Final Report Summary - AIRX (Oxygenation by efficient air diffusion system for aquaculture farms (cages and earthen ponds))
Executive Summary:
Dissolved oxygen (DO) is considered one of the dominating limiting factors in aquaculture. However, suboptimal DO levels are experienced periodically during the warm season in many fish farms. In late summer and early autumn, an unfavorable combination of high temperature (over 30 ºC), sub-critical low oxygen concentration, and increased biomass in the cages, often leads to periods where the farmers must stop or reduce feeding. This situation may lead to increased stress, lower digestive capacity of the animals, lower appetite and growth, disease outbreaks and even increased mortalities. Without sufficient oxygen supply, the welfare of the cultured stock will be put at risk and eventually lead to reduced growth, disease outbreaks and mortality. Early morning DO deficit, especially in late summer – early autumn at high water temperature, is strongly limiting the production in numerous extensive/semi-intensive cage and pond farms. This makes oxygen injection during the night a key factor to improve the farm’s productivity. In more intensively run culture, aeration should also be employed throughout the day during this part of the year to sustain a healthy rearing environment.
The AirX project has developed a new air diffuser based system for control of dissolved oxygen levels in aquaculture. The aeration concept, patented by the Norwegian company Oxyvision, is designed for use in large rearing units, and has been employed and tested in sea cages and earth ponds in the Mediterranean region during the project period. The majority of the technical development and lab-scale tests have taken place in Norway (Oxyvision, TI and IRIS), while verification and field trials have been performed in the Mediterranean region, more specifically in Portugal (F. Ribeiro, Atlantik Fish and IPMA), Greece (Zervas-Kyriazis, UPAT and UTH), and Italy (RefaMed). The AirX was project successfully ended before December 2014.
The main innovations of the AirX system:
1. Diffuser hoses connected in a grid that cover and aerate a large area (e.g. a pond or a fish cage).
2. Homogenous oxygenation throughout the culture volume (not only the surface layer) so that all fish have equal access to oxygen.
3. Possibility to direct diffusion towards areas where extra oxygen addition is most needed (i.e. to diffuse oxygen at the areas with the lowest initial oxygen levels to maximize transfer rate)
4. Diffusion of small bubbles that efficiently transfer oxygen into the water (homogeneous distribution of bubbles also gives small bubbles since bubbles concentrated in a small space tend to merge)
5. No upwelling currents (increases contact time and hence transfer efficiency)
Project Context and Objectives:
Background:
Sea bass and sea bream aquaculture is an important source of income in many Mediterranean regions, especially in Greece, Turkey and Spain that are representing some 80% of the entire production volume. Over the last years, the total annual production of these species has levelled at 300,000 MT. Aquaculture in Greece is considered ‘the 2nd most important key economic sector for the growth of Greek economy’. Other species, such as meagre and sharpsnout sea bream, are new promising candidates for so-called multi-species cultivation in Mediterranean fish farms. Grow-out farming in the largest producing countries takes mainly place in floating sea cages, while some 15% of the total volume are produced in land-based pond systems in other countries, e.g. in Portugal and Italy. Sub-optimal dissolved oxygen (DO) concentration deficit is a potential problem both in cages and ponds, and the risk of harmful deficit is generally highest in late summer – early autumn at water temperature above 25 – 27 °C. These species seem to cope rather well to low DO (hypoxia) compared to cold-water species, but long-term tests with sea bass has demonstrated reduced appetite and growth at DO saturation below 80% even at a temperature as low as 22 °C. At increasing temperature in August - October, so-called early morning DO deficit, sometimes results in critical conditions (e.g. fish kill). A well-known contributing factor to such critical situations is the rising oxygen consumption in fish at increasing temperature. Reported problems with sub-optimal and even critical DO in Mediterranean fish farms was the basis for a performed project applying aeration in order to better control DO.
The AirX-project:
A research project, both incorporating research institutions and commercial partners in Greece (Universities of Patras & Thessaly, Zervas-Kyriazis fish farm), Portugal (IPMA, Atlantik Fish, F.Ribero Lda.), Italy (RefaMed) and in Norway (OxyVision, TI, IRIS), has been carried out over the last two years. The project, AirX, was funded from the 7th Framework Programme of the European Union.
Among the main objectives are optimization of diffuser based aeration, mapping of DO deficit problems in commercial farms, and comparative tests of cost – benefit employing aeration technology (OxyVision) in ponds and cages. Additionally, the lacking knowledge of effects of DO deficit and fish density in sea bream culture has been compensated for by performed tests at IPMA.
Efficiency of diffusers:
Numerous combinations of diffuser hoses with regard to structure/material, pre-treatment, puncture density, inner and outer hose combinations, etc. were tested in an experimental tank at OxyVision’s lab. The decisive parameter, ‘Standard aeration efficiency’, SAE, was determined in all tests and the most efficient diffuser hose was selected for further in-field tests at the facilities in Greece and Portugal.
