Municipal Wastewater and Sludge Are a Resource, Not a Waste: Coping with Tightening Water Supplies and Limited Landfill Availability

As in many parts of the world, water districts in Southern California are adapting to meet new challenges in supplying potable water and providing wastewater treatment.

Southern California’s water supply has become less reliable and, in the case of the Tapia Water Reclamation Facility, ecosystem concerns are resulting in increasingly stringent limits on the volume of wastewater treatment effluent that can be discharged to surface waters. One solution to both of these challenges is potable reuse of wastewater treatment plant effluent. Dr. Adam Zacheis will describe the Pure Water Demonstration Project, which will test the proposed treatment train for a future full-scale facility that would produce up to 5,151 acre-feet per year for surface water augmentation to the Las Virgenes Reservoir. The existing Tapia Water Reclamation Facility will provide the influent for the Demonstration Project. The Demonstration Project is a fully automated and operational purification system with full-scale components (open platform design with ultrafiltration, reverse osmosis, and an ultraviolet advanced oxidation process), but done at a relatively small scale to minimize costs. In contrast to other pure water projects, this Demonstration Project must address the challenges of seasonal variability in effluent volumes, feed water quality issues, high reliability, and potential stabilization and quenching of chlorine/chloramine.

Another challenge related to wastewater treatment in Southern California is limited landfill space. Brett Dingman will explain that instead of being disposed of in a landfill, municipal wastewater treatment sludge from the Tapia Water Reclamation Facility is composted in the Rancho Las Virgenes Compost Facility. This in-vessel composting process was the first municipal sludge composting facility in the western United States. The facility is unique because it was constructed with screw conveyors to move materials, centrifuges for dewatering, a plow mixer and agitators to mix feedstock, and in-process temperature monitoring to produce a consistent quality compost product. During the composting process, microbes feed on organic materials in the mix, raising the temperature to about 130 degrees F. The heat stabilizes the material and inactivates any potentially harmful bacteria that remain, while maintaining the proper temperature for beneficial “composting” microbes to do their work. The entire composting process takes approximately 45 days. All of the biosolids produced during wastewater treatment are composted into a Class A, Exceptional Quality product that is beneficially re-used without restrictions.