Measurement of transparent alcian blue-stainable materials in freshwater by a centrifugation-based method

Transparent exopolymer particles (TEP) are particularly abundant in diverse aqueous environments and regarded as a main contributor to biofilm and membrane biofouling. In this study, we optimized a centrifugation-based approach to analyze Alcian blue-stainable materials (ABSM), which cover TEP and acidic polysaccharide-related substances, for reservoirs in Taiwan. Stability of the dye in terms of time and acidic conditioning was firstly monitored intensively at pH 2.5 and 4.0, with and without stirring. Absorbance of dye-reacted solutions of the reference materials (xanthan gum) and natural ABSM sampled from reservoirs were both examined under different relative centrifugal forces (RCF). Separation efficiency of complexes generated between Alcian blue and the targeting materials under broad range of RCFs (from 1,089 to 34,957 × G) was further assessed based on particle hydrodynamic size distributions, which then provided an insight of their fates that former methods were not addressed. Our results showed centrifugation at high RCFs (higher than 12,096 ×G) was effective to separate these complexes comparing with previous studies only conducted at lower RCFs. Application of the proposed method for five freshwater samples revealed notable high concentrations of Alcian blue-stainable dissolved fraction that could be a critical factor in developing feasible antifouling strategies for membranes used in water treatment.