The best in test diffuser hose attained a SAE-value of 2.7 kg O2 transferred from air to water per KWh of electricity consumed. Compared to reported efficiencies of other types of commonly applied aerators in aquaculture (paddle wheels, propeller-aspirator-pumps) the achieved SAE-value was most promising. Not least, the efficiency was clearly higher than reported from other conducted diffuser tests in the 1980’ies.
Risk of DO deficit in sea cages:
Aeration is common practice and considered vital in many land-based culture operations. Traditional sea cage culture, however, still relies on natural water exchange replacing oxygen consumed by the fish stock. In spite of episodic fish kills due to critical DO drops, there are few reports available describing such episodes in Mediterranean cage farms. As a part of the project, monitoring of DO and water exchange has been performed at one farm site in Greece. The oxygen conditions at this locality is primarily dependent on the rhythm of the tidal water, but the diurnal algal activity will also play a role. Especially at the turn of the tidal flow, the respiration of the fish stock may cause serious DO deficit in the stagnant water column in the cages, as demonstrated at 10-11 AM on 16 November. Improved DO control by aeration and thus stabilizing the concentration above 60% of saturation would be a significant attempt to optimize the conditions for the stock.
Diffuser based aeration tests in sea cages and earthen ponds:
Surface aerators, such as paddle wheels and propeller-aspirator pumps, are commonly used aeration systems in earthen ponds. However, it is also possible to use diffuser based systems that inject fine gas bubbles, using blowers that supply air at low pressure. In large earthen ponds and fish cages, where oxygen has to be distributed over a large area, usage of submerged diffusers is advantageous because of the large interface between injected air and the water body as the fine air bubbles are slowly rising to the surface.
Several AirX prototypes have been developed as a result of continual improvements throughout the project period. The first technical tests were performed in canvas lined raceway tanks (Sardinia, Italy) in spring 2013. These tests were succeeded by aeration of earthen ponds at IPMA’s research station (Algarve, Portugal) and of sea cages at a commercial farm (Greece) in summer and autumn 2013. The tests resulted in updated diffuser layouts for commercial-scale trials initiated during the summer 2014.
The earth ponds were stocked with both meagre and sea bream, whilst the sea cages were stocked with either sea bass, or sea bream. Parameters, such as DO and total gas pressure (TGP) in the water column, and pond sediment accumulation and characteristics, were routinely monitored. The results from small-scale tests of the AirX diffuser indicated oxygen transfer efficiency up to 20% at oxygen levels of 70 – 80% DO saturation in a seawater tank. Moreover, in waters where stratification occurs, oxygen levels can be even lower at the diffuser’s depth, which might increase the efficiency. Thus, it was estimated that the system would be able to control the running DO concentration above 70 – 80% of saturation assuming sufficient air supply.
In sea cages, it is possible to inject air at larger depths than in the earth ponds. This will increase the contact time between air and water, and thus increase the oxygen transfer. However, care must be taken when injecting pressurized air at large depths to avoid gas super-saturation which may result in potential harmful conditions for the fish. It is therefore important to select appropriate injection depth and practice. Moreover, it is highly recommended to monitor the total gas pressure (TGP) when aerating continuously at large depths (> 3 – 4 m).The aeration system has been running at the Greek fish farm for several months, injecting air at 4-5 m depth without any indications of negative effects for the fish or signs of elevated TGP. The diffuser system managed to lift the mean DO in the cage by some 8% during August, even though the oxygen levels were very high (85 – 90 % of saturation).
Small-scale tests with gilthead sea bream:
Detailed studies were performed in indoor tanks at IPMA to improve the knowledge base about the required DO control in sea bream aquaculture. In brief, lower than 80% of DO saturation reduced growth rate and feed utilization, and also indicated higher haematocrit levels. Thus, DO should be kept above this limit throughout the production cycle in order to utilize the production potential of sea bream and maintain the fish’s welfare. Within a fish density range of 5 – 20 kg m-3, no significant differences were found with regard to performance of sea bream. The outcome of these studies will be published in a scientific journal.
Project Results:
The description of the main results are as follows:
*Deliverable 1.1 is a reference document identifying specific end-users needs to get a better understanding of what the end-user’s expects and requires from the AirX aeration system. The information was gathered from using a questioner in face to face meetings. . The report also provides information on other aeration systems, including case scenarios where AirX is compared with competitive products. Thus the report thus provides baseline data that will be used later in the project for evaluation of the performance of the AirX system (WP3 and WP4). A layman style document that will be used to explain the benefits of aeration and maintaining optimal oxygen conditions in aquaculture farms is attached as an annex to the deliverable.
