Standard UV vs. Photocatalytic UV: What Does the Data Actually Show?

Choosing the right UV sterilisation approach for a recirculating aquaculture system involves more than selecting a wattage and flow rate. The distinction between standard UV and photocatalytic UV — two technologies that are often conflated — has meaningful consequences for pathogen suppression, microbial stability, and ultimately, animal health.

To understand those differences properly, a controlled 10-day trial was conducted at Fresh Studio's R&D facility in Can Tho, Vietnam, comparing both approaches under real RAS operating conditions. The results provide some of the clearest comparative data yet on how each technology performs across multiple microbial vectors.

The trial setup

Three treatment conditions were run in parallel: a control system with no UV, a system running standard UV, and a system running photocatalytic UV from Biosystems. Bacterial loads, Vibrio concentrations, water mould, and EHP-related spore counts were monitored throughout the trial period, providing a detailed picture of microbial dynamics across all three conditions.

Pathogen suppression

Both UV treatments outperformed the control across all measured parameters — which establishes a clear baseline: operating without UV sterilisation in a RAS environment creates significant and measurable biological risk. However, the comparison between standard and photocatalytic UV revealed important differences.

Photocatalytic UV delivered the lowest and most consistent bacterial and Vibrio counts across the trial period. Where standard UV reduced overall loads, it still allowed periodic spikes — precisely the kind of peaks that are most closely associated with disease outbreak events. Photocatalytic UV not only brought average counts lower, but flattened the variance, reducing the likelihood of threshold-crossing events that can cascade into animal health incidents.

Fungal and spore control

Water mould and EHP-related spore counts were reduced in both UV treatment groups compared to the unfiltered control, but again the photocatalytic system demonstrated superior sterilisation efficiency. Standard UV produced meaningful reductions; photocatalytic UV produced no significant spikes throughout the entire trial. For operations where EHP is a material concern — particularly in shrimp RAS — that distinction is operationally significant.

System stability and growth risk

One of the most striking aspects of the control data was its volatility. Without UV, the system experienced large microbial blooms followed by sharp population crashes — a pattern that is highly stressful for animals and indicative of an unstable biological environment. Standard UV reduced this volatility considerably. Photocatalytic UV reduced it further still, maintaining a more stable microbial baseline throughout the trial.

Lower peak loads, reduced variance, and fewer crash events collectively translate to lower growth risk and a more predictable system — the conditions that support consistent animal performance and feed conversion.

What this means for RAS design

The trial data supports a straightforward conclusion: both UV technologies improve water quality outcomes compared to no filtration, but they are not equivalent. Photocatalytic UV demonstrated better performance across pathogen suppression, fungal control, and system stability — the three dimensions that matter most to biosecurity.

As the aquaculture industry moves towards reduced chemical inputs, tighter biosecurity protocols, and greater system resilience, the choice of UV technology deserves the same level of scrutiny applied to any other critical process component. The evidence from this trial suggests that photocatalytic UV represents a meaningful step forward, not a marginal one.

Original post: This article is based on content originally shared on LinkedIn. View the original post here.