Energy efficiency and system management in Ireland’s first pilot scale marine recirculating aquaculture system (RAS)

Jeroen van der Vlugt, Engineer, Luke Wilson, Production Manager and David O’Neill, General Manager at Bantry Marine Research Station talk to Martin Johnson (AquaTT, EWEAS project) about Ireland’s first marine recirculating aquaculture system, the challenges and benefits associated with running a closed system and the areas where water and energy efficiency gains are being made as the system enters its third season of lumpfish production.

In the southwest corner of Ireland, Bantry Marine Research Station (BMRS) perches on the edge of the hilly Sheep’s Head peninsula, overlooking Bantry Bay and the mountains of the spectacular Beara Peninsula to the North. It is in this idyllic setting that Ireland’s first marine recirculating aquaculture system has been developed by the BMRS team to research lumpfish efficacy for sealice control in the Irish and Scottish salmon farming industry. The scientific complexity of the system is striking. Tanks, pumps, sumps and rigs for degassing, cleaning and filtering the water make for an impressive demonstration of high-tech aquaculture.  The facility is lit by low power blue LED lights to reduce stress by simulating the lumpfishes’ natural habitat and also saving energy in the process.

BMRS’s first studies of lumpfish production to provide a natural means of lice control in salmon farms were in a traditional flow-through system. BMRS decided to convert the existing incubation and hatchery systems to a recirculating system with minimal new seawater inputs and to develop a pilot RAS system for growing the juvenile fish to deployment size. Luke explains that biosecurity is of paramount importance during the production of any fish species. RAS technology allows for a considerably greater biosafety margin, by reducing the amount of makeup water supplying the facility to a minimum. In addition, lumpfish are a cold-water species and RAS allows for greater control of the environment, including water temperature.

Juvenile lumpfish in a nursery tank at BMRS

System management and stability

Lumpfish thrive in water at 10 to 12 ºC  and the temperate climate in Ireland is well suited to maintaining temperatures around this range. No heating is needed in winter but a 60 kw chiller unit kicks in in the warmer months to keep temperatures from getting too high. This is probably largest energy cost annually for the system.

Chemical stability is also a major consideration for recirculating aquaculture systems. Food is respired to carbon dioxide, depleting oxygen and lowering the pH of the tanks in the process. The fish excrete ammonia which is poisonous if allowed to accumulate. CO_­2 is removed by degasser systems, in which recirculated water is sprayed through nozzles into a counter-flow of clean air, which strips our the carbon dioxide.  Additionally, small amounts of sodium hydroxide solution is slowly pumped into the systems after this stage, at the correct rate to neutralise the remaining acidity. Ammonia is removed by bioreactor and biofilter systems in which nitrifying bacteria oxidise the ammonia to relatively harmless nitrate. Oxygen is injected into the systems from an oxygen generator system that makes oxygen from air and is added to the degassing chamber.    Oxygen is also added to the tanks directly through diffusers if needed.  As stocking density, temperature or other variables change, the pressures from the above processes change. A comprehensive automated physico-chemical monitoring system, automated control of  oxygen injection and an alarm system notifying on-call staff of any deviation of pH, oxygen and other parameters from ideal values, gives valuable insights into the state of the system at all times and provides an early warning system to protect fish health.

The ammonia-removing bioreactors and drum skimmers which keep the smaller hatchery and incubation system clean.

‘The systems are dynamic and skill and experience is needed to keep them stable’ says Jeroen. ‘As the team gets to know the systems better we are able to anticipate problems before they arise, thanks to the real-time monitoring giving us rapid feedback. Training is essential for the team to have the necessary knowledge and understanding to maintain the system in a stable state’. Regular rounds with checklists are also key to ensuring every aspect of the system is working optimally and dealing with any issues rapidly as they arise. Luke says that they greatly value the knowledge and expertise of their staff. ‘It’s a complex live biological system that we endeavour to keep in balance and you need to know more than the protocols,’ he says.  ‘Without the hands on expertise we have in our staff from systems management to fish husbandry and our animal-first approach we could not produce the exceptional quality lumpfish that we do’.

