First report of components responsible for odor sensation from a vertical flow constructed wetland treating combined sewer overflow

The present study presents the first attempt to demonstrate the online monitoring of components responsible for odor sensation from a constructed wetland (CW) utilized in treating combined sewer overflow (CSO). An experimental CSO treatment plant located in the south of Chile, employing a vertical flow (VF) CW, was monitored. The components responsible for odor generation—hydrogen sulphide (H₂S), methyl mercaptan (CH₃SH), ammonia (NH₃), and volatile organic compounds (VOCs)—were tracked for 27 days. During the study, the VF CW underwent two operational phases with CSO loadings, each lasting four days. The findings reveal minimal generation of H₂S, CH₃SH and NH₃ from the VF CW during the monitoring period, regardless of its operational status or the time of the day. However, VOCs exhibited different behavior. VOCs emerged as a potential contributor to odor sensation, with elevated levels observed during specific morning hours, which intensified when the VF CW was not operational. Nevertheless, the results suggest that the VF CW treatment has a limited impact on the production of gases responsible for odor sensation. This is complementary to previous studies focusing on water quality assessment, highlighting the potential of this technology for sustainable CSO treating.