Aquaculture

Recirculating Aquaculture Systems (RAS):

Ozone is widely used in Recirculating Aquaculture Systems (RAS) for water treatment, pathogen control, and overall water quality improvement. It is a powerful oxidizing agent that helps create a cleaner, healthier environment for aquatic species while enhancing system efficiency.

Why Ozone is Used in Recirculating Aquaculture Systems:

Ozone is applied in RAS primarily to:

- Improve Water Quality – Removes organic waste, ammonia, nitrites, and other contaminants in water.

- Reduce Pathogens & Disease Risks – Destroys bacteria, viruses, parasites, and fungi, reducing infection risks.

- Enhance Biofiltration Efficiency – Helps maintain optimal conditions for nitrifying bacteria in biofilters.

- Increase Oxygen Levels – Ozone breaks down into oxygen (O₂), improving dissolved oxygen levels in water, promoting healthier fish and allowing for higher densities of fish in the water.

- Eliminate Off-Flavors in Fish – Removes geosmin and 2-methylisoborneol (MIB), compounds responsible for muddy or earthy flavors in fish.

- Reduce Water Exchange Needs – Improves water recirculation efficiency, leading to more sustainable operations.

How Ozone is Used in Recirculating Aquaculture Systems:

Ozone Injection in Water Flow

Ozone Generation

- Ozone is generated as a gas from oxygen in the ambient air.  Oxygen from the air is captured and concentrated by purging nitrogen from that air.  This oxygen is converted to ozone within the ozone generator via corona discharge.

Ozone Dissolving into Water

- In aquaculute systems, ozone is via a venturi injector or diffuser, where it dissolves and interacts with the water. The dosage is carefully controlled via dissolved ozone meters or ORP meters to balance effectiveness with safety for animal life.

- Ozone oxidizes organic matter, bacteria, pathogens, and harmful compounds safely leaving oxygen as the primary by-product

Ozone in Protein Skimmers (Foam Fractionators)

- Ozone is combined with protein skimmers to remove dissolved organic waste and fine particles.

- This method helps reduce biofilm buildup and suspended solids.

Ozone in Biofilters

- Ozone helps prevent biofilter clogging by breaking down excess organic matter.

- It enhances nitrification efficiency by maintaining stable microbial communities.

Ozone in Fish Processing & Handling Water

- Ozonated water is used in fish processing facilities, hatcheries, and live transport systems.

- Ozonated ice is used to prolong seafood shelf life

- Reduces microbial contamination on fish surfaces, equipment, and holding tanks.

Benefits of Ozone in RAS:

Pathogen & Disease Control

- Destroys harmful pathogens like Aeromonas, Vibrio, Pseudomonas, and parasites.

- Reduces the need for antibiotics and chemicals.

Organic Matter & Waste Removal

- Breaks down fish waste, uneaten feed, and dead cells, reducing total organic carbon (TOC).

- Prevents sludge buildup and biofouling.

Improved Water Clarity & Quality

- Ozone removes suspended particles, algae, and dissolved organic matter, leading to clearer water.

Off-Flavor Removal

- Eliminates geosmin and MIB, improving the taste and market value of fish.

Increased Dissolved Oxygen (DO) Levels

- Ozone decomposes into oxygen (O₂), increasing DO levels essential for fish health.

Reduced Water Exchange & Sustainability

- Improves recirculation efficiency, reducing water usage and wastewater discharge.

          *Ozone is one component in a complete aquaculture system. The image below shows an example of what a complete system may look like.

View the Questionnaire for Aquaculture so we can help design your Ozone System

White Paper Research Documents:

Below is a list of technical documents and papers on the use of ozone in aquaculture for your review. Click on text links below to open the PDF documents.

Dissolved Ozone Destruction using Ultraviolet Irradiation in a Recirculating Salmonid Culture System

Authors: Steven T. Summerfelt, Mark J. Sharrer, Jennifer Holls, Lauren E. Gleason, Scott R. Summerfelt

Abstract

This study aimed to determine the UV irradiation dosages required to eliminate dissolved ozone in a commercial-scale recirculating salmonid culture system operating at a constant 13–15°C. The research was conducted at the Conservation Fund Freshwater Institute (Shepherdstown, West Virginia), where the system’s main UV channel unit treats the entire 4,750 L/min recirculating flow with an approximately 90 mW·s/cm² UV dose.

