// March 09, 2011

Wastewater

// Case Study

This system injected hydroxyl-rich air into the odour source, which neutralized the hydrogen sulfide before it reached the surface.

// The Case

The City of Sarnia had experienced sewer capacity problems since they first implemented their system in the 1950s. Despite building an interceptor and alternative pipelines in the following decades, flows exceeding system capacity would often overflow into the St. Clair River.

In 2011, the City of Sarnia commissioned a new sanitary sewage pumping station (SPS). The design incorporated two wet wells, interconnected via a sluice-gate. The wet well was not mechanically ventilated or heated, and instead had short, stainless steel “candy cane” venting pipes.

As the SPS commenced operation, the City began receiving odor complaints from property owners near the pumping station. While they installed much taller vent pipes (to improve scent dispersion), complaints continued. The City found the venting pipes contained 15-30 ppm hydrogen sulfide, a level that could induce headaches, dizziness, nausea, coughing and vomiting in a human population.

The City of Sarnia signed up for a single Odorox machine and oxidant sensor to reduce these concentrations. It involved placing a single hydroxyl generator outdoors, which vented hydroxyls into the original intake air vent. This system injected hydroxyl-rich air into the odour source, which neutralized the hydrogen sulfide before it reached the surface.

Hydroxyl production demands are made through automated controls, which maintain a set hydroxyl concentration. This results in energy savings over an always-on configuration. After the machines were installed and tested thoroughly, Sarnia has received no more odor complaints, and hydrogen sulfide levels are now well below levels that can cause health problems for humans.