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Monitoring of biological processes in microalgae production using Fluorescence Spectroscopy
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Microalgae industrial production is nowadays viewed as a solution for environmental
conscious and sustainable alternative production of fuel, feed, food and chemicals. Throughout
the years, several technological advances have been studied and implemented that increased
the competitiveness of microalgae production. However, online monitoring and a real-time
process control of a microalgae production factory still requires development to support economic
sustainability.
In this work, fluorescence spectroscopy coupled with chemometric modelling is studied as an
online monitoring tool to be used in microalgae production. Fluorescence spectroscopy is a noninvasive
and highly sensitive technique, able to detect instantaneously several natural
fluorophores but also the interferences between them and the environmental media.
Chemometric methods are often used to deconvolute the information within the fluorescence
matrices, known as excitation-emission matrices (EMMs), and to determine the relationship
between them and the parameters to be monitored.
To prove the potential of fluorescence spectroscopy coupled with chemometric modelling
techniques, different strategies are studied. Firstly, the EEMs of the spectra are used as raw data,
without pre-treatment for removal of water scatter and inner-filter effects. Principal Component
Analysis (PCA) is used to extract the meaningful information from the spectra, resulting in
Principal Components (PCs). Through Projection to Latent Structures (PLS) modelling, prediction
models are developed using the PCs from the fluorescence EEMs as inputs, to find linear
correlations with the parameters to be monitored, the outputs. A second strategy is studied with
pre-treated EEMs. With these EEMs, two input strategies in the PLS models are tested: using
directly the EEMs in PLS or compressing the EEMs into PCs though PCA prior to PLS.
Two marine microalgae are used in these studies, Dunaliella salina and Nannochloropsis
oceanica. Five parameters are monitored – cell concentration, cell viability, pigments
concentration, fatty acids composition and nitrogen concentration – in four different processes –
cultivation, product formation (carotenoids and lipids), harvesting by membrane filtration and
permeate recover.
The combination of fluorescence spectroscopy, with its high sensitivity and resolution, coupled
with chemometric analysis for data pre-treatment and development of prediction models,
enhances the
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online monitoring fluorescence spectroscopy Principal Component Analysis Projection to Latent Structures microalgae production Dunaliella salina