| Recirculating aquaculture system(RAS) is one of the main development direction of aquaculture industry in our country, the shortage of suitable species for culturing in recirculating aquaculture system, and the high cost of the system equipments and operation are important factors for restricting the extension of RAS application in our country. Two types of recirculating aquaculture systems(type I and type II) had been designed and built, and each system was mainly composed of one sedimentation tank, one downward moving biofilm reactor, one upward moving biofilm reactor and six barrels, however, the barrels of type I were setwith the biofilm purification water bars to apply the biofilm low-carbon aquaculture techniques, as the treatment, and the type II system was not set as above, which as the control. The trials were carried out in each system, whose work conditions were set by 10 m3/d, 20 m3/d or 30 m3/d sewage water quantity treated to evaluate water treatment efficiency and find the best work condition; the trials of Pseudosciaena croceacultured in each system were implemented, which studies were focused on water treatment efficiency, water qualityimprovement and production effects; the solubleness of ozone in seawater and the application to use ultraviolet to resolve the residual ozone were researched, and the removal rate of COD, nitrite nitrogen, total ammonia nitrogen, total bacteria, total heterotrophic bacteria and the vibrio were compared between ozone utilization and UV-ozone utilization, and study the feasibility to use ozone to kill the parasites on Pseudosciaena crocea directly.The main results were as follows:1.The water treatment efficiency of type I and type II recirculating aquaculture system on different daily treating sewage water quantityAt daily treating sewage of 10m3, in the type I, the removal rate of ammonia nitrogen, nitrate nitrogen, soluble reactive phosphorus and COD were significantly higher than daily treating sewage of 20m3 by 4.56%, 10.19%, 17.76% and 15.07% respectively(P<0.05); than daily treating sewage of 30m3 by 8.25%, 22.18%, 31.68% and 26.98% respectively(P<0.05). During the experiment, aquaculture water quality in each system was complied with the national water quality standard of fishery.2.The water quality factors, biological factor and production results were compared between the type I and type IIIn type I, the concentrations of nitrite, ammonia nitrogen, nitrate nitrogen, total nitrogen, soluble reactive phosphorus, total phosphorus and COD in water quality were significantlylower than the type II by 17.26%, 18.39%, 23.33%,14.40%, 19.81%, 15.09% and 7.91% respectively(P<0.05); total bacteria and total heterotrophic bacteria were significantlyhigher than the the type II by 27.13% and 38.37% respectively(P<0.05), on the contrary, the quantity of vibrio was significant lower than the II type by 29.34(P<0.05); and the catch average body weight, survival rate and the average growing rate were significantly higher than the type II by 20.82%, 18.42% and 21.40% respectively(P<0.05).3. The application of UV-ozone in recirculating aquaculture system for Pseudosciaena crocea cultureThe ozone in the aquaculture water could be resolved by the ultraviolet. The removal rate of COD, ammonia nitrogen, the total bacteria, the quantity of heterotrophic bacteria, the quantity of vibrio in the UV-ozone were significantly higher than the control by 9.26%, 9.23%, 39.57%, 43.02% and 10.02% respectively(P<0.05)。The tolerance to ozone of Pseudosciaena crocea is significantly lower than the Amyjoodiniurn ocellaturn, so it is impossible to use ozone to kill the parasite of the Pseudosciaena crocea directly.In conclusion, the biofilm low-carbon aquaculture techniques in RAS can reduce the concentration of polluted water, relieve the load of subsequent water treatment systems and increase the efficiency of whole system. Through the optimization of the whole system process to establish a kind of harmonious microbial community, realize the high efficiency of wastewater treatment and ecological prevention, which can greatly improve the survival rate and growth rate of Pseudosciaena crocea. |
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