A second UV irradiation unit was used to collect most of the ozone destruction data by treating a side-stream flow drawn from the system’s low-head oxygenation (LHO) sump. The side-stream flow rates were set at 85, 170, 255, and 330 L/min—equivalent to 1.8–7.4% of the total recirculating flow—to create retention times of 6.7, 3.3, 2.2, and 1.7 seconds, respectively. This produced UV doses of 153.3 ± 2.1, 80.4 ± 2.6, 49.3 ± 0.6, and 35.6 ± 0.3 mW·s/cm².

Results showed that ozone removal followed first-order kinetics, depending on both inlet ozone concentration and retention time within the irradiation chamber. At 13–15°C, UV doses of 80.4 ± 2.6 and 153.3 ± 2.1 mW·s/cm² consistently removed 100% of dissolved ozone when the inlet concentration was 0.30 mg/L. A dose of 49.3 ± 0.6 mW·s/cm² achieved complete removal at an inlet concentration of 0.10 mg/L, whereas 35.6 ± 0.3 mW·s/cm² failed to fully remove ozone, even at 0.10 mg/L.

When averaged across all conditions, dissolved ozone removal rates were:

- 91 ± 2% at 153.3 ± 2.1 mW·s/cm²

- 81 ± 5% at 80.4 ± 2.6 mW·s/cm²

- 77 ± 1% at 49.3 ± 0.6 mW·s/cm²

- 58 ± 5% at 35.6 ± 0.3 mW·s/cm²

Mean inlet ozone concentrations corresponding to these doses were 0.64 ± 0.09 mg/L, 0.51 ± 0.10 mg/L, 0.41 ± 0.06 mg/L, and 0.43 ± 0.07 mg/L, respectively. These findings highlight the importance of selecting appropriate UV doses to effectively eliminate dissolved ozone in recirculating aquaculture systems. 

Read the full study here.

Ozonation and UV Irradiation - an Introduction and Examples of Current Applications

Authors: Steven T. Summerfelt

Abstract

This paper was written to introduce the 2001 AES Issues Forum’s ‘Ozone and UV Treatment’ session by providing an overview of ozone and ultraviolet (UV) irradiation technologies as well as several examples of current ozone and UV irradiation applications in aquaculture.

Read the full study here.

Ozonation of a Recirculating Rainbow Trout Culture System Effects on Bacterial Gill Disease and Heterotrophic Bacteria

Authors: Graham L Bullock, Steven T. Summerfelt, Alicia C. Noble, Amy L. Weber, Martin D. Durant, Joseph A. Hankins

Abstract

Ozone was added to water in a recirculating rainbow trout (Oncorhynchus mykiss) culture system just before it entered the culture tanks in an attempt to reduce the numbers of heterotrophic bacteria in system water and on trout gills, and to prevent bacterial gill disease (BGD) in newly stocked fingerlings. During four 8-week trials, ozone was added to the system at a rate of 0.025 or 0.036–0.039 kg ozone/kg feed fed. In the control, where no ozone was added, and in previously published research, BGD outbreaks occurred within two weeks of stocking, and these outbreaks generally required three to four chemotherapeutant treatments to prevent high mortality. In three of four trials where ozone was added to the system, BGD outbreaks were prevented without chemical treatments, but the causative bacterium, Flavobacterium branchiophilum, still colonized gill tissue. The one ozone test where BGD outbreaks required two chemical treatments coincided with a malfunction of the ozone generator. Although ozonation did reduce BGD mortality, it failed in all trials to produce more than a one log10 reduction in numbers of heterotrophic bacteria in the system water or on gill tissue. Failure of the ozone to lower numbers of heterotrophic bacteria or to prevent the causative BGD bacterium from occurring on gills was attributed to the short exposure time to ozone residual (35 s contact chamber) and rapid loss of oxidation caused by levels of total suspended solids. Rationale for ozone’s success at preventing BGD mortalities are not fully understood but may in part be due to improved water quality. Use of the lower ozone dosing rate (0.025 kg ozone/kg feed) appeared to provide the same benefits as the higher dosing rate (0.036–0.039 kg ozone/kg feed fed); however, the lower ozone dosing rate was less likely to produce a toxic ozone residual in the culture tank and would also reduce ozone equipment capital and operating costs.

Read the full study here.

