1. What is desalination and brine?

The overall procedure of sea water desalination is similar in most cases. Seawater is pumped into the plant and pre-treated to meet water quality requirements. The pre-treated water enters the
desalination unit and is divided into a highly pure product (drinking water) and waste water, commonly called brine. This by-product of the desalination process is concentrated salt water containing a mixture of chemicals used during plant operation and is pumped back into the sea.

2. Desalination technologies:

More than 90 per cent of all desalinated water in the Gulf comes from thermal desalination. Large plants use steam from power plant turbines as a heat source for desalination. Thermal processes use heat to evaporate water, leaving the salt behind in the brine. More than 80 per cent of desalinated water comes from Multi Stage Flash (MSF). Membrane processes use pressure or electricity to force water through a semipermeable membrane which blocks salts and other dissolved solids. The membrane technology is Reverse Osmosis (RO) which accounts for 6 per cent of the production.

3. Daily discharge loads into the Arabian

Gulf from desalination plants in the region:

23.7 tons — chlorine
64.9 tons — antiscalants
300 kilograms — copper

4. Arabian Gulf main producers of desalinated seawater:

Saudi Arabia — 25 per cent of the worldwide seawater desalination capacity, of which 11 per cent is in the Gulf, 12 per cent is in the Red Sea, and 2 per cent is unaccounted for.

United Arab Emirates — 23 per cent

Kuwait — 6 per cent.

5. Impact: The concentrations of different pre-treatment chemicals in Multi Stage Flash and Reverse Osmosis effluents are critical for the marine environment.

Brine

The salinity of desalination effluents can highly exceed the natural ocean levels which can affect open water organisms and seabed dwellers. While some species have adapted to the natural salinity variations, high local salinity levels around the discharge location, especially for Reverse Osmosis plants, clearly exceed natural levels and pose a threat for a variety of species.

Temperature

It has been recorded that Multi Stage Flash plants generate high thermal emissions and discharge brine at a maximum of 10-15C above ambient seawater even after being diluted with cooling water. The discharge is likely to float on the surface of the water because of the high temperature. Increased temperatures reduce the oxygen solubility in water. Significant decreases in oxygen levels can be toxic for species.

Temperature change is generally a minor problem in hot regions where large annual temperature variations are a natural phenomenon, but significant long-term alterations can be harmful
and result in the death of organisms.

Chlorine

The most commonly used “anti-fouling'' additive, chlorine, is a broad-effect agent and can have equally broad impact on marine organisms.

The photosynthesis process of plankton can be seriously reduced at concentrations of only 20 micrograms per litre. At levels of 50 micrograms per litre the composition of marine organisms can change and their variety is reduced. The known lethal values for fish species range between 20 and several hundred micrograms per litre.

Copper

The long terms effects of copper in the sediment are a major concern. Copper compounds tend to settle down and accumulate in the sediments.

They can be absorbed by benthic (seabed) organisms and even be transferred into the food chain eventually. The tolerance towards copper pollution is not yet entirely known for all species.
Copper can be toxic at higher concentrations and reduce growth and reproduction.

Antiscaling additives

Antiscaling agents can cause eutrophication — an increase in algae growth which deteriorates water quality. Degradability is moderate to poor with unknown side effects.

6. Can you live on 25 litres a day?

The minimum amount of water required to sustain human life is 25 litres per day, a reasonable supply to maintain health may be 100-200 litres per day per
capita, although in developed/industrial countries, domestic use can exceed 300-400 litres a day. In the UAE, daily water uses is rated at 550 litres on average. There are few alternatives to desalination for water-stressed countries, however it has led, in some instances, to wasteful use. The Arab Environment:

Future Challenges report cautions against mushrooming golf courses, which will double in a few years to 40 in GCC countries. It says that each course consumes about 1.3 million cubic metres annually, enough to cover the water needs of 15,000 people.

Compiled Emmanuelle Landais, Staff Reporter

Compiled Emmanuelle Landais, Staff Reporter

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Desalination: Facts and procedures