Vinasse is a liquid residue from the sugarcane-based ethanol industry. After sugarcane juice fermentation by yeast, ethanol concentration in the fermented broth is no more than 10% v/v (due to its toxicity). During distillation, the ethanol is recuperated and everything left is called vinasse. It is produced in high volumes (12-15 liters for each liter of ethanol) and is rich in minerals (Rego and Hernandez, 2006). Ethanol production in Brazil in 2012 is esti­mated at 27.9 billion liters (Empresa de Pesquisa Energetica, 2012), which means production of vinasse is around 365 billion liters.

The major problem related to vinasse is its high chemical and biological oxygen demand:

29,0 and 17,000 mgO2/L (Elia Neto and Nakahodo, 1995), respectively, 100 times more pollutant than average domestic wastewater. Vinasse pollutant strength is mainly due to high organic matter content and the presence of three important nutrients: nitrogen, phos­phorous, and potassium (Bittencourt et al., 1978). Due to its composition, vinasse is largely used as fertilizer in sugarcane cultivation. Theoretically, the amount of vinasse allowed per area is regulated by the Brazilian government, but inspection is difficult to be carried out, leading to indiscriminate use.

According to Manhaes et al (2003), soils irrigated with vinasse have high concentrations of nutrients at depths that can contaminate groundwater. Around 60% of the Brazilian ethanol is produced in Sao Paulo state (UNICA, 2010), which is located on the Guarani Aquifer, the second largest underground freshwater reserve in the world.

Given the clear environmental risk caused by poor allocation of vinasse, it is of great importance to apply technical and scientific knowledge for its better distribution, allowing further relocation in water bodies. When used in microalgae cultivation, biological and chem­ical oxygen demand (BOD and COD, respectively) can reach more than 90% reduction in BOD and more than 80% reduction in COD (DalmasNeto, 2012) in the first cycle of cultivation. Considering three cycles, reduction in BOD and COD can reach more than 95%.