Researchers at Delft University of Technology have extracted a natural dye from sludge from wastewater treatment plants. The dye could be a sustainable alternative to traditional textile dyes.

It is a melanin-like biopolymer that was extracted from the activated sludge of a wastewater treatment plant. Melanin produces stable brown to black shades and is resistant to light and heat, whilst also imparting UV-protective and antioxidant properties to fabrics. The research, carried out by Yuemei Lin from the Department of Biotechnology at Delft University of Technology, was recently published in the scientific journal *Water Research*.

Melanin

Natural melanin is found in all kinds of living organisms, ranging from mammals to bacteria. Our own skin, for example, produces it as protection against UV rays in sunlight. It also gives colour to our eyes and hair. Bacteria produce melanin in response to environmental stressors such as light, temperature, oxygen or heavy metals. In addition, the pigment has a number of other valuable properties, such as antioxidant activity.

Environmentally friendly alternative

Melanin has been used in the clothing industry for many years, and is often extracted from the ink of cuttlefish, a type of squid. This source is in limited supply and also raises ethical concerns. Melanin is also produced synthetically, but according to the researcher, the resulting substance differs too greatly from natural melanin in terms of structure and properties. Extracting this pigment from sewage sludge therefore offers an interesting, environmentally friendly alternative for the clothing industry, which is known as one of the most polluting industries in the world.

Het wolgaren vóór (links) en na het verven met het gewonnen melanine-achtige materiaal (midden: 2 mg melanine per gram garen; rechts: 4 mg melanine per gram garen). Foto: TU Delft

Wool jumper

Biotechnologist Lin managed to extract the melanin-like substance from sludge at the Harnaschpolder municipal wastewater treatment plant near Delft. No less than 11 per cent of the sludge consisted of this brown pigment. Further analysis of the sludge revealed a range of bacteria responsible for synthesising the pigment.

To put it to the test, Lin dyed some wool yarn with the pigment. It turned out to adhere to the yarn particularly quickly and effectively. Her daughter even knitted a jumper from it – the first step outside the lab.

Deze trui breidde de dochter van onderzoekster Yumei Lin van geverfde wol. Foto: TU Delft

Fashion

Lin then got in touch with the Arnhem-based fashion brand Hul le Kes, which is known for its circular and socially responsible approach to fashion. The brand was keen to hear more and incorporated the new pigment into a number of garments as an experiment. ‘I’m so pleased that they’re open to new materials,’ says Yuemei in the TU Delft press release. ‘It’s led to some beautiful garments!’

Further testing

Designs from the sustainable fashion label that have been treated with this dye have now been presented at Paris Fashion Week. The researchers emphasise that this is, for the time being, merely a proof of concept, but they believe it looks very promising. Before clothing featuring this innovative pigment can be brought to market, further testing is required, as well as approval to use the pigment in production.

Opening photo: Designs bythe fashion label Hul le Kes featuring the innovative pigment. Credits: TU Delft/Hul le Kes