Additional Information Additional Links

Wastewater Treatment


Wastewater Treatment Plant


ClarifierThe St. Peters wastewater plant uses a natural biological process to treat the wastewater before safely sending it back to the environment. When wastewater leaves a St. Peters customer's home, it moves through the privately owned sewer lateral line that ties into a huge system of underground pipes. The whole wastewater collection system was carefully designed to use the force of gravity to move the water from anywhere in the City back to the St. Peters wastewater treatment plant. The wastewater moves downhill through sanitary sewers that lead to one of two main trunks: a line along Dardenne Creek or a line along Spencer Creek. These sewer lines enter the wastewater treatment plant at the "headworks" building, where inorganic items (papers, plastics, etc.) and gritty material (coffee grounds, egg shells, seeds, etc.) are screened out and sent to the landfill.


From there, wastewater moves from the headworks building to oxidation ditches, where bacteria feed on organic material. Probes in these ditches measure the dissolved oxygen of the wastewater. This is important because the bacteria also need oxygen, which is why aerators add air to the oxidation ditches. The probes send information to software that controls the speed of the aerators, which provides the optimum treatment in the most cost-efficient manner.


The wastewater that leaves the oxidation ditches goes to three clarifiers where biosolids settle to the bottom, and oil, grease and lighter material rise to the surface to form scum. The biosolids remaining at this point of the process are either returned to the oxidation ditches, providing more nourishment for constantly feeding bacteria, or to a holding tank. The surface scum is scraped into a pit and then combined with the biosolids in the holding tank, until the biosolids are sent to a dewatering facility. Dewatered biosolids are then mixed in with ground-up yard waste to be beneficially recycled as part of the City of St. Peters' Organic Resource Recycling Program. The remaining, treated water goes through a UV disinfection system. This system destroys the ability of microorganisms in the water to reproduce. After this process, the water is hit with one more dose of air before sending it back to the environment in nearby Spencer Creek.


Just like at the St. Peters water plant, licensed operators working in the St. Peters Utilities Department control and monitor the wastewater treatment process, constantly testing the water quality to ensure all federal standards are met as the water is safely returned to the environment.


St. Peters Utilities workers are cross-trained to operate both the water plant and wastewater plant, increasing the efficiency of the City of St. Peters’ operations.




Sewer Backup? Call the City

Wastewater leaves your home and enters a "sewer lateral" that carries the waste to a sewer main. If there is a blockage in either the sewer lateral or sewer main, the wastewater in your home will back up. You, the homeowner, are responsible for maintaining your sewer lateral line. (Learn about the Sewer Lateral Repair Program.) The City of St. Peters is responsible for maintaining its sewer mains. But, no matter where the blockage might occur, St. Peters customers should notify the City of St. Peters when they encounter a sewer backup: Dial 636-477-6600 (AT&T) or 636-278-2244 (CenturyTel) and then enter ext. 1225 to file a formal concern.


If you call after hours (before 8:30 a.m. and after 5 p.m., or during weekends or holidays), please follow the instructions for water or sewer emergencies. The City of St. Peters has on-call Utilities personnel who respond to emergencies at all times.
The City will relieve all blockages that are found in the public sewer main. If the problem is caused by your sewer lateral or by some other problem on your property, the repair will be your responsibility. 


If the backup only happens when you use water and it slowly drains when you stop using water, the problem is most likely in your lateral. If the backup occurs or continues when you are not using water, there may be a blockage in the public main.


In any case, it’s important that the City check out the sewer main after any sewer backup. In the past we’ve spotted problems that can save homeowners a plumber’s bill down the road. So, please call.


Did You Know?

The City of St. Peters has a Sewer Lateral Repair Program for St. Peters residents to help offset the cost of sewer lateral repairs.




Flushing Wipes Clogs Pipes type



Utilities Department: 636.477.6600 (AT&T), ext. 1573, or 636.278.2244 (CenturyLink), ext. 1573


For sewer backups, call 636.477.6600 (AT&T) or 636.278.2244 (CenturyLink) and dial ext. 1225 to file a concern. If you call after hours or on weekends, follow the directions for emergencies.


For the Sewer Lateral Repair Program, call ext. 1278 at 636.477.6600 (AT&T) or 636.278.2244 (CenturyLink).

Back to top