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    Effect of presence of ions on surface characteristics of surfactant modified powdered activated carbon (PAC)
    (Elsevier, 2003) Basar, CA; Karagunduz, A; Keskinler, B; Cakici, A
    Modification of surface characteristics of solids using surfactants has practical implications in industrial and environmental applications. Extensive research has been conducted to explore the mechanism of surfactant sorption to different solid surfaces. However, a clear understanding yet to be found especially for heterogeneous surfaces in which pores and structure show local differences. The main objective of this study was to determine the effects of ions on the surface potential of surface modified activated carbon. In order to achieve the objective, anionic and cationic surfactants were selected and adsorptions of these surfactants to powdered activated carbon (PAC) were investigated. Then, zeta potential measurements were conducted for the surface modified PAC and finally, the effects of mono- and di-valent anions and cations on the zeta potentials of PAC surface were investigated. The results showed that even at very low cetyl trimethyl ammonium bromide (CTAB) concentrations charge reversal was observed and substantial increase was observed in zeta potential. However, linearalkyl benzene sulfonate (LABS) showed somewhat gradual decrease in zeta potential, reaching maximum when maximum sorption capacity was attained. Presence of anions in addition to CTAB effected the change of zeta potential. Similar effects were also observed for LABS modified PAC in the presence of mono- and di-valent cations. The change of zeta potential of with the valance of cations and anions were linear. (C) 2003 Elsevier Science B.V. All rights reserved.
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    Removal of CrO4 anions from waters using surfactant enhanced hybrid PAC/MF process
    (Elsevier, 2006) Basar, CA; Aydiner, C; Kara, S; Keskinler, B
    The removal of CrO42- anions from aqueous solution using surfactant added hybrid powdered activated carbon (PAC) and crossflow microfiltration (CFMF) process was performed. Experimental runs were studied at various amounts of cetyl trimethyl ammonium bromide (CTAB) as cationic surfactant, PAC as adsorbent and CrO42- ions in feed solution. CFMF unit was operated at constant values of the transmembrane pressure (150 kPa), crossflow velocity (1.18 m/s) and temperature (30 degrees C). Hybrid PAC/MF process performance was investigated in terms of CTAB and CrO42- rejections and, the flux decline. It was shown that the flux declined with time and the rejections varied for various properties of feed solution. CTAB and CrO42- rejections could be achieved as 91 and 97.2% at the conditions of 0.5 g PAC/L, 5 mM CTAB, 0.2 mM CrO42- and 120-min process time. It was found that over the critic micelle concentration (CMC), both CTAB and CrO42- rejections were in the higher values according to the values under the CMC. In addition, membrane blocking mechanisms were investigated to clarify the cake formation mechanism due to PAC. For all experimental conditions, the best results of blocking models obtained for cake filtration, intermediate blocking and standard pore blocking, respectively. It was understood that these blocking mechanisms occurred simultaneously on membrane surface in terms of high r(2) values. A cake layer formed on membrane surface (cake filtration). Pore entrance blocked partially due to particles bridging over pore opening (intermediate blocking). Free CTAB aggregates with or without CrO42- anions, entered into the membrane pores, caused to a layer formation by adsorption and entrapment on the membrane's pore walls (standard pore blocking). Besides, cake resistance (R-c), specific cake resistance (alpha), modified fouling index (MFI) and total dried solid mass of cake per unit membrane area (omega) were also determined to comprehend the reasons of clogging within the membrane and on the surface due to both CTAB aggregates and PAC, respectively. Membrane fouling (MFI) increased with the increasing of PAC, CTAB and CrO42- amounts in feed solution. As a result, flux, rejections and fouling in membrane were shown as a dynamic function of PAC, CTAB and CrO42- as the properties of the feed solution. (c) 2005 Elsevier B.V. All rights reserved.
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    Removal of surfactants by powered activated carbon and microfiltration
    (Pergamon-Elsevier Science Ltd, 2004) Basar, CA; Karagunduz, A; Cakici, A; Keskinler, B
    Direct and indirect releases of large quantities of surfactants to the environment may result in serious health and environmental problems. Therefore, surfactants should be removed from water before release to the environment or delivery for public use. Using powdered activated carbon (PAC) as adsorbent and separating particles with a membrane may be an effective technique to remove surfactants. In this study, the removal of surfactants by microfiltration and PAC was investigated and the influences of the operating parameters on the effectiveness on microfiltration were determined. An anionic (LABS) and a cationic surfactant (CTAB) were selected for the experiments. A series of batch experiments were performed to determine the sorption isotherms of surfactants to PAC. Then microfiltration experiments were carried out. The results showed that formation of secondary membrane on the surface and, within the pores of the membrane, increased the retention of surfactants significantly. Increase in transmembrane pressure and pore size of the membrane decreased the rejection rates, but increase in cross-flow velocity increased the rejection rate. Temperature had no apparent affect on the efficiency of surfactant removal. Presence of electrolyte had different effects on CTAB and LABS. The rejection rates of CTAB significantly increased when the concentration of NaCl increased; however, a slight decrease was observed in the rejection rate of LABS at the same conditions. (C) 2004 Elsevier Ltd. All rights reserved.