Plant expansion ends SSO pollution
Portage, Ind., has expanded its wastewater treatment plant, nearly doubling the plant’s treatment capacity and creating off-line storage. The $10.2 million project will accommodate the increasing demands of the growing community well into the future, and it has eliminated pollution caused by sanitary sewer overflows.
Situated about 40 miles southeast of Chicago, Portage is home to 31,000 people. Its wastewater treatment plant serves a 150-mile-long grid of sanitary sewers, which have approximately 12,000 residential connections and a nominal industrial load.
Handling wet weather was a stormy prospect for the city. Although the sewers are separate from the city’s stormwater drainage system, the area’s high water table – combined with infiltration and outdated sump pump connections – overwhelmed the treatment plant during some storms. When that happened, the overflow moved through bypasses and emptied into Lake Michigan.
In 1994, city officials began planning a plant expansion to end the pollution. EPA later notified the city that new bypasses would not be permitted after June 1, 1998, making expansion even more pressing.
The bulk of the project involved increasing the dry weather treatment capacity to 4.95 mgd from 3.5 mgd and adding the wet weather storage facilities to accommodate 18 mgd. Along with those improvements, the city added an ultraviolet disinfection system; a supervisory control and data acquisition (SCADA) system; a mixed-liquor station; a return activated-sludge pumping facility; two final clarifiers; a sludge storage building; and an air-monitoring system. It also upgraded the plant’s laboratory, standby power, and screening and grit removal operations.
Prior to construction of the mixed-liquor station, planners determined that the 30-inch pipe from the oxidation ditch to the new station could not accommodate the plant’s increased capacity, making it necessary to convert the facility from gravity to forced-flow operation. Twenty-seven pumps, equipped with variable frequency drives, maintain the required flow. Ten of the pumps, ranging from 2 horsepower to 65 horsepower, are used during dry weatheroperation.
Wet weather operation begins when two magnetic meters sense that the influent will exceed the plant’s treatment capacity. The data is relayed to the SCADA system, which activates up to three 60-horsepower pumps to divert the stream into the surface storage facility. When the flow subsides, the raw sewage is diverted into a 1.5 million gallon, concrete tank, and it is then pumped into the plant’s treatment system at a controlled rate.
Completed last fall, the plant expansion was the combined work of Chicago-based McDonough Associates (project engineer) and River City Construction (general contractor), Peoria, Ill. ITT Flygt, Trumbull, Conn., provided the pumps for the forced-flow operation.
Today, Portage’s wastewater treatment plant handles an average daily flow of 3.2 mgd in dry weather. The peak wet weather flow has been 10 mgd, during which plant bypasses remained unused.
This article was written by Ricky Dodd, superintendent of the Portage Water Reclamation Facility.