North Davis Wastewater Treatment Plant and Biosolids Phase I and II

In order to meet the demands of their growing community, North Davis Sewer District embarked on an initiative to overhaul their existing facilties. This included two separate phases of construction.
Phase I, was a $91M upgrade and expansion of the North Davis WWTP. Through collaboration with the Owner, MWH was able to realize $10M in savings over the course of the project, which increased the plant capacity from 25 million gallons a day (MGD) to 34 MGD.

Other scope included digester mixing improvements to replace the existing pump mix systems, a solids processing facility, and primary clarifier upgrades. 850,000 man hours were completed on the Phase I project with zero OSHA recordable incidents, a feat which led North Davis to integrate the MWH Health and Safety Plan into their own.

Phase II was a $49M biosolids process expansion delivered as a progressive-design-build and consisted of a primary sludge screening and thickening facility, a new cogeneration facility, and upgrades to the existing secondary digesters. The existing unheated and unmixed secondary digesters were converted to mixed mesophilic digesters by the addition of heated draft tube mixing systems and tank cover insulation. Primary sludge thickening, as well as scum concentration, were added to increase the thickness of the solids feed to the digesters, reducing the hydraulic load and heating requirements. Because of these improvements, methane gas was able to be harnessed as waste moved through the District’s cogeneration facility. This methane is used to power North Davis’s electrical generators, creating 100% of its process heating needs and 65% of its total energy needs, with a savings of $35K to $40K a month in electricity costs.