Fish Farming Technology supplement

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Innovation and service to the global aquaculture sector

Defining RASsafeguarding the future of the industry

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Fusion Marine

With concerns being raised about the impacts and safety of open water cage and pond farming, the spotlight has begun to fall upon more sustainable and environmentally friendly methods for raising

fish. Recirculating Aquaculture Systems (RAS), provide clean, sustainable and environmentally friendly products due to their closed nature, high degree of control and detachment from the surrounding environment. In order to assist the industry to develop and create its own identity, it is necessary to properly define the technology and the production methods. This is necessary in order to ensure that the integrity of the industry and the sustainability claims of RAS are safeguarded and not undermined by systems with different environmental, economical, quality and welfare limits. Engineers and biologists have been working hard for the past 20 years, and continue to do so, in order to improve and optimise the design and operations of such systems, in turn making them more profitable and more popular as a method for large scale production of high quality fish.

What is RAS?A RAS usually consists of different compartmentalised units where the waste water from the fish tanks is treated biologically and mechanically, allowing it to be reused and maintained within the optimum ranges for the species grown. As the name suggests, the water in such systems circulates in a loop with minimum discharge, and a RAS can be defined as such if the water exchange is limited to 15 or even 10 percent of the total volume per day. In order to achieve such low exchange rates (compared to flow through and partial exchange water systems, where the exchange rate is much higher) the water treatment systems must be correctly designed and sized so as to effectively deal with the waste produced. A system where the treatment processes, for purposes of economy, practicality or something else, are not sized to be able to fully process the waste produced, and therefore have exchange rates

of anything above 10 to 15 percent, should therefore be considered partial reuse.

Secondly, the circulation of the water is crucial to the definition – while some extensive static ponds may have close to zero discharge, the water is not circulated and therefore cannot be termed as RAS. The reason for this defining and demarcation is to be able to help to protect the quality of the industry and improve confidence in the sec-tor. Chris Clayburn, Director of the RAS design and engineering com-pany Aqua EcoSystems says: ‘It would eliminate those systems being classified as RAS that are not and that may be "white elephants" for the rest of us who understand the difference and the distinct advantages, the complex work and considerable experience involved in developing RAS and help clients/customers/investors to discriminate and invest in viable operations’.

Crucial to the effective running of any RAS are the treatment pro-cesses employed, such as mechanical filtration and biofiltration, while effective denitrification, degassing, aeration, pH control are also essen-tial in ensuring the optimal functioning of the system and maintaining excellent fish health. Several technologies are available to remove solids originating from fish waste or uneaten feed including: drum filters, belt filters, parabolic filters, sand filters, and bead filters among others. The selection of the proper mechanical filtration system during the design phase of RAS is the first step to ensuring a system functions as planned, with the main parameters of interest being particle sizes, solids loading and water flows. The next stage in efficient water treatment is nitrification of ammonia, produced as a by-product of the animals’ metabolism. Bacteria living in the biofilter oxidise ammonia to nitrite followed by a second oxidation of nitrite to nitrate. While ammonia and nitrite are highly toxic to fish and could be lethal if allowed to build up in the water, nitrate can be tolerated in higher concentrations before welfare of the fish becomes compromised.

In terms of the biofilter design, again there are many possi-bilities including moving bed bioreactors, trickle filters, submerged and upwelling bioreactors, and again different types of biofilter are more

Defining RAS safeguarding the future of the industry by Ivan Tankovski, Research Consultant, Pontus Aqua Ltd and Dr Jack M James, Principal Consultant, Pontus Aqua; Director, Pontus Research Ltd

002 | INTERNATIONAL AQUAFEED | Fish farming Technology


suited to different types of system and should be properly sized and designed. While nitrate has low toxicity, chronically high levels can retard the growth of the animals, reducing production potential, and is one of the main reasons for water exchange in RAS.

