Nitrogen compounds removal in closed recirculating seawater system for shrimp pond by external loop airlift bioreactor

Abstract

Packed bed external loop airlift bioreactor (PBABR) was found suitable for the treatment of wastewater containing ammonia and nitrate. The 60 litre PBABR comprised aeration and non-aeration zones both of which were packed with plastic packing to enhance the surface area for the attachment of bacteria. Experiment indicated that PBABR provided a complete removal of nitrogen compounds with both nitrification and denitrification taken place simultaneously. In other words, ammonia was decomposed by nitrifying bacteria in the aeration zone and nitrate was converted to nitrogen gas by denitrifying bacteria in the non-aeration zone. The optimal conditions for maximal nitrogen removal efficiency of this system were: dissolved oxygen of 3-4 and 0-2 mg/L in the aeration and non-aeration zones, respectively, the initial carbon to nitrogen ratio of 20-40, pH 7-8, alkalinity of greater than 100 mg (CaCO3)/L. The nitrification rate was in the range of 0.06-0.87 g NH3-N/m2-d and the denitrification rate was 0.01-0.08 g N03-N/m2-d.