Feasibility of integrating multi-vessel membrane biological reactors within a recirculating aquaculture system to treat and reuse discharged water

Authors: CROUSE, CURTIS - Freshwater Institute; DAVIDSON, JOHN - Freshwater Institute; VINCI, BRIAN - Freshwater Institute; LEPINE, CHRISTINE - Freshwater Institute; MURRAY, MEGAN - Freshwater Institute; GOOD, CHRISTOPHER - Freshwater Institute

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/4/2026
Publication Date: 4/8/2026
Citation: Crouse, C., Davidson, J., Vinci, B., Lepine, C., Murray, M., Good, C. 2026. Feasibility of integrating multi-vessel membrane biological reactors within a recirculating aquaculture system to treat and reuse discharged water. Aquacultural Engineering. 114. Article 102730. https://doi.org/10.1016/j.aquaeng.2026.102730.
DOI: https://doi.org/10.1016/j.aquaeng.2026.102730

Interpretive Summary: Recirculating aquaculture systems (RAS) used to produced food fish rely on less water resources than traditional aquaculture methods. However, significant water volumes are still required to maintain acceptable growth conditions for fish performance. Membrane biological reactors (MBR) to process waste from the RAS were evaluated and characterized. The MBR processed the waste and converted it to a reusable water resource resulting in 94% less new water use, an acceptable environment for the fish, and healthy fish performance. The water savings and husbandry environment represent an opportunity for RAS to improve operating conditions at existing farms and site new farms in previously unfeasible areas with scare water resources.

Technical Abstract: Previous research incorporating single-vessel activated sludge membrane bioreactors (MBR), an effective denitrification technology, in the recirculating aquaculture system (RAS) water treatment loop reduced water use and did not negatively affect rainbow trout (Oncorhynchus mykiss) performance; however, several operational challenges were encountered. A follow-up trial was conducted to determine if integrating a multi-vessel MBR with pulsed air membrane scouring, which decoupled essential processes, including membrane filtration and aerobic and anoxic zones for nitrification and denitrification, could improve operational efficiency. Triplicate control RAS, without MBRs and with standard dilution rates to maintain safe NO3-N concentrations, or RAS equipped with a multi-vessel MBR to return treated water from backwash and intermittent solids flushes to the RAS were compared. Pulsed air membrane scouring reduced membrane fouling, allowed for effective offline cleaning procedures, and provided better segregation and mixing of anoxic and aerobic zones in the activated sludge. Rainbow trout growth performance and welfare metrics were similar; however, deformity prevalence was lower in the RAS treated with MBR. Denitrification achieved in the MBR resulted in a 94% reduction in water use. Despite statistically significant differences between the two treatments, water quality was largely similar, providing a culture environment within established limits for rainbow trout culture. The largest difference in RAS with and without MBRs was water clarity as measured by true color (109 ± 14 vs 27 ± 3 Pt-Co Units). This difference was eliminated by low-dose ozone application during the final month of the trial. The multi-vessel MBR design with improved operational approaches and low-dose ozone addition represents a viable approach to reducing water use for RAS facilities while providing equivalent water quality for rainbow trout culture but requires relevant staff experience and expertise for optimal performance.