NO143753B - PROCEDURE FOR REDUCING EMISSIONS OF ORGANIC SUBSTANCE FROM CELLULOSE FACTORIES - Google Patents

Description

In recent years, general attention has increasingly been directed at the destruction of lakes, rivers and ocean bays, coastal waters and, in the longer term, the open sea, which emissions from cellulose factories cause. The cooking effluents themselves are now increasingly used as fuel and for other purposes, but diluted washing water, e.g. from cookery and strainers, still burden recipients. In addition, all effluents and washing water are usually discharged from bleachers.

It has previously been proposed to use ion exchangers of

weak basic type to remove colored matter, primarily lignin, from these liquids, and to regenerate the ion exchanger by elution with an alkaline solution which is then steamed in and burned. However, the chloride ions in the bleach effluents are firmly bound to the ion exchanger, and to avoid an excessively high concentration of chloride in the eluate, a separate elution of the chloride ions must be carried out, e.g. with sodium sulphate, or you have to carry out a so-called activation of the ion exchanger, which means that this e.g. transferred to hydrogen sulphite form before the waste water is brought into contact with the ion exchanger. Because of this, however, the chemical costs become very high, and furthermore, the absorption of all other ions present in the effluents which bind more loosely than chloride is prevented. By elution with sodium sulfate, these ions are obtained to the extent that they are taken up by ion exchange in the eluate that goes to waste. The purification is therefore largely limited to the removal of lignin. Other substances, e.g. organic acids, formed from carbohydrates such as formic acid, glycolic acid, aldonic acids, uronic acids and saccharin acids, are allowed to go with the sewage. As can be seen from published works, the method is suitable for the effluent from the extraction step at sulphate factories, but not for other effluents from a sulphate factory's bleaching plant. At a sulfate factory stems

however, the very largest part of the colored substances in the effluent from the extraction step, and in the case of sulphate factories with a recipient which is only sensitive to colored substances, the method therefore has obvious advantages. However, the main part of the organic material from the bleaching plant goes to avlbp when this method is used, and this despite the very high costs of carrying out the process. In the case of sulphite factories, the effect is worse, partly because a greater amount of lignin is usually obtained in the second stage.

For the removal of aromatic products such as lignin

and breakdown products of lignin, adsorption resins without anion exchange properties can alternatively be used. A porbs' resin of such a type containing phenolic hydroxyl groups has long ago been proposed to separate lignin sulphonic acid from other non-adsorbable compounds in sulphite liquors, and has been used on a laboratory scale for decolorizing bleach liquors.

Positive results have been reported, but judging from the literature, no large-scale trials have been carried out. Primarily, this was due to the fact that the cleaning effect is not considered to correspond to the costs that the procedure entails. Decomposition products of carbohydrates are also not rendered harmless by this method.

The present invention relates to a method for

free wastewater at cellulose factories from organic matter by adsorption on water-insoluble polymers, preferably cross-linked polymers, and to make this substance useful, and the method is characterized by a part of the wastewater with a low content of inorganic anions, such as sulfate and chloride ions, called fraction A, brought into contact, both with one or more adsorption resins and with one or more organic anion exchangers in hydroxide, carbonate or free base form, in order to remove primarily organic acids or anions and adsorb organic non-electrolytes, that another part of the waste water, called fraction B, preferably such waste water with a high content of chloride, e.g. waste water from chlorination and chlorine dioxide bleaching is brought into contact with an adsorption resin with such a structure that aromatic compounds present in fraction B are adsorbed while chloride ions remain in the solution, and that the anion exchanger is regenerated after the adsorption step with an active alkali, hydroxide and/or carbonate-containing solution , without any previous elution with acid or electrolyte solution, which solution then for or

preferably, after the regeneration, all or part of it is used for desorption of substances adsorbed on the adsorption resin.

The method according to the invention provides a significantly better purity than any of the above-mentioned methods with operating costs that are, surprisingly, significantly lower. In addition, the organic matter can be used for useful purposes for the greater part, e.g. as fuel.

In or for a bleaching plant, one or more alkaline extraction or alkaline processing steps usually occur, e.g. hot-alkali refining and, somewhat less frequently, cold-alkali refining. These are called the E-step in the following. If an E-stage is placed for some bleaching with chlorine-containing bleach, the effluent from the E-stage can be obtained practically free of both chloride and organically bound chlorine. This is particularly beneficial when bleaching sulphite pulp, where in a first stage a noticeable delignification, resin removal and carbohydrate release is obtained, and where the risk of corrosion due to the introduction of chloride into the recycling system is significantly higher than with processes where the effluents are more alkaline. The waste water from such an E-stage can be included in fraction A according to the invention. This waste water can advantageously also contain residues of cooking liquors, e.g. sulphite liquor or black liquor, whereby the recovery of these is integrated into the recovery according to the invention. This method is particularly suitable when a so-called closed silo is inserted between the cooker and the E stage, but it can. is also used if the mass for the E-stage is unscreened or screened in a silage of the usual type. An integration of the recovery of residues of cooking liquor offers particular advantages when the first chemical treatment after the cooking is carried out by an E stage or another treatment without chlorine-containing bleaches, e.g. an oxygen gas bleach. However, it can also be advantageously used when the first step contains chlorine-containing bleaches.

