Dose-dependent decomposition rate constants of hydrogen peroxide in small-scale bio filters Lars-Flemming Pedersen a, * , Per Bovbjerg Pedersen a , Ole Sortkjær b a Danish Institute for Fisheries Research, Department of Marine Ecology and Aquaculture, North Sea Centre, P.O. Box 101, DK-9850 Hirtshals, Denmark b National Environmental Research Institute, Department of Freshwater Ecology, Vejlsøvej 25, P.O. Box 314, DK-8600 Silkeborg, Denmark Received 27 January 2005; accepted 22 March 2005 Abstract This study investigated rates of hydrogen peroxide (H 2 O 2 ) degradation in biofilters, to provide information for more accurate treatment regimes in recirculation systems and more accurate prediction of effluent H 2 O 2 concentrations. Sodium percarbonate (2Na 2 CO 3 3H 2 O 2 ) was applied to small-scale recirculation systems with active bio filters. Three different treatment dosages corresponding to an initial hydrogen peroxide (H 2 O 2 ) concentration (C 0 ) of 13.0, 26.0 or 39.0 ppm were used (N = 18). Decomposition rate constants (k e ) of H 2 O 2 were identified by exponential regression analysis of recurrent water samples from treatment start to complete decomposition. The chemical fate of H 2 O 2 obeyed first order kinetics with half-lives inversely correlated with C 0 . Decomposition rate constants were significantly related to the amount of organic matter (BOD 5 ) and initial dosage of H 2 O 2 , and ranged from k e = 0.451 (C 0 = 26 ppm; BOD 5 = 2.0 mg O 2 /l) to k e = 3.686 h 1 (C 0 = 13 ppm; BOD 5 = 16.1 mg O 2 /l). Surface specific reduction (SSR) of H 2 O 2 in biofilters was positively related to dosage concentration for both levels of BOD 5 , where SSR from 55 to 220 mg H 2 O 2 m 2 t 1 were found. Oxygen liberation was positive correlated to C 0 and BOD 5 , indicating that hyperoxic conditions can arise if large amounts of sodium percarbonate are added to water with high organic matter content. This study assesses the environmental fate of H 2 O 2 in a closed recirculation system with biofilters, simulating recirculation aquaculture systems. The information can be applied to hydraulic model to predict actual treatment concentrations in aquaculture facilities and to assess effluent pulse from simulated treatment regimes. # 2005 Elsevier B.V. All rights reserved. Keywords: Aquaculture; Degradation; Recirculation; Hydrogen peroxide; BOD 5 ; Dosage www.elsevier.com/locate/aqua-online Aquacultural Engineering 34 (2006) 8–15 * Corresponding author. Tel.: +45 33 96 32 15; fax: +45 33 96 32 60. E-mail address: lfp@dfu.min.dk (L.-F. Pedersen). 0144-8609/$ – see front matter # 2005 Elsevier B.V. All rights reserved. doi:10.1016/j.aquaeng.2005.03.005