Small municipal treatment system upgrades to Blue PRO® reactive filtration for phosphorus removal.

Project Background & Challenges

Located in Chippewa CountyWisconsin, about two hours east of Minneapolis, is the city of Bloomer, population 3,539. Bloomer is built along Duncan Creek, only 15 miles from Chippewa Falls, and in the heart of the United States’ lake-rich Upper Midwest region.

Like many municipalities across North America facing environmental concerns over phosphorus—particularly those in the Great Lakes watershed—Bloomer was given a new Total Phosphorus (TP) limit that its existing wastewater treatment was unable to achieve.

Regulators in Wisconsin frequently issue permits based on a Total Maximum Daily Load (TMDL), which refers to the maximum amount of any nutrient a body of water can receive, while still maintaining water quality standards. While phosphorus objectives in Wisconsin and the rest of the United States vary substantially, some states are now seeing TMDL-based limitations as low as 0.022 mg/L. The permit issued to Bloomer included a TP limit of <0.075 mg/L and a TSS limit of 5 mg/L.


The Nexom Solution

The Blue PRO® reactive filtration process for phosphorus removal was identified as a technology of interest for its ability to achieve very low contaminant residuals while minimizing operating costs with mechanical simplicity. The phosphorus compliance upgrade was sized for 0.369 MGD average daily flow, with a 1.42 MGD peak flow. With contract deliverables of <0.075 mg/L TP, and <5 mg/L TSS a Blue PRO solution was further investigated to meet Bloomer’s discharge permit cost effectively.

The Blue PRO system was installed after the existing secondary clarifiers and before disinfection. Nexom provided a total of 5 filter cells in a single-stage configuration featuring n+1 redundancy with associated ancillary equipment.

Meeting <0.075 mg/L Phosphorus with Minimal O&M

Reactive filtration includes multiple features that allow it to be successful at Bloomer. It overcomes contact inefficiencies common with other technologies, which are critical process obstacles to achieving low residuals cost effectively.  Blue PRO achieves better contact by providing extensive adsorptive surface area, resulting in guaranteed contact between the contaminant and hydrous metal/ferric oxide (HFO) and its amenable adsorption kinetics. A vital benefit is that reactive filtration costs roughly 30-50% less in chemical and power to achieve treatment compared to other available technologies. Less chemical used also translates into less chemical sludge produced onsite. Additionally, the adsorptive surface in reactive filtration is a continuously regenerated coating forming on the surface of the sand media. The result is an efficient, phosphorus-scrubbing technology that is not limited by surface site exhaustion, unlike conventional adsorbents.

As shown in the diagram (above), influent enters the tank (A) and is distributed through the filter (B) near the bottom of the media column. Water is then filtered upward, and the sand coated with hydrous ferric oxide (HFO) attracts and reacts with the phosphorus. The sand (C) moves counter-currently downward by gravity to an airlift device (D). While the filtered water exits near the top of the filter (E), the airlift transports the phosphorus laden media up into the washbox (F) where the discharged HFO coating and adsorbed contaminates are separated from the media into a backwash stream. Water velocities in the washbox are carefully designed to carry away the contaminates (G) while allowing the media to fall to the filter bed (H). The freshly scrubbed media from the washbox is recoated with HFO as its cycle continues. 

Upgraded System Performance

Installation of the Blue PRO filters began in late 2020 and they were commissioned during the summer of 2021.

The phosphorus concentration into the Blue PRO was <0.8 mg/L and TSS <20mg/L. Following commissioning, the updated wastewater treatment plant easily achieved its contract targets of 0.075 mg/L TP and <5 mg/L TSS, and continuously meet its phosphorus and TSS targets since.

Project Information

Project Type: Municipal wastewater treatment

Completion Date: June 2021

Treatment Objectives

Design Flow:

  • 0.369 MGD (Average)
  • 1.420 MGD (Peak)

Effulent Objectives:

  • <5.0 mg/L TSS
  • <0.075 mg/L TP
  • <20 mg/L TSS

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