Also when the E stage is admitted after a treatment with chlorine-containing bleaching agents such as chlorine and chlorine oxides, e.g. chlorine dioxide, according to the invention the effluent from the E step can usually be wholly or partially included in fraction A. That is. It is therefore appropriate to use known means to keep the chloride content in the waste water at a low level, e.g. when washing and pressing for the E-stage and/or using chlorine dioxide in the stage used for the E-stage and when using chlorine to adapt the conditions so that the chloride content is as low as possible in the subsequent E-stage.

According to a preferred embodiment, fraction A contains waste water from an alkaline bleaching step in which oxidation is carried out. Examples of such bleaching steps are oxygen gas-alkali bleaching and E-step with the addition of peroxide or other per compounds or ordinary bleaching steps with peroxide. It is particularly appropriate to use oxygen gas-alkali bleaching as the first bleaching step after the cooking, whereby the effluent from the step fully or partially enters fraction A. According to a particularly suitable embodiment, the effluent from the oxygen gas-alkali bleaching is used in part to displace cooking effluent in a known manner way, while another part, which may have a lower concentration, goes into fraction A. A part of the liquor can possibly be returned to the bleaching step itself so that the fiber content is as high as possible. With such a method, extraction of liquid from the oxygen gas bleaching can be almost completely avoided, whereas with previously known methods one had to count on approx. fifty percent recovery if this occurred only by displacing cooking liquor.

As already mentioned, fraction A is treated with an anion exchanger to remove organic acids and non-electrolytes from it. It is known that compounds with very high molecular weight, e.g. high molecular weight lignin sulfonic acid, adsorbs very poorly or possibly not at all on anion exchangers; of the gel type with a high degree of saturation ("non-porbse" ion exchangers). In order for such compounds to be absorbed, the anion exchanger must contain pores of such dimensions that the high molecular compounds can penetrate into the solid polymer. Several types of porous anion exchangers are known and they are also commercially available under the designations macro-pore or macroreticular anion exchangers. If you want to free fraction A from organic matter in a single step and at the same time get an almost complete adsorption of them. hby molecular products, an anion exchanger with hby porosity must be used. However, it has been shown that anion exchangers with high porosity when used in accordance with the invention have a short lifetime compared to ordinary anion exchangers of the gel type and porous anion exchangers with lower porosity, but that the cleaning effect of the latter types becomes unsatisfactory when high demands are placed on color removal.

According to a preferred form of production, fraction A is treated with both anion exchangers and with adsorption resin. This achieves tangible advantages not only with regard to color removal, but also, surprisingly enough, with regard to the economy of the process. In this case, it is advantageous to use anion exchangers of the gel type, respectively porous ion exchangers with low or medium porosity. The treatment with adsorption resin usually takes place before the treatment with anion exchangers. This significantly increases the lifetime of the anion exchanger. However, the treatment provides similar cleaning effects if adsorption resin is used after the anion exchanger.

In the event that the cleaning requirements are very strict, one resin can be used for the anion exchanger and another, preferably of a different type, after the anion exchanger.

A particular advantage of this embodiment is that from the regeneration of the anion exchanger. eluates obtained can be used for regeneration of the resin.

Fraction A, which is indicated above with anion exchange • Qg and possibly also treated with adsorption resin, can be used in whole or in part for the preparation of cooking liquids, bleaching liquids and/or as washing liquids in order in this way to supply or replace water at a place in the production.

In certain cases, it is economically important to utilize or prevent the release of metal cations present in the waste water, preferably sodium ions. This can happen by, according to the invention, treated waste water, preferably that which has been treated with anion exchangers, being brought into contact with a cation exchanger in hydrogen form (free acid form) for the removal of metal cations, e.g. sodium ions.

In the case of certain types of ion exchangers, preferably of the weak basic type, in order for fraction A to be able to be purified effectively, it is appropriate to lower the pH value to a value below 9. This also applies when waste water is treated with adsorption resin according to the invention. According to a preferred embodiment, the pH value in fraction A is lowered to the range 1-8, advantageously 2-7, and preferably 2-4, for the treatment according to the invention.

