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How St. Charles City treats 1.7 billion gallons of wastewater a year — and what happens to the solids
Summary
St. Charles City treats about 1.7 billion gallons of wastewater annually, runs roughly 16,500 lab tests a year, and produces about 3,500 dry tons of biosolids that are land-applied to farmers in Kane and DeKalb counties, city water officials said on the City Insider podcast.
St. Charles City treats roughly 1,700,000,000 gallons of wastewater each year and returns disinfected effluent to the Fox River, Garrett Guthrie, Environmental Services Division Manager (Wastewater), said on the City Insider podcast.
Christina Smith, Laboratory Supervisor for the city’s Public Works water division, said the city’s environmental lab runs “just under 16,500 tests each year” and collects about 35 samples a day from plant influent, effluent and biosolids to monitor performance and regulatory compliance.
The treatment process operates in stages, Guthrie said: large solids are screened out, water moves through aeration tanks where bacteria remove roughly 90% of organics, solids settle out, and the clear water is disinfected with ultraviolet light before being released. Smith said the lab tracks pH and biochemical oxygen demand among other measures to confirm the plant remains ‘‘well under’’ Illinois EPA (IEPA) and U.S. Environmental Protection Agency (EPA) permit limits.
“The lab is very important to how the wastewater treatment plant operates,” Guthrie said, describing a daily feedback loop: lab staff identify microbial indicators such as filaments or amoebas and notify operators, who then adjust feeding, wasting or dissolved-oxygen levels to keep the plant in an optimal operating range often described as a target ‘sludge age.’
Smith described how microscopic organisms help operators read plant health: certain ciliates or flagellates indicate a healthy system, while an excess of filamentous bacteria can signal the need for operational changes. Those observations, she said, allow the team to give operators “pretty specific” guidance about plant adjustments.
Biosolids — the nutrient-rich, treated solids produced by wastewater plants — are an intended product, Guthrie said. St. Charles City produces about 3,500 dry tons annually; the city’s biosolids are land-applied to farms in Kane and DeKalb counties in accordance with state and federal regulations. Guthrie offered a visual: roughly one full football field of material stacked about six feet high.
For regulatory oversight, Guthrie said the city submits monthly Discharge Monitoring Reports (DMRs) to the IEPA for each plant, quarterly biosolids reports, and an annual EPA submittal to demonstrate permit compliance.
City staff also described workforce and outreach efforts: Smith and Guthrie encouraged student visits, job shadows and internships, noting many wastewater and lab skills can be learned on the job and that the city offers training for entry-level hires.
Why this matters: the combination of daily sampling, lab analysis and operator adjustments keeps treated water within permit limits, reduces pollutant loads to the Fox River and allows the city to safely reuse biosolids on farmland. The city’s approach also supports local STEM outreach and workforce development.
St. Charles City operates two treatment plants — the main plant (near Riverside Avenue/public works) and a West Plant (Carl Mattson Drive/Route 38) — and maintains about 180 miles of sanitary pipe and 20 lift stations that collect wastewater from homes, businesses and institutions.
