Aquacultural Engineering 64 (2015) 1–7 Contents lists available at ScienceDirect Aquacultural Engineering jo ur nal home p ag e: www.elsevier.com/locate/aqua-online Hydrogen peroxide decomposition kinetics in aquaculture water Erik Arvin a,∗ , Lars-Flemming Pedersen b a Technical University of Denmark, Department of Environmental Engineering, DTU Environment, Miljoevej, Build. 113, DK-2800 Kgs. Lyngby, Denmark b Technical University of Denmark, DTU Aqua, Section for Aquaculture, North Sea Research Centre, PO Box 101, DK-9850 Hirtshals, Denmark a r t i c l e i n f o Article history: Received 3 July 2014 Accepted 21 December 2014 Available online 30 December 2014 Keywords: Aquaculture Hydrogen peroxide Degradation Kinetics Enzyme inactivation Microbial water quality a b s t r a c t Hydrogen peroxide (HP) is used in aquaculture systems where preventive or curative water treatments occasionally are required. Use of chemical agents can be challenging in recirculating aquaculture sys- tems (RAS) due to extended water retention time and because the agents must not damage the fish reared or the nitrifying bacteria in the biofilters at concentrations required to eliminating pathogens. This calls for quantitative insight into the fate of the disinfectant residuals during water treatment. This paper presents a kinetic model that describes the HP decomposition in aquaculture water facilitated by microbial enzyme activity. The model describes how the hydrogen peroxide removal declines and even- tually stops at relatively low chemical oxygen demand (COD) concentrations. It is hypothesized that this is due to an enzyme deficit because it is destructed due to the reactive radicals created during the HP decomposition. The model assumes that the enzyme decay is controlled by an inactivation stoichiometry related to the HP decomposition. In order to make the model easily applicable, it is furthermore assumed that the COD is a proxy of the active biomass concentration of the water and thereby the enzyme activ- ity. This was, however, not measured. The model developed successfully described the removal of HP in aquaculture water from three types of RAS and model parameters are estimated. The model and the model parameters provide new information and are valuable tools to improve HP application in RAS by addressing disinfection demand and identify efficient and safe water treatment routines. © 2014 Elsevier B.V. All rights reserved. 1. Introduction Hydrogen peroxide (HP) has shown promising results in the treatment of a number of different protozoan and fungal infections on fish (Schreier et al., 1996; Lilley and Inglis, 1997; Avenda ˜ no- Herrera et al., 2006; Heinecke and Buchmann, 2009; Giménez Papiol and Roque, 2013). An advantage of using HP over formalin (e.g. Masters, 2004) is that HP workwise is less hazardous. HP decomposes relatively fast to oxygen and water (Block, 1991) and the break down does not include harmful disinfection by-products as is the case for other chemicals applied in aquaculture (Dawson et al., 2003), hence hav- ing the potential to be sufficiently eliminated prior to discharge and to comply with discharge regulations for land based aquaculture systems (Schmidt et al., 2006). The studies conducted with HP have mostly concentrated on the parasite treatment efficiency and the tolerance of different fish species to HP in bath treatments (Rach et al., 2000). The treatments conducted in flow-through systems or in fish tanks have included ∗ Corresponding author. Tel.: +45 40628153. E-mail address: erar@env.dtu.dk (E. Arvin). a restricted treatment period, typically carried out using hydrogen peroxide doses of around 50–100 mg/L for 30 min to 2 h (Arndt and Wagner, 1997; Gaikowski et al., 1999; Bowker et al., 2012). This intermittent treatment procedure in freshwater systems markedly differs from short term dip baths to control sea lice where HP con- centrations above 1000 mg/L are applied for a few minutes (Adams et al., 2012). Use of HP in RAS is associated with prolonged con- tact time and precautions regarding potential impact on biofilter performance, calling for low dose applications. Knowledge on low dose (<20 mg/L) HP treatment efficiency and treatment regimens (contact time and active concentration) in RAS are limited and findings on potential damaging effects on aquacul- ture organisms and nitrifying populations in biofilters has impeded the use of HP in RAS so far (Schwartz et al., 2000; Pedersen and Pedersen, 2012). An effective and a safe threshold level for HP dose and contact time in relation to inhibition of nitrification in biofilters is complicated to assess as it depends on a number of parame- ters. Further research is hence needed to describe the underlying mechanisms of HP degradation and inhibition. The decomposition of HP in a pilot scale RAS has previously been studied by Pedersen et al. (2006). HP degraded exponentially with a rate depending on the organic matter concentration mea- sured as biochemical oxygen demand (BOD 5 ) of the water. It was http://dx.doi.org/10.1016/j.aquaeng.2014.12.004 0144-8609/© 2014 Elsevier B.V. All rights reserved.