Wood-based biochar filtration for ammonium and off-flavor removal in recirculating aquaculture: a pilot-scale AQUASERV transnational access study

Authors: Victor Lobanov (presenter)¹, Aline Brossin², Sylvain Yvorel², Nicolas Larrañaga², Stef Ghysels³, Frederik Ronsse³, Lies Harinck⁴, Diederik P.L. Rousseau⁴, Alyssa Joyce¹

Affiliations:

¹ Department of Conservation, University of Gothenburg, Gothenburg, 40530, Sweden

² INRAe-PEIMA, UE0937, Fish Farming Systems Experimental Facility, Sizun, France

³ Thermochemical Conversion of Biomass Research Group, Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Coupure Links 653, 9000 Ghent, Belgium

⁴ Laboratory for Industrial Water and EcoTechnology (LIWET), Department of Green Chemistry and Technology, Faculty of Bioscience Engineering, Ghent University, Campus Kortrijk, Graaf Karel de Goedelaan 46, 8500 Kortrijk, Belgium

Presenting author e-mail: victor.lobanov@gu.se

Abstract:

Recirculating aquaculture systems (RAS) are the most environmentally sustainable form of finfish aquaculture, achieving high production rates alongside thorough waste removal from the water column. Especially under periods of elevated temperatures, it is critical to maintain water quality levels so as not to excessively stress fish. Furthermore, while not directly impacting fish health, the accumulation of off-flavor compounds (OFCs) such as geosmin and 2-methylisoborneol (2-MIB) in the water column decreases the sale value of fish. This requires a period of depurination whereby fish are starved 1-2 weeks before slaughter.

In this study, a fixed bed of commercially available wood biochar was tested for its capacity to remove wastes (dissolved carbon and nitrogen species) from the water column alongside OFCs. Through AQUASERV transnational access (PID 40879) we ran six beds (10 L, 1 kg biochareach) in two rainbow trout RAS rooms at INRAe-PEIMA, Sizun, France, for seven weeks. Both rooms held 14.4 to 17.1 °C for four weeks; one was then warmed to 21.4 °C, the other held at 17.7 °C.

Ammonium removal averaged 56 ± 18% (control) and 48 ± 17% (warmed), or 1.3 to 1.5 mg N per day per bed, with no significant treatment effect (paired Wilcoxon p = 0.44). Performance tracked operating time and hydraulic loading, not temperature. Steady-state total organic carbon removal was modest (16% and 5%). Control beds reduced geosmin by 31% and 2-MIB by 42%. Amplicon sequencing recovered no bacterial or fungal DNA from used biochar, while FTIR showed surface oxidation and deposition, indicating abiotic adsorption rather than biofilm activity.

Biochar filtration is therefore a low-cost depuration-support option rather than a nitrification substitute. Its policy interest lies downstream: the bed that polishes farm water leaves the recovered nutrients (mainly nitrogen) on a stable carbon carrier that can then be applied to soil. The two issues of aquaculture waste treatment management and sustainable land fertilization are both addressed by this study, with implications for other points of connectivity between food production systems.