Chemical free and energy efficient desalination system

A desalination system comprising an intake unit pumping seawater via an intake pipeline and providing the pumped seawater to a pre-treatment unit connected to a reverse osmosis (RO) desalination unit, the desalination system characterized in that:

• the intake unit is arranged to operate at a flowing speed between 1.5 and 3 m/sec in the intake pipeline to prevent settling of larvae in the intake pipeline,
• the pre-treatment unit comprises an upflow biological flocculator and a downflow filter, and is arranged to supply the seawater to the upflow flocculator at a flowing speed between 15 and 60 m/hour,
• the biological flocculator comprises a layer of porous particles arranged to mechanically support biofilm generation to bind and flocculate colloids from the water without adding coagulants or flocculants of any type to the water,
• wherein the pre-treatment unit is further arranged to separate floc from the porous particles, and
• wherein a height and a composition of the downflow filter are selected to reduce an oxygen level below saturation in the pretreated water, and remove remaining floc, to suppress microbial attachment and growth in the RO unit.

A method of operating a reverse osmosis desalination system, the method comprising:

• supplying seawater at a flowing speed between 1.5 and 3 m/sec selected to prevent larvae settling in an intake pipeline,
• biologically flocculating organic and mineral colloids in the supplied seawater to generate floc,
• mechanically removing the floc to generate an accessible organic carbon level lower than 2.5 ppm,
• reducing an oxygen content below saturation to prevent microbial attachment to membranes and growth in the water, to produce feed water,
• extracting product water and brine from the feed water by reverse osmosis,
• disinfecting the product water, and
• simultaneously recovering gauge and osmotic power from the brine and operating the reverse osmosis at a recovery rate reduced from a maximal recovery rate by 10%.