*Deliverable 1.2 is a report with detailed description of the requirements of the foreseen AirX system and design considerations. The product design specification is a document where one can find all the requirements for the AirX system. The requirements are divided in general and specific determined by the importance. The general requirements are more open and “nice to have” functions, while the specific are based on success criteria and important for the validation of the system. The PDS is based on input from state of the art competitive systems, input from project SME partners and the expertise of the RTD partners. The need for oxygen in fish cages and earthen ponds has been reviewed as well as use of aeration as a way to meet oxygen demands of fish. The main aim is to create an overview of today’s available and practical methods for adding oxygen in ponds and cages, and identify potential barriers related to aeration. The review covers different aeration and oxygenation methods, water quality parameters, gas theory for aeration, and types of aerators. Economical considerations have been reported as well to get a picture of the economic advantages accompanying each choice and a view of alternative aeration strategies, a topic which is central for the AirX project.
* Deliverable 2.1 is the diffusers and mock-up models that has been manufactured for the small scale tests. A technical report that describes the Work-In-Progress prototypes has also been provided for this deliverable. Furthermore, preparatory work and commissioning at the first field trial during winter/spring 2013 is described in the report, including a case scenario assessing water quality parameters and economics of using AirX at this farm.
*Deliverable 2.2 is a report prepared by TI that accommodates the final prototype delivery of the AirX prototype version 2. This prototype was manufactured by Oxyvsion and installed in the large earth pond at IPMA’s research station in May 2014. Chapter 1 of this report includes results from the latest lab scale oxygen transfer tests performed at Oxyvisions’ lab in Norway, Nov 2013, in order test and optimize the diffusers. In Chapter 2 we investigate how the AirX and two other diffusers’ capacities and pressure requirement varies with diffuser’s length. Chapter 3 provides results from a test performed in Dec 2013 and Jan 2014 looking at how the air flow capacity changes over time, using the AirX diffuser prototype version 1. In chapter 4, the layout of the new AirX prototype 2 at IPMA’s research station is described. In addition, a brief assessment of the earth pond’s aeration needs during the test is presented.
*Deliverable 3.1 is a confidential document describing some of the tests performed with mock-up models and early stage prototypes. The report presents the main results and includes recommendations and conclusions on the various designs tested. The report is split in two main chapters: Chapter 1 presents results of gas transfer tests with mock-up model diffusers under indoor lab conditions in a small tank. The aim is to identify and select suitable diffuser designs that we indented to use as bases for further development and testing. This task was finalized in March 2013.Chapter 2 presents results from up-scaled mock-up models tested in larger tanks and ponds. The main aim of this task is to solve mechanical issues regarding the diffusers and pressurized air delivery system.
* Deliverable 3.2 is an extensive report of the work performed in relation to Tasks 3.3 and 3.4. For convenience, the report has been divided in two major parts, of which Chapter 1 deals with the trials performed in earthen ponds and indoor tanks in Portugal, whilst Chapter 2 provides data from the tests that was initiated in sea cages in Greece. The first chapter includes data from trials performed to test the prototype in earthen pond rearing environment and to investigate how different stocking densities and low levels of dissolved oxygen affected gilthead sea bream’s behaviour and performance. The second chapter presents the preliminary results from trials at Zervas-Kyriazis cage farm in Skala Atalantis, Greece, including monitoring of dissolved oxygen saturation to gather relevant background data from the farm site. A similar prototype to that tested in the earthen ponds was also employed in the sea cage.
*Deliverable 4.1 is related to tasks 4.2 (System integration) and 4.3 (Long-term testing of functional prototype). Chapter 1 deals with the trials in Portugal, whereas Chapter 2 deals with the trials in Greece. In the case of Portugal, some tests were done in Atlantik fish farm, whereas the main bulk of the trials were run at the research facilities of IPMA. This chapter presents results on the efficiency the Air X prototype tested for 4 months at an industrial scale in the earth ponds of the Aquaculture Research Station (EPPO), from the Portuguese Institute for the Sea and Atmosphere (IPMA). In addition an attempt to install a prototype at the fish farm Atlantik fish is also described. All industrial scale trials in Greece for the integration and testing of the AirX prototype were run at the cage farm facilities of Zervas-Kyriazis. There are three main components in the trials in Greece: (i) monitoring of oxygen and temperature in seabass from May to August, (ii) large-scale trials with sea bass (mid-August to mid-September), and (iii) large-scale trial with sea bream (mid-September to early November).
*Deliverable 5.1 is the a press release prepared for the project. The press release was sent out to magazines and internet media targeting relevant aquaculture sectors.
*Deliverable 5.2 is the AirX Consortium Agreement.
*Deliverable 5.3 is the project web site (www.airx-project.com)
*Deliverable 5.4 is Interim Plan for Use and Dissemination of project results, and lists the events that the AirX partners have/plan to attend, planned publications, etc.
*Deliverable 5.5 is the an operating and maintenance manual, which includes product information and technical specifications, safety information, user guidelines, quick guide on ‘how to get started’, recommendations on how to wash and disinfect AirX, and instructions for assembly of AirX networks including an assembly diagram, and more.