Recently, denitrification reactors have been designed to facilitate the removal of nitrate from RAS, thus minimising water exchange or facili-tating the reduction in water exchange rates. Other factors which will affect the exchange rate are dissolved gas build up, which in the case of carbon dioxide can cause low oxygen absorption even under high oxygen conditions, and nitrogen which can lead to gas bubble disease. It is therefore essential to design a suitable degassing system into a RAS to prevent these issues. In reducing the loading of very fine solids in the system, technology such as protein skimming or foam fractionation is utilised, which can assist in particle bound phosphorus removal and reduction in ammonia due to removal of organics.

Finally, the use of effective systems to monitor and control param-eters such as oxygen concentration, temperature, pH, water flows and levels can also prove to be key to running a successful RAS as it allows the farmer to be aware of all essential parameters at all times, and to react quickly should a problem arise. Adoption of any of the design factors mentioned will depend on a range of prevailing environmental and economic factors, such as cost/benefit of technologies, location of the operation, cultured species, water availability, local discharge regula-tions and environmental conditions, among others.

Why use RAS technology at all?RAS provides a unique opportunity to grow fish practically anywhere and provides a great opportunity to expand aquaculture into areas where it might previously have been impossible, thereby getting produce physically closer to markets, reducing food miles and carbon footprints. All environmental parameters can be monitored and strictly controlled: temperature, oxygen saturation, pH, CO2 concentration, suspended solids and photoperiod, allowing the commercial produc-tion of virtually any species regardless of environmental preferences, even in geographical locations which normally would be wholly unsuit-able for a certain species. For example The Fresh Shrimp Company produces tropical shrimp in England while the Abu Dhabi company Asmak produces cold water salmon in their 500,000 square metre onshore site.

The main benefits of RAS farming are:• Feeding is constantly observed and can be controlled by robots

so that overfeeding is easily avoided. Feed conversion in RAS is therefore much higher compared to other systems, reducing the amount of feed necessary to grow the fish to market size, thus reducing expenses and maximising profit.

• Growing fish in RAS allows the farmer to maintain uniformity in his stock through size-grading and the adjustment of feeding rates.

• Exposure to disease is reduced as contact with the outside environment is minimised through strict biosecurity protocols and incoming water can be sourced from known clean sources or can be treated before being introduced to the system. Additionally, many RAS designs include the use of ultraviolet light and ozone for water sterilisation. As well as ensuring high welfare standards, this reduces the use of antibiotics and other pharmaceutical products, highly undesirable in aquaculture when considering environmental impacts of such chemicals, and the perception of the consumer.

• Fish are not exposed to extreme weather conditions, and any unusual behaviour can be recognised and reacted to accordingly, and any dead fish can be promptly removed.

• Many concerns have been voiced over the mixing of wild populations with fish escaping from nets in sea and lakes reducing the genetic variability in nature, and this risk is removed in RAS operations.

• Crucially, RAS allows the collection, treatment and potential uti-

lisation or treatment of waste products, including heat and CO2 as well as biological waste, reducing the impact of farming on the environment. For example, with proper design waste heat energy from equipment such as pumps or chillers can be harvested and used to heat other parts of the farm or other operations.

Identifying the potential pitfalls, and avoiding themAs with any novel undertaking or technology, RAS can and does come up against challenges. Chris Clayburn states that: ‘There will be some genuine RAS that fail even when operating within certain defined limits, which may be down to margins because RAS is an inherently expensive way to produce fish [which] should be mitigated by thorough feasibility study.’ Indeed research by CEFAS highlighted several cases of RAS operation failings for a variety of reasons, including poor understanding and planning, high costs, lower than expected sales values, poor design, market challenges, environmental concerns and more.

Initially, building a RAS requires high capital investment and as such must be well funded through the initial stages of growth through to full production, which may be in the range of 12 to 18 months. This can be off-putting to investors, but RAS must be seen as a long- term investment, with potentially significant returns having. In addition to this, high operational costs when using traditional energy sources can be a barrier to development. However, through careful planning, proper feasibility analysis and forward thinking, incorporating renewable energy generation through solar, wind, gasification of waste or biomass genera-tors and, in the case of exotic species in temperate climes, siting nearby sources of waste heat such as power stations can make operations significantly more viable. Even under standard energy conditions it is possible to significantly reduce energy consumption through proper design, bringing it in line with flow through systems. When considered in tandem with reduced feed conversions, limited risks of stock failure, reduced impact on local environment, the economic and environmen-tal balance of RAS then become much more favourable.

