Airborne bacteria and mould in paper production facilities

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Airborne bacteria and mould can reach very high levels in the pulp and paper manufacturing plants.

Process water contains sugars, starch, and other components that support and promote the growth of bacteria and, certain yeasts and moulds.

Interestingly, the non-biological and biological waste present in wastewater from pulp and paper production facilities can be treated using specific bacteria and certain moulds. This process known as biological wastewater treatment works by using specialized microorganisms (bacteria and mould) that naturally use the waste as food sources.

The type of microorganisms chosen for remediation must be carefully selected by examining the toxins present in the wastewater. Examples of bacteria used to treat wastewater include Pseudomonas putida, Citrobacter sp., and Enterobacter sp. Examples of fungi used to treat wastewater include Pencillium sp., Trametes versicolor, Pycnoporus sanguineus, Pleurotus ostreatus, and Phanerochaete chrysosporium.

Before one can understand where airborne bacteria and mould are produced during the process of paper-making, however it is important to understand the process. Figure 1 is an overview of the paper-making process and, Figure 2 expands on the steps of the paper-making machine.

Depending on the type of pulping process used for paper making, certain toxic chemicals are generated. In the early 1900s, sulphite pulping was most dominantly used in Canada until it was replaced by the Kraft process. Unfortunately, the Kraft process is still a main source for toxic pulp mill effluents and is now being challenged by chemithermo-mechanical pulping (CTMP) which usually meets pollution effluent standards.

Figure 1 Paper article new2

Biosolids or “sludge” are a major waste product produced in pulp and paper mills. Biosolids provide ideal conditions for the presence and growth of microorganisms, some of which may be pathogenic. Biosolids become airborne through the release of dust and water droplets creating bioaerosols. Bioaerosols are airborne particles that consist of bacteria, viruses and moulds or, metabolites, toxins or fragments from the microorganisms.

Inhalation of airborne bacteria and mould by individuals who suffer from allergies, are immuno-compromised, young children, pregnant women, or the elderly can lead to inflammation, respiratory allergies and sometimes infection. The high speed of the paper making machine (up to 2000 m/min) often creates aerosolization of process water. Debarking drums also splash and aerosolize water.

A type of bacteria often found in pulp and paper biosolids is Klebsiella pneumonia. These bacteria do not typically infect healthy individuals, however those with weakened immune systems as described above can suffer from infection. The most common form of infection caused by Klebsiella is pneumonia however, Klebsiella can also cause urinary tract infection, cholecystitis, diarrhea, upper respiratory tract infection, wound infection, meningitis, bacteremia, to name a few.

Klebsiella pneumonia, Acinetobacter sp. and Enterobacter sp., which are examples of Gram-negative bacteria that are often found in debarker water and process water. These Gram-negative bacteria and yeasts are able to thrive in debarkers because of favourable conditions including low temperature, high humidity and lack of biocides. Refer to Figures 1 and 2 for areas within the paper-making process that are common sources of airborne bacteria and mould.

Figure 2 Paper Making Machine

In one study performed by Sillanpa et. al (1985) the nasal cavities of workers in three paper and board mills were examined. The nasal cavities of many workers working with the debarkers were contaminated with Klebsiella pneumoniae, other coliforms, yeasts or moulds. However, the host defenses of the workers seemed to protect them from illness.

Table 1: Bioaerosol concentrations measured in paper mills

Workplace Total bacteria(CFU/m³)a Gram negativebacteria(CFU/m³) ThermophilicActinomycetes(CFU/m³) Molds(CFU/m³)
Outdoors 10² 101 101 103
Paper mill effluents 104 103 101 104
Papermill 106 102-3 103

*This table was derived from Bioaerosols in the Workplace: Evaluation, Control and Prevention Guide – Nicole Goyer, Jacques Lavoie, Louis Lazure, and Genevieve Marchand, (2001)

In order to control the growth of microbes in process water, biocides are regularly added. Even so, high numbers of bacteria (106 – 108 growth units/mL) usually occur in various parts of the paper making process such as the head box or coated broke. The head box or flow box is the tank the delivers pulp onto the wire for paper making (refer to Figure 2). The coated broke consists of rejects of quality mixed paper with process water and then reused for paper making.

Table 2: Dominant bioaerosols in paper mills

Paper Aspergillus, Penicillium, Chaetomium, Acremonium, Beauveria, Cladosporium, Epicoccum, Papulospora, PhomaScopulariopsis, Ulocladium

*This table was derived from Bioaerosols in the Workplace: Evaluation, Control and Prevention Guide – Nicole Goyer, Jacques Lavoie, Louis Lazure, and Genevieve Marchand, (2001)

Sampling to test for airborne bacteria and mould is typically done by an Andersen pump with an impactor using nutrient media specific for total bacteria, Gram negative bacteria, total mold or the mold Aspergillus fumigatus. An example of the recommended sampling flow is 28.3 L/min for 1-5 minutes. (If you are interested in taking samples or renting a pump, you can contact us for help or to provide you with the equipment).

For more information about our mould or bacteria testing services, please contact Mold & Bacteria Consulting Laboratories. Please call our Ontario, Mississauga Office at 905-290-9101 or the British Columbia, Burnaby Office at 604-435-6555.


Goyer N, Lavoie J. 2001. Identification of sources of chemical and bioaerosols emissions into the work environment during secondary treatment of pulp mill effluents. Tappi Journal. 24(2):2-13.

Goyer N, Lavoie J, Lazure L, Marchand G. (2001). Bioareosols in the Workplace: Evaluation, Control and Prevention Guide. Technical Giode T24, Montreal, IRSST, 72 pages.

Murray, W. April 1992. Pulp and Paper: The Reduction of Toxic Effluents. Library of Parliament Research Branch. Ottawa, Canada: Canada Communication Group. Retrieved 2013-04-03.

Niemelä, SI, Väätänen P, Mentu J, Jokinen A, Jäppinen P, Sillanpää P. (1985). Microbial Incidence in Upper Respiratory Tracts of Workers in the Paper Industry. Appl. Environ. Microbiol. 50(1):163-168.

Pokhrel, D, Viraraghavan, T. 2004. Treatment of pulp and paper mill wastewater-a review. Total Science of the Environment. 333:37-58.

Forcier, F. September 2002. Biosolids and Bioaerosols: The Current Situation. Prepared for Quebec Ministry of Environment.

Thompson G, Swain J, Kay M, Froster CF. 2001. The treatment of pulp and paper mill effluent: a review. Bioresour Technol. 77(3):275-286.

Velema, G. 2004. Management and benefits of pulp and paper mill residuals at Domtar Cornwall. Pulp & Paper Canada.105(7):150-156.

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