IISc researchers come up with solutions to reduce presence of heavy metals in groundwater

Most current methods for removing heavy metal contamination rely on pumping out water from the ground, followed by purification using chemical precipitation, adsorption, ion exchange, and reverse osmosis carried out at a different location

Researchers from the Indian Institute of Science (IISc) have developed a nanomaterial-based solution that can effectively reduce the presence of heavy metals like chromium in groundwater.

According to IISc, chromium typically enters soil and groundwater through effluents from industries such as leather tanning, electroplating, and textile manufacturing.

Current methods

Most current methods for removing heavy metal contamination rely on pumping out water from the ground, followed by purification using chemical precipitation, adsorption, ion exchange and reverse osmosis carried out at a different location. The IISc team instead proposes an on-site alternative which involves using iron nanoparticles that can remediate the heavy metals.

“Heavy metals enter the environment because of urbanisation and certain mismanagement by industries. If the groundwater is contaminated, we can inject these nanoparticles into the subsurface groundwater region where it will react with the chromium and immobilise it, resulting in clear water,” said Prathima Basavaraju, PhD student at Centre for Sustainable Technologies (CST) and lead author of the study.

The group first tried synthesising nanoparticles consisting of nano zero-valent iron (nZVI). This form of iron can react with the toxic and carcinogenic form of chromium (Cr6+) and reduce it to a less harmful form (Cr3+) which in turn results in co-precipitation. However, the team soon realised that the nZVI particles tend to clump together, limiting their application.

To prevent clumping, the team turned to carboxymethyl cellulose (CMC). “We modified nZVI by coating it with CMC. It forms a stabilising layer around nZVI separating individual particles,” Ms. Prathima added.

Preventing oxidation

The CMC coating additionally prolonged the life of the material by preventing oxidation of the iron core. The team also boosted the reactivity of the CMC-nZVI by exposing it to sulphur-containing compounds in anoxic conditions. This enabled the formation of a protective iron sulphide layer on the surface, a process called sulphidation. These modifications improved the stability of the S-CMC-nZVI and maintained its reactivity and efficiency.

S-CMC-nZVI showed nearly 99% efficiency at Cr6+ removal under different conditions such as different pH levels and the presence of other competing ions that might be found in groundwater. The team tested this enhanced nanomaterial in conditions that mimic the natural environment of groundwater aquifers. When they pumped contaminated water through sand columns containing the nanomaterial, they observed robust remediation activity. Experiments were also conducted on contaminated soil and sediments using nZVI to immobilise the heavy metals. Scaling up experiments are still in progress.

The authors suggest that S-CMC-nZVI is a promising material for on-site remediation of chromium-contaminated groundwater.

Lakes of Bengaluru

“Places like Bellandur lake in Bengaluru have a lot of contaminated sediments. The technique developed can also prove quite useful in remediating contaminants such as cadmium, nickel, and chromium in contaminated sediments of Bellandur lake,” said G.L. Sivakumar Babu, Professor at CST, Department of Civil Engineering (CiE) who is also the co-author of the study which was published in the Journal of Water Process Engineering.

Apart from CST, CiE, members from Department of Instrumentation and Applied Physics (IAP) were also part of the study team.

Published - September 19, 2024 09:00 pm IST