JPS5948154B2 - Wastewater purification method - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for purifying wastewater, and more particularly to a method for purifying oily wastewater containing silicic acid and metal salts.

Oil wastewater containing silicic acid and metal salts is used in the automotive industry,
Emitted from manufacturing processes at various establishments such as the industrial machinery industry.

As a purification treatment method for these oil wastewaters, since these oil wastewaters are alkaline, the pH is generally adjusted to 4 to 5 using mineral acid.
Then, add a flocculant with or without adding an emulsion decomposer, and then add an alkaline agent to
A method has been used in which H is set to 8 to 9, the contained substances are coagulated and precipitated, and the purification treatment is performed by solid-liquid separation.

However, such conventional methods do not sufficiently remove metal salts, especially zinc, and organic pollutants represented by oil and BOD and COD, resulting in low treatment effects.

An object of the present invention is to provide a treatment method for effectively removing metals, oil, and organic pollutants expressed as BOD and COD from oil wastewater containing silicic acid and metal salts.

The method for purifying wastewater according to the present invention includes adding a water-soluble silicate to oil wastewater containing sulfuric acid and metal salts when the silicic acid concentration in the wastewater is less than about 500 ppm. After adjusting the acid concentration to about 500 ppm or more, water-soluble aluminum salt and slaked lime were added to adjust the pH to 10 to 1.
2.5, remove the generated precipitate, and then add mineral acid to adjust the pH to 6 to 8 and bring it into contact with a solid adsorbent.

Typical silicic acid and metal salts contained in oil wastewater, which are the targets of the method according to the present invention, are ionic and/or metal salts.
or colloidal silicic acid and zinc and/or iron salts.

The water-soluble silicates used in the wastewater purification method according to the present invention include sodium silicate, potassium silicate,
Examples include ethyl silicate, but sodium silicate is preferred because it is the most easily available and is most effective.

In addition, the present inventors have discovered that metals and oil in wastewater, BOD,
As a result of various studies on the coagulation and precipitation removal of organic pollutants expressed by COD, it was discovered that the amount of ionic and colloidal silicic acid in wastewater has a significant effect.

That is, when the silicic acid concentration in the wastewater is about 500 ppm or more, the above-mentioned contents are effectively coagulated and precipitated, and about 500 ppm or more
If it is less than ppm, the coagulation and sedimentation effect will be poor.

Therefore, in the method of the present invention, water-soluble silicates are added such that the silicic acid concentration in the oil wastewater is about 500 ppm or more.

Furthermore, the oil wastewater that is the subject of the method of the present invention contains silicic acid, and it is known that this silicic acid is well dispersed in water in ionic form, that is, in the form of a solution, or in the form of a sol or a colloid close to this. Desirably, the concentration is about 500p.
pm or more, the addition of water-soluble silicate may be omitted.

Preferred examples of water-soluble aluminum salts added to the wastewater in the method of this invention include polyaluminum chloride and aluminum sulfate.

In the method of this invention, after water-soluble aluminum silicate and water-soluble aluminum salt are added to wastewater, slaked lime is added to adjust the pH to 10-12.5, preferably 11.5.
After adjusting to ~12, the formed precipitate is removed.

Prior to removing the precipitate, a polymer flocculant other than polyaluminum chloride, such as sodium polyacrylate, polystyrene sulfonate, water-soluble urea resin, etc., is further added to the wastewater as required.

The wastewater from which the coagulated sediment has been removed is then adjusted to pH 6 to 8 with mineral acids such as sulfuric acid and hydrochloric acid, and then passed through a layer of solid adsorbents such as activated carbon and activated clay, or stirred with them. , and contacted with a solid adsorbent to remove residual organic substances.

In each step of adding various chemicals in the method of this invention, necessary stirring and, in some cases, necessary heating, are performed in order to promote uniform mixing with additives, reaction, and coagulation and ripening of precipitates. Of course.

By the method of this invention as detailed above, metals, especially zinc, in oil wastewater can be removed to zero. lppm or less, n-hexane extractables less than 1 ppm, BOD and COD 20 ppm
m, and an excellent treatment effect can be shown.

The method according to the present invention will be explained in more detail below based on Examples.

In the following Examples and Comparative Examples, oil wastewater from Table 1 was used.

Note: All of these are process wastewater from the automobile manufacturing industry.

Example 1 Sodium silicate was added to oil wastewater A so as to increase the SiO□ concentration in the wastewater by 500ppm, and then polyaluminum chloride and slaked lime were each added to 11,000pp to adjust the pH to 12.4, and the mixture was heated at 130 rpm. 5
The mixture was stirred for 1 minute, and then sodium polyacrylate was added in an amount of 1-, and the mixture was stirred for 10 minutes at a rotational speed of 3 Orpm, and left to stand for 20 minutes.

After filtering through filter paper to remove coagulated precipitates, sulfuric acid was added to the solution to adjust the pH to 7.0, and 13. The mixture was stirred at Orpm for 2 minutes and then passed through a layer of activated carbon.

The analytical values of the obtained treatment liquid are shown in Table 2 together with the following Examples and Comparative Examples.

Example 2 Oil wastewater B was treated in the same manner as in Example 1.

Example 3 The same treatment as in Example 1 was performed except that sodium silicate was not added to oil wastewater B.

Example 4 The same treatment as in Example 1 was performed except that activated clay was used instead of activated carbon.

Example 5 The same treatment as in Example 2 was performed except that activated clay was used instead of activated carbon.

Comparative Example 1 Sulfuric acid was added to oil wastewater A to adjust the pH to 5 and make it 130 ppm.
Stir for 3 minutes at
m, stirred for another 3 minutes, added sodium carbonate to adjust the pH to 8.6, then added sodium polyacrylate to 1 ppm, and stirred at 40 rpm.
After stirring for 10 minutes, the mixture was allowed to stand for 20 minutes, and the flocculated precipitate was side-vortexed using filter paper.

Comparative example 2 Oil wastewater B was treated in the same manner as in Comparative Example 1.

Note: Sample oil wastewater B of Comparative Example 2 contains 752 ppm of silicic acid, and thus shows a relatively good treatment effect.

As described above, the wastewater purification method according to the present invention can effectively remove metals, oil, and organic pollutants expressed as BOD and COD from oil wastewater containing silicic acid and metal salts. Therefore, it is extremely effective in purifying oil wastewater discharged from manufacturing processes in business establishments such as automobile manufacturing industry and industrial machinery industry, and has great industrial utility value.

Claims (1)

[Claims] 1. If the silicic acid concentration in the wastewater is less than about 500 ppm, water-soluble silicate is added to oil wastewater containing silicic acid and metal salts to reduce the silicic acid concentration to about 500 ppm. After adjusting the pH to 500 ppm or more, water-soluble aluminum salt and slaked lime are added to adjust the pH to 10 to 12.5. After removing the generated precipitate, mineral acid is added to adjust the pH to 6 to 8, and the solid adsorbent is adjusted to 10 to 12.5. A wastewater purification method characterized by contacting the wastewater. 2 The silicic acid contained in the oil wastewater is ionic and/or
or colloidal silicic acid, the metal salts being zinc and/or colloidal silicic acid;
or iron salts, the method for purifying wastewater according to claim 1. 3. The method for purifying wastewater according to claim 1, wherein the water-soluble silicate is sodium silicate. 4. The method for purifying wastewater according to claim 1, wherein the water-soluble aluminum salt is polyaluminum chloride or aluminum sulfate, and has a pH of 11.5 to 12 when slaked lime is added. 5. The method for purifying wastewater according to claim 1, wherein the solid adsorbent is activated carbon or activated clay.