REUSE OF HATCHERY EFFLUENT FOR SPAT BREEDING USING MEMBRANE PROCESS
The aim of the study was to test the possibility of reusing an effluent from adult oyster breeding to feed an oyster spat with membrane process (ultrafiltration). The objective was two-fold: (i ) treat a real hatchery effluent and (ii) use ultrafiltered water for juveniles.
A pilot able to treat 20 m3 .d -1 , equipped with hollow fiber membranes with a pore size of 0.02 µm, was continuously fed for two months with real effluents from oyster breedings. This discharge contained feces, pseudo feces and microalgae. Simultaneously, the treated water was used to feed an oyster spat (i.e. sensitive species) .
For the reuse of treated effluent, growth performances of a spat (2500 oysters) were followed and compared to a control spat raised in the same conditions (quantity of food, temperature, flow) but fed with a control seawater filtered 1 µm and UV treated. Water quality of the two spats was controlled with bacteria and physico-chemical parameters measurements.
For effluent treatment, retention performances were controlled with total suspended solids (TSS) and bacteria measurements. Total bacteria and Vibrio bacteria concentrations, potentially harmful for shells concentrations were controlled.
For the treatment of effluent, TSS measurement highlighted a retention up to 99 % with a constant TSS concentration (>2 mg.L-1) in permeate whatever the feed quality.
A total retention of Vibrio bacteria was obtained, the process offers a protection of shellfish toward these bacteria genus. Moreover, a lower total flora concentration is measured in ultrafiltred effluent than in control sweater (1 µm + UV). Ultrafiltration is efficient to treat effluents from oyster breeding. Hydraulic performances controlled on the duration of the tests demonstrated the sustainability of the process facing this effluent. Indeed, chemical cleanings were necessary every 12 h of filtration.
Ultrafiltered water produced was used for oyster spat breedings. Physico -chemical parameters, identical in two water qualities led to a similar spat growth for 2 months in the two water conditions (Figure 1).
To conclude, the study showed the efficiency of ultrafiltration to treat an effluent from oyster farm with (i) a removal of bacteria potentially harmful for oysters (ii) a removal of TSS and (iii) a resistance of the process facing an organic effluent. Moreover, this process produces a water with a quality adapted to hatchery nursery applications such as the growth of juveniles, a sensitive oyster stage of life. Ultrafiltration could be a solution to reuse effluents in shellfish farms.
