Powdered Activated Carbon Dose Research Articles

Optimizing enhanced coagulation with PAC: A case study

Enhanced coagulation plus PAC achieves required NOM removals at minimum cost.Enhanced coagulation can remove only a finite fraction of the natural organic matter (NOM) in water. Supplementing enhanced coagulation with powdered activated carbon (PAC) increases the removal of NOM and disinfection by‐product (DBP) precursors. The removal of total organic carbon (TOC) and DBP precursors from Colorado River water was evaluated in an experimental matrix of jar tests using four ferric chloride dosages and four PAC dosages. On the basis of the chemical dosages used, the cost of each combination of coagulant and PAC addition was estimated. For a given TOC removal goal, a particular combination of ferric chloride and PAC dosages resulted in the lowest chemical costs. The analysis also indicated that this same dosage combination would produce the least sludge at the water treatment plant. This study shows that the combination of a chemical coagulant and PAC can be more cost‐effective than a chemical coagulant alone for meeting the requirements of Stage 1 of the Disinfectants/DBP (D/DBP) Rule. In addition, the combination of a chemical coagulant and PAC may be a cost‐effective alternative to granular activated carbon for meeting the requirements of Stage 2 of the D/DBP Rule.

Toxicity screening, assessment, and reduction in an industrial wastewater treatment plant

The toxicity reduction capacity of a central wastewater treatment plant (CWTP) receiving 21 000 metric ton/d of industrial wastewater was thoroughly investigated using a whole‐effluent approach with a Microtox™ Toxicity Analyzer System. It was found that the highly toxic wastewater introduced into the CWTP was almost completely detoxified during secondary treatment with a recycled activated‐sludge system. The removal mechanism was shown to be a combination of adsorption, volatilization, and biodegradation, the first two being more clear than the other. Fractionation of toxic streams within the treatment plant provided valuable information about the general characteristics of the toxicity‐causing agents in the wastewater, namely that they were primarily composed of filterable and dissolved solids, volatile organics, and nitrogenous compounds. A toxicity reduction evaluation survey within the plant revealed that the observed Microtox™ toxicity could be readily removed by treatment with powdered activated carbon (PAC) and mechanical aeration at properly selected operating conditions. The correlation between toxicity removal and the applied PAC dose was found to be exponential and asymptotic to the ultimate effective toxicant concentration of the effluent. Reductions in chemical oxygen demand and dissolved organic carbon during PAC treatment were also related to the applied PAC dose and the initial concentrations of the parameter. Removal of volatile components of toxicity by aeration was correlated with detention time by a power function.

Predicting the Capacity of Powdered Activated Carbon for Trace Organic Compounds in Natural Waters

The purpose of this research was to develop a simple method for predicting the powdered activated carbon (PAC) capacity for micropollutants in natural water. The herbicide atrazine and the odor-causing compound 2-methyl- isoborneol served as target compounds. Isotherm data from experiments conducted with a constant initial adsorbate concentration and varying adsorbent doses exhibited nonlinearity in both single- and multi-solute systems. However, at any given adsorbent dose, the PAC capacity for the micropollutant in multi-solute systems was directly proportional to the initial micropollutant concentration. Using the ideal adsorbed solution theory (IAST), an equation was derived that validated the experimentally observed direct proportionality between PAC capacity and initial micropollutant concentration at a given adsorbent dose. The results of this study show that the PAC dose to remove any amount of micropollutant from natural waters can be estimated without the use of mathematical models from a single...

Bromate ion removal by activated carbon

Bromate ion removal by powdered activated carbon (PAC) in batch mode and granular activated carbon (GAC) in continuous mode was evaluated under various operational conditions. For PAC, removal kinetics were found to be prohibitively slow, with high PAC doses required; removal improved with decreasing pH and decreasing natural organic matter. GAC was also influenced by these same water quality conditions, with an additional influence by empty bed contact time (EBCT). Bromate ion was found to be reduced to bromide ion and not all bromide in bromate was recovered supporting the theory that bromate reduction involves non-equilibrium sorption-reduction mechanisms. Both PAC and GAC results were found to be carbon-specific.

