Journal of Chemical Technology and Biotechnology J Chem Technol Biotechnol 81:158–166 (2006) DOI: 10.1002/jctb.1373 Decolourisation of dyes and dyehouse effluent in a bubble-column reactor by ozonation in the presence of H 2 O 2 , KMnO 4 or Ferral Mohammad M Hassan, 1,2∗ Christopher J Hawkyard 1 and Peter A Barratt 3 1 Department of Textiles, UMIST, PO Box 88, Sackville Street, Manchester M60 1QD, UK 2 Wool Research Organisation of New Zealand (WRONZ), Private Bag 4749, Christchurch, New Zealand 3 Air Products Ltd, European Technology Group, Crockford Lane, Chineham, Basingstoke RG25 3LH, UK Abstract: The decolourisation of aqueous solutions of dyes by ozonation in the presence of hydrogen peroxide, potassium permanganate or Ferral using a bubble column reactor was investigated. Addition of hydrogen peroxide in the ozonation reaction of dyes did not affect its decolourisation efficiency. The addition of potassium permanganate considerably increased the decolourisation efficiency during ozonation of all of the dyes studied. Ferral showed excellent catalytic activity under acidic conditions but in alkaline conditions its catalytic activity diminished. The effect of the ozonation on COD was also monitored and was found to be highly effective in reducing the COD of aqueous dye solutions. In addition to studying the effect of addition of hydrogen peroxide, potassium permanganate or Ferral on the ozonation of aqueous solutions of individual dyes, tests were carried out on effluent from a commercial dyeing unit.  2005 Society of Chemical Industry Keywords: dyes; decolourisation; ozonation; catalytic ozonation; Ferral; hydrogen peroxide; potassium permanganate INTRODUCTION Ozone has been used for more than 100 years for the disinfection of drinking water and more recently has found use also for wastewater treat- ment. Decolourisation of dyes and dyehouse efflu- ent by ozone has been investigated by several groups and was found to be effective. 1–6 Sev- eral researchers even observed that chemical oxy- gen demand (COD) and biological oxygen demand (BOD) decreased after ozonation. 2,3,7 It was also reported that COD decreased only in the case of pure dye solutions, but for a real wastewater the COD remained unchanged 1 and the total organic carbon (TOC) content was also unaffected by ozone. 8 This indicates that the dye chromophore degrades to a form that may not decompose further by normal ozonation. As ozonation is very expensive and not very effective for COD and TOC reduction, investigation was continued in order to determine whether catalysts could be used to reduce the ozone consumption while simultaneously lowering the COD and TOC. In the early 1980s it was found that the use of a catalyst could accelerate the oxidation reaction of ozone and reduce ozone consumption. 9 It was also observed that some catalysts, such as CoSO 4 , TiCl 3 , MnSO 4 , NiSO 4 and FeSO 4 , were also effective for reduction of the TOC of wastewater. 10 In several studies, ferric oxide was found to be effective as a catalyst in ozonation processes. 8,11,12 During ferric oxide-catalysed ozonation of industrial and domestic wastewater containing phenol and ethyl acetoacetate, a substantial reduction of TOC was also observed. 11,12 It was reported that in the Fe 2 O 3 - catalysed decomposition of ozone, a high degree of initial ozone decomposition was observed but the catalytic activity decreased after a certain time. 12 In recent years, manganese-catalysed ozonation has been extensively investigated. The catalytic effect of manganese salts and manganese dioxide in ozonation have been investigated by several researchers and found to be effective in increasing the efficiency of pollutant destruction in the ozonation process. 13 – 15 Ma et al . reported that addition of manganese oxides (MnO x ) supported on granular activated carbon (GAC) enhanced the oxidation of nitrobenzene by ozone. 16 Although hydrogen peroxide-catalysed ozonation was found to be ineffective for the decolourisation of textile dyehouse effluent, 17,18 it was demonstrated to be highly effective in enhancing the efficiency of oxidation of several organic compounds, including ∗ Correspondence to: Mohammad M Hassan, Wool Research Organisation of New Zealand (WRONZ), Private Bag 4749, Christchurch, New Zealand E-mail: hassan@wronz.com Contract/grant sponsor: Air Products Ltd, Environmental Technology Group (Received 10 January 2005; revised version received 29 April 2005; accepted 27 May 2005) Published online 23 September 2005  2005 Society of Chemical Industry. J Chem Technol Biotechnol 0268–2575/2005/$30.00 158