EFFLUENT TREATMENT

Abstract: A method of treating chemical liquid effluent to render it more environmentally acceptable, comprising the addition of hydrogen peroxide, or a compound capable of liberating hydrogen peroxide, to the effluent to react with and break down a sequestering agent. The reaction rate may be enhanced by the addition of a small amount of a compound including a transition metal ion, especially the nitrate or sulphate of iron or manganese.

Description: ^ EFFLUENT TREATMENT This invention relates to effluent treatment and in particular to the removal of environmentally 5 undesirable components from photographic processing machine effluents. The overflow from a photographic processor will typically consist of polluting substances such as heavy metal ions, sequestering agents, substances that have a 10 high oxygen demand and colour developing agents and their derivatives, straight disposal of which contravenes sewer regulations in many parts of the world. It is therefore essential that the overflow is converted by chemical or physical means to a liquid which can be poured into the 15 sewer and/or a residual solid which can be removed to a place of safe and legal disposal. The sequestering or complexing agents, such as EDTA, PDTA AND DTPA (ethylene and propylenediamine- tetraacetic acid and diethylenetriaminepentaacetic acid 20 respectively) are particularly undesirable in liquid effluent discharges as they tend to assist the dissolution of toxic heavy metals into the water as it flows toward municipal treatment works and as it seeps through the ground. They also often have a high oxygen demand. The 25 use of an ion exchange resin to remove such an agent is already known, for example as disclosed in "Ion Exchange Resins" 1981, published by .D.H. However this is costly, bulky and transfers the water problem elsewhere and can clean up only about 3 times the volume of the resin bed. , 30 It has now been found that the addition of * hydrogen peroxide, or a compound capable of liberating ,1 hydrogen peroxide, to the effluent causes the sequestering agent to break into fragments with less complexing ability. Although the rate of reaction is slow and may 35 take up to one week at room temperature it may be particularly suitable for adding to a holding tank before it is discharged to the sewer or delivered to the treatment works. It has further been found that the rate of reaction may be enhanced by the addition of a small amount e.g. 1 ppm, of a compound including a transition metal ion, such as iron and manganese, preferably in the form of the nitrate or sulphate. According to the present invention therefore there is provided a method of treating chemical liquid effluent to render it more environmentally acceptable, comprising the addition of hydrogen peroxide, or a compound capable of liberating hydrogen peroxide, to the effluent to react with and break down a sequestering agent. Compounds capable of releasing hydrogen peroxide include metal peroxides; compounds which include hydrogen peroxide in their crystal structure such as sodium percarbonate; other peroxy compounds such as sodium perborate, persulphate, or peroxysilicate; or soluble organic peroxides, such as butyl peroxide or benzyl peroxide. The hydrogen peroxide or a compound such as mentioned above is added in a sufficient quantity to enable the oxidising reaction with the sequestering agent to take place in a convenient length of time. For example, if commercially available 30% hydrogen peroxide is used, from 20 to 100 ml/litre of effluent, preferably 30 to 50 ml/1, is generally found to be suitable. Alternatively a greater volume of a weaker solution is equally suitable e.g. from 75 to 375 ml 8% hydrogen peroxide/litre effluent or from 200 ml to 1 litre 3% hydrogen peroxide/litre effluent. Although the addition of hydrogen peroxide to destroy a sequestering agent is of particular importance to the photographic industry, it may be applied to any waste liquor containing such an agent. The invention will now be described with reference to the following example which does not in any way limit the scope of the invention. Example Solutions were made of various sequestering agents at concentrations of nominally lOOOppm. To each of these solutions was added lOg/1 potassium hydrogen carbonate, to simulate the likely pH and carbonate conditions in a photographic effluent. To samples of each of these agents was added 50ml/litre 30% hydrogen peroxide. The amount of sequestering agent remaining after 7 days keeping at 20 C was measured by ion chromatography. A similar set of experiments were set up with the addition of lppm manganese, as the sulphate, to each sample. The amount of remaining sequestering agent was measured after 3 days keeping at 20°C. Another set of experiments was set up and this time iron was added at lppm, as the nitrate. Again the sequestering agent concentrations were measured after 3 days keeping at room temperature. The results of all these experiments are shown in the table below. Re idual Se uesterin A ent m The results show that the sequestering agents are being destroyed substantially by the peroxide and that the metal i accelerate the process, especially the iron ion.

Claims: Claims 1. A method of treating chemical liquid effluent to render it more environmentally acceptable, comprising the addition of hydrogen peroxide, or a compound capable of liberating hydrogen peroxide, to the effluent to react with and break down a sequestering agent. 2. A method as claimed in claim 1, in which the effluent comprises overflow from one or more photographic processes. 3. A method as claimed in either of the preceding claims, in which 30% hydrogen peroxide is used in an amount of from 20 to 100 ml/litre effluent. 4. A method as claimed in claim 3, in which from 30 to 50 ml 30% hydrogen peroxide/litre effluent is used. 5. A method as claimed in either of claims 1 and 2, in which 8% hydrogen peroxide is used in an amount of from 75 to 375 ml/litre effluent. 6. A method as claimed in either of claims 1 and 2, in which 3% hydrogen peroxide is used in an amount of from 200 ml to 1 litre/litre effluent. 7. A method as claimed in any one of the preceding claims, in which the sequestering agent is ethylenediaminetetraacetic acid, propylenediamine— tetraacetic acid or diethylenetriaminepentaacetic acid.. 8. A method as claimed in any one of the preceding claims, in which a compound including a transition metal ion is added to the solution. 9. A method as claimed in claim 8, in which the transition metal ion is iron. 10. A method as claimed in claim 3, in which the transition metal ion is manganese. 11. A method as claimed in any one of claims 8 to 10, in which the compound is in the form of the nitrate or sulphate.

Inventors: FYSON JOHN RICHARD, FYSON, JOHN, RICHARD
Applicants: EASTMAN KODAK CO, KODAK LTD, EASTMAN KODAK COMPANY, KODAK LIMITED
Application year: 1991
Main classification: C02F1
IPC codes: C02F1, G03C5