Abstract:Biofilter is the key water treatment unit of marine RAS(Recirculating Aquaculture System), and it plays an important role in water soluble nitrogen removal. A pilot scale experiment study was systematically carried out with synthetic aquaculture wastewater. The performances of ammonia removal in start up and steady state period were examined in the marine biofilters packed with bamboo medium. The hydraulic retention time, temperature, gas/water ratio, C/N and pH were 1 hour, 18~25℃, 3∶1, 3∶1 and 8.05～8.53, respectively. Results showed that marine biofilter packed with bamboo substrate enabled the nitrifying bacteria to grow rapidly, and the number of ammonia oxidizing bacteria and nitrite oxidizing bacteria was 4.5×105 CFU/ml、1.5×105 CFU/ml（smooth） and 1.1×106 CFU/ml（crude） in steady state period, respectively. The ammonia removal rate of biofilter was highly efficient. The ammonia nitrogen concentration in the effluent of bamboo biofilters was below 0.06 mg/L, which was much lower than the toxic leve
