UC professor researches graywater treatment and reuse

Graywater accounts for 80 percent of our total household wastewater. Every time you wash dishes, do laundry, brush your teeth or take a shower, you produce graywater.

Graywater is different from traditional wastewater – it doesn’t contain many of the dangerous pathogens found in wastewater from toilets. Lower pathogen levels means graywater is more treatable, and thus a prime candidate for reuse.

In an age of urban living, where densely populated areas consistently stress water resources, recycled graywater can be a key factor for water sustainability.  

Cincinnati currently uses a biological process for large-scale wastewater treatment. Wastewater flows into a holding tank populated by microorganisms that consume the wastewater’s pollutants and nutrients. After the microorganisms have consumed the vast majority of pollutants, the plant uses gravity to separate these microorganisms from the treated wastewater. The plant releases the treated wastewater into the river, while the microorganisms return to a holding pool to repeat the process.

Chae is proposing to separate graywater from wastewater at the residential level, before it even gets to the wastewater treatment plant. He plans to combine a traditional biological process, as seen at a large-scale plant, with membrane separation.

Membrane separation is a common filtration process for wastewater treatment. Wastewater goes through a permeable membrane, which acts as a filter to remove waste components, like bacterium and microorganisms, from the wastewater. In the past, membrane separation wasn’t easily possible with biological processes, primarily because of membrane fouling.

“Membrane fouling occurs when microorganisms attach on the membrane surface and prevent water flow through the membrane,” Chae says. “My idea is to minimize those occurrences using a multi-functional carbon nanotube membrane.”

Chae can mitigate fouling by attaching a carbon nanotube to a conventional membrane filter. Rather than chemically cleaning a fouled membrane, which can be expensive and inefficient, Chae’s technology can send electric power through carbon nanotubes attached to a membrane filter.

This work has vast real-world applications, reflecting UC’s strategic direction, Next Lives Here.

The novel membrane can also effectively remove trace organic compounds, an emerging pollutant that conventional wastewater treatment plants traditionally have difficulty removing. Additionally, because Chae’s carbon layer is electrically conductive, one can easily monitor potential membrane fouling through electric signals.

By intentionally separating graywater from more contaminated wastewater, Chae can make the wastewater treatment process much more efficient, as the treatment process won’t have to address the major pathogens and viruses that come from wastewater in toilets. Once the graywater is recycled, homeowners and building owners can then reuse the water for irrigation, gardening and other indoor purposes.

As accessible fresh water becomes scarcer across the country and around the world, novel engineering solutions such as Chae’s transform how we address these global problems.

Featured image at top: A view of sedimentation tanks at a water treatment plant. Photo/DengdaiFengQi/Pixabay