CS258755B1 - Waste water treatment method - Google Patents

Abstract

The solution concerns the purification of wastewater containing coagulated organic substances, in smaller quantities biodegradable organic substances and various types of industrial dyes. In addition to the basic coagulant, powdered activated carbon is added to the wastewater, after an optional increase in alkalinity, while the water with the coagulant and sorbent is subjected to rapid mixing for 5 to 10 minutes and slow mixing for 10 to 20 minutes and is led to sedimentation. The settled sludge is removed in a conventional manner. The method according to the invention, consisting of the combined effect of chemical coagulation and sorption in one stage, achieves much better results compared to two-stage purification, namely a reduction in color by 90 to 95%, COD by 65 to 70% and BOD-5 by 68 to 73%

Description

The invention relates to waste water treatment which comprises coagulable organic substances, biodegradable organic substances and various kinds of industrial dyes.

Waste water of the above-mentioned nature is currently treated mainly by chemical coagulation, which uses the effect of various types of basic and auxiliary coagulants, or by biological methods, depending on the species and amount of polluting organic substances. In the case of high levels of organic substances, which are present in suspended, colloidal and dissolved forms, a combination of chemical and biological processes can be used to achieve good purification effects, both according to the chemical oxygen demand indicator permanganate or dichromate (COD) and biochemical indicator. oxygen consumption in 5 days (BOD-5).

The use of chemical coagulation in bleaching water from pulp and pulp production is dealt with, for example, in the Treatment of Waste Water from Paper Making Process (Yamada H. et al., Japan Kokai, Japan, 5PP) and Recent Status of the Treatment of Dyeing Waste Water ( Daiichi Kogyo Sieyaku Shaho 378, 4-11). Aluminum sulphate and sodium aluminate are used as coagulants and regeneration of the basic coagulants is envisaged. Further work by Centrifuge. plus Lime limits Lignin in Waste Water (Moll R., Southern Pulp Paper Mfr. 39, (6), June 76, 14-15)) deals with the treatment of waste water from kraft pulp production, where the color forming substances consist mainly of lignin compounds. , lime.

It is a chemical coagulation by alkaline lime precipitation without the application of sorbents. The precipitated coloring substances pass into the sludge, which is dewatered by centrifugation and incinerated in a lime kiln with the simultaneous regeneration of lime. Color Removal in Kraft Dear Wastewaters with Magnesium (Oldham W.K. and Rush R.J., Jawwa 50, (1), 1978, 40-45) describes the removal of coloring substances from wastewater from the production of unbleached kraft pulp and bleaching processes.

It is carried out with magnesium sulfate and lime with the addition of an anionic electrolyte as flocculant. Good effects have also been achieved for separately conducted wastewater from alkaline bleach extraction. In Polish Patent No. 4,103,623, the Decoloration of Pulping Waste Water describes chemical coagulation in combination with biological cleaning without the application of sorbents. Aluminum sulfate or ferrous sulfate and lime are used. In the Preliminary Study of Pulp Milli Effluent Decolorization by the Method of Simultaneous Cofulation (Zielinski J. et al., Przegl Pap. 32, (5), May 1976, (157-162)), a coagulant is added to the aeration tank of a biological wastewater treatment plant. vod.

The mixture of chemical precipitate and activated sludge forms a substrate with a high sorption capacity, which binds both biodegradable and color-forming substances to its surface. The advantage of this procedure is that it takes place on an existing biological treatment plant and that it does not require additional investment costs for the completion of the coagulation stage. Very good discoloration and BOD-5 reduction was achieved at a dosage of about 500 mg / L Al ₂ (SO 4).

The process is economically acceptable if the waste water contains a large amount of biologically degradable substances (carbohydrates) and less severely degradable substances (lignin). The object of U.S. Pat. No. 3,998,731 is a purification method which allows the reduction of BOD-5 in waste water by mixing the water with granular Al ₂ O ₃ in gamma form at pH 2.2 to 3 achieved by the addition of mineral and then the sludge is separated from the process containing the trapped organic matter, dewatered and thermally recovered to recover Al ₂ O ₃ in gamma form and returned to the process.

Using a combination of coagulation and sorption methods for decolorizing water, Ademoroti CM and Sridhar® have been investigated. K. in Fluidized Bed Technique in Physicochemical Treatment (EWTJ 19, (6), June 1979, (291-298)). They report that the waters clarified in Stage 1 Al ₂ (SO 4) ₃ or FeCl ₃ were refined under pulverized activated carbon (PAH) applied in the fluidized state under laboratory conditions. A COD reduction of 96% was achieved at a PAU dose of about 200 mg / l. In the work of Floating Treatment of Waste Water from Polycationic Coagulating Agents (Ochiai K., Sen'i

26, (7), (297-301)), chemical coagulation and sorption are conducted in one step and performed with aluminum sulfate and bentonite.

