Study On The Key Technology Of Water Treatment In A Closed Recirculating Seawater Nursery System For Seed Argopecten Irradians

Conventional nursery modes are facing serious challenges as the deterioration ofcoastal environment pollution. While more seeds are demanded as the expansion ofaquatic product market and the increase of aquaculture areas. So the development ofclosed recirculating seawater nursery system is becoming more and more urgent andsignificant. In this study an experimental-scale closed recirculating seawater nurserysystem was established for the culture of breeding scallop and seed Argopectenirradians. Firstly, the biofilter which is the core of the system was studied. Theinoculation of biofilter in close recirculation seawater seeds nursery system wasconducted by selecting a plant-support packing and introduction of additivescontaining effective nitrifying bacteria. The results of operating the system showedthat an effective and steady ammonia removal rate can be reached quickly even in lowtemperature. The factors that influencing the nitrification such as temperature,ammonia hydraulic retention time and influent ammonia concentration were discussedby laboratory experiments. The operation performance of the biofilter during thelong-term seeds nursery production revealed that the biofilter run effectively.Concentrations of ammonia (NH4 -N), nitrite (NO2 -N), nitrate (NO3 -N) and COD in + - -the recirculation system are far below the quality requirement levels. Secondly,experiment for the culture of breeding scallop and seed Argopecten irradians in theclosed recirculating seawater nursery system was conducted. During the process ofnursery, water qualities of the nursery tank were monitored and the operational effectsof the water treatment facilities were evaluated. Water qualities in the recirculatingsystem and conventional pond production system were also compared during theculture of breeding scallop. The operation performance of the system revealved thatthe water treatment facilities worked efficiently and the water qualitiy of the systemwas controlled in good condition. Problems about the system were also found duringthe long-term operation and improvement was implemented. A feasible watertreatment procedure of closed recirculating seawater nursery system was achieved.Thirdly, the formation process of biofilm on the surface of support packing wasstudied in the recirculating seawater system. The influences of different supportpacking and influent ammonia concentration on the process were compared. Thechanges of fixed biomass concentration(μg /cm2) and specific activity of nitrifyingbiofilm during the process were also examined. The periodicity of the process wasachieved which can be useful for the maintenance and management of the biofilter.