Title of Invention

A METHOD FOR BIOLOGICALLY TREATING WASTE WATER CONTANING DYE FROM THE TEXTILE AND LEATHER INDUSTRY

Abstract

The invention relates to a method for biologically treating waste water containing dye from the textile and leather industry, in particular waste water containing azo and sulphur dyes. According to said method: the waste water containing dye is fed to an anaerobic preliminary stage with a negative redox potential, (1st treatment stage); the waste water then passes to an optionally anaerobic or aerobic activated-sludge stage, (2nd treatment stage) and is fed to an aerobic secondary treatment stage (3rd treatment stage). According to the invention, in a chemical/oxidative treatment stage, ozone or a combination of ozone and hydrogen peroxide is added as an oxidation agent to the waste water or recycled water that has been treated in the known manner and at least the main portion of the recycled water is subsequently fed back to the production process as process water.

Full Text

A method for biologically treating waste water containing dye from the textile and leather industry, in particular waste water containing azo dyes and sulphur dyes, the waste water containing dye being fed to an anaerobic preliminary stage with a negative redox potential (first treatment stage), it being passed, after a minimum residence time in the anaerobic preliminary stage that is dependent on the type of dye, to an optionally anaerobic or aerobic activated sludge stage (second treatment stage) in which activated sludge is cultivated at a loading rate per unit volume of > 1.0 kg BOD/(m3 x d) (biological oxygen demand per cubic metre of waste water and per day) and with a positive redox potential of between 0 mV and +180 mV, the activated sludge, after sedimentation, being partially fed back to the activated sludge stage and partially to the anaerobic preliminary stage and otherwise removed after inspissation, nutrients being added to the waste water in the preliminary stage and/or the activated sludge stage and the negative redox potential being maintained in the preliminary stage and the waste water leaving the activated sludge stage being fed to an aerobic after-treatment stage (third treatment stage). Environmental awareness which has changed over the last few years and changes in the waste water treatment regulations based thereon require a substantial reduction in substances polluting waste water such as textile auxiliary agents, halogenated hydrocarbons and dyes from the textile and leather industry. Previously, chemical and physical treatment methods which, in individual cases, had been combined with aerobic biological processes had been used almost exclusively to treat such dye-containing waste water. From DE 197_l£i._B.39,~which constitutes a special category, it is known that waste water leaving the anaerobic after-treatment stage can be introduced into a receiving water or passed to some other utilisation stage. By using, in this known process, adapted microorganisms produced in a highly polluted, optionally anaerobically or aerobically operated activation stage (second treatment stage), in an anaerobic/anoxic preliminary stage (first treatment stage), the digestion, by reduction, of compounds which are difficult to degrade aerobically or are aerobically persistent, including AOX (halogenated hydrocarbons) is effected which are then finally, by the subsequent biological oxidation (third treatment stage) effectively removed together with the other waste water components. By way of the specially adapted bacteria, the degradation process is, moreover, substantially accelerated compared with the biological processes previously known. The sedimentation of the activate sludge can take place in a separate sedimentation stage or by retaining the sludge in the optionally anaerobic or aerobic activation stage (second treatment stage). The known process takes place with a high degree of effectiveness at a low input of energy. The task of the present invention now consists essentially of indicating a process by means of which, with a relatively limited additional effort, it is possible to eliminate a residual coloration, that may persist, from waste water obtained according to the state of the art and to make it reutilisable as process water. According to the invention, this task is achieved by passing to the waste water treated in this way = recycling water in a chemically oxidative treatment stage, ozone or ozone in combination with hydrogen peroxide as oxidising agent and subsequently recycling at least the predominant part of the recycling water as process water into production. The desired decoloration of the recycling water can be achieved merely by the addition of ozone. The combination of both oxidising agents additionally leads to a substantially increased degree of mineralisation which, up to a degree of mineralisation of 30 %, causes a substantially increased degree of ozone utilisation compared with the use of ozone as such. According to a further proposal of the invention, it is possible to proceed by using ozone and hydrogen peroxide in a hypostoichiometric molar ratio of H202/03 of 3/8 to 7/8. According to a further proposal of the invention, it is anticipated to use an ozone mass stream of 1.0 to 16.0 g of ozone/m3 for the recycling water with an average transparency colour index of > 4"1. Finally, the invention proposes that recycling water be filtered after the aerobic after-treatment and before the chemically oxidating treatment stage. For this purpose, the recycling water is, as a rule, passed to the chemically oxidative treatment stage and from there, as process water, back into the production operation. Depending on the amount of process water required, the recycling water can be passed partially or, in a borderline case, as a whole directly into a communal clarification plant after the aerobic after-treatment. However, depending on the requirement situation present in practice, it is also possible to reintroduce process water for less stringent demands directly after aerobic after-treatment - i.e. without chemically oxidative treatment - as process water into the production process. In the following part of the description, an embodiment of the process according to the invention is described by way of a graphic representation. The waste water containing dye leaving a textile finishing or leather processing plant passes first into a preliminary treatment tank 1. The preliminary treatment tank is initially used as a mixing and equalising basin. A mixing and equalising basin is