Conception d’un réacteur tubulaire sous pression d’ozonation pour l’enlèvement des organismes fongiques et des moisissures aquatiques des eaux piscicoles

Abstract

Recirculating aquaculture systems have high biomass production rates and save the space necessary for that production. This increase in production is characterized by a higher fish density in breeding ponds and therefore a higher risk of disease transmission. Epidemics represent a major issue for piscicultures and the prohibition of malachite green use as an antifungal agent amplifies this problem. The aim of this thesis is to develop a new type of ozonation reactor for fish farms with the objective to resolve this epidemics issue. A horizontal tubular ozonation reactor was built and installed on the fish breeding basins of the Pisciculture Gilbert. Tests of microorganisms removal and ozone decomposition kinetics in the ozonation reactor were performed. The determination of physical and chemical properties of water quality showed a water quality that was under the tolerance threshold of fish. Water samples were collected directly in the fish farm and analyzed in the laboratory. The addition of ozone reduced fungal and semi-fungal organisms’ number by 1.2 ± 0.3 log with an ozone treatment corresponding to a Ct value of 3.0 mg⋅min/L. The ozonation tests illustrated an ozone consumption in this system that obeys the law of first-order reactions and has two distinct rate constants : 0.004 ± 0.001 s-1 et 0.013 ± 0.004 s-1. The difference of one order of magnitude is explained by an increase in the fish farm recirculation flow rate. A pump problem stopped the fresh water input, therefore increasing the recirculation flow rate, which caused an increase of one order of magnitude in the rate constants. In addition, the ozone consumption rates vary with the amount of organic matter and micro-organisms’ number. Plastic mesh was installed inside the tubes to maximise the reactor turbulence (10200 Re with a friction factor of 0.06) while improving water and gas mixing with the installation of 40 static mixers along the reactor. The reactor has a hydraulic efficiency λ of 0.96, indicating a good flow without stagnant zones. The results of microorganisms removal and the reactor operating conditions support the application of this reactor in fish farms. Ozonation therefore constitutes an alternative to the antifungal agents currently used in the aquaculture industry.

Date	21 Dec 2022
Original language	French
Awarding Institution	École de technologie supérieure
Supervisor	Robert Hausler (Supervisor)