Sustainable Seawater Reverse Osmosis Desalination as Green Desalination in the 21st Century

Seawater reverse osmosis desalination (SWRO) requires less energy compared with the distillation method and thus is an important technology except Middle Eastern countries whereenergy costs are higher. Recently, even Middle Eastern countries where the distillation method is still a major technology, have begun adopting the RO method in new desalinationplants in line with government policy and the trend is for the development of larger (in excess of half mega-ton per day or mega-ton per day size) so-called “Mega-SWRO” plants.With these trends in the global market, the requirements of sustainable SWRO desalination as green desalination for the 21st century are summarized under three subjects: 1) Energyresources:Renewable energy, 2) Seawater RO system: Advanced membrane and membrane system, 3) Reduction of marine pollution: Green desalination. The “Mega-ton Water System” projecthas been conducted to solve issues related to subjects 2) and 3) as Japanese national project.a. By combining a low pressure SWRO membrane and a low pressure two-stage high recovery SWRO system, 20% energy reduction was possible. And 30% energy saving in totalwas also possible as the SWRO-PRO hybrid system.b. For low environmental impact as green desalination, less chemical and less chemical cleaning for reliable operation have been established.c. Low-cost renewable energy, particularly solar energy, is now available to solve issues related to subject 1. By combining these sophisticated technologies, the cost of seawaterdesalination will be $ 0.50/ m3/day or less.