*Deliverable 5.6 is the Final Plan for Use and Dissemination of project results, and lists the events that the AirX partners have/plan to attend, planned publications, etc
*Deliverable 5.7 is a short the video presentation of the AirX system.
*Milestone 1: Product Design Specification completed. Completed report. This milestone was successfully accomplished during Reporting Period 1.
* Milestone 2: Material selection for diffusers completed. Materials fulfils requirements set by Product Design Specifications. This milestone was successfully accomplished during Reporting Period 1.
*Milestone 3:Puncturing and sewing tools ready for manufacturing of test-series. Tools ready for production of test series. This milestone was successfully accomplished during Reporting Period 1.
*Milestone 4: Mock-up models ready for testing (tests-series). All mock-up models assembled and ready for performing test-series. This milestone was successfully accomplished during Reporting Period 1.
*Milestone 5: First prototype version installed and ready for testing to determine gas transfer - Installed on-site at fish farm and ready for testing. This milestone has been successfully met during Reporting Period 2.
*Milestone 6: Test trials for prototype completed – Troubleshooting finished. Prototype fulfils requirements specified in the Product Design Specifications. This milestone has been successfully met during Reporting Period 2.
*Milestone 7: Working prototype installed and ready for long term testing - Prototype installed at farm site and ready for ,long term testing (ponds and cages). This milestone has been successfully met during Reporting Period 2.
*Milestone 8: All results obtained from long term trials in fish farms - Report on integration and results from industrial scale tests. This milestone has been successfully met during Reporting Period 2.
Potential Impact:
Oxygen deficiency can constitute a challenge in aquaculture, especially when water temperatures are high. This challenge manifests itself in decreased appetites, low-level feed utilisation, slow growth rates, increased stress among the farmed stock, and higher production costs. The factors resulting in oxygen deficiency typically coincide during summer and early autumn – at a time when the stocking densities are normally quite high. This can result in prolonged periods with low oxygen levels, making it necessary for the farmer to alter husbandry practices in order to reduce the need for oxygen
The AirX project has developed and tested a new technology that uses air to control dissolved oxygen levels in aquaculture. The concept, which has already been patented, is designed for use in large farming facilities, including earth ponds, sea cages, tanks and raceways. Currently, cage farmers rely singularly on the ability of the sea current to replace oxygen consumed by farmed fish. In earth ponds, on the other hand, aeration devices such as paddle wheels and air jets are commonly used. However, the existing aeration devices used in ponds have low efficiency, whereas for cages there are no realistic options available. At critical periods with low oxygen levels, feeding is reduced and productivity of the industry is heavily influenced. Mortalities may appear accumulated stress may result in decreased appetite and thereby decreased growth, and decreased feed utilization.
Tests have shown that AirX is able to add oxygen in an efficient and homogenous manner throughout the water volume. The diffusers system is also designed to direct diffusion towards areas in the rearing unit where oxygenation is mostly needed. Other benefits of using AirX for the end-users are higher growth rates of stock, improved feed conversion rates, higher production capacities, and reduced energy costs.
The target market for the AirX system are cage and earthen pond farmers in the Mediterranean, which periodically experience problems with reduced growth rate, increased feed conversion factor (FCR), stress and mortality of stock due to low oxygen content in the water. Other relevant markets include pond farming of fish and shrimp in Asia and in the Americas, and also for restoration of lakes
The consortium has been active in dissemination throughout the second period of the project.
The partners have been at 6 international aquaculture conferences with poster exhibitions and oral presentations at the ‘Summer Meeting of The Crustacean Society 2013’, the ‘Asian-Pacific Aquaculture Conference 2013’, the ‘Offshore Mariculture 2014’, the ‘International Conference on Recirculating Aquaculture 2014’, and ‘Aquaculture Europe 2014’, and the ‘Hydromedit conference 2014’
In addition three papers are under preparation for publication peer-reviewed journals. Also, the project has been presented 3 articles in different aquaculture magazines, including in ‘The Global Aquaculture Advocate’, ‘Hatchery International’, and ‘Aquaculture Magazine’.
There has been good response from potential end-users that wish to try out the new system. The project partners have been on contact with cage farmers from Malta and Sardinia that are interested in the system. Furthermore, there have been inquiries from farmers located in Germany, Iceland, Finland, the US and many other places. Moreover, Oxyvision has been working hard to try to set up a demonstration project where AirX is used in pond culture of shrimp and fish in Vietnam. They are further promoting the system for lake restoration applications in Norway. The commercialization process always takes some time when launching a new product, but given all this interest before the commercial product documentation has been established, this seems very promising for 2015 and 2016. Two trial sales have been performed in 2014; one sale has been to a fish farm, Emilsen Fisk AS, and another to the Oppegård Municipality for use in restoration of Lake Kolbotn, both located in Norway.
List of Websites:
A project webpage has been established, where the public can read about the project.