The pH lowering can conveniently be achieved by mixing in acidic manufacturing liquids such as diluted acidic cooking effluents, e.g. washing water from sulphite boiling, S02-containing and/or acetic acid-containing solutions, such as condensate. Also treat-

treatment with carbon dioxide and solutions from acid bleaching steps,

e.g. chlorine dioxide bleaching, can be used. Alternatively, the pH lowering can be achieved by bringing fraction A into contact with a cation exchanger in hydrogen form, preferably of the carboxylic acid type. Ion exchangers of the sulphonic acid type can also be used, preferably sodium-based sulphite factories, where the sodium ions are eluted and used for acid preparation in a manner known per se. It has proven particularly advantageous to carry out the treatment with cation exchangers in two stages: (1) cation exchanger of the carboxyl type in free acid form (2) cation exchanger of the sulfonic acid type in H+<-> form.

Regardless of whether the cation exchanger of the carboxyl type is used alone or in combination with other methods of pH lowering, it is appropriate to carry out the regeneration with water containing CO2 under pressure, whereby the bicarbonate solution obtained is advantageously used to replace sodium loss and water anywhere in the fabrication, e.g. in a cookery, laundry, chemical recycling or bleaching plant.

In the case of a sodium-based sulphite factory, the embodiment enables strong acidification of fraction A, e.g. to pH 2 or lower, as well as subsequent treatment with anion exchangers of a weakly basic type, a rational and efficient way of neutralization and simultaneous utilization of the organic substances in fraction A. In this way, acidification takes place with the help of a cation exchanger, preferably of the carboxyl type, and in this way, the cation exchanger is regenerated with a SO2-containing water solution, whereby eluted sodium ions are supplied to the factory's acid system.

At a sulphate factory, this method can be carried out so that the regeneration of the cation exchanger e.g. occurs with acidic solutions which are obtained by scrubbing exhaust gases and which may have acid added, e.g. waste acid from chlorine dioxide production and/or the chloralkali reaction. Also other acidic solutions, e.g. hydrochloric acid or acetic acid can be used.

Regardless of the type of factory involved, the treatment must be adapted to the requirements for purification, respectively the energy prices and the chemical losses (mainly sodium and sulfur losses) that must be covered during manufacture. The more efficiently sodium ions and metal cations are removed by cation exchange, the longer the absorption of organic acids with weakly basic anion exchange can be carried on. In the case of the highest requirements for purification, i.e. when the organic substance must be removed practically completely from fraction A, it is possible to use a strongly basic anion exchanger. This method is particularly suitable in such cases where you lack or have poor access to cheap acids for the regeneration of cation exchangers. The disadvantage of strongly basic anion exchangers is primarily that a significant excess of alkali is required for the regeneration. According to the method according to the invention, the problem is solved in such a way that the eluate from the ion exchanger is used to regenerate the adsorption resin, respectively the adsorption resins. It is often appropriate to combine the use of strongly basic anion exchangers with the use of weakly basic anion exchangers, whereby the eluate from the strongly basic anion exchanger is usually used for elution of the weakly basic anion exchanger, and the eluate from this for regeneration of the adsorption resin. For the treatment with the weakly basic anion exchanger, sodium ions are removed from the solution by means of cation exchange, for example in one of the ways indicated above. Such weakly basic anion exchangers, which have previously been described for the adsorption of sulphite leachate and of colored substances in bleaching waste, can be used. The structure of these weakly basic anion exchangers is not known in detail, and there is strong evidence that the adsorption of many substances, e.g. those with phenolic groups, do not depend on pure ion exchange, but that other interactions are also of decisive importance. Suitable ion exchangers of this type are described in the literature and are available under the names "Amberlyst" and "Duolite".

In a preferred embodiment, fraction A is divided

into two sub-fractions, one with a very low chloride content (e.g. lye from an E-trihn or an oxygen gas bleaching step that has been added without the mass being treated with chlorine-containing agents), and one with a higher chloride content (e.g. from the E-step after chlorination or C102 treatment). The first partial fraction is subjected to a treatment with a strongly basic anion exchanger in hydroxide form to absorb inorganic acids. The second fraction is treated with a weakly basic anion exchanger, preferably after acid-

reproduction according to one of the above-mentioned methods.

As adsorption resins, one can use both types that have previously been used for the adsorption of lignin and other types that, as far as is known, have not been used for this purpose, but which are suitable for the adsorption of non-polar compounds and/or aromatic compounds from dilute water solutions. The adsorption resin is usually made of a polymer cross-linked with covalent bonds, but other water-insoluble polymers can also be the basis for the adsorption resin.

