Integrating Microalgae Cultivation with Wastewater Treatment for Biodiesel Production

Abstract

Microalgae are responsible for more than half of the world’s primary production of oxygen. They are the simplest and most abundant form of plant life on the earth (Energy from algae (Technical Summary. Scott Maden, 2010). These photosynthetic organisms are categorized under third generation biofuels and are known to have high oil and biomass yields, can be cultivated with wastewater, do not need arable land for cultivation, do not compete with common food resources and very efficiently use water and nutrients for growth (Hannon et al., Biofuels 1:763–784, 2010). There are various routes of metabolism which microalgae have adopted for their growth and survival viz., autotrophic, heterotrophic and mixotrophic. They are capable of shifting their metabolism in response to changes in the environmental conditions (Devi et al., J Renew Energy 43:276–283, 2012). Algal cultivation for biodiesel production is considered more amenable a technology than the cultivation of oil crops (Chisti, Biotechnol Adv 25:294–306, 2007) because the yields of algae-derived oils are much higher (Abou-Shanab et al., J Power Energy Eng 1:4–6, 2010). Autotrophically algae gain energy through light by fixing atmospheric CO2 (Devi and Venkata Mohan, Bioresour Technol 112:116–123, 2012). However, low biomass yields, requirement of cultivation systems with large surface area and shallow depth for better access of light are some of the disadvantages associated with autotrophic mode of nutrition. In the absence of light, the photosynthetic process gets suppressed and algae gain energy from alternative organic processes using heterotrophic pathways that convert sugar into lipids (Perez-Garcia et al., J Phycol 46:800–812, 2010). This pathway leads to significantly denser biomass, facilitating greater lipid yields.