World Aquaculture - June 2023

WWW.WAS.ORG • WORLD AQUACULTURE • JUNE 2023 63 (CONTINUED ON PAGE 64) is reduced to chloride ions that can be oxidized again into active chlorine at the anode of the electrochemical reactor, so the overall reaction (Eq. 3) does not include the chloride ion. A beneficial byproduct of Eq. 1 is that the generated chlorine, apart from oxidizing ammonia, acts to disinfect the water, and is also capable of oxidizing organic compounds that cause off-flavor, such as geosmin and MIB. Eq. 1: Chlorine generation 2Cl- + 2H+ ➝ Cl 2 + H2(g) Eq. 2: Ammonia oxidation 3Cl2 + 2NH4 + ➝ N2(g) + 6Cl - + 8H+ Eq. 3: Overall reaction 2NH4 + ➝ N2(g) + 3H2(g) + 2H+ Advantages of Electrooxidation Many advantages can be listed for operating RAS with no biofilters. The main incentive to apply electrooxidation in aquaculture is the single-step oxidation of TAN directly into N2(g). However, application of an electrochemical reactor as a water treatment component in RAS has further benefits. From a general engineering or operational standpoint, a single component that serves a multi-purpose solution — ammonia removal, disinfection and off-flavor prevention — is often advantageous over an application of several consecutive treatment steps of nitrification, denitrification and disinfection. The system is also characterized by temperature independence, ease of operation, no startup period, the ability to turn the system on and off at will and lower facility footprint compared to biofilters. BioFishency ELX™ – Performance and Capabilities An advanced electrochemical water treatment system for costefficient ammonia removal and water disinfection, BioFishency ELX™ compares favorably with biological RAS, all in a fully controlled environment, while eliminating off-flavor agents, to deliver a reliable and high-quality product year-round. Suitable for both coldwater and warmwater species. Disinfection is part of a multi-stage solution is built into a single operation, BioFishency ELX™ directly transforms ammonia to nitrogen gas. The system supports a small carbon footprint, requires considerably less space and energy and operates immediately upon electrical supply. Several proof-of-concept and pilot studies were conducted using BioFishency ELX™ technology with several species and systems, as presented below, from fingerlings to grow-out, and as a purging unit under a regular feeding regime and water discharge typical of RAS. Atlantic Salmon A proof-of-concept study was conducted by the RASLab team, Bergen, Norway, using Atlantic salmon Salmo salar smolt stocked at 190 g for 54 days. The objectives were to demonstrate a RAS operation based solely on the BioFishency ELX™ system and compare fish growth rate and health and welfare parameters. Fish growth, survival, production and feed conversion were similar between the BioFishency ELX system and a conventional RAS (Table 1). Fish health was evaluated using a methodology developed by Quantidoc (Quantidoc - Hjem | Quantidoc) that analyzes mucous cell size, density and distribution to assess whether cells are in a defensive or healthy state. Once mucous cells are in a defensive state, environmental conditions and the effect of external stressors are not optimal due to causes such as handling, pharmaceuticals and other factors such as water chemistry. Fish sampled after termination of the experiment indicated that the fish in the BioFishency ELX™ system were in better health. Mucous cell size and density was smaller than in the biofilter system, indicating a TABLE 1. Comparison of Atlantic salmon production in a BioFishency system compared to conventional RAS. Stocking Harvest Initial Final Initial Final FCR number number weight weight biomass biomass (g) (g) (kg) (kg) Biofilter 150 144 190 383 29 55 0.90 Bio-Fishency ELX 163 163 190 371 31 60 0.81 TABLE 2. Comparison of gilthead sea bream production in a BioFishency system compared to a flowthrough system. Criteria BioFishency ELX™ Flow-through Survival (%) 95.3 98 FCR 1.04 1.09 Growth rate (g/d) 0.30 0.27 Fish health NPS** NPS** Water consumption (m3) 2.97 540