Better understanding in-sewer processes with on-site continuous mass spectrometric analysis of sewer gases

Abstract

Sewer systems are an important part of the urban water cycle, because they protect public health and natural aquatic environments from contamination. However, adapting our sewer systems to future challenges requires a better understanding of important transport and transformation processes, such as emission of greenhouse gases or unwanted infiltration of clean groundwater. In this short communication, we propose that monitoring of gases with mass spectrometric methods can deliver a better insight into biochemical transformation and exchange processes than what is currently possible with conventional wastewater analytics. The results from three case studies provide insight into the dynamics of GHG, such as CH4 and CO2, and use Helium as a tracer to assess both groundwater infiltration and sewer airflow patterns. In the future, this can be used to design novel experiments, e.g. by simultaneously analyzing inert and active gas species, or actively injecting tracer gases into the ground- and wastewater. Future work should investigate better filtration or indirect sampling methods to sample gas from sewage, such as specially-tailored flux chambers. For network-wide analyses, boundary conditions regarding sewer ventilation, as well as sources and sinks of gases need to be better understood.