Dairy wastewater treatment by Tetradesmus sp. in open system: molecular identification and the effect of light intensity and organic load in the process

In this study, microalgae were isolated and identified as Tetradesmus obliquus from the Northeast of Brazil, according to its morphological and molecular characterization. Its potential to be used in bioremediation of effluents was evaluated in the treatment of dairy wastewater through mixotrophic cultivation in open system. Experimental conditions were tested in different whey concentrations (0.5, 1, 2 and 4% v/v) and light intensities (25, 50, 100 and 200 µmol m −2 s −1 ) for 14 days. The whey was characterized with high contents of chemical oxygen demand (COD) (52,886 mg L −1 ), total nitrogen (TN) (1563 mg L −1 ) and total phosphorus (TP) (663.5 mg L −1 ). It was found that the presence of exogenous microorganisms did not inhibit microalgae growth and they alone did not treat efficiently the wastewater (control). Dry cell weight (microbial sludge) reached values between 200 and 600 mg L −1 . Increasing whey concentration was positive for COD removal capacity in terms of the amount removed, reaching up to 80% of removal rate, even though be better to work up to 1% of diluted whey (legislation requirements of discharge). Higher TN (83–94%) and TP (almost 100%) removal rates were obtained when higher light intensities (100 and 200 µmol m −2 s −1 ) and lower concentrations (0.5 and 1% of whey) were applied. Nitrogen and phosphorus content in biomass varied between 4–11% and 0.5–1.4% (dry cell weight), respectively. Graphical abstract