In Color Removal in Kraft Dear Wastewaters with Magnesium (Oldham WK and Rusf RJ, JWPCF 50, (1), Jan. 1978, (40-45)), waste water from bleached kraft pulp production is purified by chemical coagulation with soluble magnesium salt and lime . A precipitate of Mf (OH) 2 with high sorption activity is formed, which binds organic color-forming substances to its surface.

The clarified water was neutralized with C0 ₂ from pH 11 to about pH 9.5. The precipitated CaCO ₃ is separated by sedimentation. The coagulation organomagnesium sludge is adjusted to about pH 7.5 by addition of CO ₂ , whereby magnesium is regenerated as Mg (HCO ₃ > ₂ and returned to coagulation in solution. The rest of the sludge and CaCO ₃ sludge are dewatered and burned in a lime kiln In this process, CaO and CO ₂ are recovered for re-use in the process.

The color reduction is 90 to 95 ». Bartušek P. (Waste Water in the Textile Industry, SNTL, pp. 103 to 104) cites the works of Nosek and Horning, who applied to decolorize waste water in sorption on pulverized coal in a separate stage from coagulation and worked with high doses of sorbent in an alluvial manner. , 5 to 2.5 g PAU / L). In addition, Bartušek reports Weis, in which pulverized coal was applied to improve the flotation effect in waters from refineries together with Na ₂ CO ₃ , aluminum salt and polyelectrolyte, where 97 to 99% dye removal was achieved.

Suzuki M. and CHO BR used aluminum sulphate and powdered activated carbon to purify organically heavily polluted waters from wood pulp production in their work Treatment by Coagulation and Adsorption by Powdered Activated Carbon and Reactivation of Sludge (Kogyo Yosui, 248, 1979, 33-40). in high doses and found the conditions of heat recovery of the sorbent, without which the process would be economically unacceptable.

The results of operation of waste water treatment plants from paper and pulp production in Czechoslovakia show that the chemical chemical coagulation using aluminum or iron salts as the basic coagulants and various types of polyelectrolytic flocculants, especially on the base of polyacrylamide as auxiliary coagulation means suspended solids in the range of 90 to 98%, COD reduction of about 40 to 60% and BOD-5 reduction of 20 to 40 S. Application of mechanical-biological treatment tends to reduce the content of suspended substances by 85 to 95%, COD reduction by 30 to 40% and a BOD-5 reduction of 85 to 95 Ϊ.

Each of the two purification processes has advantages in terms of the effects achieved and interferes with another part of the organic purification, so that, depending on the predominant nature of the organic substances, it is preferable to the one which is more effective under the given conditions. In view of the high investment costs, a combination of a chemical and biological treatment method is chosen, allowing high purification effects in both BOD-5 and COD only rarely, if there is a large amount of wastewater and at the same time have a high degree of organic pollution.

However, some productions result in large amounts of waste water heavily contaminated with undissolved and colloidal substances, which in addition contain industrial dyes or color-forming substances and less organic contamination by biodegradable substances. Such types of waste water are produced, for example, in the manufacture of colored paper. The use of chemical coagulation primarily reduces the content of suspended solids and colloidal substances and partially the color component, while the substances projected into the BOD-5 value decrease slightly.

Water after coagulation cannot be returned to the production due to the residual coloration, where it would affect the visual properties of products with a different color shade, nor can it be discharged to the recipient where it would impair the limited quality of river water. Inclusion of biological treatment after coagulation is not useful in this case. Indeed, experience from the operation of biological treatment plants has shown that wastewater treatment with BOD-5 values of up to 100 to 150 mg / l works with an efficiency below 50%,

In addition, biological processes do not remove color-forming substances, but rather produce biochemical decomposition products, which deepen the color of purified water.

The aforementioned drawbacks of the wastewater treatment methods used so far, which are heavily contaminated with undissolved and colloidal substances and additionally contain colorants and minor amounts of BOD-5 substances, eliminate the treatment method of the invention. It consists in the combined effect of chemical coagulation and sorption in one step, which achieves good effects on both COD and BOD-5 reduction and in particular on the removal of color-forming substances. Said purification method consists in adding to the waste water to be treated with coagulation treatment, after mixing with the base coagulant, powdered activated carbon, optionally increasing the alkalinity by, waste water with lime or sodium or potassium hydroxide or optionally alkaline waste to increase the hydrolysis of the base coagulant , and then the base coagulant and powdered activated carbon are preferably added in the form of an aqueous suspension.

