Engineers develop odour eaters for pulp mills

Professor Grant Allen, director of University of Toronto's Pulp and Paper Centre in the chemical engineering department, is researching biofiltration techniques that use bacteria to 'eat' smelly, air-polluting by-products created by the paper and pulp making process.

'All industrial processes have air emissions and, in the case of pulp and paper mills, the smell can be quite overwhelming,' said Professor Allen. '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 autumn, Allen and his co-researchers explain how they managed to create a biofilter that operates in temperatures as high as 70 degrees Centigrade (C).

Most biofilters currently in use are said to 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 said. It can be used in any industry that produces biodegradable air pollutants and is low cost, low maintenance and environmentally friendly.