A glass of water can look clear and still contain contaminants that cannot be seen, tasted, or smelled. In several parts of India, groundwater contains naturally occurring arsenic and fluoride, pollutants that can pose serious health risks when people are exposed to them over long periods.
The challenge becomes even bigger when both are present in the same water. Removing one contaminant does not necessarily mean removing the other, making treatment more complicated and often more expensive.
Now, researchers at IIT Guwahati have found a way to tackle both at the same time.
The team has developed a rotating-anode electrocoagulation (RA-EC) reactor that can remove up to 98.2% of arsenate and 91.8% of fluoride within minutes. Even more importantly, the initial demonstration puts the estimated operating cost at just Rs 18 to Rs 58 for every 1,000 litres of treated water, depending on the concentration of contaminants.
A small change that makes a big difference
So, how does it work?
The idea builds on a familiar water-treatment process called electrocoagulation, where electricity and metal electrodes are used to help pull pollutants out of water.
But the IIT Guwahati team made one important change. Instead of keeping the aluminium electrode stationary, they made it rotate.
That movement may sound simple, but it changes what happens inside the reactor. As the aluminium anode rotates, it improves the mixing of water, helps pollutants come into better contact with the treatment process and continuously renews the electrode surface.
The process also encourages the formation of aluminium hydroxide flocs — tiny particles that act like pollutant catchers.
Unlike conventional electrocoagulation systems with stationary electrodes, the rotating design helps keep the aluminium surface active and reduces electrode passivation. Photograph: (IIT Guwahati)
When electricity passes through the reactor, aluminium ions and hydroxide ions combine to form these microscopic flocs. Arsenic and fluoride attach to them and can then be removed from the water through adsorption, coagulation and precipitation.
The rotating electrode also addresses another problem that can affect conventional electrocoagulation: electrode passivation. In simple terms, material can build up on a stationary electrode over time, reducing its effectiveness. The rotating design helps keep the electrode surface active.
Why removing both matters
Groundwater serves as the primary source of drinking water for millions of people across India. In several regions, however, it contains both arsenic and fluoride, two contaminants that pose significant long-term health risks.
“Treating them together has remained particularly challenging because they behave differently during conventional purification processes and compete for removal sites,” says Prof Mihir Kumar Purkait, Department of Chemical Engineering, IIT Guwahati.
The researchers wanted to know whether their reactor would continue to work when faced with the kind of complex chemistry found in actual groundwater — rather than only controlled laboratory water.
The IIT Guwahati team tested the technology under realistic groundwater conditions, including samples collected from Assam containing naturally occurring ions. Photograph: (BioTechNika)
So, they tested how factors including rotational speed, current density, electrode spacing and treatment time affected its performance. They also tested the system with naturally occurring ions such as calcium, magnesium, bicarbonate, sulphate and phosphate, as well as real groundwater samples collected from Assam.
“Our technology was also tested under realistic groundwater chemistry, including the presence of naturally occurring ions such as calcium, magnesium, bicarbonate, sulphate, and phosphate, as well as real groundwater samples collected from Assam,” says Mr Mukesh Bharti, Research Scholar, Department of Chemical Engineering, IIT Guwahati.
Taking the technology beyond the lab
The potential applications go beyond a single treatment system. The researchers say the technology could be adapted for community drinking-water purification, decentralised rural water-treatment systems and groundwater affected by arsenic and fluoride.
It could also be explored for industrial wastewater treatment or combined with technologies such as adsorption and membrane filtration.
The team hopes to take the reactor from the laboratory to communities, making cleaner groundwater treatment more effective and affordable. Photograph: (Meer)
The findings have been published in the peer-reviewed Chemical Engineering Journal.
But the researchers are already looking ahead. The next phase will focus on developing a pilot-scale, continuous-flow version of the reactor — a step towards seeing how the system could work outside the laboratory and at a larger scale.
The team also plans to introduce sensors and automated controls that can monitor parameters such as pH, conductivity, electrical current and rotational speed in real time.
For communities where clean groundwater remains difficult to access, innovations like this could eventually make treatment not just more effective, but more affordable too. And sometimes, it is a relatively simple rethink, like making an electrode rotate, that can move a promising idea one step closer to becoming a real-world solution.
