Belinda Smith
Belinda Smith is a science and technology journalist in Melbourne, Australia.
By 2030 the world is predicted to face a 40% shortfall between demand and supply of clean water. The World Economic Forum ranks the looming water crisis as the number one risk facing society, according to its Global Risks 2015 report.
Meanwhile, two million tonnes of sewage, industrial and agricultural waste flow untreated into the world’s waterways each day.
Can we tackle both problems at once with a cheap, efficient and fast way to make dirty wastewater suitable for human use?
The system could clean industrial wastewater so well it could be safely discharged into waterways.
Mehdi Khiadani, an engineer at Perth's Edith Cowan University, believes an answer might be found in tiny bubbles.
The first step to purifying water is to clean out the particles floating in it. These are usually removed by adding a chemical called a coagulant, which clumps the solids in the water . Gravity then takes over and the clumps slowly sink. Clear water is channelled off the top.
But the process is slow and needs large basins or swathes of land.
Khiadani’s method, known as dissolved air flotation, is faster and more compact. A set-up of less than two square metres can clarify 500 litres per hour. It also uses fewer chemicals – around half that of the gravity-driven approach.
“I see great potential for households,” Khiadani says.
First the water is mixed with a small amount of coagulant in a tank where clumps of solid particles form. The water is then moved into a chamber where air bubbles about the size of a dust particle are introduced to the bottom of the tank under high pressure.
As they rise the bubbles expand, acting as a sieve to carry clumps of coagulated solids to the surface.
The solids are skimmed off to leave clear water underneath.
Scaled up, this process could clean industrial wastewater so effectively it could safely be discharged into waterways.
Depending on the source of the water, after the bubble treatment the water might only need a simply disinfection step to make it safe for drinking.
The system can also be scaled down for transport to rural and disaster-stricken areas.
The system does have some disadvantages – it requires some technical expertise to operate, as well as a power source and chemical coagulants. But it can be powered by renewable energy and Khiadani’s team is researching the minimal amounts of coagulant to get the best results, with the aim of further cutting chemical use.
“The less we use, the better,” he says.
