Materials: Making a Positive Difference

Article by Adam Duckett

Adam Duckett talks to the engineers developing technologies to reduce the environmental impact of our clothes

PULLING on your socks each morning is such a mundane aspect of our everyday lives that it’s easy to lose sight of the extraordinary impact that our clothing has on our wider world. Yet the numbers are startling. The Ellen Macarthur Foundation, a charity pushing for the development of a circular economy, reports that textile production emits more greenhouse gases than international flights and maritime shipping combined; contributes half a million tonnes of plastic microfibres to the ocean each year; and with less than 1% of the material used to produce clothing being recycled, more than US$100bn worth of materials are lost each year. Chemical engineers are well placed to make a positive difference, and this is certainly the case when it comes to helping textile manufacturers reduce the huge volumes of water they consume and wastewater they produce.

The World Bank estimates that textiles production uses around 93bn m3/y of water, equivalent to 4% of global freshwater withdrawal. This number feels too large to fathom so let’s put it another way. It’s estimated that producing just one t-shirt requires 2,700 L of water – enough drinking water for one person for two-and-a-half years. A pair of jeans requires more than 9,000 L of water.

The World Bank estimates that textiles production uses around 93bn m3/y of water, equivalent to 4% of global freshwater withdrawal. This number feels too large to fathom so let’s put it another way. It’s estimated that producing just one t-shirt requires 2,700 L of water – enough drinking water for one person for two-and-a-half years. A pair of jeans requires more than 9,000 L of water.

The numbers become so large because water is required at every stage of the textile manufacturing process, as well as watering the crops that are cultivated for natural fibres. The key wet processes involved include washing, bleaching, dyeing, printing and finishing, and they employ a cocktail of chemicals (see boxout). In its Pollution Prevention and Abatement Handbook, the World Bank notes that the industrial wastewater resulting from these processes is a major source of pollutants. The wastewater is typically alkaline, and has high biological and chemical oxygen demand It can contain oil; toxic organics, including phenols from dyeing and finishing; halogenated organics from bleaching; while dye wastewaters often contain unused dyes and heavy metals.

The resulting wastewater should be remediated before it’s released into the environment, but lax regulation and poor compliance means it is frequently discharged without treatment. Or the wastewater is treated, but the resulting sludge rather than being safely disposed of is stacked at the side of rivers so that when it rains the pollutants are washed in. This creates a viscious cycle. The rivers that communities rely on for bathing, fishing and irrigating crops are being poisoned. An infamous example is Indonesia’s Citarum River, whose name is derived from the indigo plants that grow alongside it and were once an important source of dye. But the river is now synonymous with heavy pollution, including untreated wastewaters replete with synthetic dyes, that are released from the heavy concentration of textile manufacturers that fringe the river’s banks. In 2013, the Blacksmith Institute, a charity that works to remediate industrial pollution and has since renamed itself Pure Earth, put the Citarum River among the world’s top ten toxic threats. And Indonesia is not the only country affected. Other countries with large garment manufacturing industries, including China and Bangladesh, are also struggling with pollution.

Reference: Swedish Chemicals Agency; Ellen Macarthur Foundation, World Bank

Let’s look at a selection of innovative projects working to tackle these issues and help prevent the materials we wear from having such an oversized impact.

Reducing the chemicals input (and much more beside)

Colorifix is a UK-based biotech company that has designs on overhauling the dyeing process. The company says that compared to conventional dyeing of cotton, its technology reduces water use by 49%, electricity use by 35%, and emissions by 31%. Colorifix takes the genetic codes for colour found in nature and copies them into microbes to produce the dyes and then fix them during the dyeing process.

“For example, if you really like a certain shade of blue that you find in a specific flower, you can find the genetic recipe inside of the genome for that plant,” says Fernanda Farias, who works as a Senior Bioprocess Engineer at Colorifix. Before taking on this engineering challenge, Farias worked in the biofuels industry developing second-generation production plants in Brazil to help reduce the use of fossil fuel feedstocks. She says she thought: “Why not try to get into another field that is also very detrimental to the world and try to develop a better, more environmentally-friendly way of doing things? That’s why I end up ended up working at Colorifix.”

