nonequilibrium (two-site) convection-dispersion equation (CDE) models to determine transport and sorption parameters under various water and carbon contents. Analysis with batch data indicated that neglect of the partition-related term in the calculation of solute velocity may lead to erroneous estimation of travel time of bromacil, i.e. an overestimation of the solute velocity by a factor of R. The column experiments showed that arrival time of the bromacil peak was larger than that of the bromide peak in soils, indicating that transport of bromacil was retarded relative to bromide in the observed conditions. Extent of bromacil retardation (R) increased with decreasing water content and increasing PAC content, supporting the importance of retardation in the estimation of travel time of bromacil even at small amounts of organic carbon for soils with lower water content.

Powdered activated carbon and membrane bioreactors (MBRPAC) for tannery wastewater treatment: long term effect on biological and filtration process performances

This paper describes the findings of an experimental investigation carried out on a pilot scale membrane bioreactor (MBR) with the addition of powdered activated carbon (PAC) to analyze improvements in effluent quality and in the filtration process. The results refer to a pilot plant monitoring stretched over a period of 594 days: 380 without PAC, 123 with a PAC concentration of 1.5 g/L and 91 with 3 g/L. The sludge residence time and hydraulic retention time were maintained between 30 and 90 days and 50 and 100 hours respectively. Improvements in COD removal were found to be low, but not negligible, and greater than the PAC adsorption effect alone. COD removal stability appeared to increase as PAC concentration increased. No effects were observed on the nitrification processes. The filtration process was evaluated in terms of sludge filterability, fouling rate and fouling reversibility. The fouling rate decreased with an increasing PAC concentration and showed complete reversibility both in presence and in absence of PAC.

Desorption Kinetics of Benzene in a Sandy Soil in the Presence of Powdered Activated Carbon

Desorption kinetics of benzene was investigated with a modified biphasic desorption model in a sandy soil with five different powdered activated carbon (PAC) contents (0, 1, 2, 5, 10% w/w) as sorbents. Sorption experiments followed by series dilution desorption were conducted for each sorbent. Desorption of benzene was successively performed at two stages using deionized water and hexane. Modeling was performed on both desorption isotherm and desorption rate for water-induced desorption to elucidate the presence of sorption-desorption hysteresis and biphasic desorption and if present to quantify the desorption-resistant fraction (q (irr)) and labile fraction (F) of desorption site responsible for rapid process. Desorption isotherms revealed that sorption-desorption exhibited a severe hysteresis with a significant fraction of benzene being irreversibly adsorbed onto both pure sand and PAC, and that desorption-resistant fraction (q (irr)) increased with PAC content. Desorption kinetic modeling showed that desorption of benzene was biphasic with much higher (4-40 times) rate constant for rapid process (k (1)) than that for slow process (k (2)), and that the difference in the rate constant increased with PAC content. The labile fraction (F) of desorption site showed a decreasing tendency with PAC. The experimental results would provide valuable information on remediation methods for soils and groundwater contaminated with BTEX.

Drinking water production by ultrafiltration of Songhuajiang River with PAC adsorption

In recent years, membrane ultrafiltration (UF) of surface water for drinking water treatment has become a more attractive technology worldwide as a possible alternative treatment to conventional clarification. To evaluate the performance of ultrafiltration membranes for treatment of surface water in North China, a 48-m2 low pressure hollow fiber membrane ultrafiltration pilot plant was constructed. Ultrafiltration was operated in cross-flow and with powdered activated carbon (PAC) adsorption. Turbidity was almost completely removed to less than 0.2 NTU (below Chinese standard 1 NTU). It was found that PAC addition enhanced organic matter removal. The combined process of PAC/UF allowed to 41% removal of CODMn, 46% removal of DOC and 57% decrease in UV254 absorbance. The elimination of particles, from average 12000/ml in the raw water to approximately 15/ml in the permeated, was observed. When PAC concentration was below 30 mg/L, backwashing could recovery the membrane flux with backwash interval/backwashing duration of 1/30.

Application of microfiltration systems coupled with powdered activated carbon to river water treatment

A bench scale submerged microfiltration system coupled with high concentration of PAC (powdered activated carbon) was applied in order to purify a river water containing secondary effluent. The system was operated with four different modes: Run-1, -2, -3 and -4. The PAC concentration was set at 0, 4 and 40 g/L with same filtration rate of 1.0 m/d (42 L/m 2/h) which correspond to Run-1, -2 and -3. In Run-4, the filtration rate was set at 0.5 m/d (21 L/m 2/h) with PAC concentration of 40 g/L. The effluent turbidity showed below 0.1 NTU for all runs, and the removal rates more than 90% were observed. As for TOC removal, almost no removal of TOC was observed in Run-1 while the higher removal rates were obtained with the higher dosage of powdered activated carbon. Run-3 and 4 with PAC dose of 40 g/L showed the removal of 85% regardless of the filtration rates. Removal of UV254 was similar to that of TOC: removal of 13% at Run-1 and 90% at Run-3 and -4. As for the filtration efficiency, an average filtration time for TMP to reach 60 kPa was checked for each runs. The filtration time of around 5 days was observed in Run-1 and Run-2, 2 days in Run-3 and 60 days in Run-4. According to the results, the effluent water quality got better with higher dose of PAC and the filtration efficiency was enhanced with higher dose of PAC and lower filtration time.

