PhD Student, Indian Institute of Technology Guwahati
Algal biomass production technology for bioenergy.
Microalgae are microscopic photosynthetic organisms, usually grows in freshwater as well as seawater. As they are photosynthetic, they utilize sunlight, carbon dioxide, water and essential minerals that exists in the nature. These biological entities were found as a great bio resource for biodiesel, a renewable and sustainable substitute to conventional petro-diesel. Apart from this advantage, some other types of microalgae were found to produce high value products like pharmaceuticals, nutraceuticals. While growing microalgae for biodiesel, humankind will be served with dual benefits i.e., mitigation of harmful carbondioxide from industrial flue gases as well as production of the environment friendly biodiesel. Unfortunately, our scientific community stuck in developing an economical and commercial platform for the production of biodiesel from microalgae. The major bottle neck lies in the ‘growth technology’ itself, i.e., achieving high biomass production. Hence, my project goal was decided to develop a low-cost “biomass production technology” for growing microalgae.
Abstract: As a result of mixing and light attenuation, algae in a photobioreactor (PBR) alternate between light and dark zones and, therefore, experience variations in photon flux density (PFD). These variations in PFD are called light/dark (L/D) cycles. The objective of this study was to determine how these L/D cycles affect biomass yield on light energy in microalgae cultivation. For our work, we used controlled, short light path, laboratory, turbidostat-operated PBRs equipped with a LED light source for square-wave L/D cycles with frequencies from 1 to 100 Hz. Biomass density was adjusted that the PFD leaving the PBR was equal to the compensation point of photosynthesis. Algae were acclimated to a sub-saturating incident PFD of 220 µmol m(-2) s(-1) for continuous light. Using a duty cycle of 0.5, we observed that L/D cycles of 1 and 10 Hz resulted on average in a 10% lower biomass yield, but L/D cycles of 100 Hz resulted on average in a 35% higher biomass yield than the yield obtained in continuous light. Our results show that interaction of L/D cycle frequency, culture density and incident PFD play a role in overall PBR productivity. Hence, appropriate L/D cycle setting by mixing strategy appears as a possible way to reduce the effect that dark zone exposure impinges on biomass yield in microalgae cultivation. The results may find application in optimization of outdoor PBR design to maximize biomass yields.
Pub.: 19 Apr '12, Pinned: 12 Mar '18
Abstract: Maximum photobioreactor (PBR) efficiency is a must in applications such as the obtention of microalgae-derived fuels. Improving PBR performance requires a better understanding of the "light regime", the varying irradiance that microalgal cells moving in a dense culture are exposed to. We propose a definition of light regime that can be used consistently to describe the continuously varying light patterns in PBRs as well as in light/dark cycles. Equivalent continuous and light/dark regimes have been experimentally compared and the results show that continuous variations are not well represented by light/dark cycles, as had been widely accepted. It has been shown that a correct light regime allows obtaining photosynthetic rates higher than the corresponding to continuous light, the so-called "flashing light effect" and that this is possible in commercial PBRs. A correct PBR operation could result in photosynthetic efficiency close to the optimum eight quanta per O(2).
Pub.: 16 Nov '10, Pinned: 12 Mar '18