The doubling of fish consumption over the past 50 years is driven by its recognition as a healthy dietary component, leading to an increased establishment of fish farms worldwide to address the growing demand while preventing overfishing. To conserve water, energy, and costs, fish farms are adopting Recirculating Aquaculture Systems (RAS), wherein the recirculated water undergoes filtration to remove fish waste. Ensuring water disinfection is vital for maintaining fish health, and the most effective, chemical-free, and environmentally friendly method for achieving this is through UV disinfection systems.
The Reasons Why UV Radiation is Used
Microorganisms, collectively referred to as MO, encompass bacteria, viruses, yeasts, molds, algae, protozoa, and parasites. While these microorganisms play crucial roles in various processes, they can also contribute to food spoilage and the transmission of diseases among animals, including fish.
Disinfection can be achieved through different methods, including the removal, killing, or inactivation of microorganisms (MOs). The primary objective of a UV disinfection system is to effectively deactivate MOs. When MOs are inactivated, their ability to reproduce is halted, rendering them harmless in the process.
The replication process of microorganisms (MOs) relies on the replication of their DNA (or RNA). UV-C radiation can disrupt this process by causing damage to the thymine in DNA or the uracil in RNA strands. This damage results in the formation of a “pyrimidine dimer.” When sufficient damage occurs, the biological repair mechanisms are unable to fix the damaged DNA or RNA, preventing further reproduction from taking place.
DNA and RNA molecules have the ability to absorb electromagnetic energy within the wavelength range of 200-280nm, which is commonly referred to as UV-C radiation (sometimes called UV-C light, despite being invisible to the human eye). The energy required to inactivate microorganisms (MOs) varies depending on the specific MO. By appropriately sizing a UV system based on the application’s specific parameters, a reliable disinfection process can be achieved.
Key Considerations for Sizing a UV Disinfection Aquaculture System
To determine the appropriate size for a UV system, several factors must be taken into account. One crucial factor is the physical treatment of the water, as it significantly impacts the effectiveness and sizing of the UV treatment system. The presence of Total Suspended Solids (TSS) in the water should be reduced to a level below 1 FTU (Formazin Turbidity Units).
Additionally, the dissolved solids in the water affect its UV transmittance for UV irradiation. A lower transmittance level necessitates a higher UV power requirement. Therefore, considering these factors is vital to ensure accurate sizing of the UV system.
In the case of disinfecting intake water with a single disinfection passage, it is essential for the UV lamps to irradiate the entire water volume simultaneously. To achieve maximum disinfection effectiveness in this scenario, the presence of total suspended solids (TSS) should be minimized, ideally close to zero. On the other hand, in a recirculation process, the water undergoes UV disinfection at regular intervals, leading to reduced power consumption compared to intake water applications.
Fish farms utilize different systems, either closed piping or open channel systems, and the UV system needs to be tailored accordingly. VGE Pro UV systems offer versatile options to accommodate these variations. For fresh water applications, a closed chamber system constructed from stainless steel is available, while for saltwater applications, an HDPE (High-Density Polyethylene) closed chamber system is provided. Additionally, there are submersible UV systems designed for installation in open channels or tanks, catering to specific requirements of fish farms.
UV intensity sensors monitor the UV disinfection process, verifying if the minimum required level is achieved and ensuring the necessary UV dose is administered.
Also read: Influencing Factors in UV Water Treatment
Pros and Cons of Using UV Disinfection
UV disinfection plays a crucial role in preventing the spread of diseases caused by microorganisms (MOs) through water. It’s important to note that MOs attached to fish or surfaces are not affected by UV disinfection since there is no residual effect.
In a well-designed UV disinfection application, fish are not directly or indirectly exposed to the UV radiation, ensuring their safety. Unlike chemical disinfection, UV disinfection is not selective, and all microorganisms (MOs) can be inactivated based on the applied UV dose. This is in contrast to chemical disinfection methods, which may produce toxic disinfection by-products that can potentially harm the health of the fish.
UV disinfection:
- Proven technology;
- Energy efficient;
- Easy system integration;
- Fresh and salt water suitable materials used
- Low headloss.
Aquaculture Applications of UV Disinfection
UV technology offers numerous benefits when utilized in aquaculture systems. Primarily, it is employed for disinfection purposes, playing a vital role in maintaining control over the microbiological levels.
The objective of the recirculation process is to achieve a healthy equilibrium among the various types of microorganisms (MOs) present in the water.
When UV disinfection is employed to treat intake water, a significantly higher UV dose is often utilized to prevent the entry of foreign pathogens into the Recirculating Aquaculture System (RAS). These pathogens, if introduced, can lead to diseases and substantial financial losses for the farmer. It is not uncommon for the UV dose in this scenario to exceed 10 times the recommended dosage for regular RAS applications.
UV systems have applications beyond disinfection. In cases where ozone is utilized to enhance water conditions through oxidation, it is crucial to eliminate any residual ozone to prevent harm to the fish. UV irradiation provides an effective solution by instantly breaking one of the oxygen bonds in the ozone molecule, thereby destroying residual ozone in the water. This process safeguards the well-being of the fish and ensures a healthy aquatic environment.
An additional application of UV technology in aquaculture is through the utilization of Advanced Oxidation Process (AOP). AOP implementation in aquaculture aids in reducing micropollutants such as geosmin and MIB, which can impart an undesirable flavor to the fish’s fatty tissue. By combining UV with an oxidant like hydrogen peroxide or ozone, hydroxyl radicals are generated. These hydroxyl radicals serve as powerful oxidants, making them highly effective in water environments.
Welcome to visit Puritor. Get in touch with us to learn more about the use of ozone in aquaculture and check our UV Water Purifier for Home, Industrial UV Water Purifier and Municipal Open Channel UV Water Treatment System.
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