Improvements of ferrate(VI) pretreatment on membrane flux and membrane rejection using cheap NaClO reagent

Abstract

Ferrate(VI) pretreatment can effectively alleviate membrane fouling during the ultrafiltration (UF) process, while instability and high expenditure limit its application. This study discovered that the cheap NaClO reagent would improve the performance of ferrate(VI) pretreatment, i.e., establishing Fe(VI)/NaClO (FC) process. 20 μM of Fe(VI) group can increase J/J0 from 0.323 to 0.391, while the optimization process of 20 μM Fe(VI)/4 μM NaClO [FC (5:1)] increased it to 0.491 at the end of cycle 1 filtration. Meanwhile, the reversible and irreversible membrane fouling resistance decreased by 50% and 56% in FC (5:1). This was attributed to the suppression of ferrate(VI) decomposing and in-situ formation of more dispersed ferric nanoparticles in FC process [730.33 nm in Fe(VI) and 606.80 nm in FC (5:1)] by applied NaClO. The rejection ratio of dissolved organic carbon (DOC) increased from 27.18% of Fe(VI) group to 40.34% of FC (5:1) due to the repulsive interaction amplification of acid-base (AB) interaction energy. That was derived from the hydrophilia promotion of the treated sample and the electrical property evolution of in-situ formed ferric nanoparticles by NaClO. It suggested that AB interaction energy, presenting repulsive interaction in membrane-foulants and foulants-foulants, was a major role in Fe(VI) group and FC process. There was no more side effect induced by FC pretreatment, which was confirmed by the result that FC caused no increase in the disinfection by-products (DBPs) formation potential. The present study provided insight into improving the effect of ferrate(VI) pretreatment without inducing side effect, and reduced the costs of ferrate(VI) pretreatment during the process of UF.