Synthetic dyes in wastewater pose threat to ecosystem

A study has found that dyes commonly used in textiles, food and pharmaceuticals pose a pressing threat to plant, animal and human health, as well as natural environments around the world.

Each year, billions of tonnes of dye-containing wastewater enter water systems. A group of researchers from the UK, China, Korea and Belgium say that new sustainable technologies including new membrane-based nano-scale filtration are needed to solve the issue, adding that legislation is needed to compel industrial producers to eliminate colourants before they reach public sewage systems or waterways.

Published in Nature Reviews Earth & Environment, the study highlights that up to 80% of dye-containing industrial wastewaters created in low- and middle-income countries are released into waterways untreated or used directly for irrigation. According to the authors, this poses a wide range of direct and indirect threats to human, animal and plant health.

Despite these threats to health and ecosystem, the authors say that there is inadequate infrastructure, investment and regulatory effort for making dye usage more sustainable, or for treatment of dye-containing wastewater.

Dr Ming Xie, a lecturer in the Department of Chemical Engineering at the University of Bath (UK), believes that a multipronged approach is needed to combat the issue.

“Dyes create several problems when they reach water systems, from stopping light reaching the microorganisms that are the bedrock of our food chains, preventing their reproduction and growth, to more direct consequences like the toxic effects on plants, soils, animals and humans,” Xie said.

“There are several potential ways to remove dyes from water including chemical, biological and membrane-based techniques, but different dyes required different approaches, and once they reach wastewater systems treatment processes can be highly energy intensive.

“A worldwide regulatory effort is needed to stop dyes reaching wastewater or other water systems such as irrigation. Given the complexity of treating dye-containing wastewater, one solution would be to shift from the concept of centralised or regional treatment methods, to decentralised and site-specific treatment at source, by compelling industries to remove dyes from the wastewater they create before it reaches public water systems.”

Dyes are used in the rubber, leather tanning, paper, food, pharmaceuticals and cosmetic industries, while the biggest user, the textile business, consumes 80% of produced synthetic dyes and generates about 70 billion tons of dye-containing wastewater annually.

China, India and Bangladesh combined discharge around 3.5 billion tonnes of textile wastewater each year. In water bodies, untreated dyes can cause colouration, reducing visible light and hindering photosynthesis for aquatic plants.

The review explores the variety of remediation technologies for dye-containing wastewater, including chemical, biological, physical and emerging advanced membrane-based techniques. The authors found that no single technique presents a ‘silver bullet’ for removing dyes, while several promising methods are not yet ready at scale.

In light of this, the researchers suggest a collective effort, led by policymakers, to increase the adoption of advanced remediation technologies and change textile processing methods to minimise the use of the most toxic dyes.

The authors also highlight a potential commercial impetus with industries potentially able to create new revenue streams from the processing, separation and reuse of wastewater materials.

Dr Dong Han Seo, co-author of the study, said the research provides insight on how to effectively manage the challenge from the perspective of a circular economy, recycling dyes from wastewaters using strategies to recover both useful dyes and clean water.

“This review provides the examples on how we can reduce the dye footprints from production stages using new dyeing techniques. Guidance on effective solutions to dye-containing wastewaters could be used to treat other challenging wastewater streams, safeguarding lives and the environment for future generations,” said Dr Jiuyang Lin, from the Chinese Academy of Sciences.

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