Contents lists available at ScienceDirect Algal Research journal homepage: www.elsevier.com/locate/algal The physiology of Chlorella vulgaris grown in conventional and biodigested treated vinasses Camila Candido ⁎ , Ana Teresa Lombardi Post - Graduate Program in Ecology and Natural Resources (PPGERN), Laboratory of Algae Biotechnology, Federal University of São Carlos (UFSCar), Rodovia Washington Luís, km 235 - SP-310, CEP 13565-905 São Carlos, São Paulo, Brazil ARTICLE INFO Keywords: Microalgae Photosynthesis Mixotrophy Sugarcane residue PAM ABSTRACT Conventional and biodigested vinasses are organic and nutrient rich residues from the sugar cane alcohol in- dustry. 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 (α) and light sa- turation (I K ) 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 mix- otrophically 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. 1. Introduction Microalgae are photosynthetic organisms that can present several metabolic pathways for carbon and energy acquisition, which can be summarized as photoautotrophy, heterotrophy and mixotrophy. Although literature results show that the majority of microalgae can have mixotrophic metabolism [1–4], this has not been investigated using techniques that measure its photosynthetic performance and in- corporation of organic carbon at the same time. Photosynthesis can be divided into photochemical and biochemical steps [5], the light dependent and independent reactions, respectively. In the photochemical step, light energy hits photosystem II (PSII) and photosystem I (PSI), where it is captured and transferred to the pair of chlorophyll a in the reaction centers. From there, excited electrons begin their way through the electron transport chains [6]. In the light dependent stage, O 2 , ATP and NADPH are generated, with the last two molecules being used to form glucose in the light independent reac- tions. The efficiency with which the light reactions occur can be mea- sured by PAM fluorescence, a technique that can tell about the algal physiological status. Information about the energy that goes to the photochemistry step of photosynthesis or the fraction that is lost due to stressful situations are easily detected. According to Lombardi and Maldonado [7], problems in photosystem II are identified by this technique. So, information regarding its photosynthetic condition and health status can be obtained. Vinasse is a liquid residue from sugar cane industry that is turbid, fetid and rich in organic matter and mineral elements and it is produced in amounts as high as 12 L vinasse/L alcohol. Due to its high pollutant potential [8], vinasse disposal in water bodies is unsafe, forcing alter- native uses and/or treatments, as its biodigestion (vinasse anaerobic fermentation). This process generates biogas, which is used by the sugar industry as energy source, but the polluting potential of the resulting biodigested vinasse remains [9]. In the present text, vinasse is classified as conventional (raw vinasse) or biodigested (fermented vinasse). Due to vinasse mineral richness and organic content, a possible application is its use as a culture medium for microalgae, which is the target of this study. Thus, vinasse is a residue that could support mix- otrophic metabolism in microalgae, a situation where illumination https://doi.org/10.1016/j.algal.2018.01.005 Received 23 April 2017; Received in revised form 4 January 2018; Accepted 5 January 2018 ⁎ Corresponding author. E-mail address: cacandido90@gmail.com (C. Candido). Algal Research 30 (2018) 79–85 2211-9264/ © 2018 Elsevier B.V. All rights reserved. T