Light enhancement strategies improve microalgal biomass productivity

The rapid increase in global energy demand, global warming and climate change have driven the search for alternative renewable sources of energy with lesser environmental impact. Microalgae have immense potential as renewable energy feedstocks. Microalgal biomass can be used to generate a variety of biofuels including biodiesel, bioethanol, bio-hydrogen, bio-methane and syngas. One of the major hurdles to the commercialization of microalgae-based biofuels and products is limited biomass productivity. Considerable amounts of research have been conducted into enhancing microalgal biomass production due to its potential sustainability and variety of applications. The traditional methods of improving biomass productivity are limited to adaptation of cultivation conditions and more recently genetic engineering. Light is a crucial factor that governs microalgal growth. Research on the adaptation and manipulation of natural light rather than adaptation of microalgae has been very limited. Microalgae utilize only a small fraction of light wavelengths from the wide spectrum of solar radiation for photosynthesis. In order to enhance microalgal biomass, improved photosynthetic efficiency is essential. This can be accomplished by the manipulation of the light spectrum to achieve an optimal balance between photosynthesis and photoprotection. Manipulation of incident irradiance may be viable for increased light harvesting by algae. This not only reduces unused wavelengths but also concentrates the wavelengths in a range utilized by algae. This would allow for a maximum utilization of the light spectrum by microalgae. This review critically analyses different light manipulation techniques that modify the spectrum of light received by the algae to improve biomass productivity.