Media Selection And Water Treatment Performance Of Biological Trickling Filler In The Recirculating Aquaculture System

Recirculating aquaculture systems（RASs）play an important role in aquaculture,and water purification is the key technology for RASs.The waste and residue of cultured species is the main source of ammonia and nitrite.The efficiency of ammonia and nitrite removal is the critical problem in recirculating aquaculture systems.Different types of filters have an important effect on the nitrification performance of biological filtration system.Three different commercial filter media（carbon fiber,non-woven polyester and industrial filter paper）were evaluated in lab-scale trickling filter.The characteristics of biofilms,ammonia removal rates and microbial communities in three reactors were compared with each other.The weight of biofilms on CTFs with carbon fiber carriers was the maximum(45.97 g·m^-2),and the ammonia nitrogen removal efficiency（86.76%）of this CTFs was higher than the other filters or reactors（61.96⁷8.76%）.In an addition,the concentration of the accumulated nitrite in the carbon fiber CTFs was the lowest among three reactors.The microbial communities of biofilms in the three biofilters were evaluated by the high-throughput Illumina-Mi Seq sequencing technology.The results showed that the species richness and biological diversity of biofilms in the carbon fiber CTFs were higher than those in the others.The relative abundance of Nitrospira genus was highest,and the corresponding removal efficiency of ammonia nitrogen was also higher in the carbon fiber CTFs.With carbon fiber media,the nitrifying efficiencies with different conditions such as flow rate,temperature,initial ammonia concentration and C/N ratio were investigated.The biofilms of carbon fiber filter grew more quickly,and had better stability and nitrogen removal efficiency than the biofilms of other two filters did.At 30℃,with 10 mg/L of the initial ammonia concentration,the ammonia removal rate of filter with carbon fiber reached 97%after 6 h reaction.The efficiency of ammonia removal can be improved with the flow rate increasing within a certain range.The average ammonia removal rate of carbon fiber trickling filter increased to 0.5 mg/（L·h）,while initial concentration of ammonia was 15 mg/L.Response surface methodology was used to investigate forecast model of ammonia removal rate,flow rate had significant effect,and the interaction of flow rate and initial concentration of ammonia also had significant effect in CTFs.Carbon fiber CTFs were started up within 20 days in a pilot Brocarded Carp RAS.With different culture densities,the VTR of trickling filter was obviously different in the culture process of pilot system,as 35.29 mg TAN/m²·d and 211.7 mg TAN/m²·d.The water flow rate also had a certain effect on ammonia removal rate;Using Biolog?ECO-plates to analyze the microbial metabolism situation at different stages,it was shown that aquaculture density had significant effect in utilization rate of carbon.With high feeding and water flow rate,the utilization of carbon sources was strong in biofilms.High throughput sequencing analysis was shown that with the increase of culture density,the relative abundance of Proteobacteria and Bacteroidetewereincreased,butCyanobacteriawasonthecontrary.Anaerolineaceae_uncultured,Saprospiraceae_uncultured could survive in a high ammonia nitrogen conditions.At the same time Planctomycetaceae_uncultured,Nitrospira also had high relative abundances in high density.The above results laid the foundation experiment for trickling filter in RAS.