ENVIRONMENTAL ASPECTS AND EFFICACY OF PERACETIC ACID TREATMENT TO IMPROVE ELEMENTAL CHLORINE FREE BLEACHING PROCESSES

The pulp bleaching process is mainly responsible for the generation of toxic substances in the whole paper making process. The modification of conventional ECF (elemental chlorine free) bleaching was studied using an oxygen stage, a peracetic acid stage and an oxygen followed by peracetic acid stage in the following bleaching sequences: OD0EOPD, PaaD(0)E(OP)D, OPaaD(0)E(OP)D and QOPaaD(0)E(OP)D. The PaaD(0)E(OP)D sequence reduced the COD, BOD, color, TDS and AOX by 36.8, 37.0, 52.4, 39.8 and 53.9%, respectively, in comparison with D0EOPD. Moreover, PaaD(0)E(OP)D has better optical effluent properties, compared to the OD0EOPD sequence. OPaaD(0)E(OP)D reduced the chlorophenols, chloroguaiacols by 73.3 and 89.3%, and improved the brightness and whiteness by 1.7 and 3.1 units, respectively, in comparison with the D0EOPD bleaching sequence. The QOPaaD(0)E(OP)D sequence improved the pulp viscosity by 0.8 units in comparison with OPaaD(0)E(OP)D. The amendment of the conventional bleaching sequence was found to be effective for achieving an improvement in optical properties and effluent quality at reduced dose of chlorine dioxide.