| Studies with various substituted, nonionized phenolic compounds showed that these could cause substantial membrane water flux drop even in dilute solutions (negligible osmotic pressure) and that the organics could significantly adsorb on a cross-linked aromatic polyamide membrane (FilmTec FT30-BW) during the RO process. Specifically, studies performed with several ortho-substituted phenolics indicated that the greater adsorbing organic caused a greater membrane water flux drop, in the order 2-aminophenol {dollar}>{dollar} 2-nitrophenol {dollar}>{dollar} 2-chlorophenol {dollar}>{dollar} 2-fluorophenol {dollar}>{dollar} phenol. Studies with selected chlorophenols, nitrophenols, and benzene dilute solutions found water flux drops in the order 2,4-dinitrophenol {dollar}>{dollar} 2,4,6-trichlorophenol {dollar}>{dollar} 2,4-dichlorophenol {dollar}>{dollar} 2-chlorophenol {dollar}>{dollar} 2-nitrophenol {dollar}>{dollar} benzene {dollar}>{dollar} phenol. These results indicated that both specific and non-specific interactions were possible. A non-specific interacting compound, benzene, caused smaller water flux drop ({dollar}<{dollar}8%) even though it was more highly adsorbed (2.91 {dollar}times{dollar} 10{dollar}sp{lcub}-6{rcub}{dollar} mol/cm{dollar}sp2{dollar}) compared to a specific-interacting compound such as 2,4,6-trichlorophenol which was adsorbed to a lesser extent (9.23 {dollar}times{dollar} 10{dollar}sp{lcub}-7{rcub}{dollar} mol/cm{dollar}sp2{dollar}) but caused substantially more water flux decline (almost 50%). It was proposed that the specific-interactions involve hydrogen bonding of the phenolics to the carbonyl groups of the polyamide membrane polymer, thus reducing the number of hydrophilic sites of the polymer and giving it a more hydrophobic character.; Fundamental transport models were developed based on the solution diffusion model and the finely-porous (diffusion/convection) model to include the effects of organic sorption and adsorption to describe membrane water flux and organic separation for a batch RO system; several adsorption rates were examined. The resulting systems of ordinary and partial differential equations were solved numerically using the routine LSODE and the NAG Fortran Library routine D03PJF. The steady state and unsteady state models formulated were able to describe water flux, rejection, and feed concentration with water recovery reasonably well for the organics studied. However, it was found that some of the transport parameters were concentration dependent.; Analysis of the FT30-BW membrane by X-ray photoelectron spectroscopy (XPS) was utilized to determine membrane composition, and XPS with argon ion sputtering (etching) allowed estimation of the membrane barrier layer thickness. Attenuated total reflectance infrared spectroscopy (ATR-IR) was used to examine the membrane functional groups. These characterization techniques were also used to analyze a membrane containing an adsorbed organic compound. |