Removal of Toluene Vapor with Dispersed Activated Carbon

This work considers the mechanisms of mass transfer in a process of dispersed sorbent injection. During experiments, an air supply was dosed with toluene vapor, at partial pressures between 4 and 15 Pa. Powdered activated carbon (PAC) was added to remove the toluene from the air, and the resulting mixture was passed through a 3-m-long, tubular, aluminum test section. Toluene concentrations were measured at seven axial locations within the test section. Comparing the measurements with mathematical models indicated the importance of adsorption kinetics. At reduced toluene inlet concentrations the PAC removed a slightly bigger fraction of toluene from the air stream. This fraction increased with PAC concentration. The effect on removal of varying the air temperature between 25 and 85°C was small. Alternative models incorporating either pore diffusion or surface diffusion were fitted to the results. The quality of the fits was fair only, but sufficient to show that the pore diffusivity that gave the best fit was far larger than would be expected from the Knudsen diffusivity in the pores. That is, surface diffusion was an important part of the intraparticle mass transfer.

Development of a microfilter separation system coupled with a high dose of powdered activated carbon for advanced water treatment

Filtration experiments using a bench-scale immersed membrane separation system combined with PAC (powdered activated carbon) were conducted in order to investigate the effects of PAC on the efficiencies of operation and treatment and to evaluate the performance of the system. The experiments were carried out under such operation conditions as a filtration rate of 1 m/d (or 42 l/m 2/h), water temperature of 20–25°C, and PAC dose of 0 g/l (PAC-0), 10 g/l (PAC-10) and 40 g/l (PAC-40). Synthetic secondary wastewater was used as a raw water; the influent concentrations of TOC (total organic carbon), UV254 (UV absorbance at 254 nm) and NH 4 +-N (ammonia nitrogen) were 9.09 mg/l, 16.4 1/m and 5.0 mg/l, respectively. TOC removal of 51, 74 and 83%, and UV254 removal of 63, 89 and 95% were obtained for PAC-0, PAC-10 and PAC-40, respectively. Ammonia oxidation was observed only for PAC-40, which started to occur on the 20th d from the operation and was completed in 25 d. Average filtration times up to TMP (transmembrane pressure) of 70 kPa were 32, 61 and 97 h for PAC-0, PAC-10 and PAC-40, respectively. The amounts of organic compounds attached to the membrane pore were 380, 280 and 64 mg of TOC per 1 m 2 of membrane surface area for PAC-0, PAC-10 and PAC-40, respectively. This study found that the filtrate quality and the performance efficacy were enhanced with the increase in the concentration of PAC introduced into the filtration system.

Adsorption of dark coloured compounds from peach pulp by using powdered-activated carbon

The potential of powdered-activated carbon (PAC) for the adsorption of dark coloured compounds from peach pulp was studied at different PAC concentrations (0.5, 1, 3, 5 kg PAC per m 3 peach pulp) and for the temperature range of 20–60 °C. The isotherm studies were carried out to evaluate the effect of adsorbent dosage, contact time and initial absorbance. For equilibrium adsorption curves, the Langmuir, Freundlich, Temkin and Frumkin models were attempted by using the absorbance data at 420 nm and model parameters were obtained for different temperatures. The results clearly showed that the adsorption data of dark coloured compounds present in peach pulp onto PAC fits well to the Langmuir and Temkin models having correlation coefficients higher than 0.90 at all temperatures. Five kinetic models including the first-order equation, second-order equation, the modified Freundlich, the pore diffusion model and the Elovich equation were tested to follow the adsorption processes. Results of the kinetic studies show that the adsorption reaction was well represented by the Elovich model. The activation energy of adsorption was found to be 13.79 kJ/mol. The low activation energy indicated that the adsorption reaction was also diffusion controlled.

Removal of trace organics from water using a pumped bed-membrane bioreactor with powdered activated carbon

A pumped bed-membrane bioreactor (PB-MBR) combining powdered activated carbon (PAC) adsorption with bacterial degradation was studied for the purification of tap water, spiked with 2 mg/l of phenanthrene, to sub-ppm levels. The feedwater was supplemented with nitrogen and phosphorous to reach a COD:N:P ratio of 100:10:1. PAC concentration was maintained at 5 g/l. Polyacrylonitrile (PAN) flat-sheet membranes of 250 and 1500 kDa MWCO were tested. The overall efficiency during long term operation was tested at different hydraulic conditions with intermittent biosolids wastage and high frequency-chemical cleaning (every 2–3 days) or without chemical cleaning and without sludge removal. With intermittent PAC dosage-high frequency chemical cleaning steady fluxes of 150–200 l/m 2 h were maintained. With no chemical cleaning-no solids wastage, steady fluxes of 22.5±3.8 and 28.8±4.8 l/m 2 h were achieved for the 250 and 1500 kDa membranes, respectively. An almost complete removal of phenanthrene was observed in all cases, regardless the type of membrane, operating protocols or hydraulic conditions applied (permeate concentration was consistently below 5 μg/l). The relatively high permeate fluxes and constant filterability observed are attributed to the turbulent flow regime and high PAC-slurry recirculation ratio generated.