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Fire Destroys MN Biosolids Treatment Plant: Short Timeline Requires Fast Thinking

Northfield, MN 55057, USA
Bolton & Menk

Government Champion

City of Northfield Public Works


3.7 Million USD

Project Status

Operational since 2021

At a Glance

The City of Northfield's biosolids treatment building suffered a catastrophic fire, damaging all equipment beyond repair. Within a short timeline, an interim biosolid treatment option needed to be identified and a new system developed to both fit in the existing building while meeting the city’s requirements.

Problem Addressed

The City of Northfield experienced a catastrophic fire in their biosolids treatment building on May 29, 2018. The fire is believed to have started in the pasteurization vessel and damaged the entire biosolids treatment process along with other equipment. HVAC ductwork and odor control vessels were severely damaged by the heat and smoke with the walls and ceiling stained black from the smoke and soot. Thankfully, only the biosolids building was damaged and all other buildings and treatment processes were not harmed. The adjacent finished biosolids storage building had minimal smoke damage. Interior inspections began immediately, revealing severe damage to both the building and existing equipment. Structural engineers investigated the building and determined there was no significant structural damage.

A State of Emergency for the biosolids system was declared, allowing the city to move quickly to determine how to proceed for both interim and long-term fixes. The city's insurance helped pay for improvements as well as the cost to replace the original equipment. Insurance also covered the cost for interim treatment while the new process was still being designed and constructed.

Many decisions had to be made quickly to keep the treatment process operating and meeting limits. The city still produced 45,000 gpd of biosolids and needed a place to put it. Northfield has limited storage as the aerated storage tank is located below the biosolids processing building. The city was still able to pump to the storage tank but could not aerate or pump anything away from the tank. The city decided to pump liquid biosolids and haul to any facility that had capacity for additional product. The biosolids were hauled using 7-10 tanker trucks a day to other local municipalities. While this worked temporarily, the city needed to find an interim treatment option.

Twenty-one days after the fire, the City of Northfield rented a temporary biosolids treatment system from Schwing Bioset that included a screw press, polymer feed system, lime feeder, Schwing Bioset reactor, and a discharge chute. This temporary equipment required new piping for the biosolids feed and a 7,500-gallon temporary tank to be installed, allowing a constant feed of biosolids into the temporary system. In the meantime, the city worked with Bolton & Menk to put together plans to install temporary biosolids equipment. The temporary unit was delivered to the project site on July 30, 2018 and was installed and processing biosolids by September 2, 2018.

The City of Northfield used/is using quick thinking and effective planning to address this/these challenge(s).

Solution(s) Used

In October 2018, the City of Northfield hired a contractor to start removing the contents of the fire-damaged building. The contractor removed everything from the building in approximately three weeks; screw presses, biosolids processing equipment, two odor control units, chemical feed equipment and tanks, electrical conduit and wiring, as well as lights. Structural engineers determined two wall panels on each end of the building could be fully removed without structurally compromising the building to help remove the old equipment and bring in the new. Once all equipment was removed, the building was cleaned from November 2018 to mid-December 2018 to remove smoke and soot from the walls, ceilings, and floors. Temporary walls were then installed to seal the building.

Bolton & Menk started the design to place the new equipment in the existing building. The process was tricky as the new equipment needed to fit within the existing building footprint and meet the various structural limitations. With the biosolids storage located beneath the building, there were restrictions on what could be placed on top of the storage tank. The plans and specifications were only for installing the equipment as the city was procuring the major pieces of equipment (screw presses, Schwing Bioset unit, odor scrubber, and chemical feed equipment). Layout meetings were conducted with the city and the building official to work through any code-related items.

In May 2019, Shank Constructors started work on piping, concrete pad demo, pouring new floors and concrete pads, and interior painting. The odor scrubber build was finished at the factory in May 2019 and delivered in June for installation. All new electrical conduit and wiring was placed, new HVAC duct work and equipment and new pumps and piping were also installed. The biosolids equipment started arriving in mid-November 2019 and the final shipment arrived in mid-December 2019.

The aeration system was inoperable for about 1.5 months and during that time, solids settled into the diffuser system and plugged some of the aeration headers. Through continued use of the new blower, the plugging improved, however the aeration system needed to be replaced. The sludge storage tank’s aeration system was replaced in the summer and fall of 2019 and required bypassing of the storage tank into existing, unused circular clarifiers, to store biosolids before pumping them to the temporary treatment system. This required piping from the existing primary clarifier building and installing overland piping to the circular clarifiers. From these temporary storage clarifiers, additional pumps and hose fed the interim treatment system while the new aeration system was installed.

Equipment start-up and commissioning began in late-March 2020 and continued through mid-April 2020. Once the new equipment was running and producing a Class A product, the contractor dismantled the temporary equipment, removing it from the site in mid-April.


  1. In under two years, the city lost their biosolids system, ran a temporary system, removed damaged equipment, and installed a new Class A biosolids process within the existing building.
  2. Quick thinking and effective planning allowed for minimal complications while the temporary biosolids treatment facility was in action, keeping the costs lower and the project on schedule.

Something Unique

Bolton & Menk was challenged with designing a wastewater treatment plant that would not only fit in the existing building and meet structural limitations, but also meet city requirements. During the design process, a temporary treatment structure had to be developed, ensuring all wastewater needs would continue.

Who Should Consider?

Communities dealing with an unforeseen circumstance with their essential treatment facilities who need temporary solutions to keep operations running during design and construction.

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