THE ROLE OF ULTRAFILTRATION AND NANOFILTRATION ON THE MINIMIZATION OFTHE ENVIRONMENTAL-IMPACT OF BLEACHED PULP EFFLUENTS

Today the bleaching stages of the pulp industry are faced with an enor mous challenge concerning the minimisation of the environmental impact of its effluents. Organochlorinated compounds (TOX) and mainly the lo w-molecular-weight fraction of the extractable compounds (EOX) are maj or pollutants because of their lipophilicity and bioaccumulation abili ty. This work evaluates the performance of ultrafiltration (UF) and na nofiltration (NF) on the reduction of organochlorinated matter and col our in the effluents from the first alkaline extraction (El) of two di fferent bleaching sequences, one with chlorine/chlorine dioxide and th e other only with chlorine dioxide. Three types of membranes were used . Ultrafiltration membranes, CA-400 and ETNA01A, and nanofiltration me mbranes, CDNF50. The substitution of chlorine/chlorine dioxide by chlo rine dioxide in the first bleaching stage reduces 84% of EOX, 82% of T OX and 72% of colour in the El effluent. The highest removal of TOX an d colour achieved by ultrafiltration is 72 and 92%, respectively. The total removal of colour and more than 90% removal of TOX is achieved b y nanofiltration. The two operations, by themselves or integrated, can serve the regulatory and/or mill demands.