Microalgae growth in winery wastewater under dark conditions

Wine-making process leads to large amounts of wastewater. Winery wastewaters (WWW) are produced from different activities of wine production: washing, transferring and storage operations. Tank cleaning and filtration equipment are responsible for the release of the largest amount of wastewater, whose polluting power is mainly due to both the large volumes produced and the high organic load. Because of the latter problem, biological WWW treatments are particularly appropriate. Microalgae, often used to treat civil and different industrial wastewaters, are unicellular organisms that can be grown either in autotrophic or heterotrophic mode using various organic and inorganic carbon sources. Their importance is related to their high growth rate, use to produce different biofuels, use in human or animal nutrition, and extraction of chemicals and pharmaceuticals. Purposes of this work were to reduce WWW environmental impact and to find a cheap growth medium able to reduce the microalgae production costs. In this study, three different wastewaters were used, namely WWW from first (1W) and second (2W) washing tanks, and WWW from filtration apparatus (3W). They were 20:80 (v/v) diluted with Bold Basal medium and treated batchwise with a co-culture of Arthrospira platensis and Chlorella vulgaris. Microalgae were grown under dark conditions in 0.5-L flasks with continuous air supply for 15 days. Biomass concentration was quantified daily by measurements of cell dry weight and optical density at 625 nm and expressed in grams of microalgae per liter (g/L). Chemical Oxygen Demand (COD) and total polyphenols content (by the Folin-Ciocalteu method) of WWWs were quantified daily, in order to evaluate the degradation capability of the co-culture. At the end of cultures, the lipid content of microalgal biomass was also quantified. Biomass grown in the presence of WWW reached final concentrations three times higher than the control. In general, COD was reduced by more than 90 % after 15 days, polyphenols concentration was reduced by 40, 90 and 100 % in 1W, 2W and 3W, respectively, while lipid content of biomass grown in 1W and 3W increased from 7 to 11 and 15 %, respectively. In conclusion, the results of this study demonstrate that microalgae can grow efficiently under dark conditions in media enriched with WWW, hence reducing its environmental impact.