Choosing coagulants and flocculants for the local treatment of wastewater of pulp and paper industry

Summary

The results of studies on removing lignosulfonates, suspended solids and sulfur-containing compounds from pulp and paper industry wastewater by chemical treatment are presented. As chemicals the following coagulants were studied: alumina, ferrous sulfate, iron (III) sulfate, and flocculants Praestol and RusFloc, that differ in charge, molar mass, and ionic activity. In the course of the experiment, it was found that the most effective removal of lignosulfonates and sulfur-containing compounds from wastewater proceeded in the presence of ferrous sulfate coagulant and Praestol 810 cationic flocculant. In this case, easily settling thickened sludge is formed and the efficiency of removing sulfide ion is 92%, the color of water decreases 3–4 times. The optimal dose of the coagulant as metal ion is 300 mg/dm³, the dose of the flocculant is 1.5 mg/dm³. Comparison of the activity of RusFloc cationic flocculants in terms of settling time, sludge layer thickness, clarified water COD, showed that the use of RusFloc 504 cationic flocculant is most effective for the coagulation of wastewater containing lignosulfonates. The optimal dose of the chemical was 5 mg/dm³. Studies on wastewater treatment by coagulation-flocculation in the presence of ferrous sulfate coagulant and RusFloc 504 flocculant at pH 8.5 showed 70% reduction of COD of organic compounds – lignosulfonates, and more than 90% color. On the basis of the conducted studies, the choice of conditions and effective chemicals for the local treatment of pulp and paper industry wastewater is substantiated.

Key words

coagulation , pulp and paper industry , flocculation , optimal dosage of chemical , pulp production , lignosulfonates , sulfide-ion