Photo: courtesy of Sustainable Water
In the spring of 2015, Emory University in Atlanta commissioned an innovative campus water reclamation and reuse system known as the WaterHub. Treating up to 400,000 gallons each day, the system can recycle the equivalent of two-thirds of the university's wastewater production and reduce the campus water footprint up to 40 percent.
In less than one year, the WaterHub at Emory has garnered a lot of attention in the water industry, having been named the 2015 Innovative Project of the Year by the WateReuse Association (WRA), the industry's leading research institution for the advancement of water reclamation and reuse. Sustainability enthusiasts, including Gina McCarthy, administrator of the U.S. Environmental Protection Agency (EPA), have dubbed the WaterHub at Emory “a model for us all” for onsite water management.
Perhaps the first system of its kind installed in North America, the WaterHub at Emory mines wastewater from the campus sewer system and repurposes it for beneficial reuse using an engineered blend of technology and nature. In its first month of operation, the facility reclaimed 6.2 million gallons of water, and is expected to save millions of dollars in water and wastewater utility costs for the university over a 20-year period.
Perfect storm of water-related challenges
Located only 15 minutes from downtown Atlanta, Emory University has witnessed the perfect storm of water-related challenges. In Metro Atlanta, consistent seasonal drought is exacerbated by the region's location in one of the smallest watersheds for a metropolitan area of its size. Regional water stress is further compounded by a long-standing political dispute over rights to water supply between Georgia and the neighboring states of Florida and Alabama.
Unfortunately, these difficulties are only part of the story when discussing the region's many water stresses. Aging infrastructure not only negatively impacts level of service, but in some cases has resulted in federal consent decrees to resolve critical infrastructure failures, which have and will continue to result in skyrocketing water and wastewater costs to most utilities in the region.
Consequently, sustainable water management has become a critical issue for the region and a specific operational focus for large water consumers in the Metro-Atlanta area. Using close to 350 million gallons of water annually, Emory University began to deploy somewhat conventional water conservation tactics ranging from low-flow fixtures to stormwater reuse systems. However, the magnitude of the stresses and challenges dictated a more strategic and impactful water management solution: campus-wide water reclamation and reuse.
Emory University is known as a top-tier research institution recognized for its medical school and various professional programs. Like most major universities, Emory is a bulk consumer of clean, potable water and, thus, is a significant producer of wastewater discharge. In 2014, the university consumed more than 330 million gallons, despite significant cuts in potable water consumption over the years. Of this, 40 percent is considered non-potable demand, or uses for which scarce potable-quality water is neither required nor cost effective.
The largest categorical use of campus water is for utility (heating and cooling) functions. Emory has five major chiller plants and one steam plant that provide critical heating and air conditioning services to the campus. Together, these six utility plants consume 30 percent of total campus water supply, or approximately 105 million gallons annually. Extensive non-potable water demands at centralized locations presented a unique opportunity to displace potable water through a campus-wide water reclamation strategy.
Water reclamation through ecological design
In 2013, the university engaged with Sustainable Water to design a reclamation system that could offset extensive campus utility water demands. Sustainable Water and its development team — including the engineering, surveying, and planning firm of McKim & Creed, Inc. and contractor Reeves/Young — designed Emory's water reclamation system utilizing the latest techniques in ecological engineering. Needless to say, the WaterHub — considered an adaptive, ecological wastewater treatment system — looks much different than traditional biological or mechanized treatment processes.
The facility was planned to occupy two small disconnected and underutilized areas wedged between other structures. Due to the topography involved, these areas have come to be known as the “upper site” and “lower site.” The upper site houses the major feature — a 3,000-square-foot glasshouse that resembles a greenhouse and contains the initial stages of the hydroponic reactors. The lower site features a series of largely underground concrete processing tanks (including additional hydroponics and reciprocating wetlands) whose upper few feet are visible above ground. This above-ground portion appears to be ornamental landscaping, but beneath the surface is a highly engineered system that processes 400,000 gallons of raw wastewater daily.
How the system works
Photo: courtesy of Sustainable Water
The WaterHub's reclamation process begins with wastewater extraction from an 18-inch municipal sewer line. Raw sewage is extracted from a sewer interceptor and pumped to the upper site through a self-cleaning primary fine screen to remove debris entrained in the wastewater. Flows exiting the screen discharge directly into the initial treatment reactors.
