GB1597342A

GB1597342A - Treatment of aqueous effluents containing a dyestuff

Info

Publication number: GB1597342A
Application number: GB1308377A
Authority: GB
Original assignee: Courtaulds PLC
Current assignee: Akzo Nobel UK PLC
Priority date: 1977-03-29
Filing date: 1977-03-29
Publication date: 1981-09-03
Also published as: FR2385650A1; BE865452A; JPS53125366A; FR2385650B1

Description

(54) TREATMENT OF AQUEOUS EFFLUENTS CONTAINING A DYESTUFF (71) We, COURTAULDS LIMITED, a British Company, of 18, Hanover Square, London, WIA 2BB, England, do hereby declare the invention, for which we pray that a Patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to treating coloured aqueous effluents. Such coloured effluents containing dyestuffs are encountered at factories carrying out various industrial processes, particularly at printing works of all types, dyehouses and textile finishing works.

U.S. Patent 3,944,383 describes a process for clarifying an aqueous effluent containing a dye in which the effluent is treated at a pH of at least 7.0 with an alkaline earth metal hypochlorite and then with aluminium sulphate.

We have found that particularly good results can be obtained in clarifying aqueous effluents containing a dyestuff by treating the effluent with certain free radical oxidizing agents and subsequently or simultaneously with a metal salt precipitant.

According to the invention a process for clarifying an aqueous effluent containing a dyestuff comprises treating the effluent with an oxidising agent selected from chlorine used at a pH below 7, ozone, and hydrogen peroxide used in the presence of a reducing metal ion, and subsequently or simultaneously treating the effluent with a metal salt precipitant.

The use of a free radical oxidising agent and a metal salt precipitant according to the invention markedly reduces the quantity of metal salt required to treat the coloured effluent to any desired degree of purity. One suitable free radical oxidising agent is chlorine which can be introduced as chlorine gas or as chlorine water, but it is essential that the pH during chlorine treatment is below 7, for example a pH of 46, because it is believed that only at this acid pH does chlorine have the effect of a free radical oxidising agent.

Other free radical oxidising agents which can be used are ozone and hydrogen peroxide, provided that the peroxide is used in the presence of a reducing- metal ion such as ferrous ion. Hydrogen peroxide alone does not generally act as a free radical oxidising agent and is less effective.

When the effluent is treated with chlorine or ozone as free radical oxidising agent, it is preferably oxidised before being treated with the metal salt precipitant. For best results the treatment with the matal salt should be at least 10 minutes after the oxidation. When the effluent is treated with hydrogen peroxide in the presence of reducing metal ion a ferrous salt is preferably used both as the source of reducing metal ion and as the metal salt precipitant so that the effluent is treated with the oxidising agent and metal salt precipitant simultaneously.

Oxidation can be carried out using conventional equipment and conditions althdugh a temperature slightly above ambient, for example 25--40"C, may be preferred for most economical utilisation of oxidising agent. The aqueous effluent from a dyehouse is usually warm, for example 30--35"C, so that no temperature adjustment is usually made.

The amount of oxidising agent used depends on the amount of dyestuff in the aqueous effluent. Generally at least 5 parts per million of chlorine based on total effluent will be used and 50--200 parts per million of chlorine have been found effective in treating dyehouse effluents.

Ozone and hydrogen peroxide are also preferably used at 50--200 parts per million for treating dyehouse effluents.

The amount of chlorine or other free radical oxidising agent generally used is much less than that required to completely oxidise the dyestuffs in the effluent and there is little reduction in chemical oxygen demand (C.O.D) after oxidation, typically about 5 per cent.The immediate effect of the chlorine is usually a colour change rather than any obvious removal of colour, for example a green or blue effluent generally changes to a muddy yellow colour. We cannot fully explain the effectiveness of the pre-treatment, but suggest that the chlorine or other free radical oxidising agent may oxidise those parts of the dyestuff molecule which tend to prevent precipitation of the dyestuff by the metal salt.

The metal salt precipitant is any watersoluble salt of a metal which is capable of forming a water-insoluble hydroxide.

