RU2263078C1 - Method of the pulp-and paper production sewage purification - Google Patents

Abstract

FIELD: environmental protection; purification of sewage of pulp-and-paper production from lignine materials.

SUBSTANCE: the invention is pertaining to the field of environmental protection, in particular, to purification of sewage of pulp-and-paper production and may be used for purification of sewage of pulp-and-paper production from lignine materials. For realization of the method the sewage is treated with salts of aluminum, iron, zinc or magnesium in a combination with calcium compounds in the mediums with pH of no less than 10.5 at a following batching of the components: salts of metals - 0.3-12 mg-equiv/l, calcium compounds - 40-150 mg-equiv/l and separate the formed suspended matters. The method ensures a decrease of consumption of reactants used for effective purification of sewage at reduction in price of the purification process of sewage of pulp-and-paper production.

EFFECT: the invention ensures a decrease of consumption of reactants used for effective purification of sewage at reduction in price of the purification process of sewage of pulp-and-paper production.

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Description

The invention relates to environmental protection and is intended for wastewater treatment of pulp and paper production (pulp and paper industry).

It is known that the treatment of wastewater by the pulp and paper industry is carried out exclusively by the biological method, in which the main pollutants of wastewater, namely lignosulfonates (LS) and organochlorine compounds formed during bleaching of cellulose, in particular chloro lignin, are not eliminated and, therefore, fall into natural bodies of water from a biological treated wastewater.

An urgent task is to find methods and means for the selective removal of lignin substances from wastewater of the pulp and paper industry.

A known method of treating wastewater of pulp and paper industry with metal salts with the conversion of lignin substances into an insoluble state with their subsequent separation. (Chernoberezhsky Yu.M., Diaghileva A.V., Barysheva I.A. Coagulation wastewater treatment of the pulp and paper industry // ZhPKh. 1994. - T.67. - No. 3. - p.402-406.) . The method includes processing a model aqueous solution of a drug with an aluminum salt at pH 4.8, followed by separation of the precipitate. The drug content when using this method is reduced by 92%. However, our experimental verification of this method directly on sulphite liquor showed its low efficiency.

A known method of treating wastewater from organochlorine and lignosulfonate compounds by precipitation in the form of water-insoluble mixed complexes using zinc salt in combination with imidazole or its derivatives (RF Patent No. 2159532, MKI 6 02 F 1/58, 1999). This decision was made by us for the prototype.

When testing this method on a model solution of lignosulfonates, a high purification efficiency for drugs of 90% is achieved. However, the method was not tested on natural wastewater; in addition, the proposed method is characterized by a very high consumption of reagents: the consumption of salts is from 80 to 120%, as well as imidazole (an expensive and scarce reagent) from 80 to 120% with respect to seized pollutants. This is an insurmountable obstacle to the practical use of the method.

The task to which the invention is directed is to reduce the consumption of reagents and to reduce the cost of the method of wastewater treatment for pulp and paper industry.

This is achieved by the fact that in the method of wastewater treatment for pulp and paper industry, including the introduction of metal salts and the separation of the resulting suspension, the wastewater is treated with metal salts in combination with calcium compounds (oxide, hydroxide or salts), at dosages from 45 to 150 mEq / l, the treatment is carried out at a pH of at least 10.5, after which the precipitated ligninous substances are separated by known methods.

Comparison of the proposed method with the method according to the patent of the Russian Federation No. 2159532 revealed the following new features: a) the treatment of effluents with metal salts is carried out not in combination with imidazole, but in combination with calcium compounds, b) the effluent is treated at a pH of at least 10.5, c) the dosage of metal salts is from 0.3 to 18 mg equivalent / liter of wastewater, and the dosage of calcium compounds from 45 to 150 mg equivalent / liter of wastewater.

To implement the proposed method, proceed as follows: take wastewater containing lignin substances, introduce a metal salt in it in combination with any of the calcium compounds, if necessary, adjust the pH of the medium to 10.5 or more using some alkaline agent, for example sodium hydroxide, is further mixed and the precipitate formed, containing ligninous substances, is separated from the treated water by one of the known methods (sedimentation, filtration, centrifugal separation).

The possibility of implementing the proposed method is illustrated by examples.

Example 1

We took alkali-containing wastewater generated in the production of sulphite viscose pulp. Water had the following characteristics: the content of lignosulfonates, found by the standard Pearl-Benson method, was 2.48 g / l, the total solids content was 5 g / l, the acidity in pH units was 3.35, the content of SO ₂ compounds was directly titrated 0, 0006%, easily cleaved 0.006%. A solution of aluminum sulfate with a concentration of 64 g / l Al ₂ O _{3 was} introduced into 100 ml of wastewater at a rate of 6 mEq / l and a 10% solution of calcium chloride at a rate of 150 mEq / l, then the pH of the medium was adjusted to 12 using a 17.5% sodium hydroxide solution, after mixing the medium and separating the precipitate formed, the residual drug content was determined to be 1.28 g / l; therefore, the cleaning effect, taking into account dilution during processing, was 48%.

In parallel, for comparison, the specified wastewater was treated with a solution of aluminum sulfate at a dosage of 6 mEq / l and at pH 4.8; 7.0; 10.5 and 12.0 (when using sodium hydroxide); in all cases, the cleaning efficiency did not exceed 10%. In parallel, the same wastewater was treated only with a solution of calcium chloride at a dosage of 150 mEq / L and pH 12.0, the cleaning efficiency was 7.5%.

