Identification and quantification ofmicrobiological risks in board production : A study of ATP bioluminescence and redox potential

Abstract: Stora Enso is a well-established provider of renewable solution packaging and board materials.Board products for liquid packaging and folding cartons for food are particularly sensitive tothe microbiological contaminants. In the manufacturing process, microbiological growth occursdue to environmental favourable conditions. Most of the microorganisms eventually die in theboard machine. The microflora in the process consists mainly of bacteria from genera Bacillusand Paenibacillus, and these species have a unique characteristic of forming endospores. Thespores are non-vegetative capsules transformed from the dying bacteria, with its purpose ofprotecting the bacterial genome from the unfriendly environment as it passes through in theboard machine. The levels of spores found in the board products are usually low, but suddenpeaks of spores in the board products are unwanted for food and health safety. Bacterial andspore cultivation is a standard method to investigate microbiological activity. The method isinaccessible due to 48-hour incubation time for obtaining test results and does not provide anyoverview in a short time frame of where in the process that might triggered sporulation. In thelong run, it can cause production losses that affect the prospects of the board production.The purpose of this study is to investigate a new analysis method to facilitate identification andquantification of microbiological activity with ATP bioluminescence (AdenosineTriphosphate) measurement and redox potential, and as well investigate the main process sitethat possibly causes the issue. ATP bioluminescence measures the concentration of ATP inrelation to the number of bacterial cells. The study was limited to the broke system due to theclosed system and accumulation of microorganisms. The broke system manages the reuse ofdowngraded new paper board. For the laboratory work, 15 process positions were selected inthe broke system. Pulp were sampled from each process position for each laboratory workday,and measurements of ATP bioluminescence, redox potential, pH, temperature, TOC (totalorganic carbon), retention time, and bacterial and spore cultivation were completed as well. Thecollected data were studied in a multivariate analysis and correlograms were produced for eachprocess position. In addition, a parallel study of a lab scale broke tower simulation wasperformed to further investigate if the broke tower could be the source of the microbiologicalactivity.The obtained results showed low correlations between the process parameters and the totalbacterial and spore concentration. Similar results were obtained for ATP bioluminescence andredox potential, resulted in a low correlation to the total bacterial and spore concentration aswell. The simulation gave additional insight in the function of ATP bioluminescence and redoxpotential.The conclusion is that ATP bioluminescence is an accessible method due to high repeatability,however the reliability is lacking. The analysis is not reliable because of low correlationbetween the total bacterial and spore concentration. Redox potential is both a reliable andaccessible method to identify and quantify the microbiological growth in the system, becauseit signifies the environmental conditions for the bacterial growth. It has been proven in the brokesimulation. Further research is needed to understand the representation in relation to thebacterial growth behind each analysis in order to fully consider the analysing measurementapplicable. Due to low correlations between the variables in each process position, anyassumptions cannot be considered in any specific process position that might be main cause ofraised spore values in board products.