Application of central composite design approach for optimization nitrate removal from aqueous solution by immobilized Pseudomonas putida

Optimal nitrite degradation by isolated Bacillus subtilis sp. N4 and applied for intensive aquaculture water quality management with immobilized strains

The toxicity of nitrite is an issue that cannot be overlooked in nitrogen pollution within aquaculture. A highly efficient bacterium capable of simultaneous nitrification and denitrification was screened from natto, and its 16S rRNA gene sequence was compared to existing records, confirming its identification as Bacillus subtilis sp. N4. The optimal conditions for nitrite degradation by B. subtilis sp. N4 were identified using response surface methodology as 167 rpm, pH 6.4, 1 g/8 mL feed, 0.6 OD600, and 30 °C, with a predicted 99 % nitrite removal efficiency. The B. subtilis sp. N4 demonstrated a maximum nitrite concentration tolerance of 60 mg/L, with μmax and Ks values calculated using a Monod model analysis of 1.67 mg/L/h and 0.29 mg/L, respectively. Immobilized B. subtilis sp. N4 could be reused for ten cycles while maintaining a nitrite degradation efficiency of >99 %, and retained a high nitrite-degrading ability after being refrigerated at 4 °C for three months. Immobilized B. subtilis sp. N4 effectively reduced ammonia nitrogen, nitrite, and nitrate concentrations in Nile tilapia aquaculture, maintaining them at consistently low levels. Therefore, free or immobilized B. subtilis sp. N4, with both nitrification and denitrification capabilities, has considerable potential for application in the aquaculture industry in the future.

Applying response surface methodology to optimize partial nitrification in sequence batch reactor treating salinity wastewater

In this study, the operation parameters of a partial nitrification process (PN) treating saline wastewater were optimized using the Box-Behnken design via the response surface methodology (BBD-RSM). A novel strategy based on the control of the carbon/nitrogen ratio (C/N), alkalinity/ammonia ratio (K/A), and salinity in three stages was used to achieve PN in a sequence batch reactor. The results demonstrated that a high and stable PN was completed after 50 d with an ammonia removal efficiency (ARE) of 98.37 % and nitrite accumulation rate (NAR) of 85.93 %. Next, BBD-RSM was applied, where ARE and NAR were the responses. The highest responses from the confirmation experiment were 99.9 % ± 0.04 and 95.25 % ± 0.32 when the optimum C/N, K/A, and salinity were identified as 0.84, 2, and 5.5 (g/L), respectively. The results were higher than those for the nonoptimized reactor. The developed regression model adequately forecasts the PN performance under optimal conditions. Therefore, this study provides a promising strategy for controlling the PN process and shows how the BBD-RSM model can improve the PN performance.