Aquaculture Canada 2024: research highlights benefits of ozone on trout RAS farm

Dave Gilbert, president and owner of EmO3, an ozone air and water treatment company, has revealed the results of a study of ozone in water treatment for trout land-based farms.

Gilbert gave the presentation—on water physicochemical parameters following ozone dosing for recirculating aquatic system of land-based trout farm—to a group of interested listeners at the Aquaculture Canada conference and trade show in Prince Edward Island.  

He presented a three-year research project conducted by École de technologie supérieure in collaboration with MAPAQ (ministère de l’Agriculture, des Pêcheries et de l’Alimentation), Quebec’s ministry of Agriculture, fishery and agrifood and Pisciculture Gilbert, a Quebec trout farm.

Ozone is a gas that acts as a disinfectant to effectively control microorganisms. It’s 3,000 times faster than chlorine.

The president said on the land-based farm site used for the research, there was an issue of significant parasitic growth on brook trout (Salvelinus fontinalos) impacting the mortality rate, yield and quality of the product. He said a parasitic outbreak caused 10 per cent mortality and a shock treatment with formaldehyde resulted in stress for the aquatic environment and caused reduced production yields.

Ozone injection set-up

Recirculating pump: 8 m3/h (35.2 gpm) at 310 Kpa (45 PSI), water flow was varied between 75 and 132 L/min. The contact chamber was composed of a 2″ PVC tube, with a length of 95m (314 ft). The volume size was 0.62 m3 and the contact time was 135 seconds. Ozone production was 100 g/Nm3 at 2.1 L/min (35 g/h). The turnover rate was 22.5 hours.

The first thing that we wanted to understand was the degradation of the ozone at different concentrations. So they had different dosing concentrations, 1.28 up to three, and the initial dosing in the actual contact chamber at t zero was .38, milligrams per litre of dissolved ozone, Gilbert said. He said they wanted to ensure that the ozone going back to the basin was at a safe level, and the safe level was below point 05, milligrams per litre.

Results

Turbidity in the ozonated water basin was 0.95 compared to 1-65-3.6 in the non-ozonated water basin. The total suspended solids decreased by around 50 per cent to 4.4mg/L, and the total volatile suspended solids decreased from 5.6 to 2.2mg/L. 

Chemical oxygen demand went down to 15-16 mg – 02/L  from 27-48 mg – 02/L and the biological oxygen demand5  (BOD5 ) reduced to 2-5 mg – 02/L from 3-8 mg – 02/L. Ozone also affected the total organic carbon lowering it to 42-48 mg -C/L from 49-56 mg -C/L.

Ozone eliminated nitrites but had no impact on ammonical nitrogen. It helped reduce BOD5 further enhancing the nitrification process. Over 125 days of comparing the feed rate between the ozone basin and the control basin, speckled trout consumed more food in ozonated water. They observed a 90 per cent increase in feed rate resulting in increased growth. 

Speckled trout did not die from an ozone concentration of 0.05 mg-03/L water. There was a reduction in the mortality rate of speckled trout because of the reduced number of microorganisms pathogenic to fish. Finally, there was a qualitative improvement in the water colour, transparency and odour.