VOC emissions from primary clarifier weirs

Volatile organic compounds (VOCs) are emitted from wastewater treatment processes via stripping and volatilization. Significant progress has been made in modeling these emissions, but questions remain regarding operative mass transfer mechanisms in certain processes. In the case of flow over weirs and drop structures, two approaches have been presented: mass transfer is modeled as taking place either (1) entirely in the nappe, or (2) entirely in air bubbles entrained by falling water in the tailwater pool. In the present work, these two very different modeling approaches are evaluated using experimental results on liquid-side concentrations of chlorinated solvents above and below a primary clarifier weir. The model locating the primary emission mechanism within entrained air bubbles in the tailwater pool is found to predict observed liquid-side VOC concentrations better than the model which considers only emissions from the weir nappe.