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United States Department of Agriculture

Agricultural Research Service

Research Project: DEVELOPMENT OF SUSTAINABLE LAND-BASED AQUACULTURE SYSTEMS

Location: Cool and Cold Water Aquaculture Research

Title: Process Requirements for Achieving Full-Flow Disinfection of Recirculating Water Using Ozonation and UV Irradiation

Authors
item Summerfelt, Steven - THE CONSERVATION FUND FWI
item Sharrer, Mark - THE CONSERVATION FUND FWI
item Tsukuda, Scott - THE CONSERVATION FUND FWI
item Searheart, Michael - THE CONSERVATION FUND FWI

Submitted to: Aquacultural Engineering
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: October 15, 2008
Publication Date: January 1, 2009
Citation: Summerfelt, S.T., Sharrer, M.J., Tsukuda, S.M., Searheart, M. 2009. Process Requirements for Achieving Full-Flow Disinfection of Recirculating Water Using Ozonation and UV Irradiation. Aquacultural Engineering. 40:17-27.

Interpretive Summary: We determined the process requirements necessary to use ozone followed by ultraviolet (UV) irradiation to disinfect a water flow before it is reused for fish culture. A proportional-integral (PI) feed-back control loop was able to automatically adjust the concentration of ozone generated in the oxygen feed gas (and thus added in the low head oxygenator) in order to maintain the dissolved ozone residual or oxidative reduction potential (ORP) at a pre-selected set-point. Use of PI control at an ORP set-point of 450 and 525 mv and a dissolved ozone set-point of 20 ppb provided almost complete full-flow inactivation of heterotrophic bacteria plate counts (i.e., producing < 1 cfu/ml) and improved water quality (especially color and % UVT) in a full-scale recirculating system. Achieving this level of treatment required adding a mean dose of approximately 29 ± 3 g ozone per kg feed, which required approximately 0.34-0.39 mg/L of applied ozone dose. Process safety requirements are also described. These findings can be used to improve biosecurity and product quality planning by providing a means for continuous water disinfection in controlled intensive recirculating aquaculture systems.

Technical Abstract: A continuous water disinfection process can be used to prevent the introduction and accumulation of obligate and opportunistic fish pathogens in recirculating aquaculture systems (RAS), especially during a disease outbreak when the causative agent would otherwise proliferate within the system. To proactively prevent the accumulation of fish pathogens, ozonation and ultraviolet (UV) irradiation processes have been used separately or in combination to treat water in RAS before it returns to the fish culture tanks. The objective of the present study was to determine the process requirements necessary to disinfect the full RAS flow, using ozonation followed by UV irradiation, just before the flow was returned to the fish culture tank(s). We found that a proportional-integral (PI) feed-back control loop was able to automatically adjust the concentration of ozone generated in the oxygen feed gas (and thus added in the low head oxygenator) in order to maintain the dissolved ozone residual or ORP at a pre-selected set-point. We determined that it was easier and effective to continuously monitor and automatically control ozone dose using an oxidative reduction potential (ORP) probe (in comparison to a dissolved ozone probe) that was located at the outlet of the ozone contact chamber and immediately before water entered the UV irradiation unit. PI control at an ORP set-point of 450 and 525 mv and a dissolved ozone set-point of 20 ppb provided almost complete full-flow inactivation of heterotrophic bacteria plate counts (i.e., producing < 1 cfu/ml) and improved water quality (especially color and % UVT) in a full-scale recirculating system. Achieving this level of treatment required adding a mean dose of approximately 29 ± 3 g ozone per kg feed. However, because water is treated and reused repeatedly in a water reuse system, the mean daily ozone demand required to maintain an ORP of 375 - 525 mv (or at 20 ppb dissolved ozone) was 0.34-0.39 mg/L, which is nearly 10 times lower than what is typically required to disinfect surface water in a single pass treatment. These findings can be used to improve biosecurity and product quality planning by providing a means for continuous water disinfection in controlled intensive RAS.

Last Modified: 7/28/2014
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