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  • New Project Harnesses Solar Power to Dry Biosolids at Tres Ríos

    A long-closed landfill is about to get a new lease on life, thanks to a new Pima County Regional Wastewater Reclamation Department (RWRD) project. 

    The Ina Road Landfill, located on the east bank of the Santa Cruz River south of Ina Road, will be used to help dry the biosolids that are produced at the nearby Tres Ríos Water Reclamation Facility. The landfill closed in June 2010 after reaching capacity. 

    During the wastewater treatment process, the organic matter in sewage is digested by anaerobic bacteria. This produces the biogas that is then refined to pipeline quality at the Tres Ríos Renewable Gas Center so that it can be sold to Southwest Gas. 

    The process also leaves behind organic solids, known as biosolids. Biosolids are rich in nutrients and are considered a high-quality fertilizer. 

    Despite the name, biosolids consist of about 80 percent water, even after dewatering—which makes it more cumbersome, and more expensive, to transport the biosolids to farms. 

    “Every time we haul biosolids we’re primarily hauling water,” said RWRD Deputy Director Jeff Prevatt. 

    The new drying facility will be designed to change that. Once it begins drying the biosolids, their water content will be reduced to roughly 20 percent. That will mean fewer trucks transporting biosolids to farms. 

    Currently, Prevatt said, as many as 12 truckloads a day are hauled to farms at an annual cost of over $2 million. After the new drying facility is completed, only about two truckloads would be hauled away each day, saving the County on fuel costs and removing one of the largest solids disposal bottlenecks facing water reclamation facilities. 

    In addition, the dried biosolids act as a slow-releasing fertilizer, lessening the risk of leaching contaminants into groundwater. 

    During the project, the landfill will be capped with additional soil from a nearby gravel pit requiring the installation of an access ramp allowing trucks and construction equipment to cross the Chuck Huckelberry Loop near the confluence of the Cañada del Oro Wash and the Santa Cruz River. Then, an array of concentrated, and possibly photovoltaic, solar panels will be installed. The concentrated solar will provide the thermal energy needed to dry the biosolids at the Tres Ríos facility. 

    Construction is expected to be completed in 2024.