Effects of hydrocarbon additions on gas-liquid mass transfer coefficients in biphasic bioreactors

The effects of aliphatic hydrocarbons (n-hexadecane and n-dodecane) on the volumetric oxygen mass transfer coefficient (k(L)a) were studied in flat alveolar airlift reactor and continuous stirred tank reactors (CSTRs). In the flat alveolar airlift reactor, high aeration rates (> 2 vvm) were required in order to obtain efficient organic-aqueous phase dispersion and reliable k(L)a measurements. Addition of 1% (v/v) n-hexadecane or n-dodecane increased the k(L)a 1.55-and 1.33-fold, respectively, compared to the control (superficial velocity: 25.8 X 10(-3) m/s, sparger orifice diameter: 0.5 mm). Analysis of the gas-liquid interfacial area a and the liquid film mass transfer coefficient k(L) suggests that the observed k(L) a increase was a function of the media's liquid film mass transfer. Addition of 1% (v/v) n-hexadecane or n-dodecane to analogous setups using CSTRs led to a k(L)a increase by a factor of 1.68 and 1.36, respectively (superficial velocity: 2.1 X 10(-3) m/s, stirring rate: 250 rpm). These results propose that low-concentration addition of oxygen-vectors to aerobic microbial cultures has additional benefit relative to incubation in purely aqueous media.