For further questions, please contact the Coordinator of the project:
Mr. Martin Gausen
Company: OxyVision AS
Mobile: +47 482 04 041
Email: martin@oxyvision.com
Website: www.oxyvision.com
Dissolved oxygen (DO) is considered one of the dominating limiting factors in aquaculture. However, suboptimal DO levels are experienced periodically during the warm season in many fish farms. In late summer and early autumn, an unfavorable combination of high temperature (over 30 ºC), sub-critical low oxygen concentration, and increased biomass in the cages, often leads to periods where the farmers must stop or reduce feeding. This situation may lead to increased stress, lower digestive capacity of the animals, lower appetite and growth, disease outbreaks and even increased mortalities. Without sufficient oxygen supply, the welfare of the cultured stock will be put at risk and eventually lead to reduced growth, disease outbreaks and mortality. Early morning DO deficit, especially in late summer – early autumn at high water temperature, is strongly limiting the production in numerous extensive/semi-intensive cage and pond farms. This makes oxygen injection during the night a key factor to improve the farm’s productivity. In more intensively run culture, aeration should also be employed throughout the day during this part of the year to sustain a healthy rearing environment.
The AirX project has developed a new air diffuser based system for control of dissolved oxygen levels in aquaculture. The aeration concept, patented by the Norwegian company Oxyvision, is designed for use in large rearing units, and has been employed and tested in sea cages and earth ponds in the Mediterranean region during the project period. The majority of the technical development and lab-scale tests have taken place in Norway (Oxyvision, TI and IRIS), while verification and field trials have been performed in the Mediterranean region, more specifically in Portugal (F. Ribeiro, Atlantik Fish and IPMA), Greece (Zervas-Kyriazis, UPAT and UTH), and Italy (RefaMed). The AirX was project successfully ended before December 2014.
The main innovations of the AirX system:
1. Diffuser hoses connected in a grid that cover and aerate a large area (e.g. a pond or a fish cage).
2. Homogenous oxygenation throughout the culture volume (not only the surface layer) so that all fish have equal access to oxygen.
3. Possibility to direct diffusion towards areas where extra oxygen addition is most needed (i.e. to diffuse oxygen at the areas with the lowest initial oxygen levels to maximize transfer rate)
4. Diffusion of small bubbles that efficiently transfer oxygen into the water (homogeneous distribution of bubbles also gives small bubbles since bubbles concentrated in a small space tend to merge)
5. No upwelling currents (increases contact time and hence transfer efficiency)
Project Context and Objectives:
Background:
Sea bass and sea bream aquaculture is an important source of income in many Mediterranean regions, especially in Greece, Turkey and Spain that are representing some 80% of the entire production volume. Over the last years, the total annual production of these species has levelled at 300,000 MT. Aquaculture in Greece is considered ‘the 2nd most important key economic sector for the growth of Greek economy’. Other species, such as meagre and sharpsnout sea bream, are new promising candidates for so-called multi-species cultivation in Mediterranean fish farms. Grow-out farming in the largest producing countries takes mainly place in floating sea cages, while some 15% of the total volume are produced in land-based pond systems in other countries, e.g. in Portugal and Italy. Sub-optimal dissolved oxygen (DO) concentration deficit is a potential problem both in cages and ponds, and the risk of harmful deficit is generally highest in late summer – early autumn at water temperature above 25 – 27 °C. These species seem to cope rather well to low DO (hypoxia) compared to cold-water species, but long-term tests with sea bass has demonstrated reduced appetite and growth at DO saturation below 80% even at a temperature as low as 22 °C. At increasing temperature in August - October, so-called early morning DO deficit, sometimes results in critical conditions (e.g. fish kill). A well-known contributing factor to such critical situations is the rising oxygen consumption in fish at increasing temperature. Reported problems with sub-optimal and even critical DO in Mediterranean fish farms was the basis for a performed project applying aeration in order to better control DO.
The AirX-project:
A research project, both incorporating research institutions and commercial partners in Greece (Universities of Patras & Thessaly, Zervas-Kyriazis fish farm), Portugal (IPMA, Atlantik Fish, F.Ribero Lda.), Italy (RefaMed) and in Norway (OxyVision, TI, IRIS), has been carried out over the last two years. The project, AirX, was funded from the 7th Framework Programme of the European Union.
Among the main objectives are optimization of diffuser based aeration, mapping of DO deficit problems in commercial farms, and comparative tests of cost – benefit employing aeration technology (OxyVision) in ponds and cages. Additionally, the lacking knowledge of effects of DO deficit and fish density in sea bream culture has been compensated for by performed tests at IPMA.
Efficiency of diffusers:
Numerous combinations of diffuser hoses with regard to structure/material, pre-treatment, puncture density, inner and outer hose combinations, etc. were tested in an experimental tank at OxyVision’s lab. The decisive parameter, ‘Standard aeration efficiency’, SAE, was determined in all tests and the most efficient diffuser hose was selected for further in-field tests at the facilities in Greece and Portugal.
