Chemical cleaning of a cross-flow microfiltration membrane fouled by microalgal biomass

• Performance of NaOCl, NaOH, HNO3 and citric acid as cleaning agents in membrane fouled by microalgal biomass was studied.
• Alkaline agents more effectively removed the foulant layer than the acidic agents.
• 0.75% NaOCl with Tc of 60 °C exhibited the best performance obtaining 98% recovery.

In this study, we experimentally investigated the water flux recovery following the chemical cleaning of the CA membrane with different chemical cleaning agents. Besides flux recovery analysis, SEM analysis and zeta potential measurement of the membrane samples before and after chemical cleaning were also conducted. Moreover, effect of temperature on cleaning performances was also investigated. The results show that alkaline cleaning agents more effectively removed the foulant layer on the membrane surface than the acidic cleaning agents. In addition, among the tested alkaline agents, 0.75% NaOCl exhibited the best cleaning performance, obtaining approximately 98% flux recovery and removing almost all the major foulants and causing the membrane surface to become almost as porous and clear as it was before the fouling; the latter results were confirmed by SEM analysis. Meanwhile, cleaning with 0.75% NaOH was less effective, resulting in only 68% flux recovery. The SEM analysis found that the acidic agents (HNO3 and citric acid) failed to remove the foulant layer from the membrane surface, which accounts for their poor flux recovery. This study also confirmed that the cleaning temperature affected the flux recovery after each repeated cycle of fouling and cleaning. In general, higher temperatures resulted in higher flux recovery. A Tc of 60 °C significantly improved the cleaning of a fouled membrane and attained 98% recovery after the first two cleaning cycles. This effect, however, was not observed with temperatures higher than 60 °C.