The Allegheny County Sanitary Authority (ALCOSAN) achieved a major milestone on October 2, increasing its wet-weather treatment capacity to 480 million gallons per day (MGD), and officially meeting a key compliance target established under its Consent Decree.

On Sunday, October 11, ALCOSAN successfully sustained flow of over 295 MGD during that day’s rainfall. 

The ability to treat 480 MGD is one of the most significant operational changes since the plant opened in 1959. It marks a fundamental step in ALCOSAN’s larger Plant Expansion Program, which is one of four pillars of its Clean Water Plan. 

Previously, ALCOSAN had the capacity to treat up to 295 MGD during wet weather.  That was increased from the previous 250 MGD last fall.  

With the plant flow increases over the last thirteen months, system overflows will be reduced by approximately 3.4 billion gallons. 

The 185 MGD increase means that during wet weather, substantially more wastewater will enter the plant for treatment, instead of contributing to overflows in the region. 

“This is much more than an increase in a number,” said Arletta Scott Williams, ALCOSAN Executive Director. “Today, ‘480’ reflects years of planning, construction and work by our employees and partners, demonstrating ALCOSAN’s commitment to clean waterways.”

Construction has been underway since 2019 as part of the effort to expand ALCOSAN’s treatment facility, in turn increasing capacity and reduce sewer overflows during heavy rain. The program includes new treatment tanks, expanded preliminary and secondary treatment facilities, upgraded disinfection tanks and other critical infrastructure improvements. 

Reaching 480 MGD is the next step toward the plant’s ultimate goal of treating up to 600 million gallons per day, more than doubling its previous wet-weather treatment capacity. 

“This is a significant moment for the people who operate and maintain this plant every day,” said Doug Jackson, Director of Operations and Maintenance. “We are introducing new equipment and operating processes that allow us to manage volumes of wastewater the plant has never handled before. Going forward, the region should see cleaner waters as a result of less overflows.” 

Among those improvements is an improved process for handling solids, where solids are removed from the secondary process to be thickened and sent directly to ALCOSAN’s existing dewatering facilities for disposal. That change allows for a bypass mechanism when flow exceeds 295 MGD during wet weather events. 

For more information about ALCOSAN and the Clean Water Plan, visit alcosan.org.