Farias works with Colorifix’s clients helping with the technology transfer to their sites. Colorifix is looking to turn the existing dye supply business model on its head. Rather than send dyehouses bulk shipments of concentrated dye, the company installs a bioreactor at the dyehouse and sends the customer just a 5 mL sample of modified microbes to ferment its own dye.

“We sell the knowledge for them so they can produce the pigments in-house,” Farias says.

“Right now we have our technology being implemented simultaneously in three different dyehouses, one of which we have already been working with since 2020.”

Reference: Swedish Chemicals Agency

Fashion sells fast

While it’s still early days for the company, the clothes its technology has dyed have already proved popular. Last year, Colorifix and a dyehouse produced a special collection for clothing brand Pangaia which sold out within half an hour of being listed online. Since then, the company has been updating its processes and machinery but Farias expects its customers to begin production again very soon.

The technology offers various advantages over conventional synthetic dyeing methods. Firstly, it eliminates the fossil fuel feedstocks needed to produce synthetic dyes, with the bacteria fed on sugars and plant byproducts. It also reduces the footprint of shipping bulk volumes of dyes. And beyond the installation of a bioreactor, the technology can be used without altering the existing dyehouse machinery. The bioreactor installed at the client’s facility can be connected directly to the dyeing machines and the dye liquor pumped straight in. Farias explains that in conventional dyeing processes, the dyehouse must add lots of auxiliary chemicals to fix the dye to the fabric. These are added and then the dye machine is heated and held at a certain temperature for a length of time. Then another chemical is added, and the dye machine is ramped up to a higher temperature for another length of time, and so forth.

“It’s a very long, time-consuming process compared to ours,” she says, noting that its dye is fixed without the need for chemicals, heavy metals or organic solvents. The bacteria that produces the dye also fixes it to the fabric.

“When we raise up the temperature we kill the bacteria and that’s something that we really want to do because it’s a GMO bacteria. We don’t want to let it live in the environment.”

Farias says the Colorifix process also helps to save water. The way she explains it, synthetic dye processes use water twice. Once to produce the dye before shipping, which has to be concentrated to remove water to reduce transportation costs, and then the dyehouse has to put the water back in to dilute the dye. 

Colorifix takes the genetic codes for colour found in nature and copies them into microbes to produce the dyes and then fix them during the dyeing process

Bioreactor pivot

Asked about the engineering obstacles the company has overcome so far, Farias says the company developing its own bioreactor was an unexpected challenge. It had planned to buy third-party bioreactors but found that what the market had to offer was targeted at the pharmaceutical industry and too needy in terms of maintenance and the use of consumables.

“We started with a company where the idea was ‘Let’s produce colour. Let’s produce different microorganisms’. And we ended up with not only that part but also the machinery part”, Farias says.

“We now have a machine that we know works well and is reliable, and it gives us very good reproducibility in terms of fermentation.”

Another challenge is overcoming conservatism, and convincing dyehouses to produce their own dyes rather than buy them in bulk.

“I would say that every new customer is a big challenge on that matter. Usually, getting it to a new customer means that a part of the company or the owner really liked the idea and wants to see it working. But then once you get to the production level and with people who have been working the same way their whole lives, they’re usually very resistant. They’re usually like, ‘Oh, no! No way this is going to happen. Forget about it. No, no way.’”

Farias giggles as she describes the production team’s typical surprised reaction to the first batch of Colorifix dyed clothes.

“They usually say ‘Oh God, this really works!’ You need to charm them a little bit in the beginning. The production guys especially.”

The company is being very selective with who it chooses to work with and visits its client’s sites to make sure their operations are environmentally responsible.

The spent liquor produced by dyehouses using Colorifix technology can be readily processed through conventional wastewater processes. “We do have some parallel plans on reusing that water, for example treating it a little bit and then maybe reusing it again into the process. But these are very early stage projects,” Farias says.

