Abstract
A novel 28 L photobioreactor for growing algae was developed from a previous bubble column system. The proposed design uses the air lift principle to enhance the culture circulation and induce light/dark cycles to the microorganisms. Optical fibers were used to distribute photons inside the culture media providing an opportunity to control both light cycle and intensity. The fibers were coupled to an artificial light source, however the development of this approach aims for the future use of natural light collected through parabolic solar collectors. This idea could also allow the use of non-clear materials for photobioreactor construction significantly reducing costs and increasing durability. Internal light levels were determined in dry conditions and were maintained above 80 µmol/(s•m2). The hydrodynamic equations of the air lift phenomena were explored and used to define the geometric characteristics of the unit. The reactor was inoculated with the algae strain Chlorella sp. and sparged with air. The reactor was operated under batch mode and daily monitored for biomass concentration. The specific growth rate constant of the novel device was determined to be 0.011 h-1, similar to other reactor designs reported in the literature, suggesting the proposed design can be effectively and economically used in carbon dioxide mitigation technologies and in the production of algal biomass for biofuel and other bioproducts.
Highlights
Microalgae have several advantages over other biological sources as a feedstock for biofuels and bioproducts
The minimum average light intensity in the illuminated chamber was 89 μmol/(s·m2) with the proposed arrangement of 11 fiber optic cables per level; in excess of the defined lower target of 80 μmol/(s·m2) and validating the calculation that determined the number of fibers required from the reactor section mock-up
Some biofilm was detected on the walls of the reactor for three of the tests, the air bubbles demonstrated an effective cleaning effect over the fiber optics as evidenced by the fact that the fiber optic cables tips were never found to be clogged during the visual inspections after three months of operation
Summary
Microalgae have several advantages over other biological sources as a feedstock for biofuels and bioproducts. Microalgae can be used for starch production and its subsequent ethanol production through yeast fermentation, achieving efficiencies similar to the best available crops (Harun et al, 2010) Another characteristic of algae is that it can double its biomass at an exponential rate requiring less surface area for the production of biofuels and bioproducts (Framptona et al, 2013). Photobioreactors provide an isolated environment with a much lower probability of contamination by other algal strains or microorganisms. These reactors require less land for the same biomass production (Borowitzka, 1999). Photobioreactors could extend the growth potential from a current few microorganism strains used in open systems to more than thousands of strains of phototropic algae (Tredici, 1999)
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