GB2296238A - Improvements in or relating to effluent treatment - Google Patents

Abstract

The present invention relates to a composition for the removal of dyes from effluents, such composition comprising a synergistic combination of components comprising a ferrous salt, a polyamine or polydadmac and a dicyandiamide complex. The composition not only removes dyes from the effluent but ensures that no residual colour remains in the treatment water.

Description

IMPROVEMENTS IN OR RELATING TO EFFLUENT TREATMENT The present invention concerns improvements in or relating to treatment of effluents. More particularly, the present invention is concerned with colour removal of dyes from effluents.

There is an increasing concern, particularly from water authorities, at the present time regarding the discharge of dyes to fresh water courses from industries, particularly the textile industry. Many companies have treatment works which remove COD and BOD by the use of a combination of chemical and biological treatments. Even though such treatment processes are utilised, it has been found it is comparatively common for the commercially available dyes to remain unaffected by such treatment processes and to emerge at the end of the treatment process either with full absorbancy intact, or a substantial proportion thereof remaining intact. As a result thereof, waters are discharged which have a significant colour content either in the form of a tinge or a full deep colour.

Companies involved in discharge of dyes to fresh water courses have utilised several method treatments in an attempt to reduce the amount of colour discharged from any given system. Such methods can be divided into three treatment types, namely primary treatment, secondary treatment and tertiary treatment.

Primary Treatment Such treatment involves blending of raw effluents from a treatment works to produce a balanced feed to a clarification device (float or sink).

Coagulants of various kinds have been added in an attempt to insolubilise the dyes present in the effluent. Normally, effluent from a treatment works is alkaline resulting from scouring and dyeing, etc. and after addition of any coagulative reagents, the pH is typically adjusted to a neutral value of approximately 7-8, the solids are separated therefrom and the clarified liquors are then either discharged or are subjected to further treatment by a biological process.

In many treatment plants, the only treatment effected in the primary stage is to adjust the pH prior to biotreatment so as to avoid shock pH swings to the biomass.

In a typical treatment procedure, water from a textile plant will have a COD of approximately 2,0003,000 ppm which is composed mainly from dyes and surfactants used in the various treatment processes.

Depending upon the effluent criteria existing in a particular situation, it may be necessary to significantly reduce such COD level prior to discharge of the water. The coagulants which can be conventionally used in such procedure are as follows: a) Aluminium salts may be used to remove suspended solids and effect partial dye removal and, to a degree, effect pH depression. However, the use of such salts is not a complete answer, since many dyes do not respond thereto, particularly the reds.

b) Ferric salts may be used and these have similar results to those identified in a) above in respect of aluminium salts.

c) Polymers may be used which act as coagulants.

There are various types of generic polymers which can be used in this regard and typical examples thereof are: i) polyamines - epichlorhydrin amine condensates can be-utilised but these tend to have a specific response in respect of certain dyes but to be completely ineffective against other dyes.

ii) polydadmacs - diallyldialkylammonium polymers may be utilised either in the form of homopolymers or heterocopolymers. Whilst these polymers are effective in certain specific cases, many dyes are totally unaffected when treated with such polymers.

iii) Dicyandiamide-formaldehyde-ammonium chloride concentrates may be utilised. Such products are recognised dye fixatives and can be used in a particular process to increase dye uptake on a cloth.

Such condensates tend to have a broad spectrum of effectiveness in their removal capacity for any given dye as compared to the polymers identified above.

iv) Melamine-formaldehyde resins dissolved in a dilute acid may be used. These products are also effective over a broad spectrum of dyes; however, such products tend not to be used due to the prohibitive cost thereof.

In primary treatment, the cost of treatment is typically prohibitive in obtaining a complete dye removal. In the circumstances, it is usual to attempt to remove dyes in a tertiary treatment after biotreatment when most of the other interfering surfactants and COD has been removed. However, this usually results in a lower use quantity of the types of products described above.

Secondary Treatment Such treatment normally involves the use of one of the many kinds of conventional bioreactors, e.g.

activated sludge anaerobic digestion or any other form of oxygen injection in conjunction with biomass. The purpose of such process is to digest the unwanted organics in the effluent liquors and to reduce them to an acceptable level. Generally, the COD loading can be reduced efficiently, but the removal of colour tends to be by adsorption onto the biomass and not by biological degradation, albeit that there are now reported biological species that are capable of digestion of certain dyestuffs. The net result is that a coloured biomass is produced but the bulk of the colour in the liquor is not removed and will tend to 'tramp' through the system requiring further treatment to precipitate the colour using reagents as identified in relation to the primary treatment described above.

Tertiarv Treatment Such treatment is normally only required where a regulatory authority stipulates that the degree of colour removal must be almost complete. There is often a specification giving absorbancies at specific wavelengths from 400-600 nm. - The treatment plants use tertiary treatment with either inorganics or synthetics to achieve the degree of colour removal required.

Typically, the products used will be selected from the list given above and separation of the solids is usually accomplished by flotation or sedimentation, possibly followed by filtration.

It is an object of the present invention to provide a composition or product which can be utilised for colour removal, viz. the removal of dyes, from effluents, which at least minimises the disadvantages referred to above.

