A FIELD-SCALE EVALUATION OF THE AIRSTRIPPING OF VOLATILE ORGANIC-COMPOUNDS BY SURFACE AERATORS

The stripping of volatile organic compounds (VOCs) by surface aerators was evaluated in experiments performed at field scale. Each experimen t consisted of dosing a tank containing tapwater with a selection of V OCs, activation of the aerator, and subsequent monitoring of the disap pearance of the compounds. The tank contents were deoxygenated before the experiment thereby allowing concurrent measurement of the uptake o f oxygen. Experiments were performed with two aerators with differing power inputs and aeration patterns and over a range of temperatures fr om 3 to 22 degrees C. Overall mass transfer coefficients were calculat ed for each compound in each experiment. The impacts of temperature an d aerator horsepower on the mass transfer coefficients of the candidat e compounds were examined and relationships were calibrated with the e xperimental data. The fundamental gas and liquid mass transfer coeffic ients were calibrated and the ratio of gas to liquid phase mass transf er coefficient was estimated to rang from 16 to 24. The estimated rati o of k(g)/k(l) was found to be relatively insensitive to variations in the Henry's Law coefficient over the range typically observed in the literature. The observed ratio was lower than that previously reported in the literature and would suggest a greater impact of gas phase res istance than previously thought. The lower value of the ratio may be a ttributed to mass transfer limitations caused by entrained air.