Transfer coefficient reaeration

KLa air-water oxygen transfer coefficient, reaeration constant (s-1, h-1 or... 

Under equiUbrium or near-equiUbrium conditions, the distribution of volatile species between gas and water phases can be described in terms of Henry s law. The rate of transfer of a compound across the water-gas phase boundary can be characterized by a mass-transfer coefficient and the activity gradient at the air—water interface. In addition, these substance-specific coefficients depend on the turbulence, interfacial area, and other conditions of the aquatic systems. They may be related to the exchange constant of oxygen as a reference substance for a system-independent parameter reaeration coefficients are often known for individual rivers and lakes. 

Determination of reaeration relies on the measurement of the air-water oxygen transfer coefficient (Section 4.4.2). Measurement of this coefficient — the reaeration coefficient — in gravity sewer lines follows basically the methods that have been developed for and applied in rivers. Methods for determination... 

Jensen and Hvitved-Jacobsen (1991) developed a direct method for the determination of the air-water oxygen transfer coefficient in gravity sewers. This method is based on the use of krypton-85 for the air-water mass transfer and tritium for dispersion followed by a dual counting technique with a liquid scintillation counter (Tsivoglou et al 1965,1968 Tsivoglou andNeal, 1976). A constant ratio between the air-water mass transfer coefficients for dissolved oxygen and krypton-85 makes it possible to determine reaeration by a direct method. Sulfur hexafluoride, SF6, is another example of an inert substance that has been used as a tracer for reaeration measurements in sewers (Huisman et al., 1999). 

Several empirical relationships for reaeration coefficients were recently reviewed and tested by Moog and Jirka (1995), who found that the form of the relationship given in Eq. (20.15) best characterized stream reaeration rates. A liquid mass transfer coefficient for each compound, ki can then be determined from a ratio of the Schmidt numbers (Mackay and Yven, 1983) ... 

We must next formulate an expression for the mass transfer rate N g and here we encounter the same difficulty we had seen in Illustration 2.2 dealing with the reaeration of rivers. In both cases the interfacial area is unknown and we must therefore resort again to the use of a volumetric mass transfer coefficient Kji where the unknown interfacial area a (m /m column volume) is lumped together with If the gas phase is assumed to be controlling, we can write... 

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