Biofilm (sticky masses of microbes) can be a big hindrance in paper production. In an industry that relies on water for its process, it is not surprising that bacteria can be prevalent. This is a threat to paper quality, machine efficiency and productivity that needs to be managed.¹ These films / slime adhere to areas in the machinery and to the paper itself.²

The water used in paper production is recycled and used in several stages of production which contributes greatly to the formation of microbial slime.³ There are also other factors involved that make the conditions ideal for microbial growth such as favourable operating temperatures and water pH. As well as this, the paper's components can act as nutrients for bacteria / fungi.⁴

Changes in the way that paper is produced that are beneficial in other ways (e.g more environmentally friendly) may also be contributing to a higher incidence of slime formation. Modern techniques can provide the perfect conditions for microbial growth. These processes include not using chlorine for bleaching, recycling paper and the use of closed cycles.⁵

Due to the issues arising from biofilms forming during the production process, biocides are often used to treat the water on a continuous basis. Despite this, the problem can overwhelm any chemical interventions and become unmanageable.⁶

Another difficulty with using biocides for managing microbial slime in paper production is that a single treatment will not treat all of the different types of micro-organisms present. Some microbes may be resistant to the treatments and while other bacteria / fungi may be inactivated by a biocide, resistant microbes may be left to thrive and overwhelm the other microbes that had been present.⁷

The other limitations of biocidal treatments is that they are mostly effective against free flowing planktonic microbes and have very little impact on established biofilms. Slimes that have formed in paper production machinery can be persistent, viscous and difficult to treat.⁸ This is one reason why biofilms provide an advantageous opportunity to survive and are the favoured existence of micro-organisms.⁹

Treatments other than chemical interventions have been investigated (such as ultrasonic treatment)¹⁰ but biocides are still largely the most used inhibitive measures.

Microbial contamination can occur throughout the paper making process. However, some stages of production are more likely to provide conditions that are beneficial to micro-organisms. Paper is produced by first creating a pulp using raw materials. This pulp is mixed with water and other additives to make what is referred to as 'slurry'. The liquid is drained from the slurry (this liquid is then called white water), separating it from the wet paper. The paper then goes through several phases of pressing and drying. The earlier stages of this process (involving water and nutrients), play a big part in how microbes become an issue in paper production.¹¹

Water used during production can support the growth of many types of microbes but only a few will survive the later stages of the paper making process. The microbes that can endure more extreme conditions (such as sudden changes in temperature during paper drying), usually produce endospores. These endospores are highly resistant to unfavourable environments that microbes couldn't usually survive.¹²

Examples of damage that can be caused by microbial contamination in paper production includes blockages in machinery, corrosion damage to equipment and holes in paper. 13 Paper can also develop blemishes and inconsistencies in colour.¹⁴

It is not just the impact on the product or machinery that should be considered when monitoring microbial contamination in paper production. Employee health can also be affected as one study found that air samples around wet areas in the paper mill included much more bacteria than outside of these areas (50 times the amount).¹⁵

As well as treatments, monitoring of biofilms may also be carried out. Equipment such as slime boards are used to 'collect' slime within white water over time. These are checked periodically to assess the levels of slime that are present.¹⁶

There is not one 'catch all' solution to dealing with microbiological contamination in paper production but multiple strategies should be employed to deal with the issue. The brilliant article 'Mini-review: Microbial problems in paper production' recommends a multi-faceted approach that could include:

Regular monitoring of the system (possibly by using sensors).

Actively working to inhibit microbial growth by use of treatments but also by maintaining conditions that are not favourable. An example given of how this can be achieved is by monitoring raw materials for microbiological contaminants so that these do not get into the system in the first place.

Implement plans that are akin to other management and control plans such as those used for food safety programmes (similar to HACCP).¹⁷

The authors accept that this approach may not be straightforward to implement at first and may be costly. However, as they point out, the expense and inconvenience caused by machine shutdowns and damaged product are a great financial and time burden.¹⁸

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If you are interested in monitoring levels of free flowing microbes in your paper mill / production facility, our paper mill dipslides can be found here: Paper Mill Process Water Dipslides

References

1, 2, 3, 6
Zumsteg A, Urwyler SK, Glaubitz J. Characterizing bacterial communities in paper production-troublemakers revealed. Microbiologyopen. 2017;6(4):e00487. doi:10.1002/mbo3.487

4
Desjardins E, Beaulieu C. Identification of bacteria contaminating pulp and a paper machine in a Canadian Paper Mill. Journal of Industrial Microbiology & Biotechnology. 2003;30(3):141-145. doi:10.1007/s10295-002-0017-x

5, 9, 11, 15, 16, 17, 18
Flemming H-C, Meier M, Schild T. Mini-review: Microbial Problems in paper production. Biofouling. 2013;29(6):683-696. doi:10.1080/08927014.2013.798865

7, 8, 12
Projects & Results | Cordis | European Commission. Microbiology in paper making. https://cordis.europa.eu/project/id/E17. Published March 5, 2003. Accessed March 30, 2023.

10
Klahre J, Flemming H-C. Monitoring of biofouling in Papermill Process Waters. Water Research. 2000;34(14):3657-3665. doi:10.1016/s0043-1354(00)00094-4

13,14
Chiellini C, Iannelli R, Lena R, Gullo M, Petroni G. Bacterial community characterization in Paper Mill White Water. BioResources. 2014;9(2). doi:10.15376/biores.9.2.2541-2559