Ferrous and aluminium salts are preferred, particularly salts of strong acids such as the sulphates. Zinc, copper and manganese salts are examples of alternative salts which can be used but are generally less effective. The use of metal salts as precipitants to clarify water is known but they have generally been used to treat fairly pure but cloudy water having a low C.O.D. The use of metal salts as precipitant for concentrated coloured effluent streams of the type coming from dyehouses has been regarded as uneconomical.

The equipment used for the precipitation may be that conventionally used for metal salt precipitation, the metal salt precipitant being suitably added in the form of an aqueous solution. The temperature of the effluent need not be adjusted. The preferred pH at which the metal salt treatment is carried out depends on the metal used as in other metal salt precipitation processes.

Aluminium salts work best at a pH below 7.

Ferrous salts work best a pH above 8.

The amount of metal salt used depends on the C.O.D. of the effluent but is usually 1/2 to 1/10 the amount which would be needed to achieve the same effect without the chlorine pre-treatment, if indeed the same effect could be achieved. Generally at least 15 parts per million by weight of metal salt precipitant is used based on total effluent, with a range of 150 to 500 parts per million by weight being preferred depending of the C.O.D.

The process of the invention can generally produce water clear enough to be used as clean water for another dyeing. It is usually impossible to produce water of this clarity from dyehouse effluent using metal salt precipitation alone or metal salt precipitation followed by oxidation. The process of the invention can for example be used to treat an aqueous effluent, for example the main drain effluent, of a dyehouse and the water can be re-used as clear water for a dyeing process or for any of the processes generally carried out in a dyehouse, for example in scouring, bleaching, in making up the dye liquor and in dye wash-off.

The process of the invention has the important secondary advantage that the flocculation of the precipitate is improved.

The precipitate is obtained in larger particles and is easier to physically separate from the clarified water. However, it is often desirable to add a polyelectrolyte after precipitation and before separation of the precipitate to help agglomerate it. This procedure is frequently used for the precipitates formed by iron and aluminium salts and suitable polyelectrolytes are commercially available. Anionic polyelectrolytes are preferred.

The invention is applicable to the treatment of aqueous effluents containing any of the dyestuffs widely used in dyeing textile materials and any of the auxiliaries and finishes generally used in the textile dyeing industry.

The process of the invention has been used effectively with acid dyes such as azo, anthraquinone, triphenylmethane, azine, xanthene, nitro, and nitroso acid dyes and pre-metallized acid dyes, basic dyes such as triarylmethane, azo, azine, xanthene, thiazine, polymethine, oxazine, and acridine basic dyes, disperse dyes such as azo, anthraquinone, nitroarylamine, and quinoline disperse dyes, and reactive dyes such as azo, anthraquinone, phthalocyanine and stilbene reactive dyes.

The process of the invention may also be used with ingrain azoic dyes, direct dyes such as dis-azo, tris-azo, and poly-azo dyes, mordant dyes, solvent dyes, sulphur dyes, vat dyes such as anthraquinone and polycyclic quinone vat dyes, and indigo.

Effluents treated according to the invention have also contained dye levelling agents such as anionic levelling agents for disperse dyes for polyester, cationic levelling agents for basic and acid dyes, non-ionic levelling agents based on alkyl aryl polyglycol ethers and nitrogenous condensation products used as levelling agents for direct dyes, surfactants such as detergents and softeners, for example an anionic surfactant based on an alkyl aryl sulphonate, sulphonated amides derived from n-methyl taurine and fatty acids, soil release agents such as an aqueous dispersion of a hydrophilic polymer and wetting agents, for example based on an ester and a polyvalent alcohol, dye carriers such as aromatic hydrocarbons and ethers, dispersing agents, for example an anionic dispersing agent based on a naphthalene sulphonate, fixing agents for direct and reactive dyes such as nitrogenous condensation products and anti-foaming agents such as silicones. The effluents have been successfully clarified when containing these materials.

The process of the invention can be carried out as a continuous process. If chlorine is used as the oxidising agent the free chlorine level in the treated effluent can be monitored and the chlorine feed adjusted apropriately. Likewise the clarity of the product can be monitored and the feed of metal salt precipitant adjusted accordingly.

