UV in RAS
Re-circulation Aquaculture Systems, better known as RAS, are sophisticated and highly intricate systems with various design-philosophies, layouts and solutions offered by design companies. RAS systems create a fascinating, delicate dynamic between two focal points in the system: on the one hand, the fish tanks and on the other hand, the bioreactor. A chemical-physical change in one focal point immediately affects the balance of the other, and prodigious intervention is needed to restore harmony to the system. It is no less than an art.
Apart from the chemical-physical balance to be maintained in RAS, the microbiological load is extremely important as well. Again, a delicate balance is required: on the one hand, a sterile environment is undesired and even disruptive as it may give rise to opportunistic bacteria or produce feeble fish, while on the other hand one wants to prevent disease outbreak which means medical treatment and biomass loss. Most RAS designs incorporate UV systems in the traditional open-flow manner. A quick survey of UV systems normally used in RAS reveals an awkward tendency to use multi-lamp submerged or open-channel low-pressure UV systems. Why? Since very little study has been done to date on the the benefits of UV in RAS, the main consideration has become price and head-loss. In reality, open-channel or submerged UV systems are extremely difficult to maintain properly due to the egregious amount of lamps, they offer little or no control and monitoring, and present poor disinfection capabilities. How many times have you visited a RAS site where the UV systems were shut down or operated with only a few lamps ‘ON’ because no-one really cared if it operated or not? I have been to quite a few. The use of open-channel and submerged UV systems in RAS cannot be supported by any actual measurable production benefits. It is simply there, whether it works or not.
An effective UV design for RAS provides a sane, controlled-growth-environment in the fish tanks that governs the delicate microbiological balance. The function of UV in RAS is similar to a Surge Protector: it enables a stable and defined current to pass while chopping off the harmful spikes. The "current" in this metaphor would be the water-bore microbiological load. From Atlantium's experience in RAS applications, a correct UV design can positively affect fish growth and prevent disease outbreak. Moreover, sites that have installed Atlantium’s UV RAS application have moved from a reactive approach to disease outbreak—responding with formalin or other measurements once disease is detected—to a pro-active approach, preventing disease outbreak altogether. The affect on production costs, fish welfare, mortality and production stability are enormous. Atlantium has fully realized that implementation and integration of UV disinfection solutions in re-circulation applications requires a different approach in order to effectively utilize the real power of UV disinfection.
What is an efficient UV disinfection design for RAS? As I have mentioned above, it really depends on the RAS philosophy, which differs from one company to another, but the general guidelines remain the same:
- A consistent, minimum UV dose level capable of creating controlled growth environment.
- Minimum amount of lamps
- Low head loss
What is the effective UV dose design to achieve #1 above? That is the real secret and the beauty of this delicate and intriguing application, which aims to maintain harmony in an eco-system which constantly generates chaos. But like anything else in this industry, the approach should be scientific and based on actual performance measurements, and not on "common beliefs".