Recirculating aquaculture systems are designed to save water and maintain stable conditions, but that efficiency creates its own challenge.
Because the same water is treated and reused again and again, microbiological control becomes critical. If unwanted microorganisms begin spreading through the loop, the problem can quickly affect the entire system.
One fish farm working with a recirculating aquaculture system (RAS) needed a water-disinfection method that would fit into its existing treatment chain without adding chemicals and without exposing the fish directly to UV light.
The initial setup
The site already had a functioning RAS layout.
Water moved through the usual treatment stages:
mechanical filtration;
biological filtration;
pumping and recirculation back to the fish tanks.
The farm wanted to improve microbiological control within this system while preserving the current engineering layout as much as possible.
The practical requirements were:
treatment of flows from 115 m³/h and above;
no residual chemicals in the water;
separate protection for each of four circulation lines;
stable operation under changing conditions;
no direct UV exposure in the fish habitat.
That last point matters in aquaculture. The water should be treated, but the irradiation zone should remain outside the fish tanks themselves.
Why a single device was not the whole answer
At first glance, this looks like a standard UV-water-treatment task: place a reactor after filtration and disinfect the returning water.
But real systems are rarely that straightforward.
Different circulation lines may have different hydraulic behavior, different installation space, and different constraints on pipe routing. In retrofit projects, that often leads to a more flexible design rather than a one-size-fits-all solution.
In this case, the final arrangement used two types of UV equipment:
a conventional inline UV reactor for the main treatment stage;
a submersible UV module installed inside a pipe section to function as a custom reactor.
That second part is what makes the project especially interesting.
The inline reactor
One part of the configuration used a multi-lamp inline stainless-steel reactor placed after the biofilter.
According to the source data, its operating ranges were approximately:
up to 200 m³/h at 25 mJ/cm²;
up to 120 m³/h at 40 mJ/cm²;
up to 70 m³/h at 30 mJ/cm².
The reactor body was made of stainless steel and designed for operation in pressurized water lines. The complete set included the UV chamber, lamp, quartz sleeve, ballast, viewing window and control cabinet.
This is the more familiar part of the system: a dedicated UV reactor installed directly into the circulation loop.
The more unusual part: a submersible module inside a pipe
The second part of the solution was less conventional.
A high-power submersible UV module was placed inside a 160 mm pipe section about 1700 mm long. One end was fixed using a PTFE sealing bushing, while the other end was stabilized within the pipe.
In practice, this created a custom irradiation channel using a submersible lamp assembly inside a pressurized line.
Why do this instead of using only standard inline reactors?
Because retrofit engineering often involves compromise.
Sometimes a submersible module can be adapted to an existing geometry more economically than a completely new reactor body, especially when the client already has constraints on space, pipe routing or procurement.
Why this hybrid approach can make sense
A mixed configuration like this can be useful for several reasons.
- Different lines may require different solutions
Even if the flow targets are similar, the physical installation conditions may not be.
One line may have enough room for a standard UV reactor. Another may be easier to modify using a custom pipe section with a submersible module inside.
- High-power lamps can be used in a controlled zone
The submersible module in this case used a high-power amalgam lamp, allowing the disinfection stage to remain outside the fish tanks while still treating the circulation water.
- Existing infrastructure can often be reused
Instead of redesigning the entire treatment loop, the project adapted the UV stage to the infrastructure already on site.
That is often one of the most practical goals in industrial retrofits.
Why chemical-free treatment was important
In aquaculture, adding chemical disinfectants directly into recirculating water can create operational complexity.
Depending on the method, it may require:
dosing control;
residual monitoring;
additional neutralization;
compatibility checks with fish and biofilters.
UV treatment avoids residual chemicals because it acts through irradiation rather than chemical oxidation inside the water.
That does not mean UV solves every water-quality issue by itself. It works best as one stage in a broader treatment chain that already includes mechanical and biological filtration.
The pressure-sealing issue
One of the technical difficulties in the project was the sealing assembly for the submersible module.
A submerged UV module is usually straightforward when installed in a tank or reservoir. But when placed inside a pressurized pipe, the sealing requirements become more demanding.
The project required modification of the sealing node so that the system could operate reliably under the specified pressure conditions.
This is an important engineering detail: a module that works well in an open tank may need additional design work before it can function as part of a pressurized line.
Why pipe diameter mattered
The custom installation depended on a 160 mm pipe section.
That diameter had to be compatible with:
the module geometry;
the quartz sleeve dimensions;
water flow conditions;
mounting and stabilization of the lamp assembly.
The pipe itself was sourced separately by the client, while placement recommendations and layout guidance were provided as part of the engineering work.
This highlights another common reality of projects like this: the success of the UV stage often depends on ordinary mechanical details such as pipe size, mounting tolerances and service accessibility.
Four circulation lines, four protection points
The farm wanted individual protection for each of its four circulation lines.
This matters because a multi-line RAS can behave a bit like several connected ecosystems. If each loop has its own disinfection point, the risk of microbial spread across the full system may be reduced.
From an operational point of view, separate UV stages can also make troubleshooting easier.
If one line behaves differently, it can be inspected and adjusted without treating the whole facility as a single undifferentiated loop.
What this project shows
This case is interesting not because it uses UV in aquaculture — that part is familiar — but because it shows how UV systems are often adapted in real engineering conditions.
The important lessons are:
microbiological control in RAS has to fit into an existing treatment chain;
the hydraulic layout often determines the final equipment design;
inline reactors are not always the only practical format;
submersible modules can sometimes be adapted for pipe-based operation;
sealing, pressure and service access matter just as much as lamp power.
Most importantly, UV treatment in aquaculture is not just about installing a lamp.
It is about deciding where in the water loop the irradiation should happen, how it will interact with the rest of the treatment process, and how it can be maintained under real operating conditions.
In this fish-farm project, the answer was a hybrid system: part conventional inline reactor, part custom in-pipe installation.
And that is often how industrial engineering works in practice — not as a catalog solution, but as a response to the constraints already present on site.
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