Membrane characterizations for mitigation of organic fouling during desalination and wastewater reclamation

Measurements of contact angle, zeta potential, and pore size distribution for clean, cationic surfactant coated, and organic fouled membranes, were conducted to obtain membranes properties, from perspectives of organic fouling mitigation. Interaction between natural organic matter (NOM) and the membrane surface was investigated using contact angle measurements, with the results being attempted to be used for mitigation of NOM fouling. Several different membranes, one nanofiltration (NF; NE70), one ultrafiltration (UF; GM), and three reverse osmosis (RO; SR, BE, FRM3) membranes, were tested. With NOM fouled membranes, contact angles obtained from the sessile drop method increased compared to corresponding clean membranes. For cationic surfactant coated membranes, contact angles measured with NaCl and sea salts solutions were substantially lower than those measured with deionized pure water, implying the cationic surfactant modification can have a potential to reduce hydrophobic organic fouling during desalination or relatively high salts containing wastewater reclamation processes. For NOM fouled membranes, contact angle increases and the surface charge increases negatively compared to corresponding clean membranes; the membrane surface exhibits greater hydrophobicity and less negative charge, which is supported by the FTIR spectrum measurements.

Two distinct different membranes [one NF (NE70) and one UF (GM)] membranes were selected to be characterized in terms of contact angle, zeta potential, and FTIR spectrum, and these results were used for mitigation of membrane organic fouling during desalination and wastewater reclamation. The NF and UF membranes could be categorized into relatively hydrophilic and highly negative charged, and relatively hydrophobic and moderately negatively charged membranes, respectively, as identified using contact angle and zeta potential measurements. They contained similar functional groups in terms of FTIR spectra. Both the membranes became more hydrophobic when being fouled with wastewater effluent organics and exhibited much lower contact angles (i.e., greater hydrophilic) when measured with very salty solutions after the membranes were coated with cationic surfactants. These facts imply that organic fouling (especially from hydrophobic interaction), under high ionic strength (or high salty) conditions, could be reduced if the membranes were pre-coated with surfactants.