Cultivation of micro-algae for lipids and hydrocarbons, and utilization of spent biomass for livestock feed and for bio-active constituents

Abstract

The demand for energy is ever increasing, and concurrently the depletion of fossil fuels has been so rapid that it could lead to an energy crisis in the near future. At the same time, reducing the carbon footprint to mitigate global warming has been a subject of immediate attention. Production of energy through photosynthetic organisms such as micro-algae by harnessing solar energy might be a viable solution to some of these issues. In pursuit of renewable energy sources, efforts worldwide focus on identifying those organisms that can accumulate high quantities of biomass and produce molecules that can be converted to combustible materials. Economically viable processes for large-scale cultivation and downstream processing of biofuel precursors, such as lipids and hydrocarbons, have been a challenge, requiring adoption of technologies needing reduced inputs of energy and chemicals. Prudent energy audits to assess the viability of bio-energy processes are a necessity. The utilization of micro-algae for bioenergy production would be viable only when the whole process has a net energy gain, with complete utilization of algal biomass for biofuel and the co-products thereof used to produce food, feed and chemicals. The spent algal biomass—which is rich in proteins, carbohydrates, minerals and bio-active compounds—is ideal for feed applications. The paper outlines biorefinery approaches to integrated utilization of algal biomass for bio-energy, with co-production of valuable metabolites and nutrients as feed, with full utilization of all the fractions for economic viability of the process. These aspects are dealt with in detail in the various sections to provide a comprehensive overview of micro-algal technology for biofuel programmes vis-à-vis feed applications.