Assessment of fieldscale zero liquid discharge treatment systems for recovery of water and salt from textile effluents

Treatment systems consisting of physico-chemical treatment, biological treatment, ozonation, reverse osmosis system, nanofiltration system, multiple effect evaporator, crystalliser and solar evaporation pans set up by three dyeing units in Tirupur, India, were assessed in the present study. The composite samples were analysed for colour, pH, TSS, TDS, chlorides, sulphates, COD, total iron, silica, SDI, LSI and total hardness. The results indicated that the physico-chemical treatment alone is inadequate to achieve the feed water quality norms for spiral wound RO membranes. It is recommended that the primary treatment may incorporate biological treatment and ultrafiltration to reduce COD and SDI in the feed water. Water recovery by reverse osmosis and salt recovery using nanofilter were 87% and 71%, respectively. It was also found that there is substantial direct profit in recovering water using reverse osmosis and sodium chloride in solution using nanofiltration as compared to the recovery of Na2SO4. The study also revealed that high quality water could be produced by treatment system incorporating membrane technology at affordable costs and recycled back into the process in the textile dyeing industry.