ST. LOUIS, MO, Jan. 2, 2014 -- One of the largest ultraviolet (UV) wastewater disinfection systems in the country was recently completed at the Lemay Wastewater Treatment Plant disinfection facility in St. Louis, Mo.
Constructed over a year and a half, KAI Design & Build, partnering as a sub-consultant with global construction management consultant CH2M HILL, served as construction manager on the Metropolitan St. Louis Sewer District's (MSD) $21.2 million plant, which included development of a cutting-edge UV wastewater disinfection system utilizing 3,600 individual UV bulbs and with a treatment capacity of 240 million gallons of effluent per day.
Construction layout and dimensioning of the UV disinfection system's UV channels was a critical component of the project, said KAI Resident Project Representative Dave Tesson. Requiring approx. 6,500 cubic yards of concrete, an estimated 10,400 wire terminations to connect the UV power and controls, and 560 tons of reinforcement, the system's UV channel widths had to be constructed to an accuracy of +1/2” minus zero inches.
The project also required two 144" pre-stressed 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. Further, 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.
"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," said Tesson. "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."
UV irradiation systems disinfect by inactivating pathogenic microorganisms, such as viruses, bacteria and parasites, according to the UV system's manufacturer Ozonia. In the UV-C light spectrum (200-280 nm), the wavelength 254 nm has been proven to be the most efficient wavelength to inactivate micro-organisms by damaging the nucleic acids (DNA and RNA), which disrupts the organisms' ability to replicate. UV has the added advantage that no chemicals are added to the water being treated and no disinfection by-products are formed.
MSD's current boundaries cover 525 square miles and encompass all of St. Louis City and approximately 80 percent of St. Louis County. MSD serves a population of approximately 1.3 million and has over 425,000 single-family residential, multi-family residential and commercial/industrial accounts. MSD currently operates seven wastewater treatment facilities, treating a combined average of 370 million gallons of wastewater per day.