Pilot-Scale Studies of Volatile Chemical Emission to Air from Warm Water in the Absence of Wind

Abstract

Toxic chemical emissions to air from wastewater treatment vessels, aqueous hazardous waste storage basins, open channels and receiving streams are of on-going concern. These emissions continue in the absences of wind. However, the process has not been investigated and no verified correlations are available for estimating the transport rate coefficients. An investigation was undertaken to quantify the magnitude of these emissions using surrogate compounds to model the toxic chemicals in a pilot-scale simulation of the no-wind volatilization process. Buoyancy-driven turbulence, both above and below the air-water interface of surface impoundments, maintains high rates of chemicals transport to air in the absences of wind. Laboratory simulations of volatile chemical emissions were performed with diluted aqueous solutions of acetaldehyde, acetone, isopropanol and methanol and model compounds. The water temperature ranged from 30° to 40° and air from 20° to 30°C. Existing correlations developed for heat transfer from plates were modified to correlate the mass transfer coefficients for the test chemicals. Correlations for coefficients on both sides of the interface are proposed and tested. The results indicate that significant volatile chemical transport to air can occur under moderate temperature differences (TH2O>Tair) in absence of wind.