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Progressive Design-Build Ammonia Treatment and Biosolids Dewatering Improvements

City of Longmont
Longmont, Colorado

Project Overview

City of Longmont upgrades it treatment process to reduce ammonia and eliminate off site transport and treatment of biosolids

The City of Longmont serves a community of 98,700 residents. In 2012, new permit requirements along with process capacity and redundancy constraints drove the need for plant upgrades and process modifications. The City hired Carollo to manage its $32 million progressive design-build project, including the design, permitting, and construction of its ammonia treatment and dewatering system at its Longmont Wastewater Treatment Plant.

The first stage of the project focused on modifying the secondary treatment process to meet more stringent daily ammonia limits.

The progressive design-build approach enabled the City, Carollo, and project stakeholders to collaboratively develop a robust, cost-effective solution to maximize the improvements.

Project components included:

  • Upgrade the secondary treatment process to reliably remove ammonia.
  • Process 100 percent of the generated biosolids.
  • Replace the existing biosolids dewatering facility with a new centrifuge dewatering facility to provide more efficient and less costly solids disposal.
  • New maintenance building.
  • Demolition of the old headworks, bio-disc, and maintenance buildings.
  • Upgrades/replacement of ancillary facilities

Results and Highlights

The new biosolids processing facility has the capacity to treat 100% of produced biosolids, eliminating the need to use tanker trucks for off-site treatment. This results in an annual operational cost savings of $275,000.

New aeration basins and clarifiers enable the wastewater treatment process to meet new discharge limitations for ammonia.

The progressive Design-Build delivery model supported the City's desire for an integrated project team that included their plant operations and maintenance staff.

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