ammonia, nitrate and nitrite has been performed in bioreactors using denitrifying bacteria (2-5) and polyvinyl alcohol (PVA)immobilized photosynthetic bacteria with denitrifying activity (6). The authors noted in a previous study that the purification of an aquarium for breeding fish (carp) could be accomplished using a simple circulating filtration system that was packed with alginate gel immobilized photosynthetic bacteria with denitrifying ability (7).