Nitrification and Denitrification

In a recir­cu­la­ting aquacul­tu­re sys­tem, the­re are gene­ral­ly accu­mu­la­ting resi­dues in the water through the animal’s excre­ti­on and through unea­ten feed. One pos­si­bi­li­ty to keep the water of the faci­li­ty clean, is to cla­ri­fy it with freshwa­ter. Having a salt­wa­ter faci­li­ty, this can beco­me quite cost-inten­si­ve, becau­se of the new­ly inser­ted freshwa­ter also spe­cial sea salt has to be added and this is expen­si­ve. The­r­e­fo­re, the goal is to exch­an­ge as less water as pos­si­ble. The SEAWATER Cube only exch­an­ges up to 1% of the water per day. This equa­tes to just 700 liters and is com­pared very litt­le to other recir­cu­la­ting sys­tems (they nor­mal­ly exch­an­ge 10% of the dai­ly water). This nee­ded addi­ti­on of water occurs due to the water loss through the puri­fi­ca­ti­on of cer­tain fil­ters and through eva­po­ra­ti­on on the water sur­face. So, how exact­ly does our Cube mana­ges to add mere­ly such a small amount of freshwater?

Within the SEAWATER Cube num­e­rous fil­ter com­pon­ents make sure that the water is fresh and clean. One of the­se com­pon­ents is the aero­bic (func­tions with oxy­gen) bio­fil­ter, the so cal­led “nitri­fi­ca­ti­on”. This pro­cess within con­verts toxic ammo­ni­um, which is dis­sol­ved in the uri­ne of the fish, into nitra­te. The lat­ter is in fact less toxic than ammo­ni­um, but with our low water exch­an­ge rate nitra­te would also accu­mu­la­te and put the animal’s wel­fa­re at risk. That is the reason ano­ther fil­ter is instal­led in the tre­at­ment pro­cess of the Cube: within the anae­ro­bic (func­tions only wit­hout oxy­gen) bio­fil­ter, the used pro­cess cal­led deni­tri­fi­ca­ti­on con­verts nitra­te into nitro­gen. In all the­se bio­fil­ters, bac­te­ria are the essen­ti­al workers. To ensu­re their pre­sence and cul­ti­va­ti­on, tho­se fil­ters are fil­led with spe­cia­li­zed bio­fil­ter pel­lets. Made out of pla­s­tic mate­ri­al, they offer a very lar­ge sur­face gene­ra­ted through spe­ci­fic struc­tures. The bac­te­ria adhe­re to the­se sur­faces as a bio­film and the­re­wi­th do not float free­ly in the water any­mo­re. During two par­al­lel exe­cu­ted steps, they com­ple­te­ly con­vert the nitra­te into gas­eous nitro­gen, which can easi­ly escape into the air.

This kind of com­bi­na­ti­on of nitri­fi­ca­ti­on and deni­tri­fi­ca­ti­on has been known in the was­te­wa­ter tre­at­ment plant tech­no­lo­gy for a long time. Howe­ver, ven­ti­la­ted and non-ven­ti­la­ted sec­tions are cou­pled the­re. Within freshwa­ter aquacul­tu­re, this con­cept does not exist. For the­se sys­tems, it is easier and simul­ta­neous­ly lower cost to just exch­an­ge the water ins­tead of ope­ra­ting ano­ther fil­ter. Nitri­fi­ca­ti­on and deni­tri­fi­ca­ti­on are though essen­ti­al for the sta­ble and eco­no­mic ope­ra­ti­on of a salt­wa­ter aquacul­tu­re sys­tem like the SEAWATER Cube . While plan­ning and con­s­truc­ting the fil­ter steps, the­re have various para­me­ters to be coor­di­na­ted, so that the bac­te­ria work as plan­ned and com­ple­te­ly con­vert the toxic sub­s­tances. It beco­mes appa­rent, that the ope­ra­ti­on of the­se two bio­lo­gi­cal fil­ters con­ta­ins a lot of exper­ti­se as inten­si­ve rese­arch, expe­ri­ence of many years and tech­ni­cal­ly matu­re automation.

Further informationen about the SEAWATER Cube

Check out more facts about our sys­tem and the technology.


van Rijn, J.; Tal, Y.; Schrei­er H. J.: Deni­tri­fi­ca­ti­on in recir­cu­la­ting sys­tems: Theo­ry and appli­ca­ti­ons. Else­vier B.V., 2005.
Lom­pe, D.; Wies­mann, U.: Bio­lo­gi­sche Deni­tri­fi­ka­ti­on nitrat­hal­ti­ger Abwäs­ser und Grund­wäs­ser. VCH Ver­lags­ge­sell­schaft mbH, Wein­heim, 1991.
Lee, P. G.; Lea, R. N. et al.: Deni­tri­fi­ca­ti­on in aquacul­tu­re sys­tems: an exam­p­le of a fuz­zy logic con­trol pro­blem. Else­vier Sci­ence B.V., 2000.
Soares, M. I. M.: Bio­lo­gi­cal deni­tri­fi­ca­ti­on of ground­wa­ter. Klu­wer Aca­de­mic Publishers, 2000.

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