Silicon Valley Clean Water weighs nutrient synergy for $1.1bn reuse program

Silicon Valley Clean Water weighs nutrient synergy for $1.1bn reuse programThe California utility is advancing a phased indirect and direct potable reuse initiative in partnership with the SFPUC, aiming to align the project with upcoming nutrient removal mandates to optimize treatment costs.

The PureWater Peninsula project is planned as a two-phase initiative, starting with 6 MGD of indirect potable reuse (IPR) to Crystal Springs Reservoir and expanding to 12 MGD with direct potable reuse (DPR) capabilities.

Construction costs are estimated at $1.1 billion in 2024 dollars, with life cycle unit costs ranging between $5,240 and $6,910 per acre-foot.

SVCW is evaluating a "split-stream" membrane bioreactor (MBR) approach for nutrient removal that could improve feedwater quality and eliminate specific treatment steps for the reuse facility.

Preliminary estimates suggest aligning the reuse project with the MBR nutrient removal strategy could result in avoided costs of over $100 million.

The SFPUC identifies the initiative as its "most viable" alternative water supply project, with a planning and design horizon extending through 2035.

Silicon Valley Clean Water (SVCW) presented a status update on the PureWater Peninsula Project, a regional potable reuse initiative being developed in partnership with the San Francisco Public Utilities Commission (SFPUC) and the Bay Area Water Supply and Conservation Agency (BAWSCA). The project is designed to bolster drought resilience for the San Francisco Peninsula through a hybrid Indirect Potable Reuse (IPR) and Direct Potable Reuse (DPR) approach. Authority Manager Matthew Zucca outlined the project's phasing. Phase 1 involves constructing an Advanced Water Purification Facility (AWPF) to treat 6 million gallons per day (MGD) of wastewater to IPR standards for augmentation of the Crystal Springs Reservoir. Phase 2 would expand capacity to 12 MGD, incorporating DPR connections to local drinking water distribution systems. The Basis of Design Report (BODR) estimates total construction costs at approximately $1.1 billion (2024 dollars). This figure reflects the complexity of a regional system requiring extensive conveyance infrastructure, including over 20 miles of pipelines and multiple pump stations, rather than just the treatment plant itself. Life cycle unit costs are projected between $5,240 and $6,910 per acre-foot. A central focus of the discussion was the potential synergy between the reuse project and SVCW’s impending nutrient removal mandates. Manager Zucca described a strategic "fork in the road" regarding the agency's "STAR" (Strategic Treatment Advancement Roadmap) nutrient removal efforts. The agency is weighing two primary options: "intensification" of the existing biological treatment process or the construction of a "split-stream" membrane bioreactor (MBR). Zucca highlighted that the MBR option would produce significantly higher quality effluent (Total Inorganic Nitrogen of 5 mg/L) compared to the intensification method (25 mg/L) or the current conventional treatment (50 mg/L). This improved water quality could allow the reuse facility to forego certain treatment processes required under the current BODR, such as ozone, biological activated carbon, and microfiltration. "Potentially we can get away from the ozone, the carbon, the microfiltration," Zucca noted. Furthermore, the MBR approach might allow the repurposing of an existing 2-million-gallon recycled water tank in Redwood City, avoiding the construction of new equalization storage. Preliminary estimates indicate that aligning the reuse project with the MBR nutrient removal strategy could result in significant savings. "The numbers are at least initial estimates over $100 million... that we could be saving," Zucca stated, referring to avoided costs for the region. Steve Ritchie, Assistant General Manager for Water at the SFPUC, confirmed the strategic importance of the project, calling it the "most viable project... left standing" among the agency's alternative water supply options. He outlined a timeline where planning and environmental review would proceed through 2035, with construction following. Ritchie emphasized that while the timeline is long, the project represents "the future of water in California." The Commission must decide on the nutrient removal technology path within the next year to avoid precluding these potential cost savings. Zucca emphasized the need to determine the "lowest total cost project" that maximizes benefits for ratepayers across both wastewater and water agencies.