Hydrogen sulfide (H2S) causes severe problems in collection systems when wastewater is pumped over long distances. To limit rotten-egg odors and to mitigate premature asset deterioration, utilities often add neutralization agents to the wastewater. However, without a dynamic overview of the H2S concentrations in the wastewater, the optimal chemical dosing rate remains unknown. This lack of information implies that there will be either under- or overdosing and time consuming optimizations.
A Danish water utility wanted to optimize the dosing of ferrous sulfates (FeSO4) in a force main discharge well to reduce the consumption of chemicals and to improve the mitigation of potential H2S related odor and corrosion issues in the collection system.
A small, self-contained dosing system was installed at the force main discharge well consisting of a SulfiLoggerTM H2S sensor, a dosing pump, and a chemical tank. In this setup, the SulfiLoggerTM sensor’s real-time H2S signal was used as a dynamic control input for the dosing pump. By measuring directly in the raw wastewater at the end-of-pipe transition inside the well, the SulfiLoggerTM sensor was able to quickly detect changes in the composition of the wastewater and thereby allow the fast reacting chemicals to be added in just the right quantity. The dosing rate was simply proportional to the H2S signal.
To measure the effect of the dosing setup, an additional SulfiLoggerTM sensor was installed in the sewage in a manhole 1.2 km downstream in the gravity system, and using these two measurement points, different dosing strategies were implemented and compared.