Construction And Application Of Sequencing Batch Double-Cycle Recirculating Aquaculture System

In order to improve the water treatment stability of industrial recirculating aquaculture system,increase the aquaculture density and survival rate,a sequencing batch double-cycle industrial recirculating aquaculture system was constructed.The hydraulic retention time increased by intermittent operation of biofilm for fully degradation of nitrogen pollutants.Through continuous operation of arc screen to filter solid particulate matter.The system has good treatment of aquaculture wastewater.The main contents include:1.Biofilm reactor start-up.(1)Domestication and cultivation of nitrifying bio-floc:Heterotrophic bioflocs was cultivated with sewage outlet sediment as seed sludge after 26 days,grouper feed powder and red sugar as nitrogen and carbon sources.Next,nitrifying bioflocs were cultivated by gradually reducing carbon source.Compared with the seed sludge,the total relative abundance of nitrifying bacteria flocs was greatly increased in biological,and nitrifying bioflocs were formed in 32 days.The effluent water quality is stable.The highest concentration of ammonia nitrogen is only 0.04 mg/L.Nitrite nitrogen concentration gradually decreases and tends to be stable.(2)Biofilm reactor Start-up:Nitrifying bioflocs were mixed with sponge fillers.Feed powder was used as nutrient source.The mature biofilm had high nitrogen removal efficiency.The concentration of ammonia nitrogen in effluent approached 0 mg/L,and the concentration of nitrite nitrogen was about 0.1 mg/L.The sponge fillers had well nitrate nitrogen removal ability.The nitrification rate of biofilm on sponge fillers was determined at the volume ratio of sponge filler to seawater is 1:4.The biofilm can degrade 1.81 mg/L ammonia nitrogen and 1.62 mg/L nitrite nitrogen to 0.09 mg/L and 0.05 mg/L within 4 hours.Thus,the reaction time of biofilm was determined to be 4 hours.2.Parameter optimization of arc-shaped sieve.The filtration effects of arc-shaped sieve at five different sieves and different flow velocities was determined.The arc-shaped sieve operated at 150 mesh and 1200 L/h flow velocities can control the turbidity of culture water from 0.8 to 1.1 NTU during the 66 d culture experiment.3.The system performance evaluation.The grouper culture experiment was carried out with 30 kg/m~3 as the initial aquaculture density.After 66 days of culture experiment,the average body weight of grouper increased from 273±12.22 g to 552.52±107.04 g,and the final culture density reached to 60.78 kg/m~3.The removal rates of ammonia nitrogen and nitrite nitrogen was gradually increased from13.33%and 14.84%to 93.73%and 93.50%.In addition,it was found that the combination of foam separation and arc screen to form an aerated arc screen can remove fine particles and decreased the wash frequency of the arc screen.In conclusion,the Sequencing batch double-cycle industrial recirculating aquaculture system can effectively remove suspended particulate matter by aerated arc screen,reduce the wash frequency of the arc screen.And the increase of hydraulic retention time of intermittent biological filter can effectively control the water quality of aquaculture water.This system can culture high-density grouper,improve the survival rate of grouper and finally increase the economic benefits.