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Azo dye: A popular but hazardous dye should be eliminated from industrial process

A carcinogen is a substance, organism or agent capable of causing cancer. Do you know that almost 20 out of 300 known azo dye varieties, mostly consisting of a benzidine-based chemical, are recorded as carcinogens?

You know color has an important role to play in textile, food, printing, pharmaceutical and cosmetic industries. Azo dye, a type of dye that is strictly regulated in many countries due to the health risk posed by certain varieties, is extensively used as coloring agent in most of the industrial processes. It represents the by far most important class of textile dyes. Their biotransformation by various skin bacteria may release aromatic amines (AAs) which might be dermally absorbed to a major range. Certain AAs are famous to have genotoxic and/or carcinogenic properties. Congruently, azo dyes releasing one of the 22 known carcinogenic AAs.

So, it has posed a challenge for the textile industries for its removal from the industrial waste water.

Azo dye is widely used in the local garments market of Bangladesh, which uses a great amount of dye to color a wide range of clothes. But the amount and types of azo dye used in the industry in Bangladesh is unknown.

A source from the Department of Textiles, owners require a go-ahead for setting up textile industries in the country. Though the department does not have a role to advise how much color or chemical a textile factory might need to use, which leaves a gap in the system.

Properties of azoic dye:

Some key properties of azoic dye are:

  • Mostly used for lighter shade dyeing
  • Directly insoluble in water
  • Insoluble azo group present in it
  • Brightness of azoic dye is decent
  • Addition of salt increases substantively
  • High fastness characteristics and rightness of shade of this dyestuff are admirable
  • Dyeing operation is completed by two bath arrangement: developing bath and impregnating bath
  • Always contains azo groups in its chemical structure
  • Always used in cellulosic materials
  • Wash fastness is very good here
  • Napthol dispersed in alcohol T.R.O
  • Coupling is necessary for color production
  • Mainly applicable for cellulose fibres
  • Application time has needed more here
  • Azoic dye is comparatively cheap than other dyes.
  • Dyeing process is done by using three processes here: coupling, naptholation and diazotization.
  • Final color is produced within few seconds after immersing the next materials in the dye solution

Some Azoic dyes

In today’s fast-consuming world, whenever a synthetic dye particle needs to be used, azo dye is the answer as it offers a vast diversity in usage at reasonable cost along with resilience, easy manufacturing and disposable features.

Health and environment are suffering

The readymade garment industry (RMG) is the biggest export sector of Bangladesh and earnings from RMG in the 11 months of FY22 increased by 34.87 per cent to $38.52 billion. The industry is using different types of dyes. According to Bangladesh Bank data, in the fiscal year 2020-21, products worth Tk6,329.7 crore were imported that were related to dyeing, tanning, pigmenting and coloring textiles.

By releasing of azo dye through textile effluent, textile industry is the main cause of water pollution resulting into acute effect on environment and human health. Though the carcinogenic azo dyes are completely banned as factories in Bangladesh are advancing towards Zero Discharge of Hazardous Chemicals (ZDHC) program. 28 variants of azo dye have been listed as hazardous to health.

Most of the reputed buyers have strict requirements and they insist on curbing the use of azo dye in manufacturing clothes. The standard is sustained through the testing of the finished clothes through multiple local and international testing organizations. There is no chance for the existence of any harmful chemical in our finished products.

According to a BUTEX professor, nearly 700-800 dye factories have been established in the country for the export-oriented market. However, for local customers, this number can go up to 5,000. And our factories import azo dye mainly from India and China, and these countries produce low-quality dye.

To meet the demand of the local market, our industries use at least 10,000 tons of chemicals every year. Our garment industry has long enjoyed the benefit of relaxation against the profit they bring.

The European Union has banned 22 variants of azo dye citing carcinogenic aromatic amine from textiles. India banned the presence of azo dye first in 1997 by prohibiting the handling of a total of 112 azo- and benzidine-based dyes.

In Bangladesh, no such law is present. Only benzidine was found to be restricted in the Hazardous Wastes and Shipbreaking Waste Management Rules of 2011.

The way to reduce the effect of azo dye

Development of any eco-friendly and cost-effective method that may address the disadvantages to physical or chemical methods of dye elimination is the recent global priority. A research paper titled ‘Degradation of synthetic azo dyes of textile industry: A sustainable approach using microbial enzymes’ noted that physical or chemical methods for textile wastewater pretreatment are of high cost, extremely energy consuming, and environmentally low efficient and generate toxic sludge. Thus, the use of microbial technique for textile dye degradation will be eco-friendly and is probably a lucrative alternative to physico-chemical processes.

Microbial enzymes, viz. laccase and azoreductase, are cost-efficient, easy to harvest, easily downstream processable, and effortlessly mobilizable. Recent research trends on nanoparticle-microbial enzyme conjugates are also highly efficient to remove the azo dye from textile waste within a few minutes, the research highlighted.

But unfortunately, due to some gap between academia and industry, these methods remain only limited up to laboratory and its industrialization is still a challenge. The present review is a proved compilation of the use of microbial enzymes in removal of textile dyes.

The writer, a business analyst is Executive Director, Skyros Trading Ltd.

If anyone has any feedback or input regarding the published news, please contact: info@textiletoday.com.bd

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