A research team at the Indian Institute of Technology Mandi, led by Dr Sumit Sinha Ray, Assistant Professor, School of Engineering, has developed a fibrous membrane filter using a biopolymer-based material to remove heavy metals from water. The results of this research have recently been published in the prestigious Elsevier journal, Polymer. The paper has been co-authored by Dr Sinha Ray and his research scholar, Ashish Kakoria, along with Dr Suman Sinha Ray, Adjunct Assistant Professor, University of Illinois at Chicago.
Acid mine drainage containing large quantity of heavy metals is a menace. Heavy metals in water could lead to several neurological problems in human including Alzheimer's, Parkinson’s, and multiple sclerosis, and it is important to develop filters to treat effluents that are released into water bodies to prevent pollution.
Background
Heavy metal pollution of water is a serious concern. “The problems of arsenic pollution in the Ganga basin are well known in India,” says Dr Sumit Sinha Ray. The Indian National Science Academy reports that the major hazardous metals of concern for India in terms of their environmental load and health effects are lead, mercury, chromium, cadmium, copper, and aluminium, that are released into the water through anthropogenic activities such as mining, manufacturing, electroplating, electronics, and fertiliser production, among others.
These membranes contain adsorbents — materials that attract and hold the metals to binding sites in question. “In this work, we have provided a novel, industrially scalable method of production of adsorbents that can bind to heavy metals. One specialty of these adsorbents is that they contain a large amount of a biopolymer, Chitosan, derived from crab shells that is mixed with a well-known polymer, Nylon,” explains the lead researcher.
While normally the fibres used to make regular cartridge filter-assemblies are processed by a method called melt blowing, the IIT Mandi researchers have used a process called “solution blowing”. Solution blowing produces fibres that are nanometres in diameter — a hundred thousand times thinner than a single human hair. When the fibres get finer, their surface area increases tremendously, which results in better adsorption of heavy metals.
“Apart from producing nanofibres, solution blowing processes can enable blending of natural polymers like chitosan, lignin etc. with synthetic polymers like Nylon, and Poly (methyl methacrylate)," says Dr Sumit Sinha Ray. The replacement of synthetic polymers with natural polymers is a welcome move in this era of environmental consciousness. Using the solution blowing technique, the IIT Mandi team could replace 40 per cent of the nylon with chitosan, which means 40 per cent less fossil-fuel-derived, polluting plastics.
Proof of principle
Along with this, the researchers have also observed that while normally adsorbent fibres bind to the target metal only at their surface, in their nanofibre membranes, the adsorption was seen to happen at the sub-surface scale as well, which translates to higher metal removal efficiency as per the researchers’ hypothesis, like — for copper almost 302 mg of metal ion could be adsorbed per 1g of adsorbent.
The membranes could be reused at least eight times before there was considerable reduction in the efficiency of metal adsorption. Recovery of the adsorbed metal in a metal-hydroxyl nitrate form was also easy, which is a value-addition to the membrane filter.
“We tested with a prototype with four litres of heavy metal-laden water in the lab and have seen impressive results,” says the scientist. The researchers tested their membrane with copper laden water, to establish proof of principle.
Dr Sumit Sinha Ray and his research team at IIT Mandi are all set to scale up the technology to industrial scales, to handle larger volumes of metal-contaminated water. This study is funded by the Ministry of Mines, Government of India.