Dynamics and dynamic modelling of H2S production in sewer systems

Accurate and reliable predictions of sulfide production in a sewer system greatly benefit formulation of appropriate strategies for optimal sewer management. Sewer systems, rising main systems in particular, are highly dynamic in terms of both flow and wastewater composition. In order to get an insight in sulfide production as a response to the dynamic changes in sewer conditions, several measurement campaigns were conducted in two rising mains in Gold Coast, Australia. The levels of various sulfur species and volatile fatty acids (VFAs) were monitored through hourly sampling for periods ranging from 8 to 29 h. The results of these field studies showed large temporal as well as spatial variations in sulfide generation. A dynamic sewer model taking into account the hydraulics and the biochemical transformation processes was formulated and calibrated and validated using the data collected during the four measurement campaigns at the two sites. The model was demonstrated to reasonably well describe the temporal and spatial variations in sulfide, sulfate and VFA concentrations. Application of the model was illustrated with a case study aimed to optimize oxygen injection to one of the two mains studied, which is being used as a means to control sulfide production on this site. The model predicted that, moving the current oxygen injection point to a location close to the end of the sewer line could achieve the same degree of sulfide control with only 50% of the current oxygen use. This study highlighted that the location at which oxygen is injected plays a major role in sulfide control and a dynamic model could be used to make a proper choice of the location.