Society

China looks to take salt out of seawater

By Cheng Yingqi (China Daily)
Updated: 2011-04-09 08:01

BEIJING - China will quadruple its ability to desalinate seawater in the next 10 years, a senior marine official told a recent conference.

Speaking in Tianjin municipality on Wednesday at an international conference on seawater desalination, Chen Lianzeng, deputy director of the State Oceanic Administration, said the country plans to be able to produce from 2.5 million to 3 million tons of desalinated water a day by 2020.

China can now put out 600,000 tons of desalinated water a day, which is 20 times more than it could in 2000.

Seawater desalination has been used in 125 countries throughout the world to supply water to more than 100 million people.

And China has regarded desalination for more than 40 years as an important means of dealing with its water shortages.

According to statistics from the State Oceanic Administration, the country collects about 40 billion cubic meters of fresh water from rainfalls every year. Even so, 400 cities throughout China have been subject to droughts in recent times.

In 2005, the Chinese government published a specific plan for dealing with water shortages in coastal areas and in inland regions.

Tianjin, Hebei, Zhejiang, Shandong and Liaoning now have desalination plants that can put out 100,000 tons of fresh water a day, Chen said.

"Desalination plants use distillation techniques to reduce the amount of chloride ions contained in seawater to a level safe for irrigation and for drinking," said Xia Qing, former deputy director of the Chinese Research Academy of Environmental Sciences.

One liter of seawater contains 40,000 milligrams of chloride ion. A liter of drinking water, according to recommendations, should only contain 250 mg of the substance.

Meanwhile, the use of saltwater on crops can cause the underlying soil to become barren.

Xia said the largest barrier to a greater reliance on seawater desalination is the procedure's cost. "While the plants are used to reduce chloride levels, they also must do so in a way that keeps the cost of desalinized water close to that of regular tap water," he said.

Statistics from the State Oceanic Administration show that desalinating a ton of water costs 5 yuan (76 cents). But Xia said that figure hides the fact that the cost is likely higher when production is undertaken on a large scale.

"If the plants manage to cut the cost to 6 yuan per ton, then more producers will use desalination technology," Xia said.

According to previous reports, tap water prices vary from 2 yuan per ton to 5 yuan throughout China, and will continue to rise at a rate of 10 percent a year for the next 10 years.

Meanwhile, experts have warned that the practice of pumping seawater likely entails environmental risks.

"If the plants pump too much water at one time and from a single place, the pollution in the water could increase temporarily and lead to red tides," said Zou Ji, vice-president of Renmin University of China's school of environment and natural resources.

Zou said authorities should take such risks into consideration when choosing which sites to pump water from.

"The desalinized water is most likely to be used in dry areas in the north, such as Tianjin, Dalian in Liaoning province and Qingdao in Shandong province," Zou Ji said.

"Even as the cost of desalination goes down, it will still be too expensive to ship the water across thousands of kilometers to Northwest China."