A greener jeans dye? Thank you, transforming E. coli
Researchers at the University of California, Berkeley, are trying to make the process of making blue jeans more environmentally friendly. They’re doing so by modifying bacteria to produce the indigo dye that gives jeans their unique color.
“Unfortunately, indigo dyeing of denim is a very polluting process.” So says John Dueber, co-lead author of the study and professor of bioengineering. Their research was recently published in the journal Nature Chemical Biology.
The blue color of jeans comes from indigo-dyed yarn.
Transforming E. coli
A cleaner way to synthesize indigo
The vast majority of jeans are dyed with synthetic indigo, a dye that mimics the dye derived from the wood blue plant (Indigofera). The indigo dye synthesis process requires a variety of toxic chemicals, including formaldehyde, as does the dyeing process. This results in huge amounts of pollution. In some parts of the world, rivers near denim factories turn blue, poisoning and killing fish and affecting the health of workers and residents. With more than 40,000 tons of indigo dye produced each year, the pollution caused by indigo became a serious problem.
The team sought to develop an indigo dye that would reduce the chemicals needed for the synthesis process and also not require as many chemicals to be added during the dyeing process.
“To make this new dye, we took inspiration from the way indigo is naturally synthesized by plants. The team modified an E. coli bacterium to become a “chemical factory” for producing the indigo precursor. The precursor is stable and can be stored until it is needed. Traditional synthetic indigo requires a chemical process to reduce and dissolve the indigo dye so that it can be precipitated on cotton fibers. Unlike this E. coli-produced precursor, it requires only one additional enzyme. The final product is “exactly the same” as traditional synthetic indigo, says Dibell.
This scarf is dyed with indigo produced by E. coli.
Going to market
The lab-to-mass-production dilemma
To get bacteria-produced indigo for the mass market, two major problems had to be overcome, says Dibell. First, indigo dyes best at high pH, and most denim factories use a pH of about 10.5. But the enzymes that Dibell’s team uses in the process are only effective at pH 8. So now the team is working on treating this enzyme so that it can react in higher pH environments as well. The second issue is scaling up production.
“We can scale up this method, and we’re confident of that.” Dibell says, “but there’s always a lot of work to do to get from lab scale to industrial mass production.”
The indigo produced by the bacteria could be used in small-scale production of custom jeans in a few years. People desperately need a better production process, Dibell said.
“Now that many countries that produce denim fabrics are starting to consider environmental management measures, there may be more pressure to adopt new production processes in these areas.
Pollution not solved
The wash-and-die step is still producing dirty water
Peter Hauser, a retired textile engineering professor from North Carolina State University, used to study indigo dyes. He agrees with Dibell, but he believes that techniques such as those used by Dibell’s team do not solve the entire problem.
Hauser believes that a lot of the contamination that occurs in denim manufacturing comes from rinsing after dyeing and sanding for an aged look. Denim, even if it is dyed with indigo produced by bacteria, still produces dirty effluent when rinsed.
“Once the application begins, this bacteria-produced indigo will not cause any less contamination than it did originally.” Hauser said.
Some eco-conscious manufacturers are returning to natural indigo dyes, which would reduce the use of chemicals but have long been shunned for cost and yield reasons. In Tennessee, a company called Stony Creek Colors has begun encouraging farmers to grow indigo to replace tobacco, hoping for a renaissance of natural indigo. But even with natural indigo, the rinsing process in manufacturing can still contaminate water bodies.
Another solution is to not dye jeans with indigo at all. Most dyes will actually penetrate the fibers, but indigo will only adhere to the surface of the yarn, which is why the rinsed indigo will run off into the water. This is also why jeans will turn white with wear. While other dyes can dye denim blue, they do not give the unique and sought-after worn white effect that indigo does.
“Indigo is actually a pretty bad dye.” Hauser says, “but because of the special properties-it lightens and washes out-people like indigo so much.”