Typical primary treatment settles and removes heavier solids. Unfortunately, primary treatment can be a significant source of potential odors and can remove a source of food that enables certain biological processes to function most efficiently. To significantly reduce this risk while also balancing food sources for biological nutrient removal, primary treatment at the WaterHub is handled only by screening, followed immediately by a series of moving-bed bioreactors (MBBR) able to operate selectively as anaerobic, anoxic, or aerobic. The sealed MBBRs, with access through airtight hatches, vent all gasses through activated carbon air filters, eliminating virtually all odors from the primary treatment process.
The three MBBRs are located behind the glasshouse (see Figure 1). In addition to typical suspended growth, a neutral buoyancy plastic substrate is colonized by various bacteria that form an attached biofilm; this begins the biological treatment process. These MBBRs utilize coarse bubble diffusers and mixers that selectively supply oxygen and mixing energy to achieve optimum biofilm thickness and growth. Stainless steel screens on the inlet and outlet pipes retain the media inside the reactors.
The first MBBR was designed as an anoxic reactor to “select” for the growth of microorganisms. This provides denitrification by selectively stripping the oxygen for nitrates and nitrites for their respiration, thereby liberating nitrogen as harmless offgas.
The next two MBBRs are aerated with coarse bubble diffusers. They are the first fully aerobic portion of the treatment process and remove a large fraction of the carbonaceous material, measured as biochemical oxygen demand (BOD), in the influent. They also strip odorous gasses and begin conversion of ammonia to nitrates and nitrites for eventual recirculation and decomposition in the anoxic zones.
Hydroponic reactors follow the primary MBBRs and are located within the glasshouse. These reactors reduce remaining BOD to secondary levels and complete the nitrification process. These reactors are covered with vegetation supported on racks, and are aerated with fine bubble diffusers that provide the oxygen required for treatment and to keep the tank contents mixed. The roots of the vegetation — low-maintenance, hardy plants that produce long, dense root systems — provide ideal surfaces for the growth of attached microbial populations.
The vegetation serves as habitat for beneficial insects and organisms that graze on microbial biomass. This grazing reduces the sludge volume and maintains the microbes at optimal growth rates, resulting in less solids discharge to the municipal sewer. This presence of more diverse and complex life forms provides an additional degree of efficiency, resiliency, and resistance to process upsets. Also, the vegetation and racks decrease the surface turbulence in the reactor, which reduces the formation of aerosols and volatilization of odor compounds.
Photo: courtesy of Sustainable Water
A layer of lightweight, expanded shale aggregate atop the racks creates a natural biofilter colonized with bacteria that remove any residual odor compounds. A ventilation system with activated carbon scrubbers provides a multiple barrier for odor control within the indoor hydroponic reactors. Direct access to the wastewater is only through secure hatches.
To optimize total treatment volume and accommodate shallow bedrock on the upper site, additional hydroponic reactors on the lower portion of the site blend seamlessly with the demonstration tidal wetland cells and feature native and naturalized plant species.
While a significant portion of the suspended solids is consumed in the hydroponic reactors, remaining solids and dissolved phosphorus must be removed. The solids are passively settled in the quiescent clarifier tank, which removes solids to less than 10 mg/l. A portion is pumped back to the beginning of the treatment process to provide ample bacterial communities for the treatment process, and a small amount is discharged to the municipal sewer.
A disc filter located between the glasshouse and MBBR tanks removes any remaining suspended solids and delivers a highly transparent effluent to the downstream UV disinfection system, which inactivates any remaining microorganisms. To maintain a disinfection residual in the water reuse piping back to the cooling towers and other reuse applications, a small amount of chlorine is added. Online instrumentation verifies turbidity and UV transmissivity. The entire process requires approximately 12 hours from extraction to distribution.
Once treated, the reclaimed water is reused as process make-up at four of the six central utility plants on Emory's campus, and plans are under way for extension and expansion. Additional uses for reclaimed water will include toilet flushing at select residence halls and irrigation at major athletic fields in the future. Recycled water is currently distributed across the campus via a comprehensive distribution and controls system that fully integrates with the existing campus framework and enables the demand-based delivery system to be actively and proactively managed and optimized.