Removal of pesticides from surface waters by combined physicochemical processes. Part I: Dodine

The simultaneous action of powdered activated carbon and several coagulant agents on the removal of the fungicide dodine from spiked distilled water, was studied. As coagulants, ferric chloride (FeCl 3) and basic polyaluminium chlorosulfate ([Al(OH) xCl y(SO 4) z] n) were examined, using polyacrylamide, in certain cases, as coagulant aid (polyelectrolyte). The efficiency of dodine removal was investigated with respect to the added amount of powdered activated carbon (PAC), the pH value, as well as the type and dose of coagulant and polyelectrolyte. The experiments were performed applying the standard jar-test procedure. The initial concentration of dodine was 250 μg/L. At this concentration and pH range 5–8 it was found that a dose of 100 mg/L PAC was necessary to achieve more than 98% removal of dodine, whereas lower removal (91–93%) was obtained applying half the dose of PAC under the same conditions. However, when 10–100 mg/L FeCl 3 were simultaneously added with PAC, the removal efficiency increased to >98%, even with the half PAC dose.

Color removal from dye wastewaters by adsorption using powdered activated carbon: Mass transfer studies

AbstractColor removal from synthetic dye wastewater which typically emanates from the Taiwan textile industry has been studied using powdered activated carbon (PAC) as an adsorbent. The CIE colorimetric system has been used in the measurement of color for the treatment of disperse‐red‐60 dye wastewater. The effect of contact time, dye concentrations and PAC dosage on color and color removal has been investigated. A film‐pore double resistance diffusion model for mass transfer has also been used in this study to determine the effective diffusivity, Deff, for the adsorption of disperse‐red‐60 dye wastewater to PAC.

UF with pretreatment for removing DBP precursors

Combined UF–PAC treatment can be effective for DBP precursor removal, depending on the level of removal desired.Although ultrafiltration (UF) is an efficient disinfection process, it is relatively ineffective because of its high‐molecular‐weight cutoff for removing the natural organic matter that contributes to disinfection by‐product (DBP) formation. A pilot study was conducted to evaluate the efficacy of powdered activated carbon (PAC) as a UF pretreatment to provide enhanced removal of trihalomethane and haloacetic acid precursors. PAC addition did not impair the permeability of the UF membrane and, in one case, appeared to retard membrane fouling. DBP precursor removals increased with increasing PAC dosages. Because bromide was not removed by this treatment, changes in relative DBP speciation were observed after chlorination of the permeate from the UF–PAC process.

Enhanced removal of phenol and m‐cresol in PAC additional activated sludge system

Abstract The addition of powdered activated carbon (PAC) to activated sludge (AS) reaction units to enhance removal of specific toxic organic compounds such as phenol and m‐cresol using with synthetic wastewater was investigated in bench‐scale laboratory system. Adsorbability of test materials were studied along with selected commercial PAC to examine the adsorptive capacity of PAC without biological growth using a gyratory shaker assembly. Several tests were made to determine the removal efficiency of priority pollutants in PAC‐AS system. These tests indicated that the PAC‐AS system capable of reducing highly concentrated organic priority pollutants to below toxic threshold values. Results from steady‐state bioreactor studies showed that the PAC dose, sludge age and PAC concentration in activated sludge mixed liquor are important variables. Adsorption of nonbiodegradable organics by PAC seemed to be the main mechanisms of improved COD removal in the PAC‐AS system, the process increased the removal effici...

Treatment of Landfill Leachate by Crossflow Microfiltration and Ozonation

Abstract Laboratory scale experiments were conducted for the treatment of landfill leachate using crossflow microfiltration (CFMF) with periodic backflush as a declogging technique. Powdered activated carbon (PAC) was used as for pretreatment, and ozonation was used as posttreatment for CFMF. Single channel tubular ceramic membranes of 0.2 and 1.2 μm pore size were used in this study. The results showed that permeate flux increases with an increased dose of PAC added to the leachate. When membranes of different pore sizes were compared, the 0.2-μm membrane performed better than the 1.2-μm membrane, giving a higher flux as well as higher removal of color and COD. The optimum PAC dose for CFMF was found to be 30 g/L whereas the optimum value for the batch test was found to be 60 g/L.