Ozonation of a Recirculating Rainbow Trout Culture Systems 

Authors: Graham L Bullock, Steven T. Summerfelt, Alicia C. Noble, Amy L. Weber, Martin D. Durant, Joseph A. Hankins

Abstract

Ozone was added to water in a recirculating rainbow trout (Oncorhynchus mykiss) culture system just prior to the culture tanks in order to oxidize nitrite and organic material, improve overall water quality, and assist removal of solids across the microscreen filter. Data from four 8-week studies on ozonation and an 8-week no ozone control indicated that adding ozone reduced the mean concentration of total suspended solids (TSS) by 35%, chemical oxygen demand (COD) by 36%, dissolved organic carbon (DOC) by 17%, and color by 82% within the water entering the culture tanks. Additionally, ozone reduced the mean nitrite concentration by 82% within the culture tanks. Adding ozone did not affect turbidity. Changes brought on by ozonation, particularly as it affected the characteristics of the suspended solids, also improved suspended solids removal across the microscreen filter by an average of 33%. In addition, adding ozone decreased plugging of the microscreen filter panels, as indicated by an average of 35% fewer filter wash cycles, 53% less filter sludge flow produced, and 79% more settled solids volume in the microscreen filter effluents. Comparison of two different ozone dosing rates indicated that adding ozone to our recirculating system at a rate of 0.025 kg ozone per kilogram feed was nearly as effective as adding ozone at a rate of 0.036–0.039 kg ozone per kilogram feed.  

Read the full study here.

Ozonation Followed by Ultraviolet Irradiation Provides Effective Bacteria Inactivation in a Freshwater Recirculating System

Authors: Steven T. Summerfelt, Mark J. Sharrer

Abstract

Recirculating aquaculture systems may require an internal disinfection process to control population growth of pathogens and heterotrophic bacteria. Ozonation and ultraviolet (UV) irradiation are two technologies that have been used to treat relatively large aquaculture flows, including flows within freshwater systems that recirculate water. The objective of the present study was to evaluate the effectiveness of ozone application alone or ozone application followed by UV irradiation to reduce abundance of heterotrophic and total coliform bacteria in a water reuse system. Results indicate that when only ozone was applied at dosagesdefined by the product of the ozone concentration times the mean hydraulic residence time (Ct)– that ranged from 0.10 to 3.65 min mg/L, the total heterotrophic bacteria counts and total coliform bacteria counts in the water exiting the contact basin were reduced to, respectively, 3–12 cfu/mL (1.1–1.6 LOG10 reduction) and 2–18 cfu/100 mL (1.9–3.1 LOG10 reduction). Bacteria inactivation appeared to be just as effective at the lowest ozone ct dosage (i.e., 0.1 mg/L ozone after a 1 min contact time) as at the highest ozone ct dosage (i.e., 0.2 mg/L ozone after a 16.6 min contact time). As with our previous research on UV inactivation of bacteria, we hypothesize that the recirculating system provided a selection process that favors bacteria that embed within particulate matter or that form bacterial aggregates that provides shielding from oxidation. However, when ozonation was followed by UV irradiation, the total heterotrophic bacteria counts and total coliform bacteria counts in thewater exiting the UVirradiation unit were reduced to, respectively, 0–4 cfu/mL (1.6–2.7 LOG10 reduction) and 0–3 cfu/100 mL (2.5–4.3 LOG10 reduction). Thus, combining ozone dosages of only 0.1–0.2 min mg/L with a UV irradiation dosage of approximately 50 mJ/cm2 would consistently reduce bacteria counts to near zero. These findings were orders of magnitude lower than the bacteria counts measured in the system when it was operated without disinfection or with UV irradiation alone. These findings indicate that combining ozonation and UV irradiation can effectively disinfect recirculating water before it returns to the fish culture tank(s).

Read the full study here.

The Control of Water Quality and Hygienic Conditions in Aquaculture Recirculation Systems (RAS): The Use of Foam Fractionation and Ozone

Authors: U. Waller, J. Orellana, M. Sander

Abstract

The proper management of water quality is the key factors determining the successful operation of recirculation aquaculture systems (RAS). In this study a new engineering concept for a marine RAS was tested. The RAS involved a two-step solid separation procedure (swirl separator and ozone enhanced foam fractionation), biofiltration, and additional modules for water conditioning (pH, dissolved oxygen). European sea bass (Dicentrarchus labrax) was the target fish species. Water quality within the rearing tanks was continuously monitored during the experimental period and maintained within safe limits. Water replacement in the system accounted on average about 1% per day of the total system volume. The two step solid separation techniques allowed to maintain clear water conditions. Fine solids and bacteria were efficiently removed by foam fractionation. In doing so, coastal water quality could be maintained throughout the rearing period. The data proof a good growth of European sea bass from less than 10 g to table-sized fish of 300g in approximately one year.  

