Abstract
Benthic species of algae and cyanobacteria (i.e., those that grow on surfaces), may provide potential advantages over planktonic species for some commercial-scale biotechnological applications. A multitude of different designs of photobioreactor (PBR) are available for growing planktonic species but to date there has been little research on PBR for benthic algae or cyanobacteria. One notable advantage of some benthic cyanobacterial species is that during their growth cycle they become positively buoyant, detach from the growth surface and form floating mats. This 'self-harvesting' capability could be advantageous in commercial PBRs as it would greatly reduce dewatering costs. In this study we compared the growth rates and efficiency of 'self-harvesting' among three species of benthic cyanobacteria; Phormidium autumnale; Phormidium murrayi and Planktothrix sp.. Phormidium autumnale produced the greatest biomass and formed cohesive mats once detached. Using this strain and an optimised MLA media, a variety of geometries of benthic PBRs (bPBRs) were trialed. The geometry and composition of growth surface had a marked effect on cyanobacterial growth. The highest biomass was achieved in a bPBR comprising of a vertical polyethylene bag with loops of silicone tubing to provide additional growth surfaces. The productivity achieved in this bPBR was a similar order of magnitude as planktonic species, with the additional advantage that towards the end of the exponential phase the bulk of the biomass detached forming a dense mat at the surface of the medium.
Highlights
Algal productivity is up to an order of magnitude greater than that of most terrestrial crops making them a promising feedstock for many industrial processes (Packer 2009; Stephens et al 2010)
This feature has been observed in the environment and in our cultures (Wood et al 2010). This ‘self-harvesting’ capability would be advantageous in commercial applications as it has the potential to greatly reduce the dewatering cost of biomass harvesting. In this manuscript we describe experiments aimed at providing data for the development of a novel benthic PBR system
We investigated alternative benthic PBRs (bPBRs) systems with the ideal that productivity would be similar to planktonic species but that the benthic cyanobacteria would ‘self-harvest’
Summary
Algal productivity is up to an order of magnitude greater than that of most terrestrial crops making them a promising feedstock for many industrial processes (Packer 2009; Stephens et al 2010). Biofuel production offers potential recycling of anthropogenically-released carbon from fossil stores. Their high productivity has led to a great deal of interest in commercialscale algal production. There are two main ways of Cyanobacteria are an ancient group of prokaryotic organisms that have evolved many unique physiological adaptations including; the ability to scavenge limiting resources (Kim et al 2010; Carlsson et al 2007), the presence of distinct and extremely efficient light harvesting complexes known as phycobilisomes (Grossman et al 1993), the ability to store significant amounts of nitrogen and phosphorous in excess of their immediate requirements and a tolerance to a wide range of physiochemical conditions (Whitton and Potts 2000). These features make them amenable for commercial growth, and they are presently one of the few species of algae that are successfully grown commercially (Carlsson et al 2007)
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