Oxygen and hydrocarbon volumetric transfer coefficients in the production of an oil-degrading bacterial consortium: emulsifying activity and surface tension in a bioreactor
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Our work shows that in multiphase systems, it is more important to take into account the mass transfer of oil rather than that of just oxygen. The oxygen volumetric transfer coefficient is important in aerobic bioreactor design. However, in multiphase systems with non-soluble substrates, oil transfer can impose larger restrictions but is usually not considered. Emulsification and surface tension could play an important role due to effects on oil droplet size and interfacial transfer area. Petroleum oil and is derivates such as diesel can negatively affect living organisms. This study evaluated the effects of the volumetric transfer coefficients (k(L)a) of hydrocarbons and oxygen on the production of an oil-degrading consortium in an airlift bioreactor relative to emulsifying activity and surface tension, which play important roles in the biodegradation of non-soluble substrates such as diesel due to a combined mass transfer constraint. Our results showed a clear difference in k(L)a values, which ranged from 15 to 91 h(-1) for oxygen and from 0 to 0.0014 h(-1) for diesel. Most aerobic biodegradation studies focus on the oxygen volumetric transfer coefficient (k(L)a(oxygen)), but our results indicated that non-soluble constraints, such as the volumetric transfer coefficient of diesel (k(L)a(diesel)), could be more important. Additionally, d(32diesel) decreased as superficial gas velocity (Ug) increased. Lower Ug rates (0.15 cm s(-1)) resulted in higher values of d(32diesel) (0.38 cm(-1)), whereas higher Ug rates (2.7 cm s(-1)) resulted in lower values of d(32diesel) (0.21 cm(-1)) at the beginning of the cultivation.
