Treatment of textile wastewater with natural coagulants

The textile industry is an important consumer of water. Textile wastewater usually has a large amount of residual dyes from the dyeing processes. These effluents also contain large amounts of residual electrolytes and are highly alkaline. Conventional biological treatments are inefficient in the elimination of dyes from water. Most dyes, as reactive dyes, usually are highly stable and poorly biodegradable. In this work two natural coagulants, Moringa Oleifera and Acacia Mearnsii, were studied in order to compare their efficiency to remove the colour of residual dyebaths. Initially, Acacia Mearnsii was used to treat simulated dyebaths prepared with different reactive dyes (Crimson, Navy, Yellow). Different concentrations of Acacia Mearnsii (250 – 1,000 mg/L) and different pH (5 - 11) were tested. It was possible to eliminate more than 95% of dye from the water. Afterwards, real residual dyebaths collected from a local textile company were treated with natural coagulants. Alkaline conditions of water (pH ≥ 10) were not modified. 1,000 mg/L and 2,000 mg/L of Moringa Oleifera and Acacia Mearnsii were tested. Moringa Oleifera eliminated up to 88% of colour. Whereas, Acacia Mearnsii only reached 25% of colour removal. Finally, water samples taken from the wastewater treatment plant of the textile company were treated with both coagulants. Alkaline conditions of water (pH ≥ 8) were not modified. Moringa coagulant eliminated up to 90% and Acacia coagulant up to 80% of colour from these kind of wastewater. Treated wastewater and residual reagents would be reused. Because most of the electrolytes and alkali remain on supernatant after the treatment This supernatant could be used for new dyeing processes, thus promoting the circular economy in the textile sector.