Concrete pipe Grrreat for Sanitary Sewer

Battle Creek - In the home of Tony the Tiger, mascot for Kellogg's Frosted Flakes cereal, concrete pipe is grrreat for a sanitary sewer receiving approximately 920,000 gallons per day from the Kellogg cereal company. The 3,000-foot run of sanitary sewer was needed by the City of Battle Creek to replace an 80-year-old clay pipeline that collected sewage for treatment in a facility located 24 miles away in Fort Custer. The primary challenge that had to be overcome by the pipeline designers was the acidic characteristic of the sewage. A low pH threatened the service life of the concrete pipeline and a sewage spill, unless the concrete mix was fortified with an admixture that would resist the potential effect of sulfuric acid in the effluent.

There are some 300 miles of sanitary sewer mains located throughout the Battle Creek metropolitan area. Wastewater generated by residences and businesses must be cleaned and treated to meet all federal and state standards before it is discharged into the Kalamazoo River. The city prefers specifying concrete pipe for sewers greater than 24 inches in diameter. The acidic nature of the sewage, however, was the reason for first specifying the pipeline SDR 26 PVC, despite the city's preference, and sections where the pipe would be buried deeper than 15 feet. The specification was changed to reinforced concrete pipe, once the client was assured that an admixture would destroy anaerobic bacteria responsible for the production of hydrogen sulfide gas (H₂S) when it makes contact with the concrete surface.

Anaerobic bacteria, which do not require oxygen for survival, form in raw sewage and produce hydrogen sulfide gas that has a distinct odor of rotten eggs. Factors that do contribute to the rapid growth of Thiobacillus (a common form of anaerobic bacterium) are temperature, retention time, high biochemical demand (BOD₅), and turbulence. Turbulence from force mains, drop structures in manholes, steep grade changes, and pumping stations allows the hydrogen sulfide gas to release into the atmosphere in pipes and manholes. The gas is then converted into sulfuric acid (H₂SO₄) by the Thiobacillus bacteria that grow on surfaces of the concrete pipe and manholes above the wastewater flow. Only Thiobacillus can convert H₂S to H₂SO₄.

Pipe designers at Premarc are familiar with several additives used in concrete mixes to resist the corrosion of concrete by acidic soils and sanitary sewage. The design team proposed the use of ConShield, a liquid admixture that molecularly bonds to the cement particles in a concrete mix, to enhance the performance of the concrete sewer to meet the design life of the pipeline. The active ingredient in the admixture forms a colorless, odorless, and positively charged polymer. When a single cell Thiobacillus bacterium comes in contact with the admixture, the cell membrane ruptures, and the organism dies. Since nothing is transferred to the dead cell, the admixture does not lose strength and is ready for contact by the next bacterium.

The city approved the use of the ConShield admixture in the concrete pipe cement mix designed for the project, and changed the specification. The challenge for the contractor, however, had just begun. The alignment of the new sewer was first planned within ten feet of the existing clay pipeline. When the clay pipeline was uncovered, its integrity was breached and sections of pipe began to collapse when exposed. The contractor had to bypass the clay pipeline from manhole to manhole to avoid causing a sewage spill. In addition, the contractor had to install the pipeline between August 1 and October 3, 2008 to meet MDOT's schedule for pavement replacement.

During the planning and design stage of a sanitary sewer, the potential biochemical profiles of the system should be determined along with current rates of acid development, and projected rates for the design life of the sewer. Once determined, the pipe can be protected by additives and liners. Concrete pipe can also be produced with an increase in total alkalinity using calcareous aggregates. It is also common to increase the concrete cover over the reinforcement. Known as sacrificial concrete, the rate of deterioration of the system can be matched to the design life of the project.

Where acidic effluent is anticipated, designers need to determine the pH, including cyclic variations, as well as continuous or intermittent flow characteristics. The pH and total acidity for the design life of the system is critical. In addition, designers must determine the potential for the development of sulfuric acid due to potential changes to the environment of the interior atmosphere of the sewer. Technology is now in place for making concrete pipe more reliable than it has ever been before. Decades of research and development of many aspects of concrete pipe have enabled concrete pipe producers to change concrete mixes and pipe design to provide products that can withstand a complete range of underground environments and effluent profiles.

The Battle Creek concrete sanitary sewer that receives considerable effluent from the Kellogg Company was carefully designed with full knowledge of the nature of the sewage and design life of the pipeline. An innovative additive used to create an environment that can accommodate reinforced concrete pipe, has also contributed to the city's sustainable infrastructure.

Project:	Sanitary Sewer City of Battle Creek Battle Creek, Michigan

Owner:	City of Battle Creek Battle Creek, MI

Contractor:	Peters Construction Company Kalamazoo, MI

Quantities:	40 feet of 12-inch diameter C-76 Class IV RCP 2,720 feet of 24-inch diameter C-76 Class IV RCP 240 feet of 30-inch diameter C-76 Class IV RCP Ten 48-inch diameter manholes Four 60-inch diameter manholes Four 72-inch diameter manholes Two 84-inch diameter manholes One 96-inch diameter manhole

Producer:	Premarc Corporation Durand, MI

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