The Pursuits of Ultimate Membrane Technology including Low Pressure Seawater Reverse Osmosis Membrane developed by “Mega-ton Water System” Project

Reverse osmosis (RO) technology has been widely applied to water treatment such as seawater desalination, and large RO plants are many in operation around the world. Moreover, much larger plants will be required to secure sufcient water resource in the near future because global water shortage and quality problems are still getting more serious. Mega-ton Water System project was carried out for sustainable management of water environment and for low-carbon path to develop advanced key technologies of water treatment. Lowpressure RO membrane for seawater desalination has been studied in the project as a part of the core technologies to realize mega plant that is capable of producing 1,000,000 m3 of freshwater per day. Fundamental and scientifc research for RO membranes based on fne structure analyses by means of transmission electron microscopy with a special technique was conducted, and practical tools for designing new innovative RO membrane were acquired by the structure analyses to quantify the physicochemical and chemical properties of RO membranes. As the result of studying on structural design of RO membrane, low pressure SWRO membrane was obtained to reduce energy consumption compared to conventional ones in the past of SWRO. The vision of the “Mega-ton Water System” is sustainable desalination and reclamation. The missions are: 1) energy reduction (20-30%), 2) water production cost reduction (50%), and 3) low environmental impact (fewer chemical operations). Water cycle in “Mega-ton Water System” is separated into two parts including i) Seawater RO (SWRO) system, and ii) Seawater RO system with PRO system. The main challenge of development goal is the construction of mega-ton-scale system for seawater desalination for half the current cost. Accordingly, we developed the world’s frst low-pressure, multi-stage, high yield RO system, using a low-pressure seawater desalination membrane, and as a result of incorporating into it the elemental technologies gained from research in subthemes, such as highly-efcient pressure energy recovery, low-cost and highly durable plastic piping, pretreatment without the use of chemicals.