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.
Original language | English |
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Qualification | Doctor Degree |
Awarding Institution |
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Supervisors/Advisors |
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Award date | 20 Jan 2012 |
Place of Publication | Espoo |
Publisher | |
Print ISBNs | 978-952-60-4454-5 |
Electronic ISBNs | 978-952-60-4455-2 |
Publication status | Published - 2011 |
MoE publication type | G5 Doctoral dissertation (article) |
Keywords
- papermaking
- wet end chemistry
- variation
- oxidizing biocide
- microbial control
- electrochemical treatment
- online measurement
- runnability
- web break