Since their accidental discovery by Sir William Henry Perkins in 1853 azo dyes have become one of the most popular forms of synthetic colourant used in the industrial manufacture of a variety of products ranging from clothing and upholstery to cosmetics and tattoo ink as well as many others. Although azo-dyes are widely regarded as a safe and stable form of synthetic colourant some of them can take on dangerous properties after they have been broken down by enzymes in the guts of organisms. In the textile industry alone, the annual production of dyestuff amounts to millions of tons globally with azo dyes representing two thirds of this value. In many countries, the leftover dye effluent produced by industrial manufacturers is often not properly disposed of, or removed, during water treatment. This results in the accumulation of azo dyes in water bodies where they are then ingested by aquatic organisms. The products of this enzymatic breakdown have been found to be both mutagenic and carcinogenic and have been linked to increased occurances of several different forms of cancer if they enter the food chain. Despite this toxicity and it's potential effect on human health, little to no effort has been made to dispose of these leftover azo dyes more responsibly.
The Solution: Goodbye AzoDyes, UCL iGEM Team 2014
For our iGEM project we developed a process for controllably degrading and detoxifying the excess azo-dye effluent at the source - the textile factories - before they ever reach the water systems. We achieved this goal by introducing the genes for three enzymes related to the degradation of these dyes: azoreductase, laccase, and lignin peroxidase into a host E.coli cell to create an enhanced azo-dye decolourising organism. We also designed an integrated end-of-pipe method for detoxifying dye factory wastewater effluent streams by incorporating our engineered E. coli strain in a two-stage process to ensure optimal conditions for the degradation of azo dyes within a batch bioreactor system. The development of such a process would be an attractive and effective approach to dealing with azo dye contamination of the environment. As a financial incentive, we also looked at maximizing the profitability of various potential breakdown products as well as investigated the application of microbial fuel cell technology to an aerobic bioreactor system, for simultaneously detoxifying azo dyes and generating electricity. The potential for scalability of this method would present various economic and environmental advantages for industries that generate large amounts of dyestuff. The system we have developed could also be enhanced to become a modular bioprocess method for wastewater treatment of other toxic, normally recalcitrant chemicals.
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