42 - Challenges for microalgae cultivation in sugarcane processing wastewater (vinasse) for biodiesel production: From the bench to pilot scale

Abstract

Microalgae culturing coupled with wastewater treatments has gained much attention as alternative to conventional processes, with the great advantage of generating alternative feedstock to biodiesel production and other high added-value components such as proteins, carbohydrates, and pigments. Several strains of green microalgae (Chlorophyceae) show high cell viability and good tolerance to temperature and pH changes in different wastewaters. However, albeit all extensive research efforts dedicated over the last decades, few pilot-scale studies concern microalgae heterotrophic cultures, i.e., using organic molecules as a substrate without a light source. Vinasse is the main wastewater from sugarcane processing, with acid pH and a high organic matter content. Our research group evaluated different culturing conditions on a bench scale (temperature, initial pH, the carbon/nitrogen ratio of vinasse) aiming the accumulation of lipids in microalgal biomass to produce biodiesel in a pilot scale. The experiments were set up in a heterotrophic bioreactor with 700L of medium containing sugarcane vinasse. Microalgae remained in the exponential growth phase for up to 9h, with a maximum concentration of about 3gL−1. Both carbon and nitrogen removal from vinasse followed zero-order kinetics (non-limiting). Lipid productivity was around 360mg per liter per day, similar to bench-tests values at selected conditions. Despite all the challenges associated with pilot-scale cultivations, highlighted and discussed in this chapter, sugarcane vinasse is a potential substrate for microalgae biomass production.