Engineering design and performance evaluation of super high density recirculating aquaculture system

In order to research the change of water quality, growth of fish and economic benefits of the recirculating aquaculture system (RAS) under high density rearing conditions, a super high density RAS was developed. The system consists of three parallel water treatment branch equipped with some new technology, such as culture tank dual drain technology, radial flow settler, micro-screen drum filter, boiling type moving bed biofilm reactor, multiple chamber spraying oxygenator, CO2 degassing tower and etc. The paper also put forward a RAS design method which is based on three main water quality parameters, total ammonia nitrogen(TAN), dissolved oxygen concentration (DO) and total suspended solids(TSS). Using tilapia as the rearing object, 6 months experiment showed that the growth of tilapia was good, the highest culture density reached up to 104.2 kg/m3, the feed coefficient was 1.4 and the survival rate was 92.2%. During this period, TAN could be controlled at average (1.09±0.55) mg/L, DO 4-9 mg/L, pH 6.45-7.41. Economic evaluation results showed that the running cost of the system was about 25Yuan/kg fish, which was a little higher than the market price of tilapia. But considering the environment cost, the water saving effect of the system is significant, which is only about 0.3-0.5 m3 water per day, based on the measurement of the researchers. So, by properly simplifying the system and choosing some more suitable fish variety, recirculating aquaculture system will be valuable in the future.