Innovative Low-Level Phosphorus Compliance Project Receives Grand Award

Posted By: Eric Lynne Awards, Blog,

Written by: Eric Lynne, PE, Donohue & Associates

The City of Medford’s wastewater treatment plant was faced with equipment issues and a future ultra-low level (0.075 mg/l) effluent phosphorus limit that could not be met with its existing four-cell deep bed sand filter system.

In collaboration with Donohue & Associates, the City was able to develop a simple, cost-effective system that filters out the phosphorus before returning it to the environment.

The team designed a chemical feed system to achieve low effluent phosphorus and a disk filtration system to replace the existing sand filter system. A typical approach to phosphorus compliance (membranes) would have cost the City millions of dollars more. The operations staff were integral in providing input, evaluating alternatives, and selecting the final solution that met their goals.

This facility is the first in the state to merge rapid mix coagulation, flocculation with polymer, and physical separation of the precipitate using disk filtration to achieve high quality effluent for the pristine headwaters of the Black River. Phosphorus is an essential element for plant life, but too much phosphorus in the water causes algae to grow faster than ecosystems can handle. Significant increases in algae harm water quality, food resources and habitats, and decrease the oxygen that fish and other aquatic life need to survive (eutrophication). Through this project, the project team was able to cost-effectively reduce Medford’s phosphorus discharge to the Black River, which also assists with the State’s nutrient reduction goals in minimizing phosphorus loadings to the Mississippi River.

The solution developed extends existing equipment’s useful life, fits within existing buildings, and reduces power consumption. The new system does not require additional operator attention or compromise permit compliance during maintenance. The project included advanced on-line analyzers, which provide the operators with up-to-date data for use in determining the level of chemical dosing required. Using this detailed information to determine the optimal level of chemicals saves money and minimizes the environmental carbon footprint.

The City’s goal was to find a cost-effective, operator-friendly solution that would help the City minimize demands on their already limited staff. Other non-traditional alternatives evaluated to meet the low level P limits were not feasible, such as adaptive management, water quality trading, and variances. Donohue assisted the City with manufacturer qualifications before assembling bidding documents to improve construction coordination. A low-cost, operator-friendly solution proven to work full-scale at the City is changing this dynamic. The solution designed by Donohue is proof that clean water is possible at an affordable rate.

The City proudly shares their experiences with other communities in a way that develops a new network of phosphorus minimization specialists. These specialists will lead the water sector into the future as these tightened phosphorus limits are required at more facilities throughout the Midwest.

One of the truly unique aspects of this project is that the disk filter technology is universally scalable for both small and larger size plants. In fact, based on the City’s success, significantly larger communities (including Brookfield, Wausau, and La Crosse) are currently designing disk filter systems to meet low-level phosphorus limits. These operator-friendly, cost-effective filters are being used in place of traditional membranes, saving millions of dollars for rate-payers in these communities.

Former City Coordinator John Fales remarked, “This project was a highly collaborative effort between the engineer (Donohue), the manufacturer (Veolia), the construction contractor (Staab Construction), and our dedicated City personnel. This was a true partnership with all parties, as the installation is one of the first in the country to achieve the consistent low-level limits that we are experiencing. Prior to this project, our 10-year average for phosphorus was 0.64 mg/l; we are now averaging 0.04 mg/l with our new system, meeting our permit requirements years ahead of schedule.”

By achieving compliance before the deadline, the City may forgo many iterations of status reports and planning documents that are required for non-compliant facilities, saving thousands of dollars. With an ability to readily expand tertiary treatment flow capacity, the City is in a position to accommodate additional flows from regional communities who are faced with the same strict low level limits but would otherwise be unable to comply without expending significant capital.

About the Guest Blogger

Eric Lynne, PE is a project manager and senior wastewater engineer at Donohue & Associates, and has worked with the City of Medford for the past decade. He earned a master’s and bachelor’s degrees in civil and environmental engineering from South Dakota State University. Donohue & Associates, Inc. has been practicing client-focused water, wastewater and stormwater engineering services since 1997 with a reputation for expertise, quality, and service.

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