Development of a method to measure transparent exopolymer particles (TEP) : fresh and saline water applications

Transparent exopolymer particles (TEP), an abundant form of acidic polysaccharide in surface water, have been implicated as one of the main causes of organic fouling of ultrafiltration systems and biological fouling of reverse osmosis system. However, quantifying and monitoring these substances have only been done extensively in limnology and oceanography. Latest modifications of the method have been proposed to monitor TEP in integrated membrane systems, but several aspects of the procedure still need to be verified. This study aims to take a critical look of the existing and modified method of measuring TEP for fresh and saline water applications. Most of the work focused on checking the existing protocol developed by Passow and Alldredge (1995) plus some of the modifications introduced by Villacorte et al. (2009b). The latest modified method includes filtration of water samples through polycarbonate filters (0.4 and 0.05 æm) to retain particulate (>0.4æm) and colloidal (0.05-0.4æm) TEP. The TEP retained on the filters are stained with Alcian Blue, rinsed with ultra-pure water, dissolved in acid and then absorbance is measured at 787nm. Based on the absorbance, the relative concentration of TEP is calculated in terms of abs/cm/L. The current procedures for preparation of Alcian blue (AB) dye solution were analysed. It was found that mixing the dye solution for 18 hours at 1000 rpm can improve the solubility of the dye. Pre-filtration of dye solution with smaller pore-size polycarbonate filters was possible through 0.05um (52.2 % removal) and 0.03um (74.4 % removal) polycarbonate filters but was not possible through 0.015um filters (98.5 % removal). Pre-filtration through 0.05um filters was eventually adopted since filtration through 0.03um filters were very prone to leaking. Coagulation of stored dye solution was also investigated but no significant indication that the dye solution had coagulated during 4 weeks of storage (dark at 4oC). The wavelength of the maximum absorbance signal of Alcian blue solutions were determined by scanning the absorbance signals at 200-900nm wavelengths. The maximum absorbance signal for the colorimetric determination of AB 8GX in acetic acid solution was at 610 nm wavelength while the maximum signal was observed at 788nm for Alcian blue dissolved in sulfuric acid solution.The selectivity of Alcian blue staining was investigated at different solution pH. At solution pH 2.5, AB 8GX specifically stained acidic polysaccharides while staining was minimal for neutral polysaccharides and protein, an indication that this dye is reliable for TEP staining. Blank measurements with ultra-pure water and artificial seawater revealed that salinity have a significant effect to Alcian blue staining. This effect was verified by tests using synthetic TEP solution (alginate) and actual seawater samples