Physicochemical characterisation of sectorial effluents of Cenibra

摘要

The bleached kraft pulp mills is one of the biggest fresh water consumer and they generate big amounts of effluent as well. A lot of alternatives have been done to minimize the water consumption, mainly at the bleaching plant. The environmental legislation - which have been turned more rigorous - the reduction of specific water consumption and lower environmental impacts, bring the necessity of a better knowledge about effluents sent to effluents treatment systems. Therefore, to have better understanding of their effects on the effluents treatment system, on the treated effluents quality and on the possibilities of reduction of fresh water comsumption, the physicochemical characterization was made. Three batches of samples were colected, during three consecutives days for each batch. The effluents consisted of weak black liquor evaporator condensates and bleaching stages filtrates of the two fiber lines. The samples were collected before and after the mill general shut down. The parameters evaluated were: pH, conductivity, chemical oxygen demand (COD), biochemical oxygen demand (BOD_5), total organic carbon (TOC), toxicity (Microtox~®), adsorbable organic halogens (AOX), extractives, carbohydrates, methanol, reduced sulfur compounds (TRS). TAPPI, ISO and Standard Methods of the Examination of Water and Wastewater methods were used. Gas chromatography was used to determine methanol and HPLC was used to determine carbohydrates. The digester and evaporator condensates characteristics of the two productions lines were very different, specially because of the high value of COD, BOD_5, TOC, methanol and toxicity at the fiber line #2 effluents, which determine the high loaded effluent characteristics. The first chlorine dioxide stage of the Fiber Line 1 presented higher COD, BOD_5, TOC contents and conductivity than the first extraction stage, which was unespected. However, the first chlorine dioxide stage and the first extraction stage of the Fiber Line 2 presented equivalent values. The first chlorine dioxide stage have the highest values of AOX. On the other hand, the alkaline extraction stage and the second dioxide stage have the highest oxidant residuals. The filtrates from the second chlorine dioxide stage and the last bleaching stage of the Fiber Line 2 presented very high values of COD, which can cause harmful effect at the cellulose dryer machine. Observing the results, we can conclude which effluents have the major influence on the quality of high organic loaded effluents, and consequently, on the treated effluents. Specifics characteristics of some effluent can be explained, in all cases, by bad process adjustments that can modify the microbiology of the effluent treatment system, affecting their performance. Based on the results, it will be evaluated possibilities of operational and process improvements to increase the effluents quality and decrease the fresh water consumption.