We’ve all driven by a sewer and caught that familiar whiff of rotten eggs. That is the distinctive smell of hydrogen sulfide (H2S), a colorless, flammable gas that is the result of bacterial breakdown or decomposition of organic matter in sewers. The bacteria rely on organic material in wastewater to oxidize into sulfuric acid. This can lead to deterioration and corrosion of sewer pipes. The odor and potential corrosion make this a concern for cities. The authors of a recent paper in the Journal of Environmental Engineering sought to analyze wastewater and determine the H2S distribution and emission in a sewer system.
Researchers Letian Sun, Xiao-Jie Shi, Tong Yu, David Z. Zhu, and Adam Shypanski used a 6.2-mile stretch of the western Edmonton, Canada, sewer system as a case study. They selected a gravity sewer trunk line with laterals and several sanitary pump stations upstream servicing primarily residential properties. Their field research collected wastewater samples in two rounds of field measurement. The water quality of the samples was analyzed to provide an overview of the wastewater characteristics in the trunk and laterals, specifically sulfide levels and gaseous H2S concentrations. Learn more about how this research can help utility and sewer systems to manage H2S emissions. Get the full results of their study at https://doi.org/10.1061/JOEEDU.EEENG-7691. The abstract is below.
Abstract
Fieldwork was carried out in the western area of Edmonton, Alberta, Canada to assess the H2S contribution of a long force main and to investigate the source of H2S generation in a complex sewer network. The study sewer trunk has a length of 10 km, a diameter of up to 1.95 m, and flow rate of up to 0.6 m3/s. In the upstream, there is a 5.6 km forcemain, and the pump station operation can cause a sudden increase of H2S in the sewer air of the discharge manholes to reach 500 ppm. Wastewater samples were collected in 14 manholes in the sewer network and analyzed for sulfide and other relevant parameters. The maximum values of sulfide were 9.7 mg S/L and pH remained mostly neutral. For predicting the sulfide generation rate, an empirical model was applied with readily biodegradable organic matter. Then the emission of H2S in gravity pipes was investigated, and it was found over 90% of H2S stayed in the liquid phase when wastewater flowed in gravity sewer pipes. Finally, the mass transfer in a drop structure of 8 m was investigated. The liquid phase H2S concentration in the upstream was 2.6 times that of the downstream, and about 62% of the H2S was released in this drop structure indicating the significant emission of H2S in drop structures.
Get the details on how your utility can better manage H2S emissions through this study at the ASCE Library: https://doi.org/10.1061/JOEEDU.EEENG-7691.
