Biorefinery of microalgae biomass cultivated in wastewaters

Abstract Microalgae are an important source of oils and other molecules that can be used as feedstocks to produce biofuels and high-value products, having the potential of becoming a significant renewable energy source. However, large-scale production of microalgal biofuels faces numerous technical challenges, which hinders the growth and development of the microalgae biorefinery industry. The cultivation of the biomass using wastewaters as the main source of nutrients is one of the strategies that can significantly improve the economics of the process. The use of waste nutrients and energy coming from local industrial and waste treatment sites is an option that has the advantages of providing a constant and affordable source of nutrients with the added benefit of wastewater treatment. The variability among the different sources of liquid wastes makes it, though, difficult to predict the outcomes and makes the need to study every case individually. There are, however, common factors that need to be addressed when planning to use wastewaters as the main source of nutrients to cultivate algae. These are the concentration and ratio of nutrients, the interaction of ammonia content and pH, the concentration of heavy metals, and the barriers of light penetration found in turbid liquid wastes. Significant cost reductions of biomass production can be also achieved by fitting the biomass production system colocated to industries generating waste nutrients, water and energy, and useful for biomass growth; by the integration of a nutrients recycling process to the biomass production process; and by means of an efficient biomass fractionation and utilization. These approaches have been analyzed critically in this chapter.