Under normal conditions the facility runs as a ‘nearly closed system’ with only a small fraction of the water being replaced on each circulation through the system. In situations where algal blooms or pathogens, or storm-driven turbidity in the incoming seawater become problematic the system can be completely isolated from the seawater input for days at a time. Jeroen explains that alterations need to be made in order to keep the system within bounds under these circumstances:  ‘We need to reduce the feed input to reduce oxygen demand, acidification and ammonia increase, so fish growth slows temporarily, but we are able to protect the fish and the facility from damaging or deadly events with this approach’. As the oceans warm and storms and harmful algal blooms increase in frequency, the ability to isolate land-based aquaculture systems from such events will be of increasing importance.

System optimisation for energy efficiency

Optimising the system for energy efficiency is important to ensure that the operation is profitable. However, the most cost effective gains in efficiency have not been in the most obvious places. Expensive pumps with higher efficiencies do not survive long enough in the salty environment to payback in energy savings before they need replacement. In particular it is the exterior and ancillary components that fail due to corrosion. ‘We have backup pumps in the system and new and reconditioned pumps on the rack ready to go’ Jeroen says. Failure of the pumps is not an option!

On-site renewables are currently not being considered. The location, with craggy hills to the south and west, the prevailing wind direction, mean that wind power is probably not feasible. Solar PV would in theory work well as the peak in generation would coincide with the period of maximum consumption as the chiller runs in the summer. However, initial outlay and payback time is too great be a spending priority until the system is more established. Better subsidy or support loans would help to make an earlier investment in renewables here.

Major energy efficiency gains in the system were found in relation to management of the stock levels.  ‘As the stocking density increases, the system has to work harder to maintain stable conditions’ Jeroen says. ‘So it’s most important to manage the flow of lumpfish out of the facility to our research partners in such a way that we keep stocking density to a minimum’. As originally configured, oxygen became a limiting factor. The team solved this problem by using ‘oxygen cones’ in which supersaturated air from the oxygen generators is dissolved in the recirculated water before it is distributed to the tanks. This raises the baseline oxygen level and the requirement for direct bubbling to the tanks is significantly reduced. ‘This has significantly reduced the work being done by the oxygen generators.’ Jeroen tells me. ‘We’re saving energy and can achieve a higher stock capacity in our nursery system .’

Jeroen stands in front of the oxygen cones which have reduced energy usage and increased maximum stock density in the large nursery tanks.

Future improvements

The team are always looking to make improvements to the system and are very interested in making energy and water savings, both from a cost and an environmental impact point of view. On-site renewables, more efficient equipment and steps to insulate pipes and tanks are all being considered for future implementation. However, balancing the benefits against the payback time and up-front cost is an important consideration when margins are tight at the start of a new endeavour such as this and the ‘low hanging fruit’ is the obvious place to start.  One such opportunity is freshwater usage. The facility uses fresh treated water in washing down floors and surfaces and cleaning equipment. There are plans in development to build a large rainwater collection tank draining from the roof, to save water and money. ‘Saving water and energy in a cost-effective manner is a basic easy solution that solves supply issues and is sustainable’, says David O’Neill, GM of BMRS.

The lumpfish pilot facility demonstrates how a combination of technology, husbandry, and knowledgeable and skilled staff members conscious of sustainability can create an innovative project that benefits aquaculture and the environment sustainably, whilst being economically beneficial.   The future looks bright for the innovative facility BMRS have developed on Ireland’s wild west coast, who will begin trials on Wrasse, another cleaner fish, in the coming months.

One of the large nursery tanks

Further information

BMRS, originally a research outpost of University College Cork, is now an independent SME, leading innovations in the seaweed, shellfish and finfish aquaculture sector as well as conducting EU and nationally-funded scientific research across the marine, wild fisheries and aquaculture domains. For more information visit http://bmrs.ie

AquaTT is a not-for-profit SME providing leadership in scientific knowledge transfer and dissemination in the marine and aquaculture research sectors and also more broadly across the areas of environment, health, food and sustainable development. https://www.aquatt.ie

EWEAS is an EU ERASMUS+ project which focuses on enhancing knowledge and competence of professionals working with water and energy issues in the aquaculture sector. It aims to improve water and energy efficiency in aquaculture facilities by providing specialised training that includes improved management practices and environmentally safe and cost-effective solutions. To achieve this, EWEAS is creating an e-learning platform designed to upskill aquaculture workers with a knowledge on how to reduce excessive water and energy consumption, minimise ecological footprint, understand the different concepts of billing of energy supplies and perform self-assessments of their farms by ‘learning by doing’. For more information and to subscribe to the project mailing list please visit http://eweasproject.eu or email info@eweasproject.eu