THEORY OF EMISSION OF VOLATILE COMPOUNDS FROM AERATION BASINS OF WASTEWATER TREATMENT PLANTS

Emission of odors and organics from aeration basins is a well-known problem that has been studied from a mass transfer and equilibrium viewpoint. Correlations have been developed and experimentally tested on the rate of mass transfer of volatiles from the wastewater phase to the gas bubble phase. However, the effective rate of transport is a product of the mass transfer coefficient, usually determined experimentally, and the interfacial surface area. It is known that the interfacial area is significantly larger, mainly due to turbulence caused by the surface bursting of the gas bubbles. The essential problem is in estimating the interfacial area of the turbulent interface and how this area varies with gas flow rate, size of the gas bubbles, and their terminal velocity.In this paper, an equation has been developed which incorporates the interfacial surface energy, kinetic and potential energy into a comprehensive energy balance thereby allowing the interfacial area to be calculated for various bubble sizes and gas flow rates. Experimental data on volatile emission rates were re-examined in light of this new equation and it was discovered that the actual interfacial area can be significantly higher than the quiescent area of the gas-liquid interface, and that the volatile emission rates consequently can also be much greater than obtained from the empirical mass transfer coefficients. This finding has significant impact on validating experimental data on volatile emission rates with empirical conventional mass transfer analysis.