Water Saver: The Hydroponics Experiment at Emory University

A WaterHub process at an Atlanta university is dramatically reducing city water use on campus and serving as a research center for students and staff.
Water Saver: The Hydroponics Experiment at Emory University
Plants in the hydroponic reactor sit on racks with their roots extending into the wastewater, forming a substrate for organisms that consume waste. The reactors also contain a synthetic root system to increase the bacteria population.

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Researching water treatment and supply is nothing new in the classrooms at Emory University. While some research is involved in the university’s latest endeavor, its main goal is to reduce the use of potable water on campus by reclaiming wastewater through ecological treatment processes, mainly hydroponics.

It’s called the WaterHub, a compact facility that uses bacteria on plant roots to clean wastewater. It reduces potable water demand by about 35 percent on campus and could help build understanding about water reclamation. The program is having a big impact on the water footprint at the university in Atlanta, Georgia.

“It’s not just a drop in the proverbial bucket,” says Brent Zern, Emory environmental engineer. “This is making a huge holistic impact across our campus.” Potable water use could be cut by as much as 110 million gallons a year.

Innovative agreement

Zern and a colleague first proposed the WaterHub in 2011 after being approached by Sustainable Water of Glen Allen, Virginia, which developed the technology and owns and operates the system on campus. It went online in May 2015.

“We have an innovative water purchase agreement with the vendor team and purchase as much of the reclaimed water as they’re able to produce,” says Zern. The school also receives sewer credits because so much of its water is diverted from the municipal sewer system.

While the terms and costs are confidential, Zern says the several-million-dollar facility will save the school millions of dollars over the next 20 years by replacing potable water with reclaimed water. The region has supply issues: Georgia instituted statewide conservation mandates during a drought in 2007-08, and Atlanta has the highest water rates in the nation for most customer groups.

Emory’s water demand is about 1.1 mgd, 34 percent of that consumed by six major utility plants and five satellite plants that heat and cool the campus. That demand for potable water has been cut by 90 percent — the main steam plant and three chiller plants can now use 100 percent recycled water. A new residence hall has a dual plumbing system and will use excess WaterHub effluent for toilet flushing.

Multi-step process

With a capacity of 400,000 gpd, the WaterHub takes sewage from a county line that runs across the north part of the campus. Most of the flow is from college buildings, but some comes from a Centers for Disease Control complex next door.

A 6 mm primary screen removes inorganics before the wastewater flows through three moving-bed bioreactors (MBBR) containing BioPortz biofilm (Entex Technologies) with coarse-bubble diffusers and mixers. An anoxic MBBR provides denitrification and removes BOD. Two aerobic MBBRs remove carbonaceous material and odorous gases, which are put through activated carbon filters.

Then it’s on to a greenhouse where vegetation takes over the treatment process in a hydroponic reactor. There are three more outdoor hydroponic reactors nearby. All told, the treatment systems take up just under 4,000 square feet. “We have beautiful plants that were specially selected because of the type of roots they produce,” says Zern. “That’s where the good bacteria live that eat the organics out of the wastewater.”

Wetlands included

Fine-bubble diffusers provide oxygen and keep contents mixed properly. Plants are held in racks with their roots directly in the water, where microbes reduce remaining BOD to secondary levels and complete the nitrification process. The roots are augmented by a BioWeb synthetic root system (Entex) to provide more surface area for bacteria. The vegetation also supports beneficial insects and organisms that eat the microbial biomass, reducing sludge volume.

A layer of lightweight shale on the racks creates a habitat for bacteria that serves as a natural biofilter to remove residual odor. The greenhouse also has activated carbon scrubbers to prevent odors.

While most of the flow goes through the hydroponic reactors, up to 2,000 gpd is diverted to a wetland system near the outdoor hydroponic cells. “We thought it was important to include it so we could understand the differences in natural treatment techniques and students can do research,” says Zern.

The four wetland cells also contain natural organisms that consume wastewater compounds and residual organic carbon and reduce nitrates. The wetlands require frequent filling and draining of the cells. That process is computer controlled and uses high-efficiency pumps and automated valves.

It takes 16 to 20 hours for water to go through the hydroponic system and well over 24 hours for wetland treatment. The effluent from both goes to a traditional clarifier. A disc filter removes remaining suspended solids. That is followed by UV disinfection and addition of chlorine to provide a residual in the distribution piping. Online instrumentation and periodic testing verify system performance.

Commercial potential

The Rollins School of Public Health at Emory includes the Center for Global Safe Water, which researches technologies to provide clean water in developing countries. “They not only need a way to treat their wastewater, but also need a clean drinking water source,” notes Zern. “A facility like this could possibly accomplish that.”

It could also help build a case for reclaimed water here at home. “In the United States, our regulations are sophisticated enough that they say we can’t use the water for potable purposes,” says Zern. “They also tell us the water needs to be cleaned to a level of purity that is basically drinking water quality. If it is indeed clean enough to drink and we can verify that through simple chemical analysis, then why not?”

The WaterHub is available for research to all Emory students and staff. “We hope to engage environmental studies students, maybe some law students to understand the regulatory hurdles, business students to look at the economics. So there’s lots of learning potential,” says Zern.

One thing he’s learned by working on the WaterHub is that the various treatment technologies are not all that different from one another: “It’s basically using Mother Nature’s tried and true concepts and tweaking them with engineering, logic controls, pumps and pipes, just to make it more efficient and faster. That, to me, is the ultimate in sustainability.”


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