In brief
- Stanford researchers developed a framework showing that coordinating infrastructure upgrades across Bay Area wastewater treatment plants could substantially reduce costs of meeting new nitrogen pollution limits.
- Applied to three nearby treatment plants, the tool found that coordination could cut combined capital and operating costs by up to 48%, saving $268 million over 30 years.
- Researchers say starting coordination now, rather than waiting until infrastructure decisions are locked in, would generate additional savings and could help convince utilities to work together.
Treating polluted water flowing into San Francisco Bay to meet regulatory requirements is going to cost ratepayers money. Exactly how much depends, in large part, on whether the region’s wastewater treatment plant operators are willing and able to coordinate infrastructure construction and operation to meet these requirements, according to a Stanford University study published Sept. 24 in Nature Water.
The paper features a framework that calculates the most cost-effective way for multiple treatment facilities to jointly plan, build, and operate infrastructure to remove excess nitrogen from wastewater before it is discharged to the bay. Applied to three Bay Area treatment plants within a few miles of each other, the tool found that coordination could cut total capital and operating costs by up to 48%, a savings of $268 million over 30 years compared to the cost of building infrastructure independently.
“If you don’t coordinate, each facility has to build and finance small infrastructure projects on its own,” said study lead author Sinan Abi Farraj, a PhD student in civil and environmental engineering in the Stanford Doerr School of Sustainability and School of Engineering. “The coordinated solution reduces how much infrastructure gets built and how much that infrastructure costs.”
Recovering resources from wastewater affordably and sustainably
In response to algal blooms, fish-kill events, and other damaging impacts of nitrogen pollution, regulators have ordered a 40% reduction in nitrogen discharges into the San Francisco Bay by 2035. Meeting those limits the conventional way, with each of the region’s 37 plants independently upgrading its own facilities, is projected to cost more than $10 billion and require annual sewer rate increases of roughly $200 per household.
Until now, utilities and planners have had no reliable way to calculate how much coordination could actually save them. Existing tools are designed to optimize upgrades within a single facility, not across multiple plants sharing a watershed. This leaves utilities largely dependent on inconsistent models created by consultants to estimate potential savings from working together.
The researchers point out that nitrogen removal doesn’t have to happen at each plant individually. Construction costs don’t scale proportionally with capacity. If a larger facility can remove nitrogen more cheaply than a smaller one, it makes economic sense for the larger plant to handle more of the load while the smaller one builds less or nothing at all.
“Regional facilities rarely coordinate their decadal capital improvement plans or monthly operations because independent agencies monitor them and issue separate discharge permits,” study senior author Meagan Mauter, a professor of civil and environmental engineering. “We have developed a transparent framework that reveals the magnitude of the cost savings that coordinated infrastructure design and operation unlocks for the Bay.”
The framework models monthly capital and operational decisions over 30 years across multiple facilities simultaneously, identifying the lowest-cost portfolio of upgrades across a watershed rather than within any single plant’s fence line. The researchers found that a staged scenario in which plants delay construction until it’s needed, rather than building in advance of permit deadlines, generated meaningful savings. However, the largest gains came from staged and full coordination: jointly deciding what to build, where, and when across all three plants.
Timing matters too. The analysis found that beginning coordination now would save an additional 32% compared to waiting until 2045, by which point many plants will have already locked in their infrastructure decisions and their debt.
Several Bay Area utilities are in conversations about forming a regional coordination effort, according to Abi Farraj, but most are waiting for regulators to approve an official coordination framework before committing.
“The only way you convince a plant to coordinate is to show them exactly how much their ratepayers will save and give them confidence that they will still be able to maintain regulatory compliance,” said Abi Farraj. “That’s what this tool is designed to do.”
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Study co-author Akshay Rao is a PhD student in civil and environmental engineering, a joint department of the Stanford School of Engineering and the Stanford Doerr School of Sustainability.
Mauter is also a senior fellow at the Stanford Woods Institute for the Environment and the Precourt Institute for Energy, both in the Stanford Doerr School of Sustainability. She is also an associate professor of photon science and, by courtesy, of chemical engineering.
The research also received funding from the Natural Sciences and Engineering Research Council of Canada (NSERC) Postgraduate Scholarship-Doctoral (PGS D) award.
This story was originally published by Stanford Woods Institute for the Environment.
Writer
Rob Jordan
