Corrosion of Concrete Sewers

Introduction
Concrete sewers are an integral part of any wastewater management system. However, their service life can be limited due to corrosion caused by various factors. In this context, corrosion refers to the deterioration of concrete due to chemical reactions with its environment.

Causes of Corrosion
One of the primary causes of corrosion in concrete sewers is the anaerobic decomposition of sewage solids. This process produces hydrogen sulfide gas, which can react with water to form sulfuric acid. The sulfuric acid can then react with the calcium hydroxide in the concrete to form calcium sulfate and water. This reaction can cause the concrete to weaken, crack, and crumble over time.

Other factors that contribute to corrosion in concrete sewers include:

• High pH value of sewage: This can cause the concrete to alkalize, leading to the breakdown of its structure.

• Aerobic decomposition of sewage solids: This process can produce carbon dioxide gas, which can react with water to form carbonic acid. This acid can then react with the calcium hydroxide in the concrete, leading to its deterioration.

• High velocity of flow of sewage: This can cause erosion of the concrete surface, leading to its degradation.

Prevention and Maintenance
To prevent corrosion of concrete sewers, it is essential to control the production of hydrogen sulfide gas. This can be achieved by:

• Reducing the retention time of sewage in the system

• Increasing the flow rate of sewage

• Adding chemicals such as chlorine or hydrogen peroxide to the wastewater to inhibit the growth of anaerobic bacteria

• Coating the interior of the sewer with an acid-resistant material

In addition, regular inspection and maintenance of the sewer system can help identify and address any corrosion issues early on. This can include:

• Cleaning the sewer regularly to remove any buildup of solids or debris

• Repairing any cracks or leaks in the concrete

• Replacing any severely corroded sections of the sewer

Conclusion
Corrosion of concrete sewers is a significant problem that can lead to significant damage and costly repairs. However, by controlling the production of hydrogen sulfide gas and implementing regular inspection and maintenance procedures, it is possible to extend the service life of these critical infrastructure components.