Cultivo de Chlorella vulgaris em vinhaça convencional e biodigerida tratadas : uma abordagem ecofisiológica
Resumo
Vinasse is a waste of sugarcane industry and, due to the presence of organic matter and mineral
nutrients, it has been used for the irrigation of the sugarcane crops. However, its composition
limits such application due to soil salinization. The anaerobic fermentation of vinasse generates
biogas that is used as energy source in the sugarcane industry itself. The fermented vinasse
results in biodigested vinasse. The development of techniques for residue use can contribute to
cleaner production systems. In this research, we evaluated treated conventional and biodigested
vinasses for the growth of Chlorella vulgaris. The treatment consisted of filtering the vinasses
through smectite clay and activated carbon, or centrifugation. Concentrations of 10, 20, 30, 40,
50, 60, 70, 80, 90 and 100% of treated vinasses were tested. Cell density, absorbance at 570 nm,
pH and electrolyte conductivity were quantified daily in a six day experiment. Based in cell
density, specific growth rates were calculated. Growth rates higher than the controls were
obtained in 60% conventional filtered vinasse and 10% conventional centrifuged one, as well as
in 80% biodigested filtered vinasse and 20% biodigested centrifuged vinasse. In general, the
filtered vinasse was superior in relation to the centrifuged one regarding higher residue
concentration that supported microalgae growth. After microalgae acclimation we evaluated the
photosynthetic performance of C. vulgaris in the best vinasses conditions and the biochemical
composition of the biomass present in the vinasse, which besides the microalgae contained other
microorganisms, such as bacteria and fungi, since it was not sterilized. Specific growth rate for
C. vulgaris in 60% filtered conventional vinasse was 1.6 d-1 and 1.5 d-1 in the 80% filtered
biodigested vinasse, representing increases of up to 84 x in cell density compared to the initial.
In the LC Oligo control the growth rate was ~ 0.9 d-1 and in the BG11 it was 1,1 d-1. Although
the better C. vulgaris growth in the treated vinasses, photosynthetic efficiency and its related
parameters were better in the control than in the vinasses. These results together with those of
chlorophyll a concentration suggest that the microalgae have possibly used a mixotrophic
metabolism while in the vinasses. We observed higher biomass accumulation in the vinasses
than in the controls. A reduction of total dissolved organic carbon and dissolved mineral
elements up to 50%, as well as bacteria and fungi, were detected in the vinasse after microalgae
growth. This study is a contribution to the knowledge of microalgae physiology in a residue and
to the development of cleaner ethanol production system.