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RAS tech: Engineering the future

First trialled for carp in Japan in the 1950s, recirculation aquaculture systems (RAS) underwent a revival in the 1980s as technological advances made them more viable, and have become increasingly popular ever since. Fish Farming International looks at their application today and the advances giving the technology a growing future.

According to the Lux Report, “Blue Revolution: The Fast-growing $7.2 Billion Water Treatment Opportunity in Aquaculture” produced in February 2015, RAS production has increased considerably in the past 15 years, as aquaculture has grown by an exceptional 8.3 percent per year.

RAS systems currently account for 6 percent of total production in China, and 12 percent in both the United States and Europe. The report predicts that by 2030, aquaculture will meet 62 percent of global fish demand, 40 percent of which will be supplied by advanced recirculating systems. This represents a $13.3 billion market for water treatment, growing from $7.2 billion today.

According to its author Abhirabh Basu, China is expected to become a major user of RAS technology for high-volume lower-value species, whilst Europe will see more marine species grown in RAS systems. Producers in North America and Canada are also expected to turn increasingly to high-efficiency, biosecure land-based fish farming, as the debate continues on the environmental impacts of open aquaculture.

Research institutes in Nordic countries including the Denmark Technical University (DTU Aqua) and Nofima in Norway, which currently operates the largest RAS system in Europe, are working to improve the efficiency and environmental integrity of these systems.

According to Jacob Bergnballe, business director of land based aquaculture for Akva Group, one of the world’s largest providers of RAS systems, the major benefit of using recirculation technology is that it provides stable, environmentally controlled conditions for rearing fish in terms of temperature, oxygen content, pH and overall water quality. This in turn promotes greater fish health, better quality, superior growth rates, improved feed conversion ratios, reduced disease outbreaks and lower use of therapeutants. There is also a considerable advantage in being able to site a farm anywhere.

In treating large volumes of low-grade wastewater, recirculating systems use 80 percent less water than conventional pond cultures. Treatments are used to control biological oxygen demand, nutrients and dissolved oxygen, which enable production to be boosted per unit of water.

Mechanical filters remove solid particles over 50 microns, whilst bio filters remove organic matter and ammonia products, and micro particle filters remove suspended particles in the 2-50 micron range.  Also essential are UV filters, which control bacterial dynamics and ecto-parasites, and CO2 strippers, which remove CO2, nitrogen and sulphide residues.

Traditional systems recirculate 90 percent of the water and return the treated remainder to the environment. Some of the latest systems now offer zero-discharge suitable for both freshwater and marine fish, with water addition limited to compensate for evaporation losses only.

However, Basu forecasts that as systems get larger and more is demanded of them, traditional treatment technology is unlikely to provide the quality of water necessary to support delicate, densely packed fish populations.“The sector is definitely overdue for more innovation and this has led to wastewater companies moving into the game, leveraging their expertise to tap into the RAS market,” he said.

For example, Kruger Kaldnes, a Veolia subsidiary, has adapted its traditional moving bed biofilm reactor for aquaculture, whilst among promising start-ups, BioGill uses vertical membrane sheets, and BioFishency has built an “all-in-one” plug-and-play solution.

From small fish to large…

Bergnballe explained that current use of RAS is very good for small fish and can give them an excellent start in life.

“There are hatchery and fry systems all over the world using this technology, which is where I see its strength developing,” he said. “It’s not just about the technology though; time, effort and skill put in to give fish the best conditions when they are young, results in healthy juveniles that experience fewer problems during growout. In the salmon sector we are increasingly seeing smolts raised on land in RAS, before being put to sea,” he said.

RAS technology for land based fattening farms to produce market size fish is more advanced in the freshwater sector, although there is a growing number of large RAS units in the United States, Russia, Canada and the Nordic States growing salmon to commercial size. However, these still need to prove that they are commercially viable in the long term, particularly for production targets over 500 tonnes per year.

Unfortunately there is a substantial global track record of company failures when using RAS, for reasons including challenges of economic viability and the difficulty of operating systems at commercial scale. It is expected that the economic barrier to using RAS will gradually be lowered as technology improves and economies of scale are realized, but this is still some way off.

It is particularly important for the ‘fish farms of the future’, about which there is much current speculation. These will be installed on the edge of large cities, to enable the population to have fresh fish on the doorstep. Their close proximity to market will also significantly reduce the costs of distribution, and therefore the overall cost of growing a fish from egg to plate.

It is expected that the economic barrier to using RAS will gradually be lowered as technology improves and economies of scale are realized, but this is still some way off.

“In the seabass and seabream sector, there is increasing use of recirculation systems for growout and it has long been common for trout to be farmed from egg to plate in this way. In the Middle East, projects are being developed for seabream, grouper and barramundi. For larger-scale production of tilapia, which is particularly needed in China, we need to make the systems bigger and cheaper to make them attractive and profitable,” said Bergnballe.

Akva and its competitors are looking at options to improve performance and lower cost, and are finding that as well as mastering the technology, they are having to become experts in managing major civil engineering projects.

Specialist feed…

Feed used in most recirculation systems has traditionally been the same commercial diets produced for cage or pond production systems, with minor or no adjustment. However, the major feed manufacturers are now producing more dense, RAS specific diets, and these are increasingly playing a larger role in their R&D efforts.

Louise Buttle, Senior Scientist at EWOS Innovation, explained that RAS feed has to be high performing, with a precise amino-acid profile, use quality raw materials to ensure high digestibility, and have optimal physical characteristics to make them attractive to the fish.

BioMar’s Executive Vice President Niels Alsted spoke at a recent workshop about the special challenges of formulating feed for RAS.

“In order to optimize both fish growth and biofilter performance, it is advantageous to make as few changes as possible in the diet over time, but volatile raw material markets impose flexible use of raw materials, with more frequent changes in the formulation of diets. This calls for intensive research into the effect of substitution, not just on a nutritional level, but also on the impact it has on biofilter performance and water parameters,” he said.

BioMar’s latest generation of Orbit feed for RAS reduces the nitrogen load and the amount of organic matter in the water column, and makes removal of faeces in sludge cones and mechanical filters easier. This in turn improves the growth conditions for the fish, increases the capacity of the biofilter, and allows for larger scale production.

RAS technology has come a long way over the last 30 years, but it is still at a relatively early stage of development for large-scale commercial grow-out, particularly of marine species. However, with a growing global population needed fish protein and the potential for success continuing to attract investment in R&D, a major breakthrough and success can be only just around the corner.