The best in test diffuser hose attained a SAE-value of 2.7 kg O2 transferred from air to water per KWh of electricity consumed. Compared to reported efficiencies of other types of commonly applied aerators in aquaculture (paddle wheels, propeller-aspirator-pumps) the achieved SAE-value was most promising. Not least, the efficiency was clearly higher than reported from other conducted diffuser tests in the 1980’ies.
Risk of DO deficit in sea cages:
Aeration is common practice and considered vital in many land-based culture operations. Traditional sea cage culture, however, still relies on natural water exchange replacing oxygen consumed by the fish stock. In spite of episodic fish kills due to critical DO drops, there are few reports available describing such episodes in Mediterranean cage farms. As a part of the project, monitoring of DO and water exchange has been performed at one farm site in Greece. The oxygen conditions at this locality is primarily dependent on the rhythm of the tidal water, but the diurnal algal activity will also play a role. Especially at the turn of the tidal flow, the respiration of the fish stock may cause serious DO deficit in the stagnant water column in the cages, as demonstrated at 10-11 AM on 16 November. Improved DO control by aeration and thus stabilizing the concentration above 60% of saturation would be a significant attempt to optimize the conditions for the stock.
Diffuser based aeration tests in sea cages and earthen ponds:
Surface aerators, such as paddle wheels and propeller-aspirator pumps, are commonly used aeration systems in earthen ponds. However, it is also possible to use diffuser based systems that inject fine gas bubbles, using blowers that supply air at low pressure. In large earthen ponds and fish cages, where oxygen has to be distributed over a large area, usage of submerged diffusers is advantageous because of the large interface between injected air and the water body as the fine air bubbles are slowly rising to the surface.
Several AirX prototypes have been developed as a result of continual improvements throughout the project period. The first technical tests were performed in canvas lined raceway tanks (Sardinia, Italy) in spring 2013. These tests were succeeded by aeration of earthen ponds at IPMA’s research station (Algarve, Portugal) and of sea cages at a commercial farm (Greece) in summer and autumn 2013. The tests resulted in updated diffuser layouts for commercial-scale trials initiated during the summer 2014.
The earth ponds were stocked with both meagre and sea bream, whilst the sea cages were stocked with either sea bass, or sea bream. Parameters, such as DO and total gas pressure (TGP) in the water column, and pond sediment accumulation and characteristics, were routinely monitored. The results from small-scale tests of the AirX diffuser indicated oxygen transfer efficiency up to 20% at oxygen levels of 70 – 80% DO saturation in a seawater tank. Moreover, in waters where stratification occurs, oxygen levels can be even lower at the diffuser’s depth, which might increase the efficiency. Thus, it was estimated that the system would be able to control the running DO concentration above 70 – 80% of saturation assuming sufficient air supply.
In sea cages, it is possible to inject air at larger depths than in the earth ponds. This will increase the contact time between air and water, and thus increase the oxygen transfer. However, care must be taken when injecting pressurized air at large depths to avoid gas super-saturation which may result in potential harmful conditions for the fish. It is therefore important to select appropriate injection depth and practice. Moreover, it is highly recommended to monitor the total gas pressure (TGP) when aerating continuously at large depths (> 3 – 4 m).The aeration system has been running at the Greek fish farm for several months, injecting air at 4-5 m depth without any indications of negative effects for the fish or signs of elevated TGP. The diffuser system managed to lift the mean DO in the cage by some 8% during August, even though the oxygen levels were very high (85 – 90 % of saturation).
Small-scale tests with gilthead sea bream:
Detailed studies were performed in indoor tanks at IPMA to improve the knowledge base about the required DO control in sea bream aquaculture. In brief, lower than 80% of DO saturation reduced growth rate and feed utilization, and also indicated higher haematocrit levels. Thus, DO should be kept above this limit throughout the production cycle in order to utilize the production potential of sea bream and maintain the fish’s welfare. Within a fish density range of 5 – 20 kg m-3, no significant differences were found with regard to performance of sea bream. The outcome of these studies will be published in a scientific journal.
Project Results:
The description of the main results are as follows:
*Deliverable 1.1 is a reference document identifying specific end-users needs to get a better understanding of what the end-user’s expects and requires from the AirX aeration system. The information was gathered from using a questioner in face to face meetings. . The report also provides information on other aeration systems, including case scenarios where AirX is compared with competitive products. Thus the report thus provides baseline data that will be used later in the project for evaluation of the performance of the AirX system (WP3 and WP4). A layman style document that will be used to explain the benefits of aeration and maintaining optimal oxygen conditions in aquaculture farms is attached as an annex to the deliverable.
