Application and development of membrane desalination technology

Desalination refers to the desalination of 35000mg / L seawater to the drinking water below 500mg / L. At present, the main desalination methods used in the world are multi-stage flash evaporation (MSF), multi effect evaporation (MED) and reverse osmosis (RO). Over half a century, it has fed more than 100 million people in the world, and promoted the economic and social development in arid desert areas and coastal areas of developed countries.

According to the statistics of the international Desalination Association, by the end of 1995, there were 11066 units with a daily water output of more than 100m3 in the world, producing 20.3 million m3 of fresh water per day. By the end of 1997, the total number of units was 12451, with a daily water output of 22.73 million m3, including 13.37 million m3 of seawater desalination and 58.4 million m3 of brackish water desalination, with an annual growth rate of 10-30%. In terms of desalination, MSF is the main installed capacity, but ro has developed rapidly in recent years. MSF has had very little contract value since 1995, except for very large units. MSF decreased from 84.4% in 1989 to 76.04% in 1997. Ro increased from 5.6% in 1989 to 14% in 1997. Med1 accounted for 6.7% in 1989 and only 5.47% in 1997.

RO for desalination of coastal brackish water has an absolute advantage, accounting for 76.23%, and the cost of investment and water production is lower. About 65% and 94% of wastewater and water purification ro respectively. After 1995, the installed capacity RO of desalination and brackish water desalination was 90%. The largest RO desalination plant is built in Saudi Arabia, with daily fresh water output of 128000 / m3. The largest ro brackish water desalination plant is built in the United States with a daily output of 270000 m3.

At present, the annual sales volume of desalination units has reached more than 10 billion US dollars, and the suppliers with an annual growth rate of about 20% are mainly the United States and Japan, and the application areas are mainly the Middle East, Mediterranean and Caribbean regions, followed by Southeast Asia and North Africa.

The application of desalination technology in China started from the promotion of small-scale electrodialysis (ED) desalination device in the early 1970s. In 1981, 200m3 / D ed desalination device was built. During the Ninth Five Year Plan period, RO fresh water devices were successively built, mostly small or demonstration projects (Table 1), and Ed and RO desalination devices were exported to Maldives and Kiribati.