Reducing the environmental impact of denim dyeing

Ólafur Ögmundarson, senior lecturer at the University of Iceland Faculty of Food Science and Nutrition, is among the authors of a new scientific article published in the prestigious journal Nature Communications. The article explores production of a new blue pigment, indican, which could replace the traditional indigo to make jeans dyeing more sustainable. Billions of pairs of jeans are manufactured each year. Ólafur's colleagues in Denmark are working to establish a start-up company, based on the new method they have developed.
The study was led by Ditte Hededam Welner, a research scientist at the Novo Nordisk Foundation Center for Biosustainability at the Technical University of Denmark (DTU) – otherwise known as DTU Biosustain. This is an interdisciplinary research centre focused on searching for new ways to use enzymes and bacteria to produce various biomaterials. 

Ólafur completed his PhD in environmental management from DTU and worked at DTU Biosustain for a time before he began working at the University of Iceland. This particular study began in 2019. 

Enzymes and sunlight used to dye denim

The pigment currently used to dye blue jeans is called indigo and the process of producing the indigo and dyeing the denim has a highly negative impact on the environment. Most indigo is produced in China, before being transported to India, Bangladesh and Pakistan where the jeans are manufactured and dyed.

The research team behind the article in Nature Communications has developed a new and more sustainable way to dye denim, using the pigment indican, which reacts with either enzymes or sunlight to turn the typical blue colour of jeans. This process avoids the need to use reducing agents and is also more energy efficient, two factors which make it much more sustainable than traditional indigo dyeing. "The idea is to have a conveyor belt that dips the jeans in indican. Next the jeans are either dipped in enzymes or exposed to light, which brings out the blue colour," explains Ólafur.

According to Ólafur, Ditte Hededam Welner, research scientist at DTU and leader of the project, and her colleagues are now working on establishing a start-up company based on this method of dyeing jeans. Jeans manufacturers in Italy and Spain have also expressed an interest in adopting the process.

There is a lot to be gained by reducing the environmental impact of denim dyeing, since four billion pairs of blue jeans are sold across the world every year. In the time that it has taken you to read this news article, several hundred pairs of jeans have been sold in the world.
Ólafur stresses that the study only looks at the production and use of pigments in the denim industry, not the production of cotton or the manufacturing of the jeans themselves – these parts of the industry are much larger and have a more negative impact on the environment than the dyeing stage. 

Developing complex processes

According to Ólafur, the study has been complex, involving experiments in the lab, replicating and optimising manufacturing processes, and calculating the economic benefits of the new method. "My role in the research was to conduct the Life Cycle Assessment (LCA), which I initiated. An LCA is about looking at the environmental impact of all factors and materials needed to manufacture the pigments and the different methods of dyeing jeans. We considered the environmental impact of things such as greenhouse gas emissions, human toxicity, water consumption, lake eutrophication, and ocean acidification," explains Ólafur.

He uses the same methods in his food science and nutrition research at the University of Iceland and also teaches a course focused on sustainability assessments. 

According to Ólafur, the study published in Nature Communications is also unusual in that it considers all aspects of sustainability, including environmental impacts, the economics, and the potential societal impacts. "This new method of dyeing jeans will possibly not be happening in countries like India and Bangladesh and what will that mean for the people there currently working in this industry? They may lose their jobs, but on the other hand they may not be exposed to as many toxic substances," explains Ólafur.
This is one of the interesting things about sustainability, which most countries are now addressing, e.g. through the the UN Sustainable Development Goals. "We want to save the world – that's why we're doing this, and a lot of effort goes into it. But what consequences will our actions have? It's important to look at the whole picture, which is something we tried to do in this study."

The study has received media attention in Denmark, including in Politiken and Videnskap.