required in any case because of the uneven volume of waste waster arising and because of the uneven consistency thereof. The size of the preliminary treatment tank 1 depends on the type and quantity of the effluent and should be selected, insofar as possible such that a residence time of at least six hours is guaranteed. Immediately downstream of the preliminary treatment tank 1 follows an activated sludge tank 2 in which a highly polluted biological system operated optionally anaerobically or aerobically is maintained. The loading rate per unit volume is at least 1.0 kg BOD/ (m3 x d) (biological oxygen demand per cubic metre of waste water and day) . In the absence of nutrients, in particular phosphorus, nitrogen and trace elements which, in the present practical example, are added in the preliminary treatment tank 1, for example, it is possible to cultivate optionally anaerobic bacteria strains with a minimal supply of oxygen. This process can be enhanced by the addition of lime by means of which the pH of the waste water can be regulated. After a certain residence time in the activate sludge tank 2, the mixture of waste water and sludge passes into a settling tank 3 in which the settled activated sludge is pumped off. Part of the latter is recycled, after filtration in a fine screen facility 4, into the activated sludge tank 2 and the preliminary treatment tank 1, the ratio being approximately 2/3 (activated sludge tank 2) to 1/3 (preliminary treatment tank 1) . The remainder is passed into a sludge treatment facility where it is thickened and from which it can be removed for sludge elimination. By means of the cultivated microorganisms and by maintaining an anaerobic medium in the preliminary treatment tank 1, a redox potential of The decoloration depends, among other things, on the dry substance in the preliminary treatment tank 1. With the usual solids concentration, the content of dry substance should be > lg/1. A precondition for the growth of the microorganisms is, moreover, a sufficient supply of nutrients which can be added e.g. as fertiliser containing phosphorus and nitrogen and as easily available carbon to the preliminary treatment tank 1, as indicated in the graphic illustration. However, they can also be added to the activated sludge tank 2. Since further waste water, e.g. from the hygiene sector, may arise in such an industrial plant, this can also be used for a source of nutrient supply. Advantageously, the waste water from the hygiene sector is added to the activated sludge supplied, before it passes through the fine screen facility 4 such that the removal of solids from the waste water from the hygiene sector takes place simultaneously. The constituents remaining in the waste water after reduction can be removed biologically by means of anaerobic after-treatment. Consequently, the waste water is subsequently passed from the settling tank 3 to an aerobic after-treatment stage 5. In the treatment stage 5, the recycling water is filtered. Filters of known design can be used for this purpose. If the requirements regarding the process water are low, the filtered recycling water can then be passed to the process via a buffer tank 8. However, if high requirements are made regarding the process water, it is passed via a chemically oxidative treatment stage 7 in which ozone or ozone in combination with hydrogen peroxide are introduced as oxidising agent. The ratio of hydrogen peroxide to ozone in one practical example is a hypostoichiometric H202/03 ratio of 3/8. It has been found that decoloration of the recycling water with an average transparency colour index of By way of the addition of ozone and hydrogen peroxide, the degree of mineralisation is increased and a much higher degree of ozone utilisation achieved with a degree of mineralisation in the region of 20 to 35 % than when using ozone alone. For recycling water which is not required as process water, a direct connection exists between the anaerobic treatment stage 5 and a communal clarification plant. WE CLAIM: 1. A method for biologically treating waste water containing dye from the textile and leather industry, in particular waste water containing azo dyes and sulphur dyes, the waste water containing dye being fed to an anaerobic preliminary stage with a negative redox potential (first treatment stage), it being passed, after a minimum residence time in the anaerobic preliminary stage that is dependent on the type of dye, to an optionally anaerobic or aerobic activated sludge stage (second treatment stage) in which activated sludge is cultivated at a loading rate per unit volume of > 1.0 kg BOD/(m3 x d) (biological oxygen demand per cubic metre of waste water and per day) and with a positive redox potential of between 0 mV and +180 mV, the activated sludge, after sedimentation, being partially fed back to the activated sludge stage and partially to the anaerobic preliminary stage and otherwise removed after inspissation, nutrients being added to the waste water in the preliminary stage and/or the activated sludge stage and the negative redox potential being maintained in the preliminary stage and the waste water leaving the activated sludge stage being fed to an aerobic after-treatment stage (third treatment stage), characterised in that ozone or ozone in combination with hydrogen peroxide is passed as oxidising agent into the waste water thus treated = recycling water in a chemically oxidative treatment stage and subsequently, at least the predominant part of the recycling water is passed back into production as process water. 2. The method according to claim 1 wherein ozone and hydrogen peroxide are used in a hypostoichiometric ratio of H202/03 of 3/8 to 7/8. 3. The method according to claim 1 wherein an ozone mass stream of 1.0 to 16.0 g ozone/m is used for recycling water with an average transparency colour index of 4. The method according to one of the preceding claims wherein following the aerobic after-treatment and before the chemically oxidative treatment stage, the recycling water is filtered.

Documents:

487-chenp-2004 abstract duplicate.pdf

487-chenp-2004 claims duplicate.pdf

487-chenp-2004 description (complete) duplicate.pdf

487-chenp-2004 drawingduplicate.pdf

487-chenp-2004-abstract.pdf

487-chenp-2004-claims.pdf

487-chenp-2004-correspondnece-others.pdf

487-chenp-2004-correspondnece-po.pdf

487-chenp-2004-description(complete).pdf

487-chenp-2004-drawings.pdf

487-chenp-2004-form 1.pdf

487-chenp-2004-form 26.pdf

487-chenp-2004-form 3.pdf

487-chenp-2004-form 5.pdf

487-chenp-2004-form19.pdf

487-chenp-2004-pct.pdf