Effect of preoxidation on fouling mitigation in a low-pressure membrane system with clean-in-place (CIP) treatment

The study investigates the impact of biological (soluble microbial products), organic (humic acid), and inorganic foulants (Al, Mn, and Fe) on the structure of polyvinylidene fluoride (PVDF) and polyethersulfone (PES) membranes during filtration processes. While different forms of Al, including mononuclear (Al_a), colloidal (Al_c), and polymeric (Al_b) species, were also analyzed and a chlorination dose of 1.5 mg.L⁻¹ was used as pretreatment for the feed water. The results revealed that the PES membranes exposed to the untreated feed solution were more vulnerable to severe structural deterioration as compared to PVDF membranes, in the presence of organic/biological foulants and complex mixtures of organic and inorganic foulants. Presence of carbonate (O-C=O) and carboxylic groups on PES membranes and the reduction of hydrophilic additives on PVDF membranes after exposure to the feed streams was observed. Moreover, the pore size of the PES and PVDF membranes increased to 1308.1 nm and 287.8 nm, respectively, at the end of study. The PVDF membranes exhibited severe fouling than PES membranes due to strong adsorption potential for the foulants. Moreover, Al_b had stronger fouling effect that Al_a and Al_c, while pre-chlorination increased charge neutralization and reduced fouling due to weaker binding with the organic foulants. Results from Hermia's fouling model confirmed the occurrence of complete blocking, followed by the formation of a cake layer and intermediate fouling.