While greywater systems have gained a substantial amount of consideration in the Western United States, until recently, little interest has been apparent in the Southeast. Furthermore, most of the interest in greywater has focused primarily on residential systems, making greywater systems designed and constructed for commercial buildings rare entities. Yet with a suitable type of building, the conservation benefits of a greywater system can be seen year-round as illustrated by Emory University in Atlanta.

The Freshman Residence Hall 4 project at Emory University is an ideal type of structure for a water-conservation endeavor using collected and treated greywater. What makes a residence hall and its inhabitants such a suitable choice is the fact that a relatively steady supply and demand of water can be counted on with respect to choosing appropriate sizes of equipment to serve the greywater treatment and distribution system.

Emory University has been a leader in the U.S. Green Building Council’s LEED certification process. The university built the first LEED certified building in the Southeast and is considered a sustainable design leader with more than 1.6 million gross square feet of LEED-certified building space on campus. With the initiative for all new buildings to achieve a minimum certification level of LEED Silver, Emory University is regarded as a campus leader with its inventory of green buildings.

Freshman Residence Hall 4

This new freshman residence hall is pursuing a LEED Silver certification. Its sustainable design features include a greywater recovery non-potable water system, rainwater and condensate recovery for site irrigation, energy recovery, a green roof on the parking structure, and an energy monitoring dashboard measuring total electricity, heating energy, cooling energy consumption and per-floor electricity use in real time.

When completed and fully occupied in the fall of 2010, the 351-bed residence hall is projected to produce approximately 12,000 gallons of greywater daily. This greywater is waste water collected from showers, bath tubs, lavatories, and washing machines that will be used to supply the estimated 2,600 gallons of water needed to flush all water closets in the building on a daily basis. In an office or a classroom building, the daily fluctuation of visitors and occupants could vary so much that an estimate of greywater supply and needs on any given day would be very difficult to estimate.

Although the construction and installation cost for this greywater system is quite significant, the financial payback to the owner as well as the environmental benefit in water savings can be seen for many years to come. The major factors that drive the cost are the need for large amounts of water storage, an intense scope of filtration and treatment, and a means of distributing the water throughout the building. 

Filtration and Disinfection

When it comes to public health and safety, the biggest concern is how and to what degree should greywater be filtered and disinfected before being put to use.

In this application, the first line of filtering comes in the form of a standard lint interceptor to remove hair and other large particles before the greywater waste stream enters two 3,000-gallon storage tanks that are connected together.

Once the water reaches these initial storage tanks, it is then continuously circulated through a ultraviolet (UV) lamp assembly at a rate of 10 gallons per minute in order to kill any bacteria present in the medium as well as to impede bio-film growth in the tanks. Since the water is expected to be somewhat murky at this stage, the intensity of the UV light has been set at twice the normal dosage to compensate for reduced transmissivity of the radiation through the fluid.

From the storage tanks, a greywater supply stream is fed into a treatment skid that contains the second and third tiers of filtration. The second filter is a multimedia type that contains layers of sand to capture most contaminants 40 microns and smaller. Finally, the water passes through bag filters that remove particles down to 5 microns in diameter.

After the extensive filtration, the water is chlorinated to a level of 3 parts per million and then dyed blue to visibly differentiate the non-potable water from the clear potable water. This non-potable water is then pumped to a 1,500-gallon holding tank that supplies a booster pump, which will transport the water to five floors of toilets.  

Challenges and Solutions

Since chlorine has been chosen as the primary means of disinfection for this greywater system, an effort has been made to imitate the chlorination levels that are recommended by the CDC for public swimming pools.

Because exact requirements of how to treat greywater have yet to be established, deciding how much chlorine to use is a very important determination: Not enough chlorine and the system will not be able to keep bacteria levels in check, and too much chlorination would mean aggressive degradation to the system and specifically the rubber diaphragm in a toilet’s flush valve.

Without knowing the eventual contents of this greywater, it has been a difficult task to tailor the system to approach potable-water standards for the sake of safety and operability.

Another challenge the design team faced was related to a requirement by the International Plumbing Code that only allows the incoming greywater waste collected from the building’s fixtures to be stored for a maximum of 72 hours before being either treated or discharged into the sanitary drainage system.

A piping assembly was designed to provide continuous overflow from the greywater waste tanks’ bottom outlet so that old water is replenished with incoming new water on a continuous basis. Since the amount of incoming greywater exceeds the amount required for the facility, the greywater in the storage system is retained for less than a day under normal operating conditions. This overflow piping assembly works solely on gravity and thus removes the need for a costly pumping station to dump greywater after the three-day retention time expires.

The installation of the greywater system in this facility assists Emory University in achieving its self-made goals of lowering water and energy usage. Following a devastating two-year long drought and current statewide mandated water-conservation measures, sustainably designed buildings such as this residence hall make the university a good and responsible neighbor indeed.

Project Team

Owner: Emory University, Atlanta

Architect: Ayers/Saint/Gross Inc., Baltimore, Md.

Mechanical, Electrical, Plumbing, Fire Protection Engineer: Newcomb & Boyd, Atlanta

Cost Consultant: Palacio Collaborative

Civil Engineer: Travis Pruitt & Associates

General Contractor: New South Construction Co. Inc.

Plumbing Subcontractor: Tebarco Mechanical Corp.



Materials Used 

Siemens Water Technologies

Flo-Pak by Patterson Pumps



W. Scott King, PE, LEED AP, is a plumbing engineer with Newcomb & Boyd in Atlanta. An associate of the firm, King has had plumbing engineering responsibilities on over 25 projects, including a number of institutional and academic buildings.