Experimental study of oxygen diffusion coefficients in clean water containing salt, glucose or surfactant: Consequences on the liquid-side mass transfer coefficients

Abstract

This present paper proposes new investigations aiming at: (i) studying the effect on oxygen diffusion coefficients of the presence in clean water of some compounds usually encountered in biological media and (ii) quantifying their consequences on liquid-side mass transfer coefficients. The oxygen diffusion coefficients D were firstly measured in various synthetic liquid phases containing either salt (NaCl), sugar (glucose) or surfactant (sodium laurylsulphate). When compared to clean water, noticeable reductions of D were observed; the variation of D with the compound concentration C was modelled and found dependent on the nature of the compound added. In a second time, using the same liquid media, experiments on a train of bubbles rising in a quiescent liquid phase were carried out to determine the associated liquid-side mass transfer coefficients (k L). For all cases, as for diffusion coefficients, a decrease of k L with increasing C was clearly observed whatever the aqueous solutions. These findings firstly showed that, even if the properties of clean water (density, viscosity, surface tension) were not significantly changed by the addition of salts (NaCl), the liquid-side mass transfer coefficients could be, all the same, modified. For the aqueous solutions of glucose, the reduction of k L with diffusion coefficients D was well correlated, and mainly due to the change in viscosity with concentration. For surfactants, the hydrodynamic conditions (i.e. bubble Reynolds number) being almost kept constant for all concentrations, only the change in oxygen diffusion coefficients was thus responsible for the decrease of k L. The present study clearly confirmed the need to complete and/or account for the database related to oxygen diffusion coefficients in complex media, this condition being imperatively required to describe and to model appropriately the gas-liquid mass transfer phenomena.

Volumetric Oxygen Mass Transfer Coefficient and Surface Tension in Simulated Salt Bioremediation Media

“…This parameter is influenced by a number of factors such as agitation intensity, aeration, type and features of the bioreactor, composition of culture media, and type and concentration of microorganism [10][11][12][13][14]. In turn, oxygen mass transfer plays a fundamental role in the control of oxygen available for the metabolism of aerobic microorganisms in the bioreactor.…”

“…3). This is likely because their presence in the liquid phase altered the physicochemical properties of the bulk and then affected oxygen mass transfer [1,14,28]. Such increases were particularly high in the presence of toluene (a = 0.306, 0.363, 0.344, 0.237 and b = 0.968, 0.974, 1.052, 1.056 for BSM, LSM, BHM, and SW, respectively), whose hydrophobicity may have promoted bubble coalescence leading to larger bubbles and decreasing the interfacial area [1,22].…”

“…The volumetric oxygen mass transfer coefficient (k L a) 1) is the most important parameter in all the aerobic bioprocesses [9], which is influenced by a number of factors, among which are the agitation intensity, aeration, bioreactor features, media composition, biomass concentration, and microbial species [10][11][12][13][14]. However, above all, it plays a key role in bioreactors, where it influences the level of oxygen available to aerobic metabolism; k L a may then be used as an indicator of performance of aerobic wastewater treatments as well as of bioremediation processes [15].…”

Oxygen transfer in a pressurized airlift bioreactor

“…The antifoaming agent increases the coalescence of gas bubbles and decreases the specific gas-liquid interfacial area (a), what is corroborated by the lower e values observed for the culture medium. Presence of salts in the medium decreases oxygen diffusivity in the solution [28,29], reducing the mass transfer coefficient (k L ) [1,29]. Furthermore, the higher dynamic viscosity of the culture medium (1.2 9 10 -3 Pa s) compared to water (0.8 9 10 -3 Pa s) contributes to k L decrease, as well [30].…”

Hydrodynamic and absorption studies of carbon dioxide absorption in aqueous amide solutions using a bubble column contactor

“…In relation to the fact that the presence of this kind of substance produces a decrease in the value of the mass transfer coefficient, this behaviour is produced due to the trend of this kind of solute to accumulate molecules at the gas-liquid interface, as can be observed in the surface tension values (García-Abuín et al, 2008). The presence of molecules in the gas-liquid interface generally causes a decrease in the mass transfer rate due to an increase in transport resistance because the gas diffusivity near to the interface is reduced (Jamnongwong et al 2010). The accumulation of a compound at a gasliquid interface can be analysed on the basis of adsorption isotherms (Sardeing et al, 2006).…”