Read the full study here.

Ozone in Recirculating Aquaculture Systems

Authors: NSW Government

Abstract

Recirculating Aquaculture Systems (RAS) provide potential advantages over pond or cage-based forms of aquaculture. These include exibility in site selection, reduced water usage, lower e uent volumes, better environmental control, and higher intensity of production. However, as stock densities and levels of water re-use increase, wastes accumulate rapidly and environmental control becomes more di cult. Sophisticated systems capable of removing both particulate and dissolved organic wastes become necessary. Conventional means of solids removal, such as microscreen lters and sedimentation tanks address the removal of coarse settleable and lterable solids, but not the removal of ne coloidal solids. Similarly, bacterial nitri cation in bio lters removes dissolved ammonia and nitrite, but not other dissolved wastes. As the organic loading increases with intensity of production, the bacteria that convert nitrite to nitrate operate less e ciently, resulting in increased nitrite levels. The accumulation of ne co loidal solids, dissolved organics and nitrite in RAS can impair bio lter function, and increase biochemical oxygen demand and stress levels in the cultured stock. The net effect of this residual organic waste is a less stable, less productive system. Increasing the daily water exchange rate in an RAS wil remove accumulated coloidal solids, refractory organics and nitrite, to the detriment of water budgets and the cost of heating or cooling the system. The alternative method of removal is to breakdown these organic wastes using an oxidizing agent, such as ozone. Ozone is also widely used to sterilise supply and e uent water for RAS to remove pathogens. This advisory paper discusses use of ozone in RAS aquaculture, including methods of application, bene ts of usage and potential risks.

Read the full study here.

The Control of Water Quality and Hygienic Conditions in Aquaculture Recirculation Systems (RAS): The Use of Foam Fractionation and Ozone

Authors: Steven T. Summerfelt, Mark J. Sharrer

Abstract

Without an internal disinfection process, obligate and opportunistic fish pathogens can accumulate in aquaculture systems that treat and reuse water (RAS), especially in the event of a disease outbreak when the pathogen is propagating and shedding from its host.  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.  In freshwater RAS, previous research has also indicated that ozonation can improve water quality by improving microscreen filter performance, breaking refractory compounds and thereby eliminating the accumulation of water color, and oxidizing nitrite to nitrate.  Previous research indicates that achieving these water quality control benefits required the addition of only 15-25 g of ozone (O3) for every kilogram of feed fed to the recirculating system.  This level of ozonation has also been found to improve fish health (i.e., preventing recurring episodes of bacterial gill disease in rainbow trout without use of chemotherapeutic treatment) without providing even a 1 log10 reduction in heterotrophic bacteria counts in the water column.  To achieve an O3 residual concentration sufficient to produce significant bacteria reduction, however, the O3 demand of the nitrite and organic carbon found in the RAS waters must be overcome.  This O3 dose was unknown prior to the present study.  

Read the full study here.

The Control of Water Quality and Hygienic Conditions in Aquaculture Recirculation Systems (RAS): The Use of Foam Fractionation and Ozone

Authors: Steven T. Summerfelt, Mark J. Sharrer

Abstract

A water filtration and ozone disinfection system was installed at the U.S. Fish and Wildlife Service’s Northeast Fishery Center in Lamar, Pennsylvania, to treat a surface water supply that is used to culture sensitive and endangered fish.  The treatment system first passes the surface water through drum filters operated with 60-μm sieve panels in order to exclude the majority of debris, algae, and organisms larger than the sieve openings.  After microscreen filtration, two variable speed pumps are operated in parallel to supply between 400 to 2,400 L/min to the ozone treatment system.  Ozone contained within an approximately 95% oxygen feed gas is transferred in to the water (at 0.5-0.7 bar) through a down flow bubble contactor following each pump.  The ozonated water is then collected and piped to a 15.1 m3 ozone contact column.  The contact column provides approximately 20, 10, or 6.7 minutes of plug-flow contact time for water flows of 760, 1,500, or 2,270 L/min, respectively.  A dissolved ozone probe at the outlet of the ozone contact chamber continuously monitors the dissolved ozone concentration discharged from the contact tank.  A proportional-integral-derivative feed-back control loop is used to adjust the concentration of ozone generated (and thus added) in order to maintain the dissolved ozone residual discharged from the ozone disinfecting contact tank at a pre-selected set-point (nominally 0.2 mg/L).  The water discharged from the ozone disinfecting contact tank then flows by gravity through a second 32.1 m3 contact tank, which provides additional time for the dissolved ozone to decompose.  Any dissolved ozone remaining in the water exiting the second contact vessel is air-stripped, along with any large dissolved oxygen super-saturation, as the water flows by gravity through a forced-ventilated cascade column.  This treated water then flows by gravity to the fish culture systems.  The ozone system was evaluated during a start-up period from March through June of 2002.  During this period, the ozonation and filtration system was found to consistently inactivate bacteria and exclude the majority of debris larger than the microscreen openings, even during extreme changes in surface water quality produced by storm events.  Design and performance details are provided to offer insight into the strengths and weaknesses of the individual treatment processes. 

