Modeling of DBT biodegradation behaviors by resting cells of Gordonia sp. WQ-01 and its mutant in oil-water dispersions

A strain of dibenzothiophene (DBT) biodegradation bacteria Gordonia sp. WQ-01 was subjected to He-Ne laser (632.8 nm) irradiation to improve the degradation ability. Under the optimum condition of output power of 20 mW for 15 min, a positive mutant strain WQ-01A was acquired. Intrinsic DBT biodegradation kinetics by resting cells of the wild strain WQ-01 and its mutant strain WQ-01A in aqueous phase was determined in shaking flasks. Batch DBT biodegradation experiments were carried out in a 7.5 L fermentor by the wild strain and its mutant strain in model oil system under different experimental conditions such as initial DBT concentration, resting cell density, and oil fraction (n-dodecane was used as the model oil because of its similarity to diesel oil). Furthermore, a mathematical model considering the intrinsic biodegradation kinetics and the overall oil-water mass transfer coefficient was developed to simulate the DBT biodegradation behaviors by resting cells of both strains in oil-water dispersions. The model calculations agreed well with the experimental results. Both theoretical simulation and experimental investigation indicated that the mutant strain had a much higher DBT biodegradation activity.