Electroflotation of wastewater from synthetic fibre dyeing

Polyester yarn dyeing generates wastewater contaminated by emulsified lubricant oils, oligomer precipitates and disperse dyes. Dispersed air flotation (DAF) systems typically provide a low efficiency separation due to emulsion stability promoted by a high concentrationof surfactants. An overview on industrial processes has shown that oil separation yield exceeding 40% is rarely obtained. Electroflotation was considered a technology to contribute to the solution of this problem; this unit operation was first evaluated in a laboratory equipment; subsequently, a pilot plant was conceived and constructed. Both units provided good performances, the oil removal efficiency overcoming that obtained by DAF. A fundamental study on emulsion stability was carried out to evaluate the destabilization mechanisms in this type of wastewater.