Nitrogen Removal Characteristics in a Biofilm System for Recirculating Aquaculture Wastewater Treatment under High-Salinity Conditions and Oligotrophic Stress

Abstract

This study evaluated nitrogen removal characteristics in a biofilm system for recirculating aquaculture wastewater treatment with different carriers and aeration modes under salinity conditions (35 g NaCl L−1) and oligotrophic stress (total organic carbon<5.0 mg L−1). The results demonstrated that the nitrification process was inhibited at a high salinity concentration of 35 g NaCl L−1, and an ammonia oxidation efficiency greater than 80% required 45 days but resulted in high nitrite accumulation. No significant differences in ammonia oxidation and denitrification efficiencies were found between the polypropylene and polyurethane foam carriers, whereas compared with the polyurethane foam carrier, the polypropylene carrier with a higher aeration duration of 6 h in Phase 2 needed less time (99 days) for the acclimatization of complete nitrification. However, no denitrification efficiency was found with full-time aeration, and the highest denitrification efficiency was 34.11%±6.05% with no aeration. Poor denitrification performance was mainly due to oligotrophic stress from carbon source deficiency, and an efficient denitrification efficiency of 62.7%±8.2% was achieved with the addition of biodegradable polycaprolactone (PCL).