| Summary: | Algae are photosynthetic microorganisms that convert carbon dioxide and sunlight into biomass that can be used for biofuel production. Although
they are usually cultivated in suspension, these microorganisms are capable
of forming productive biofilms over substrata given the right conditions. This
dissertation focuses on algal biofilms and their application in biofuel feedstock
production. In particular it reports the construction and performance of an
algae biofilm photobioreactor, the physico-chemical surface properties of different
algal species and adhesion substrata, and cell-surface interactions based
on experimental results and theoretical models.
A novel algae biofilm photobioreactor was constructed and operated
(i) to demonstrate the proof of concept, (ii) to analyze the performance of
the system, and (iii) to determine the key advantages and short comings for
further research. The results indicated that significant reductions in water and energy requirements were possible with the biofilm photobioreactor. Although
the system achieved net energy ratio of about 6, the overall productivity was
low as Botryococcus branunii is notoriously slow growing algae. Thus, further
studies were focused on identification of algal species capable of biofilm growth
with larger biomass and lipid productivities.
Adhesion of cells to substrata precedes the formation of all biofilms. A
comprehensive study has been conducted to determine the interactions of a
planktonic and a benthic algal species with hydrophilic and hydrophobic substrata.
The physico-chemical surface properties of the algal cells and substrata
were determined and using these data, cell-substrata interactions were modeled
with the thermodynamic, Derjaguin, Landau Verwey, Overbeek (DLVO)
and Extended Derjaguin, Landau, Verwey, Overbeek (XDLVO) approaches and
critical parameters for algal adhesion were identified. Finally, the adhesion rate
and strength of algal species were quantified with parallel plate
flow chamber
experiments. The results indicated that both cell and substrata surface hydrophobicity
played a critical role for the adhesion rate and strength of the
cells and XDLVO approach was the most accurate model. Finally, based on
these findings the physico-chemical surface properties of ten algal species and
six substrata were quantified and a screening was done to determine algae
species substratum couples favoring adhesion and biofilm formation. === text
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