JPH03106493A - Treating waste water - Google Patents

Abstract

PURPOSE:To reduce the use amt. of coagulant and the vol. of sludge to be formed by a method wherein hydrogen peroxide is added is to settled sludge in the presence of ion salt, and its pH is adjusted so as not to exceed a specific value in order to subject the settled sludge to oxidative decomposition and the resulting decomposition products are added to the waste to be treated so as to recover coagulant. CONSTITUTION:Separately settled sludge in a sedimentation tank 2 is admixed with hydrogen peroxide (H2O2) from a pipe 17 and further with acids such as H2SO4 and HCl in an oxidative decomposition tank 3 in order to adjust its pH to a value not exceeding 4 and then subjected to the oxidative decomposition by Fenton reaction. Org. substances in the sludge are decomposed and, due to the acidic conditions thereof, the Mg compounds existing in the sludge as Mg(OH)2 are dissociated into Mg<2+> so as to be completely dissolved therein. Therefore, since the Mg<2+>, a coagulating component, is contained in the liq. decomposition product of the sludge, by the addition of this liq. to waste water, its coagulating treatment can be effected and, in this way, the amt. of the coagulant used can be reduced.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention relates to a method for treating wastewater, and particularly in a method for flocculating organic wastewater by adding a magnesium compound as a flocculant, the amount of flocculant used and sludge This paper relates to a wastewater treatment method that can significantly reduce the amount generated. [Conventional technology] Biological treatment is generally used to treat wastewater containing organic matter, but for wastewater that can be treated with waste water, such as surfactant wastewater such as nonionic surfactant wastewater and dyeing wastewater, flocculation is used. Processing is being done. In this case, aluminum-based salts, iron salts, magnesium salts, etc. are used as W1 collectors in the flocculation process. Specifically, it is known that organic wastewater, especially surfactant wastewater, dyeing wastewater, etc., is subjected to flocculation treatment using magnesium salts in seawater (Japanese Patent Laid-Open No. 48-21
668, Special Publication Showa 49-4676!5 etc.). In particular, treatment with magnesium salt C has a better flocculation effect than treatment with iron salt, and is therefore a preferred method. The sludge obtained by solid-liquid separation of the suspension produced by such aggregation treatment is dehydrated and then disposed of.

[The invention attempts to solve i! Issue I] In the flocculation treatment of organic wastewater, flocculants have traditionally been considered disposable. For example, even in the above-mentioned method of using magnesium salts in seawater, there is no study on reducing the amount of flocculant used, and no mention is made of the disposal of the generated sludge. For this reason, there was a drawback that efficiency was extremely low in terms of coagulation processing costs, sludge disposal costs, and the like.

It is an object of the present invention to solve the above-mentioned conventional problems and provide a wastewater treatment method that reduces the amount of coagulant used and reduces the volume of sludge generated by recovering the coagulant. [Means for Solving the Problems] The wastewater treatment method of the present invention includes adding a magnesium compound to raw organic wastewater, adjusting the pH to 10 to 14, separating the obtained suspension into solid and liquid, and separating it into treated water. In method C for treating wastewater that is separated into precipitated sludge, hydrogen peroxide is added to the precipitated sludge in the coexistence of iron salt, and the pH is adjusted to 4 or less to oxidize and decompose the precipitated sludge, and the resulting decomposed product is It is characterized by being added to raw water. The present invention will be explained in detail below with reference to the drawings.

