Fashion for wood could stop polluting dyes

Image: Chalmers University of Technology | David Ljungberg

A nature-based technology developed in Sweden can purify water contaminated with textile dyes using wood from trees.

Field trials in India are the next step for the collaborative researchers and the discovery could have a major impact on countries combatting the discharge of toxic dyes into rivers and lakes from the fashion and textile industry. Poor water treatment processes, antiquated equipment and a lack of environmental governance all contribute to the problem.

Clean water is a prerequisite for human health and the living environment, but it is far from a given for everyone. According to the World Health Organisation (WHO), there are currently over two billion people living with limited or no access to clean water.

“Going from discharging completely untreated water to removing 80% of the pollutants ... means significantly less destruction of nature and harm to humans."

Professor Gunnar Westman, Chalmers University of Technology

This global challenge is the focus for a research group at Chalmers University of Technology in Göteborg, which has developed a method that can easily remove pollutants from water. Led by Gunnar Westman, associate professor of organic chemistry, the group focuses on new uses for cellulose and wood-based products and is part of the Wallenberg Wood Science Center.

The woody tissue of trees is made mostly of cellulose, a long, fibrous carbohydrate that forms the walls of plant cells. The researchers have built up solid knowledge about nanocrystals found in cellulose - tiny nanoparticles that hold the key to water purification, as they have an outstanding adsorption capacity.

“We have taken a unique holistic approach to these cellulose nanocrystals, examining their properties and potential applications. We have now created a biobased material, a form of cellulose powder with excellent purification properties that we can adapt and modify depending on the types of pollutants to be removed,” says Professor Westman.

In their study, the researchers show how toxic dyes can be filtered out of wastewater using the method and material developed by the group. The research was conducted in collaboration with the Malaviya National Institute of Technology Jaipur, in India, where dye pollutants in textile industry wastewater are a widespread problem.

The treatment uses sunlight to catalyse the process, and Westman likens the method to pouring raspberry juice into a glass with grains of rice, which soak up the juice to make the water transparent.

When the polluted water passes through the filter with cellulose powder, the pollutants are absorbed, and the sunlight entering the treatment system causes them to break down quickly and efficiently. Image: Chalmers University of Technology | David Ljungberg

“Imagine a simple purification system, like a portable box connected to the sewage pipe. As the contaminated water passes through the cellulose powder filter, the pollutants are absorbed and the sunlight entering the treatment system causes them to break down quickly and efficiently.

"It is a cost-effective and simple system to set up and use, and we see that it could be of great benefit in countries that currently have poor or non-existent water treatment,” he says.

Producing one kilogram of new textiles requires between 7,000 and 29,000 litres of water, and between 1.5 and 6.9kg of chemicals. In 2021, around 327 thousand tonnes of dyes and pigments were produced in India, which is one of the Asian countries with extensive textile production, where large amounts of dyes are released into lakes, rivers and streams every year.

Gunnar Westman, associate professor at the department of chemistry and chemical engineering. Image: Chalmers University of Technology

The consequences for humans and the environment are serious. Contaminated water containing dyes and heavy metals can cause skin damage with direct contact, and increase the risk of cancer and organ damage when they enter into the food chain. Additionally, nature is affected in several ways, including the impairment of photosynthesis and plant growth.

Conducting field studies in India is an important next step, and the Chalmers researchers are now supporting their Indian colleagues in their efforts to get some of the country's small-scale industries to test the method in reality. So far, laboratory tests with industrial water have shown that more than 80% of the dye pollutants are removed with the new method, and Professor Westman sees good opportunities to further increase the degree of purification.

“Going from discharging completely untreated water to removing 80% of the pollutants is a huge improvement, and means significantly less destruction of nature and harm to humans. In addition, by optimising the pH and treatment time, we see an opportunity to further improve the process so that we can produce both irrigation and drinking water.

"It would be fantastic if we can help these industries to get a water treatment system that works, so that people in the surrounding area can use the water without risking their health,” he says.

Gunnar Westman also sees great opportunities to use cellulose nanocrystals for the treatment of other water pollutants. In a previous study, the research group showed that toxic hexavalent chromium, which is common in wastewater from mining, leather and metal industries, could be successfully removed with a similar type of cellulose-based material.

The group is also exploring how the research area can contribute to the purification of antibiotic residues.

The research is funded by the Wallenberg Wood Science Center, WWSC and the Indian group research is funded by Science & Engineering Research Board under Department of Science & Technology, Government of India.