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An enlightened approach to clean water

MSD-max-cropBreckenridge Material delivered 6,000-plus yd. to the Lemay site; Hanson Pressure Pipe shipped 425 ft. of 120-in. PCCP.
MSD-max-cropBreckenridge Material delivered 6,000-plus yd. to the Lemay site; Hanson Pressure Pipe shipped 425 ft. of 120-in. PCCP.

Metropolitan St. Louis Sewer District’s (MSD) $21.2 million Lemay Wastewater Treatment Plant disinfection facility included construction of a cutting-edge ultraviolet wastewater disinfection system utilizing 3,600 individual UV bulbs and with daily treatment capacity of 240 million gallons of effluent per day—one of the largest such facilities to date.

UV irradiation systems disinfect by inactivating pathogenic microorganisms, according to system manufacturer Ozonia. In the UV-C light spectrum (200-280 nm), the wavelength 254 nm has been proven to be the most efficient to inactivate microorganisms by damaging their DNA. UV irradiation has the added advantage that no chemicals are added to the water being treated and no disinfection byproducts are formed.

Layout and dimensioning of the disinfection system’s UV channels was a critical component, according to St. Louis-based KAI Design & Build, which served as construction manager. Requiring upwards of 6,500 yd. of concrete, an estimated 10,400 wire terminations to connect the UV power and controls, and 560 tons of reinforcement, the channel widths had to be constructed to an accuracy of half-inch tolerances.

The project also required two, 120-in. prestressed concrete cylinder pipe connections to existing structures carrying the entire plant effluent flow. The existing bulkhead gates in both structures leaked excessively, preventing the removal of the bulkhead pipe caps intended to allow future expansion. The leaks could not be fixed through conventional methods.

“Divers were brought in and were able to seal the leaks from the inside at one of the structures. The other structure required a more extreme approach. Using experience gained from a previous project, the team coordinated an effort to retain wastewater in the collection system and the plant for later treatment. This allowed crews to get inside the structure and work on it dry. Additional wastewater storage was also required to complete modifications of a weir wall within the existing plant piping system,” notes KAI Resident Project Representative Dave Tesson.

A final, flow stoppage and storage for the entire plant was required to complete upgrades to the existing incoming plant electrical switch gear. This work required additional coordination with the electric utility to shutdown both utility power feeds to the plant substation.

MSD covers 525 square miles and encompasses the City of St. Louis and approximately 80 percent of St. Louis County. The agency serves a population of approximately 1.3 million and has over 425,000 single-family residential, multi-family residential and commercial/industrial accounts.