Drive by a pulp and paper mill and one of the first things you'll almost certainly notice is the unmistakable smell. But give a University of Toronto engineering professor his way and you'll find the only thing assaulting your nose is … nothing.
Professor Grant Allen, director of U of T's Pulp and Paper Centre in the chemical engineering department, is researching biofiltration techniques that use bacteria to "eat" air pollutant byproducts from the pulp process and thereby filter out the smell. "All industrial processes have air emissions and, in the case of pulp and paper mills, the smell can be quite overwhelming. This biofilter operates like a mini ecosystem. It's a microbial community that degrades the pollutant and breaks down the compounds which cause the odour."
The filter - composed of a variety of materials such as wood chips or plastic spheres - is placed at the exit gas stream at the end of the manufacturing process before the sulphur compounds are released into the air. The sulphur compounds are food sources for the bacteria and, as the bacteria eat them, they also eat the smell.
In a paper published in Environmental Science and Technology last fall, Allen and his co-researchers explain how they managed to create a biofilter that operates in temperatures as high as 70 C. Most biofilters currently in use operate at 35 C or lower, making them prohibitively expensive to install for pulp and paper mills whose gas streams range from 50 to 70 C. With a biofilter that treats the gas stream and its pollutants at higher temperatures, the process is far easier and more cost-effective.
The application of this technology goes beyond pulp and paper, Allen says. It can be used in any industry that produces biodegradable air pollutants and is low cost, low maintenance and environmentally friendly.
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