Response of simultaneous nitrification-denitrification to DO increments in continuously aerated biofilm reactors for aquaculture wastewater treatment

Intensive aquaculture usually produces large volumes of nutrient-rich wastewater, which is essential to treat to avoid eutrophication. This study aimed to evaluate the performance of five, continuously aerated, biofilm reactors treating simulated, high-strength, aquaculture wastewater under different dissolved oxygen (DO) levels, and the effects of DO increments on simultaneous nitrification-denitrification (SND). Continuous aeration was beneficial to complete nitrification. Total inorganic nitrogen (TIN), principally ammonium, was mainly removed by SND. The SND rate response to different DO levels was fitted well by the power function of y = 54.81 + 371.58/(1 - 0.16*x)(boolean AND)(-1/0.24) (R-2 = 0.897, P = 0.000). When the TIN was removed completely, the optimal SND rate was defined and corresponded to a value of 121.8%. Accordingly, the optimal DO concentration was calculated as 2.10 mg/L, close to the actual level of 1.83 mg/L, at which the highest proportional removals of total nitrogen (58.0%) and TIN (57.3%) were obtained. Phosphorus was also removed by denitrifying polyphosphate-accumulating organisms.

Automated summary

This study evaluated the performance of five continuously aerated biofilm reactors treating high-strength aquaculture wastewater, finding that continuous aeration is beneficial for nitrification and simultaneous nitrification-denitrification (SND) mainly removes total inorganic nitrogen (TIN) primarily in the form of ammonium. The study also identified the optimal dissolved oxygen concentration for achieving the highest proportional removals of total nitrogen and TIN.