Integrated Membrane Bioreactor for Water Quality Control in Marine Recirculating Aquaculture Systems

Abstract

The aquaculture live feed organisms Acartia tonsa (a calanoid copepod, experiment 1) and Brachionus “Cayman” (a rotifer, experiment 2) were cultivated in marine recirculating aquaculture systems (RAS), respectively. The pilot plant was built as a combination of conventional RAS (cRAS) and as a modified RAS which implemented an ultrafiltration membrane bioreactor (MBR) for the removal of fine suspended solids and colloidal particles as part of the treatment system (mRAS). The two treatment schemes were connected to the same biofilter (a moving bed bioreactor). In the first experiment, the membrane was operated with no extraction of concentrate, and hydraulic retention time (HRT) of 6 hours (i.e., water exchange in the cultivation tanks of 4 times per day). In the second experiment, the membrane was operated with daily extraction of concentrate, and HRT of 12 hours. Results show that the MBR option is more efficient in removing particles from the recycle stream than conventional RAS. However, the impact this has on the number of particles in the live feed cultivation tanks is not readily apparent based on particle analysis. The amount of suspended solids added during feeding exceeds the amount removed in the recycle system. This requires a higher recirculation rate and different membrane operating conditions.

Keywords:

• colloidal particles
• copepod
• fine suspended solids
• MBR
• membrane filtration
• RAS
• recirculating aquaculture system
• rotifer

ACKNOWLEDGEMENTS

This work was financed by RFF-MIDT, Norway (project no. 209048). The studies were conducted at the NTNU Centre for Fisheries and Aquaculture (Sealab), Trondheim, Norway. The authors like to thank Sintef Fisheries and Aquaculture for equipment during the experiments, Kari Attramadal (NTNU) for many useful research discussions about microbial control, Werner Storøy (Sundsfjord Smolt) for technical help during the copepod experiment, Morten O. Alver (Sintef) for the automatic counting of rotifers, Dag Altin (BioTrix) for growing live algae feed for the copepods, and Ingrid Overrein (Lipotek) for transferring the copepod nauplii and determining copepod density.