Oxygen uptake and VOC emissions at enclosed sewer drop structures

Abstract

Municipal wastewater is currently receiving regulatory scrutiny as an emissions source for volatile organic compounds (VOCs). In response, the fate of VOCs at drop structures has been studied. The study described herein involved two major components. First, 64 pilot experiments were conducted to study the effects of drop height, liquid flow rate, and tail water depth on oxygen transfer. Second, 15 additional experiments were completed to determine the effects of the same parameters on the stripping of a cocktail comprising 10 volatile tracers. Headspace ventilation rates, chemical properties, and the differences between clean water and raw wastewater on VOC stripping were studied. Results suggest that oxygen is a useful surrogate for VOC measurements as both oxygen and VOC mass transfer were observed to be highly dependent on drop height and less on liquid flow rate. Stripping efficiencies for VOCs were observed to vary between 0.5 and 32% depending upon specific compounds and experimental conditions. VOC stripping was also observed to be greater from clean water as compared to wastewater. Gas‐liquid mass transfer of VOCs was seen to be a strong function of Henry's law coefficient, suggesting the Occurrence of gas‐phase mass transfer resistance.