Completed in December 2020, Project Clear’s new Maline Creek Storage Facility now protects the North St. Louis watershed from combined sewer overflows previously encountered during rainstorms. Penetron’s innovative antimicrobial concrete admixture protects key precast concrete elements from microbially-induced corrosion (MIC).
During times of heavy rain, the sewer system of St. Louis City and much of St. Louis County, served by aging sewer pipes, can be overwhelmed. This quickly results in combined sewer overflows (CSO) dumping untreated wastewater into area rivers and streams. One of these rivers is Maline Creek, a small tributary that runs along the northern edge of the city of St. Louis and empties into the Mississippi River.
“The existing combined sewers were constructed through the mid-1900s. They carry a set amount of rainwater and wastewater in the same pipe,” explains Christopher Chen, Director of The Penetron Group. “During calm weather, everything works fine. These pipes can handle the wastewater and collected rainwater and carry it to the treatment plant. However, during heavy rain or significant snowmelt, the wastewater can quickly exceed the capacity of the sewer system or the treatment plant, resulting in ‘combined sewer overflows,’ or CSOs.”
The Metropolitan St. Louis Sewer District (MSD) has taken steps to successively improve water quality and alleviate many wastewater concerns throughout the St. Louis region. The $82.8-million Project Clear will eliminate sewer overflows during heavy storms due to the older wastewater collection and treatment systems – and help keep the Mississippi River cleaner.
A central element of Project Clear is the new Maline Creek Storage Facility, a 2,700-foot-long, 28-foot diameter storage tunnel that was built 175 feet below the surface. Located just upstream of the confluence to the Mississippi River, the facility will store excess water and sewage during heavy weather. After the rain subsides, a pump station will transfer the stored runoff and wastewater back into the system for treatment at the Bissell Point Wastewater Treatment Plant.
Looking to Prevent MIC
The project contractors needed a solution to prevent microbially-induced corrosion (MIC) in the concrete structures of the Maline Creek Storage Facility. MSD and the project engineers pinpointed specific concrete structures that were most susceptible to MIC. Penetron worked with the precast manufacturer, to add the antimicrobial concrete admixture to protect key precast concrete elements.
Keeping Bacteria Away
Similar to the company’s well-known PENETRON ADMIX, the antimicrobial admixture is added to the concrete mix during batching. The admixture uses an electro-physical mechanism to destroy the cell-walls of micro-organisms, such as thiobacillus bacteria, on contact, which converts hydrogen sulfide gas (H2S) into biogenic sulfuric acid (H2SO4). The formation of biogenic sulfuric acid causes concrete to deteriorate, in a process known as MIC. This antimicrobial admixture is a permanent solution – it forms part of the concrete matrix and is leach-resistant. The effectiveness of this antimicrobial admixture is not lessened by repeated contact with bacteria, providing the much-needed long-term MIC protection.
Christopher Chen adds: “This new admixture will continue to provide the needed durability to the concrete and virtually eliminate any future repair of the treated precast concrete structures.”