Water treatment technology for recirculating aquaculture systems to increase efficiency by reducing the negative effects of organic matter

The project has : -Demonstrated the water flow pattern in fish rearing Tanks in LBCC-RAS to obtain improved self-cleaning early removal of particles and good water quality conditions for fish. -Assess the removal of organic matter by water treatment lines of different levels of complexity in down-scaled RAS. The project has demonstrated that the implementation of membrane filtration in RAS improves largely the water quality. The concentration of particulate organic matter (POC) and particulate N were approximatively ten times higher in the RAS without membrane than in the RAS with membrane. -Found out that main mechanisms that control production of off-flavours in RAS appear to be optimum biofilter functions, while removal of particles from the water seem less important. -Characterized the consequences of different levels of organic matter removal (high and conventional) in LBCC-RAS on: (1) conventional water quality parameters, (2) heterotrophic microbial carrying capacity, bacterial stability and nitrification efficiency, (3) the biological processes that cause off-flavour production, and (4) dissolved CO2. -A new dissolved CO2 sensor was developed and validated in bacterial cultures and fish tanks, calibrated against commercial sensors and chemical methods. The sensor will contribute to a better knowledge of dissolved CO2 dynamics in RAS systems.

-Design and set-up of a membrane based RAS system for a better removal of organic matter: the removal of organic matter is improved by the implementation of membrane and may result in better fish growth. Though, further investigations need to be carried out to confirm these findings. -Minimizing the risk of off-flavour production in commercial fish farms : The project had identified hot-spots for production of off-flavours. With this knowledge, off-flavours can be reduced for the benefit of both producers and consumers. -A new approach for fast and accurate determination of off-flavour in water and fish were developed and optimized: Analysis of fish from various aquaculture facilities demonstrated that palatability of fish can be determined with high accuracy . -New dCO2 sensing system:A new optical sensor for dissolved CO2 was calibrated against a commercial sensor and reference chemical methods, and validated in bacterial culture and fish tank monitoring.

This project aims to develop strategies and water treatment technology for removal of particulate organic matter (POM) in land based closed containment recirculation systems for aquaculture (LBCC-RAS). This will increase efficiency by reducing waste products, off-flavour compounds and carrying capacity of bacteria. Removal of POM is the key to improve the production and product quality of fish produced in LBCC-RAS. Organic matter is the determining factor of the amount of heterotrophic bacteria that can be sustained in the LBCC-RAS. Nitrification efficiency of the bio filter is affected by the competition for space and oxygen with heterotrophic bacteria. In addition, high amounts of organic matter reduces the efficiency of both UV and ozone disinfection. Heterotrophic bacterial degradation affect the consumption of O2 ,the production of CO2 and ammonia, contribute to water colour and bacteria producing off-flavour compounds, eventually reducing the value of fish and caviar. The effects of high, intermediate and low removal efficiency of organic matter on the effects on dCO2, bacteria and off-flavour prevalence will be investigated. Both tank dynamics and water treatment in the RAS loop will be used to obtain high removal efficiency. Multiple drains with optimized geometry and hydraulics will be designed for early particles collection and to be used as a strategy in combination with techniques such as advanced membrane filtration. The effectiveness of a membrane is dependent on several ambient conditions and fouling is a challenge for membrane performance. We will aim to adapt the membrane technology, optimize the operation and maintenance in a LBCC-RAS. A close collaboration with fish-producing companies safeguard that the project is applicable for commercial aquaculture.