Avon Wastewater Treatment Facility Nutrient Upgrades

Building on a master planning effort for their three interconnected wastewater treatment facilities, Eagle River Water and Sanitation District (ERWSD) initiated this Nutrient Upgrades project to address growing environmental and regulatory challenges at their Avon Wastewater Treatment Facility. ERWSD sought to meet the stringent nutrient removal standards required by Colorado Department of Public Health and Environment’s (CDPHE) Regulation 85, which governs nitrogen and phosphorus discharge limits. With increasing nutrient removal requirements and a need for improved operational flexibility, ERWSD chose to partner with Carollo to design an innovative solution that would not only meet compliance but also optimize the facility’s treatment capacity.

This $49.6-million project was delivered using the Construction Manager at-Risk (CMAR) model, in collaboration with key team members at Moltz Construction, ERWSD, Carollo, and Eidos Architects.

Carollo’s solution involved a comprehensive redesign of the facility’s biological treatment process. The project included the conversion of the existing Modified Ludzack-Ettinger process to an anaerobic-anoxic-aerobic (A₂O) configuration, with the added flexibility of operating in a five-stage Bardenpho configuration. This upgrade expanded the aeration basin volume by 50 percent, enabling the facility to maximize nitrogen and phosphorus removal and adapt to fluctuating nutrient loads in a challenging cold weather climate. A third secondary clarifier was constructed to increase capacity and redundancy. The design also included critical infrastructure improvements, such as replacing aging equipment for screening, grit removal, and primary clarification; installing a carbon-based odor control system; and significantly upgrading the electrical system. The project installed high-efficiency aeration blowers for operating at traditional and low dissolved oxygen (DO) concentrations and eliminated the need for a dedicated waste activated sludge pump station by rerouting gravity flows and incorporating control valves, streamlining the system and reducing operation and maintenance costs.

The outcome of this project is a more efficient, cost-effective wastewater treatment facility capable of handling higher nutrient removal demands, meeting compliance with regulatory requirements, and enhancing overall performance. The collaboration between Carollo, ERWSD, and the CMAR contractor (Moltz Construction) led to a smooth construction process despite the challenges of working within a tight site, respecting the proximity of neighbors and Town of Avon residents, and maintaining plant operations. The upgrades not only improved the facility’s operational efficiency and reliability but also reduced energy consumption by incorporating energy-efficient low-pressure screw blowers.

Environmental benefits include enhanced water quality in the region’s watershed, while the community gains from reduced treatment costs and improved environmental stewardship. The project’s successful execution positions the Avon Wastewater Treatment Facility to meet future regulatory standards and provide long-term value to the community and environment.