The invention is illustrated by the following examples in which parts and percentages are by weight.

Example 1 This example describes the treatment of a mixed aqueous effluent taken at hourly intervals over a 12-hour period from the main drain of a dyehouse using mostly acid and basic dyes. The initial colour of the effluent was dark blue and it had a C.O.D.

of 522.

70 parts per million of chlorine gas were added to the effluent and the pH was adjusted to 6. The sample was mixed and kept at about 300C for 10 minutes. Its colour changed to a yellowish green during chlorination but there was little clarification and very little reduction in C.O.D. 200 parts per million of aluminium sulphate were added and the pH was adjusted to 6.5 with lime. After 5 minutes of vigorous mixing 3 parts per million of Magnafloc 155-an anionic polyelectrolyte < Magnafloc is a Registered Trade Mark) were added and the sample was stirred slowly for 10 minutes. The mixture was then allowed to settle and was decanted.

The liquid decanted was visually clear. It had a C.O.D. of 175, a 67 per cent reduction.

Example 2 This example describes the treatment of a mixed aqueous effluent from a dyehouse using reactive dyes. As in the first example the sample treated is a mixture of effluents from various processes including scouring and bleaching, dyeing and rinsing after dyeing. The initial colour of the effluent was an intense emerald green and its C.O.D. was 1820.

200 parts per million of chlorine gas were added to the effluent and the pH was adjusted to 6. The sample was well mixed and kept at about 30"C for 15 minutes. 500 parts per million of ferrous sulphate were then added and the pH was adjusted to 9 with lime. After 5 minutes of vigorous mixing 3 parts per million of the Magnafloc 155 polyelectrolyte were added and the sample was stirred slowly for 10 minutes.

The mixture was then allowed to settle and decanted.

The decanted liquid was almost colourless and was sufficiently clear to be used as clean water for a further dyeing process although it was not as clear as the product of Example 1. Its C.O.D. was 580, a 69 per cent reduction.

Example 3 This example describes the treatment of aqueous effluent from a wool dyeing process using mainly acid dyes. The initial colour of the effluent was blue and its C.O.D. was 210.

50 parts veer million of chlorine gas were added to the effluent and the pH was adjusted to 6. The sample was well mixed and kept at 300C for 5 minutes. 150 parts per million of ferrous sulphate were added and the pH was adjusted to 9 with lime.

After a few minutes of vigorous mixing 3 parts per million of the Magnafloc 155 polyelectrolyte were added and the sample was slowly stirred for 10 minutes. The mixture was then allowed to settle and decanted.

The decanted liquid was visually clear. It had a C.O.D. of 120, a 43 per cent reduction.

Example 4 This example describes' the treatment according to the invention of the main drain aqueous effluent from a commercial dyehouse. This was a commission dyehouse dyeing mainly cotton, polyester, acrylic and nylon fabrics using the appropriate reactive disperse basic and acid dyes.

The effluent, still at a temperature of 30 35"C, was treated continuously at 1.5 cubic metres per hour. Its pH was adjusted to a value in the range 4--6 and chlorine gas was added at the level of 100 parts per million.

After 15 minutes the effluent was treated with 200 parts per million of aluminium sulphate. After 5 minutes of mixing 3 parts per million of Magnafloc 155 polyelectrolyte was added. The precipitate was allowed to settle. Visually clear liquid was decanted.

The clarified effluent was subsequently used at different times to dye the following fabrics: cotton fabrics with reactive dyes, polyester fabric with disperse dyes, "Tricelon" (Registered Trade Mark) fabric made from a blend of nylon and cellulose triacetate filaments was dyed with disperse dyes, acrylic fibre fabric with basic dyes, cellulose diacetate fabric with disperse dyes, nylon fabric with acid dyes, fabric formed from a blend of regenerated cellulose and cotton fibres was dyed with direct dyes and fabric from a blend of acrylic and nylon fibres was dyed with a mixture of basic and acid dyes.

