Climate change, drought, population growth and industrial development have driven up demand for water this century, raising fears that drinking water will be in short supply. According to the latest data from the international desalination organization, there are now 13,080 desalination plants in the world, which can produce a total of 566,000 cubic meters of drinking water every day, accounting for only 0.5% of the world's available water.

Although the earth is rich in water, more than 97 percent of the earth's salt is too high to drink and is fed only by rivers, lakes or groundwater. Climate change, drought, population growth and industrial development have driven up demand for water this century, raising fears that drinking water will be in short supply. According to the United Nations, more than 1 billion people are still living in places that lack water, and the number is more likely to rise to 1.8 billion by 2025.

Water is not available in the face of water

There is no doubt that oceans provide unlimited water, but because they contain salt, they have to be desalinated before they can be drunk. According to the latest data from the international desalination organization, there are now 13,080 desalination plants in the world, which can produce a total of 566,000 cubic meters of drinking water every day, accounting for only 0.5% of the world's available water. Desalination projects require a lot of energy and are expensive, and used to be used only by countries with low oil prices and a lack of water. Today, however, water shortages are no longer a single regional problem. People in most parts of the world are living with chronic drought and water shortages, which have increased demand for desalination. Even California, London and several Australian cities are planning desalination plants.

Although the project has helped to address water shortages, it has not been universally recognized in the past. Environmental groups say a large desalination plant USES as much energy as 30,000 homes a year. The process also releases greenhouse gases, causing Marine life to enter the machinery by mistake and causing casualties. But as technology has improved and desalination costs have been greatly reduced, desalination plants in Australia have been converted to wind power.

Technology comes from sugar mills

As far back as the 16th century, European explorers took the first step toward desalination by boiling water to reduce salt, but the real turning point went back to the American sugar industry in 1850. When engineers invented NorbertRillieux multi-effect distillation is used to refine crystal sugar, principle is to use a series of small rooms, let each chamber of decompression step by step, then the chamber of secrets energy demand will decline gradually, combined with the previous chamber of the generated heat can give the remaining rooms using repetition, energy consumption will fall by more than 8, greatly saves the cost of sugar, the technology was introduced in seawater desalination.

Unfortunately, only a small number of multipotent distillation desalination plants are available, because the minerals are deposited on the heat transfer surface, hindering energy conversion. Later, a new technology called thermal-desalination solved the problem. The evaporation process of seawater does not need to go through the heat transfer surface, but a large amount of hot steam is needed for the project. As a result, thermal desalination plants have to be built next to power stations, which consume a lot of energy.

Technology continues to improve

Since then, American scientists have begun studying how to increase production by blocking salinity from soluble water with permeable membranes. At first, reverse osmosis produced only a small amount of drinking water, with little effect, until 1960, when SidneyLoeb and SrinivasaSourirajan made new osmotic membranes that block the salinity of soluble water.

However, the reverse osmosis is not perfect. The soluble particles in seawater will block the osmotic membrane, which should be removed by filters and chemical materials in advance, and the osmotic membrane should be cleaned regularly. Normally, each liter of seawater contains 33 to 37 grams of soluble particles, but it takes a lot of work to convert it into drinking water. By the 1970s, new reverse osmosis membranes, processed by a cross-linkingreaction process, were available to increase water flow and withstand changes in ph and temperature, and the technology has monopolized the desalination industry ever since. The first large reverse-osmosis plant to treat seawater was built in Saudi Arabia in the 1980s, when it took 8 kilowatts of electricity per hour to produce a cubic metre of drinking water.

Reverse osmosis consumes a lot of energy, so scientists studied using an energy-recoverydevice to reduce consumption from an initial 75 per cent to 96 per cent, reducing the amount of power needed per hour of the desalination project to 3.7 kilowatts. Improved osmotic membranes and energy restorers have helped cut costs, from about $1.50 per cubic metre of drinking water in the 1990s to about $0.5 in 2003, which will be used in most desalination projects in the future. Scientists are still working on better membranes to reduce energy consumption.

The separated salt concentration of seawater after treatment is high, and it is feared that the direct discharge of seawater will affect the ecology. However, studies have shown that when the salt is discharged, the normal concentration can be restored within 500 meters of the sea.