Mass transfer and oxidation kinetics in an in situ ozone generator A.P. Mathews*, K.K. Panda*, S. Ananthi** and K. Padmanabhan** * Department of Civil Engineering, Kansas State University, Fiedler Hall, Manhattan, KS 66506, USA (E-mail: alex@ksu.edu; kkp4466@ksu.edu) ** Central Instrumentation Engineering Department, University of Madras, Chennai- 25, Tamil Nadu, India (E-mail: pradeep_1095@yahoo.com; swaminathan_kp@vsl.net) Abstract An in situ ozone generator design based on a novel type of corona discharge tube construction was tested to examine enhancements in mass transfer and ozonation efficiency over conventional systems. In this design, the discharge gap is kept juxtaposed to the tubular pathway through which the treatment fluid is passed. A porous inner electrode tube is employed in the discharge tube, and the generated ozone diffuses through this porous tube and dissolves and reacts with the contaminants in the fluid that is being treated. The inner porous ceramic tube is grounded while the outer glass electrode is positively charged for corona discharge. Oxidation studies conducted on Reactive Blue 19 dye indicate that the time required for 90% color removal is about half that of a conventional ozone generation and bubble diffusion system at the same ozone dosage. Keywords Dye oxidation; in situ ozonator; mass transfer; ozone; porous electrode Introduction Ozone has been investigated for use in wastewater treatment for the removal of color from textile and tannery effluents, the breakdown of high molecular weight organics from fermentation effluents, the prevention of microbial growth in integrated circuit process waters and cooling towers, oxidation of metal finishing wastes, and other applications (Inanc et al., 1999; Chu and Ma, 2000; Perkowsky et al., 2000). The non-biodegradable organic fraction in process effluents can be broken down to simpler molecules using ozone, and these compounds can then be degraded easily by bacteria during biological treatment. Ozone is also effective in the disinfection of stormwater, and increases oxygen levels in the discharge water, but does not result in the discharge of free chlorine or chlorinated organics into receiving waters as with disinfection using chlorine. However, the application of ozone in wastewater treatment is not widespread at present due to the high overall cost of treatment relative to that of chlorine and other oxidants. Ozonation efficiency is affected significantly by the gas–liquid mass transfer efficiency, and ozone reaction and decomposition kinetics. The high costs associated with ozone appli- cation can be reduced by increasing the mass transfer rate in the dissolution of ozone gas, and by reacting ozone as it is produced with the contaminants in the solution by developing an in situ ozone generator. Mass transfer rates are increased typically by using fine bubble diffusers in deep tanks. This results in higher ozone partial pressures, and higher interfacial area for mass transfer. Capital costs are however higher, and in addition the off-gases will need to be treated for the residual ozone and stripped VOCs. Hollow fiber membranes have been studied to provide bubble-less transfer of oxygen across membranes into the solution (Cote and Bersillon, 1989; Ahmed and Semmens, 1992). These can provide much higher transfer efficiencies by maintaining high pressures (as high as 6 atm.) on the gas side of the membrane. The overall costs of such systems utilizing hollow fiber membranes are high. Moreover, this system Water Science and Technology Vol 49 No 4 pp 19–24 © IWA Publishing 2004 19 Downloaded from https://iwaponline.com/wst/article-pdf/49/4/19/420703/19.pdf by guest on 27 November 2018