Which two gases are of concern to the IWTO besides methane and hydrogen sulfide?

The correct choice identifies oxygen and carbon monoxide as additional gases of concern to the Industrial Waste Treatment Operations (IWTO) beyond methane and hydrogen sulfide. In wastewater treatment facilities, monitoring gases is crucial for safety and operational efficiency.

Oxygen is essential because its levels can affect aerobic and anaerobic processes within treatment systems. A deficiency in oxygen can lead to undesirable anaerobic conditions which might increase the production of methane and hydrogen sulfide, leading to odor issues and potential toxicity for biological treatment systems.

Carbon monoxide poses a significant risk due to its toxic nature. Even at low concentrations, it can inhibit respiration and pose serious health risks to workers. Additionally, its presence can indicate incomplete combustion processes or other issues within the plant's operations.

The other options do not adequately reflect the concerns of wastewater treatment operations. Nitrogen is relatively inert in this context, while ozone, despite its advantages in disinfection, does not have the same level of concern compared to carbon monoxide. Sulfur dioxide, while concerning, is not as critical in the context of wastewater treatment as the carbon monoxide identified in the correct answer.