High-rate algal pond
treatment for water reuse in an integrated marine fish recirculating system:
effect on water quality and sea bass growth
G. Deviller, C. Aliaume, M.A.F. Nava, C. Casellas,
J.P. Blancheton-2004
Aquaculture, 235(1-4): 331-344
Abstract:
A high-rate algae pond (HRAP) was tested as a second
loop of water treatment in a recirculating fish rearing system to reduce
water requirements and nutrient discharge levels. Three duplicated groups of
sea bass (mean initial body weight 35±11 g) were reared under different
system conditions (flow-through system, recirculating system and
recirculating system with HRAP) for 1 year. Fish survival rate was higher in
the system with HRAP, and their mean body weight was statistically higher (p<0.05)
during the month of maximal climatic conditions for algae photosynthesis.
After 266 days of experiment, mean fish weight was significantly higher (p<0.05)
in the flow-through system than in the recirculating systems. Final fish
weight was 15% higher in the flow-through system than in recirculating
systems and was related to a higher daily-ingested food. The comparison of
mean annual nutrient concentrations in the recirculating systems gives a
statistically significant reduction of 25% of nitrogen (p<0.01)
and 9% of phosphates (p<0.01) due to the HRAP. Absorption of
nitrate form is responsible for nitrogen removal and is related to climatic
conditions for algae growth. The phosphate precipitation at high pH (above
8) was not considered. The maximal removal rates were 0.5±0.2 g N m−2
day−1 and 0.03±0.02 g P m−2 day−1
for nitrates and phosphates, respectively, and were obtained during the
optimal climatic conditions and the shortest algae harvesting frequency.
These results are favourable to complete reuse of the HRAP treated water,
all year long, in the recirculating rearing systems. In order to improve
nitrate and phosphate removal rates, a periodic harvesting of algae is
necessary and a higher water inflow in HRAP should partly make up for
inorganic carbon depletion in high nitrate and phosphate effluents.
(Département Sciences de l'environnement et Santé
Publique, UMR 5556, Faculté de Pharmacie, 15, av. Charles Flahault 34060,
Montpellier, France, e-mail of J.P. Blancheton: jpblanch@ifremer.fr)