Performance Characteristics of Rotating Biological Contactors Within Two Commercial Recirculating Aquaculture Systems

Abstract

Biological filtration is a critical determinant in the process train design of a recirculating aquaculture system. In addition to the mechanical and biological efficiency of the biofilter itself, this process must be co-developed with the various interrelated technologies involved in water quality control. This study describes the performance of rotating biological contactors as an integral part of two commercial closed recirculating fish production systems. Data is presented from replicated systems employing paddlewheel-driven rotating biological contactors. The RBC is a robust fixed-film bioreactor demonstrating excellent operational attributes in recirculating aquaculture systems. The efficiency of the RBC as biofilter is defined according to its mechanical and biological performance characteristics. In addition to highly efficient nitrification of ammonia under heavy feeding conditions (1.21 g/m2/day), the RBC has significant influence on control of secondary water quality and hydraulic considerations affecting the overall design and performance of the system. RBCs off-gas carbon dioxide, providing a level of pH control, a significant benefit in closed recirculating systems. Additional data is presented for carbon dioxide sparging efficiency, and the capacity for versatile hydraulic loading and low-head operation. This paper also provides a practical comparison of RBC design and performance considerations with other biofilter options, including the effects of design on the mechanical reliability, energy requirements, and spatial efficiency of this biofiltration system.