Performance
of a closed recirculating system with foam separation, nitrification and
denitrification units for intensive culture of eel: towards zero emission
Y. Suzuki, T.
Maruyama, H. Numata, H. Sato, M. Asakawa-2003
Aquacultural Engineering, 29(3-4): 165-182
Abstract:
The development of a closed recirculating aquaculture
system that does not discharge effluents would reduce a large amount of
pollutant load on aquatic bodies. In this study, eel were reared in a closed
recirculating system, which consisted of a rearing tank, a foam separation
unit, a nitrification unit and a denitrification unit. The foam separation
unit has an inhalation-type aerator and supplies air bubbles to the rearing
water. The growth of eel, which were fed a commercial diet, was
satisfactory, with gross weight increases of up three times in 3 months. The
survival rate under the congested experimental conditions was 91%. The foam
separation unit maintained oxygen saturation in the rearing water at about
80%. Furthermore, fine colloidal substances were absorbed on the stable foam
formed from eel mucus and were removed from the rearing water by foam
separation. Ammonia oxidation and the removal of suspended solids were
accomplished rapidly and simultaneously in the nitrification unit. The
ammonia concentration and turbidity were kept at less than 1.2 mg of N
per litre and 2.5 units, respectively. When the denitrification process was
operated, nitrate that accumulated in the rearing water (151 mg of N
per litre) was reduced to 40 mg of N per litre. The sludge was easily
recovered from the nitrification and denitrification tanks, and the
components were found suitable as compost. Based on these results, the
intensive aquaculture of freshwater fish such as eel can be achieved using a
closed recirculating system without emission.
(Department of Civil and Environmental Engineering,
Faculty of Engineering, Miyazaki University, Miyazaki 889-2192, Japan,
e-mail: suzuki@civil.miyazaki-u.ac.jp)