Figure 1 is a system diagram showing an embodiment of the wastewater treatment method of the present invention. In the method of this example, first, piping! 4 is more cohesive than 1!
Mg compounds such as magnesium (Mg) salts are added as a coagulant through pipe 12 to the raw water introduced into step 1, and at the same time iron (
Fe) A salt and an alkali such as NaOH are added as a pH adjuster, and if necessary, a polymer such as a polyacrylamide hydrolyzate is added for aggregation treatment. The optimum pH for flocculation treatment using an Mg compound is 10 to 14, but in the present invention, it is preferable to perform flocculation at PHII to 12 in order to completely precipitate excess magnesium ions (Mg"). That is, By completely sinking Mg 2+ and incorporating almost the entire amount of the added Mg compound into the precipitated sludge obtained by solid-liquid separation after aa treatment, the efficiency of circulating and reusing Mg 24'' is improved. Therefore, it is extremely advantageous. In this case, in addition to NaOH, the pH adjusting agent used for pH adjustment is an alkali such as Ca(OH)2, or in some cases HaSO4, HCJ2.
Acids such as can be used. Mg compounds used include MgSO4, MgC
j! In addition to Mg salts such as 2, MgO, Mg(OH)2, etc. In the present invention, it is effective to change the Mg compound added depending on the pH of the raw water to obtain a pH adjusting effect. That is, when the raw water is acidic wastewater, an alkaline Mg compound such as MgO or Mg(OH)2 is added. This is economical because the Mg compound acts as a flocculant and also acts as an alkaline agent to adjust pH. When the raw water is neutral or alkaline wastewater, it is advantageous to use Mg salts. Although the initial amount of the Mg compound added varies depending on the quality of the raw water, it is usually preferable to add it at a ratio of about 5 to 20 times the CODcr. Fe salt is a catalyst for oxidative decomposition, which will be described later. Therefore, Fe salt may be added to the oxidation decomposition tank 3 described later or any step upstream thereof, but by adding it to the flocculation tank m as in this example, Fe hydroxylation occurs in the flocculation system. This is extremely advantageous because it produces substances that improve the flocculation efficiency. As Fa salts, ferrous salts such as ferrous sulfate and ferrous chloride, ferric chloride,
Any ferric salt such as ferric sulfate can be used. As the polymer added to the flocculation tank 1, polyacrylic acid, dross hydrolyzate, etc. can be used. In the present invention, the addition of a polymer is not necessarily required, but the aggregation efficiency can be improved by adding a polymer. When adding a polymer, the amount added is preferably about 1 to 5 ppm based on the amount of wastewater. The flocculation treatment liquid in the flocculation tank 1 is sent from a pipe 13 to a solid-liquid separation means such as a settling tank 2 for solid-liquid separation. This precipitation 4!2 is natural precipitation! In addition, solid-liquid separation means such as a centrifuge, a filter press, and a belt press can also be used. The treated water obtained by solid-liquid separation in the settling tank 2 is transferred to the pipe 14.
The waste is discharged outside the twine, and after further appropriate purification treatment is performed depending on the company's needs, it is released into the stream. On the other hand, the settled sludge separated in the settling tank 2 is sent to the oxidative decomposition cypress 3 via pipes 15 and 16. Then, in the oxidation decomposition tank 3, hydrogen peroxide (H2 02) is added from the pipe 17, and H2 504,
Add an acid such as HCj2 to adjust the pH to 4 or less and perform oxidative decomposition by Fenton reaction. The Fenton reaction can be carried out under standard conditions. That is, H 2 0
2/F6 (weight ratio) is 1 to 100, H202
Is the concentration (ppm) CODc in treated sludge? (calculated as 0), the pH is preferably 2 to 4, and the reaction time is preferably 2 to 4 hours. Therefore, the amount of Fe salt added in the coagulation process 1 is appropriately determined so as to provide a suitable amount of Fe salt for the Fuenton reaction conditions in the oxidation decomposition tank 3. The organic matter in the sludge is decomposed by the Fuenton reaction in the oxidation decomposition tank 3, and the Mg compounds present in the sludge as Mg(OH)2 are also completely converted to Mg'' due to the acidic conditions in the system. Therefore, the decomposed product obtained by the oxidative decomposition IAFI! of the precipitated sludge in oxidative decomposition I13 becomes liquid or thin slurry. Such oxidative decomposition treated liquid is circulated to the flocculation tank 1 through the pipe 18. The Mg compound used as a flocculant in the present invention dissolves as Mg 24'' in oxidative decomposition I!3 as described above. It can be reused as a flocculant. Similarly, in the Fenton reaction, either Fe 2+ or Fe'+ has a catalytic effect, so Fe salt can also be reused.

