JPS5888089A - Purification of pulp mill waste liquor - Google Patents

Abstract

PURPOSE:To recover the separating power, esp. a water-permeating speed, of a semipermeable membrane composed of polysulfone, sulfonated polysulfone or the like, by treating the semipermeable membrane whose separating power is lowered at pH above 10 and a temp. above 55 deg.C with an aqueous surfactant solution. CONSTITUTION:A semipermeable membrane formed from a polymer selected from polysulfone, sulfonated polysulfone, polyether sulfone, poly(vinylidene fluoride), polyacrylonitrile and chlorinated poly(vinylidene chloride) whose separating power is deteriorated by treating alkali pulp mill waste liquor with it is treated under the condition of pH above 10 and a temp. above 55 deg.C by using an aqueous solution contg. 0.001-10wt% a surfactant, to recover the separating power. Said treatment of the semipermeable membrane may be performed, e.g. by detaching the membrane from a module and dipping it in the aqueous surfactant solution.

Description

[Detailed description of the invention] The present invention relates to a method for treating pulp wastewater.

The wastewater generated from pulp manufacturing plants contains large amounts of lignin, and concentrated wastewater such as black liquor is concentrated and combusted.
On the other hand, dilute wastewater such as ryohaku wastewater is generally subjected to coagulation sedimentation or biological treatment. However, coagulation-sedimentation and biological treatment produce a large amount of sludge, and its dewatering and incineration require large amounts of chemicals and energy, making the treatment expensive. For this reason, it has been proposed to treat relatively dilute pulp wastewater with a membrane, or as mentioned above, pulp wastewater contains lignin, which may form a gel layer on the membrane surface or cause the membrane to become clogged. As a result, the permeability of the membrane during membrane treatment is significantly reduced.In particular, membranes used for alkaline pulp drainage must have alkali resistance, and the pulp drainage may be heated at high temperatures. Since the gas is discharged, heat resistance is also required, and therefore semipermeable membranes made of hydrophobic polymers are often used. However, such hydrophobic polymer membranes, typified by polysulfone, are (However, once such organic substances have contaminated the membrane surface, they cannot be easily removed by conventionally known methods.)

The present invention has been made to solve the above-mentioned problems, and aims to provide a method for restoring membrane separation properties, particularly water permeation rate, which have been degraded due to membrane contamination in the treatment of alkaline pulp wastewater containing lignin. purpose.

The present invention provides a method for treating alkaline pulp effluent with a semipermeable membrane made of a polymer selected from polysulfone, sulfonated polysulfone, polyethersulfone, polyvinylidene fluoride, polyacrylonitrile, and chlorinated polyvinyl chloride, which has membrane separation characteristics. The semipermeable membrane, which has been reduced in temperature, is heated to a pH of 10 or higher and a temperature of 55°C using a surfactant water bath.
It is characterized in that the membrane separation properties are restored by treatment under the above conditions.

In the present invention, the alkaline pulp wastewater includes black liquor, washer wastewater, screen wastewater, bleached pulp alkali treatment wastewater, etc., and its pH is usually 8 or higher and contains various solutes mainly composed of lignin. Contains. Moreover, since alkaline pulp waste liquid is often discharged at high temperatures, the semipermeable membrane used must have both alkali resistance and heat resistance.
Semipermeable membranes made of hydrophobic polymers such as polyacrylonitrile and chlorinated polyvinyl chloride are preferably used. especially,
Semipermeable membranes made of polysulfone or polyethersulfone are preferred.

The surfactant used in the present invention is selected from anionic surfactants, cationic surfactants, amphoteric surfactants, and nonionic surfactants (both are one type of surfactant, and one
At least 0.001 parts by weight of water at 55°C
It is preferable to have a solubility of parts by weight.

The anionic surfactant preferably used in the present invention has the general formula % (1) (where R1 is an aliphatic, alicyclic or aromatic hydrocarbon group having 8 to 40 carbon atoms, and M is -COO -1-0SO@-1
An anionic group selected from -808- and -POs-,
Moreover, M+ represents a cation. where R
1 may have an ester group, ether group, amide group, hydroxyl group, etc. (specifically, v is an alkali metal ion such as Na", Li+, ammonium ion, etc.). Such an anionic interface Preferred specific examples of the activator include ROOONa (R is an aliphatic hydrocarbon group having 8 to 18 carbon atoms, R80sNa (R is the same as above), RO(OHsOH
zO) nsOsNa (R is an aliphatic hydrocarbon group having 8 to 18 carbon atoms, n is an integer of 1 to 6), 1 to an aliphatic hydrocarbon group (RO) mPONa (R is an aliphatic hydrocarbon group having 5 to 1 B carbon atoms) (hydrogen group), etc.

