A small plant in Atlanta that uses hydroponics to treat wastewater saves money for its host by producing reclaimed water that can be used in place of potable water for boilers and cooling towers and for toilet flushing.  

The 400,000-gpd WaterHub on the Emory University campus was developed by Sustainable Water, a private company based in Glen Allen, Virginia. One part of the plant looks like a greenhouse, and the other part looks like a park with raised-bed gardens.

The treatment process is based partly on hydroponics; plants essentially grow in the wastewater stream. The plants consume some of the nutrients in the wastewater, and their roots host bacteria that break down organic material. The treatment plant provides reclaimed water at lower cost than potable water. Additional savings come from reducing the amount of wastewater going into the municipal system.

Not at all typical

“The single most nontraditional thing about this plant is the aesthetic,” says Tim Baldwin, the plant’s designer and senior vice president of McKim & Creed, a Raleigh-based engineering company. “The smell, the noise, the look — all of that is very different.”

The plant occupies two small sites across the street from each other. The site with the greenhouse is wedged between a maintenance building and a research building, and the gardens are flanked by a fraternity house and a baseball field. The plant draws wastewater from several university buildings.

On the greenhouse side, all facilities are covered, and the airspace above the tanks is contained and scrubbed. “There is no odor of any kind because of the containment,” Baldwin says. “We collect and scrub all the headspace, all the airspace above the water level. With the additional filtering power of the plant beds, it’s very organic in both function and aesthetic.”

Microbial diversity

The influent is screened and then flows into an anoxic tank with moving bed biofilm reactors, and from there it goes to an oxygenated tank with more MBBRs. The MBBRs add habitat for the greater variety of bacteria needed to enable the plant to operate in such a small area. The stream then moves to the greenhouse, where plants are held up by rocks but are essentially rooted in the wastewater. Film and fabric media in the tanks host bacteria, as do the plants’ root systems.

“We’re creating conditions for happy, hungry bugs that eat and reproduce and make more baby bugs that are also hungry,” Baldwin says. “You are getting very large, very diverse populations of bugs in a very compact footprint and volume.

“The addition of fixed film provides habitat for additional microorganisms that may not be found in suspended growth, so it makes a more diverse ecology. That makes the plant more resilient, more able to withstand a toxic shock. The chances of having a massive die-off of bacteria from any shock are greatly reduced.”

Wetland treatment

From the greenhouse, the waste stream moves to outdoor hydroponics treatment, where plants native to Georgia are in beds with concrete walls and where the water level rises and falls several times a day, similar to a coastal wetland. That’s another way of creating habitat for a wider variety of microbes.

Some of the wastewater is diverted from the headworks to an area called the Demonstration Reciprocating Wetlands. “It provides another opportunity for study and research,” Baldwin says. “Because we’re in a college environment, it was important to provide educational and research opportunities.”

From the wetlands, the water flows into a clarifying tank. Then the effluent is filtered and disinfected with UV light. The solids from the clarifying tank are sent back to the municipal sewer system without dewatering. The reclaimed water goes into an underground storage tank to supply heating and cooling plants and to provide toilet flushing at residence halls.

The plant opened in 2015. Matt Vinson, manager of WaterHub operations for Sustainable Water, was the plant’s operations manager in its early years. “The facility generated a lot of interest,” Vinson says. “More than 4,000 people have toured through that facility — water and wastewater professionals, government officials, high school science classes.”

Adding resiliency

Big savings are built into processing water this way: “We’re treating the wastewater where it is created, and we’re using the reclaimed water right there where we clean it up. We’re saving the cost of transporting that water in two directions.”

The business model is tied to the municipal rates for water and wastewater treatment.

“In places where water is plentiful and cheap, the economics might not work out,” Vinson says. “In areas where water is in short supply or there is high cost for water or wastewater treatment, all of a sudden it makes the economics work.” Other factors make decentralized plants such as Emory’s attractive: “You have people wanting to build sustainability into their businesses. You have the redundancy and resiliency aspect of it.”

The plant, which produced more than 250 million gallons of reclaimed water in its first four years, passed a major resiliency test in its second year. The county water system sustained a break in a 36-inch water main, causing a significant drop in water pressure. Some businesses had to close, and Emory students were sent home.

“There was no water pressure on campus that day, but we were able to supply reclaimed water for the HVAC systems on campus,” Vinson says. “You have millions of dollars of research that sit in air-conditioned buildings that might fail if the air conditioning goes out. We were able to provide water for heating and cooling that the municipal system could not supply.”

Clean and beautiful

Yet another factor adds to the appeal of the treatment plant: “It’s a glass greenhouse with beautiful banana trees and ginger growing in it. It’s pretty. It doesn’t smell. It’s a nice addition to the campus, not a traditional concrete and steel building.”

Vinson helped to open another similar plant this year in Richmond. Sustainable Water has several WaterHub plants in various stages of design or development. McKim & Creed is in the design or construction of other reclaimed water facilities, including one at Chatham Park in Pittsboro, North Carolina.