It is particularly appropriate to use a cross-linked polymer containing proton-accepting groups, for example, ester groups and/or carbonyl groups. The proton-accepting ability of chemical compounds of this type can be enhanced by synthesizing the compounds in such a way that nitrogen atoms are placed near ester and/or carbonyl groups, e.g. so that the nitrogen atoms are bonded to the same carbon atom as the carbonyl oxygen.

Particularly advantageous results have been obtained by using adsorption resin containing a heterocyclic

ring containing one or more nitrogen atoms. Examples of such groups are pyrrolidone groups. Examples of adsorption resins of this type include cross-linked polyvinylpyrrolidone. As a networking tool, you can e.g. use di-yinylbenzene. Resins of this type are commercially available under the name "Polyclar".

Particularly favorable results are obtained with macroporous resins. Production of such types of resins is known from the literature regarding the production of macroporous and so-called macroreticular ion exchangers and a majority of types of macroporous resins are available under the name "Amberlite x AD". Such a resin, "Amberlite XAD-8", and which contains ester groups bound by an acrylate resin, has proven very suitable for purifying fraction B and also for, after acidification of fraction A with cation exchangers, removing aromatic products from fraction A for the treatment with anion exchangers. This and other adsorption resins of preferred types have the property that adsorbed compounds of the types present in waste water are easily desorbed in an alkaline medium. Adsorption, on the other hand, must take place in

near the neutral point or in an acidic medium. Fraction B usually contains acidic wastewater, e.g. such as from chlorination and/or chlorine dioxide treatment, but may also contain effluent from alkaline stages such as hypochlorite and chlorine-containing liquors from the E stage. The effluent from the alkaline stages is neutralized or acidified, usually with effluent from the acidic bleaching stages. Also care in other ways, e.g. as mentioned for fraction A, can be used.

If one wants to use an adsorption resin with very high chemical resistance, one can advantageously use one which essentially lacks polar groups. An example of one such resin with an aromatic structure is a porous (macro-reticular) styrene-divinylbenzene resin. Such are commercially available. The cleaning effect by using only this type of adsorption ion resin is not satisfactory in and of itself, but in combination with ion exchangers according to the method according to the invention, results are obtained that meet strict requirements with regard to the removal of both colored and uncolored substances, and this at a relatively acceptable cost level.

Adsorb the ion on non-polar macroreticular adsorb ion resins, e.g. such as consist of a porous skeleton of styrene-divinylbenzene, can in many cases be made more effective if a small number of polar groups are incorporated in connection with the polymerization and/or during the post-treatment. An example is mixing of 2 -. 10% acrylic acid in connection with the polymerization of non-polar vinyl compounds or a weak sulphonation, so that approx. 1 - 10% of the aromatic cores are sulphonated. According to these examples, the adsorption resins acquire cation exchange properties, but the capacity is very low compared to technical cation exchangers. The adsorb ion is not based on ion exchange, but on adsorption in the broadest sense, which is why the products here are included in the adsorption resins.

Also other than the above-mentioned adsorption resins of polar type, e.g. those containing phenolic hydroxyl groups can be used in the same way as those containing amide bonds (e.g. polyacrylamide) both for the treatment of fraction B and in combination with anion exchangers for fraction A.

With high requirements for cleaning, it is particularly appropriate that two or more adsorption resins of different types are used either in a mixture, e.g. in a mixed layer, or in separate units, e.g. fixed layers or moving layers. The combination of non-polar resin with one containing proton-accepting ester groups or a macroporous resin of cross-linked polyvinylpyrrolidone has been found to be surprisingly effective.

The adsorption resins and ion exchangers are used

most simply in the usual way in stationary layers, which are regenerated according to a proven timetable or after analyses, which have been carried out automatically or manually. In both cases, switching between adsorption and regeneration can be done manually or by automation, respectively automation. Intermediate washing steps in the same way as partial return of used eluent and buffer containers can also be added in a known manner. In the same way as other ion exchange and adsorption methods, the process can be carried out continuously, e.g. in that the solid polymers are moved in a known manner.

Both the ion exchangers and the adsorption resins are vulnerable to mechanical soiling, e.g. with fibres, clay particles and resin particles, which can be found in the sewage

water to be treated according to the invention. An effective mechanical cleaning in a manner known per se, e.g. when filtering using known filters such as sand filters and fine mesh nets or textile or ceramic filters should therefore usually be carried out before the cleaning according to the invention is carried out. If stationary layers are used for ion exchangers and adsorption resins, these should be equipped with devices for backwashing, e.g. with water, to flush away mechanical contamination in a known manner. To avoid resin loss, a trap for adsorption resin or ion exchange is used.

In a known manner, a flocculation and/or chemical treatment with lime can also be carried out where the local conditions require this. However, this is usually unnecessary.

