UVC induced TOC removal studies of Ponceau S in the presence of oxidants: Evaluation of electrical energy efficiency and assessment of biotoxicity of the treated solutions by Escherichia coli colony forming unit assay M.K. Sahoo a,⇑ , M. Marbaniang a , B. Sinha a , D.B. Naik b , R.N. Sharan c a Department of Chemistry, North-Eastern Hill University, Shillong 793 022, India b Radiation and Photochemistry Division, BARC, Trombay, Mumbai 400 085, India c Radiation and Molecular Biology Unit, Department of Biochemistry, North-Eastern Hill University, Shillong 793 022, India highlights " More than 50% mineralization of Ponceau S is equally by UV/H 2 O 2 and UV/(NH 4 ) 2 S 2 O 8 in acidic to basic media. " Efficiency for both systems follows the order: pH 1 > pH 3 > pH 5  pH 6.62  pH 9 > pH 13. " Treatment at pH 1 is 4.2 times more economical than at pH 6.62 in terms of electrical energy consumption. " Recommended parameters for treatment are: pH 6.62, UV intensity – 1417 lW cm 2 , oxidant – H 2 O 2 . " Complete detoxification after mineralization is achieved when the pH is adjusted to 7. graphical abstract Effect of (NH 4 ) 2 S 2 O 8 ,H 2 O 2 , KIO 3 and KBrO 3 as oxidants on mineralization of Ponceau S: [Ponceau S] = 0.05 mM; [oxidant] = 0.95 mM; exposure time = 90 min; UV intensity = 213 lW cm 2 . Inset: Effect of UV intensity and exposure time on initial solution pH: [PS] = 0.05 mM; [HP] = 0.95 mM; initial pH 6.62. 0 1 2 3 4 5 6 7 8 9 10 11 12 13 0 10 20 30 40 50 60 70 80 90 0 10 20 30 40 50 60 70 80 90 3 4 5 6 7 pH Time (min) 213 μW cm-2 453 μW cm-2 1064 μW cm-2 1417 μW cm-2 1755 μW cm-2 APS HP KIO 3 KBrO 3 Mineralization (%) pH article info Article history: Received 9 August 2012 Received in revised form 1 October 2012 Accepted 3 October 2012 Available online 12 October 2012 Keywords: Ponceau S Mineralization UV 254 /oxidant Operational variables Electrical energy per order Biotoxicity abstract Mineralization of Ponceau S (PS), an anionic azo dye, was studied using UV 254 in the presence of hydrogen peroxide (HP) and ammonium persulphate (APS). Effect of operational variables like pH, oxidant concen- tration and intensity of UV light, etc. on mineralization was analyzed. Biotoxicity of the treated solutions was evaluated by Escherichia coli (E. coli) colony forming unit (CFU) assay to know the suitability of the treated solutions to be released as effluents. HP and APS show equal efficiency towards mineralization at a given pH except 13, where higher mineralization was shown by APS than HP. The pH dependency of mineralization follows the order: pH 1 > pH 3 > pH 5  pH 6.62  pH 9 > pH 13. A preliminary study involving KIO 3 and KBrO 3 , reveals that >73% mineralization is achieved at pH 1, while it varies from 40% to 46% in the pH range of 3–9. Thus, the overall efficiency of the oxidants follows the order: APS  HP > KIO 3 > KBrO 3 in acidic to neutral pH and APS > KIO 3  KBrO 3 > HP at pH 13. The cost of treat- ment, evaluated on the basis of electrical energy per order (EE/O) was found to be higher at pH 6.62, the natural pH of PS, than at pH 1. Considering environmental impact and cost of treatment at extreme low pH, the ideal pH of treatment should be 6.62. Most importantly, the treated solutions still possess biotox- icity even after high mineralization and we are able to reduce the biotoxicity to the extent of 90%. Ó 2012 Elsevier B.V. All rights reserved. 1385-8947/$ - see front matter Ó 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cej.2012.10.002 ⇑ Corresponding author. Tel.: +91 364 2722632, mobile: +91 9436706767; fax: +91 364 2551634. E-mail addresses: mksahoo@nehu.ac.in, mihir.nehu@gmail.com (M.K. Sahoo). Chemical Engineering Journal 213 (2012) 142–149 Contents lists available at SciVerse ScienceDirect Chemical Engineering Journal journal homepage: www.elsevier.com/locate/cej