*Deliverable 1.2 is a report with detailed description of the requirements of the foreseen AirX system and design considerations. The product design specification is a document where one can find all the requirements for the AirX system. The requirements are divided in general and specific determined by the importance. The general requirements are more open and “nice to have” functions, while the specific are based on success criteria and important for the validation of the system. The PDS is based on input from state of the art competitive systems, input from project SME partners and the expertise of the RTD partners. The need for oxygen in fish cages and earthen ponds has been reviewed as well as use of aeration as a way to meet oxygen demands of fish. The main aim is to create an overview of today’s available and practical methods for adding oxygen in ponds and cages, and identify potential barriers related to aeration. The review covers different aeration and oxygenation methods, water quality parameters, gas theory for aeration, and types of aerators. Economical considerations have been reported as well to get a picture of the economic advantages accompanying each choice and a view of alternative aeration strategies, a topic which is central for the AirX project.
* Deliverable 2.1 is the diffusers and mock-up models that has been manufactured for the small scale tests. A technical report that describes the Work-In-Progress prototypes has also been provided for this deliverable. Furthermore, preparatory work and commissioning at the first field trial during winter/spring 2013 is described in the report, including a case scenario assessing water quality parameters and economics of using AirX at this farm.
*Deliverable 2.2 is a report prepared by TI that accommodates the final prototype delivery of the AirX prototype version 2. This prototype was manufactured by Oxyvsion and installed in the large earth pond at IPMA’s research station in May 2014. Chapter 1 of this report includes results from the latest lab scale oxygen transfer tests performed at Oxyvisions’ lab in Norway, Nov 2013, in order test and optimize the diffusers. In Chapter 2 we investigate how the AirX and two other diffusers’ capacities and pressure requirement varies with diffuser’s length. Chapter 3 provides results from a test performed in Dec 2013 and Jan 2014 looking at how the air flow capacity changes over time, using the AirX diffuser prototype version 1. In chapter 4, the layout of the new AirX prototype 2 at IPMA’s research station is described. In addition, a brief assessment of the earth pond’s aeration needs during the test is presented.
*Deliverable 3.1 is a confidential document describing some of the tests performed with mock-up models and early stage prototypes. The report presents the main results and includes recommendations and conclusions on the various designs tested. The report is split in two main chapters: Chapter 1 presents results of gas transfer tests with mock-up model diffusers under indoor lab conditions in a small tank. The aim is to identify and select suitable diffuser designs that we indented to use as bases for further development and testing. This task was finalized in March 2013.Chapter 2 presents results from up-scaled mock-up models tested in larger tanks and ponds. The main aim of this task is to solve mechanical issues regarding the diffusers and pressurized air delivery system.
* Deliverable 3.2 is an extensive report of the work performed in relation to Tasks 3.3 and 3.4. For convenience, the report has been divided in two major parts, of which Chapter 1 deals with the trials performed in earthen ponds and indoor tanks in Portugal, whilst Chapter 2 provides data from the tests that was initiated in sea cages in Greece. The first chapter includes data from trials performed to test the prototype in earthen pond rearing environment and to investigate how different stocking densities and low levels of dissolved oxygen affected gilthead sea bream’s behaviour and performance. The second chapter presents the preliminary results from trials at Zervas-Kyriazis cage farm in Skala Atalantis, Greece, including monitoring of dissolved oxygen saturation to gather relevant background data from the farm site. A similar prototype to that tested in the earthen ponds was also employed in the sea cage.
*Deliverable 4.1 is related to tasks 4.2 (System integration) and 4.3 (Long-term testing of functional prototype). Chapter 1 deals with the trials in Portugal, whereas Chapter 2 deals with the trials in Greece. In the case of Portugal, some tests were done in Atlantik fish farm, whereas the main bulk of the trials were run at the research facilities of IPMA. This chapter presents results on the efficiency the Air X prototype tested for 4 months at an industrial scale in the earth ponds of the Aquaculture Research Station (EPPO), from the Portuguese Institute for the Sea and Atmosphere (IPMA). In addition an attempt to install a prototype at the fish farm Atlantik fish is also described. All industrial scale trials in Greece for the integration and testing of the AirX prototype were run at the cage farm facilities of Zervas-Kyriazis. There are three main components in the trials in Greece: (i) monitoring of oxygen and temperature in seabass from May to August, (ii) large-scale trials with sea bass (mid-August to mid-September), and (iii) large-scale trial with sea bream (mid-September to early November).
*Deliverable 5.1 is the a press release prepared for the project. The press release was sent out to magazines and internet media targeting relevant aquaculture sectors.
*Deliverable 5.2 is the AirX Consortium Agreement.
*Deliverable 5.3 is the project web site (www.airx-project.com)
*Deliverable 5.4 is Interim Plan for Use and Dissemination of project results, and lists the events that the AirX partners have/plan to attend, planned publications, etc.
*Deliverable 5.5 is the an operating and maintenance manual, which includes product information and technical specifications, safety information, user guidelines, quick guide on ‘how to get started’, recommendations on how to wash and disinfect AirX, and instructions for assembly of AirX networks including an assembly diagram, and more.
*Deliverable 5.6 is the Final Plan for Use and Dissemination of project results, and lists the events that the AirX partners have/plan to attend, planned publications, etc
*Deliverable 5.7 is a short the video presentation of the AirX system.
