posted on 2014-12-02, 00:00authored byQuentin Béchet, Andy Shilton, Benoit Guieysse
While
modeling algal productivity outdoors is crucial to assess
the economic and environmental performance of full-scale cultivation,
most of the models hitherto developed for this purpose have not been
validated under fully relevant conditions, especially with regard
to temperature variations. The objective of this study was to independently
validate a model of algal biomass productivity accounting for both
light and temperature and constructed using parameters experimentally
derived using short-term indoor experiments. To do this, the accuracy
of a model developed for Chlorella vulgaris was assessed
against data collected from photobioreactors operated outdoor (New
Zealand) over different seasons, years, and operating conditions (temperature-control/no
temperature-control, batch, and fed-batch regimes). The model accurately
predicted experimental productivities under all conditions tested,
yielding an overall accuracy of ±8.4% over 148 days of cultivation.
For the purpose of assessing the feasibility of full-scale algal cultivation,
the use of the productivity model was therefore shown to markedly
reduce uncertainty in cost of biofuel production while also eliminating
uncertainties in water demand, a critical element of environmental
impact assessments. Simulations at five climatic locations demonstrated
that temperature-control in outdoor photobioreactors would require
tremendous amounts of energy without considerable increase of algal
biomass. Prior assessments neglecting the impact of temperature variations
on algal productivity in photobioreactors may therefore be erroneous.