Carbonate Effects on Sodium Hydroxide Dosage

Abstract

Hydrogen sulfide, H 2 S, causes major odor problems at wastewater treatment facilities. A primary method of removing hydrogen sulfide from air is to use a wet scrubber. In a wet scrubber the air stream comes in contact with a liquid scrubbing solution. In order for hydrogen sulfide to enter into solution, the pH of the scrubbing solution must be raised. Sodium hydroxide (NaOH) also known as caustic soda, is typically used in odor control systems to raise the pH of the scrubbing liquid. Neglecting carbonate effects leads to incorrectly low dosages for the amount of sodium hydroxide needed to raise the pH.The design of a system to add sodium hydroxide requires the correct calculation of dosage to determine feed pump requirements and storage requirements. This is also important in determining systems operating costs. For these reasons the correct calculation of sodium hydroxide dosage is important. This purpose of this paper is to:• Define chemistry terms that are used in this paper.• Show why the pH must be raised in order for hydrogen sulfide to go into solution.• Show why carbon dioxide in the atmosphere effects carbonate level in solution. • Show how the carbonate level effects sodium hydroxide dosage.• Give sample calculations for sodium hydroxide dosage and cost estimation.