We have conducted various experiments regarding dye removal from actual works effluents wherein a full range of colours have been used. Generally treatment with the above specified range of coagulants does not provide for a universal removal of colour from the effluent. Reagent (iii) referred to above came closest to achieving the desired result but on primary liquors was found to be cost prohibitive.

We have also noted, and as indicated in the literature, that ferrous iron under alkaline conditions can be used as an effective colour removal agent for most grades of dyes. Tests have been carried out in respect of ferrous sulphate and ferrous chloride and we have discovered that such compounds did remove significant amounts of colour with a broad spectrum of activity. However, the use of ferrous sulphate or chloride raw product suffers from two disadvantages, namely: 1. The requisite amount of raw product required for full treatment is substantial and produces a significant quantity of sludge from the production of ferrous hydroxide.

2. After treatment, a brown colour complex is produced, which appears to be a ferric complex which has sufficient colouration to be regarded as a polluting colour, and thus will require further treatment.

Having regard to the fact that effluents emanating from dye treatment works are generally alkaline, e.g. having a pH in the range of 8-12, we have carried out various tests to ascertain if any synergism could be produced by utilising a blend of ferrous salts with polymeric materials as described above.

Initially, it was found that a blend of polyamine and ferrous iron produced significant colour removal across a broad spectrum of dose rates. However, upon examination of the data obtained, it was repeatedly found that transmission in the 400-500 nm range (blue) was actually reduced after treatment, i.e., although the base colour, for example, red, blue, green, etc., had been removed when the sample was examined spectrophotometrically, transmission values at 600 nm had invariably risen whilst transmission values at 400 nm had actually fallen significantly. Such results were borne out by a brown/black colouration in the liquids. Discussion with potential users of such mixture revealed that such users were as concerned by the brown/black colour as by the original dye colour.

Attempts to blend dicyandiamide compounds as identified at (iii) above, with ferrous salts produced an unstable liquid product at contents > 5% in 40% FeCl2.

However, such product did appear to have a broad spectrum clarification potential.

Unexpectedly, we have discovered that by blending a selected polyamine or dadmac in conjunction with a compound identified in (iii) above in the presence of ferrous iron, such blend completely removes the problems of secondary colour production. Within certain compositional percentages, the product is stable and suitable for use for commercial decolourisation.

We have thus discovered that the addition of a dicyandiamide complex to any blend of ferrous salts and polymer removes the final brown colour from effluent treated water to give a very clear water.

It will thus be seen that the present invention provides a blended product comprising a ferrous salt, a polyamine or dadmac and a dicyandiamide complex which results in a synergistic blend which removes all colours from effluent water under alkaline conditions.

The dose rates utilised vary with dye concentration, but are usually within the range 5004,000 ppm. Such amount is a significantly lower dose, or cost performance dose, when compared with either polymers or polymer blends, or ferrous compounds.

We have also discovered that individual additions of each of the compounds forming the blended product of the invention at an equivalent does rate to that represented by their fixed proportions in the final mixture, also show the same synergism if they are mixed within close proximity in the solution under treatment.

The product of the invention ensures that no residual colour remains when effluent water is treated.

Moreover, COD is reduced roughly in direct proportion to the dye concentration and anionic surfactant concentration.

The terminal pH of the water usually ends up between 6 and 8 and is therefore eminently suitable for feed to a biotreater.

It will thus be seen that the present invention provides a composition for removal of dyes from effluents, such composition comprising a synergistic combination of components, which composition not only removes dyes from the effluent but ensures that no residual colour remains in the treatment water. In addition to the synergistic effect obtained, the composition is cost effective as compared to previously utilised materials.

Claims (12)

1. A composition for removal of dyes from effluents, as well as ensuring that no residual colour remains in the treatment water, comprising a ferrous salt, a polyamine or polydadmac and a dicyandiamide complex.

2. A composition as claimed in claim 1, in which the polyamine is an epichlorhydrin amine condensate.

3. A composition as claimed in claim 1 or 2, in which the polydadmac is a diallyldialkylammonium polymer, in the form of a homopolymer or a heterocopolymer.

4. A composition as claimed in any preceding claim, in which the dicyandiamide complex is a dicyandiamideformaldehyde-ammonium chloride concentrate.

5. A composition as claimed in any preceding claim, in which the ferrous salts ferrous sulphate or ferrous chloride.

6. A composition as claimed in any preceding claim, in which the composition is applied to effluent water in a dose rate of 500 to 4,000ppm.

7. A composition as claimed in any preceding claim, substantially as hereinbefore described.

8. A method for removal of dyes from effluents, comprising adding to effluent water a composition as claimed in any preceding claim.

9. A method as claimed in claim 8, in which the components of the composition are added at the same time to the effluent water in a dose rate within the range of 500 to 4,000ppm.

10. A method as claimed in claim 9, in which the compounds of the composition are added individually and are mixed within close proximity in the solution under treatment.

11. A method as claimed in claim 8, 9 or 10, in which the terminal pH of the water is between 6 and 8.

12. A method as claimed in any one of claims 89 to 11, substantially as hereinbefore described.