A Surface Change, But Not a Superficial One: IIPE Researchers Deliver Improvements to Water Treatment Technology

Water contamination is a pressing challenge in India, faced by both rural and urban populations. Untreated wastewater frequently finds its way into freshwater sources such as rivers. This muddy water, which encompasses riverbed sediments and wastewater residues, carries pollutants and contaminants that exacerbate water quality issues, lead to habitat degradation and species displacement, and cause diseases. Recently, researchers from the Indian Institute of Petroleum & Energy (IIPE), Vishakhapatnam, have provided a necessary fillip to India’s water treatment goals by developing a durable, cost-effective solution to enhance the efficiency and sustainability of mud water treatment. “The motivation behind our research was to find a way to improve water quality and contribute to environmental conservation and public health,” says IIPE’s Dr. Dipankar Pal, one of the authors of the paper that was published in Nature’s Scientific Reports.

The IIPE-led team also included researchers from the Assam Science and Technology University, Gauhati University, Pragjyotish College, and the Institute of Advanced Study in Science and Technology—all located in Guwahati. Mud water is commonly treated by filtration through cellulose-based membranes, which are known for their biocompatibility, eco-friendly characteristics, non-toxicity, and economic feasibility. However, the filtration efficiency of these membranes is highly impacted by a process called ‘fouling.’ Fouling occurs when particulate matter is deposited or adsorbed onto the surface of a membrane, thereby blocking its pores or reducing its filtration capacity. One of the major contributors to membrane fouling is the very nature of the membrane. Cellulose-based filtration membranes tend to be hydrophobic—they repel water and instead interact with substances in the water, leading to the build-up of contaminant particles on the membrane. Modifying the surface of the membrane to convert it from hydrophobic to hydrophilic (water-loving) is a particularly effective approach to solving the problem of fouling.

The research team assessed the outcomes of low-temperature plasma surface modification (PSM) of cellulose nitrate membranes using two different gases—nitrogen and argon—and compared the resulting surface morphology (structure and features), wettability (hydrophilicity), and surface chemistry of the membranes. “This kind of PSM is not permanent,” describes Dr. Pal. “Eventually, the membranes tend to recover their hydrophobic nature. This is known as ageing. In our research, we also paid special attention to the ageing behaviour of the membranes as they have a critical impact on their final application in wastewater treatment.” The researchers found that low-temperature PSM led to the creation and enlargement of pores in the membranes. Analysis of the membranes also revealed changes in the polymer matrix of the cellulose as well as increased surface functionalisation (addition of reactive molecules called functional groups).

Argon-plasma treatment led to a higher surface roughness in the membranes compared to nitrogen-plasma treatment, as well as greater wettability. The research team then tested the membranes using a filtration setup under normal atmospheric conditions, which used gravity as the main driver of filtration. They found that both argon- and nitrogen-plasma treated membranes showed higher filtration rates and lower fouling than untreated membranes. Of the two, the argon-plasma treated membrane showed better performance. Both membranes exhibited fast ageing in the first seven days, after which the rate of ageing slowed down and eventually stabilised. According to Dr. Pal, “We developed a diffusion-based theoretical model to study the ageing behaviour of the membranes and found a strong alignment between the theoretical and experimental results, which could help us to more easily predict the ageing behaviour of future membranes that are treated by this method.”

The research team also investigated the Cake Filtration Model—an established model for membrane fouling—and found that it was suitable to describe the behaviour of the untreated and treated cellulose nitrate membranes. “This research demonstrates an innovative application of low-temperature plasma discharge for the surface modification of cellulose nitrate membranes,” affirms Dr. Pal. This method can significantly reduce membrane fouling behaviour and, thus, enhance the efficiency, sustainability, and economic feasibility of mud water treatment. Plasma treatment is also an eco-friendly approach towards enhancing filtration membranes, as it avoids the use of harsh chemicals.

These findings could have large-scale impacts on the treatment of mud water from major rivers, such as the Godavari, Krishna, and Ganga. In particular, the Namami Gange programme—which aims to abate pollution in the River Ganga, as well as conserve and rejuvenate its waters—could be supported by the application of these research findings. This type of plasma treatment can also be applied for industrial wastewater treatment, which will, in turn, lead to lower contamination of mud water. Municipal water treatment facilities can also adopt this approach to improve public health by providing clean water to urban and rural populations. Finally, this research can also be applied in the agriculture sector, to provide treated wastewater for irrigation—a move that will not only promote sustainable farming practices but also mitigate soil contamination.

“Over the next five to ten years, we foresee the application of this research will have a positive impact on river ecosystems by reducing pollutants and contaminants, as well as supporting biodiversity and ecosystem health,” concludes Dr. Pal. Developing an eco-friendly, sustainable technology for the treatment of contaminated water is key to not only improving water quality and furthering public health, but also meeting the United Nations’ sustainable development goals. Congratulations to the team for their extraordinary results, which will surely lead to the well-being and improved quality of life for millions of people!