Effect of drum filter mesh size on RAS water quality

Drum filters play an important role in recirculating aquaculture systems (RAS) by removing particulate matter from production units. Optimizing their performance has significant importance for water quality as well as investment and running costs. One important parameter affecting both issues is the mesh size applied. This study investigates the impact of drum filter mesh size (70, 45, and 30 µm mesh size and a control group without drum filters) on water quality and system performance in a triplicate trial using rainbow trout (Oncorhynchus mykiss), for a period of eight weeks. The use of drum filters led to significantly less particulate organic matter in the RAS water (more than 60 % reduction in particles, particulate BOD, and particulate COD) as well as reduced microbial activity (50 % reduction of microbial activity in water), while no significant reduction in dissolved organic matter was observed. The removal of particulate organic matter led to improvements across most metrics studied. The study demonstrated that mechanical filters had positive effects on water quality parameters and that reducing mesh size from 70 µm to 45 µm led to further improvements in most water quality parameters, while an additional reduction to a 30 µm mesh did not further improve water quality. The findings underscore the importance of particle removal, mesh size selection, and system design to ensure the best removal rates while maintaining maximum filtration capacity. Interestingly, the changes in water quality achieved by the drum filters led to an improvement in feed utilization resulting in increased biomass production. The results suggest that optimizing drum filter mesh size, particularly utilizing 45 µm mesh, can enhance water quality and perhaps operational profitability in RAS.