In terms of the systems themselves, it is essential that the design is fit-for-purpose for the very start, and as such each farm should be treated as a unique project, ensuring all local variables are catered for. Having a system with a poor or unsuitable design, or utilising a generic system under special circumstances, could have disastrous consequenc-es. Furthermore, an in depth knowledge of the target market and spe-cies demand is also very important. It is not unheard of for farms to go bankrupt because of poor market research. Once operational, several factors must be considered for a system to be successful. One of them is organic matter and nutrient loading in the effluent water, particularly phosphorus and nitrogen which, if discharged, can contribute to the eutrophication of the receiving water bodies. Therefore the design must take account of this and have sufficient denitrification capabilities to ensure discharges are as clean as possible, and at least comply with local environmental guidelines.

While denitrification reactors can make operations economically unfeasible, less intensive methods are becoming increasingly popu-lar, such as stabilisation ponds and wetlands, which can also provide additional income to the farmer. In addition to nitrate removal, the removal or limitation of phosphorus discharge should also be con-sidered such as optimising phosphorus retention in the fish, rapid removal of solids from the water preventing phosphorous leaching or dephosphonation techniques. Of course a farm will also produce significant quantities of solid waste, which would need to be dealt with. Firstly, it is important to treat this sludge and remove as much water as possible through the use of dewatering belts, flocculation tanks, or other available technologies, the resulting water entering denitrification processes outlined above. The resulting dewatered waste can then either be removed by municipal services, be used in energy generation, or can be used as fertiliser or compost; however, in this instance other regulations should be adhered to. There are also biological methods for dealing with both dissolved

Fish farming Technology | INTERNATIONAL AQUAFEED | 003


and solid waste, where the waste of one species is used as an input for another.

For instance, aquaponics, itself in its commercial infancy, utilises dis-solved waste products for growing plant crops, while Integrated Multi-Trophic Aquaculture (IMTA) can utilise dissolved wastes in growing algae, while solids can be utilised by detritivores or filter feeders, creat-

ing a balanced system with constant recycling and utilisation of by-products and developing multiple income streams.

Finally, technologies such as the up flow sludge bed manure denitrification reactor (USB-MDR) which allows for the reduction of make-up water supply for nitrate con-trol; reduction of nitrate-nitrogen discharge; reduction of energy consumption due to a low make up water supply flow and heat pro-duction by the bacteria biomass in the USB-MDR, concentration of the drum filter solids flow; reduction of the size/volume of the post treatment of the sludges and increased alkalinity production and allows a pH neutral fish culture operation, can provide the farmer with the opportunity to reduce exchange rates to just 0.15 percent in some cases.

The future of RASRAS is a set to become a very important part of global aquaculture, just as long as the potential pitfalls are avoided from the beginning of the thought process – it can be considered the ‘clean and green future of aquaculture’. In improving the efficiency and reducing the impact of RAS, research continues to seek to optimise feeds to reduce waste production and produce faeces with high water stability and optimal particle sizes, facilitating the clean-ing process. Additionally, new technologies are being developed to optimise the nitrogen removal from the systems.

One of them, ANNAMOX – a trademark for an anaerobic ammonium oxidation process

owned by Paques - allows the direct conversion of total ammonia nitrogen into nitrogen gas under anaerobic conditions, helping to achieve 99 percent recycling in sea water systems. Moreover, as highlighted previously, energy reuse, optimising and developing energy saving equipment and using alternative energy sources are also helping in developing RAS into more sustainable and environmental friendly practice, governed by standards of best practice as well as economical drivers. The state of the art as it stands, coupled with the improvements which

are happening and will occur, will undoubtedly see RAS, with its defin-ing 10 percent or less water exchange and circulated water, develop considerably in the coming years.

www.pontusresearch.com www.pontusaqua.com

References available on request

"With concerns being raised about the impacts and safety of open water cage and

pond farming, the spotlight has begun to fall upon more sustainable and environmentally

friendly methods for raising fish"

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Fusion MarineInnovation and service to the global aquaculture sector



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