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Using Ozone with UV Disinfection

Posted by Aquatic Solutions, LLC on 21st Jul 2014

Ozone is a powerful oxidant and is very beneficial with improving water quality in Aquatic Life Support Systems (ALSS). Ozone oxidizes NO2 & NO3, helping to remove color, dissolved organic wastes, and micro-flocculates fine organic particulate, as well as improving dissolved oxygen levels.

Ozone delivers a noticeable benefit in water quality, especially when applied to Recirculating Aquaculture Systems (RAS), which is why many system designers and operators are attracted to it.

At the same time, ozone also optimizes conditions for UV disinfection. Yes, both ozone and UV disinfection can work together within the ALSS to offer superior results, specifically, improved UV light transmittance, which increases the UV system’s effectiveness—boosting the germicidal disinfection capacity.

Primary Disinfectant

Ozone is not Instant Treatment, rather it requires that the target pathogen be exposed to specific concentrations for an extended period of time. For example: successful ozone disinfection in freshwater, targeting IPNV (Infectious Pancreatic Nacreous Virus), requires an ozone concentration of 0.15 mg/l for a period of 15 minutes (Cryer, 1992 #670). If this is the case, it means a Flow-Through or RAS with a water flow of 3,000 GPM 11,355 LPM) would require an ozone contact area large enough to effectively complete disinfection, and for most RAS, this is simply not practical.

UV disinfection is Instant Treatment and at a fluence (UV dose) of 246 mJ/cm², it achieves a 4-log (99.99%) reduction of the pathogen IPNV. This means that a UV system with a disinfection capacity large enough to treat 3,000 GPM (11,355 LPM) will successfully achieve germicidal disinfection on a single-pass inside the UV vessel. Therefore, UV disinfection is the best choice as a primary germicidal disinfectant.

An Effective Combination

OZONE (clarifier) and UV (disinfectant) well work together! Ozone, being the powerful oxidizer it is, improves the UV Transmittance (UVT) in culture water, helping the UV system, positioned downstream of the ozone treatment, to perform more effectively. For instance, testing an RAS for UVT may reveal a 75%T. With appropriate ozone treatment, that 75%T could be increased to 90%T. The increased %T, from 75%T to 90%T dramatically increases the efficiency of the downstream UV system, and in many cases, reduces the size of the required UV system. All ALSS are unique, and so we are forced to apply ozone and UV differently based on the specific conditions and requirements of each application.