Microalgal biorefineries: Integrated use of liquid and gaseous effluents from bioethanol industry for efficient biomass production

Abstract

A new method for CO₂ recovery was proposed for cultivation of different microalgae. First, a chemical fixation, where CO₂ was injected in alkalinized vinasse to form (bi)carbonate salts, was performed. In addition, biological fixation with CO₂-enriched air injection was also accomplished for evaluation of the most promising results. Two bioreactor systems, a stirred-tank reactor and a bubble column reactor, were employed. A higher carbon transfer rate (43.35 g.L^-1.h^-1) was achieved in the bubble column reactor using NaOH-alkalinized vinasse, along with reductions of the chemical oxygen demand (COD), biological oxygen demand (BOD) and turbidity (TD). This allowed the cultivation of microalgae and cyanobacteria at vinasse concentrations between 70 and 100%, reaching a biomass production of 2.25 g.L^-1 in 15 days of culture. The viability of chemical CO₂ fixation together with the use of 100% treated vinasse from a bioethanol production unit for microalgae cultivation has been demonstrated in a successfully integrated biorefinery approach.

Keywords: Bioproducts; Carbon dioxide fixation; Carbon transfer rate; Microalgae; Vinasse.