Read the full study here.

Ozone in RAS Filtration Systems - Haryana, India

Authors: P. Singh, R. Gulati, R. Sharma

Abstract

This study provides a comprehensive analysis of the components and specifications employed in Recirculating Aquaculture Systems (RAS) by farmers in Haryana, India. The research surveyed 20 RAS farms, revealing diversity in the number of components used, with 40% of farmers utilizing five key components, including production tanks, drum filters, biofilter units, degassing aerators, and ultraviolet (UV) lights. Drum filters were the primary choice for 85% of farmers, with 82.35% using a 50-micron mesh screen. The study highlights the prevalence of Molecular Biofilm-Based Reactor (MBBR) for biological filtration, with all surveyed farms adopting this technology. Notably, 60% of farmers opted for K5 MBBR media. Production tanks, a fundamental component, were predominantly 50,000 liters in capacity, with some variations. Degassing aerators, UV sterilization, ozone units, and oxygen generators were commonly integrated into the RAS setups, showcasing the farmers’ commitment to water quality management. Intriguingly, sand filters were preferred by only 40% of farmers, with diverse flow rates observed. The results also present insights into the mesh sizes of drum filters with 82.35% of farmers using 50 micron mesh size, emphasizing the farmers’ consideration for efficient solid removal. The findings shed light on the technology choices made by RAS farmers in Haryana, providing valuable information for aquaculture practitioners and researchers aiming to enhance RAS efficiency and sustainability.

Read the full study here.

Estimating Biofilm Activity on Biofilter Elements in Recirculating Aquaculture Systems (RAS) for Rearing Atlantic Salmon Parr during Operation with Ozone and Peracetic Acid

Authors: Wanhe Qi, Peter Vilhelm Skov, Kim Joao de Jesus Gregersen, Samaneh Mousavi, Lars-Flemming Pedersen, Vasco C. Mota

Abstract

Chemical disinfection in a recirculating aquaculture system (RAS) may affect biofilm-associated bacteria and the nitrification performance in the biofilter units. The biofilm response to chemical disinfectants in RAS remains unclear, but it can be understood using methods to quantify biofilm activity. Here, we compared the effects of two disinfection strategies, continuous ozone at 0.06 mg/L Cl₂ equivalent (Ozone group) and peracetic acid (PAA) at 1 mg/L (PAA group) to control group without disinfectant, on biofilm activity on biofilter elements from nine identical experimental RAS with Atlantic salmon parr (Salmo salar) during a four-week trial. Biofilm activities on biofilter elements from the three groups were examined by measuring oxygen consumption rates (OCR) following sequential spiking with pure tap water, and tap water spiked with nitrite or ammonium, as well as oxygen release rate (k_or) following hydrogen peroxide (H₂O₂) addition, to estimate metabolic activities of biofilm related to endogenous respiration and substrate turnover. The results show that the applied PAA dose increased the endogenous respiration activity of biofilm by 39–133%, stimulated the rate of biofilm enzymatic decomposition of H₂O₂ by 135%, and partially impaired the biofilm metabolism for nitrite oxidation (decrease by 36%), resulting in a significant nitrite accumulation (rise by 59%) in the cultured water, compared to control over experimental period. Ozone treatment caused an enhanced endogenous respiration activity of biofilm at the beginning of the experiment (increase by 45–74%), but dropped to control levels at the end of the experiment. The results indicate that chronic exposure to PAA can alter the metabolic state of biofilm, which can have consequences for biofilter functions, while chronic exposure to ozone improved water clarity without compromising the metabolic status of biofilm. The investigations provided insights into biofilm response to chemical disinfectant in RAS, which would benefit the optimization of an effective and safe use of disinfectants in RAS.

