Aalto University, School of Arts, Design and Architecture, Department of Arts
Abstract
The objective of this thesis was to study the interactions of microbial activity, biocide usage and creation, and chemical changes in the papermaking process. The main focus was on oxidative biocide systems. In addition, new measurement and biocide production methods were applied to papermaking, and evaluated for the monitoring and control of the microbiological state and biocide usage. The measurement methods were based on portable handheld online equipments whereas the biocide production was based on electrochemical generation of biocides.
The trials were mainly performed in pilot scale with actual process samples and complemented with a few laboratory trials. Most of the pilot results were verified in several field studies at paper machines. In the studies also the applicability of monitoring tools were evaluated.
Biocide dosing itself, paper machine breaks, and poor management of broke generated chemical variations, which were detrimental to the papermaking process. Spoilage of broke due to poor broke management and poor biocide performance decreased the system pH, increased the conductivity, and caused the defects to the web. These chemical variations were also observed to cause variations in the cationic demand values. This probably caused unwanted particle flocculation generating the spots and holes to the web. Base paper defects were observed to cause runnability problems also at the coating machine. This cyclicity, where chemical variations cause breaks and breaks cause chemical variations, should be eliminated in order to restore good runnability.
When revealing many such cause-effect relations and hidden phenomena, hand-held instrumentation gives additional references for existing basic measurements such as pH, conductivity, and redox potential. This work also took in use measurements which have not been traditionally used in papermaking such as measurement of halogens, dissolved calcium, and dissolved oxygen contents. ATP content measurement using a portable luminometer was found to be useful and easy-to-use method for evaluating microbial activity and optimizing biocide performance at paper mills.
This thesis introduces a new biocide concept which can be used to prevent both microbial and biocidal problems described above. The results demonstrate how electrochemical on-site production can decrease chemical variations and improve biocide performance compared to current best practices offering an efficient and economically attractive alternative for microbial control
