Study On The Media Of The Biofilters In The Recirculating Aquaculture System

With the development of aquaculture, the culture environment and the water quality have been degraded greatly because of the wastewater drainage. The main contamination in the wastewater is the remanent diet of feed, feces, and the kind of nutriment. All of them contribute much to the increase of BOD5 and COD in the water. The accumulation of ammonia, nitrite and nitrate, which are the main productions as the nutriment decomposes, is harmful to the living fish and incurs the water enrichment. Intensive fish culture has become the new economic development point steadily in fishery. It is the representation of high-tech in fishery. It is not only development direction of the world, but also the development direction of China.To decrease the ammonia/nitrite/nitrate concentration or to remove them completely is a feasible approach to remain high level water quality and avoid environment pollution. And the biofilters play this role in the recirculating aquaculture system. The technical process is: put some medias in the filter tank, and bio- film was grown on the medias. When wastewater arrived, use the nitrobacteria to remove the ammonia/nitrite. There are many reports about the mechanics, design parameters, water treatment affects and the development of medias.The recirculating aquaculture system is reviewed in this paper, and the biofilter's media of the recirculating aquaculture system are also reviewed in this paper. The establishment of biofilter's full nitrifying function is very important to avoid the hazards for aquacultural producers. This paper compared three methods of cultivating biofilter in recirculating aquaculture system. The results show that putting appropriate load fish directly and feed lowly is the best method to establish the nitrification function of the biofilter in the production of the recirculating aquaculture system.Additionally, the characteristics of soft filler, elastic filler and semi soft filler in the closed recirculating aquaculture system are analyzed, and the removal efficiencies of Ammonia of the three biofillers are compared. The results indicated that: (1) At the same HRT, the removal rates of three biofillers are different with each other. With the higher concentrations of Ammonia, the removal rates of Ammonia are lower for the three biofillers, respectively. (2) As one biofiller, the removal rates of Ammonia are different according to different HRT. (3) Considering the difference of HRT and filling material, when the HRT is 80 minutes the highest average removal rate is 52.1% in elastic filler biofiller.