After a summer of COVID restrictions, travel and (hopefully) a bit of vacation, many of us are heading back into the office or classroom. While we might not spend a great deal of time thinking about the implications for our water use at work, NAWI friends at Phoenix Process Equipment Co. and Aquacell Water Recycling Ltd. certainly do. Over the past month, they have graciously hosted NAWI members on tours of the Salesforce Tower in San Francisco and Meta corporate campus in Menlo Park, CA (yes, that Meta) where they designed and installed onsite “blackwater” reuse facilities. They shared some important lessons in operating small-scale water treatment systems.
First the stats. Both facilities were designed to accommodate large office populations and treat between 40 to 90 thousand gallons per day of rainwater, toilet, and sink wastewater to a quality safe for additional toilet flushing and/or irrigation (of salinity sensitive redwoods!). Both facilities used roughly the same process train consisting of belt filter (with solids discharged to sewer), aerobic membrane bioreactor system (MBR), RO, ultraviolet (UV), and remineralization. While the Salesforce system was idle at the time of our visit, Meta’s system was just getting restarted after a long COVID hiatus, and will be resuming water delivery in the coming weeks.
Next the insights:
- COVID threw onsite systems a major curveball. Meta’s campus was fully populated before the 2.5 year-long COVID shutdown; the new “normal” office population (about one-third of pre-pandemic numbers) is sufficient to sustain the MBR, but is far below the original design capacity. We had some great discussions about resilient designs, including what it would take for systems to operate at a mere 10% of their design capacity for an extended period of time.
- Tanks, tanks, tanks! Water treatment and reuse systems require a LOT of water storage. This is often overlooked in academic studies. Not only are tanks expensive ($2-$10 per stored gallon) but they also have a significant footprint — not cheap when it means displacing coveted parking spots and valuable Silicon Valley real estate. Ideally, below-grade storage tanks are integrated into the original building design. Researchers probably need to do a better job of factoring storage into the total cost projections for on-site systems.
- Insensitivity (indifference?) to electricity consumption. During both of our tours, we had a hard time even finding the electrical meter and system designers often have no information about the actual system energy use once its installed and operating.
- Odor and color control is essential. Office building tenants do NOT want to smell even a whiff of typical wastewater treatment plant “fragrance”, and tenants don’t want to flush their toilets with yellow water. A lot of our process designs for onsite blackwater reuse are dictated by odor and color rather than by safety concerns. We wondered aloud where NAWI technologies could make an impact in these two important aesthetic areas.
- Permitting blackwater recycling systems remains a regulatory challenge. While greywater recycling has become significantly easier to permit over the past decade, blackwater systems are really first-of-a-kind demonstration sites in most regions. They are often held to the same standards for daily monitoring, sample collection, and thus demand frequent sensor monitoring and calibration. Technology and regulations are going to have to evolve together for building-scale reuse to really take hold.
- These systems are far too complex to be managed by a typical property manager or site engineer. Both sites we visited had real-time remote monitoring. The (operational) Meta facility had a dedicated Level 2 operator onsite, as well as a contract with a local laboratory for daily sampling collection/analysis. Additional facilities operation support and maintenance was a phone call away.