Greywater Recycling System Activated in San Francisco Condominiums

Nearly 1.5 million gallons of drinking water are saved annually by recycling gray water collected from MIRA’s luxury condominiums

Architecture by award-winning Studio Gang and a location just one block from the Embarcadero with breathtaking views of San Francisco Bay made MIRA SF one of the city’s most desirable residential high-rises. It didn’t take long for MIRA SF to be cast.

Apart from its attractiveness, MIRA SF, a 392-unit luxury condominium, features one of only two gray water recycling systems approved for operation by the San Francisco Department of Public Health (SFDPH). The G20R Aquacell System is capable of recycling up to 5,000 gallons per day of gray and rainwater for reuse for toilet flushing and landscape irrigation.

The Aquacell G20R Gray Water and Stormwater Recycling System at MIRA SF is shortlisted from the Approved Gray Water Recycling Systems in the City of San Francisco.

How the recycling system works

Nearly 1.5 million gallons of drinking water are saved annually by recycling gray water collected from MIRA’s luxury condominiums. Gray water is defined as wastewater collected from showers, bathtubs and/or hand basins. Wastewater (also known as blackwater) collected from kitchen sinks and toilets exits the building through separate pipelines and enters the municipal sewer system beneath the city’s streets. Although San Francisco allows blackwater recycling for building reuse, it was not suitable for MIRA SF. Gray water in multi-unit residential buildings is abundant and sufficient to support the nonpotable needs of the building.

The G20R Aquacell equipment and water collection tanks occupy approximately 2,000 square feet on the lower levels of the luxury high-rise. Gray water is collected and sent to the 4,700 gallon gray water buffer tank. Rainwater collected from the building’s roof is stored in a 5,000-gallon cistern. Whenever stormwater is available for treatment, it must be prioritized over graywater. This is a requirement of the SFDPH. This is achieved through the use of level sensors in the tanks and diverter valves on the incoming stormwater and gray water lines.

The gray and/or stormwater goes through a series of treatment processes prescribed and approved by the SFDPH. These treatment processes include coarse and fine filtration, aerobic biological treatment and disinfection. A water recycling system must also include processes that meet the requirements defined by the SFDPH to remove or inactivate pathogens in viruses, protozoa and bacteria.

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Maintenance is key

In order to obtain a valid operating permit, water quality must be closely monitored, analyzed and reported. Within the treatment system are critical control points that affect water quality, such as: g. turbidity and chlorine content, in real time around the clock. There is also a need to take water samples and analyze them in a certified laboratory. Parameters such as biochemical oxygen demand, total suspended solids and total E. coli must be analyzed monthly and reported quarterly. The water quality must always be within the limits set by the SFDPH. If water quality is ever found to be outside of acceptable limits, the water recycling system must be shut down until proper water quality is restored.

Aquacell by PHOENIX provides service and maintenance for the gray and rainwater recycling system at MIRA SF. Service and maintenance includes regular on-site work and 24/7 remote monitoring via the internet. The Aquacell system is designed for autonomous operation. However, tasks such as calibrating instruments, refilling chemical tanks, replacing consumables, etc. require on-site labor. The remote connection to the system allows the user not only to monitor the operation of the system but also to perform some maintenance tasks. The remote connection also alerts Aquacell to alarms.

The process by which an alternative water source system is allowed to operate in the City of San Francisco is lengthy and begins long before a drop of water is reused within the building. Before an alternative water source system is manufactured, a number of steps must be completed to meet the requirements of city regulators. These steps include completing the application and water budget calculator.

Credit: Bruce Damonte

The Water Budget Calculator is a tool developed by the San Francisco Public Utilities Commission (SFPUC). It is used to calculate the daily and annual amounts of water a building uses. A distinction is made as to which fittings must be supplied with drinking water and which can be supplied with non-potable recycled water. The city’s non-potable water ordinance states that all toilet and urinal flushing and irrigation requirements must be met with recycled rainwater and gray water. Using the SFPUC’s water balance calculator, it was determined that all of MIRA SF’s flushing and irrigation needs could be met with recycled gray and rainwater.

SFDPH requires the development and submission of an Engineering Report document for review and approval. The technical report highlights the details of the alternative water source system. The SFPUC’s review of the technical report verifies that the required treatment processes are included and that the specified water quality is achieved.

Once the water balance calculator and application have been approved, fabrication of the alternative water source system can begin. The Aquacell G20R system was manufactured on a so-called “skid” and delivered to the construction site. The rack is supplied piped and wired to minimize on-site installation effort. Onsite labor was required to connect the plumbing and electrical wiring from the building to the Aquacell skid.

Before an alternative water source system can be commissioned for continuous operation, a reliable source of wastewater must be in place. In a dwelling there must be sufficient occupancy, producing greywater that can be recycled.

Immediately after go-live, the system must go through a 90-day conditional go-live phase. During this time, the alternate water source system is fully operational, however all recycled water is directed to the sewer. During these 90 days, the water sample analysis required by the SFDPH will be increased. The system must demonstrate that it can consistently produce reclaimed water quality within the limits set by the SFDPH in order to receive a final operating license. Only after receiving the final operating license is a building allowed to start reusing the recycled water within the building. MIRA SF received its final operating license on October 19, 2021. Since then, recycled gray water has been reused in the building.

Save fresh water

As human populations continue to increase around the world, and particularly in drought-prone regions like California, the need to conserve freshwater remains. Recycling and reusing water on site can have a positive impact on fresh water supplies and ensure there is enough for everyone. MIRA SF and the San Francisco Public Utilities Commission are leading the way in demonstrating how meaningfully utilizing and reusing precious resources like water is the new standard and way of the future.