Read the full study here.

Estimating Biofilm Activity on Biofilter Elements in Recirculating Aquaculture Systems (RAS) for Rearing Atlantic Salmon Parr during Operation with Ozone and Peracetic Acid

Authors: Jitka Kolarova, Jiri Kristan, Oleksandr Malinovoskyi, Josef Velisek, Alzbeta Stara, Samad Rahimnejad, Tomas Policar

Abstract

The aim of this study was to examine the effects of ozonation on the water quality, and growth, blood biochemistry, antioxidant capacity and survival of pikeperch (Sander lucioperca) reared in a recirculation aquaculture system for 30 weeks. A group without ozone treatment was used as a control. The ozone application led to a significant reduction of the water chemical oxygen demand, biological oxygen demand and unsuspended solids concentration. The results revealed that an ozone treatment as a water treatment method has a positive influence on the intensive culture of pikeperch ensuring a higher survival rate (77%) compared to the non-treated control group (67.2%). Moreover, the ozonation prevented fin damage to a large extent and reduced the prevalence of an Ichthyophthirius multifiliis infection. Furthermore, the ozone application led to a reduction in the thiobarbituric acid reactive substance level and enhanced the superoxide dismutase activity in the fish gills. However, the effect of ozonation was null on the plasma biochemical parameters. Overall, these findings suggest that an ozone treatment, using adequate technological equipment to destroy the residual ozone, improves the water quality and protects pikeperch against any possible infection and fin damage in a recirculation aquaculture system. 

Read the full study here.

Ozone Nanobubble Treatment in Freshwater Effectively Reduced Pathogenic Fish Bacteria and is Safe for Nile Tilapia

Authors: Jitka Kolarova, Jiri Kristan, Oleksandr Malinovoskyi, Josef Velisek, Alzbeta Stara, Samad Rahimnejad, Tomas Policar

Abstract

High concentrations of certain pathogenic bacteria in water usually results in outbreaks of bacterial diseases in farmed fish. Here, we explore the potential application of an emerging nanobubble technology in freshwater aquaculture, specifically aimed to reduce the concentrations of pathogenic fish bacteria in freshwater, and assess whether nanobubbles are safe for Nile tilapia (Oreochromis niloticus). An ozone nanobubble (NB-O₃) treatment protocol was established, based on examination of nanobubble size, concentration, disinfection property, and impact on fish health. A 10-min treatment with NB-O₃ in 50 L water generated approximately 2–3 × 10⁷ bubbles/mL, with the majority of bubbles being less than 130 nm in diameter and an ozone level of 834 ± 22 mV oxidation-reduction potential (ORP). A single treatment with water spiked with either Streptococcus agalactiae or Aeromonas veronii effectively reduced the bacterial load by 26–48 fold or 96.11–97.92%. This same protocol was repeated three times. The result was a 22,058 to 109,978 fold reduction in bacteria or 99.93–99.99% decrease. In comparison, bacterial concentrations in the control tanks remained unchanged during the experiments. In Nile tilapia-cultured water with the presence of organic matter (e.g. mucus, feces, bacterial flora, feed, etc.), the disinfection property of NB-O₃ was reduced; however, we still observe a reduction of 59.63%, 87.25%, and 99.29% after the first, second, and third consecutive treatments, respectively. To evaluate the safety of NB-O₃ on fish, juvenile Nile tilapia were exposed to NB-O₃ treatment for 10 min. No mortality was observed during the treatment or 48 h post treatment. Gill histology examination revealed that a single NB-O₃ treatment caused no alteration in cell morphology. However, damage in the gill filaments, such as blood congestion, aggregates of basal cells at the secondary lamellae or loss of the secondary lamella was noticed in the fish receiving two or three consecutive exposures within the same day. Results of the experiments conducted in this study suggest that NB-O₃ technology is promising for reducing pathogenic bacteria in aquaculture systems and may be useful at reducing the risk of bacterial disease outbreaks in farmed fish.

Read the full study here.