Therefore, once the Mg compound and Fa salt are added, there is no need to add them later. However, undecomposed organic matter is concentrated in the oxidative decomposition solution, and the flocculation efficiency gradually decreases, so the sludge must be extracted from the pipe 19 and dehydrated before being disposed of, if necessary. In the method of the present invention, the sludge oxidation and decomposition treatment solution can normally be recycled 4 to 5 times or more, but if the coagulation treatment efficiency decreases, pulls out some or all of the sludge. In this case, it is necessary to add at least an amount of Mg compound and Fe salt corresponding to the amount of extraction. The extracted sludge can be dehydrated using a conventional dewatering process such as a centrifugal dehydrator, belt press, or filter press. In this case, oxidative decomposition and cyclic reuse of sludge have almost no negative effect on the dewatering properties of sludge, and the extracted sludge is efficiently dehydrated. FIG. 1 shows one embodiment of the present invention, and the method of the present invention is not limited to the illustrated method in any way.
It is possible to carry out both continuous processing and batch processing. In addition, in the method of the present invention, there are no particular restrictions on the type or properties of wastewater to be treated, but the present invention is particularly applicable to surfactant-containing wastewater such as detergent manufacturing wastewater, degreasing process wastewater, cutting wastewater, etc., and dyeing factory wastewater. It is extremely effective for colored wastewater such as wastewater, dye manufacturing wastewater, bulp manufacturing wastewater, etc., and it is said that it is possible to obtain high quality treated water with a small amount of sludge production and chemical injection. [Operation] By adding H202 in the coexistence of Fe salt to the sludge produced by the coagulation treatment of organic wastewater to make the pH below 4, the organic matter in the sludge is oxidized and decomposed by Fenton decomposition, and its volume is reduced. In addition, M present in sludge due to coagulation
Since the system is acidic, g(OH)2 becomes Mg2+ and is completely dissolved. Therefore, the oxidative decomposition solution of sludge contains Mg 2+, which is a flocculating component, and by adding Mg 2+ to raw water, it is possible to perform flocculation treatment of raw water and reduce the amount of flocculant used. This can be reduced. [Example] The present invention will be explained in more detail below by giving examples and reference examples. Example 1 According to the method of the present invention, wastewater was treated in a batch process. {11 The type and quality of raw water treated and the treatment procedure are as follows. Type: Dishwashing detergent manufacturing wastewater (contains anionic surfactant and fatty acid soda as main components, and some nonionic surfactant) Water quality: pH 6.5 CODMn-510PPffl CODcr”1 420ppm (I ) MgSO+ 300ppm (Mg conversion), Fe104 200ppm (Fe conversion) and polymer decomposition product (polyacrylamide hydrolyzate) 2p in raw water
pm was added and flocculation treatment was performed with PHII. (■) The flocculation treatment liquid was concentrated to 20% (volume), and the separated water was discharged as treated water. (III) Add H2S04 to the entire amount of the thickened sludge from (II) to adjust the pH to 3, and at the same time adjust the pH to 3.
0000pPtn (to sludge) was added and reacted for 3 hours to decompose organic matter. (IT) Sludge treated with decomposition of organic matter was mixed with raw water and subjected to flocculation treatment at pH 11. (in this case,
M g SO 4 and FeSO+ were not added.
) The flocculation treatment solution was treated in the order of (II), (Iwata!), and (TV) above. Below, (II), (III),
(rV) operation was repeated. Table 1 shows the quality of the treated water obtained for each patch. Table 1 Note that since signs of deterioration in the flocculation of raw water appeared in the fourth sludge circulation (batch shift .5), in the fifth sludge circulation m (batch ~.6), mixing of raw water and circulating sludge was carried out. MgSO in water
+100 PPnl was added, and all of the generated sludge was extracted without oxidative decomposition treatment. Example 2 The following raw water was used, and steps (1) to (r
