Chlorella vulgaris growth on anaerobically digested sugarcane vinasse: influence of turbidity

Abstract

This paper shows the influence of turbidity (in Nephelometric Turbidity Units - NTU), chemical oxygen demand (COD) and aeration (CO₂ supply) on the productivity and growth rate and lipid content of microalgae (a mixed culture predominantly composed of Chlorella vulgaris), using anaerobically digested vinasse as a culture medium. The microalgae can be cultivated in anaerobically digested vinasse, at turbidity and chemical oxygen demand of 690 NTU and 2.5 gCOD L ^-1, respectively, according to the modified Gompertz model, and removal of turbidity by filtration did not influence the microalgae productivity (≈ 77 mg L¹ d¹). Furthermore, aeration increased the productivity up to 139 mg L¹ d¹, with a biomass dry weight of 2.7 g L^-1. Finally, a maximum lipid content of 265 mg L ^-1 was obtained, while a nitrogen removal of 98% was recorded for all conditions. Thus, the combination of anaerobic digestion followed by the use of the digestate for the cultivation of microalgae may be an efficient way to treat large quantities of this residue, in turn yielding large amounts of microalgae biomass, which can be transformed into fertilizer and biofuel.

Key words
Biofuel; Gompertz model; lipid; nitrogen; wastewater