Evaluating membrane fouling potentials of dissolved organic matter in brackish water.

Isolating dissolved organic matter (DOM) is a preliminary step that improves the accuracy of its characterization. In this study, DOM in brackish water was clearly separated and evaluated by multiple characterization analyses. The sample was divided into three fractions by preparative high-performance liquid chromatography (preparative HPLC) according to molecular size. The homogeneity of each fraction was estimated by analytical size exclusion chromatography (SEC) and fluorescence excitation-emission matrix (FEEM). Pyrolysis gas chromatography-mass spectrometry (Py-GC/MS) and liquid chromatography-organic carbon detection (LC-OCD) were used to characterize the physicochemical properties of each fraction. Py-GC/MS revealed that Fraction 1 consisted of evenly distributed organic matter in order polysaccharides, proteins, polyhydroxy aromatics, lignins, and lipids. However, Fraction 2 was primarily composed of dominant lipids and low portion of proteins, and Fraction 3 was composed predominantly of lignins and lipids. The LC-OCD results showed that Fractions 1 and 2 had similar organic carbon (OC) compositions: a humic substance (ca. 37%), building blocks (ca. 10%), and neutrals (ca. 37%), whereas Fraction 3 contained a high proportion of neutrals (62%). In the fouling experiments, the distinct DOM characteristics in each fraction resulted in different declining flux behaviors, ranked as: Fraction 2 > Fraction 1 > Fraction 3.

Evaluation of fouling in nanofiltration for desalination using a resistance-in-series model and optical coherence tomography.

Resistance-in-series models have been applied to investigate fouling behavior. However, it is difficult to model the influence of morphology on fouling behavior because resistance is indirectly calculated from the water flux and transmembrane pressure. In this study, optical coherence tomography (OCT) was applied to evaluate the resistance of the fouling layer based on fouling morphology. Sodium alginate, humic acid, and bovine serum albumin (BSA) with high salts concentrations (conductivity: 23 mS/cm) were used as model foulants. At the same total fouling resistance, BSA showed the highest cake layer thickness (BSA (114.5 µm) > humic acid (53.5 µm) > sodium alginate (20.0 µm)). However, a different order was found for the cake layer resistance (BSA > sodium alginate > humic acid). This indicates that fouling thickness is not correlated with cake layer resistance. According to the Carman-Kozeny equation, fouling layer porosity decreased in the following order: humic acid (0.30) > BSA (0.21) > sodium alginate (0.20). In addition, we provided a specific value that was calculated using the ratio between the fouling thickness and cake layer resistance. The results show that alginic acid induced a stronger cake layer resistance, despite its thin fouling layer, whereas BSA showed a relatively low potential for inducing cake layer resistance. The results obtained in this study could be used for estimating and predicting fouling behavior.