Abstract

FELISSIA, Fernando E; BARBOZA, Olga M; BENGOECHEA, Dora I  and  AREA, María C.. Reduction of the recalcitrant COD of semi-chemical pulp effluents by chemical precipitation. Rev. cienc. tecnol. [online]. 2010, n.13. ISSN 1851-7587.

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 the pH, the incorporation of calcium hydroxide and sodium hydroxide, and the coagulant dosages were studied. Chemical Oxygen Demand (COD), lignosulfonate (NaLS) concentration, color, turbidity, solids, and ash were determined in the supernatants obtained from the different treatments. The largest reductions with aluminum salts were 50 % in COD and 63 % of NaLS using 1000 mg/L Al₂(SO₄)₃, and 58 % of the COD, 53 % of NaLS and 96 % of color, using 6000 mg/L of Poly-aluminium Chloride (PAC), on diluted (0.33 % solids, COD of 2280 mg/L) and concentrated (1.60 % solids and COD of 13 280) liquids, respectively. Reductions of 34 % of NaLS and COD were achieved in the diluted liquid spent with 100 mg/L of a cationic polyacrylamide. A dual system consisting of 500 mg/L of a slightly anionic aromatic resin + 1000 mg/L of a cationic polyacrylamide reduced by 25 % of COD and 87 % of color in the concentrated residual liquid.

Keywords : Liquid effluent; Semichemical processes; COD; Chemical precipitation; Aluminium sulphate.