What valuable gas is produced as a byproduct of sewage treatment?

The valuable gas produced as a byproduct of sewage treatment is methane. During the anaerobic digestion process, organic matter in the sewage breaks down in the absence of oxygen, which leads to the production of methane and carbon dioxide. Methane can be harnessed as a renewable energy source, providing a potential for energy recovery in sewage treatment plants. This makes it not only an important byproduct for managing waste but also for contributing to sustainable energy solutions.

Other gases listed, such as chlorine, hydrogen sulfide, and ammonia, do not serve the same beneficial role in sewage treatment. Chlorine is primarily used as a disinfectant and not a byproduct. Hydrogen sulfide can be produced during the breakdown of organic matter but is a toxic gas that poses safety and environmental concerns. Ammonia, while present in wastewater, is not considered a valuable byproduct like methane and can be harmful in high concentrations.