N.C. State University soil scientists investigate ways to safely treat wastewater for reuse
Why do Americans continue to flush their toilets with drinking water? It’s a question that an N.C. State University team of soil scientists contemplates every day as they work to show that small-scale wastewater reuse can be a way to ensure a safe and plentiful water supply in the face of projected nationwide water shortfalls.
Dr. Sushama Pradhan, a soils and on-site water technology research scientist, and Dr. Mike Hoover, a soil science professor and expert on on-site wastewater treatment, are leading research and outreach efforts to show that wastewater doesn’t have to be pumped all the way back to a municipal treatment plant to be safely treated and reused. This is particularly true, they say, for producing non-potable waters – those that aren’t used for drinking, cooking, showering or bathing.
Pradhan and Hoover are focusing on what they call decentralized water reuse – small-scale systems that treat and then recycle water at the point where it is initially used: for example, within a home, an apartment building or a business – for toilet flushing, landscape irrigation, building chiller systems and other non-potable purposes.
With the U.S. Centers for Disease Control and Prevention (CDC), Hoover and Pradhan are wrapping up research into technology performance and health effects of such decentralized water reuse technologies. They are studying seven systems employing different technologies to treat and reuse wastewater for non-potable purposes at apartment buildings, resort communities, schools and clusters of houses. The systems are in New York, North Carolina and Texas and have flows ranging from about 1,000 to 500,000 gallons a day.
The research is the first ever conducted in the United States on decentralized water reuse for non-potable purposes. “Australia and Germany are literally 10 years ahead of us when it comes to decentralized reuse,” Hoover said. “Research in other countries has shown the safety, but people here want research done here, in the United States.”
Systems suited for rural areas as well as cities
Pradhan noted that decentralized reuse can be successful in rural, suburban and urban communities. “Even inside the city center, where public sewers already exist, decentralized reuse can occur using a process sometimes called sewer-mining,” she said.
As an example, she pointed to the Visionaire, a 35-story building with 251 condominiums in lower Manhattan. New York City’s drinking water and sewer systems serve the building, but the building also has an on-site wastewater treatment system in its basement.
“The non-potable waters produced from the sewage are then pumped back up into the building after treatment. These waters are acceptable for use for toilet flushing, grounds irrigation, water display fountains, makeup waters for chillers and other similar uses,” she said.
“This approach diverts about half of the sewage that would normally be going into New York City’s sewers. Once this water is treated, it gets used a second time, a third time and so on. This reduces drinking water use by 48 percent in this high-rise community,” she added. “Not only does it save money, but this approach also extends the life of the city’s drinking water supply by as much as 30,000 gallons a day. The capacity of the city’s wastewater treatment plant is also extended by an even larger amount.”
Closer to home, Pradhan and Hoover have seen increased interest in decentralized water reuse. At a new city park in Raleigh, for example, there are plans to provide reclaimed water for toilet flushing. Recycled waters are also being used to irrigate golf courses from Lexington in the Piedmont to Corolla in the Outer Banks. And a high school-middle school complex in Greensboro uses harvested rainwaters and locally treated wastewaters for toilet and urinal flushing as well as for athletic field irrigation.
Meanwhile, with the support of the Irish company Anua, which has its North American headquarters in Greensboro, the N.C. State University team has been assessing pilot wastewater treatment and water reuse technologies at the T.Z. Osborne Wastewater Treatment Plant in Greensboro. Other industry partners include Reuse Innovations, a western N.C. company; Aquapoint in Massachusetts, JaMac and Associates in North Carolina, Grundfos in Denmark, BUSSE in Germany and Nubian in Australia.
The team also collaborates with public agencies, such as Chatham and Orange county governments, the New York City Green Building Committee, the city of Los Angeles’ Department of Water and Power, Los Angeles County’s Public Health Department and the Department of Infrastructure in Harris County, Texas. Federal labs and non-governmental partners include NSF International’s Wastewater Joint Committee, U.S. Environmental Protection Agency’s National Environmental Research Laboratory, the CDC’s National Center for Emerging and Zoonotic Infectious Diseases, and numerous universities and colleges.
Outreach efforts complement research
The research the team conducts is just part of what Hoover believes it will take to push past the so-called “yuck factor” and gain public acceptance of wastewater reuse. That’s why, as part of his responsibilities as a North Carolina Cooperative Extension Service specialist, Hoover gives frequent decentralized wastewater reuse presentations, demonstrations and workshops for scientists, system operators, environmental health specialists, engineers, builders and developers.
Frequently, these presentations take place at the College of Agriculture and Life Sciences’ Lake Wheeler Road Field Laboratory, where displays illustrate working demonstrations of decentralized wastewater treatment technologies.
At a January workshop, Pradhan discussed the CDC research and showed participants one of the German technologies that can be installed in a home’s basement and treat wastewater for reuse within the home and its yard. Dr. Barrett Kays, an N.C. State University Soil Science Department alumnus who leads the Raleigh-based environmental consulting firm Landis Inc., discussed several pioneering wastewater reuse systems that he’s helped develop.
Hoover told workshop participants that centralized wastewater reuse has gained increasing acceptance in recent years, with cities and large communities treating wastewater and using separate pipelines to carry the treated non-potable water to customers for irrigation and other uses.
But many North Carolinians – about 50 percent, he said – will never be served by such centralized systems and instead rely on septic systems. If these people were interested in water reuse, they would need the types of decentralized technologies that Pradhan and Hoover are studying.
Treating water to match its intended uses
While the N.C. State scientists stress the efficiency of decentralized wastewater reuse, they also emphasize the need to treat water to the safety level that matches the water’s intended uses, instead of treating all water to drinking water standards.
As Pradhan noted, getting river water clean enough to drink can get expensive, and takes a lot of energy. Yet every day the average American uses 400 gallons of water treated to drinking water standards. “Only three of those gallons are consumed,” she said. “Some more is used for cooking food and taking showers, but the vast majority of the water we bring into our houses doesn’t need to be treated to the same extent as drinking water. So that’s why our team is focusing on the non-potable water supply – on having water supplies that are fit for their purpose.” Hoover added, locally treating water supplies based on their intended purposes using this decentralized wastewater reuse approach is more efficient and less expensive than many centralized reuse options.
Extending water supply drop by drop
“It’s clear we need to improve and enhance our water supply choices. We need to be sure there is more than just one menu choice for the future of water,” Hoover said. “Decentralized reuse for non-potable water supply production is one means of doing that.
“Decentralized wastewater reuse works facility by facility, community by community, home by home, business by business,” he added. “A drop of water becomes a quart, a quart becomes a gallon, a gallon becomes thousands of gallons. Thousands of gallons become millions of gallons. Millions of gallons are a water supply for a community. And it adds up.
“Decentralized wastewater reuse is a way of extending our water supply drop by drop.”