Direct Application of Ozone in Aquaculture Systems

Authors: Adam Powell, Jacob W.S. Scolding

Abstract

Ozone (O3) is a powerful oxidant that has been used in both the aquaculture and water treatment industries to improve water quality and reduce pathogens during pretreatment, treatment of effluent, as a continual treatment during RAS operations, and for bivalve depuration. As ozone can be toxic to aquatic organisms, the technology has also been investigated to destroy invasive or nuisance species, and other research has also highlighted negative effects of residual ozone on water courses. Ozone and ozone-produced oxidants used in aquaculture operations have therefore typically been removed from water prior to entry into tanks holding stock animals. However, a growing body of research has identified direct application of ozone, here defined as exposure of residual ozone and ozone-produced oxidants to cultured species of finfish, shellfish and live feeds across various life stages. This approach appears to be increasingly employed as a beneficial technology due to proven enhancement of hygiene and water quality, provided dosages or concentrations are appropriate to maintain animal health and welfare. This review paper concentrates on the observed benefits and drawbacks of direct ozonation, influencing factors and future considerations for standardisation and uptake of the technology.

Read the full study here.

Ozone Application in Recirculating Aquaculture System

Authors: Alex Augusto Goncalves, Graham A. Gagnon

Abstract

In recirculating aquaculture systems (RAS), particulates (including feces, uneaten feed, bacteria, and algae) can cause several problems, in that they may harbor pathogens, can physically irritate the fish, and upon decomposition, release ammonia and consume oxygen. Mechanical filters, foam fractionators, and other engineered devices are used to remove particles quickly from aquaculture systems, in order to improve fish health and decrease the load on biofilters and oxygenators. Ozone is used in RAS as a disinfectant, to remove organic carbon, and also to remove turbidity, algae, color, odor and taste. Ozone can effectively inactivate a range of bacterial, viral, fungal and protozoan fish pathogens. But the effectiveness of ozone treatment depends on ozone concentration, length of ozone exposure (contact time), pathogen loads and levels of organic matter. In spite of ozone is a very effective oxidizing agent, higher ozone concentrations are a risk to cultured fish stocks causing gross tissue damage and stock mortalities, and also are a risk to bacterial films on the biofilter.

Read the full study here.

The Effect of Ozone on Water Quality and Survival of Turbot Maintained in a Recirculating Aquaculture System

Authors: Adam Powell, Purazen Chingombe, Ingrid Lupatsch, Robert J. Sheilds, Richard Lloyd

Abstract

Turbot, Psetta maxima, represent a valuable and growing subsector of global finfish aquaculture, although bacterial infections such as edwardsiellosis have adversely affected the industry in recent years. During an experiment designed to investigate the effect of direct ozonation on fish performance in RAS, a bacterial disease outbreak (Edwardsiella tarda) occurred, presenting an opportunity to record additional effects of experimental ozonation regimes on performance of turbot grown in RAS. This short note thus collates phenomenological information on survival, growth and water quality parameters recorded during a 91 day experiment with juvenile fish. Alongside antibiotic therapy, a high ozone treatment (360 mV) improved survival of stock compared to those in a non-ozonated control (200 mV) and significantly so compared to low ozone treatment (320 mV). Both experimental treatments reduced total heterotrophic and Vibrio sp. bacterial loading and nitrite concentration in culture water compared to the control. Experimental ozone treatment also suggested a trend for improved growth and feed intake. Although no confirmed link or mechanism between ozonation and reduced impacts of bacterial infection are proven in this study, the observations add further evidence to the body of work demonstrating beneficial effects of ozonation on water quality, survival and growth of farmed fish.

Read the full study here.

Ozone Control and Effects of Ozone on Water Quality in Recirculating Aquaculture Systems

Authors: Spiliotopoulou, Aikaterini; Rojas-Tirado, Paula Andrea; Chetri, Ravi K.; Kaarsholm, Kamilla Marie Speht; Martin, Richard; Pedersen, Per Bovbjerg; Pedersen, Lars-Flemming; Andersen, Henrik Rasmus

Abstract

To address the undesired effect of chemotherapeutants in aquaculture, ozone has been suggested as an alternative to improve water quality. To ensure safe and robust treatment, it is vital to define the ozone demand and ozone kinetics of the specific water matrix to avoid ozone overdose. Different ozone dosages were applied to water in freshwater recirculating aquaculture systems (RAS). Experiments were performed to investigate ozone kinetics and demand, and to evaluate the effects on the water quality, particularly in relation to fluorescent organic matter. This study aimed at predicting a suitable ozone dosage for water treatment based on daily ozone demand via laboratory studies. These ozone dosages will be eventually applied and maintained at these levels in pilot-scale RAS to verify predictions. Selected water quality parameters were measured, including natural fluorescence and organic compound concentration changes during ozonation. Ozone reactions were described by first order kinetics. Organic matter, assessed as chemical oxygen demand and fluorescence, decreased by 25% (low O3), 30% (middle O3) and 53% (high O3), while water transmittance improved by 15% over an 8-day period. No fish mortality was observed. Overall, this study confirms that ozone can improve RAS water quality, provides a better understanding of the ozone decay mechanisms that can be used to define further safe ozone treatment margins, and that fluorescence could be used as a monitoring tool to control ozone. This study might be used as a tool to design ozone systems for full-scale RAS by analysing water sample from the specific RAS in the laboratory. 

