This article was originally published by Tyler Irving on FEBRUARY 27, 2017
Can the stuffing in your sofa prove an effective tool to combat water pollution? Research conducted by a young Indian-origin scholar at the University of Toronto suggests the simple sponge has the potential to tackle such contaminants.
Pavani Cherukupally (MIE PhD candidate) has designed a system that uses ordinary sponges to remove droplets of oil or other contaminants dispersed in water. Her technology could help remediate of oil sands tailings ponds, a major environmental challenge for Canada. (Photo: Kevin Soobrian)
Oil and water don’t mix — in theory. In reality, the two liquids can be almost impossible to separate, especially from complex chemical cocktails such as the wastewater produced by Alberta’s oil sands mining operations.
Contaminated by small amounts of bitumen and other oily substances, this wastewater can’t be discharged to the environment and is held in vast ponds awaiting treatment. A new potential solution developed by U of T Engineering researchers starts with a surprisingly simple device: a sponge.
Pavani Cherukupally (MIE PhD candidate) leads the project under the supervision of Professors Chul Park and Amy Bilton (both MIE). Previous work in Park’s lab focused on designing sponges that could be deployed to soak up oil in the event of a spill — these were made of superhydrophobic materials, which repel water but attract neutrally charged substances like oil.
Cherukupally is modifying the process to treat oil-sands wastewater. Her idea is to pump the the contaminated water through the sponges: due to attractive forces, the oily contaminants should stick to the surface of the sponge, while the clean water should flow straight through.
But when Cherukupally tried this with the superhydrophobic sponges, it didn’t work at all. “The water stayed just as dirty as it was,” she says.
Drawing on her background in physical chemistry, Cherukupally realized that the problem was that oil in wastewater behaves very differently than an oil spill. Oil in wastewater is dispersed into tiny droplets, rather than forming a cohesive slick. Each of these droplets is surrounded by a layer of charged particles, which means that they will be attracted to charged surfaces, not neutral ones.
Cherukupally ditched her neutral, superhydrophobic foams for ordinary polyurethane foam, similar to the type found in couch cushions. When she did, her sponge system removed more than 99 per cent of the suspended oil.
“The slight positive charge on the polyurethane attracts the slight negative charge on the suspended oil droplets,” says Cherukupally. “As well, the pore size is small enough to provide a large surface area, but not so small that the sponge gets clogged with debris.”
“We’ve been both surprised and impressed by the results that Pavani has achieved so far,” says Park. “Her expertise in surface chemistry and physics led us in a new direction that we wouldn’t otherwise have tried.”
Now, Cherukupally is experimenting with ways of coating the sponge to modify its surface chemistry and adjust its performance to a wider range of situations. In collaboration with U of T researchers Dr. Wei Sun and Annabelle Wong, supervised by Professor Geoffrey Ozin (Chemistry), Cherukupally has created foams that have both charged and neutral areas on their surface.
When tested with oil sands tailings water, these “hybrid” sponges had an overall removal efficiency of 98 per cent, slightly less than regular polyurethane. However, their removal rate — the speed at which they suck up the pollutant particles — was six times faster.
Cherukupally was inspired to work in water treatment by witnessing the slow, gradual pollution of the Musi river in her home city of Hyderabad, India. “Nobody knew how to clean the water, and a lot of my classmates got sick,” she says. “When this project was proposed to me I thought: ‘This is what I should be doing.’”
Cherukupally did her BEng (Mechanical Engineering) from Osmania University and PhD from University of Toronto
“This water has highly concentrated organic contamination. As you might be aware, Indian rivers such as the Ganga, Yamuna, and Musi also have a high concentration of organic contamination. So, we could extend this technology to remediate Indian rivers.”
With a background also in physical chemistry, Cherukupally’s project is aimed, for now, largely at the problem of wasterwater tailings from oilsands in the province of Alberta. Even though 92% of the discharged water is treated, the remainder has added up to over a trillion litres, stored in ponds.
Her concept, now undergoing refining in the laboratory, uses the polyurethane sponge charged to attract the ions of the water’s pollutants that have opposing charges.
“The measurement techniques are new, which allows us to measure the surface charge on the materials and ensure under what conditions exactly this attachment happens and when they will have opposing charges,” she said during the course of an interview.
The system has a removal efficiency of 98%, and it then releases clean water. This particular concept has been developed for offshore filtration but another concept looks at vacuuming the polluted water into the sponge-based system, collecting contaminants and discharging the treated water.
While a lab-scale system is being built for the process, a demonstration is planned for this autumn. She said, “The system configuration to implement at the spill site is finished now.”
Field trials at a facility in Nova Scotia province are expected within a few months. Canadian government agencies such as the department of fisheries and Natural Resource Canada are supporting the research.
Her research is being undertaken under the supervision of mechanical engineering professor Chul Park and Amy Bilton. She is creating a hybrid foam with charged and neutral surface areas under the supervision of chemistry professor Geoffrey Ozin.
Cherukupally believes the technology, once fully developed, can be applied to polluted Indian rivers. Not only will it be effective but it can be used by small industries, since unlike the expensive membranes used at effluent treatment plants, the sponge-based system will be an affordable alternative.
While remove pollutants makes for a healthier environment, she is also actively looking into using the system “to remove water borne bacteria”. As she explained, “As we know, Indian rivers have many microbes in them. Therefore, this direction of the project is also very critical in extending sponge technology to polluted rivers and lakes.”