Combination of coagulation–flocculation and nanofiltration techniques for dye removal and water reuse in textile effluents

Color is one of the main problems in wastewater and many techniques can be applied to remove it. In this work, nanofiltration, coagulation–flocculation and their combination were studied to remove color from five reactive dyes. Nanofiltration was carried out using an energy saving nanofiltration membrane in a 0.5 L pilot plant at 10 bar. Coagulation–flocculation experiments were performed in a jar test apparatus using an anionic polyelectrolyte flocculant, FeCl3 as a coagulant agent and two different resins: melamine–urea–formaldehyde and polyamine resin. From the results it was concluded that nanofiltration removed in the order of 40 and 80% of color for the five dyes while coagulation–flocculation reached between 85 and 95% of color removal for four dyes except in the case of polyamine resin for RB5. The combination of these techniques dramatically improved the removals reaching over 98% of color removal for all dyes except for RB5 that achieved a 90%. The combined process also decreases COD values as it implies the use of lower resin concentration than coagulation–flocculation.