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Tuesday, July 23, 2019 10:48:43 PM
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Fresh water security

It needs a cost-effective technical solution

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Shishir Reza :
Globally half a billion people know, how water insufficiency in a year circle. For 1.5 to 2 billion people, water resources are unsatisfactory to assemble demands for at least a part of the year. Desalination technologies can provide an unrestricted, climate sovereign and fixed supply of high quality water, chiefly used by the community and industrial sectors. In particular, desalination is a vital technology in the Middle East and for tiny island nations which typically lack renewable water resources.
Nowadays almost 16,000 desalination plants are in operation in 177 countries, producing 95 million cubic meters of freshwater every day. Falling economic costs of desalination and the development in membrane technologies, particularly reverse osmosis, have made desalination a cost-competitive and attractive source of freshwater around the globe.
The increase in desalination has been driven by intensifying water scarcity due to rising water demands associated with population growth, increased water consumption per capita, and economic growth, coupled with diminishing water supplies due to climate change and contamination.
The most complete ever compiled - to revise the world's badly outdated statistics on desalination plants. Most startling was our finding that the volume of hyper saline brine produced overall is about 50% more than previously estimated.
Globally, plants now discharge 142 million cubic meters of hyper saline brine every day - enough in a single year to cover Florida under 1 foot of brine. Considered another way, the data shows that for every unit of freshwater output, desalination plants produce on average 1.5 units of brine.
Some two-thirds of desalination plants are in high-income countries, with capacity concentrated in the Middle East and North Africa. And over half - 55% - of global brine is produced in just four countries: Saudi Arabia (22%), UAE (20.2%), Kuwait (6.6%) and Qatar (5.8%).
Middle Eastern plants, which largely operate using seawater and thermal desalination technologies, typically produce 4 times as much brine per cubic meter of clean water as plants where river water membrane processes dominate. Brine disposal methods, meanwhile, are largely dictated by geography but traditionally include direct discharge into oceans, surface water or sewers, deep well injection and brine evaporation ponds.
Desalination plants near the ocean (almost 80% of brine is produced within 10km of a coastline) most often discharge untreated waste brine directly back into the marine environment. Brine raises the salinity of the receiving seawater, and brine underflows deplete dissolved oxygen needed to sustain life in the marine environment.
This high salinity and reduced levels of dissolved oxygen can have profound impacts on marine ecosystems and organisms, especially those living on the seafloor, which can translate into ecological effects observable throughout the food chain. Furthermore, the oceans are polluted with toxic chemicals used as anti-scalants and anti-foulants in the desalination process.
There is a clear need for improved brine management strategies to meet this rising challenge. This is particularly important in countries producing large volumes of brine with relatively low efficiencies, such as Saudi Arabia, UAE, Kuwait and Qatar.
In fact, we can convert this environmental problem into an economic opportunity. Brine has many potential uses, offering commercial, social and environmental gains. It has been used for aquaculture, with increases in fish biomass of 300% achieved.
It has also been successfully used to irrigate salt tolerant species, to cultivate the dietary supplement to generate electricity, and to irrigate forage shrubs and crops. With improved technologies, a large number of metals, salt and other minerals in desalination plant effluent could be mined.
These include sodium, magnesium, calcium, potassium, bromine, boron, strontium, lithium, rubidium and uranium, all used by industry, in products, and in agriculture. The needed technologies are immature, however; recovery of these resources is economically uncompetitive today.
Research and ideas related to a variety of unconventional water sources scaled up to meet the even superior deficit in freshwater supplies looming in much of the world. In particular, we need to make desalination technologies more reasonable and enlarge them to low-income and lower-middle income countries like Bangladesh.
Costs are falling from continued improvements in energy recovery systems and the coupling of desalination plants. At the same time, we have to address potentially severe downsides of desalination - the harm of chemical pollution to the marine environment and public health.

(Shishir Reza, an Environmental Analyst & Associate Member of Bangladesh Economic Association)

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