Development of Aeration-Assisted Combined Nitrification and Solid Removal Unit for a Compact Recirculating Aquaculture System

Abstract

This work focused on the development of water treatment unit, called aeration-assisted combined nitrification and solid removal (ACNS), for compact aquaculture system. Results of preliminary study indicated that aerated filtration could extend filtration time significantly and capture more solids as compared to non-aerated filtration. Operating parameters of ACNS, including screen pore size, influent flow rate, aeration rate and position of air diffuser, were determined at 130 µm, 750 L/h, 120 L/h and 1.0 cm below the base of screen, respectively. ACNS was subsequently evaluated for its performance in nitrogen and solid removal during the 60-days closed-water tilapia cultivation. Performance of aquaculture system with ACNS, as the only treatment unit, was comparable to the aquaculture system having both nitrifying biofilter and ACNS, as separated units. Specifically, ACNS could maintain suspended solids (28 ± 7.6 mg SS/L), ammonia (< 0.5 mg N/L) and nitrite (< 0.5 mg N/L) concentration below the recommended limits for extended period. ACNS also produced relatively high and constant effluent flux close to initial value despite increasing the filtration time in aerated compartment up to 7 days. This led to continuous filtration, without stopping the system to remove solids on screen, for 50 days.