The removal of azo dyes using the Nyex® RosaloxTM coupled adsorption and electrochemical oxidation process

Abstract

The textile industry, considered being the second most water intensive industry in the world produces industrial dye effluent typically high in colour, pH, temperature and salt content, causing major environmental problems. In response, effective water treatment technologies must be developed to ensure safe reuse and discharge. The Nyex® RosaloxTM coupled adsorption and electrochemical oxidation process has shown to be an effective, novel technique to remove a variety of pollutants from industrial wastewater. Previous research has shown that azo dyes can adsorb onto Nyex® and when effluent conditions were altered, this had a clear impact on the adsorption. However, it remains unclear whether they can be oxidised in situ and research to date has mainly been conducted using a clean water system, unrealistic of the composition of industrial effluent. Therefore, small-scale lab experiments simulating the Nyex® RosaloxTM process were conducted to determine if the azo dyes could be fully oxidised and removed from tap water. Additionally, a variety of effluent conditions e.g., elevated temperature, acidic/alkaline starting pH, increased salinity and dissolved organic matter (DOM) (using river water) used to determine dye removal from water more similar to that of dye effluent and dye contaminated rivers. Analysis indicated that all azo dyes used were completely oxidised, with the highest efficiency when the lowest amount of energy was used. Analysis further indicated that Nyex® can be regenerated and reused (up to at least eight times) without loss of efficiency. Extension of treatment duration showed that >98% was removed within 24 hours (with >95% removed within 8 hours), although the effectiveness of the process is dye dependent, without formation of any harmful detectable byproducts. Results also indicated dye removal is substantially increased in acidic, saline or, to a lesser extent, when DOM is present; with up to 48% more removed in acidic conditions compared to that of baseline tap water conditions. Increased temperature and alkaline conditions had the least impact, with inconsistent results across dyes. Combined these findings suggest that the Nyex® RosaloxTM process can effectively destroy azo dyes with relatively low energy, proving a cost-effective method of water treatment without producing harmful secondary pollutants. Additionally, azo dye removal using the Nyex® RosaloxTM process is hugely influenced by effluent conditions, and altering effluent parameters may be a sustainable, efficient method of improving dye removal.

Date of Award	21 Nov 2023
Original language	English
Awarding Institution	The University of Manchester
Supervisor	Stephen Boult (Supervisor) & Bart Van Dongen (Supervisor)