Surfactant effects on alpha factors in full-scale wastewater aeration systems.

Aeration is an essential process in the majority of wastewater treatment processes, and accounts for the largest fraction of plant energy costs. Aeration systems can achieve wastewater oxygenation by shearing the surface (surface aerators) or releasing bubbles at the bottom of the tank (coarse- or fine-bubble aerators). Surfactants accumulate on gas-liquid interfaces and reduce mass transfer rates. This reduction in general is larger for fine-bubble aerators. This study was conducted to evaluate mass transfer effects on the characterization and specification of aeration systems in clean and process water conditions. Tests at different interfacial turbulence regimes were analysed, showing higher gas transfer depression for lower turbulence regimes. Higher turbulence regimes can offset contamination effects, at the expense of operating efficiency. This phenomenon is characteristic of surface aerators and coarse bubble diffusers and is here discussed. The results explain the variability of alpha factors measured at small scale, due to uncontrolled energy density. Results are also reported in dimensionless empirical correlations that describe mass transfer as a function of physiochemical and geometrical characteristics of the aeration process.

Religious intermarriage in Canada, 1974-1982.

"This paper reviews recent literature, with particular reference to Canada, on religious intermarriage. The importance of intramarriage in the cross-generation maintenance of subcultural values is emphasized. Recent trends in religious outmarriage and the major explanations and correlates of these trends are considered. Recent data published by Statistics Canada is examined for the nine year period between 1974-1982."