Predicting and Verifying TOC Removal by PAC in Pilot‐Scale UF Systems

A modeling technique was developed to predict organics removal by powdered activated carbon (PAC) added as a pretreatment to hollow‐fiber ultrafiltration (UF). Model predictions were successfully verified for large‐ and small‐scale PAC‐UF pilot plants. Experiments were conducted using different water sources, PAC dosages, and backwashing frequencies. Natural organic matter in the water sources, represented by total organic carbon, was the target compound studied. The modeling procedure can be used in the design and evaluation of PAC‐UF systems.

Removal of 2,4,6-trichlorophenol and natural organic matter from water supplies using PAC in floc-blanket reactors

The objective of this study was to evaluate the addition of powdered activated carbon (PAC) to upflow floc-blanket reactors for the adsorption of natural and synthetic organic chemicals. A 15.5-1. bench-scale floc-blanket reactor was operated with PAC addition for the adsorption of 2,4,6-trichlorophenol (TCP) and natural organic matter from one groundwater and two surface waters under laboratory and field conditions, respectively. Influent TCP concentrations ranged from 21 to 415 μg/l. The PAC doses ranged from 2 to 12 mg/l. While the hydraulic residence time in the floc-blanket reactor varied from 15 to 30 min, the carbon residence time ranged from 9 to 34 h. This is due to the high solids concentration in the floc blanket, which ranged from 1200 to 8700 mg/l. Comparison between the extent of TCP adsorption through the floc-blanket reactor and the equilibrium adsorption isotherms of TCP on PAC showed that the maximum adsorption capacity of PAC for TCP was utilized in the reactor. However, this study showed that the maximum adsorptive capacity of the carbon in a continuous process is dependent on the influent adsorbate concentration. This was in agreement with isotherm studies conducted with varying initial TCP concentration. The maximum PAC adsorption capacity for natural organic matter was also achieved in the floc-blanket reactor.

Adsorption Study of Dye Wastewater with Powdered Activated Carbon

A study to determine the effectiveness of PAC on the removal of COD and colour from dye wastewater. Factors affecting treatment efficiency were investigated and included PAC particle sizes, initial dye concentration and contact time. The adsorption parameters for Langmuir, Freundlich and Dziubek′s isotherms were determined. Results indicated that a very short contact time of one hour was needed to reach equilibrium of adsorption. A COD (chemical oxygen demand) removal efficiency of 90 per cent for disperse‐red‐60 dye wastewater was obtained with PAC (powdered activated carbon). With PAC dosage of less than 15g/l the adsorption followed both Freundlich′s and Langmuir′s isotherms. The ultimate capacity of the adsorption increased with decreasing PAC particle sizes or the initial dye concentration. The mass transfer coefficient was determined in this study.

Pilot Testing the Haberer Process in the United States

Perhaps for the first time in the United States, the Haberer process was shown in a Shreveport, La., pilot unit to be capable of flocculating and removing solids from a turbid surface water (contact flocculation) and of simultaneously treating the water with powdered activated carbon (PAC) to remove soluble organic compounds. The overall reduction in trihalomethane formation potential was 63–66 percent when PAC was used in the system, but it is expected that even greater reductions could be achieved if either the type or the dosage of PAC was optimized.

Creep-fatigue interaction for 2.25 Cr1Mo steel under combined loadings: Kubo, K., Yagi, K., Kaneko, T. and Umezawa, O. J. Soc. Mater. Sci., Jpn. Dec. 1988 37, (423), 1429–1435 (in Japanese)

