A newly opened sustainable development in San Francisco that is designed to use zero potable water for non-potable purposes includes the largest private blackwater treatment system in California. Located on a 28-acre waterfront site opposite the San Francisco Giants’ Oracle Park stadium, the Mission Rock neighborhood is expected to conserve millions of gallons of water annually as a result of its various sustainable features. 

Building B and blackwater

In June, tenants began moving into The Canyon, the first of Mission Rock’s 11 proposed buildings to open. Developed by the San Francisco Giants, the real estate investment firm Tishman Speyer, and the Port of San Francisco, Mission Rock is expected to total 3.5 million square feet at full build out and comprise a mix of residential and commercial buildings. In addition to The Canyon, which was designed by the architecture firm MVRDV, Phase 1 of Mission Rock includes three other buildings.

Situated beside The Canyon is a life sciences building that has yet to open to tenants. Currently known as Building B, the structure, which was designed by the architecture firm WORKac, houses a pump station that receives blackwater from toilets, sinks, and showers located throughout the north half of the Mission Rock development. The pump station conveys a portion of the flows to the blackwater treatment system and sends the rest to the city’s sewer system.

Having a capacity of 64,000 gal/d, the treatment system comprises a series of tanks followed by ultrafiltration membranes, reverse-osmosis membranes, and disinfection by means of ultraviolet light and chlorine (see diagram). 

The treatment system is expected to generate up to 43,000 gal/d of treated water to be used onsite for nonpotable purposes, including irrigation and toilet flushing, says Michael Ahern, a senior vice president and the chief development officer for Ever-Green Energy, an operator and manager of utility systems that oversaw the design and construction of the blackwater treatment system, in collaboration with other Mission Rock partners. 

Starting the system

Currently, the blackwater treatment system is undergoing commissioning. As part of this process, the system is “starting up on clean water right now,” Ahern says. This approach enables testing of the system to “make sure everything is operating the way it should,” he says.

At the moment, the volume of blackwater generated within the development is insufficient for proper operation of the treatment system, Ahern notes. “There's not enough people living and working at Mission Rock yet to enable the system to operate the way it's supposed to operate,” he says. 

However, he expects that the blackwater system will be operating as intended by the end of this year. Operations of the blackwater treatment plant will be handled by building management staff, with guidance from Ever-Green Energy.

Upon full build out of the Mission Rock development, the blackwater treatment system is expected to facilitate the conservation of approximately 16 million gallons annually, Ahern says.

A separate purple pipe system will return recycled water for nonpotable uses within the buildings and for irrigation onsite. Initially, recycled water also will be used as make-up water for the cooling towers that are currently part of Mission Rock’s district energy system, which also was supported by Ever-Green Energy.

Renewable energy goals

To obviate the need for heating and cooling equipment in each building, Mission Rock employs a shared energy plant to supply heating and cooling across the development. This approach is “more cost-effective than if each individual building handled its own heating and cooling needs,” Ahern says.

Initially, this district energy system will comprise heat-recovery chillers and traditional boilers and chillers, Ahern says. However, the long-term plan is to employ only renewable energy sources for building uses within Mission Rock. 

To this end, the district energy system is designed to eventually use water from the nearby San Francisco Bay “as a geoexchange source to heat and cool the buildings, which, when coupled with renewable electricity, will serve all buildings with carbon-free energy,” according to a June 21 news release from Ever-Green Energy. “By replacing conventional cooling towers, the bay water exchange system is expected to conserve millions of gallons of water per year while achieving the city's goals of reducing water use,” the release states.

Although its design work is currently underway, the planned bay water exchange system will be located in The Canyon and use heat exchangers to transfer energy from the bay water to water within the district energy system, Ahern says. “Then you have heat-recovery chillers and heat pumps that will get you up to the hot water temperature you need and get you down to the chilled water temperature you need.” 

Reducing water, energy use

The bay water exchange system is intended to be constructed “once there are enough buildings that will be connected to the energy system” to make it “more financially viable,” Ahern says. “It would be too big of a system and too much cost to put in for just these first four buildings” that are being constructed as part of the first phase of Mission Rock, he says. “There's a need for size and scale to be able to justify the build out of that bay water energy system.” 

“At full build-out, the energy and blackwater recycling systems are estimated to reduce annual energy usage by 24,000 MMBtu, water and non-potable water usage by 18 million gallons, sewer discharge by 12 million gallons, and [carbon dioxide] emissions by 1,600 tons,” according to Ever-Green Energy’s release.

All told, designing and constructing the blackwater treatment system and the existing district energy system cost approximately $40 million, all of which was debt-financed, Ahern says. A joint venture of the Hathaway Dinwiddie Construction Company and Nibbi Brothers General Contractors served as the general contractor for Building B. ACCO Engineered Systems provided mechanical contracting services, while Cupertino Electric, Inc., served as the electrical contractor.