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 <i>Tetradesmus obliquus</i> (To), <i>Chlorella sorokiniana</i> (Cs), and <i>Chlorella vulgaris</i> (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 <i>Escherichia coli</i> (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.