With regard to the lifetime of the polymers, it is essential

that these are not exposed to any significant amounts of active oxidizing agents, e.g. chlorine, chlorine dioxide and peroxide. This can be avoided by mixing waste water containing aggressive oxidizing agents with such substances which are attacked by them, so that the oxidizing agents are consumed. Thus, avlbp from chlorination and chlordi-

oxide stage, and which often contains active chlorine, is mixed with a suitable amount of effluent from E-stage and/or with effluent from washing after boiling or with condensate. The mixture should then be stored

long for the active chlorine to be consumed. S02 and/or S02 water can also be used, at least temporarily, to neutralize the oxidizing agents. A suitable storage time is 0.5 - 2 hours.

Apart from mechanical contamination and oxidation

the effectiveness of ion exchangers and adsorption resins can be reduced by the binding of certain substances more or less irreversibly. Examples can be fats and wax-like substances which form part of the so-called resin in the wood and which are often modified, e.g. chlorinated, during the processes. Unknown aromatic compounds can also be bound so tightly that an elution does not

can be reached in the normal way at reasonable costs. In such cases, the polymers can be reactivated by treatment with suitable organic solvents, e.g. methanol, ethanol, dichloromethane and/or cymenv Such a reactivation which, depending on the composition of the wastewater, may be appropriate to carry out at intervals of e.g. 0.5 - 12 months, can be done either in the apparatus (e.g. layer) where the polymer is used or by removing the polymer.

As an active alkali, sodium hydroxide is often preferable to e.g. sodium bicarbonate and/or sodium carbonate. Surprisingly, in many types of plant, it is possible to achieve far-reaching purification both with regard to colored products and uncolored organic acids by supplying to the regeneration only the amount of sodium hydroxide that is necessary to cover the alkali losses in the plant. According to the invention, this is made possible by the sodium hydroxide being used in at least two stages. Generally, it is most appropriate that the sodium hydroxide is first used to regenerate used anion exchangers and then to regenerate the adsorption resin. In those cases where a very effective purification is required and especially if the sodium losses have been forced down by means of various precautions, it may be necessary and appropriate to also use active alkali that has been recovered, e.g. after burning the cooking liquor or bleach liquor or mixtures thereof. This is particularly easy with sulphur-free cooking, e.g. oxygen gas cooking and soda cooking, where sodium carbonate is obtained as ash or after wet combustion. Sodium carbonate and/or bicarbonate can also be extracted from the smelting from sulphate and sulphite factories in a way known per se. These compounds can then be used as active alkali for the regeneration of ion exchangers and adsorption resins.

At sulphate factories where there are high requirements regarding

goes the reduction of the biochemical oxygen consumption. it is most appropriate to carry out a causticisation of extracted sodium carbonate. In the case of a sulphite factory, recovery and direct use of sodium carbonate or sodium bicarbonate as active alkali in the regeneration (together with the sodium hydroxide required to cover the alkali losses) may be preferable.

Previously known methods for purifying waste water from bleaching plants with anion exchangers have been tied to weakly basic anion exchangers. In the method according to the invention, strongly basic anion exchangers are advantageously used in cases where an effective removal of organic acids is required. In order to reduce the required amount of regenerating agent, preferably sodium hydroxide, it is appropriate to use those which can be easily regenerated with alkali. Thus, with ordinary ion exchangers containing quaternary ammonium ions (-l^R^RgR^), it is appropriate that at least one of the three substituents R-^, R2

and R 1 contains a hydroxyl group, e.g. is issued by a hydroxyethyl group. The others can be expressed e.g. of methyl groups.

According to a preferred embodiment which has been shown to give particularly advantageous results, both a weakly basic and a strongly basic anion exchanger are used, whereby sodium hydroxide is used to first regenerate the strongly basic anion exchanger and then to regenerate the weakly basic anion exchanger and finally for to regenerate one or more adsorption resins. With such a scheme, the cleaning effect can be as good as when only a strongly basic anion exchanger is used, while the costs for the regeneration are significantly reduced.

Depending on how the invention is applied, it may be appropriate as active alkali in the regeneration to use liquor from oxygen gas bleaching and/or alkaline processing and/or extraction, optionally refreshed with sodium hydroxide. This embodiment is particularly appropriate when the eluate from ion exchangers and adsorption resins is to be incinerated after evaporation or wet incinerated. If leachate from hot alkali

extraction or ordinary oxygen gas bleaching is used, suitable amounts of alkali, e.g. sodium hydroxide, is added to improve elution, while a refresh with active alkali is usually unnecessary when cold alkali processing effluent is used.

