Skimmers in recirculation systems

Effec­ti­ve water tre­at­ment in aquacul­tu­re can­not do without the work of bac­te­ria, becau­se in spe­cial­ly built bio­fil­ters they often con­vert toxic excre­ments of the fish into ani­mal and envi­ron­ment­al­ly friend­ly sub­s­tan­ces. Examp­les are the pro­ces­ses of nitri­fi­ca­ti­on and deni­tri­fi­ca­ti­on. Howe­ver, if bac­te­ria are pre­sent in lar­ger num­bers in the bea­ring tank, they can cau­se unde­s­i­ra­ble side effects such as dete­rio­ra­ti­on of water qua­li­ty or the occur­rence of dise­a­ses. The­re­fo­re, in clo­sed recir­cu­la­ti­on sys­tems, mecha­ni­cal puri­fi­ca­ti­on sta­ges such as the skim­mer are used in addi­ti­on to bio­lo­gi­cal fil­ters. The pro­te­in skim­mer uses mecha­ni­cal and bio­che­mi­cal pro­ces­ses to ren­der the bac­te­ria harm­less and remo­ve them from the water circuit.
How does the skimmer work?

The skim­mer uses the flota­ti­on pro­cess to remo­ve smal­lest par­ti­cles and bac­te­ria. During flota­ti­on, very fine gas bub­bles are intro­du­ced in the bot­tom area of the device. It app­lies that with hig­her salt con­tent of the water finer gas bub­bles are for­med. Only from a salt con­tent of about 1.2% the use of a skim­mer makes eco­no­mic sen­se. The advan­ta­ge of finer gas bub­bles is the com­pa­ra­tively lar­ger reac­ti­ve sur­face. Both the­se fine gas bub­bles and the bac­te­ria are electri­cal­ly char­ged on their outer sur­faces and the­re­fo­re stick tog­e­ther. At the same time, the gas bub­bles in the water of the reac­tion cham­ber rise upwards due to their buoyan­cy and ther­eby trans­port the atta­ched par­ti­cles. By tape­ring in the head area of the reac­tion cham­ber, the gas bub­bles are collec­ted at the water sur­face and a foam is crea­ted. This foam pas­ses over the so-cal­led foam pot, wher­eby the bac­te­ria are remo­ved from the water cir­cuit tog­e­ther with the gas bub­bles. The foam collects in a chan­nel and col­lap­ses the­re over time. What remains is a sludge which is rin­sed out as was­te­wa­ter and thus con­tri­bu­tes to the loss of water in recir­cu­la­ti­on systems.

Inac­ti­va­ti­on of bac­te­ria by ozone

The effect of flota­ti­on can be impro­ved by adding ozone (O3). Ozone is pro­du­ced as requi­red in the so-cal­led ozone gene­ra­tor. The demand is main­ly based on the dai­ly amount of feed. In the ozone gene­ra­tor ozone (O3) is pro­du­ced from the oxy­gen (O2) in the ambi­ent air by means of high-vol­ta­ge elec­tro­des and the resul­ting electri­cal dischar­ge. The use of ozone sup­ports the hygie­niz­a­ti­on of the water in recir­cu­la­ti­on sys­tems in two ways:

  1. Ozone is a very reac­ti­ve sub­s­tance and che­mi­cal­ly breaks the bac­te­ri­al shell, kil­ling the bacteria.
  2. The sub­s­tan­ces from the insi­de of the bac­te­ria lead to a bet­ter foam for­ma­ti­on, wher­eby more par­ti­cles can be remo­ved at the same time.

During its reac­tion, the ozone decom­po­ses back into oxy­gen so that no resi­du­al sub­s­tan­ces remain in the water.

Tas­te advan­ta­ges through skimming

The instal­la­ti­on of a skim­mer in aqua­far­ming sys­tems brings not only clear water and the asso­cia­ted health aspects for the fish. It has also tas­te advan­ta­ges for the end pro­duct. Fish farms – both in ponds and indoor sys­tems – often have an off-fla­vor. This ear­thy, mus­ty tas­te is cau­sed by geos­min. Geos­min is pro­du­ced by cer­tain micro-orga­nisms and is the­re­fo­re often asso­cia­ted with tur­bid, par­ti­cle- or bac­te­ria-con­ta­mi­na­ted water. Fish with off-fla­vor are not par­ti­cu­lar­ly appe­aling in tas­te. The easiest way to remo­ve the off-fla­vor is to keep the ani­mals in sepa­ra­te tanks for several days or weeks, usual­ly with a con­ti­nuous high sup­ply of fresh water and without the addi­ti­on of food. A pro­cess which is very time- and resour­ce-inten­si­ve and which hides the usual­ly rather unfa­vor­able living con­di­ti­ons. The use of a skim­mer is the­re­fo­re an attrac­ti­ve alternative.

Conclusion

In the SEAWATER Cube we use the ozone-sup­por­ted skim­mer tech­no­lo­gy, which remo­ves not only bac­te­ria but also geos­min. Fish always swim in clear, almost uncon­ta­mi­na­ted water and can the­re­fo­re be taken direct­ly from the pro­duc­tion tank and pro­ces­sed without any advan­ce plan­ning or hol­ding out. This redu­ces stress for the ani­mals, saves working time and pro­du­ces the tas­tiest pos­si­ble end pro­duct. In addi­ti­on, ill­nes­ses and the use of medi­ca­ti­on are com­ple­te­ly avoided, pro­vi­ding the con­su­mer with a hig­her qua­li­ty food pro­duct and saving valu­able raw mate­ri­als such as ener­gy and water. Through the com­bi­na­ti­on with our bio­lo­gi­cal fil­ter pro­ces­ses, we achie­ve a total water recy­cling rate of 99%, so that only 1% (= 500 l) of was­te­wa­ter is pro­du­ced per day.

Refe­ren­ces:

— Image source: SEAWATER Cubes
— Wil­helm, S.: Was­ser­auf­be­rei­tung – Che­mie und che­mi­sche Ver­fah­rens­tech­nik. 7., aktua­li­sier­te und ergänz­te Auf­la­ge; Sprin­ger-Ver­lag Ber­lin Hei­del­berg, 2008.
—  Schwis­ter, K.; Leven, V.: Ver­fah­rens­tech­nik für Inge­nieu­re. 2., aktua­li­sier­te Auf­la­ge; Carl Han­ser Ver­lag Mün­chen, 2014.
—  Tim­mons, M., Guer­dat T., Vin­ci B. (2018) “Recir­cu­la­ting Aquacu­lu­re”. Itha­ca, NY.

 

Newsletter abonnieren

Du möchtest regelmäßige Updates zu SEAWATER Cubes erhalten? In unserem monatlichen Newsletter informieren wir zu aktuellen Themen und Entwicklungen rund um unser Unternehmen. Außerdem warten spannende Fachbeiträge zum Thema Aquakultur sowie exklusive Informationen zu Veranstaltungen auf Dich.

Vielen Dank! Du hast Dich erfolgreich für unseren Newsletter angemeldet.