Read the full study here.

Ozone Application in Recirculating Aquaculture System

Authors: Alex Augusto Goncalves, Graham A. Gagnon

Abstract

In recirculating aquaculture systems (RAS), particulates (including feces, uneaten feed, bacteria, and algae) can cause several problems, in that they may harbor pathogens, can physically irritate the fish, and upon decomposition, release ammonia and consume oxygen. Mechanical filters, foam fractionators, and other engineered devices are used to remove particles quickly from aquaculture systems, in order to improve fish health and decrease the load on biofilters and oxygenators. Ozone is used in RAS as a disinfectant, to remove organic carbon, and also to remove turbidity, algae, color, odor and taste. Ozone can effectively inactivate a range of bacterial, viral, fungal and protozoan fish pathogens. But the effectiveness of ozone treatment depends on ozone concentration, length of ozone exposure (contact time), pathogen loads and levels of organic matter. In spite of ozone is a very effective oxidizing agent, higher ozone concentrations are a risk to cultured fish stocks causing gross tissue damage and stock mortalities, and also are a risk to bacterial films on the biofilter.

Read the full study here.

Sludge Pre-Treatment through Ozone Application: Alternative Sludge Reuse Possibilities for Recirculating Aquaculture System Optimization

Authors: Frederike Schmachtl, Bjorn Mayr, Christopher P. Franz, Sabine Strieben, Gregor Jaehne, Kai Lorkowski, Matthew J. Slater

Abstract

Recirculating Aquaculture Systems (RAS) reduce water consumption by efficient filtration to maintain appropriate levels of accumulating compounds and sludge. Sludge is mechanically separated by drum filters and disposed of to the detriment of overall system water budgets. Dissolved nitrogen compounds are reduced via nitrification–denitrification filters, requiring commercial external carbon sources. The reuse of sludge after ozone pre-treatment may represent the next step in RAS optimization. The present study analyzes the content of sludge from RAS and tests ozonation as a pre-treatment for recycling as carbon source. The dissociative effect of ozone and the physicochemical changes due to ozonation lead to a significant increase in soluble carbon availability. Predominantly long-chain fatty acid (FA) (saturated and unsaturated) with 16 and 18 carbon atoms independently of the treatment were found in the profiles. Saturated FA concentrations in solution increased after 20, 40, and 60 min ozonation. The solid content of the sludge was practically unaffected by ozonation in terms of FA profile: only saturated FA slightly increases after 40 min treatment. The implications of these findings for denitrifying bacteria are discussed.

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The Effect of Ozonation on Particle Size Distribution for Recirculating Aquacultural Seawater

Authors: Mindong Ji, Kang Wu, Jianping Li, Zhangying Ye, Haijun Li & Songming Zhu

Abstract

Solids removal is very important for water quality maintenance in recirculating aquaculture systems (RAS). Ozonation is a practical water treatment which can promote the solids removal. However, the characteristics of ozonation effects on particles are still unclear. In this study, the effect of ozonation on particle size distribution (PSD) was investigated for seawater from a RAS of Pacific white shrimp (Litopenaeus Vannamei). Both flocculation and breakup of particles were demonstrated during ozonation treatment, which resulted in changes of PSD. By using a fractal characteristic value (D_f), the flocculation process could be divided into three stages of preparation, growth and steady. Besides, the flocculation efficiency varied parabolically with contact time. A higher ozone dosage resulted in a shorter preparation stage, along with a longer growth stage (namely lasting a longer flocculation effect) and thus a relatively higher limit of parabolic flocculation efficiency. However, the limit would reach a peak and probably be accompanied with a more breakup of particles. The best flocculation efficiency was 43% at ozone dosage of 3.5 mg/L with 5 min contact time. Furthermore, a higher ozone dosage could produce more ammonia.

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Description and Assessment of the Surface Water Filtration and Ozone Treatment System at the Northeast Fishery Center

Authors: Steven Summerfelt, Julie Bebak-Williams, John Fletcher, Anthony Carta, Duncan Creaser

Abstract

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