Emissions of Volatile and Potentially Toxic Organic Compounds from Wastewater Treatment Plants and Collection Systems (Phase 2). Volume 2. Wastewater Collection System Study

摘要

The report was completed to assess the potential for volatile organic compound (VOC) emissions from wastewater collection systems. The study focused on two important phenomena: (1) partitioning of VOCs between sewer atmospheres and wastewater, and (2) convective transport of VOCs by gas exchange with the ambient atmosphere. Tracer studies were completed in operating sanitary sewers, resulting in data used to evaluate methods for predicting VOC partitioning. An oxygen transfer model was suggested with theoretically based adjustments for VOCs. Several mechanisms were studied as driving forces for ventilation of sewer atmospheres. Fluid mechanical analyses were applied to hypothetical flow circuits, and the importance of individual mechanisms were compared. It was concluded that no single mechanism dominates sewer ventilation under all situations, but environmental conditions, wastewater flow conditions, and physical characteristics of a collection system were identified under which some mechanisms become dominate. A set of one-dimensional, two-phase finite volume models were developed to predict dynamic mass transport of VOCs in collection systems. Over one thousand hypothetical scenarios were simulated to ascertain the importance of physical characteristics of sewers, flow characteristics, and physico-chemical properties of VOCs. Results provide guidance in identifying potential points of high emission, and the relative importance of collection systems compared to wastewater treatment systems.