FIELD: process of purifying waste water. SUBSTANCE: waste water is an acidic solution of sodium sulfate and hydrosulfate with a tall lignin content of 20-50 g/l at 3,5-4,5 pH. To remove the latter the solution is treated in an evaporator, then washing is performed using hot water or condensate with preceding concentrating to 150 - 200 g/l at a cyclone and then the residue is finally thickened at a centrifuge to receive tall lignin which moisture content equals at least 40-50 %. EFFECT: increased efficiency of process.