Photo: courtesy of Sustainable Water
By utilizing a natural treatment approach, the WaterHub has significantly reduced energy demands compared with other biological or membrane treatment systems. Natural systems exhibit an intrinsic ability to diffuse oxygen into the systems. This helps reduce the energy required for aeration, which is typically one of the most significant energy and cost factors in a wastewater plant. These efficiencies are also complemented by solar energy production via two large photovoltaic panels located on either side of the treatment plant.
Innovative project financing
Using a model similar to a Power Purchase Agreement, the turnkey WaterHub reclamation system was built through a financing vehicle called a Water Purchase Agreement (WPA). The project was designed, built, and operated by a private special purpose entity which bore all project development costs. The university's only commitments are a long-term ground lease and commitment to buy the produced water at agreed-upon rates. These rates are guaranteed to remain below the prevailing local water and sewer rates, resulting in guaranteed savings from the first day of operation. All compliance and operational risks and costs, as well as predictive and preventative maintenance requirements, are also absorbed by the project company under the WPA.
A more resilient campus
By providing an alternative source of water for critical heating and cooling, the campus now has N+1 redundancy for a large portion of its water demand. With the addition of a 50,000-gallon clean water storage tank, the campus has a tertiary level of redundancy that allows the campus heating and cooling to safely operate for an average of seven hours, depending on seasonal operating demands, in the case of a disruption in water availability.
After only three months of operation, this redundant water supply system was put to the test when a 48-inch potable water main ruptured only a few miles from campus. Pressure losses affected nearby hospitals, as well as the university's neighbor, the Centers for Disease Control (CDC). While the CDC was forced to close its doors, the university's utility operations served by reclaimed water were largely unaffected, and the campus remained open.
Photo: courtesy of Sustainable Water
Localizing water supply through onsite reuse provides greater control over supply, water quality, and long-term costs. Overall, the WaterHub at Emory provides a number of environmental, social, and economic benefits to the university and broader community, including pollution abatement through reduced wastewater discharge, extended lifespan of community water-related infrastructure, redundant water supply, and long-term cost savings. The facility itself is also completely compatible and supportive of the university's mission, providing a platform for curriculum enhancement and research opportunities, as well as a robust public outreach and education program.
Emory is one of many bulk water consumers in need of a higher level of resiliency in the face of water scarcity and other looming water management risks. Douglas Hooker, director of the Atlanta Regional Commission, reiterated this point as he spoke to a crowd of a few hundred people during the WaterHub's commencement ceremony in April 2015, saying, “This WaterHub will shine as a model for other universities, other governments, and commercial campuses to replicate. The benefits of this project are not theoretical or abstract; they're very real, very measurable, and they're very immediate, leaving no doubt of the direct beneficial impact that sustainable practices can have on our water systems.”
The facility has attracted the attention of universities, engineers, and water management professionals around the country. EPA Administrator Gina McCarthy requested a private tour of the facility prior to it being fully operational. Impressed with the system, McCarthy tweeted that the WaterHub is “a model for us all.”
In addition to being named WRA's 2015 Innovative Project of the Year, the WaterHub at Emory University has received an Atlanta E3 Award (Liquid Assets category) from the Metro Atlanta Chamber, the Construction Management Association of America's Project Achievement Award (Infrastructure Private Sector category), the Superior Environmental Performance Award from the Georgia Safety, Health and Environmental Conference and the Georgia Chapter of the American Society of Safety Engineers, and a Grand Award for Engineering Excellence from the American Council of Engineering Companies of North Carolina.
Daniel Allison is an environmental planner with Richmond, Va.-based Sustainable Water LLC, a developer of commercial-scale water reclamation projects across the U.S. Sustainable Water's mission is to change the paradigm associated with water management, which enables a more resilient, sustainable future for generations to come.
Tim Baldwin, P.E., is senior vice president with Raleigh, N.C.-based McKim & Creed, Inc., an employee-owned firm with more than 350 staff members in offices throughout the U.S. McKim & Creed specializes in civil, environmental, mechanical, electrical, plumbing, and structural engineering; industrial design-build services; airborne and mobile LiDAR/scanning; unmanned aerial systems; subsurface utility engineering; and hydrographic and conventional surveying services.