Challenge

A west coast U.S. municipality treats 40-60 million gallons per day of wastewater through its collection system.  The city was feeding sodium chlorite into the pump station wet wells to control hydrogen sulfide (H₂S) and associated odors.  These wet wells operated intermittently, pumping 10-20% of the time into the force main, leaving it untreated most of the time.  This single chemical approach did not adequately control odors associated with H₂S generated by bacteria in all sections of the collection system. Consequently, supplemental treatments were required at multiple remote sites.

Solution

A recommendation was made to modify the chemical program, utilizing multiple technologies to optimize the treatment results without increasing the cost to the municipality. New feed point sites were chosen based upon the ability to continuously treat the line.  In addition, intermittent feed of hydrogen peroxide and sodium nitrate  were recommended to supplement the sodium chlorite program.

Results

The addition of hydrogen peroxide and sodium nitrate significantly reduced the level of H₂S and the associated odor present in the system.   The use of multiple technologies allowed the municipality to optimize treatments by adjusting for seasonal, weather and diurnal variations.  As a result the municipality was also able to discontinue treatments at remote sites.  The benefit to the municipality was a 55% cost saving over a three-year period.