| Summary: | The objective of this work was to study chemical precipitation as an alternative to eliminate the COD of the final effluent, to comply with the regulations. The work involved liquids entering the primary treatment of a neutral sulfite semichemical pulp (NSSC) mill. After performing the overall characterization of the liquids, the flocculation with coagulants and flocculants was tested. The influence of pH, the incorporation of calcium hydroxide and sodium hydroxide, and the coagulant dosages were studied. Chemical Oxygen Demand (COD), lignosulphonate (NaLS) concentration, colour, turbidity, solids, and ash were determined in teh supernatants obtained from the different treatments. The greatest reductions with aluminum salts were 50% in COD and 63% of NaLS using 1000mg/L Al2(SO4)3, and 58% of the COD, 53% of NaLS and 96% of color, using 6000mg/L of Poly-aluminum Chloride (PAC), on diluted (0.33% solids, COD of 2280mg/L) and concentrate (1.60% solids and COD of 13 280) liquids respectively. Reductions of NaLS and COD were achieved in the diluted liquid spent with 100 mg/L of a cationic polyacrylamide.
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