Liquid purification or separation – Processes – Ion exchange or selective sorption
Patent
1993-03-04
1994-09-27
McCarthy, Neil
Liquid purification or separation
Processes
Ion exchange or selective sorption
210669, 210721, 210726, 210759, 210694, 210683, 210912, C02F 128, C02F 142, C02F 162, C02F 172
Patent
active
053505220
DESCRIPTION:
BRIEF SUMMARY
This invention relates to effluent treatment, and in particular to the removal of polluting materials from photographic effluent to render it more environmentally acceptable, by the sequential treatment of the effluent with chemical reagents which will cause differential precipitation of the pollutants.
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 poured into the sewer and/or a residual solid which can be removed to a place of safe and legal disposal.
It is known that addition of an oxidising agent to liquid effuent will reduce the chemical oxygen demand (COD) of the mixture by converting the reducing sulphur compounds to their oxidised form by destruction of thiosulphate and by precipitation of silver salts, as described in the Proceedings of the SPSE conference on "Environmental Issues in Photofinishing" 1987. Furthermore, Japanese Patent No. 51099854 describes the use of an oxide, hydroxide or water soluble salt of an alkaline earth metal to precipitate heavy metal ions in a photographic waste effluent.
The use of activated carbon to remove colour developing agents, and of an ion-exchange resin to remove a sequestering agent, such as ethylene diamine tetraacetic acid (EDTA) is also established in the art.
However, nowhere has there been described or even suggested that these steps may be combined into a sequential effluent treatment, preferably effected in a single vessel, in which polluting materials are removed from a liquid chemical effluent by adding reagents that sequentially cause different pollutants or their derivatives to precipitate. A time delay may be necessary between additions to allow one reaction to complete before another is started, if the reactions will or might interfere. Such a differential precipitation technique has many advantages in that the mechanical means, number of steps for separations and total process times are all reduced by removing transfer and separation procedures. Treatment in one vessel is less expensive than using individual units, allows a small compact module for treating the effuent at small processing sites and results in a small mass and volume of easily disposable solid wastes.
The process can be applied to the mixed overflows from all the baths in the photographic processing machine or to the overflow from a single bath that is contaminated by more than one polluting substance.
The effluent to be treated may, for example, have arisen from any of the photographic processes described in Item 308119, Research Disclosure December 1989, Industrial Opportunities Ltd., Hants., U.K., and especially sections XIX, XX and XXIII thereof.
The one-vessel method would be applicable furthermore to any liquid chemical effuent that was deleterious to the environment providing a chemical or physical means of precipitating the damaging components could be found.
The solids produced from the above reactions can be removed by some mechanical means in one process step, such as centrifugation or filtration, in particular as described in co-pending U.K. application No. 9019607.2, filed on even date herewith, in which an inert powder of high bulk increases the effectiveness and rate of filtration. Preferably this powder may be added during sequential precipitation treatment rather than as a final stage of the effluent treatment.
According to the present invention therefore there is provided a method of treating photographic effluent by precipitating or otherwise removing harmful pollutants to provide an environmentally acceptable liquid phase and a disposable solid phase. Preferably the separation is carried out by differential precipitation of the pollutants through sequential addition of chemical reagents
REFERENCES:
patent: 3829549 (1974-08-01), Andersen et al.
patent: 4128424 (1978-12-01), Geyken et al.
patent: 4332687 (1982-06-01), Daignault et al.
patent: 4874530 (1989-10-01), Kobayashi et al.
Eastman Kodak Company
McCarthy Neil
Roberts Sarah Meeks
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