The cationic surfactant preferably used in the present invention has the general formula % (1) (where P has a carbon number of 8 to 40 containing a quaternized nitrogen atom).
represents an aliphatic, alicyclic or aromatic hydrocarbon group, and X represents a halogen. ), where R1 may contain an ester group, an ether group, an amide group, a hydroxyl group, etc. (X is specifically chlorine, bromine, etc.). Preferred specific examples of
sl''CJ- (R is the same as above), etc.

Further, the amphoteric surfactant preferably used in the present invention has a general formula (wherein, Y- represents -000-1 or -08O@-,
One of R1, R1, BI and R6 has 8 to 20 carbon atoms
represents an aliphatic, alicyclic, or aromatic hydrocarbon group, and the others represent hydrogen or an aliphatic, alicyclic, or aromatic hydrocarbon group having 1 to 8 carbon atoms. Any of the above hydrocarbon groups may contain an ester group, an ether group, an amide group, a hydroxyl group, a carboxyl group, etc. Preferred specific examples of such amphoteric surfactants include those mentioned above.

The nonionic surfactant preferably used in the present invention has the general formula % () (where R represents an aliphatic, alicyclic or aromatic hydrocarbon group having 8 to 20 carbon atoms, and A represents 10 -1-COO- and -c
represents a divalent organic group selected from oNli-, and n and m represent integers satisfying the conditions of 2≦n≦30.04m<28 and 4≦n10m≦30. ), general formula (where p, q and r are 15≦p≦50 and 206p+
Indicates an integer that satisfies the condition q+r≦80. ), or general formula (wherein R8 represents an aliphatic, alicyclic or aromatic hydrocarbon group having 8 to 20 carbon atoms, and s and U each independently represent an integer of θ to 5), Preferred specific examples of these nonionic surfactants are OisHms-0(OHsOHsO)nH(n
is the same as above], ROOO(OHzOHsO)nu (R is an aliphatic hydrocarbon group having 12 to 18 carbon atoms, n is the same as above), and so on.

In the present invention, the concentration of surfactant is usually o, ooi
-10% by weight, preferably 0.1-5% by weight. If the concentration is too low, the effect of restoring the membrane separation properties will be poor, and even if the concentration exceeds 10% by weight, the effect will not be substantially different from that in the above range, which is not economical.

When treating a semipermeable membrane with degraded membrane separation characteristics with the above-mentioned surfactant aqueous solution, the pH is set to 10 or higher and the temperature is set to 55"C or higher. The higher the treatment pH, the higher the solubility of lignin in particular. This is because membrane contaminants whose main component is lignin can be effectively removed.Practical, L, and optimally 10.
5 to 13. Even if a surfactant aqueous solution is used, the treatment p
When H is less than 10, the membrane separation properties are hardly recovered. p:E [As the alkali for conditioning, sodium hydroxide, potassium hydroxide, sodium carbonate, etc. are preferably used, but are not limited to these. Furthermore, the higher the treatment temperature, the more soluble the membrane contaminant is, and the easier it is to remove it. Preferably it is 60-100°C.

Specifically, the semipermeable membrane may be treated by, for example, removing the membrane from the module and immersing it in an aqueous surfactant solution, or attaching it separately to the module and circulating a surfactant bath solution through it. Alternatively, the aqueous surfactant solution may be circulated directly through the pulp wastewater treatment module. Although the treatment time depends on the degree of membrane contamination, it is usually 5 minutes or more, preferably 10 minutes to 24 hours.

It goes without saying that the method of the present invention can be applied to flat membranes, hollow fiber membranes, and spiral membranes regardless of the shape of the semipermeable membrane. It may contain builders (cleaning aid IJ) such as ethylenediaminetetraacetic acid, sodium polyphosphate, and sodium silicate.

In the method of the present invention, when the separation characteristics of the membrane deteriorate in the membrane treatment of alkaline pulp wastewater as described above, by treating the membrane with surfactant water f# solution at high pH and high temperature, Since membrane separation properties are restored, pulp wastewater can be treated while maintaining good membrane properties.

