Wong, Alfred; Prahacs, Steven; Dorica, Joseph;

Treatment of pulp mill effluents

A multi-step method is provided for the purification of waste water, especially pulp mill effluents. It comprises a number of steps carried out in a specific sequence. The first step involves passing an oxygen-containing gas through the waste water while the waste water is in intimate contact with a finely divided activated carbonaceous material, preferably including, as a preliminary step, the addition of the finely divided activated carbonaceous material to the waste water. The second step involves adding a clarification agent selected from one or more of a coagulant, a flocculant, and a polyelectrolyte to the treated waste water provided by the first step. The third step involves recovering a solids-free effluent by known means, e.g. by a clarification step carried out by gravitational, flotational or centrifugal means to provide the waste water free of the suspended material originally contained therein and a sludge including the suspended material originally contained in the waste water, the added carbon and the added clarifying agent. Optionally, it includes the fourth step of regenerating the carbonaceous material from the sludge, and/or the fifth step of regenerating the clarification agent from the sludge.

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What is claimed is:

1. A multi-step physical-chemical method for the purification by adsorption, catalytic oxidation and chemical precipitation of kraft pulp mill effluent waste water containing undesirable solid materials in suspended and/or dissolved form, which comprises the following sequential steps:

1. passing an oxygen-containing gas through the waste water at a rate of 0.05 scfh/1-5.0 scfh/1. while the waste water is in intimate contact with a finely divided activated carbonaceous material present in a concentration of 10-8000 mg/l to catalytically oxidize said undesirable materials;

2. adding a clarification agent selected from the group consisting of a coagulant, a flocculant, a polyelectrolyte and mixtures thereof with the provision that when a polyelectrolyte is provided, it is in a concentration of 0.1-20 mg/l and when a coagulant and/or flocculant is provided, it is in a concentration of 10-2000 mg/l, to resultant waste water provided by step (1) to chemically precipitate said undesirable materials;

and 3. separating suspended solids in the form of sludge from the waste water by gravitation, flotation or centrifugation.

2. The method of claim 1 wherein said separating of step (3) is conducted by gravitation.

3. The method of claim 2 further comprising a fourth step of thermally regenerating the carbonaceous material at 600-900.degree. C from the removed sludge.

4. The method of claim 3 including a fifth step of regenerating the clarification agent from the removed sludge by acid leaching.

5. The method of claim 1 further comprising a preliminary step of adding fresh finely divided activated carbonaceous material to the waste water to physically adsorb undesired materials.

6. The method of claim 1 wherein the activated carbonaceous material is produced from flyash, bark, woodwaste, green liquor dregs, wood charcoal, or bone charcoal and mixtures thereof, and activated carbon fabric.

7. The method of claim 6 wherein the activated carbonaceous material has a surface area of 100-1800 m.sup.2 /g, and wherein the amount of said carbonaceous material is 25-2000 mg/l.

8. The method of claim 1 wherein the amount of said carbonaceous material is 25-2000 mg/l.

9. The method of claim 1 wherein the gas is passed through the waste water at a rate of about 0.5 scfh/1.

10. The method of claim 1 wherein the clarification agent is a polyelectrolyte provided in an amount of 0.1-20 mg/l.;25;

11. The method of claim 1 wherein the clarification agent is a coagulant and/or a flocculant provided in an amount of 10-2000 mg/l.

12. The method of claim 1 wherein the waste water is an effluent from the manufacture of bleached kraft pulp.

13. The method of claim 12 wherein the finely divided activated carbonaceous material is powdered bark char.

14. The method of claim 1 wherein the clarification agent is a mixture of alum and polyelectrolyte.

15. The method of claim 14 wherein the dosage of activated carbonaceous material is about 200 mg/l, the gas flow rate is about 0.5 scfh/1, alum is employed in a dosage of about 100 mg/l and the polyelectrolyte dosage is about 1 mg/l.

16. The method of claim 15 wherein the activated carbonaceous material is powdered bark char having a particle size of minus 325 mesh.

17. The method of claim 1 wherein the finely divided activated carbonaceous material is fresh or thermally regenerated carbonaceous material.

18. The method of claim 1 wherein said separating of step (3) is conducted by flotation.

19. The method of claim 1 wherein said separating of step (3) is conducted by centrifugation.