RR1105 - The microbiology of paper mill process waters

Process water used in the commercial production of paper and board is susceptible to contamination with a large and diverse population of micro-organisms. Workers can potentially be exposed to these organisms, primarily by inhalation, if aerosols are generated. In some instances, conditions may be ideal for growth of the potentially pathogenic bacterium Legionella. However, little is known about the extent to which Legionella contamination is present in the papermaking process.

The aim of this study was to gather evidence on the microbial populations typically present in the process water used in paper manufacture and to assess if conditions are conducive to the multiplication of Legionella bacteria.

Water samples were taken from various locations in the papermaking process at nine paper mills. In many instances, culture-based analysis yielded more than one million bacteria per ml and in some cases more than ten million per ml.Culture analysis yielded few positive Legionella samples;however, molecular methods showed most samples tocontain Legionella DNA, although not necessarily as viable bacteria.

The results confirmed that large numbers of bacteria are present in paper mill process waters, and that Legionella is detectable. Risk assessment and microbial control is therefore important not only for product quality but also worker health protection, by reducing overall microbial levels.

This report and the work it describes were funded by the Health and Safety Executive (HSE). Its contents, including any opinions and/or conclusions expressed, are those of the authors alone and do not necessarily reflect HSE policy.

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Updated 2021-04-15