Growth of Chlorella vulgaris in treated conventional and biodigested vinasses

Vinasse is a residue of the sugarcane industry. It can be biodigested or not, in this case referred as conventional. The conventional or biodigested vinasses have high content of organic matter and mineral elements, leading to their common use as soil fertilizer for the sugarcane crop. However, vinasses are toxic residues and they can salinize the soil if used too much. On the other hand, the production of photosynthetic microalgae is costly and using a residue to support its growth may contribute to cost reduction. However, because of the vinasse dark color and toxicity, high dilution is necessary to accomplish microalgal growth. Here we present results on the growth and biomass yield of Chlorella vulgaris in conventional and in biodigested vinasses that have been treated by filtration or centrifugation before their use as microalgae culture medium. A concentration range of 10 to 100 % was tested and microalgal growth occurred in vinasse concentration as high as 80 %, with no nutrient addition. We evaluated pH, electrical conductivity, absorbance at 570 nm, and cell density every 24 h in a 6-day incubation experiment. Specific growth rates were calculated and the results showed that in 60 % filtered conventional and 80 % biodigested vinasses, C. vulgaris performed as well as the controls in nutrient rich synthetic culture media, with growth rates of up to 1.2 day(-1). Thus, we propose the use of treated vinasse as culture medium for lowering the costs of microalgae production, with the advantage of increasing the residue value.