The physiology of Chlorella vulgaris grown in conventional and biodigested treated vinasses

Conventional and biodigested vinasses are organic and nutrient rich residues from the sugar cane alcohol industry. Their disposal in running waters and soils are controlled due to their eutrophication potential. Using it as algal culture medium, lower costs and residue remediation can be achieved. Here, we report on the physiology of Chlorella vulgaris grown in 60% conventional and 80% biodigested treated vinasses in 6 days experiments. Cell densities, chlorophyll a concentrations and pulse amplitude modulated (PAM) fluorometry were used for culture monitoring. Maximum and operational quantum yields, photochemical (qP) and non-photochemical quenchings (qN and NPQ) and rapid light response curves were determined and efficiency of light use (a) and light saturation (IK) obtained for all treatments. The results showed that C. vulgaris grew better in vinasse (1.5-1.6 d(-1)) than in controls (0.9-1.2 d(-1)). PAM fluorometry showed that, despite the increased algal growth in vinasses, photosynthesis was higher in controls than in the residues, supporting that C. vulgaris used organic carbon as energy source. We suggest that the high competitiveness of the microalgae was due to its ability to grow mixotrophically in the residue even though heterotrophic contaminants were present. A reduction of the vinasses eutrophication potential was obtained after the microorganisms' growth. This study is a contribution to the knowledge of microalgae photosynthetic physiology in organic rich residues, information that can help improve algal biomass production in residues at the same time that performs its remediation.