CONTROL OF VOC EMISSIONS FROM SEWERS - A MULTIPARAMETER ASSESSMENT

A computational model is described which facilitates multi-parameter a nalyses of VOC emissions from sewers. The model, CORAL+, was used to s imulate more than 3.6 million combinations of five system parameters, including sewer channel slope, relative depth of now, pipe diameter, H enry's law coefficient and headspace ventilation rate. Lumped results were analyzed using a graphical frequency array approach to identify p arameter combinations that lead to potential VOC emission hot spots. A dditional modeling was completed to provide examples of passive VOC em ission reductions through control of system parameters. Computational results provide information related to combinations of parameters that either never or always lead to potential VOC emission hot spots, inde pendent of the values associated with all other parameters. Results in dicate that the common assumption of infinite ventilation can lead to significant overestimates of VOC emissions, and that controlled headsp ace ventilation can be used to reduce VOC emissions by an order of mag nitude or more. This may be of significance with respect to reducing e missions from on-site industrial sewers by maintaining biodegradable V OCs in solution prior to discharge to a downstream biological treatmen t system. Results also suggest that VOC emissions are highly sensitive to wastewater flow rate, increasing as flow rate decreases. This is a n important observation with respect to the fact that some municipalit ies encourage industrial discharges at night for purposes of flow equa lization.