Degradation and effect of hydrogen peroxide in small-scale recirculation aquaculture system biofilters Martin Sune MÖller 1 , Erik Arvin 1 & Lars-Flemming Pedersen 2 1 Department of Environmental Engineering,Technical University of Denmark, Lyngby, Denmark 2 North Sea Research Centre, National Institute of Aquatic Resources, Section for Aquaculture,Technical University of Denmark, Hirtshals, Denmark Correspondence: L-F Pedersen, North Sea Research Centre, National Institute of Aquatic Resources, Section for Aquaculture,Technical University of Denmark, PO Box101, DK-9850 Hirtshals, Denmark. E-mail: lfp@aqua.dtu.dk Abstract From an environmental point of view, hydrogen perox- ide (HP) has bene¢cial attributes compared with other disinfectants in terms of its ready degradation and neutral by-products. The rapid degradation of HP can, however, cause di⁄culties with regard to safe and e⁄cient water treatment when applied in di¡erent systems. In this study, we investigated the degradation kinetics of HP in bio¢lters from water recirculating aquaculture systems (RAS). The potential e¡ect of HP on the nitri¢cation process in the bio¢lters was also examined. Bio¢lter elements from two di¡erent pilot- scale RAS were exposed to various HP treatments in batch experiments, and the HP concentration was found to follow an exponential decay. The bio¢lter am- monia and nitrite oxidation processes showed quick recuperation after exposure to a single dose of HP up to 30 mg L  1 . An average HP concentration of 10^13 mg L  1 maintained over 3 h had a moderate inhibitory e¡ect on the bio¢lter elements from one of the RAS with relatively high organic loading, while the nitri¢cation was severely inhibited in the pilot- scale bio¢lters from the other RAS with a relatively low organic loading. A pilot-scale RAS, equipped with two bio¢lter units, both a moving-bed (Biomedia) and a ¢xed-bed (BIO-BLOK s ) bio¢lter, was subjected to an average HP concentration of  12 mg L  1 for 3 h. The ammonium- and nitrite-degrading e⁄ciencies of both the Biomedia and the BIO-BLOK s ¢lters were drastically reduced. The ¢lters had not reverted to pre-HP exposure e⁄ciency after 24h, suggesting a possible long-term impact on the bio¢lters. Keywords: aquaculture, bio¢lter, hydrogen perox- ide, degradation, nitri¢cation, reaction kinetics Introduction Disinfectant agents are widely used in aquaculture to control problems with parasites, fungus and other pathogens (Heinecke & Buchmann 2009; Summerfelt, Sharrer,Tsukuda & Gearheart 2009). Formalin is cur- rently one of the most commonly used therapeutic agents because of its high treatment e⁄ciency and substantial knowledge on the dose^response e¡ect. Furthermore, formalin does not appear to be harmful for ¢sh or bio¢lters in recirculating aquaculture sys- tems (RAS) in the doses relevant for treatment (Ri- ntamÌki-Kinnunen, Rahkonen, Mannermaa-KerÌnen, Suomalainen, MykrÌ & Valtonen 2005; Pedersen, Pedersen & Sortkj×r 2007). There are, however, growing concerns that the ex- cess formaldehyde imposes an ecological problem in the recipient water bodies (Masters 2004; Gearheart, Masters & Bebak-Williams 2006; Pedersen & Peder- sen 2006), and recent studies show that formalin is connected with worker safety issues (IARC 2004; Cogliano, Grosse, Baan, Straif, Secretan, El Ghissassi & The Working Group forVolume 88, 2005; Shangina, Brennan, Szeszenia-Dabrowska, Mates, Fabianova, Fletcher, t’Mannetje, Bo¡etta & Zaridze 2006). There- fore, a need for alternative disinfectants has emerged. Hydrogen peroxide (HP) has shown promising re- sults in the treatment of a number of di¡erent para- sites and fungus on ¢sh and ¢sh eggs (Lilley & Inglis 1997; Montgomery-Brock, Sato, Brock & Tamaru 2001; Rach, Valentine, Schreier, Gaikowski & Craw- ford 2004; Heinecke & Buchmann 2009). An advan- tage of using HP over other chemotherapeutic agents is that the end-products consist of non-toxic substances (Block 1991). Furthermore, as HP decom- poses relatively fast in the aquaculture system, it has Aquaculture Research, 2010, 41 , 1113^1122 doi: 10.1111/j.1365-2109.2009.02394.x r 2009 The Authors Journal Compilation r 2009 Blackwell Publishing Ltd 1113