In 1994 we delivered a RAS to a University in the US (North Carolina State University, NCSU), to be tested and compared with previous system they have examined. The system was 4 tanks each 5 m3, equipped with our then patented ECO-TRAP system for solids removal directly from the tank. The system had a water exchange rate of 10 % per day (99.5 % by flow through the tank). The test was carried with Tilapia, and the results showed 40-50 % better growth in our system compared to previous tested systems. NCSU conclude in their publication that this is due to the better water quality made by the ECO-TRAP system. This is published in international journals and conferences (ref. Dr Tom Losordo, NCSU).
In 1995 we supplied a RAS for Atlantic Salmon (smolt) to Nutreco ARC, Lerang research station, a system of 6 tanks each 5 m3, and the system was used in the seasons of 1996 and 1997, from start-feeding (0.15g) to smoltification ( 50-70 grams) 55 000 pcs.
Their results show clearly that it is possible to produce a smolt ready for sea the first spring, using recirculation and control of temperature. Nutreco also ordered a system for seawater, ø8m tank, were the fish were kept up to 1 kg, with good growth and survival. Ref. operational manager Arne Berge.
1994 - 1996
Test of own system for recirculation (RAS) at North Carolina State University, USA
1995 - 1997
EU-funded project in 1995-1997 (EU Innovation program – development of recirculation system in aquaculture) – 2 commercial fish farms and 3 supplier companies and IFREMER.
1996 - 1998
Test of RAS in cooperation with JIFAS, Japan
2004 - 2005
Aquareg project in 2004-2005 with Isidro de la Cal Group, Luso-Hispana de Acuicultura S.L regarding use of new larvae tank for rearing og pollack.
2008 - 2009
Adapon, EU FRP7, 2008-2009, Development of an automatic process of in-house collection, storage and application of adaptive bacteria culture for fish farms (ADAPOND) and has received funding from Research Council of Norway (NFR) and Innovation Norway regarding its product development activity in several projects from 1993 – 2007.
Since 1998 AquaOptima has supplied commercial RAS world wide for different species, fresh and sea-water, warm and cold water.
Technical description of the technology
All experts from scientific institutions working with recirculation in aquaculture claim the necessity of control of solids as particulate organic matter. This is important to keep stable and good water quality with low levels of ammonia and nitrite.
AquaOptima has the most effective double drain system on the market, and the ECO-TRAP is documented to remove more than 90 % of settleable solids in flow-through system (98% of feed waste and 91 % of excrements), and ca 50 % of total suspended solids in RAS. (ref SINTEF and NCSU).
These particles are removed before the main effluent leaves the tank, which avoid that the large particles being crushed and creating a lot of smaller particles. This makes it possible to design RAS with less biofilter than other systems, and gives a more stable water quality. We have developed our own recirculation system based on this system for solids removal.
Microscreens have typical 50 -55 % efficiency, so a significant amount of organics is then passing to the biofilter. The biofilter will receive extra high loading of organics in periods of overfeeding, if there is no double drain system for solids removal in the tank.
The toxic ammonia excreted by the fish is reduced to nitrate in the biofilter, and this nitrification process is becoming less effective if the amount of organics coming to the biofilter is too high.
Use of solids removal directly from the tank makes it possible to design RAS with less biofilter. The figure below shows organic loading of biofilter in a system with and without ECO-TRAP.
(Numbers according to NCSU study).
Operational experience from RAS not having systems for solids removal in tank, show that high levels of ammonia can occur in periods with overfeeding, leading to mortalities.
Systems without solids removal from tanks are often designed with an extra biofilter with heterotrophic bacteria to reduce organic matter before nitrification. Such submerged biofilters must be cleaned regularly, by use of flushing pumps or manual cleaning.
AquaOptima has chosen processes in the recirculation system that are easy to operate and gives stable water quality. Correct feeding and regular cleaning of hoses from ECO-TRAP is what is needed to obtain a reliable system.
We started using trickling filters as biofilters, they are simple in operation and gives in combination with ECO-TRAP a stable water quality. These filters need however to be cleaned regularly, an operation most fish farmers like to avoid to have to do. For this reason we have since October 2007 entered into a cooperation with KrügerKaldnes AS (a subsidiary to Veolia) to use their Kaldnes™ moving bed process (MBBR).
They are the owner of the patented moving bed process, both the media and the process, and have many years experience of design and deliveries of such reactors for biofiltration of water, municipal and industrial waste water as well as for RAS. We offer now a biofilter solution based on moving bed process only.
To improve effect of microscreen and biofilter further we often add ozone to the effluent pipe before the microscreen, it helps coagulation of fine particles, reduces level of organics which gives improved nitrification, and reduces risk of periodical high levels of nitrite.
Experience from commercial RAS
Tiger Puffer Fish, Japan – The figure below show similar effect in farming of Tiger Puffer Fish in Japan, where bad conditions in sea cage farming effect the growth in a significant way. It shows that the fish in AquaOptima RAS became 1 kg after 13 months, while in sea cage the fish only reached 500 grams in same period, farmed by the same company. It clearly shows the effect of having stable temperature and water quality compared to the natural fluctuations that always occur in the sea.
Atlantic Salmon, Norway – AquaOptima RAS was installed at Aakvik Settefisk (Salmon smolt farm) in 2004 for one ø8m (100 m3) as test for evaluation of the use of RAS. After 2 seasons the farmer decided to rebuild the farm for all ø8m tanks outside. Summer 2006, 2 months after smolt release to the sea cages, they had an IPN disease in the sea. The fish was put in the cages in a way so they could separate the smolts coming from flow-through tanks and the tank with recirculation. According to survival registrations, the fish that came from tank with AquaOptima RAS had less than 50 % mortality of the fish coming from flow-through tanks (see table below).
This show that recirculation can be of advantage, because the tanks can be operated with sufficient water flow (independent of periods with droughts), and RAS is also creating a more stable water quality because variations in water quality due to rainfall and other conditions are avoided.