The enhancement in efficient wastewater treatment processes is one of the greatest significant problems mainly in textile dyeing units. Textile dyeing wastewater holds huge quantities of chemically diverse manmade dyes, surfactants, and other mineral substances, which are accountable for a severe toxicity on municipal wastewater treatment facilities. In this study, the colored wastewater contains mainly a Crystal violet dye from a local dyeing unit was treated by batch coagulation test using algal alginate as a coagulant extracted from Sargassum sp. marine brown algae. The raw algal alginate and dye loaded alginate was characterized by Fourier transform infrared spectroscopy and scanning electron microscopy techniques. The effect of various parameters like alginate dose, calcium dose, and settling time was investigated. It was noted that the maximum color removal of 97.3% at optimum conditions of 50 mg/L of alginate dose, 6 g/L of calcium dose was achieved. The sludge volume index (SVI) was examined at the maximum dye removal condition and compared with alum. The preliminary kinetic study on dye removal process shows that, it follows a second-order kinetic equation. The present study reveals that the algal alginate, a biopolymeric compound extracted from brown algae Sargassum sp. can be an efficient coagulant for Crystal violet dye removal in the wastewater from the textile dyeing unit. © 2020 Desalination Publications. All rights reserved.