Treatment of pulp and paper wastewater with reducing agent and a polymer for color removal

摘要

A process for removing colour from a pulp and paper wastewater contg. aldehyde and keto-enol colour producing functional gps. comprises (a) treating the wastewater with an effective amt. of reducing agent, selected from sodium bisulphite, sodium hydrosulphite and sodium persulphate, to convert at least some of the colour producing functional gps. to anionically charged addn. prods., the wastewater pH being 6.0-11.0; (b) subsequently treating the wastewater with a cationic polymer which is capable of removing colour, including the addn. prods. from the wastewater, where the cationic polymer is at least one polymer and/or copolymer selected from an epichlorohydrin-dimethylamine polymer, polyethyleneimine cpds., polydiallyldimethyl ammonium chloride, copolymers of polydiallyldimethylammonium chloride and acrylamide and an ethylenedichloride-ammonia polymer; and (c) removing the colour including the addn. prods. from the wastewater.