Remoção de nitrato e fosfato presente em efluente sintético, por meio do cultivo de Chlorella vulgaris, com foco preliminar para produção de biodiesel

Abstract

Industrialization, urbanization and agriculture practices have generated an increasing amount of effluent in the past years. Effluents contain nutrients such as nitrogen and phosphorus that can lead to the eutrophisation of aquatic ecosystems. The eutrophisation phenomenon is strongly correlated to the bloom of algae and aquatic plants, which can result in the loss of component species and loss of the ecosystem functions. For these reasons, it is important to submit the effluent to the correct treatment in order to decrease the concentration of nitrogen and phosphorus compounds. Therefore, this project aimed to cultivate the microalgae Chlorella vulgaris in batch systems inside photobioreactors in four different growth conditions (sun light; 16000 lux; 11000 lux with aeration; and 9500 lux) and subsequently evaluate their growing capacity, nutrient removal and the biomass oleaginous potential in order to assess their suitability for biodiesel production. Five weeks of tests were held, in which three different mother cultures were used (sun light – C1 –, artificial light with aeration – C2 –, and artificial light without aeration – C3). The initial concentrations of nitrate were 130 mg/L, 60 mg/L, 40 mg/L, 4 mg/L and 7.5 mg/L in the first, second, third, fourth and fifth week of study, respectively. The initial concentrations of phosphate were 32.1 mg/L, 15 mg/L, 10.8 mg/L, 1.02 mg/L and 2.3 mg/L in the first, second, third, fourth and fifth week of study, respectively. The greater biomass growth obtained was 2700%, with a pH increasing of 3.67, by the culture kept under 16000 lux, in the first week of experiment (inoculated with C2). The greater nitrate removal was 96.67%, by the culture kept under 11000 lux with aeration, in the fifth week of experiment (inoculated with C2), while the greater phosphate removal was 95.10%, by the culture kept under 11000 lux as well, but in the fourth week (inoculated with C2). The results indicate that C2 provided the best growth conditions and that it generated more efficient cells in terms of nutrient removal and growth rates. Aeration was probably a driving factor in those results. After using C. vulgaris to remove nitrate and phosphate in synthetic wastewater, the biomass was treated in order to extract lipids and convert them into biodiesel by using the transesterification method. It was concluded that the biodiesel obtained from microalgae biomass, which contained 10.12% of their dry mass formed by lipids, was similar to traditional diesel.