JPS6253235B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for treating pulp wastewater, and in particular provides an improved method for coagulation-sedimentation treatment using slaked lime and an anionic polymer flocculant. In recent years, with the strengthening of environmental administration, regulations on waste discharged from various factories have become even more stringent, and new standards have been set for COD, SS values, etc. for wastewater discharged from pulp and paper factories. It is strictly regulated. Conventionally, methods for treating the so-called pulp waste liquid discharged from various processes of pulp manufacturing, such as the cooking process of kraft pulp, sulfite pulp, etc., and the pulp bleaching process with chlorine, caustic soda, hypochlorite, chlorine dioxide, etc., include: Coagulation precipitation methods using iron or aluminum salts, resin adsorption methods, activated carbon adsorption methods, activated sludge methods, etc. are known. However, these treatment methods have drawbacks such as the need to use relatively large amounts of expensive treatment agents in order to obtain sufficient treatment effects, and the treatment effects themselves are insufficient, so the results are not always satisfactory. Not obtained. A lime-adding coagulation-sedimentation method (hereinafter referred to as the "lime method") has been proposed as one method for improving these drawbacks. In this lime method, slaked lime is first added as a flocculant to pulp wastewater to cause a flocculation reaction, and then an anionic polymer flocculant (e.g., polyacrylamide, modified polyacrylamide, sodium polyacrylate, modified polyacrylic This method aims to reduce the COD and chromaticity in the wastewater by adding acid soda, etc.) to form a larger floc and removing the precipitate. The lime method uses inexpensive slaked lime and a relatively small amount of anionic polymer flocculant, and is an economically advantageous treatment method. However, problems such as a significant decrease in floc formation may occur depending on the temperature of the waste liquid, COD conditions, etc., and improvements have been desired. The applicant of this application has developed a method in which pulp wastewater is subjected to coagulation and precipitation treatment using slaked lime and an anionic polymer flocculant, in which slaked lime is added to the pulp wastewater in multiple stages, in which the slaked lime is added to the pulp wastewater in two or more times. A patent application was filed for a method for making it huge (Japanese Patent Application Laid-Open No. 1983-
35965). The present inventors have investigated methods other than increasing the size of flocs by multi-stage addition of slaked lime, or a method in combination with this method to further increase the processing efficiency of pulp wastewater, and found that the sedimentation rate of flocs can be further promoted. We focused on the fact that the treatment efficiency could be increased accordingly, and conducted various tests on methods for accelerating the sedimentation rate.
As a result, it was confirmed that if the pulp wastewater was diluted before adding slaked lime to the pulp wastewater, the sedimentation rate of COD flocs produced by the lime method would be faster. Although tap water and industrial water are effective as a diluent for the pulp waste liquid, it is more effective to reuse a portion of the supernatant liquid produced during coagulation and precipitation treatment using the lime method. The treated liquid is originally discharged into the ocean, etc., but it is better to use a part of it to dilute the pulp waste liquid before treatment than to dilute it with industrial water, etc.
The reason why COD flocs can be settled more quickly is that, for example, industrial water only has the effect of diluting the pulp wastewater, whereas when using the supernatant liquid, In addition to the dilution effect, some dissolved matter from the previously added slaked lime and anionic polymer flocculant remains, which has an even more positive effect on the enlargement of COD flocs and, as a result, promotes sedimentation. It is thought that this will happen. Although industrial water and the like can provide a diluting effect, there is a problem in that the amount of treatment (release) increases by the amount newly added for dilution. It goes without saying that an increase in the amount of treated (discharged) liquid is not environmentally friendly. In this respect, the supernatant is a treated liquid that should be discharged, and since a portion of it is reused, there is no problem of increasing the amount of treatment (discharge). From this point of view as well, it is actually more preferable to dilute with the supernatant liquid than with industrial water or the like. There is no particular limit to the dilution concentration of the pulp wastewater, as the sedimentation velocity efficiency of the COD flocs is good enough to keep it diluted. The decision will be made after consideration. The present invention can be applied directly to the conventionally known reaction method (one-stage addition method of slaked lime) to speed up the sedimentation rate and improve the efficiency of wastewater treatment, and can also be applied to the previously applied multi-stage addition method of slaked lime. If applied to the law, even greater treatment effects can be achieved. The present invention will be explained in more detail with reference to Examples below. Example 1 Pulp effluent (COD 593ppm, PH10.5, water temperature 30
The supernatant liquid (COD
COD at 250ppm, PH12.5, water temperature 30℃)
It was diluted into three types: 558ppm, 523ppm, and 488ppm.
Take two samples each of the pulp waste liquid and the diluted waste liquid into two volume beakers, and add slaked lime to each as shown in Table 1 (all proportions to COD are the same).
After stirring for 7 minutes with a propeller mixer at a rotation speed of 100 rpm, the rotation speed was reduced to 60 rpm, and an anionic polymer flocculant (trade name "Sunpolymer 305" manufactured by Sankyo Kasei Co., Ltd.) was added in the proportions shown in Table 1. ) and stirred for 3 minutes. Add these processing solutions to a volume of 2
, transferred to a sedimentation tube with a height of 1 m, and the sedimentation velocity (m/
h), Volume of settled sludge after 15 minutes (sludge volume cc) and
The COD reduction rate (converted from the COD value of the supernatant) was measured. The results were as shown in Table 1.

[Table] Example 2 Pulp effluent (COD850ppm, PH10.6, water temperature 30
The supernatant liquid (COD250ppm, PH
12.5, water temperature 30℃) COD is 800ppm, 750ppm,
A sedimentation test was conducted in the same manner as in Example 1, except that the dilution was performed in three different amounts at 700 ppm. The results were as shown in Table 2.

[Table] Example 3 Pulp wastewater (COD980ppm, PH10.6, water temperature 30
The supernatant liquid (COD250ppm, PH
12.6, water temperature 30℃) COD is 931ppm, 882ppm,
A sedimentation test was conducted in the same manner as in Example 1, except that the dilution was performed in three different amounts at 780 ppm. The results were as shown in Table 3.

[Table] Example 4 Pulp effluent (COD684ppm, PH10.5, water temperature 30
The supernatant liquid (COD250ppm, PH
12.5, water temperature 30℃) COD is 630ppm, 580ppm,
Dilute to 530 ppm, and add slaked lime to each in one step as shown in Table 4 (Same as Examples 1 to 3, add slaked lime in the order of anionic polymer flocculant)
and two-stage addition method (divide slaked lime into two times, add slaked lime to
Anionic polymer flocculant - slaked lime (added in the order of slaked lime) (the amount of slaked lime added in the same ratio to COD), and the sedimentation rate of the treated liquid, volume of settled sludge and COD were added in the same manner as in Example 1. The rate of decrease was measured. The results were as shown in Table 4.

【table】

Claims (1)

[Scope of Claims] 1. A coagulation-sedimentation treatment method in which slaked lime is added to a pulp waste liquid to flocculate suspended matter, and an anionic polymer flocculant is further added to make the floc large. A method for treating pulp wastewater, characterized by accelerating the sedimentation rate of COD flocs by pre-diluting COD. 2. The method for treating pulp waste liquid according to claim 1, wherein the diluted pulp waste liquid is a supernatant liquid produced when the pulp waste liquid is coagulated and precipitated with slaked lime and an anionic polymer flocculant. 3. The method for treating pulp waste liquid according to claim 1, wherein the diluent of the pulp waste liquid is virgin water.