What is the primary cause of corrosion in manholes?

The primary cause of corrosion in manholes is hydrogen sulfide gas. This gas is produced during the breakdown of organic matter in wastewater, particularly in anaerobic conditions. When hydrogen sulfide is present in the wastewater, it can escape into the air in manholes and other confined spaces. Over time, this exposure leads to a chemical reaction with moisture, resulting in the formation of sulfuric acid. This acid seriously contributes to the deterioration of concrete and metal components in manholes, which can compromise structural integrity and lead to costly repairs.

While other factors such as carbon dioxide exposure and oxygen depletion can contribute to corrosion processes, they do not have the same direct and damaging effect on manhole materials as hydrogen sulfide. Heavy metal contamination can be a concern in terms of pollution and environmental health, but it is not typically identified as a primary cause of corrosion specific to manholes. Hence, hydrogen sulfide stands out as the main culprit due to its direct involvement in producing corrosive conditions.