Paso Robles always discharged its treated effluent into California’s Salinas River. That is until changing influent and prolonged drought conditions spurred improvements at the city’s wastewater treatment plant. The plant now reclaims previously wasted resources, showcasing a sustainable and cost-effective approach to water quality and water supply resilience.

With Black & Veatch as the designer and engineer of record, the project added tertiary treatment facilities to the 4.9-mgd (million gallons per day) plant to reduce reliance on the Paso Robles Groundwater Basin, whose levels had fallen significantly from overdraft, and produce California Title 22-compliant recycled water for irrigation of area parks, golf courses and vineyards.

It also added a first-of-its-kind nutrient harvesting system at a municipal wastewater processing plant in California. In addition to keeping phosphorus, nitrogen and ammonia from overloading and polluting area waterways, the system converts the struvite into fertilizer the city can sell to subsidize its operating costs.

Engineered for Efficiency, Quality and Sustainability

• The new facilities were added within the plant’s existing footprint.
• The plant has the flexibility to discharge high-quality water to the Salinas River when demand for recycled water is low and minimize the use of UV for disinfection, saving energy while still meeting discharge requirements.
• The tertiary treatment process flows by gravity. This eliminates the need for pumping, reducing equipment and energy expenses.
• A nutrient management system was planned for the plant, but its development was accelerated and completed when operators discovered – during construction of the tertiary treatment facilities – that filtrate laden with phosphorus was causing struvite buildup in pipes and inhibiting treatment processes.
• Secondary sedimentation tanks that had sat unused were repurposed for flow equalization, allowing disinfection processes to operate continuously and at a more constant rate.
• The features and approach of the upgrade helped Paso Robles secure a $4 million Green Project Reserve grant for environmentally innovative projects.

“The project is a milestone in our long-term plan to create a resilient and sustainable water supply,” said Paso Robles Wastewater Resources Manager Matt Thompson. “We now can produce high-quality recycled water without building a purification plant. Black & Veatch helped us optimize existing assets and minimize capital and future operating costs in the process.”

Packed with innovations that optimized its physical and environmental footprint, the improvements won the Global Water Awards’ 2020 Wastewater Project of the Year. The prestigious international award program rewards achievements that advance the water industry in terms of improved operating performance, innovative technology adoption and sustainable financial models.