Chemical-free system removes arsenic from drinking water

A chemical-free system for removing arsenic from drinking water has been installed in the US after helping rural communities in India.

The technology, developed by engineers from Queen’s University Belfast, is used to add oxygen to the water to effectively reverse the process of arsenic accumulation in underground wells.

The Subterranean Arsenic Removal (SAR) system provides a relatively cheap and simple way of making drinking water safe without any waste products, according to its creator, Dr Bhaskar Sen Gupta.

Water is pumped to the surface and run through simple showerhead attachments to add oxygen. It is then returned to the aquifer where the arsenic is gradually removed as it reacts with other elements to form a mineral layer on the inside of the well.

‘It only requires the pumping costs,’ Sen Gupta told The Engineer. ‘You don’t have any costs of chemicals or sludge disposal. And we tried to make the technology in a way that anyone can use it.’

Sen Gupta and his colleagues first trialled the system in West Bengal from 2005 and after three years set up six plants producing safe drinking water.

The technology has now been installed at a site in northwest Washington state in the US, where arsenic has accumulated from geogenic sources in the rock.

Sen Gupta also plans to take SAR to Cambodia and hopes to develop a zero-carbon wind-powered version.

Arsenic can collect naturally in aquifers but is also deposited through bioleaching, where microbes from fertilisers enter the wells and, in the absence of oxygen, break down minerals to create a soluble form of the poisonous element.

Adding oxygen to the water stops the microbes breaking down the minerals but also encourages dissolved iron to precipitate, taking the arsenic and other elements with it as it forms a new layer of solid mineral.

The amount of oxygen added is controlled to stop the precipitate from developing too quickly and blocking the well’s pores, so the process can take six to 10 weeks depending on the location and the specific mineral content.

Because of changes to farming methods in the last few decades, water contamination with arsenic has become a severe problem in parts of Bengal, Bangladesh and Southeast Asia.

‘Arsenic doesn’t have any taste or smell,’ said Sen Gupta. ‘Even with highly contaminated water that is extremely dangerous for health, people didn’t know and were drinking it for years until the symptom of dark patches on their skin appeared.’

Existing techniques for making water safe tend to rely on absorption beds that bind the arsenic with aluminium oxide.

SAR provides a cheaper, longer-lasting option, with a 20-year plant that produces up to 6,000 litres of water a day costing under £2,500 to set up and £14 a month to run.

‘Anyone can operate it,’ said Sen Gupta. ‘We have a very qualified, retired chief engineer of Boeing operating our plant in the US and an illiterate farmer operating our plant in the Bengal Delta.’