Municipal Wastewater Treatment

Sample Engagements:

Failure Analysis and Replacement of Concrete Coatings in WWTP Primary Clarification Headspaces:


In 1994, the construction of a large regional wastewater treatment plant in the northeastern United States was being completed. The concrete in the headspaces in the covered primary clarifiers (launder troughs) and connecting channels were coated with 18 to 25 mils DFT of modified amine-cured epoxy and/or coal-tar epoxy coatings. Following plant start-up in early 1995, blistering-type failures of the coatings occurred after 10 months in service. Hydrogen sulfide (H2S) gas concentrations in the headspaces were measured to be over 350 ppm. Surface pH values on the attacked surfaces were measured at below 1.0. Acidic attack of the concrete was underway and gypsum (calcium sulfate) formation was present. Gypsum is the main reaction compound when sulfuric acid reacts with hydrated Portland cement concrete. The coating failure analysis indicated a permeation-related failure with blistering, followed by substrate attack and associated delamination of the coatings.


The failed coatings had previously performed very well in wastewater treatment plant headspaces, but that was in local, smaller wastewater treatment plants for the same metropolitan area. The new regional plant involved longer detention and transit times for the wastewater resulting in much higher dissolved H2S production in the collection system. This ultimately caused higher H2S gas and sulfuric acid concentrations in the affected headspaces of the plant.


CPI recommended that the existing coatings be removed and that a 1/8" thick, trowel-applied, blended amine-cured epoxy mortar system be applied over the concrete surfaces in these headspaces. The recommended coating system was installed in 1997. These linings have been re-inspected routinely since, and they have continued to perform well with no evidence of delamination, blistering, or other signs of failure.

Customer Benefits

The recommended lining systems have performed successfully in providing greater permeation resistance to H2S and sulfuric acid, and thereby preventing further concrete deterioration in the primary clarifier headspaces and connecting channels.


Service Areas

  • Corrosion and Materials Engineering
    • Corrosion Control/Protection Design
    • Corrosion Analysis and Material Selection Consulting
    • Failure Analysis - Mode and Root Cause Analysis
    • Cathodic Protection System Design and Evaluation
  • Structural and Mechanical Rehabilitation Services
    • Structural Design Engineering
    • Mechanical Design Engineering
    • Condition Assessment Evaluations
    • Structural Evaluation and Analysis
    • Shop and Field QC Inspection and Support
  • Mechanical Integrity and Inspection Design Services
    • Pressure Vessel and Tank Program Development and Implementation
    • Systematic Inspection Design (SID)
    • Risk-Based Inspection
    • Integrity Evaluation and Analysis
    • Fitness-for-Service Evaluations
    • Welding Consulting and Inspection
  • Coatings and Linings Engineering
    • Consulting
    • Failure Analysis
    • Project Management
    • Quality Control and Inspections
  • Project and Quality Management Services
    • Cost Estimating Services for all Construction Disciplines
    • Project Management Services, Including Planning, Scheduling, and Project Controls
    • Quality Control Inspection and Testing Services
    • Quality Assurance Program Development for New and Rehabilitation Construction
    • Quality Assurance Program Auditing and Oversight Services
  • Training Services
    • Alloy Selection for Corrosive Environments
    • Solving Corrosion and Materials Problems for Plant Engineers
    • Welding Essentials for Plant Engineers
    • Brick and Tile-Lined Equipment Inspection and Repair
    • FRP Essentials for Pulp and Paper Mills
    • Concrete Restoration and Protection
    • Quality Assurance for Capital Projects

home  |  projects  |  services  |  experience  |  contact
© Copyright 2009-2017 Corrosion Probe, Inc.

Website design and development by Optimum Technology Solutions, Albany GA