HETEROGENEOUS PHOTODEGRADATION OF EFFLUENT FROM KRAFT PULP BLEACHED WITH CHLORINE

The wood cellulose pulp must be bleached to reach a high commercial value. Chlorine is very effective in bleaching for pulp obtained by chemical process, but it also produces highly polluting and toxic byproducts. Other bleaching chemicals have been proposed to reduce toxicity, but they are more expensive and less versatile. Catalytic photodegradation using ultraviolet radiation (UV) was performed to assess the potential for reducing the content of pollutants in an effluent from bleaching cellulose pulp by using chlorine. The Pinus taeda cellulose pulp was produced and bleached in laboratory. Three liters of effluent received 3g of titanium dioxide (TiO2) and were submitted to UV radiation. UV was produced with the use of a mercuryvapor bulb in high-pressure of 250 W (12,500 Lm) for 240 min. Photodegradation to 25 degrees C for 240 min with UV decreased about 43% of the color, 40% of the BOD5 (biochemical oxygen demand), 50% of the COD (chemical oxygen demand), 40% of calcinable material and 45% of TOC (total organic carbon), in addition to decreasing the toxicity LC50 (lethal concentration - 50%) for the treated effluent. The bioindicator Artemia salina showed the survival time greater than 1,000% for the treated effluent. The experimental points distribution from 0 to 240 min suggests that the photodegradation must be extended. Thus, the reduction of pollutants observed suggests that advanced oxidation process (AOP), using UV-TiO2 photocatalytic oxidation may be convenient to treat chlorinated bleaching effluents. This can enable the safe use of chlorine bleaching.