Chemical cleaning strategy of full-scale low-pressure reverse osmosis (Lpro) membrane process: Case study

In this study, fouled reverse osmosis (RO) membranes from the full-scale low pressure reverse osmosis (LPRO) plant were autopsied in March (RO-M) and September (RO-S), and investigated before and after the chemical cleaning. The characteristics of residual matters on LPRO membrane surfaces were then determined via several analysis methods including excitation–emission matrix, molecular weight distribution, thermogravimetric analysis, and organic analyses. The foulants were predominantly composed of hydrophobic organic matters with dense structures on RO-S, while loose structure of CaSO₄ and BaSO₄ scaling dominantly covered membrane surfaces on RO-M. Interestingly, loose structure of scaling provided more significant growth of biofilm and subsequently higher organic mass per unit area on RO-M. The order of basic-acidic cleaning showed improved flux recovery (87%) than acidic-basic cleaning (79%) due to the dense structure of biofilm layer on RO-S. In case of RO-M, foulants were easily removed without regarding the order of chemical cleaning (higher than 93% of initial flux recovery) due to the loose structure of fouling layer. The results proposed that the membrane foulants might have seasonal differences, and the cleaning order of basic-acidic chemicals would provide higher flux recovery in the case of the fluctuation in influent quality.