The eluate obtained during the regeneration of anion exchangers can optionally be fed back in a suitable proportion and used for further elution of anion exchangers - for they are used in whole or in part to regenerate adsorption resin or adsorption resins. The eluate can then, apart from evaporation and burning or wet burning, separately or in a mixture with cooking effluent, be used as washing water, e.g. by mesa washing, and for dissolving ash obtained after combustion or for in another way adding water to the fabrication in such a way that the organic substance is burned directly or at a later time. A typical example is the eluate's use for displacing cooking effluent after the end of cooking.

Between the regeneration step and a subsequent adsorption step, it is appropriate to wash both ion exchangers and adsorption resins with water or diluted water solutions. Obtained weak alkali can be completely or partially fed back and, after refreshing with active alkali, used for regeneration. The weak lyes can also be fractionated and used according to the countercurrent principles,

so that the losses are low and the concentration as high as possible. Weak lye (used washing water) can be used to replace water

in the process, e.g. for washing pulp, mesa or similar purposes.

The invention shall be explained in more detail by the following examples.

Example 1

In a sodium-based sulphite factory, both paper pulp and hot-alkali treated rayon pulp are produced. See fig. 1. The wood is added to the boiler 1, after which the pulp obtained is washed in the laundry 2, so that 97 percent by weight of the fiber is recovered. The washed mass then goes to the closed silo 3 from where

no emissions occur. From the silage, the mass is fed to the press 4 where it is pressed to a tSrr content of 30%. The mass is then transferred to step 5, which constitutes the first treatment step in the bleach plant, and where the mass is treated with alkali (sodium hydroxide).

In the bleach plant, the pulp is chlorinated in chlorination stage 6, after which it is subjected to mild extraction in extraction stage 7, treatment with chlorine dioxide in chlorine dioxide stage 8 and treatment with hypochlorite in hypochlorite stage 9.

Effluent from the alkali treatment stage 5 is returned to this and is also used in a known manner for washing the unbleached mass.

In this way, approx. 20% of the dry matter content as fuel

in connection with the burning of the sulphite effluent, and a corresponding recovery of the alkali used in the extraction step 5 is achieved. The Swedish portion of the effluent from the extraction step 5 together with the washing water from the laundry 2 which could not be returned constitutes fraction A according to the invention and is fed to the container A.

In the bleaching plant, the washing between steps is carried out in such a way

that the amount of waste water did not become too large so that the quality of the mass was not put at risk. Hereby, countercurrent washing is applied in a known manner. The mixed effluent from the bleaching step and the washing step is fed to container B and constitutes fraction B according to the invention.

Fraction A, which has a pH value of around 10, is fed from container A to a sand filter 10 and, after passing through this, to a layer a 1 of a weakly acidic cation exchanger of the carboxylic acid type in free acid form ("Amberlite IRC-50") , whereby the pH value was reduced to approx. 3. Then the acidified fraction was allowed to pass through a layer a 2 of an adsorption resin (macropore styrene-divinylbenzene resin, "Amberlite XAD-4"), where approx. 50% of the colored substances in the fraction were retained, while more than 90% of the substance showing biochemical oxygen consumption (BOD^) passed through. The effluent from the adsorption resin layer a 2 was quickly passed through a strongly acidic cation exchanger a 3 of the sulfonic acid type, which was essentially in hydrogen form ("Dowex 50X-8"). This removes remaining sodium ions to a significant extent. The effluent from the cation exchanger a 3 was quickly passed through a macropore anion exchanger • a 4 containing weakly basic groups (amino groups) with such a structure that colored substances of the lignin type were bound by the ion exchanger ("Duolite"), which ion exchanger has previously been described as suitable for adsorption of sulphite effluent and too colored substances in bleaching effluent. The effluent from layer a 4, in contrast to the effluent which was treated only with adsorption resin or with only anion exchangers, could be used for the preparation of caustic acid, which entails significant advantages.

During the treatment steps, a total of approx. 95% by weight of the colored substances, primarily lignin, and approx. 90% by weight of the total colored substances originating from the bleaching plant in fraction A were removed. the coking liquor, was essentially back in the output from the anion exchanger a 4. If desired, this sugar can be eliminated by absorption on a strongly basic anion exchanger, not shown in Fig. 1. The sugar present, however, gave no detectable interference when the thus purified fraction A was used for cooking acid preparation.

Fraction B was quickly passed through two series-connected buffer containers 11 and 12, in which the residence time was so long that the active chlorine present in the fraction was destroyed. An appropriate time for this was 0.5-2 hours. The fraction B was then quickly passed through the sand filter 13 and through two series-connected with layer adsorption resin. The first layer b 1 contained a non-polar macropore adsorption resin of the styrene-divinylbenzene type ("Amberlite XAD-4"), while the second layer b 2 contained a macropore adsorption resin of the acrylic ester type ("Amberlite XAD-8"). The conditions were adjusted so that approx. 90% by weight of the colored substances in fraction B were adsorbed. This eliminated more than half of the chemical oxygen consumption, while the effect on the biochemical oxygen consumption was lower. The effluent from layer b 2 was rich in chloride and went to avlbp.

