Nitrification performance of nitrifiers immobilized in PVA (polyvinyl alcohol) for a marine recirculating aquarium system

Characteristics of the nitrification processes with immobilized nitrifier consortium were evaluated for the development of the marine recirculating aquarium system. In order to evaluate the activity of the nitrifiers, a 45 1 airlift reactor was used for the determination of ammonia removal rate for 40 days of operation. The ammonia removal efficiency rate was 98% with 23 g ammonia-N/m(3)/day, respectively. The activity of immobilized nitrifiers in polyvinyl alcohol (PVA) beads treated by boric acid at the concentration of 15% was fully recovered, and the ammonia removal rate increased to 70 g ammonia-N/m(3)/day with 18 days of operation time. An acclimation experiment of the immobilized nitrifiers from freshwater to seawater system was carried out For 60 days using a 2.5 1 airlift reactor with increased salt concentration. The ammonia was completely removed, and nitrite accumulated up to 6 mg/l but decreased to less than 0.1 mg/l after 30-40 days of operation. The salt concentration was related to the time to stabilize the system. Another operation was carried out to evaluate the optimum hydraulic retention time (HRT) of the marine nitrification process for 35 days. The HRT was set in the ranee of 6.12-0.7 h. The highest ammonia removal rate, 63 g/m(3)/day, was observed when the HRT was 1.0 h. (C) 2001 Elsevier Science B.V. All rights reserved.