Case Study: Municipal Wastewater Treatment – Headworks Sulfide Control

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INTRODUCTION:

There is a concern about worker safety at a small European wastewater plant. The plant receives primarily residential wastewater at a flowrate of 0.95 MGD.
The first process unit is a 32,000 gallon flow equalization tank (nominal retention time - 48 minutes). From there it is pumped to coarse screening/grit removal.

INVESTIGATION:

Plant staff often work in the coarse screening and grit removal building where H2S levels of 40 to 100 ppm have been measured.

• The manager wants to lower the sulfides to less than 10 ppm, the alarm level.
• A concentration of < 5 ppm would allow the staff to work in the building for extended periods.

IMPLEMENTATION:

975 - UNITED CARUSOL® C is injected into the collected wastewater as it enters the equalization basin – initially at a 100 mg/L dosage.

• After 2 hours the sulfide level in the room dropped from 20-25 ppm to 5 ppm.
• Permanganate treatment was lowered to 50 mg/L and sulfides dropped to a steady 2-3 ppm.
• Eventually the dosage was lowered to 35 mg/L with no change in sulfide level.

RESULTS:

The safety goal of <5 ppm was achieved.