Water Desalination : A Silver Lining For The Future

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Humans cannot drink saline water, but it may be converted to freshwater, which has numerous applications. The method is known as ‘desalination’, and it is increasingly being employed around the world to give people much-needed freshwater. Most of the countries around the world have, or can obtain, abundant freshwater supplies for drinking. However, the scarcity of fresh water has raised concerns over the years, and Bangladesh is no stranger to this concern, being a vastly populous nation.
Unfortunately, 97.5% of available freshwater is salty, limiting its usage to a large extent. Just 2.5% of the earth’s water resource remains as freshwater in icebergs, lakes, rivers, and other sources, and only 0.014% is directly available for mankind and animals. Many countries are suffering from a lack of water supply and storage as a result of this.

Bangladesh is endowed with a large reserve of freshwater, both above and below ground. However, pollution has rendered a substantial amount of freshwater worthless in recent days, as arsenic contamination of groundwater further exacerbates fresh water shortage. As a result, it makes the nation one of the most vulnerable countries to global climate change and sea-level rise, especially the southwest part of the country, which has an elevation lower than 10 m. Therefore, there is a higher demand for long-term solutions to ensure safe drinking water for the inhabitants of the southwest coastal regions of Bangladesh.

 

Unfortunately, 97.5% of available freshwater is salty, limiting its usage to a large extent. Just 2.5% of the earth’s water resource remains as freshwater in icebergs, lakes, rivers, and other sources, and only 0.014% is directly available for mankind and animals.

 

The world is moving fast towards desalination of saltwater to fulfil the rising demand for water in households and industry, as well as to decrease the exploitation of rare freshwater, which accounts for only 2.5% of all surface and subsurface water on the planet. The suggestion for Bangladesh too, is that rather than relying on rapidly decreasing groundwater, the Bangladesh Economic Zones Authority (BEZA) conducted its own study for the two coastal tourism parks – Sabrang and Naf – proposed in Cox’s Bazar district to provide a solution to water demand in the Mirsarai economic zone. The findings of the study, conducted for BEZA by the Institute of Water Modelling, show how saltwater from the nearby Bay of Bengal can be a long-term solution to water needs for industries in the Bangabandhu Sheikh Mujib Shilpa Nagar, the country’s largest economic zone, being developed in Chattogram’s Mirsarai.

 

However, the expense of converting seawater to freshwater is four times that of ordinary water treatment. This is why, despite the fact that 97.5% of the world’s water is saltwater, desalinated water accounts for only 1% of the world’s freshwater. According to BEZA research, a desalination plant with a capacity of 5 MLD would cost $7 million to build, with a production cost of BDT 60-70 ($0.70-$0.80) per cubic metre – 1.5 times the commercial rate of WASA water. In Singapore, desalinated water costs USD 0.33 per cubic metre, while in Israel, it costs USD 0.16 cubic metre.

 

According to the study, such plants may demand up to 15 acres of land. A desalination treatment plant requires a lot of electricity to run. It goes on to say that the average power required for a 50 MLD plant is 200 MWh/day. The study, whose first phase was finished in November 2020, looked into the various financing options for such plants, and recommended that the desalination industry be privatised.

It was considered that the build-operate-transfer (BOT) or design-build-operate (DBO) business models may be used in desalination projects with direct government incentives or funds, as seen in some countries where 70-80% of projects are paid by industrial end-users or the government.

It is projected that the overall investment for a 50,000 cubic metre per day (50 MLD) desalination facility may be up to USD 30 million or more, which is over 3 to 4 times the cost of a standard water treatment plant with the same treatment capacity, according to the report.

BEZA is constructing 50 deep tubewells to extract 50 MLD of subsurface water to cater to the economic zone’s water demand, which is expected to reach 500 MLD by 2031. Electrical energy accounts for roughly 35-40% of overall desalination plant running expenses, and energy recovery devices can cut energy consumption by up to 60% according to the report which also mentions renewable energy as a feasible option to run desalination plants.
According to the BEZA study, proximity to the Bay of Bengal makes the Mirsarai economic zone a good location for desalination plants because it is being developed on 30,000 acres of land along the coast between Sonagazi and Mirsarai upazilas and helps to avoid high costs for intake pipelines and complex intake structures. The study further found seawater reverse osmosis (SWRO) as suitable for economic zones in Bangladesh for less energy-consuming technology.

 

The findings of the study, conducted for BEZA by the Institute of Water Modelling, show how saltwater from the nearby Bay of Bengal can be a long-term solution to water needs for industries in the Bangabandhu Sheikh Mujib Shilpa Nagar, the country’s largest economic zone, being developed in Chattogram’s Mirsarai.

 

Water treatment via reverse osmosis (RO) is efficient. RO uses a semipermeable membrane to separate dissolved particles, ions, and even bacteria from water. A pump pushes water through the membrane at a higher pressure than the system’s osmotic pressure. Only water can enter through the membrane. For this procedure, commercial polymers are used to create membranes.

The RO method necessitates proper preparation of water before use, which raises expenses.
It also needs to be treated with chlorination or UV rays following the process. The membrane must be changed on a regular basis, and the expense of maintenance is substantial. Though it is an expensive process, with the rising cost of gasoline, RO is becoming a more reliable method for the future, and more research is being conducted to improve it.

The world is hardly sitting still, as efforts continue to be made to reduce the overall cost of desalination through technological innovation. Desalination costs have decreased by more than half in the last three decades, when the process experienced significant expansion due to technological advances and the rising costs of other sources of water. Globally, 300 million people use desalinated water, says the International Desalination Association.
However, prices prevent low-income countries from tapping their seawater potential and minimising groundwater exploitation. The major issue with these technologies is determining the best economic design and evaluation of combination plants in order for them to be economically viable for poor countries. Distillation plants take more energy and have a higher unit capital cost than membrane plants, and they generate a lot of waste heat.
Manzoor Qadir, an environmental scientist with the United Nations University’s Water and Human Development Programme says that the desalination business is expanding and there will be additional plants in the next 10 years. “In low-income countries, essentially nothing happens,” he told The New York Times.

On the other hand, membrane processes are increasingly the technique of choice for desalination in developing nations, as efforts to minimise total energy usage and lower the cost of water production continue.

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