MAINTAINING WATER QUALITY STANDARDS IN RECIRCULATING AQUACULTURE SYSTEMS: CRITICAL REVIEW OF AVAILABLE DISINFECTION TECHNOLOGIES
Production in recirculating aquaculture systems (RAS) is increasingly sustainable with technical improvements promising zero exchange systems where water reuse and effluent management is essential. The technical background required to achieve water quality standards include the integration of mechanical filtration, biofiltration and disinfection methods. All these procedures are necessary to remove potentially dangerous accumulating waste and dissolved compounds as well as bacteria from the systems. Otherwise, water quality deterioration can affect production yields. Defining water quality standards is not straightforward as each species has different requirements. Ozone and UV are among the most widely used methods to guarantee best rearing conditions. Yet, not all bacteria in the system is dangerous or necessarily vulnerable to these methods . Moreover, safety issues and economic aspects motivate new evolving a lternative technologies in aquaculture. In this study, three different disinfection approaches (ozone, hydrogen peroxide (H2O2) and ultrasound treatment) were tested and we compare the main available tools for disinfection in aquaculture .
A pilot study comparing the effects of ozone (3.5 g/h) and H2O2 (15.8 mg/L/h) in a 5 m3 RAS rearing European seabass showed promising results in terms of oxygenation and disinfection (Fig.1, Table 1). Comparative results of an up-scaling assay in a 200 m3 RAS rearing shrimps will be presented. In this system, 4-8 L/h H2O2 should supply or improve the disinfection effect commonly achieved by ozone (10 g/h). Additionally, we present the first results of a pilot research on ultrasound disinfection using a device especially conceived for aquaculture purposes and tested in our facilities. In this case, ozone (3.5 g/h) is tested against the disinfection potential of ultrasound (different frequencies / continuous vs. pulse) applied to a 5 m3 RAS rearing European seabass. We analyse the impact of these three methods on the bacterial composition within the rearing tanks and list prospective benefits and drawbacks of their use as well as recommendations for application based on our practises.