Examples of the present invention are listed below. In addition, in the examples,
The cleaning recovery rate (4) is a value defined by when a semipermeable membrane with reduced water permeability is treated with a surfactant water bath solution.

Examples 1 to 3 Kraft pulp bleached alkaline waste liquid (COD 2300-9
/l.

A 172-inch diameter tubular membrane module (NTU-3 manufactured by Nitto Electric Industries, Ltd.) equipped with a polysulfone semipermeable membrane (pH 11.0) was used.
508, membrane area 2.3") and operating pressure 8/
cd, flow rate 2.6 m/s, temperature approximately 50°C.
The membrane treatment was carried out by continuously circulating and supplying the solution for 00 hours and concentrating it 20 times. The amount of water permeable through the semipermeable membrane used is
Under water flow conditions of 5 DEG C. and 1'/C- pressure, the initial performance was 1151/d.hours through water, which decreased to 351/IIIJ.hours after the above operation.

This semipermeable membrane with reduced water permeability was removed from the module and attached to a small module Q with a membrane area of 0.034 wI, and a pH 12 membrane containing 0.5% by weight of Neogen R (Daiichi Kogyo Seiyaku flavored sodium alkylbenzenesulfonate) was attached. ，
The membrane was washed by circulating an aqueous solution of No. 0 for 2 hours at the temperature shown in Table 1 at a temperature of 4 - d/d.

After washing, water was supplied to the membrane module at a temperature of 25°C and a pressure of 211/cd, and the washing recovery rate was determined from the amount of water permeation.

The results are shown in Table 1. For comparison, the membrane was cleaned in the same manner as above, except that the cleaning was performed at a lower temperature, and the cleaning recovery rate was measured. As shown in Table 1, the water permeability of the membrane is hardly recovered by cleaning at low temperature.

Table 1 Examples 4 to 12 A polysulfone semipermeable membrane with a water permeation rate reduced to 351/11 IJ·hr in the same manner as in the previous example was treated with a pn 12.5 water bath solution containing various surfactants shown in Table 2. temperature 60
Washed for 2 hours at °C. Table 2 shows the water permeation amount and cleaning recovery rate after cleaning. As Comparative Example 3, the membrane was washed in the same manner with water containing no surfactant at pH 12.5 and temperature 60''C.

Examples 13 to 15 Table 3 shows a water bath solution containing 0.25% by weight of Amhitol 24B (Kao Soap ■7' Lucyl Betaine) for a polysulfone membrane whose water permeability decreased by 351,711' hours in the same manner as in the above Examples. After adjusting the pH, it was washed for 2 hours under the conditions of Table 3: temperature 60°C and pressure 4Q+/cj. The water permeation amount after washing was measured under the same conditions as in the above example,
The cleaning recovery rate was determined. When the pH of the surfactant aqueous solution is lower than 10, the amount of water permeation hardly recovers even after washing.

Example 16 Kraft pulp washer effluent (OOD 90000
q/l, solid content 13%, pH 12.0) with a 1/2 diameter tubular membrane module (Nitto Electric Industry ■) equipped with a polysulfone membrane.
Made by NTU-3020P 18B, membrane area 0.78㎜1
), operating pressure BKp/cj, flow rate 3.2 m 7
Two-fold concentration treatment was carried out for a long period of time at a temperature of 50°C. The water permeability of the membrane at the time of use is 250171 when water is supplied at a temperature of 25°C and a pressure of 2IQ/C-.
It was M'・hour, but after the above operation it was 6017M?・Decreased at times.

This membrane was washed under various conditions shown in Table 4, and the washing recovery rate was determined. According to the present invention (Example 163, the cleaning recovery rate reached 95%, but the recovery rate was extremely small at pH 5.0 (Comparative Example 6), and even when an oxidizing agent was used instead of a surfactant, the recovery rate was 95%. rate is significantly smaller.

Claims (1)

[Claims] In a method of treating alkaline pulp effluent with a semipermeable membrane made of a polymer selected from polysulfone, sulfonated polysulfone, polyether sulfone, polyvinylidene fluoride, polyacrylonitrile, and chlorinated polyvinyl chloride, the above-mentioned membrane separation property is deteriorated. A method for treating pulp effluent, comprising treating a semipermeable membrane with a surfactant water bath solution at a pH of 10 or higher and a temperature of 55°C or higher to restore membrane separation properties.