Characterization of fouled ultrafiltration membranes from a full-scale wastewater reclamation plant in iron and steel industry

Iron- and steel-making industry is one of the most water-intensive industries. An industrial wastewater purification plant using ultrafiltration and reverse osmosis is utilized by the iron and steel production industry to reclaim wastewater from the manufacturing processes. After sustained operation, the ultrafiltration membranes suffered from severe fouling problems. The frequent and necessary chemical cleaning results in raised operating cost, reduced permeate, and shortened membrane lifetime. The objective of this research was to identify the major foulants that result from long-term real-world operation of the ultrafiltration system. The fouled ultrafiltration membrane samples were collected four times during a 1.5-year period. Scanning electron microscope with energy-dispersive spectrometer, loss on ignition, and fouling resistance analysis were conducted to characterize the foulants. We identify iron (Fe) and manganese (Mn) oxides as the major foulants on the membrane surface and in the pores. We also demonstrate that irrecoverable fouling as the major contributor to fouling resistance, accounting for approximately 43 ~ 47% of the total increase in resistance. Based on our data, the irrecoverable fouling likely begins with the deposit of Fe and Mn ions and oxide particulates within the membrane pores, following by accumulation of additional oxides in part through an autocatalytic process, which ultimately leads to pore clogging. Therefore, pretreatment of the ultrafiltration influent to remove Fe and Mn ions can be a sound strategy to mitigate irrecoverable fouling.