Using sludge to clean the air
Paper mills produce sludge. They also give off toxic emissions containing oxides of nitrogen including NOX, a byproduct of combustion. Now, researchers at the Illinois Institute of Technology have developed and patented a process by which sludge from municipal waste water or paper mills can be turned into activated carbon, an ingredient used by manufacturing plants to remove toxic chemicals like NOX from their emissions.
“Activated carbon is used by virtually every manufacturing plant to remove NOX in order to comply with the 1990 Clean Air Act Amendment,” says Nasrin Khalili, assistant professor of chemical & environmental engineering. “We have come up with a way to turn toxic paper mill sludge into something manufacturers (including paper mills) need.”
Sludge from manufacturing plants needs to be specially treated and dried before it can be deposited into landfills – an expensive process. “Paper mills are happy to give me their sludge – otherwise it costs them money to get rid of,” says Khalili, who holds the patent on the process.
Khalili turns the sludge into activated carbon -- a catalyst that helps remove NOX, a toxic byproduct of combustion, from smokestack emissions. She calls the black, powdery activated carbon IIT Carbon, after the Illinois Institute of Technology.
Currently, activated carbon is pressed into a wafer-like filter that is fitted into the smokestack. As emissions pass through the filter on their way out, NOX is removed. “But the process isn’t very efficient,” says Khalili. “The NOX isn’t in contact with the activated carbon for very long as it passes through the filter. I am working on developing a method where the activated carbon is introduced into the smokestack as a aerosol. That way, the emissions will interact with the activated carbon during their entire trip through the smokestack instead of just at one point,” Khalili explains.
Khalili gets her sludge for free from a paper mill in Green Bay, Wisconsin. She has tested her activated carbon against the commercially-produced equivalent and found that her product works better with a NOX removal capability of 66 percent to 94 percent.
Khalili is currently working on combining IIT Carbon with bacteria that metabolizes NOX to produce a biocatalytic activated carbon. This product would do an even better job of eliminating NOX.
Founded in 1890, IIT is a Ph.D.-granting technological university awarding degrees in the sciences, mathematics and engineering, as well as architecture, psychology, design, business and law. IIT’s interprofessional, technology-focused curriculum prepares the university’s 6,200 students for leadership roles in an increasingly complex and culturally diverse global workplace.
