A Study of Reactor and System Dynamics in a Simulated Freshwater Recirculating Aquaculture System for Achieving Efficient High‐Rate Nitrification using Packed‐Bed Biofilm Reactor

Abstract Aquaculture makes a crucial contribution toward ensuring global food security. Recirculating aquaculture system (RAS) is regarded as a sustainable, high‐yielding aquafarming technique. Achieving robust and efficient ammonia removal by nitrification is of foremost concern in RAS. Packed‑bed biofilm reactors (PBBRs) can achieve high‐rate, robust nitrification in RAS. Minimizing tank exchange rate (ER), in conjunction with high‐rate nitrification, is vital for enhancing the efficiency of the system. Despite its importance, research on ER and high‐rate nitrification in RAS is limited. This study aims to underpin the impact of ER on reactor and system dynamics using high‐rate nitrifying PBBRs (of 1.91 and 3.98 L volumes, culture tank (CT) to biofilter volume ratio: ≈50 and 25) using a simulated lab‐scale freshwater RAS. The PBBRs, at ammonia loading rates of ≈1900 and 900 g N (m 3 ·d) −1 , show ammonium removals >99.5%, maintaining N‐NH 4 + <1 mg L −1 in the CT at stocking densities up to 46 kg m − 3 . Assessment of reactor dynamics reveals that 3.98 L PBBR is oversized. ERs ≥ 14.4 d −1 maintain N‐NH 4 + <1 mg L −1 in the CT, while ERs <14.4 result in an exponential rise in the concentration. The findings can be leveraged to make RAS more compact and cost‐effective.