In all cases dyeing was carried out on commercial dyeing apparatus using the conditions of time and temperature conventionally used for dyeing with particular fabric. The sheets of the dyed fabrics were satisfactory by commercial standards even when dyeing to pale shades.

The fabrics also passed the appropriate rubbing tests, alkali and acid perspiration tests and light fastness tests.

Example 5 The effluent from a blue acid dyeing on Celon had a COD of 1360 and a pH of about 6 (Celon is a Registered Trade Mark).

This was treated by adding 25 ppm of H202 and 400 ppm FeSO4 simultaneously and agitated for ten minutes. The pH was then raised to 8.4 with lime and the resulting precipitate flocked with 2 ppm of Magnafloc 155. The liquid product after separation had a COD of 780, was colourless and was used successfully both for a further commercial scale nylon dyeing and for laboratory text dyeings on several other fabric types.

WHAT WE CLAIM IS: 1. A process for clarifying an aqueous effluent containing a dyestuff, comprising treating the effluent with an oxidising agent selected from chlorine used at a pH below 7, ozone, and hydrogen peroxide used in the presence of a reducing metal ion, and subsequently or simultaneously treating the effluent with a metal salt precipitant.

2. A process according to claim 1 in which the temperature of treatment with the oxidising agent is 25 to 400C.

3. A process according to claim 1 or 2 in which from 50 to 200 parts per million of oxidising agent based on the effluent are used.

4. A process according to any of claims 1 to 3 in which the effluent is treated with chlorine or ozone as oxidising agent before it is treated with the metal salt precipitant.

5. A process according to any of claims 1 to 4 in which the metal salt precipitant is an aluminium salt.

6. A process according to any of claims 1 to 4 in which the metal salt precipitant is a ferrous salt.

7. A process according to claim 1 in which hydrogen peroxide in the presence of a ferrous salt is used as both oxidising agent and metal salt precipitant.

8. A process according to any of claims 1 to 7 in which 150-500 parts per million by weight of metal salt precipitant is used based on total effluent.

9. A process according to any of claims 1 to 8 in which a polyelectrolyte is added to the treated effluent after metal salt precipitation.

10. A process according to any of claims 1 to 9 in which the aqueous effluent contains a dyestuff which has been used in dyeing textile material.

11. A process according to claim 10 in which the aqueous effluent contains a dye levelling agent, surfactant, dye carrier, dispersing agent, fixing agent and/or antifoaming agent.

12. A process for clarifying an aqueous effluent containing a dyestuff carried out substantially as described in any one of the foregoing Examples.

13. A process for dyeing textile materials in which aqueous effluent from a dyehouse is treated according to any of claims 1 to 12 and the clarified effluent is separated from the precipitate formed and is subsequently used as clear water in a process performed in a dyehouse.

14. A process for dyeing textile material in which aqueous effluent from a dyehouse is treated according to any of claims 1 to 12 and the clarified effluent is separated from the precipitate formed and is subsequently used as clear water in a dyeing process.

15. Textile material which has been dyed by a process according to claim 13 or 14 or other process in which aqueous effluent from the dyeing process has been clarified by a process according to any of claims 1 to 12.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims

**WARNING** start of CLMS field may overlap end of DESC **. rubbing tests, alkali and acid perspiration tests and light fastness tests. Example 5 The effluent from a blue acid dyeing on Celon had a COD of 1360 and a pH of about 6 (Celon is a Registered Trade Mark). This was treated by adding 25 ppm of H202 and 400 ppm FeSO4 simultaneously and agitated for ten minutes. The pH was then raised to 8.4 with lime and the resulting precipitate flocked with 2 ppm of Magnafloc 155. The liquid product after separation had a COD of 780, was colourless and was used successfully both for a further commercial scale nylon dyeing and for laboratory text dyeings on several other fabric types. WHAT WE CLAIM IS:

1. A process for clarifying an aqueous effluent containing a dyestuff, comprising treating the effluent with an oxidising agent selected from chlorine used at a pH below 7, ozone, and hydrogen peroxide used in the presence of a reducing metal ion, and subsequently or simultaneously treating the effluent with a metal salt precipitant.