Liquid purification or separation – Processes – Chemical treatment
Patent
1993-06-17
1995-05-30
Wyse, Thomas
Liquid purification or separation
Processes
Chemical treatment
210763, 210908, 210910, C02F 172
Patent
active
054198402
DESCRIPTION:
BRIEF SUMMARY
This invention relates to effluent treatment and in particular to the removal of environmentally 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 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 removed to a place of safe and legal disposal.
The sequestering or complexing agents, such as EDTA, PDTA and DTPA (ethylene and propylenediaminetetraacetic acid and diethylenetriaminepentaacetic acid 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 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 B.D.H. However this is costly, bulky and transfer the water problem elsewhere and can clean up only about 3 times the volume of the resin bed.
The use of hydrogen peroxide for decomposing iron-EDTA complexes is briefly mentioned, without specific exemplification, in the Journal of Imaging Technology 14, (1988) No. 6 in an article primarily concerned with the recovery of silver from effluent treatment from photofinishing processes. Large amounts of hydrogen peroxide, up to 2.1 lb per gallon of effluent are described as being required, in a process that requires heating up to about 60.degree. C.
U.S. Pat. No. 4,693,833 describes a method of treating radioactive waste water with hydrogen peroxide at a temperature of 60.degree. C.-90.degree. C. in the catalytic presence of copper ions or copper and iron ions.
It has now been found that the addition of hydrogen peroxide, or a compound capable of liberating hydrogen peroxide, in a concentration of as little as 0.6 to 3% by weight of the effluent causes the sequestering agent to break into fragments with less complexing ability, even at room temperature and without the necessary for a catalyst. Although the rate of reaction is slow and may 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/liter of effluent, preferably 30 to 50 ml/l, is generally found to be suitable. Alteratively a greater volume of a weaker solution is equally suitable e.g. from 75 to 375 ml 8% hydrogen peroxide/liter effluent or from 200 ml to 1 liter 3% hydrogen peroxide/liter effluent.
Although the addition of hydrogen peroxi
REFERENCES:
patent: 3721624 (1973-03-01), Fisch et al.
patent: 4332687 (1982-06-01), Daignault et al.
patent: 4693833 (1987-09-01), Toshikuni et al.
patent: 5178772 (1993-01-01), Daley et al.
Journal of Imaging Technology, vol. 14, No. 6, Dec. 1988, Springfield US, pp. 154-156; H. Knorre, et al.: "Chemical Treatment of Effluent from Photofinishing Plants".
Eastman Kodak Company
Roberts Sara Meeks
Wyse Thomas
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