Autopsy of SWRO membranes from desalination plant in Ceuta after 8 years in operation

Ceuta sea water reverse osmosis (SWRO) desalination plant was established in 1997 with a nominal capacity of 15,000 m3/d and a recovery rate of 40%. It is fed from an underwater intake pipe and a conventional pretreatment was applied based on hypochlorite disinfection, sand filtration, phosphonate addition and cartridge filtration. RO facility was made up of three frameworks, laid out in one step and one stage. Membranes' alkaline cleansing was achieved once every two months and once a week using biocide cleansing. By this system, the membranes have remained operative for periods of up to eight years, after which a membrane autopsy was performed in order to evaluate the effectiveness of pretreatment and cleaning operations. The membrane autopsy was performed by optical microscopy, SEM/EDS, TOC, elemental analysis, ICP-MS and XRD. The fouling layer was heterogeneous and was most significant underneath or in the vicinity of the strands of the feed spacers. The main components of the fouling layer were quartz and clay, mainly muscovite, chlorite and albite. Foulant comes from the influent as the conventional pretreatment does not prevent them from reaching the membrane. The absence of biofilms, significant organic deposits or salt precipitation was also notable.