Abstract: Two artificial intelligence techniques, artificial neural network and genetic algorithm, were applied to optimize the fermentation medium for improving the nitrite oxidization rate of nitrite oxidizing bacteria. Experiments were conducted with the composition of medium components obtained by genetic algorithm, and the experimental data were used to build a BP (back propagation) neural network model. The concentrations of six medium components were used as input vectors, and the nitrite oxidization rate was used as output vector of the model. The BP neural network model was used as the objective function of genetic algorithm to find the optimum medium composition for the maximum nitrite oxidization rate. The maximum nitrite oxidization rate was 0.952 g NO₂^--N·(g MLSS)^-1·d^-1, obtained at the genetic algorithm optimized concentration of medium components (g·L^-1): NaCl 0.58, MgSO₄·7H₂O 0.14, FeSO₄·7H₂O 0.141, KH₂PO₄ 0.8485, NaNO₂ 2.52, and NaHCO₃ 3.613. Validation experiments suggest that the experimental results are consistent with the best result predicted by the model. A scale-up experiment shows that the nitrite degraded completely after 34 h when cultured in the optimum medium, which is 10 h less than that cultured in the initial medium.

Key words: BP neural network, genetic algorithm, optimization, nitrite oxidization rate, nitrite-oxidizing bacteria

摘要： Two artificial intelligence techniques, artificial neural network and genetic algorithm, were applied to optimize the fermentation medium for improving the nitrite oxidization rate of nitrite oxidizing bacteria. Experiments were conducted with the composition of medium components obtained by genetic algorithm, and the experimental data were used to build a BP (back propagation) neural network model. The concentrations of six medium components were used as input vectors, and the nitrite oxidization rate was used as output vector of the model. The BP neural network model was used as the objective function of genetic algorithm to find the optimum medium composition for the maximum nitrite oxidization rate. The maximum nitrite oxidization rate was 0.952 g NO₂^--N·(g MLSS)^-1·d^-1, obtained at the genetic algorithm optimized concentration of medium components (g·L^-1): NaCl 0.58, MgSO₄·7H₂O 0.14, FeSO₄·7H₂O 0.141, KH₂PO₄ 0.8485, NaNO₂ 2.52, and NaHCO₃ 3.613. Validation experiments suggest that the experimental results are consistent with the best result predicted by the model. A scale-up experiment shows that the nitrite degraded completely after 34 h when cultured in the optimum medium, which is 10 h less than that cultured in the initial medium.

关键词: BP neural network, genetic algorithm, optimization, nitrite oxidization rate, nitrite-oxidizing bacteria