The Israeli Journal of Aquaculture - Bamidgeh 54(2), 2002
The Annual Dan Popper Symposium


Micha Eshchar, Michael Fediuk, Noam Mozes*

Israel Oceanographic and Limnological Research, National Center for Mariculture, P.O.Box 1212, Eilat 88112, Israel


A super-intensive recirculating aquaculture system (RAS) was developed at the National Center for Mariculture in Eilat, Israel. Fish density, which reaches 70-90 kg/m³ in super-intensive systems, is limited by high toxic CO2 concentrations. In such a system (which is enriched with pure oxygen), CO2 accumulates, reducing the pH of the water.The decrease in pH could also be attributed to carbonate alkalinity consumption during nitrification, when a nonvolatile carbon species (bicarbonate) is changed into a volatile form (CO2). Further aeration in the biofilter removes CO2, reducing the total carbonate carbon CT. Water pH dominates the CO2 fraction of CT in an inverse correlation.

In our system, paddlewheel aerators were used to strip CO2. The transfer coefficient (KLa) for CO2 stripping by a paddlewheel (1 kw) was measured. At an average CO2 concentration of 8 mg/l, the stripping was 1170 g CO2/h (28 kg/d). In seabream (Sparus aurata) culture, this enables a feeding rate of 40 kg feed/d. The cost of energy to remove 1 kg CO2 is estimated at $0.06.

Mass budgets showed that the main CO2 sink was stripping by paddlewheel aerators. The main carbonate alkalinity source was makeup sea water, while sinks were nitrification and water discharge. pH values were low (6.7-6.9). CO2 concentrations were not accordingly high, due to the low CT.

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