Turning grey (water) into gold

Grey-water recycling helps the environment, but can these systems be economically viable?
August 11, 2010

Although most A/E/C professionals view grey-water recycling as an application only for the most radical "green" buildings, these systems are slowing making their way into the mainstream building market, thanks to rising water rates and the growth of sustainable design.

Typical buildings discharge a tremendous amount of grey water, including water from sinks, showers, bubblers, laundry machines, dishwashers, stormwater runoff, and HVAC condensate. Instead of funneling this water into the sewer system for treatment, progressive Building Teams with forward-looking owners are finding innovative ways to pipe this discharged water back into the building for reuse in non-potable applications (see sidebar below).

"Since the inception of modern indoor plumbing, people have been using perfectly clean potable water for every need within a building," says Julie Paquette, design engineer with Vanderweil Engineers, Boston. "But as far back as Ancient Rome, water streams were separated. So it's innovative, but actually more of a historical approach."

Clearly, the main driver of these eco-friendly systems is the sustainable design movement, specifically owners looking to achieve LEED certification from the U.S. Green Building Council, Washington, D.C. The LEED program offers credits toward certification for re-use of grey water, as well as installation of other water-conservation technologies, such as dual-flush toilets or waterless urinals.

Making the case for grey

Steadily rising water rates in some areas of the country may actually make grey-water recycling economically beneficial.

Take Boston, for instance. Water/sewer rates have jumped from $7.60 per 1,000 gallons in 2000 to $8.20 in 2003 and are forecasted to exceed $12 by 2010, according to a 2000 study by the Massachusetts Water Resources Authority.

There, Vanderweil has worked on several projects where payback — not sustainable design — is driving the project.

In 1996, the firm designed a system for the 30-story, 25-year-old 1 Federal Street building as part of an interior renovation of floors 2-11 for a new tenant. The building had existing water-reclamation systems in place for reusing steam condensate for cooling tower make-up and to supply an adjacent car wash. The condensate is also used to pre-heat city water.

Vanderweil's design added pumps and dual-piping infrastructure so that steam condensate and cooling tower blowdown could also be re-used as flushing water on floors 2-11.

The result: 1.3 million gallons of flushing water is conserved annually, saving the owner approximately $19,000 a year.

Paquette says the payback was actually within months because the Building Team incorporated existing infrastructure — including two 11,000-gallon fire-water tanks that had extra storage space — into the new system, and the installation costs for the dual-piping was paid for by the new tenant.

She adds that the local plumbing code requires that all flushing water supply pipes be painted yellow, and that color be added to the recycled water. "It a protective measure so that someone does not mistakenly tie a bubbler into that line," she adds.

Payback analysis

Vanderweil performed payback analysis for a similar system intended for a 12-story, 30-year-old office building in Boston. The owner elected not to install the system.

 
Under construction, the Frank Gehry-designed Stata Center research lab at Massachusetts Institute of Technology, Cambridge, will recycle grey water for reuse as flushing water. Designed by Boston-based Vanderweil Engineers, the system will collect rain water, reverse osmosis reject water from the water-purification system.

The firm estimated that its design would save 6,500 gallons of water per day by reusing steam condensate and cooling tower blowdown as flushing water. The steam condensate would also be used to heat incoming fresh city water, saving about 2 million BTU in energy per day.

The $190,000 system would have paid for itself within five years, thanks to $44,000 in annual savings in water and energy costs.

In Aruba, the Netherlands Antilles, where water costs are more than $13/1,000 gallons, payback on grey-water systems can be even faster. Consequently, building owners there have taken water reclamation to new extremes. Hyatt Regency Aruba, for instance, recycles laundry water for reuse as make-up in the hotel's cooling towers.

The system saves Hyatt 4.5 to 6 million gallons of water annually, resulting in savings of more than $50,000 in water and sewage costs a year. Designed by Evanston, Ill.-based energy consultant and engineer Grumman/Butkus Associates, the system recently received an ASHRAE Technology Award for innovative design from the American Society of Heating, Refrigerating, and Air-Conditioning Engineers, Atlanta.

The wastewater from the laundry is pumped through a 177-micron particulate filter and then into a 4,000-gallon storage tank. There, the water is constantly recirculated through a 5-micron multimedia filter and back into the tank. Water is slowly bled off the discharge from the filter into the cooling tower. Chemical treatment is provided for foaming, pH balance, and biological growth, according to Alexander Butkus Jr., vice chairman of Grumman/Butkus Associates.

Butkus says the system recovers more than 90% of the wastewater, which is much more efficient than other laundry water recovery systems. Most systems tend to use the wastewater back into the laundry system and, therefore, require fresh water to be blended in with the recycled water to make the system work.

The system also recycles condensate from the hotel's air-conditioning units. "It's not a very big flow, but every bit counts," adds Butkus.

Butkus is doubtful that owners can justify such a system in the U.S. "The return on this system is probably four times better in Aruba than in Chicago, because of low water cost." Water/sewer costs in Chicago are just $2.29/1,000 gallons.

"Water is pretty cheap everywhere," he adds. "Water bills are typically much smaller than the energy bills."

John Apostolopoulos, corporate engineer with Vanderweil Engineers, concurs, but insists that owners need to think about the environmental payback.

"When you move into green design like this, the payback is usually not 4-5 years, it's most likely 10-15 years," says Apostolopoulos. "And then you get the argument that in 15 years the pumps will have to be replaced, and there's actually no payback. Well, I think there's a payback — environmental payback. But the clients have to be educated."

Projected savings

Payback period = five years
Source: Vanderweil Engineers


No daytime cooling water $11,300
Reduced night time cooling water for disposal $3,150
Reduced fresh flushing water $6,100
Reduced blowdown and condensation disposal $10,350
Reduced water heating $13,350
Total annual savings $44,250
Initial system costs $190,000

         
 

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