MODELING THE EMISSION AND DISPERSION OF VOLATILE ORGANICS FROM SURFACE AERATION WASTE-WATER TREATMENT FACILITIES

A methodology has been developed for predicting volatile organic concentration levels immediately downwind of wastewater treatment facilities, as well as further away, under neutral or stable atmospheric conditions. For the case of a ground-level well-mixed continuous-flow basin with intense mechanical aeration at the surface, the rates of mass transfer of organic pollutants to the atmosphere are obtained by assuming that the entire resistance to mass transfer resides in the stagnant film at the liquid phase interface. The atmospheric transport of the organic emissions downwind are then predicted by a three-dimensional atmospheric dispersion equation, considering dry deposition as a sink mechanism and accounting for variations of wind velocity and vertical diffusivity with height above the ground. The variation of downward concentration levels with Henry's constant is examined for different atmospheric stabilities, deposition velocities, surface roughnesses and basin surface areas.