V), except that the processing conditions were changed as shown below.
Wastewater was treated in the same manner as in Example 1. Soil type: Dyeing factory general wastewater purchase: pHm8.0 CODMj1-66ppm CODc, 157ppm Appearance: Reddish brown Process (I): MgSO4 chemical injection amount 500ppm (Mg conversion) F6150411 injection amount 1 20 Gl pm (F 6 conversion) process (■):
The amount of sludge produced relative to raw water is shown in Table 2. All sludge is sent to the process (!!). Step (IV): H20a chemical injection amount - 3400 ppm (relative to sludge) The quality of the treated water obtained for each batch is shown in Table 2. As is clear from Table 2, the fourth sludge circulation (Batch work.5), the flocculation was also very good, and high quality men's water was obtained.In addition, the produced sludge obtained in Patch cell.1 and the 4th sludge circulation (Batch work. COD In% CODcr of the oxidized decomposition treated liquid obtained in Step 5)
were as shown in Table 3 below. In addition, the amount of oxidized decomposition treated liquid obtained in the fourth sludge circulation (to batch .5) was 12VO% relative to the raw water. Table 3 From these results, the following is clear. CODM of sludge generated in this example! 1 and C O D C
The rNO decomposition rate is the sludge (CO
DMj1-770ppm%CODcr snow 996ppm)
The final oxidative decomposition treatment solution for 5 batches of CODM II ■ 315ppm% CODc, m362
Since it is ppm, COD decomposition rate: 770x 5-315 x10o, 9,896770X
5 CODC, decomposition rate: 996x 5-362 x 100,,,,,996XS, all of which are extremely high at over 90%. Moreover, in this example, the amount of sludge finally produced was 12 voj of the raw water of the 5th batch! %, and is approximately 1/5 of the amount of sludge produced (sum of sludge amounts shown in Table 2) when the sludge generated in each batch is discharged without any treatment.
(=127 (10+10+11+11+10)). Reference Example 1 The wastewater used as raw water in Example 1 was subjected to Fe salt flocculation or Mg salt flocculation under the conditions shown in Table 4, and the quality of the resulting treated water and the amount of sludge produced (volume ratio to raw water) were 4
It is shown in the table. Table 4 shows. Table 5 *Optimum conditions for Fe salt flocculation From the results in Table 4, for the wastewater used in Example 1,
It is clear that Mg salt aggregation has a higher aggregation efficiency than Fe salt AX, and better results can be obtained. Reference Example 2 The wastewater used as the raw water in Example 2 was subjected to Fe salt coagulation or Mg salt coagulation under the conditions shown in Table 5, and the water quality and appearance of the resulting treated water are shown in Table 5. From the results, it is clear that even for the wastewater used in Example 2, Mg salt 81& has a higher aX efficiency than Fe salt coagulation, and good results can be obtained. [Effects of the invention] As detailed above, according to the wastewater treatment method of the present invention, ■ The amount of magnesium compound used as a flocculant is significantly reduced to, for example, 1/4 to 1/5 of the conventional method. It will be done. ■ The amount of iron salt required for oxidative decomposition of sludge is also relatively small. ■ The amount of sludge generated is significantly reduced. Therefore, the amount of sludge to be disposed of is reduced. It is said that the effects of this method are profound, and it is possible to treat wastewater efficiently at low cost.

[Brief explanation of drawings]

Figure 1 shows the fiF of the wastewater of the present invention! It is a system diagram showing an example of the method. 1... Coagulation, 2... Sedimentation tank, 3... Oxidation decomposition tank.

Claims (1)

[Claims] (1) Adding a magnesium compound to raw organic wastewater,
In a wastewater treatment method in which a suspension obtained by adjusting the pH to 10 to 14 is separated into treated water and precipitated sludge by solid-liquid separation, hydrogen peroxide is added to the precipitated sludge in the coexistence of iron salt, and the pH 4 or less to oxidize and decompose the settled sludge,
A wastewater treatment method characterized by adding the obtained decomposition product to raw water.