In the process, the sodium ions taken up by the cation exchangers a 1 and a 3 were utilized in a known manner for the preparation of caustic acid. Instead of fresh water, the effluent from container a 4 was also used for the preparation of the SO2 water in container 15 which is used in the regeneration of the cation exchangers a 1 and a 3. The path of the elution liquid is marked in fig. 1 with dashed lines. The fresh SOg water was thereby first quickly passed through the strongly acidic cation exchanger of the sulfonic acid type a 3 and then the weakly acidic cation exchanger of the carboxylic acid type a 1. The eluate from a 1 was used after refreshing with sodium ions and a solution containing S02 or S02~ as caustic acid. For the regeneration of the anion exchanger a 4 and the adsorption resin layer a 2, a sodium carbonate solution is used which is obtained by separating sodium sulphide and sodium carbonate from the melt obtained from the combustion of the effluent by fractional leaching, whereby the sodium carbonate was obtained in solid form and the sodium sulphide in solution. The sodium carbonate solution which was prepared in container 14 from solid sodium carbonate and recovered washing water and which contained 100 g of Na^ CO^ per liter was added to the layer of weakly basic anion exchanger a 4. The first part of the eluate a 4 was used to regenerate the adsorption resin layers a 2, block 2 in the mentioned sequence, while the last part of the eluate from a 4 was recovered and used in the next elution cycle as first eluent for the anion exchanger a 4 and the adsorption resin layers a 2,

b 1 and b 2, followed by fresh sodium carbonate solution. The eluate from the adsorption resin layer b 2, which had been diluted with the solution remaining in the layers, was evaporated and incinerated together with the cooking effluents. In order to achieve a more complete elution, a solution containing 50 g of NaOH per liters quickly through the anion exchanger a 4 and the adsorption resin layers a2, b 1 and b 2 in the aforementioned order. After washing with water, which was then partially returned to the process, the eluate was burned together with the eluate obtained by elution with carbonate. The concentration rate in the adsorption steps was approx. 12 layer volumes per hour by adsorption and approx. 1 layer volume per hour. during regeneration and washing.

According to this embodiment, both fraction A and fraction B were effectively purified with regard to colored matter, primarily lignin, from both bleaching and cooking plants. Purification with a view to non-coloured organic acids, which are primarily the source of BOD^ in the bleach effluent, was effective for fraction A, but not for fraction B, where the main proportion of the organic acids went to effluent in the same way as in previous methods together with the chlorides. By dividing the bleach effluent into two fractions according to the invention, it has become possible to adapt the fractions so that the amount of organic acids is small in fraction B compared to fraction

tion A. Applied to the production of rayon pulp, according to the scheme described here, 90% or more of the non-coloured organic acids in fraction A were obtained. These were recovered in an amount of approx. 90%, which means that more than 80% of the total amount of organic acids was recovered. In addition, approx. 90% of the colored substances from the bleaching plant and the main part of the cooking liquor residues that otherwise usually go down the drain.

Example 2

The procedure according to example 1 was repeated with the exception that an extra layer of porous, cross-linked polyvinylpyrrolidone resin (PVP) was inserted after the strongly acidic cation exchanger a 3> and that the porous and weakly basic anion exchanger a 4 was replaced by a conventional non-porous or low-porous anion exchangers of the weak basic type. The elution with active alkali occurred in the order anion exchanger, PVP resin, a 2, bl, and b 2. No change in the cleaning effect was noted, but with unchanged cleaning effect and volume for the anion/exchanger, the time intervals could between regenerations is increased by 20% from 5 to 6 hours.

Example 5

The procedure according to example 1 was repeated with the difference that the strongly acidic cation exchanger a 3 was slbyfet. The cleaning effect with regard to colorless organic acids in fraction A was reduced by approx. 30%, but surprisingly, the substances that prevent the use of a non-anion-exchanged fraction A in the preparation of caustic acid were removed, so completely that the fraction purified in this way could be fed back for caustic acid preparation.

