Optimization of the anaerobic denitrification process mediated by Bacillus cereus in a batch reactor

The purpose of this work was to study the performances of a facultative denitrifying bacterium, Bacillus cereus, in an anaerobic condition in presence of synthetic wastewater enriched of nitrate. Here, the kinetics of nitrate and nitrite consumption operated by Bacillus cereus in a specifically devised batch bioreactor, in anoxic condition and with acetates and sucrose as the organic substrate, was characterized. In particular, the effect of pH and BOD concentration on the denitrification performances was assessed. A complete denitrification was found in the presence of [BOD] > 4 g/L and with a pH buffered around 7. When the initial concentration of nitrates was in the range 100–200 mg/L, the denitrification process took place in about 30 h with a kinetics described by a zero-order mechanism with respect to nitrate and nitrite concentration. The denitrification process was characterized by calculating the degradation kinetic constants: kd NO3 −=0.5±0.1 mg L−1 min−1 and kd NO2 −=7.3±1.5×10−2 mg L−1 min−1 for nitrate and nitrite ions, respectively. Moreover, a thorough analyses in terms of Monod kinetics yielded a bacterial growth yield Y=5.7±0.2× 10−3 gVSS/mgN−NO3 −, a specific denitrification rate SDR = 89.5 mgN−NO3 −/gVSS h−1 and a maximum bacterial growth rate μmax=0.86± 0.03 h−1. These results allow one to consider Bacillus cereus one of most efficient denitrifying bacilli to be employed in industrial wastewater treatment plants (e.g. dairy farm). © 2019