Semi-continuous microalgae cultivation on dairy wastewater considering low dilution rates: insights about cultivation stability and contaminant removal.

Industrial wastewater pollution is an environmental problem that affects ecosystems and communities. Phycoremediation offers an eco-friendly alternative for contaminant removal. This study evaluated the efficiency of Tetradesmus obliquus (To), Chlorella sorokiniana (Cs), and Chlorella vulgaris (Cv) in treating dairy wastewater. Microalgae were cultivated in photobioreactors at four dilution rates (0.20, 0.25, 0.30, and 0.35d^-1). The initial wastewater contained pH 7.79 ± 0.50, total nitrogen (TN) 188 ± 0.50 mg L^-1, total phosphorus (TP) 20.45 ± 0.17 mg L^-1, chemical oxygen demand (COD) 8400 ± 52mgO₂L^-1, Mn 2.02mgL^-1, Al 217.43mgL^-1, Cr 0.04μgL^-1, total coliforms (TC) 3800CFUmL^-1, and Escherichia coli (EC) 100CFUmL^-1. All microalgae showed high removal efficiency, with 0.20d^-1 as the optimal rate. After treatment, To0.20 reduce TN 97.3 ± 0.71mgL^-1, TP 2.39 ± 0.16mgL^-1, COD 570 ± 2mgO₂L^-1, Mn 0.06 ± 0.00mgL^-1, Al 0.07 ± 0.00mgL^-1, Cr 0.02 ± 0.00µgL^-1, TC and EC not detected. Cs0.2, it was TN 4.94 ± 0.35mgL^-1, TP 6.59 ± 0.23mgL^-1, COD 432 ± 13mgO₂L^-1, Mn 0.06 ± 0.00mgL^-1, Al 0.03 ± 0.01mgL^-1, TC 4 ± 0CFU mL^-1, Cr and EC not detected and Cv0.2, it was TN 5.15 ± 0.89mgL^-1, TP 5.77 ± 0.05mgL^-1, COD 450 ± 14mgO₂L^-1, Mn 0.06 ± 0.00mgL^-1, Al, Cr, TC and EC not detected. The best treatment was Cv0.20, which eliminated 99% TN, 72% TP, 95% COD, and 100% TC and EC. This study provides new insights into using different microalgae and dilution rates to produce remediated effluent meeting irrigation standards.