Example 4

In a sulphate cellulose factory with bleaching scheme chlorination

in chlorination step 1, extraction in extraction step 2, hypochlorite in hypochlorite step 3, chlorine dioxide in chlorine dioxide step 4, extraction in extraction step 5, chlorine dioxide in chlorine dioxide step 6 according to fig. 2 and with such a location that the recipient was very volatile towards colored matter, but little volatile towards uncoloured organic matter, the residue from the first extraction step 2 was introduced into fraction A according to the invention and taken to container A. The fraction was then acidified by passing through a layer a 1 containing a cation exchanger of the carboxylic acid type ("Amerlite IRC-50") to pH . The fraction was then passed through a layer a 2 containing a non-polar adsorption resin of the styrene-divinylbenzene type ("Amberlite XAD-4"), and a layer a 3 of an adsorption resin with ester groups ("Amberlite XAD-8"), as well as to finally a layer a 4 containing a low porosity weakly basic anion exchanger ("Duolite").

The effluent from hypochlorite stage 3, chlorine dioxide stage 4, extraction stage 5 and chlorine dioxide stage 6 was collected to

. container B and constituted fraction B according to the invention. The

was filtered and quickly passed through two layers b 1 and b 2, containing the same adsorption resin as the layers b 1 and b 2 in example 1.

The sewage well b 2 was rich in chloride and quickly became sewage. During the treatment, colored material in fraction B was removed in an amount of

about. 90 percent by weight. The same was the relationship in fraction A, but

here, approx. was also removed. 50% of the colorless organic acids. The regeneration took place by the sodium hydroxide solution from the container 7 passing through the layers in the sequence a 4, a 3,

a 2, b 1 and b 2. The eluate was combined with the boiling liquor and then

burned together with this. If it was necessary to increase the recovery of non-coloured organic substance, this happened by further acidifying fraction A with a cation exchanger of the sulphonic acid type (not shown in Fig. 2). The weakly acidic cation exchanger in layer a 1 was regenerated with COg-water under pressure, while the sulfonic acid-type cation exchanger, not shown, was regenerated with waste acid■

which then went quickly through layer a 1. With these precautions, approx. 80% of the organic acids in fraction A.

Claims (11)

1. Procedure for freeing wastewater at a cellulose factory ker from, in addition to colored organic matter, also the majority of uncolored organic matter in treated waste water by adsorption on water-soluble polymers, preferably cross-linked polymers, and to make use of this substance, characterized in that a part of the waste water with a low content of inorganic anions, such as sulphate and chloride ions, called fraction A, are brought into contact, both with one or more adsorption resins and with one or more organic anion exchangers in hydroxide, carbonate or free base form, in order to remove primarily organic acids or anions and adsorb organic non-electrolytes, that another part of the waste water, called fraction B, preferably such waste water with a high content of chloride, e.g. wastewater from chlorination and chlorine dioxide bleaching is brought into contact with an adsorption resin with such a structure that the aromatic compounds present in fraction B are adsorbed while chloride ions remain in the solution, and that the anion exchanger is regenerated after the adsorption step with an active alkali, hydroxide and/or carbonate-containing solution, without any prior elution with acid or electrolyte solution, which solution is then used before or preferably after regeneration in whole or in part for the desorption of substances adsorbed on the adsorption resin. 2. Method according to claim 1, characterized in that fraction A, as an essential component, contains waste water from an alkaline extraction step or alkaline processing step installed in or before the bleaching plant. 3. Method according to claim 1 or 2, characterized in that fraction A, as an essential component, contains waste water from an oxidative alkaline bleaching step, e.g. from oxygen gas alkali bleaching. 4. Method according to any one of claims 1-3, characterized in that fraction A, after the treatment, is used in whole or in part for the preparation of cooking liquids, bleaching liquids or as washing liquids, or to otherwise add water to a part of the fabrication. 5. Method according to any one of the preceding claims, characterized by. that the waste water treated with the anion exchanger is brought into contact with a cation exchanger in hydrogen form to remove sodium ions. 6. Method according to any one of the preceding claims, characterized in that the pH value in fraction A is lowered to the interval 1-8, preferably 2-7, and preferably 2-4 before the treatment according to the invention. 7. Method according to claim 6, characterized. in that the pH lowering takes place by bringing fraction A into contact with a cation exchanger in hydrogen form, preferably of the carboxylic acid type. 8. Method according to any one of claims 1-7, characterized in that fraction A is treated with a strongly basic anion exchanger. 9. Method according to any one of claims 1-8, characterized in that fraction A is divided into two sub-fractions, one with a very low chloride content, which is treated with a strongly basic anion exchanger for absorption of organic acids, and one with a higher chloride content, which treated with a weakly basic anion exchanger. 10. Method according to any one of claims 1-9, characterized in that sodium hydroxide is used to first regenerate a strong basic anion exchanger and then to regenerate a weakly basic anion exchanger, and then to regenerate adsorption resin. 11. Method according to claims 1-10, characterized in that the active alkali used in the regeneration is liquor from oxygen gas bleaching and/or alkaline processing and/or extraction, optionally refreshed with sodium hydroxide.