Sounding out Congo Red
Brightly colored dyes such as the shimmering Congo Red commonly used in silk clothing manufacture are notoriously difficult to dispose of in an environmentally benign way.
However, Srinivas Sistla and Suresh Chintalapati, from Hyderabad, India, suggest that sonolysis, break down of an organic compound with ultrasound, has so far been investigated only rarely as an alternative remediation technology. Under well-established 'extreme' conditions, materials irradiated with sound at frequencies around 50 kHz are essentially ripped apart by the formation of free radicals, say the researchers. Carbon dioxide and water are the usual products, although with the case of azo dyes, nitrogen would also feature in the byproducts.
Sonication of Congo Red in the aqueous phase with 50 kHz ultrasound transforms it into a milieu of less toxic intermediates that can then be broken down still further by conventional industrial waste water biodegradation treatment. As a proof of principle, the researchers suggest that the combination of ultrasound and biodegradation could allow the color to be removed from dye-contaminated industrial effluent effectively and the toxicity reduced to negligible levels. "The results obtained from this study revealed the ability of ultrasonic irradiation to transform the aromatic inhibitory compounds to less toxic intermediates, which can be further utilized in aerobic/anaerobic oxidation," the researchers conclude.
Source: physorg.comAdded: 29 August 2008