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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 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.