Eventually, the company wants to expand out of Europe and work with dyehouses in Asia and the Americas, and spread its technology to other sectors including packaging and plastics.

To close, I ask if there are any particular challenges around colour development. Farias has already explained that if they develop a dye that has poor colour fastness – that is, it fades too quickly or runs – redevelopment involves re-engineering the microbe. But is it, for example, difficult to develop a really strong purple? What colour is it that the bioengineers are struggling to crack?

“Purples are actually quite easy to produce. We have a full range of purples. I would say that black is a very big challenge. We’re getting closer. But the thing is in nature you don’t have full black – deep, dark black. It’s usually more a mixture of the surface structure itself plus dark melanin, and lots of it, that gets you that sensation of black. But it’s not really real, real black. So getting that from the bacteria has been very challenging, but we’re getting there. We’re pretty close now.”

Colorifix developing its own bioreactor was an unexpected challenge

Closed-loop water treatment

Meanwhile, trying to clean up the existing wastewater problem is the Waste2Fresh consortium. This EU-funded project is a collaboration of 17 partners working to develop a modular closed-loop wastewater treatment process that would allow textile manufacturers to collect, recycle and reuse their water as well as salts and metals for use in other applications. At the heart of the process is a plant-based nanostructured material called Nanofique whose catalytic properties degrade dyestuff in wastewater, removing the colour and toxic effects.

The ambition is to increase resource and water efficiency by 30% compared to the current state-of-the-art. Not only will this help to reduce environmental pollution but reduce water use which would be a boon for water-stressed regions like those in Bangladesh that are home to textile manufacturing hubs but struggle with water provision and pollution.

Richard Burke, founder of Nanofique Limited who leads the Waste2Fresh project, said: “At the moment, what’s happening is that 20% of water contamination comes from textile dyeing and treatment. If you look at the amount of water used by the textile industry it works out at more than an Olympic swimming pool per second. The volumes are enormous.”

Burke once worked in India and saw people pumping drinking water that was stained purple.

“As a young engineer you put two and two together and think ‘Well that doesn’t look very good’ but you don’t really know what to do about it. It was many years later when I started looking at different types of technology that I came across some initiatives around the use of nanomaterials for degrading dyestuff.”

“I said to them ‘This has a great future and there is a big need for it because textile plants have a problem with wastewater, particularly from the dye unit. Anything that can improve that is good.’ I set up Nanofique Limited with the objective of scaling this up to use within the industry.”

Burke says treating dyes is particularly challenging because, as Farias noted, they are designed to be robust. The Waste2Fresh system will use a combination of catalytic nanotech, photocatalytic processes and nanobubbles to treat the wastewater.

The Waste2Fresh partners have been separately running pilot trials of the individual technologies at their own sites across the world. The target is to integrate these into a demonstration plant that will begin operations at a denim factory in Turkey next year. It will have the capacity to process 40 m3/d of wastewater, which is in line with the output of typical dye machines, Burke says. Once demonstrated, the goal is to have the technology ready for commercial deployment in 2025.

Karnopara Canal in Dhaka has turned purple due to discharge of wastewater from nearby dyeing factories

Treatment today

Conventional treatment plants for textile wastewater vary depending on the chemicals used. Commonly, they involve primary treatments including screening, sedimentation, flocculation and chemical coagulation; followed by secondary operations that might include aerobic and anaerobic treatment, activated sludge processes, and trickling filtration; and then tertiary processes involving membrane technologies, adsorption, oxidation, photocatalytic degradation, and thermal evaporation.

George Williams, a chemical engineer at the UK’s Centre for Process Innovation which is responsible for scaling up the process and leading the overall design of the Waste2Fresh system, outlines how the system is expected to work. It begins with a course filtration stage used to remove particles of pumice stone used to distress the denim.

“You then go into your Nanofique reactor. This is your bed of fibrous material that’s going to break the chromophore bond in the dye.”

At this point, if it works as planned, the dark blue wastewater stream from the denim factory that entered the process should now be clear and colourless. That then passes into a photocatalytic reactor to continue degrading the dye constituents and the organics present in the system.

