World Aquaculture Magazine - March 2021

WWW.WA S .ORG • WORLD AQUACULTURE • MARCH 2021 67 Ultrafiltration of Oyster Spermatozoa Filtration performance was monitored continuously over 30-h tests (Fig. 2a- b). To determine fouling caused by spermatozoa during tests, evolutions of permeability were compared to tests with seawater without gametes under the same filtration conditions (Fig. 2b). Irrespective of operating conditions, the decrease in permeability was substantially greater in the case of filtration of seawater dosed with spermatozoa, but the fouling was moderate. The drop of permeability observed over the 30 h of test was around 250 L/h m 2 bar. Variations in permeability indicated the importance of air backwash to control membrane fouling. There was a substantial gain in hydraulic performance following backwash with air injection in seawater effluent dosed with oyster spermatozoa. Spermatozoa concentrations at different points of the system (membrane inlet, backwash, air backwash and permeate) were followed by flow cytometry over the 30 h of the test. An example of evolution of spermatozoa concentration is presented in Figure 3. The average membrane inlet spermatozoa concentration was 7,432 spz/mL, with minimum and maximum values of 1,305 and 19,318 spz/mL. In this range of conditions, the spermatozoa concentration in the permeate was always below the detection limit of the flow cytometer (350 spz/mL). From the concentration factor in the membrane during the filtration cycle, it was possible to calculate removal, which varied on average between 2 and 4 log between the beginning and the end of the filtration cycle for the experiment with the higher concentration. These removals were significant and testified to the effectiveness of FIGURE 4. Evolution of permeability during five hours for the treatment of spermatozoa (a-b) or oocytes (c-d) (J = 60 L/h m 2 and t filtration = 60 min; accidental release). a-c. Test 1 and b-d. Test 2. A. B. C. D. FIGURE 3. Evolution of spermatozoa concentration versus time (chronic release; J = 60 L/h m 2 ; t filtration = 30 min). ( C O N T I N U E D O N P A G E 6 8 )