The application of powdered activated carbon (PAC) as an advanced wastewater treatment step for the removal of organic micropollutants (OMP) necessitates complete separation of the PAC particles, e.g. by coagulation. In this study, potential positive or negative indirect or direct effects of coagulation on the adsorption of OMPs onto PAC in treated wastewater were investigated. Although the concentration of dissolved organic matter (DOM) was significantly reduced by coagulation, the selective removal of mainly larger DOM components such as biopolymers and humic substances did not improve subsequent OMP adsorption onto PAC, demonstrating that coagulation has minor effects on DOM constituents that are relevant for direct competition or pore blocking. The combination of coagulation and adsorption yielded the sum of the individual removals, as adsorption predominantly affected smaller compounds. While the formation of flocs led to visible incorporation of PAC particles, no significant mass transfer limitations impeded the OMP adsorption. As a result, the dosing sequence of coagulant and PAC is not critical for efficient adsorption of OMPs onto PAC. The relationships between adsorptive OMP removal and corresponding reduction of UV absorption at 254 nm (UVA254) as a promising surrogate correlation for the real-time monitoring and PAC adjustment were affected by coagulation, leading to individual correlations depending on the water composition. Correcting for UVA254 reduction by coagulation produces adsorptive UVA254 removal, which correlates highly with OMP removal for different WWTP effluents and varying coagulant doses and can be applied in combined adsorption/coagulation processes to predict OMP removal and control PAC dosing.

Optimizing the Removal of Geosmin and 2‐Methylisoborneol by Powdered Activated Carbon

The purpose of this study was to determine the conditions under which removal of the taste‐ and odor‐causing compounds geosmin and 2‐methylisoborneol (MIB) by powdered activated carbon (PAC) was most efficient. It was observed that a PAC dosage as low as 5 mg/L could reduce commonly occurring concentrations of these organics (up to 20 ng/L) to acceptable levels. Chlorine and monochloramine residuals appeared to have an adverse effect on the adsorption of geosmin and MIB by PAC, as did the presence of background humic acid. Filtration rate and contact time did not significantly affect removal efficiency.

Optimizing the Removal of Geosmin and 2‐Methylisobomeol by Powdered Activated Carbon

The purpose of this study was to determine the conditions under which removal of the taste‐ and odor‐causing compounds geosmin and 2‐methylisoborneol (MIB) by powdered activated carbon (PAC) was most efficient. It was observed that a PAC dosage as low as 5 mg/L could reduce commonly occurring concentrations of these organics (up to 20 ng/L) to acceptable levels. Chlorine and monochloramine residuals appeared to have an adverse effect on the adsorption of geosmin and MIB by PAC, as did the presence of background humic acid. Filtration rate and contact time did not significantly affect removal efficiency.

Adsorption of Synthetic Organic Shock Loadings

A pilot plant designed to simulate conventional water treatment processes augmented by powdered activated carbon (PAC) and granular activated carbon (GAC) adsorption is operated to investigate the removal of combined shock loadings of isomers of trichloro‐ and tetrachlorobenzene, C‐46, and C‐56 present in the same influent matrix. Applications of each of the organic compounds are made as an increasing step function, with a cycle consisting of one series of four concentration steps (2,10,100, and 200 μg/L). In order to study desorption reactions, each step loading lasts 32 hours separated by a 24‐hour period during which no applications of the organic compounds are made. A total of three cycles are evaluated; the resulting data demonstrates that PAC dosages as high as 50 mg/L are not as effective as a GAC adsorption bed with an empty bed contact time of 10 minutes. The Freundlich isotherm is found to closely describe the equilibrium condition with correlation coefficients ranging from 0.948 to 0.986 for each of the compounds. Desorption of the organics from the upper layers of the GAC bed is observed as early as the first cycle of operation.

Treatment of a landfill leachate in powdered activated carbon enhanced sequencing batch bioreactors

AbstractAddition of powdered activated carbon (PAC) significantly improved treatment of a chemical waste landfill leachate in sequencing batch bioreactors (SBRs). Concentrations for many of the monitored halogenated organic compounds in the effluent were below their respective detection limits. Excellent treatment efficiency was achieved under a variety of operating conditions: wastewater composition, feed rate, hydraulic retention time, organic loading, PAC dosages, biomass and PAC concentrations in the bioreactors. The PAC‐SBR performance was unaffected when wastewater feeding was suspended during weekends and holidays. The PAC‐SBR treatment cost is much lower than either that of the conventional granular activated carbon adsorption technology or the two‐stage process of biodegradation and carbon treatment.