Waste water with powdered sorbent coagulant is subjected to rapid agitation for 5 to 10 minutes, followed by slow agitation for 10 to 20 minutes during which flocculation occurs, and is then led to sedimentation where the concentrated sludge suspension containing the trapped pollutants is separated. substances from purified water. The settled sludge is withdrawn from the sludge zone of the sedimentation plant and is conventionally thickened, dewatered and incinerated or exported to a depot. The purified 'water' is reused in production or sent to the recipient.

The higher purification effect of the present invention results from the following comparison.

For colored paper waste water that has been purified by chemical coagulation with aluminum sulphate and polyacrylamide, with pre-alkalinization with lime, and then biologically refined, (according to the results of experiments carried out at eight paper mills and available literature) S, COD reduction of 55 to 57% and BOD-5 reduction of 60 to 62%.

These waste waters from three paper mills were subjected to the purification tests of the present invention and were found to reduce coloration by 90-95%, COD by 65-70% and BOD-5 by 68-73%. The fact that this treatment is carried out in one step also results in considerable savings in investment costs.

The basic possibilities of using the invention are evident from the following example, which is based on the verification of the conditions of application of the new method at one paper mill.

Example

Waste water from a papermaking plant that produces different types of color papers and cartons using a wide range of dyes on four papermaking machines, from titanium white to different shades of yellow, blue, green, red to black spot and coxyl dyes, is delivered at 312m ³ / h per sewage treatment plant. The average pollution values of the effluent are around 390 mg / l suspended solids, 180 mg / l COD and 58 mg / l BOD-5. The sewage treatment plant is equipped with a 150 m ³ buffer tank, pre-treatment chemical, multi-component dosing pumps, 30 m rapid mixing tank, flocculation of 55 m tanks, flow divider and four MW settling tanks to achieve approx. , 5 to 2 hours waste water residence time.

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The sediment is thickened in two cylindrical sludge thickeners of 30 m each, dewatered on a two-sieve press and exported to a landfill. Purified water is used for washing machines on paper machines, for diluting and washing the process equipment.

According to the original equipment, chemical coagulation was performed with aluminum sulfate (50 mg / l) and polyelectrolyte (2 m ·; /!), Which were prepared and dosed in the form of 5% and 0.1 µl solution, sulfate into mixer and polyelectrolyte at water inlet into the flocculator. The treated wastewater carried on average residual pollution: 35 mg / l suspended matter, 100 mg / l COD, 37 mg / l BOD-5 and around 4/5 of the original color, corresponding to the effects achieved by 91% removal of suspended matter, COD reduction by 45%, BOD-5 reduction by 35% and color removal from 21.5%.

After expansion of the preparation plant and dosing of chemicals with a reservoir of calcium hydrate powder 3 3 (30 m), dispenser (capacity 35 kg / h), calcium hydrate dilution tank (4 m), pump (output 3 3 m / h), powder dilution tank coal (4 m) and powdered charcoal slurry metering pump (20-200 l / h), 15-25 mg / l CaO was fed into the wastewater as a 4% lime slurry, 30-50 mg / l Al2 SO4. in the form of a 5% solution and 10 to 20 mg / l of powdered activated carbon Ga-05 (manufactured by VCHZ, Hnúšta-Likier) in the form of a 10% suspension.

The lime slurry is metered into the effluent from the buffer tank, the aluminum sulfate at the mixer inlet, and the activated carbon slurry into the mixer. The treated waste water shows an average residual contamination: 27 mg / l suspended matter, 59 mg / l COD, 17 mg / l BOD-5 and slight discoloration. The purification effects achieved are 93% reduction in suspended matter, 67% reduction in COD, 71% loss of BOD-5 and 92.8% removal of dyes. Sludge from sedimentation tanks is disposed of in an established way and the purified water is used 80% back in production, 20% is discharged to the recipient, where it does not cause any problems with its residual pollution.

Claims (1)

Wastewater treatment process containing undissolved and colloidal coagulable substances in addition to dyes or color-forming substances and in addition to biochemically degradable substances, contained in minor amounts corresponding to five-day biochemical oxygen consumption values up to 150 mg.I ^{-1 by} coagulation and sorption characterized by waste water is mixed with an alkalizing agent such as lime at a dose corresponding to 50-100% of the stoichiometric amount needed to completely hydrolyze the subsequently added trivalent metal basic coagulant such as aluminum sulfate, the resulting mixture is subjected to rapid stirring for 5-10 minutes, and then the activated carbon powder, preferably in the form of an aqueous suspension, is added in an amount corresponding to a weight ratio of 1: 2 to 1: 4 to the base coagulant, then the resulting mixture is stirred slowly for 10 to 20 minutes and then sedimented with residence time 90 to 120 minutes, where the formed sludge is separated from the purified water.