Prediction of odour emissions from sewage pump stations and vents on sewerage mains

摘要

There are many complicating factors that will determine the odour emissions from vents at sewage pump stations and on rising mains. One of the main factors is the formation of sulfide which is dependent on residence time of the sewage and the surface area to volume ratio of the wet well and rising main. A case study of sulfide formation modelling for a holding tank, rising main and vent located on the receiving gravity main is presented in this paper. ASK has developed software that calculates the concentration of sulfide formed within wet wells and rising mains based on Uniquest's Sewex methodology of modelling the biochemical reactions with the rising main modelled as a plug flow system (Sharma et al, 2008). Initial concentrations and relevant parameters of the sewage, where unavailable, were assumed and tested to match the model predictions to measured values as closely as practicable. This approach takes into account the temporal and spatial variation of sulfide concentrations, in contrast to most models which assume a steady-state system. Another key factor of the release of odour is the rate at which hydrogen sulfide is released from the sewage, which is dependent on the concentration of sulfide in the liquid phase, the saturation concentration at equilibrium dependent on pH and temperature, and the turbulence of the system. When appropriate assumptions and initial conditions are set, the sulfide predictions match reasonably well with observations reported by Sharma et al (2008).