In municipalities, many of the existing wastewater systems are deteriorating, at the same time population demands are pressing upon cities to expand their wastewater collection capabilities. More and more municipalities are addressing this growing health and environmental challenge by paying increased attention to rehabilitating corroded manholes. By most industry estimates, leaking manholes account for an estimated 20% – 30% of the unnecessary groundwater infiltration and inflow that overtax and threaten the sanitary sewage system.
Advanced, high-performance polyurea coatings are increasingly becoming more popular in manhole rehabilitation due to their corrosion resistance and long-term effectiveness. Featuring higher film builds, faster dry times and other advantages, these new protective coating formulations offer cost-effective solutions to municipalities seeking to reduce downtime, restore access and minimize the costs associated with sewer system repair.
A primary cause of corrosion in municipal sewer environments is MIC or Microbiologically Induced Corrosion. MIC occurs when bacteria of the genus Thiobacillus, “concrete-eating bacteria,” oxidize sulfur from hydrogen sulfide, “sewer gas,” and produce sulfuric acid as a by-product. Sulfuric acid is highly corrosive to concrete, steel and non-ferrous metals. When concentrated and heated by summer temperatures, it is extremely damaging to the concrete and non-ferrous metals used in most wastewater structures. Construction materials in such environments quickly lose their ability to support loads, maintain their shape, transport liquids and function as designed. Manholes may be among the toughest environments encountered.
Many municipalities have discovered that high-performance polyurea coating systems offer the easiest and most effective way to rehabilitate manholes without having to excavate. These corrosion control coatings form a protective layer between the substrate and the chemical attackers — essentially prohibiting the environment from reaching the concrete. In the absence of major structural damage, advanced corrosion-resistant systems can offer 50 to 100 years of service life with proper maintenance.
These coatings are also suitable for other wastewater treatment facilities where hydrogen sulfide concentrations frequently can occur such as wet wells, lift stations, dewatering buildings and odor control buildings. When coated with polyurea, concrete and steel substrates can be submerged, buried or driven upon in just minutes. This fast reaction time is particularly appealing in municipal wastewater rehabilitation because it permits quick installation and a nearly immediate return to service.