Aquacultural Engineering xxx (2003) xxx–xxx Impact of ozonation on water quality in marine recirculation systems Martin S. Tango, Graham A. Gagnon ∗ Department of Civil Engineering, Dalhousie University, Halifax, NS, Canada B3J 1Z1 Abstract Ozone (O 3 ) is a powerful oxidant and is becoming popular in various aquaculture systems for dis- infection and improving water quality by oxidation of inorganic and/or organic compounds. However, the use of ozone in marine-based aquaculture systems has been limited because of the potential to form bromate, which is formed during the oxidation of naturally occurring bromide by ozone. Be- cause bromate is a human carcinogen, there are concerns with its chronic impact on fish health. In addition, the use of O 3 is hindered by lack of quantitative as well as qualitative design and performance information on O 3 for recirculating systems. This study investigated the application of ozonation to control pathogens and enhance the process water quality in a recirculating aquaculture system while minimizing bromate formation. A field scale monitoring program was conducted on process water quality from Atlantic halibut (Hippoglossus hippoglossus) recirculating systems. Ozonated modules showed reduction of 15% total organic carbon (TOC) and less than 25 g/l bromate concentration was formed. In addition, ozonated modules showed reduction in nitrate, color and suspended solids, as compared to those that did not use ozone. The results of this study elucidates the formation of bromate in marine water recirculation systems. © 2003 Elsevier B.V. All rights reserved. Keywords: Ozonation; Marine recirculation systems; Atlantic halibut 1. Introduction Recirculating systems have been employed in the last two decades for applications in aquaculture systems. Limited suitable water supplies and stringent control of wastewater and nutrient discharges from pond and raceway facilities prompted the demand for recirculating systems. ∗ Corresponding author. Tel.: +1-902-494-3268; fax: +1-902-494-3108. E-mail address: graham.gagnon@dal.ca (G.A. Gagnon). 0144-8609/$ – see front matter © 2003 Elsevier B.V. All rights reserved. doi:10.1016/S0144-8609(03)00061-X