Challenges in the Design and Operation of an Efficient Photobioreactor for Microalgae Cultivation and Hydrogen Production

The major challenge in the production of biofuels from microalgae is the need to generate sufficient quantities of microalgal biomass and an environmentally friendly and cost-effective method for extraction of oil from the biomass. Biomass can be generated by cultivating microalgae in open ponds or closed photobioreactor systems. When using a photobioreactor system, it is possible to have better control over parameters such as temperature, pH, light intensity, dissolved oxygen and dissolved carbon dioxide. However, they consume more energy and are expensive to operate. Cultivation of microalgae in open ponds is cheaper, and it utilises less energy as compared to closed photobioreactors. But, it is not possible to control physical parameters like temperature and light intensity as they depend on the environmental conditions. Also, contamination from other predators, parasites and weeds needs to be addressed. Considering, the overall cost-effectiveness, it may be possible to cultivate microalgae in open ponds under semi-continuous systems. Direct production of hydrogen using photosynthetic microorganisms such as microalgae may also be considered since it can be energetically more favourable than cultivating, harvesting and processing the biomass for biofuel production. In such cases, degradation of the hydrogen produced by the hydrogenase enzyme present in the system needs to be managed. Considering future energy demands, the possibility of CO2 sequestration and bioenergy production from microalgae and the overall ease of cultivation, it may be possible to use semi-continuous cultivation in open ponds for generating microalgal biomass with better biomass yield.