The Effect of pH on Hydrogen Sulfide and Carbon Dioxide Absorption in Packed Towers

Packed tower wet scrubbers have been the work-horse technology for hydrogen sulfide removal in the odor control industry for over 20 years. They typically operate at high pH through addition of an alkali such as sodium hydroxide, and with an oxidant such as chlorine added as sodium hypochlorite. Wet scrubbers provide high levels of hydrogen sulfide removal when operated at their designated design and operating parameters.Carbon dioxide is a natural component of the ambient air. It is also a by-product of microbial respiration. Therefore it is present in the headspace of sewers and covered wastewater treatment processes where biological activity may be occurring, and where the gases from this activity may be released, such as from the headworks of wastewater treatment plants, aerated grit chambers, primary clarifiers and aeration tanks. Like hydrogen sulfide, carbon dioxide is an acid gas and is absorbed in alkaline conditions. As a result its absorption adds to the alkali demand and operating cost of wet scrubbers.This paper presents the results of an optimization study of a wet scrubber odor control system that evaluated hydrogen sulfide and carbon dioxide removal, operating pH and chemical usage. Hydrogen sulfide and carbon dioxide removal were monitored at varying operating pH levels using continuous gas phase analyzers with data logging capabilities.This paper provides important insight into potential cost saving operating strategies for owners and operators of wet scrubber systems.