DE2944283A1 - Purifying waste water by electro:flotation - esp. for liquors from mercerisation processes - Google Patents

Abstract

Method for purifying waste water comprises subjecting it to electroflotation in a closed system, then transferring the gas-laden water to a flotation pond where pure water is filtered off and the sludge flushed out. A further electroflotation stage can be carried out in the flotation pond and a flocculating agent (pref. a metal salt or, in the case of mercerisation process liquors, a peroxide), can be added before treatment. Appts. for this process consists of a chamber, fitted with many electrodes, having an inlet for water at the bottom and outflow to the flotation pond, at the top. The method is esp. used to treat liquor from mercerisation (of cotton and linen), consisting mainly of NaOH and dissolved impurities. Complete removal of impurities is achieved and the liquor can be reused.

Description

Process for purifying waste water

The invention relates to a method for purifying waste water, in particular of mercerizing liquor, which consists essentially of sodium hydroxide solution and from the mercerized Goods are made up of washed-out impurities, with the wastewater being an electroflotation and then mechanically the gel that forms from the impurities is separated from the water.

Cotton and linen yarns are stretched at the same time Treated with cold caustic soda of about 25 to 300 Be, which makes the yarn stronger and becomes brighter and takes on color more easily.

In order to largely avoid wastewater pollution, the used Mercerizing liquor, which was diluted in the treatment of the yarn, except for theirs original concentration evaporated. The mercerizing liquor evaporated in this way can can then be reused. When the goods are tiercerisiert, however from this impurities washed out. So far, attempts have been made to remove these contaminants to be eliminated by filtering, electrofloting, Sediment or centrifugation wanted to separate the dirt and lye.

The character of this impurity, mainly polysaccharides and other starch degradation products, as well as fiber impurities, agglomerated with hardness components of water poses great difficulties to such purification. The impurities are mostly in colloidal form, with reversible and irreversible transitions take place from the dissolved sol to the flocculated gel, so that you always do not defined system has to do. The concentration of the mercerizing liquor not excreted In this way, contaminants are constantly increasing, so that after repeated use the lye can no longer be used. The waste liquor that can no longer be used must be neutralized resulting in additional costs. The alkali neutralized with acid leads to an undesirable salt load in the wastewater.

It is already known that the mercerizing liquor from electroflotation to subject, with electrodes arranged in the flotation tank at a relatively large distance are. The lower electrode is preferably an anode on which oxygen is formed. There is an oxidative attack on the impurities instead, whereby the charge states change in such a way that the colloidal system collapses and coagulation sets in. The gel that forms is through the Gas bubbles floated upwards and discharged from there.

It is known to use hydrogen peroxide in electroflotation add, which favors the oxidative attack on the impurities.

However, it has been shown that this method does not meet all requirements is sufficient because the type of waste water pollution is different, so that ratios occur in which the impurities partially resist oxidative attack. In addition to the Type of contamination, this is also dependent on, among other things the level of the concentration of the impurities and the degree of alkali concentration.

This problem occurs in principle with all types of wastewater, especially with textile wastewater, but most notably with mercerising liquor.

The task is to improve the method mentioned at the beginning in such a way that that contaminants of all kinds and concentrations of wastewater, especially from textile wastewater and especially mercerizing liquor can be separated.

This problem is solved by the features of claim 1.

Advantageous embodiments of the method and a device for Carrying out the method can be found in the subclaims.

The process sequence is shown schematically on the basis of the figure.

The contaminated wastewater, e.g. an evaporated or not yet evaporated percerizing liquor is fed via a line 1 to a chamber 2, in which an electroflotation takes place.

The chamber 2 is separated by perpendicular electrodes 3 Sub-chambers 4 divided, each of which has an inflow 5 in the lower region.

A flotation tank 6 adjoins the chamber 2 directly. The drains 7 in the upper area of each sub-chamber 4 open into the flotation tank 6 below its liquid level 8.

The bottom of the flotation basin 6 is formed by a sieve plate 9, which is covered by a filter felt. This felt is preferably on the Upper side smoothly calendered. The sieve bottom 9 runs obliquely from the chamber 2 downward.

Grid-shaped electrodes 10 are arranged just above the sieve bottom 9.

