Kinetics of p-Aminoazobenzene Degradation by Bacillus subtilis Under Denitrifying Conditions

Bacillus subtilis is an organism capable of degrading an azo dye, such as p-aminoazobenzene (pAAB), under both aerobic and anoxic conditions. In both cases, pAAB is co-metabolized with a main carbon source and under anoxic conditions denitrification is observed. Kinetic experiments were carried out with a pure culture of B. subtilis and a mathematical model that accurately describes both biodegradation of pAAB under anoxic conditions and the denitrification process under both carbon- and nitrate- or nitrite-limited conditions is developed. Presence of pAAB in culture medium causes an inhibition of bacterial growth and of nitrite accumulation. Bacterial growth and pAAB degradation rates are found to be slower under anoxic conditions compared to the corresponding rates under aerobic conditions.