“The aim is to break that down into CO2, water and small amounts of other contaminants that can be dealt with later on.”

It then passes to a heavy metal removal system, and after this point most of the contaminants should be stripped out, leaving salt.

“There’s a lot of salt that you add to help with the dyeing, but also there’s a lot of sodium that gets added in the bleaching stages,” Williams explains.

“So then there’s a desalination and water polishing stage. So that’s to remove the salt and if the previous process is working it should be a fairly pure salt, or hopefully pure enough that it could be reused in the textile industry.”

Williams says at this point all that should be left is a clear wastewater that ought to meet the Zero Discharge of Hazardous Chemicals (ZDHC) wastewater guidelines that have been adopted by major clothing brands and suppliers including H&M, Levi Strauss, Nike, BASF and Huntsman.

“You’ve got a choice of what you can do with that wastewater. You can send it off into the river or you can send it back into the process. We’re also looking at developing a hydrogen storage system. There’ll be a solar array powering an electrolyser using the clean water out of the system. And that will store hydrogen for use in fuel cells when power is needed for the factory at night time.” The photocatalytic unit will use sunlight from solar concentrators and there will be an LED-powered photoreactor for use at night time that will run off hydrogen produced during daylight hours.

Development and integration

Asked what’s unique about the process, Williams says: “I think the major difference is breaking down the colour at the start. It takes away that harmful effect of the dye going into the wastewater stream and blocking the sunlight. It opens up the use of a photocatalytic reactor to degrade your organics.”

He notes the technologies involved are all currently at quite low technology readiness levels so it’s a challenge to jointly develop and integrate them. He says proving to potential customers that the technology is economical and uses less energy will be key to them adopting it.

Richard Burke with the pilot system at Konya Technical University in Turkey which is coordinating the Waste2Fresh project

Burke and Williams say a small footprint and modular nature stand the technology in good stead. Williams adds: “You think of wastewater treatment now, and you probably think of massive circular tanks taking days or weeks to slowly treat water, whereas this would be a turnaround time of a few hours.”

Asked what excites him about the project as a chemical engineer, Williams points to the real-time sensors being developed to monitor heavy metals by project partners from the National Academy of Sciences of Ukraine.

“They’re looking at an online system using a range of enzymes that are then calibrated against each other. For waste metals, normally you’re looking at offline ICP analysis, which will cost you an arm and a leg. And unless you’ve got the ICP analysis on site it’s going to take a long time as well, which isn’t very good for a continuous process if you’re trying to feed it back in or straight to discharge.”

Burke points out that due to Russia’s invasion of Ukraine, researchers from the sensors team have become refugees and the partners have rallied to provide them with facilities to continue their work. He also notes that the safety element of the project is important, pointing to the work being done by Germany’s Fraunhofer research society to ensure the handling and shipping of nanomaterials is safe for everyone involved throughout the supply chain.

Where does it end?

Burke is hopeful that the representatives from the ZDHC that are on the project’s advisory group will help push the adoption of the technology. Though he recognises that brands must walk a tricky public affairs tightrope when it comes to lauding greener practices, because there’s the reputational risk of being asked to explain the harmful practices that came before. And how will developing economies reliant on cheap textile manufacturing for significant portions of their national income balance economic security and the desire for further growth with the imposition on industry of more stringent and expensive environmental regulations? It’s hard to know, but Burke’s vision of the future is one where a textile manufacturer is required to continually recycle and reuse just the volume of water needed to carry out its operations.

“There’s your 2,000 cubic meters of water,” he says, imagining a future conversation with a dyehouse, “and that’s your lot. You’ve just got to keep reusing it’.

He accepts that might be too strict but he expects the demand for an end to industrial pollution will force a change.

“My vision is to use the technology to end dye pollution so that this 20% of contamination coming from textile dyeing and treatment is ended. It’s a long road and it’s very ambitious. But you have to start somewhere. It’s all about taking one step at a time.”

Article by Adam Duckett

Editor, The Chemical Engineer

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