Abstract:

In order to produce commercial nitrobacteria for the removal of nitrites in aquaculture water, the sequential experimental design including the Plackett-Burman design, the factorial design, the steepest ascent method and the central composite design was used to optimize the fermentation medium of nitrobacteria isolated from a shrimp pond. The optimal composition of the medium was determined as 1.86 g/L NaHCO₃, 2.04 g/L NaNO₂, 0. 2 g/L Na₂CO₃, 0. 2g/L NaCl, 0. 1 g/L KH₂PO₄, 0. 1 g/L MgSO₄.7H₂O , and 0. 01 g/L FeSO₄.7H₂O. The results indicate that, by using the nitrobacteria cultured with the optimal medium, the nitrite oxidation rate increases from 580. 7mg/（g · d） to 859.5 mg/（ g · d）, and the nitrites in both the simulated and the field aquaculture systems can effectively be oxidized.

Key words: nitrobacterium, culture medium, optimization, sequential experimental design, Plackett-Burman design, steepest ascent method, central composite design