Desalination holds the answer: Beza’s own study shows the way

The world is moving fast to desalination of seawater to meet the growing demand for water for households and industries and to reduce exploitation of scarce fresh water, which accounts for only 2.5% of all water on earth—both surface and underground.

Instead of banking on fast-depleting groundwater, Bangladesh Economic Zones Authority (Beza) can seek an answer to water demand in the Mirsarai economic zone in its own study for the two coastal tourism parks – Sabrang and Naf – planned in Cox's Bazar district.

Findings of the study, done for Beza by the Institute of Water Modelling, can show how saltwater from nearby Bay of Bengal can be a long-term solution to water needs for industries in the Bangabandhu Sheikh Mujib Shilpa Nagar, the official name of the country's largest economic zone being developed at Mirsarai of Chattogram.

But turning seawater into freshwater involves a cost which is four times as much as the cost of normal water treatment. This is why desalinated water still accounts for only one percent of the world's fresh water though 97.5% of water on earth is saline.

India operates two desalination plants in Chennai purifying the Bay of Bengal water to serve both households and industries. One of the plants cost $78 million with a capacity to produce 100 million litres per day (MLD). Cost of production is $0.44 per cubic metre (m3).

The Beza study estimates a capital cost of $7 million for a desalination plant with a capacity of 5 MLD and production cost at Tk60-Tk70 ($0.70-$0.80) per m3—1.5 times higher than the commercial rate of Wasa water.

Cost of desalinated water is $0.33 in Singapore and $0.16 per m3 in Israel.

About 15 acres of land may be required for such plants, the study says. Power is a major requirement to run a desalination treatment plant. The approximate power requirement for a 50 MLD plant can be 200 MWh/day, it adds.

The study, whose phase-1 was completed in November 2020, analysed the possible modes of financing for such plants, suggesting introduction of privatisation in the desalination business.

"Private finance initiative is an alternate method of raising finance for capital projects without adding to the national debt," it said, suggesting that private companies can form consortiums and raise funds through stock market and other means.

"If traditional financing is not available for the project, BOOT (build, own, operate and transfer) financing can be considered as an alternative," the Beza study said, citing such a project taken up by Rajuk for the water supply of Purbachal City.   

Build-operate-transfer (BOT) or Design-build-operate (DBO) modes of business can also be tried in desalination projects with direct incentives or funds from the government as seen in some countries where 70-80% of the projects are financed by the industry end users or the government, it felt.

It is estimated that for a 50,000 m3/day (50 MLD) desalination plant, the overall investment can be up to U$30 million or more, which is almost three to four times the cost of a normal water treatment plant with the same treatment capacity, it stated.

The Beza is installing 50 deep tubewells to pump out 50 MLD of underground water to meet the demand for water in the economic zone and the requirement is estimated to reach 500 MLD in 2031.

Electrical energy is about 35% to 40% of total operating costs of desalination plants and energy recovery devices can reduce energy consumption by as much as 60%, it pointed out, citing renewable energy as one possible alternative.

Proximity to the Bay of Bengal makes strong ground for Mirsarai economic zone, being developed on 30,000 acres on the coastline between Sonagazi and Mirsarai upazilas, to have desalination plants as the Beza study says, location greatly matters to the operation cost of desalination plants as it helps to avoid high costs for intake pipelines and complex intake structures.

The Beza study finds sea water reverse osmosis (SWRO) as suitable for economic zones in Bangladesh for less energy consuming technology.

The world is not sitting idle as efforts are on for technological innovation to bring down the overall desalination cost. As the technology is evolving and cost of other sources of water is increasing, the desalination cost has dropped by more than half in the last three decades when the process saw a massive growth.

Since the 1960s, some 20,000 facilities have so far been built globally to turn seawater into freshwater, with Saudi Arabia topping the list accounting for a fifth of the world's total.

Australia and Israel are also among major players.

The United Arab Emirates and North Africa are at the centre of recent growth, while most other countries are increasingly exploring their seawaters to meet fresh water needs.

Globally, 300 million people use desalinated water, says the International Desalination Association.

But costs hold the low-income countries back from exploring their seawater potential and reducing extraction of groundwater.

Manzoor Qadir, an environmental scientist with the Water and Human Development Programme of United Nations University, said the desalination industry is growing and there will be more and more such plants in the next 10 years.

But, he told The New York Times, "In low income countries, almost nothing is happening."

Cost stands in the way as desalination technology is expensive and it requires huge amounts of energy, putting researchers worldwide, including those in Saudi Arabia, into work to make the process more affordable and accessible.