The promise of one day using algae as a low-cost source for biofuels is coming closer and closer to fruition. Existing algal strains are already producing high lipid content, which can be extracted and converted to fuels. New strains and genetically-modified strains are also continually being researched, as well as variations in many different culture conditions in order to increase lipid and desirable co-product production.
The PBR101 is useful in determining the right strain and environmental factors for optimal production.
A recent study(3) examined the effect of light and temperature variations on the growth and physiology of the biofuel candidate marine microalgal species Nannochloropsis oculata. An array of interconnected PBR101 photobioreactors integrated with metabolic sensors was used to vary light and temperature conditions, varying them according to sinusoidal day/night light/dark and heating/cooling cycles.
The specific experiments were performed with algal cultures maintained at a constant 20°C versus a 15°C to 25°C diel temperature cycle, where light intensity also followed a diel cycle. While no differences in algal growth were found, it was determined that the changes in environmental conditions had a great effect on the metabolic processes.
The combination of strong light and high temperature in the second set of experiments caused greater damage to this second photosystem. In addition, overnight metabolism also was found to perform differently; this was thought to be due to the effect of temperature on respiration.
These experiments demonstrated the prediction of the effectiveness of deploying Nannochloropsis oculata in similar field conditions for commercial biofuel production. In addition, this study showed that the PBR101, with high-level environmental control features combined with high-resolution monitoring of algal growth and physiology, can be used to answer many unresolved questions in algal biofuel production.
A related study(4) provided the first in-depth analysis of CO2 limitation on the biomass productivity of Nannochloropsis oculata using PBR101 photobioreactors. Net photosynthesis decreased by 60% from 125 to 50 μmol O2L-1h-1 over a 12 h light cycle as a direct result of carbon limitation. Continuous dissolved O2 and pH measurements were used to develop a detailed diurnal mechanism for the interaction between photosynthesis, gas exchange and carbonate chemistry in the PBR101 photobioreactor.
Gas exchange determined the degree of carbon limitation experienced by the algae. Carbon limitation was confirmed by delivering more CO2, which increased net photosynthesis back to its steady-state maximum.
Further research examined the induction of oil accumulation in algae for biofuel production(5).
This effect is often achieved by nitrogen starvation. However, withholding nitrogen also often reduces total biomass yield, which reduces crop yield. In this report, it was demonstrated using the PBR101 photobioreactor that Chlorella sorokiniana will not only accumulate substantial quantities of neutral lipids when grown in the absence of nitrogen, but will also exhibit unimpeded growth rates for up to 2 weeks, a finding with significant commercial ramifications.
References: 3. Bojan Tamburic, Peter J. Ralph, et al., (2014) PLoS ONE 9(1): e86047; 4. Bojan Tamburic, Peter J. Ralph, et al., (2016) ChemSusChem, in press; 5. Sangeeta Negi, Amanda N. Barry, Richard Sayre et al., (2015) J Appl Phycol, published on-line 08 July.