In parallel, the same wastewater was treated at the above dosages of aluminum sulfate and calcium chloride at the following pH values: 4.8; 7.0; 10.0; 10.5; 11.0; 12.0. The processing results are presented in table 1, from which it follows that a sufficiently high cleaning effect is achieved only at a pH of at least 10.5.

Table 1. pH of the medium 4.8 7.0 10.0 10.5 11.0 12.0 The degree of removal of drugs,% 2,5 2.0 14.0 21.0 30,0 48.0

Example 2

To study the effect of the dosage of the metal salt, wastewater was used under the conditions of Example 1, experiments were carried out at a constant dosage of calcium chloride of 150 mEq / L and pH 12.0. From the results of the study, presented in table 2, it is seen that a sufficiently significant cleaning effect is achieved even with a dosage of aluminum salt of 0.5 mEq / l. In a separate experiment conducted with waste water containing 0.81 g / l of lignosulfonates, it was found that when it was treated with aluminum sulfate and calcium hydroxide (in the form of milk of lime) at a dosage of 45 mEq / l, a sufficiently high cleaning effect was achieved even at an aluminum salt flow rate of 0.3 mEq / L.

Table 2. Consumption of aluminum salt, mEq / l 0 0.5 1 2 4 6 8 12 eighteen The degree of removal of drugs,% 14 27 34 42 48 52 56 60 63

Example 3

To study the effect of the dosage of calcium compounds, wastewater taken under the conditions of Example 1 was used. Calcium compounds were introduced in the form of acetate, and aluminum sulfate was used as a metal salt at a dosage of 6 mEq / L. The treatment was carried out at pH 12 with the addition of a 17.5% sodium hydroxide solution. The cleaning results are shown in table 3.

Table 3. Dosage of calcium salt, mEq / l 0 fifty 75 100 150 180 The degree of removal of drugs,% 0 6 thirty 36 49 fifty

As can be seen from the presented results, in the absence of calcium compounds, the efficiency is 0%, and as the dosage of calcium compounds increases from 50 to 150 mEq / L, the efficiency reaches 50%, with a further increase to 180 mEq / L, the effect stabilizes.

Example 4

In experiments, along with aluminum salts, salts of iron II and III, zinc and magnesium were also used at the same dosage (6 mEq / l). As a calcium compound, hydroxide in the form of milk of lime was used at a dosage of 70 mEq / L. The experiments were carried out with wastewater taken under the conditions of example 1. The pH of the medium in all experiments was 12. The results are presented in table 4.

Table 4. Type of salt The degree of removal of drugs,% Zinc chloride thirty Iron Sulfate II 40 Iron Sulfate III 35 Aluminum sulfate 52 Aluminum nitrate fifty Magnesium Sulfate 35

Example 5

In alkali-containing water, taken under the conditions of example 1, aluminum sulfate was introduced in an amount of 6 mEq / l and calcium compounds: oxide, hydroxide (in the form of milk of lime), chloride, nitrate, acetate. The pH of the medium in all experiments was 12. In experiments with calcium salts, sodium hydroxide solution was added to maintain the pH of the medium. The results are shown in table 5.

Table 5. Type of Calcium Compound Calcium Compound Dosage, mEq / L The degree of removal of drugs,% Calcium oxide fifty thirty Calcium hydroxide (milk of lime) fifty fifty Calcium chloride 150 fifty Calcium nitrate 150 fifty Calcium acetate 150 55

Example 6

We took the wastewater generated during cellulose bleaching with a lignin content of 1.56 g / l, treated with aluminum sulfate at a rate of 6 mEq / l and calcium hydroxide (in the form of milk of lime) at a rate of 40 mEq / l. The cleaning effect is 44%.

Only when using all the features of the proposed method in their totality is an effective purification from ligninous substances achieved. So, if only metal salts are used, the cleaning effect is close to zero both at low and at high pH values (see example 1); if you use only calcium compounds without metal salts, for example calcium hydroxide (in the form of milk of lime), then the efficiency of wastewater treatment from lignin substances is also low (example 1); a low degree of purification is also achieved when the effluent is treated with metal salts in combination with calcium compounds if the pH of the medium is less than 10.5.

Dosages of metal salts and calcium compounds have a significant effect on the cleaning effect. As can be seen from example 2, when the dosage of metal salts is less than 0.3 mEq / l of wastewater, the achieved cleaning effect is negligible even with a sufficient dosage of calcium compounds and pH; an increase in the dosage of metal salts from 0.3 to 18 mEq / l increases the cleaning efficiency, a further increase in the dosage is impractical. Accordingly, it can be seen from Example 3 that a rational dosage of calcium compounds is from 45 to 150 mEq / L. Example 4 compares the results of treating wastewater with salts of various metals, and example 5 compares the effectiveness of treating wastewater with an aluminum salt in combination with various calcium compounds.

Claims (1)

A method of treating wastewater from pulp and paper production from lignin substances, comprising introducing metal salts and separating the resulting suspensions, characterized in that the treatment is carried out with aluminum, iron, zinc or magnesium salts in combination with calcium compounds at a pH of at least 10.5 at following dosage of components: Metal salts 0.3-12 mEq / L Calcium compounds 40-150 mEq / L