The North Davis Sewer District’s biosolids treatment processes were operating over capacity and relying on inefficient and outdated equipment. The $58-million, design-build capital improvement project provided upgrades and expanded capacity to sustain the area’s growth through 2030, all while minimizing the environmental footprint and complying with current and future regulations.

Constructing new buildings and systems alongside aging infrastructure demanded significant collaboration and complex sequencing over a four-year period.

Key improvements included mechanical mixers and heating upgrades for the secondary digesters, a new primary solids-thickening building and a cogeneration facility, which houses two 1,100-kW, high-efficiency, advanced reciprocating engine-system lean-burn generators. They allow owner NDSD to generate 100% of the plant’s heating needs, 75% of its current energy needs and up to 90% of future demands. In contrast, the previous cogeneration system could generate only 55% of the electrical power needed.

The new engine generators will also operate at more than 40% electrical efficiency, a 36% increase over the aging engines they replaced. Additional improvements include a boiler for the backup heating supply, heat-recovery systems and a new biogas treatment system that will substantially reduce maintenance costs.

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