*Milestone 1: Product Design Specification completed. Completed report. This milestone was successfully accomplished during Reporting Period 1.
* Milestone 2: Material selection for diffusers completed. Materials fulfils requirements set by Product Design Specifications. This milestone was successfully accomplished during Reporting Period 1.
*Milestone 3:Puncturing and sewing tools ready for manufacturing of test-series. Tools ready for production of test series. This milestone was successfully accomplished during Reporting Period 1.
*Milestone 4: Mock-up models ready for testing (tests-series). All mock-up models assembled and ready for performing test-series. This milestone was successfully accomplished during Reporting Period 1.
*Milestone 5: First prototype version installed and ready for testing to determine gas transfer - Installed on-site at fish farm and ready for testing. This milestone has been successfully met during Reporting Period 2.
*Milestone 6: Test trials for prototype completed – Troubleshooting finished. Prototype fulfils requirements specified in the Product Design Specifications. This milestone has been successfully met during Reporting Period 2.
*Milestone 7: Working prototype installed and ready for long term testing - Prototype installed at farm site and ready for ,long term testing (ponds and cages). This milestone has been successfully met during Reporting Period 2.
*Milestone 8: All results obtained from long term trials in fish farms - Report on integration and results from industrial scale tests. This milestone has been successfully met during Reporting Period 2.
Potential Impact:
Oxygen deficiency can constitute a challenge in aquaculture, especially when water temperatures are high. This challenge manifests itself in decreased appetites, low-level feed utilisation, slow growth rates, increased stress among the farmed stock, and higher production costs. The factors resulting in oxygen deficiency typically coincide during summer and early autumn – at a time when the stocking densities are normally quite high. This can result in prolonged periods with low oxygen levels, making it necessary for the farmer to alter husbandry practices in order to reduce the need for oxygen
The AirX project has developed and tested a new technology that uses air to control dissolved oxygen levels in aquaculture. The concept, which has already been patented, is designed for use in large farming facilities, including earth ponds, sea cages, tanks and raceways. Currently, cage farmers rely singularly on the ability of the sea current to replace oxygen consumed by farmed fish. In earth ponds, on the other hand, aeration devices such as paddle wheels and air jets are commonly used. However, the existing aeration devices used in ponds have low efficiency, whereas for cages there are no realistic options available. At critical periods with low oxygen levels, feeding is reduced and productivity of the industry is heavily influenced. Mortalities may appear accumulated stress may result in decreased appetite and thereby decreased growth, and decreased feed utilization.
Tests have shown that AirX is able to add oxygen in an efficient and homogenous manner throughout the water volume. The diffusers system is also designed to direct diffusion towards areas in the rearing unit where oxygenation is mostly needed. Other benefits of using AirX for the end-users are higher growth rates of stock, improved feed conversion rates, higher production capacities, and reduced energy costs.
The target market for the AirX system are cage and earthen pond farmers in the Mediterranean, which periodically experience problems with reduced growth rate, increased feed conversion factor (FCR), stress and mortality of stock due to low oxygen content in the water. Other relevant markets include pond farming of fish and shrimp in Asia and in the Americas, and also for restoration of lakes
The consortium has been active in dissemination throughout the second period of the project.
The partners have been at 6 international aquaculture conferences with poster exhibitions and oral presentations at the ‘Summer Meeting of The Crustacean Society 2013’, the ‘Asian-Pacific Aquaculture Conference 2013’, the ‘Offshore Mariculture 2014’, the ‘International Conference on Recirculating Aquaculture 2014’, and ‘Aquaculture Europe 2014’, and the ‘Hydromedit conference 2014’
In addition three papers are under preparation for publication peer-reviewed journals. Also, the project has been presented 3 articles in different aquaculture magazines, including in ‘The Global Aquaculture Advocate’, ‘Hatchery International’, and ‘Aquaculture Magazine’.
There has been good response from potential end-users that wish to try out the new system. The project partners have been on contact with cage farmers from Malta and Sardinia that are interested in the system. Furthermore, there have been inquiries from farmers located in Germany, Iceland, Finland, the US and many other places. Moreover, Oxyvision has been working hard to try to set up a demonstration project where AirX is used in pond culture of shrimp and fish in Vietnam. They are further promoting the system for lake restoration applications in Norway. The commercialization process always takes some time when launching a new product, but given all this interest before the commercial product documentation has been established, this seems very promising for 2015 and 2016. Two trial sales have been performed in 2014; one sale has been to a fish farm, Emilsen Fisk AS, and another to the Oppegård Municipality for use in restoration of Lake Kolbotn, both located in Norway.
List of Websites:
A project webpage has been established, where the public can read about the project.
For further questions, please contact the Coordinator of the project:
Mr. Martin Gausen
Company: OxyVision AS
Mobile: +47 482 04 041
Email: martin@oxyvision.com
Website: www.oxyvision.com