The EU-funded DeammRecirc project is looking to find innovative solutions for aquaculture waste treatment that may reduce the costs of ‘recirculation aquaculture systems’ (RAS) that purify and reuse the water in fish farm tanks.
RAS technology reduces the flow of harmful chemicals such as nitrates into the environment, in particular into rivers and seas. It achieves this by converting them into harmless nitrogen gas which is released into the atmosphere.
But according to the DeammRecirc team, the problem with current practice is that it does not go far enough. They suggest that the end point of the fish-farming process should restore nitrogen to the atmosphere as harmless nitrogen gas, rather than letting it accumulate as a pollutant.
So the partners involved in the project have adapted an existing ‘deammonification’ technology, used successfully in the waste water treatment industry, to the particular needs of RAS aquaculture.
A first step for the partners was to create an ‘anammox’ bacterial culture that could convert ammonia and nitride to nitrogen in fresh and salt-water environments.
Then in a test reactor, waste water and sludge underwent a nitrification pre-treatment that partly converted the ammonia into nitrite. The effluent was then passed to the main anammox reactor containing the sludge and converted to nitrogen gas through bacterial action.
By the end of the project, the technology had undergone successful tests using pilot plants. In one, which was in operation for ten months, very high anammox activity was observed.
Partners are now working on further developing DeammRecirc’s technology with the aim of creating commercial applications for the aquaculture sector.
They expect that a fully developed and automated technology will reduce production costs, have a lower carbon footprint, reduce the levels of nitrates released to the environment and reduce the extraction of clean water.
The technology is also expected to give the partners a competitive advantage in the rapidly growing global markets for farmed fish products, including the South African partner, the Marine Finfish Farmers Association of South Africa, which plans to implement the technology further.