Design And Experimental Study Of Cyclo-bio Fluidized Sand Bed In Recirculating Aquaculture Systems

In recent years, with increasingly lacking of water resources, highlightingenvironmental issues, and demand for food safety and quality, recirculatingaquaculture system will be more and more popular to realize the sustainabledevelopment strategy of aquaculture. The treatment of aquaculture wastewater is thebase of recirculating aquaculture system, and the biofiltration is the key of treatmentof aquaculture wastewater. The selection of biofilters is critical for recirculatingaquaculture system. So the study on biofilters will get more and more attention. Andthe Cyclo-Bio Fluidized Sand Beds (CB FSB) is developing potential andcompetitive.The dynamics of CB FSB was studied by the combination of theoreticalcalculation, experimental measurement and simulation. Further, the structure could beoptimized and the dynamics of large-scale CB FSB will be forecasted. The lab-scaleCB FSB recirculating aquaculture system was designed basing on the former study.The forming process of biofiltration in freshwater and seawater was studied. And theinfluence of operating condition on treatment of wastewater was studied. To a certainextent, model test could be instead by simulation, the cost and the time of study willbe cut down. The experimental study could guide the application of CB FSB inaquaculture. There were five parts of this study.1Flow pattern, minimum fluidization velocity, relationship between velocity andbed expansion of CB FSB were studied by the method of theoretical calculation andexperimental measurement. The results show that the CB FSB was in particulatefluidization; the particles were distributed uniformly; the interface was steady andclear. The minimum fluidization velocity of CB FSB was predicted by Ergun equationwhen the diameter of particles was in0.1-0.7mm. The relationship between velocityand bed expansion of CB FSB was in depended of static height of particles. The key parameters of influencing the dynamics in CB FSB included: diameter, density andhardness of particles.2The setting of models in simulation was studied to insure the anastomosis ofsimulation and actual situation, including force analysis of particles, multiphasemodel and turbulence model. The diameter of particle and the drag force in simulationwere emphatically studied. The results show that when Eulerian two-phases modelwas selected as multiphase model, RNG k-ε as turbulence, Gidaspow as drag forcecoefficient, Syamlal-Obrien as granular kinetics viscosity, the diameter of silica sandas0.55mm in simulation, the results of simulation was well consistent with theexperimental measurement. So they were as the basic setting in other conditions.Besides, the bed expansion at a lower flow rate was smaller in the experiment than inthe simulation; the opposite was true for a higher flow rate. If the flow rate was nearto the crossing point, the error was smaller. Generally, the bed expansion wascontrolled near the crossing point, the error was in the range of5%-15%.3The key parameters: cone height, cone diameter and slot width were adjustedto optimize the structure of CB FSB by the method of simulation and orthogonal test.The preliminary study of dynamics in pilot-scale CB FSB was done based on theup-scaling theory. The results show that the importance of cone height, cone diameterand slot width to bed expansion was less and less. The structure of optimized CB FSBwas more reasonable, particles distributed more uniformly, and the bed expansion waslarger than original by the experiment of prototype. The dynamics in pilot-scale wassimilar to the lab-scale CB FSB by simulation. A lab-scale CB FSB recirculatingaquaculture system was designed basing on the former study. And it was producedand was validated the effect of wastewater treatment.4The forming process of biofiltration in freshwater and seawater was studied.This part of experimental study could guide the application of CB FSB in aquaculture.The results show that the standard of complete of forming process of biofiltration wascombination of steady TAN remove rate and concentration of NO2-N. The trend ofdissolved waste was similar in freshwater and seawater during the forming process ofbiofiltration. However, the complete time was different, the freshwater54days (about 8weeks), the seawater73days (about10weeks). There was no significant differenceon the final effect of wastewater treatment. The reason maybe was that theconcentration of dissolved waste was low. Besides, the remove of phosphorus wasweak and the NO3-N was accumulated. The combination of other biofilters and CBFSB was proposed to treat the wastewater better.5The influence of operating condition (bed expansion and C/N) on treatment ofwastewater was studied. The results show that the anti-shock loading capability andthe effect of wastewater treatment were stronger as the increase of bed expansion,where the bed expansion was in the range of50%-100%. With the increase of C/N,the capacity of treat wastewater reduced. The effluent concentration of dissolvedwaste increased besides phosphorus, which was harmful to the growth of fish. Thevolumetric TAN convention rate of CB FSB system was823-881g/m~3.d with C/Nfrom0to2, when the bed expansion was100%and the influent concentration ofNH4-N was3.5mg/L. It was higher than the similar biofilters in cold water system.And it was also near to the maximum VTR in warm water system at the similarcondition. All of them indicated that the effect of waste water in optimized CB FSBwas quite high. The purpose of the study was achieved.