Optimization of chemical cleaning of a reverse osmosis membrane from a desalination plant by means of two-step static tests

Research in cleaning procedures of reverse osmosis membranes used in seawater desalination to minimize costs and achieve high efficiency is necessary. Multi-step cleaning can represent a useful tool, since the cleaning efficiency can be improved by means of utilization of different chemicals with complementary cleaning mechanisms. The objective of this work was the optimization of a two-step cleaning procedure to recover the membrane properties and reduce power costs. Spent Hydranautics SWC3 membranes (USA) were supplied by a desalination plant. Cleaning tests were performed in three stages: one-step static cleaning, two-step static cleaning and characterization of the membrane surface after the cleaning process. Four cleaning agents at two different concentrations were used. All possible combinations of them were considered, including sequence effect. After the cleaning process, membrane surface was characterized by field emission scanning electron microscopy coupled with energy dispersive X-ray spectroscopy and atomic force microscopy. One-step static cleaning test indicated that sodium dodecyl sulphate 1% w/v was the most efficient cleaning solution, followed by NaOH 2% w/v. Two-step cleaning tests showed that the procedure that maximized permeate flux recovery was surfactant-alkaline cleaning, whereas the one that maximized the recovery of the salt rejection index was alkaline-acid sequence. Characterization of the membrane surface after the cleaning steps confirmed that fouling deposits were significantly removed.