| Aeration is an essential process in the majority of wastewater treatment processes, and accounts for the largest fraction of operating costs. Aeration systems can achieve gas transfer by shearing the surface (surface aerators) or releasing bubbles at the bottom of the tank (coarse- or fine-bubble aerators). The effectiveness of gas transfer processes is reduced by the presence of dissolved contaminants, i.e. surface active agents, in the liquid medium.; Surface active agents accumulate at gas-liquid interfaces, and reduce mass transfer rates. This reduction in general is larger for smaller bubbles. Surface active agents are present as measurable trace contaminants at all environmental and at most industrial gas-liquid interfaces. The quantification of gas transfer depression caused by surface active agents is necessary to calculate increased energy costs when designing and specifying aeration systems.; Datasets from previous experiences in our laboratory were assembled and analyzed in this study. These included concurrent measurements of dynamic surface tension and mass transfer coefficients. Data were recorded in both time-dependent and time-integrated experiences. In this work, the parameters describing the evolution of bubble interfacial contamination over time were also enclosed. This was done by calculating surfactant interfacial accumulation, surfactant surface diffusivity, and corrected interfacial gas diffusivity for each bubble surface age using a time-dependent adsorption model.; A dimensional analysis was performed on the system, resulting in correlations that present the results in dimensionless fashion. The resulting correlations were statistically significant. Results are consistent with expectations and correct previous Frossling-like dimensionless correlations for systems without contamination. The results formally describe observed transport phenomena, and offer a tool for mass transfer prediction from flow regime and dynamic surface tension properties. |
