GB2211180A - Improvements in or relating to effluent treatment - Google Patents

Abstract

A method for the treatment of effluent emanating from a neutral sulphite semi-chemical (NSSC) process for the production of paper or board material, comprising the addition of an ionic acrylamide polymer resin for removing undesired impurities therefrom.

Description

IMPROVEMENTS IN OR RELATING TO EFFLUENT TREATMENT The present invention concerns improvements in or relating to effluent treatment. More particularly, the present invention is concerned with the treatment of effluent emanating from apparatus for making paper, board or the like material. Various methods and apparatus are known for the treatment of effluent emanating from apparatus for making paper, board and the like material.

Paper, board or the like materials, are generally produced by mechanical or chemical pulping techniques and subsequent paper or board formation. Mechanical pulping methods are used chiefly for coniferous woods and aim at a high yield rather than a pure pulp. Chemical or cooking methods remove more of the unwanted materials, resulting in a lower yield but a higher quality pulp.

Such chemical or cooking methods are generally divided into two categories: acid liquor and alkaline liquor.

The effluent emanating from mechanical or chemical pulping techniques and subsequent paper or board formation can be suitably treated so as to satisfy statutory requirements regarding permitted content of impurities in the water to be discharged. In the chemical processes referred to above, the impurities, mainly sludge emanating from the pulp manufacture is clarified by the addition of suitable clarifiers and any fibres or fillers in the effluent are considered to constitute treatable dispersions.

After passing through various stages in order to clarify the effluent, same is mixed with a flocculating agent, usually a non-ionic polyacrylamide, which flocculates material in the effluent which can then be removed therefrom in a settlement tank. The thus treated effluent is then generally suitable for discharge.

A particular problem has recently been encountered in the production of paper by a so-called neutral sulphite semi-chemical (NSSC) process. Whilst such process is extremely useful in the preparation of material, usually corrugated, for strengthening cardboard, the effluent emanating therefrom contains undesirable material which, heretofore, has not been recoverable from the effluent.

The NSSC effluent material contains various impurities, such as a black liquor type impurity and none of the previous material used in effluent treatment such as treatment with polyacrylamide which produces a floating flocculant has proved satisfactory in removing such liquor from the effluent.

We have unexpectedly discovered that a particular type of resin, when added to the effluent, assists in the successful removal of the NSSC effluent impurities therefrom, at least to a substantial degree.

According to the present invention there is provided a method for the treatment of effluent emanating from a neutral sulphite semi-chemical (NSSC) process for the production of paper or board material, comprising the addition of an ionic acrylamide polymer resin for removing undesired impurities therefrom. Preferably the ionic acrylamide polymer resin is added to the effluent stream of the NSSC process after the formation of the web on the cloth or wire for example. Alternatively, or additionally, the resin may be added prior to the web formation.

Preferred acrylamide polymers utilised in the process of the present invention comprise: (i) at least 60 weight percent of units derived from unsubstituted acrylamide, (ii) at least 5 weight percent of hydrophobic units derived from a vinyl- or vinylene group containing monomer, (iii) at least 2 weight percent of substituted acrvlamide units of the formula

wherein R and Rlare the same or different (C1#c ) alkyl 3 group and (iv) 0-10 weight percent of hydrophilic anionic units.

The hydrophobic units are preferably derived from styrene or from methyl methacrylate.

In the above formula, R and R1 are each preferably methyl groups The anionic units preferably have the formula

and are present in number up to the number of said substituted acrylamide units.

A preferred resin comprises: (i) units derived from acrylamide, (ii) units derived from styrene, end (iii)units of the formula:

said units being present in a molar ratio of 85:10:5 respectively-and in total forming at least 90 mol percent of the polymer.

In general, the ionic acrylamide polymer is added to the effluent emanating from the plant prior to the effluent being flocculated, although it is possible for such resin to be added during the paper or board making process.

The effluent can also be treated with clarifiers, for example, alum, polyamines, mannich bases, polyethylene imines and cationic polymers, as well as being subjected to mechanical separation of the impurities in the effluent, by means of overflow tanks and the like. It is possible black liquor from a digestor may be added to the NSSC process effluent and such may be treated in the same manner.

It has been found that since the polymer utilising the process of the present invention is shear insensitive, then when the effluent is passed through various pumps etc., the effectiveness of the polymer is in no way effected or is only minimally effected.

By utilisation of the ionic acrylamide polymer in accordance with the method of the present invention, it has been possible to produce an effluent containing acceptable levels of impurities which can be discharged not only from the NSSC process but also from other paper or board processes of- the plant.

The present invention will be further illustrated, by way of example, with reference to the following informal schematic illustration of a plant utilised in the production of various grades of paper and board material.

As illustrated the processes 1, 2, 3 on the right-hand side of the sketch are involved in the production of various types of paper and/or board material from which te effluent emanating therefrom is treated in accordance with utilisation of normal materials, such as clarifiers and coagulants. For example, polyamines as coagulants are added to the effluent at the point A prior to the effluent passing through various overflow tanks B and then being transmitted by pump means C to a flocculatirig tank D containing polyacrylamide.

The process 4 on the left-hand side of the drawing is utilised in the production of strengthening material for cardboard by the NSSC process. The effluent emanating therefrom is treated with alum and/or polyamine and/or polyethylene imine and/or PDADM at point E as coagulants and then would normally mix with the effluent emanating from the other sections of the plant. We have found that by adding an ionic acrylamide polymer resin in accordance with the present invention suitably at point F in particular, the impurities, e.g. black liquor, contained in the effluent are suitably dispersed, the colour of the effluent water being clarified and material being flocculated out in the flocculation tank D.

The ionic acrylamide polymer utilised in the invention can be added at other points in the treatment process and even in the section of the plant in which the material is being manufactured. The treatment process is applicable to other liquors, such as black liquor.

Any other suitable coagulant material or clarifiers can be added as desired.

It will thus be seen that the process in accordance with the present invention produces an effluent which is suitable for discharge from the plant without contravening any environmental regulations.

Claims (8)

1. A method for the treatment of effluent emanating from a neutral sulphide semi-chemical (NSSC) process for the production of paper or board material, comprising the addition of an ionic acrylamide polymer resin for removing undesired impurities therefrom.

2. A method as claimed in claim 1, in which the ionic acrylamide polymer resin is added to the effluent stream of the NSSC process after the formation of the web on the cloth or wire.

3. A method as claimed in claim 2, in which alternatively, or additionally, the resin may be added prior to the web formation.

4. A method as claimed in any preceding claim, in which the acrylamide polymer comprises: (i) at least 60 weight percent of units derived from unsubstituted acrylamide, (ii) at least 5 weight percent of hydrophobic units derived from a vinyl- or vinylene group containing monomer, (iii) at least 2 weight percent of substituted acrylamide units of the formula

wherein R and R1 are the same or different (c1-c3) alkyl group and (iv) 0-10 weight percent of hydrophilic anionic units.

5. A method as claimed in claim 4, in which the hydrophobic units are derived from styrene or methyl methacrylate.

6. A method as claimed in claim 4 or 5, in which R and R1 are each methyl groups.

7. A method as claimed in claim 4, 5 or 6, in which the anionic units have the formula

and are present in number up to the number of said substituted acrylamide units.

8. A method as claimed in claim 1, 2 or 3 in which the resin comprises (i) units derived from acrylamide (ii) units derived from styrene, and (iii) units of the formula