Modelling VOC emissions at wastewater drop structures

A mechanistic model was developed to predict VOC emissions at drop structures. The mass transfer mechanisms that have been incorporated into the model include the falling film (disintegrating jet), turbulent mixing in the area of jet impact, and bubbles in the tailwater resulting from air entrainment. Air entrainment appears to be the most significant mechanism affecting VOC emissions, following by the falling film. A sensitivity analysis was also performed using parameter values that are considered “typical” for wastewater drop structures and operating conditions. The largest variation in stripping was associated with air entrainment, liquid and air flow, Henry's law coefficient and degree of equilibrium for entrained bubbles.