The city of Tooele, Utah, was established in 1851 and today has a population of more than 30,000 residents. In order to meet the demands of the growing community and prepare for future growth, the existing wastewater treatment facility required an expansion. Part of this growth included meeting the city’s goal of providing energy-efficient, environmentally conscious solutions for its wastewater facility.
Phase 1B of this expansion included the construction of a new ultraviolet disinfection system and a new solids drying facility. As an alternative to open bed sludge drying, the greenhouse construction was the most challenging aspect of the project.
As the first solar drying greenhouse in the U.S. dedicated to the drying and stabilization of municipal wastewater sludge, the building uses free solar energy to dry the biosolids.
A conveyor transports the biosolids into the building, where they are protected from the elements. The biosolids then are spread across the 49,000-sq-ft greenhouse. The size of the space—310 ft long—posed a challenge as construction crews assembled the concrete framework, since enough space had to be allocated for the sludge turning mechanisms to span the length while maintaining an elevation of 1/4 in.
The new technology dries the sludge and, as a result, the overall volume of the biosolids is reduced by 75%, from 300 tons of 16% solids wet sludge to 50 tons of 98% dry solids per month. The process produces an easily transported, dry granule that can be sold to the public as a soil conditioner.
“Sludge drying and stabilization is energy-intensive for some facilities,” said Stan Miller, project manager. “This is a system that can reduce operational costs.”