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Abstract:
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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 . |