Emission of hydrogen sulfide (H2S) at a waterfall in a sewer: study of main factors affecting H2S emission and modeling approaches.

Hydrogen sulfide (H2S) represents one of the main odorant gases emitted from sewer networks. A mathematical model can be a fast and low-cost tool for estimating its emission. This study investigates two approaches to modeling H2S gas transfer at a waterfall in a discharge manhole. The first approach is based on an adaptation of oxygen models for H2S emission at a waterfall and the second consists of a new model. An experimental set-up and a statistical data analysis allowed the main factors affecting H2S emission to be studied. A new model of the emission kinetics was developed using linear regression and taking into account H2S liquid concentration, waterfall height and fluid velocity at the outlet pipe of a rising main. Its prediction interval was estimated by the residual standard deviation (15.6%) up to a rate of 2.3 g H2S·h-1. Finally, data coming from four sampling campaigns on sewer networks were used to perform simulations and compare predictions of all developed models.