Design and optimization of parameters for continuous denitrification of water by methane using Hyphomicrobium denitrifi cans in a packed bed reactor

In the present study, the continuous denitrification of water was carried out using Hyphomicrobium denitrificans coupled with methane in a packed bed reactor containing a mineral packing medium. The response surface methodology based on the Box-Behnken design was applied to examine the interaction effects of pH (6-8), temperature (20 degrees C-30 degrees C), and methane/air mixture flow rate (20-60 mL min(-1)) on the nitrate removal (initial concentration of 100 mg L-1) using the Hyphomicrobium coupled with the methane. Analysis of variance results indicated that the methane/air mixture flow rate had a maximum effect on the nitrate removal efficiency in comparison to the pH and temperature variations. The experimental design results indicated that the optimum values of pH 6.9, temperature 30 degrees C, and flow rate 53 mL min(-1) led to maximize the denitrification capacity of Hyphomicrobium in a packed bed reactor. The maximum experimental denitrification capacity was found to be 2.85 mg NO3-N L-1 h(-1) which was in good agreement with the predicted value by the Box-Behnken analysis (2.81 mg NO3-N L-1 h(-1)). The effluent nitrate concentration reached less than 50 mg L-1 in the nitrate flow rates of 1.4 and 2.5 mL min(-1). The obtained results demonstrated the high capability of Hyphomicrobium denitrificans coupled with methane for denitrification of water.