Document Type: Review Paper
Toray Industries, Inc.
Seawater desalination using a reverse osmosis (SWRO) membrane requires less energy compared with the distillation method and so is an important technology in non-Middle Eastern countries where energy 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 desalination plants in line with government policy and the trend is for the development of larger (in excess of half mega-ton or mega-ton 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) Energy resources: Renewable energy, 2) Seawater RO system: Advanced membrane and membrane system, 3) Desalination drainage (brine) to reduce marine pollution : Green desalination. In Japan, a national project called the “Mega-ton Water System” project has been conducted to solve issues related to subjects 2) and 3).
a. 20% energy reduction was possible in the SWRO system of the “Mega-ton Water System” by combining a low pressure SWRO membrane and a low pressure two-stage high recovery SWRO system. 30% energy reduction was possible using 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 seawater desalination will be $ 0.50/ m3/day or less.