Issues in the corrosive wet space environment

Corrosive wet space environments in concrete structures have always been an issue. Hydrogen sulphide (H₂S) generation in wastewater treatment facilities has always been present. It causes decay in the form of sulphuric acid attack of concrete in sewer collection/treatment systems. Gaseous condenses on aerated, wet concrete surfaces; is metabolised by sulphur-oxidising bacteria and is oxidised to form dilute sulphuric acid (H₂SO₄).

In recent years there has been a general trend toward higher H₂S concentrations in wastewater treatment facilities which has promoted much higher concrete corrosion rates in domestic treatment plants (especially in larger regional plants) than seen in the past. This increase in H₂S is due in part to longer transport distances to district or regional plants and longer retention times, which increases the amount of septic wastewater. Additionally, the trend to more pump stations and less gravity-flow reduces aeration. Without atmospheric exits, aeration is obstructed leading to precipitation as the only sink for sulphide.

Perhaps, most importantly, the dramatically lowered allowable levels of heavy metal ions in waste streams has resulted in significantly increasing the bacteria responsible for aqueous sulphide production. This has resulted in more sulphide-related corrosion in the last 25 years.

EpiMax has pioneered the development of thin set performance protection systems for these projects. These provide greater protection at significantly reduced material and installation cost.

EpiMax has worked with wastewater utility management, and consultants like GHD and SKM to:

Protect and maintain the physical properties and structural and mechanical integrity of assets by using properly selected and applied protective coating and lining materials
Optimize life cycle cost of protective coatings
Avoid premature deterioration and failure of structures and equipment
Avoid premature failure of protective coatings through the proper selection, specification and inspection of coatings work
Address the tropical conditions and the fact that an ambient temperature increase of 5 C increases the amount of H₂S produced by 40%
Take advantage of newer protective coating technologies (specifically “boutique” novolac chemistry)

Thin set, new technology options available:

EM 333AR High Build Acid Resistant Coating