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

Today the bleaching stages of the pulp industry are faced with an enormous challenge concerning the minimisation of the environmental impact of its effluents. Organochlorinated compounds (TOX) and mainly the low-molecular-weight fraction of the extractable compounds (EOX) are major pollutants because of their lipophilicity and bioaccumulation ability. This work evaluates the performance of ultrafiltration (UF) and nanofiltration (NF) on the reduction of organochlorinated matter and colour in the effluents from the first alkaline extraction (El) of two different bleaching sequences, one with chlorine/chlorine dioxide and the other only with chlorine dioxide. Three types of membranes were used. Ultrafiltration membranes, CA-400 and ETNA01A, and nanofiltration membranes, CDNF50. The substitution of chlorine/chlorine dioxide by chlorine dioxide in the first bleaching stage reduces 84% of EOX, 82% of TOX and 72% of colour in the El effluent. The highest removal of TOX and colour achieved by ultrafiltration is 72 and 92%, respectively. The total removal of colour and more than 90% removal of TOX is achieved by nanofiltration. The two operations, by themselves or integrated, can serve the regulatory and/or mill demands.