-The carbon source is the most expensive nutrient for Spirulina production; effluents from anaerobic digestion contain this nutrient in the form of HCO 3 -. The aim of this study was to assess the growth kinetics, composition and fatty acid profile of Spirulina sp. LEB-18 grown in standard Zarrouk medium (NaHCO 3 16.8 g L -1) and in Zarrouk medium replaced with 20% (v/v) effluent with reduced concentrations of NaHCO 3 (5.3 and 2.8 g L -1 ). The use of effluent and lower concentrations of HCO 3 -was found to be an alternative to reduce the costs of Spirulina production, because there were no significant differences in growth parameters (μ max 0.324 -0.354 d -1 ; P max 0.280 -0.297 g L -1 d -1 ), in the different culture medium used. Lipids ranged between 4.9 and 5.0%; the media with effluent had higher levels of linoleic acid compared to the standard medium.