Municipal and industrial sewers have come under increased regulatory scrutiny as sources of volatile organic compound (VOC) emissions to the ambient atmosphere. A well-ventilated municipal sewer interceptor that receives significant quantities of VOC-laden industrial wastewater was studied to quantify VOC emissions. Headspace outgassing rates across four manhole covers were as high as 2300 m3/h. Emissions were greatest for toluene, approaching 100 g/h from a single manhole cover at the mid-point of the 24-hour event. Significant diurnal and weekday/weekend trends were observed. Emissions from a single manhole cover rivaled or exceeded those summed over aerated grit chambers and aeration basins at four large municipal wastewater treatment facilities in Southern Ontario. The primary source of VOC stripping was observed to be a series of large drop structures, with aromatic VOC stripping efficiencies ranging from 25 to 38% across two drops. Finally, an existing model that predicts VOC emissions from sewers was observed to reasonably predict measured stripping efficiencies. An important conclusion of this study is that large fractions of VOCs may be removed from wastewater and emitted to the ambient atmosphere prior to entering a downstream treatment facility.

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