The wastewater entering the chamber 2 becomes relatively narrow due to the mutually arranged electrodes subjected to intensive electroflotation, at the same time the impurities are exposed to an oxidative attack. Since the chamber 2 is closed at the top and the drains 7 below the upper end are arranged, there is an overpressure inside the chamber, which reduces the oxidative Attack on the impurities and the fumigation of the sludge that forms favors.

After the fumigated wastewater has passed, the pure liquor is passed through the felt and the sieve bottom 9 peeled off. The sludge that results from electroflotation has formed, is discharged in the upper part of the basin 6 at the end of the sieve bottom 9.

In order to prevent the felt arranged on the sieve bottom 9 from clogging and thereby the throughput comes to a standstill, are the grid-shaped electrodes 10 provided, which have the task of gas evolution, the settling sludge stir up and loosen up.

It has proven to be beneficial to the wastewater that the electroflotation is supplied to add a flocculant at. As flocculants are common Iron and aluminum hydroxides, however, what if the wastewater from lye medium Concentration exists, has the disadvantage that undesired salts are brought into the lye and compact flakes are formed in the lye.

This is avoided when the metal in question is after anodic oxidation is introduced into the thin liquor.

A part of the caustic supplied via the line 1 is via the line 11 branched off. If necessary after adding water over the management 12 the lye reaches a vessel 13 which is filled with metal chips 14. the Metal chips 14 are connected as an anode and via a diaphragm 15 from a cathode 16 separated.

The lye running through the vessel is then mixed with the other Part of the liquor is mixed again and then fed to chamber 2.

In certain applications, the pure liquor can, if not has the necessary degree of purity, via a line 17 again the chamber 2 are fed.

Claims (13)

Method for purifying waste water, in particular of mercerizing liquor, which essentially consists of sodium hydroxide solution and of the mercerized Goods are made up of washed-out impurities, with the wastewater being an electroflotation and then mechanically the gel that forms from the impurities is separated from the water, thereby indicated that the electroflotation takes place in a closed room, from which the fumigated water is in a flotation tank where the pure water is filtered off and the sludge is flushed out. 2. The method according to claim 1, characterized in that g e k e n n z e i c h n e t, that another electroflotation is carried out in the flotation tank. 3. The method according to claim 1, characterized in that g e k e n n z e i c h -n e t that a flocculant is added to the wastewater supplied to the electroflotation will. 4. The method according to claim 3, characterized in that g e k e n n z e i c h -n e t that the flocculant is a metal salt. 5. The method according to claim 3, characterized in that g e k e n n z e i c h -n e t that peroxide is used as a flocculant when cleaning a mercerising liquor will. 6. The method according to claim 1, characterized in that g e k e n n z e i c h n e t, that part of the wastewater is diverted before the electroflotation, possibly with water diluted through a vessel with metal chips, which are connected as an anode and remixed with the other part of the wastewater before electroflotation will. 7. The method according to any one of claims 1 to 6, characterized g e -k e n It should be noted that the sludge is dried and then subjected to pyrolysis will. 8. Device for performing the method according to one of the claims 1 to 7, characterized in that the closed space is made up of a chamber (2) is formed in the. a plurality of electrodes (3) are arranged, the Inflow (5) is in the lower chamber area and the outlet (7) is in the upper chamber area is located, the transfer opening to the flotation tank (6) in this below its liquid level (8) mouth. 9. Apparatus according to claim 8, characterized in that g e k e n n z e i c hn e t that the chamber (2) is subdivided into several sub-chambers (4) by means of electrode plates (3) are separated from one another and each have an inlet and outlet (5,7). 10. The device according to claim 8, characterized in that g e k e n n z e i c hn e t that at the bottom of the chamber (2) grid-shaped, causing an electroflotation Electrodes are arranged. "11. The device according to claim 8, characterized in that it is e k e n n z e i c hn e t that the bottom of the flotation basin (6) is designed as an optionally inclined sieve plate (9) which is covered by filter felt, which is smoothly calendered on the top can be. 12. The device according to claim 11, characterized in that it is 9 c hn e t that above the bottom grid-shaped electrodes causing an electroflotation (10) are arranged. 13. Apparatus according to claim 6, characterized in that it is e k e n n z e i c hn e t that they have a vessel (13) filled with metal chips (14), which is connected as an anode and separated from a cathode (16) by a diaphragm (15).