Jones Island and South Shore WRF Disinfection Process Improvements

As water quality standards continue to evolve, utilities across the country are being challenged to deliver more effective treatment under increasingly complex conditions. That was the case for the Milwaukee Metropolitan Sewerage District (MMSD), which faced new disinfection permit limits for E. coli at its two major water reclamation facilities: the Jones Island Water Reclamation Facility (JIWRF) and the South Shore Water Reclamation Facility (SSWRF). With peak flows of 425 and 375 million gallons per day (MGD), respectively, these high-capacity facilities required a disinfection strategy that could reliably meet regulatory requirements across a wide range of flow conditions, without compromising sustainability goals or operational continuity.

To meet this challenge, MMSD partnered with Carollo to lead the design and construction of a hybrid disinfection system that combines both ultraviolet (UV) and chemical disinfection. At the heart of the solution is a dual approach: a new UV system sized for dry weather flows (150 MGD at JIWRF and 135 MGD at SSWRF) and an upgraded sodium hypochlorite/bisulfite system designed to handle the full flow range at each facility. This flexible configuration enables effective, energy-efficient disinfection across all operating scenarios while providing redundancy and reducing chemical use.

Carollo’s design process included full-scale pilot testing of both UV and chemical disinfection systems to verify dose values and performance under real-world conditions. Multiple UV system manufacturers were evaluated, and a comprehensive greenhouse gas analysis was performed to compare alternatives and identify the lowest-impact option. The final design retrofits an existing chlorine contact basin into a UV disinfection system at JIWRF, while a new greenfield UV facility was designed for SSWRF, each enclosed in protective structures to safeguard operations from the elements.

Construction sequencing was another critical component of the project, with detailed planning to maintain uninterrupted disinfection during installation. The team also secured Focus on Energy grant support to offset costs and further align the project with MMSD’s sustainability priorities.

By combining innovation with practical implementation, Carollo is helping MMSD modernize its disinfection systems and reduce environmental impacts. This work supports compliance across all flow conditions and sets a new benchmark for high-capacity wastewater treatment.