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

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 four-month 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 NO 3 -N concentrations, or RAS equipped with a multi-vessel MBR to return treated water from backwash and intermittent solids flushes to the RAS operated at 14 °C, 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 with an 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 addresses an important bottleneck for RAS adoption and siting by 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.