Abstract:To improve the removal efficiency of nitrogen pollutants by the biological aerated filter (BAF) system in a recirculating aquaculture system (RAS) and reduce the accumulation of nitrates and the amount of aeration, a type of iron-based composite biological filler was introduced into the BAF system. The environment of aerobic, anoxic, and anaerobic cycling, in turn, was built with intermittent aeration in this BAF system. The surface morphology characteristics of the fillers were investigated using a scanning electron microscope. The treatment performance of nitrogen pollutants under different proportions of the two substances in the composite filler and different aeration operation modes were investigated. Then, single-factor tests were used to optimize the important operating parameters (including temperature, hydraulic loading rate, and influent ammonia nitrogen load) of the BAF with the iron-based composite biological filler. The results showed that the denitrification efficiency improved by approximately 10%, the accumulation of nitrous nitrogen was reduced by 25%, and 50% of the amount of aeration was saved after adding iron-based packing in the BAF system.The BAF system with the iron-based composite biological filler exhibited the best removal performance under the following operating conditions: Intermittent aeration time of 12 h, composite proportion of the polypropylene carbonate gel hydrophilic filler and sponge iron in the composite filler of 3∶1, the temperature of 30℃, hydraulic loading rate of 1.2 m3/(m2·d), and the influent ammonia nitrogen load of 1 mg/L. The introduction of the biological sponge iron composite filler and intermittent aeration could improve the removal efficiency of nitrogen pollutants in the BAF system. It significantly reduced the accumulation of nitrite nitrogen and reduced the power consumption of the operation. The results of this study will be useful in understanding how aerobic and anaerobic environments promote nitrogen transformation. This study also optimized the operating parameters for the actual application of the BAF system with the iron-based composite biological filler in RAS.
