Chemical free and energy efficient desalination system
A desalination system ( 100 ) having an intake unit ( 110 ) providing seawater to a pre-treatment unit ( 120 ) connected to a reverse osmosis (RO) desalination unit ( 130 ) and a post treatment unit ( 150 ). The desalination system ( 100 ) is configured to operate without any external addition of chemicals to simplify logistics and regulation concerns. The units of the system are configured to prevent biofouling, scaling and corrosion by mechanical and biological means including high flow speeds, biological flocculation of colloids, and making the water entering the RO units inhospitable to bacteria and other organisms that cause biofouling, hence preventing their settlement and removing them with the brine. Recovery rate is lowered and energy is recovered to increase the energetic efficiency and minerals that are added to the product water are taken from the brine.
1. A pre-treatment unit in a reverse osmosis (RO) desalination system, comprising:
an upflow biological flocculator, arranged to receive seawater at a flowing speed between 15 and 60 m/hour, and comprising a layer of porous particles arranged to mechanically support biofilm generation to bind and flocculate organic and mineral colloids from the water without adding coagulants of any type to the water, the biological flocculator further arranged to maintain at least oxygen saturation in the water to support biofilm generation, wherein floc is removed from water exiting the biological flocculator, and
a downflow filter receiving the water exiting the biological flocculator and having at least one filtering layer, of which a height and a composition 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 pretreated seawater, wherein the downflow filter comprises a downflow biological filter followed by a downflow sand filter.
2. The pre-treatment unit of claim 1 , wherein the porous particles in the upflow biological flocculator are ground tuff, and the porous particles in the downflow biological filter are ceramic.