Reverse osmosis pretreatment alternatives: Demonstration plant in the seawater desalination plant in Carboneras, Spain

This paper presents the results of a demonstration study for the RO pretreatment that was performed on an AcuaMed open intake desalination plant in Carboneras (Almería, Spain). The main goal was to test different configurations of conventional pretreatments in order to establish the limit of each process as well as their reliability. The pretreatment processes tested were Actiflo® (a process that consists of coagulation, polymer and microsand injection, maturation and settling of microsand ballasted flocs), multimedia filtration at atmospheric pressure, pressurized dual-media filtration and pressurized three-layer filtration. During the tests, the silt density index (SDI) of the filtered water was regularly measured and then evaluated in probability graphs. The raw seawater SDI ranged from 4.5 to 25. The results from this study showed that the Actiflo® system followed by two pressurized multimedia filters (dual-media and three-layer filters) in series, provided effluent SDI values lower than 3 with a reliability of 95% under the optimized operating conditions. These results were obtained when the Actiflo® system included coagulation, flocculation (with flocculant and microsand addition) and maturation stages or just working as a coagulation stage.