Estimating Air Emissions from Unit Treatment Processes with Weirs

摘要

Estimating air emissions from dynamic unit process at wastewater treatment (WWT) facilities presents a challenge for scientist and engineers. In particular, the weirs that are design features of several different types of unit treatment process such as primary treatment, secondary treatment, filtration, and dissolved air fiotation, are important sources for estimating air emissions from these unit treatment processes. There are several predictive models that accommodate these predictions, however, mass balance and ambient air studies have determined that these estimates are usually conservative in nature. The USEPA Technical Guidance Series suggest both indirect and direct measurement technologies for the purpose of estimating air emissions from weirs. Indirect technologies are inviting since they are not affected by the size/shape of the unit treatment equipment. However, the ambient background around a unit treatment usually precludes this approach. Direct emission measurement technologies, on the other hand, have proven to be useful including the USEPA surface emission isolation fiux chamber. Given the dimensions of the weir, it is possible to use this direct measurement approach to test for emissions at two locations in the weir design: 1) in the liquid stream immediately down-gradient from the weir fall in the aerated zone; and 2) on an adaptor box designed to isolate the three dimensional weir and weir channel with aerated waste water. Both locations/approaches seem to provide representative emission data. This paper will present the challenge of assessing air emissions from weirs, discuss the theory behind the increased emissions from the weir fall and how that relates to the assessment approach used, validation data for assessing air emissions from weirs, and results from field studies and modeling efforts that show predicted air emissions from both the quiescent and aerated surfaces from unit treatment process with weirs.