The effect of algal and bacterial filters on sea water quality during closed system culture

Abstract

The potential of using filamentous algae for biological filtration in closed culture systems was tested by comparing water quality changes in bacterial and algal filtration systems over a two month period. Juvenile Penaeus indicus Milne Edwards were cultured in 125–1 recirculation systems and periodic analyses of inorganic nitrogen compounds (ammonia, nitrite and nitrate), total inorganic carbon, oxygen, major cation and trace metal concentrations were made. In both the algal and bacterial filtration systems, no significant changes occurred in the Ca ^{+ +}, Mg ^{+ +}, Na ⁺and K ⁺, and trace metal concentrations (Cu, Fe, Zn, Mn and Co). Depletion of inorganic carbon due to nitrification occurred in the bacterial filtration systems, whereas in the algal filtration systems inorganic carbon increased. An explanation for the latter occurrence is offered. The presence of algae did not give rise to oxygen shortages during periods of darkness. Although the filamentous algae used showed a reduced ability to take up nitrite, the build-up of ammonia and especially nitrate was effectively curbed. One of the only disadvantages of algal filtration appeared to be the lack of mechanical filtration of the water afforded by this method.