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Decolourisation, mineralisation and detoxification of mixture of azo dyes using Fenton and Fenton-type advanced oxidation processes

John Elisa Kumar, Tsungom Mulai, Wanshanlang Kharmawphlang, Rajeshwar Nath Sharan, and Mihir Kumar Sahoo

Centre for Advanced Studies in Chemistry, Department of Chemistry, North-Eastern Hill University, Shillong, India



Received: 27 January 2020  Accepted: 29 March 2020


COD and TOC removal studies of mixture of two azo dyes viz. Ponceau Xylidine and calconcarboxylic acid by Fenton and Fenton-type processes were undertaken using ({ ext{H}}_{2} { ext{O}}_{2}) (HP) and ({ ext{Na}}_{2} { ext{S}}_{2} { ext{O}}_{8}) (SPS) as oxidants. A decolourisation of 94% in 1 min was achieved under optimised parameters, although mixing of dyes caused a retardation of mineralisation when compared with individual dyes. The study has established that treatment can be carried out at the natural pH of the dye solution in ({ ext{Fe}}^{2 + })/SPS system. This makes the treatment process economically viable. ({ ext{Fe}}^{2 + })/SPS system at pH 3 and 4.9 was found to be more efficient than ({ ext{Fe}}^{2 + })/HP system as far as mineralisation is concerned. We could achieve 100% consumption of HP within 5 min of reaction, and therefore, no interference of HP on COD measurement is expected. The removal efficiency of different water quality parameters was found to be in the order: colour > ({ ext{COD}}_{ ext{eff}}) > ({ ext{TOC}}_{ ext{eff}}). Both COD and TOC removals followed pseudo-first-order kinetics. During the degradation process, 74% azo bonds were found to convert to ({ ext{NH}}_{4}^{ + }) and the rest to other nitrogenous products. Different ions and intermediates have been identified by ion chromatography. Based on the toxicity assay, we have recommended microorganism selection criteria for toxicity assay depending on the nature of recipient water body. Our results of detoxification measurement suggest that Escherichia coli-based assay could be used for fresh water and Vibrio fischeri for marine environment.

Keywords: Mixture of dyes; Fenton and Fenton-like processes; TOC and COD removal kinetic study; Conversion of azo bond to ({ ext{NH}}_{4}^{ + }); Product identification and mechanism; Microorganism selection criteria for toxicity assay

Full paper is available at

DOI: 10.1007/s11696-020-01147-9


Chemical Papers 74 (9) 3145–3159 (2020)

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