JPS62152597A - Waste water treatment - Google Patents

Abstract

PURPOSE:To separate treatment water at a high rate of separation by mixing surplus sludge consisting of Ca and Ng carbonate and activated sludge with waste water containing said component, turning the same into soluble salt and treating a treatment liquid biologically. CONSTITUTION:Surplus sludge consisting of CaCO3 and MLSS and Ca(OH)2 as neutralizing agent are added and mixed with HNO3 waste water. By the reaction, Ca content generates CO2 and is solved into the liquid, and only MLSS is separated and removed as solid content during solid-liquid separation process. The separation liquid is led to the denitration process of biological treatment, and denitrated in the presence of CaCO3, MLSS and hydrogen donor of slightly more than theoretical amount. Then, NO3 and organic substances are cracked biologically to generate CO2 and N2, and Ca content is separated out as CaCO3. The liquid after treatment is exposed to air and released after separating from solid content. By said process, energy saving is achieved.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to a wastewater treatment method including biological treatment used to purify acid wastewater containing nitric acid or organic acids, general organic matter-containing wastewater, etc. .

(Prior art and its problems) In recent years, a large amount of highly concentrated nitric acid-containing wastewater has been produced from various denitrification devices such as stainless steel and silicon etching processes and flue gas denitrification. However, since no effective treatment method has been established to independently purify nitric acid-containing wastewater that is satisfactory in terms of processing efficiency, equipment, and operating costs, it is not possible to treat wastewater that contains nitric acid by simply performing neutralization treatment. Currently, it is uniformly treated by mixing it with pond wastewater, and nutrient enrichment due to nitrogen in the treated water and salt pollution have become major problems.

On the other hand, in the case of ordinary organic wastewater such as sewage or wastewater containing organic acids, 801) is generally removed by biological treatment using activated teta mud under aerobic conditions.

However, in this type of aerobic biological treatment, since the rate-limiting element supply is rate-limiting, there is a limit to high-load operation aimed at increasing the concentration of activated sludge due to the aeration rate, and the sludge concentration is high. This poses a problem in that swelling phenomena such as bulking are likely to occur.

Means for Solving Problem C) This invention was made in view of the above circumstances, and enables good denitrification and desalination of nitric acid-containing wastewater (hereinafter referred to as HNO3 wastewater) by biological treatment. It is possible to perform high-load operation under high sludge concentration of organic matter-containing wastewater and organic acid-containing wastewater (hereinafter referred to as organic matter wastewater and organic acid wastewater), and it is also possible to perform efficient combined treatment of these wastewaters. The purpose is to provide a wastewater treatment method with low treatment cost.

That is, the wastewater treatment method according to the present invention, for the above purpose, includes a dissolving step of mixing excess sludge consisting of Ca or Mg carbonate and activated sludge with acid component-containing wastewater to dissolve Ca or Mg as a soluble salt. , a solid-liquid separation step in which the activated sludge is separated and removed after this dissolution, and a biological treatment in which the separated liquid is biologically treated in the presence of the carbonate and activated sludge, and the carbonate is produced as a by-product from the soluble salt. a solid-liquid separation step for separating treated water after biological treatment from the carbonate and activated sludge, and a return step for sending the separated excess sludge to the dissolution step.

(Action of the Invention) The biological treatment in this invention is carried out in the presence of Ca or Mg carbonate and activated sludge (hereinafter referred to as MLSS).

In other words, the above-mentioned carbonate functions as a biological carrier of MLSS, and since the biota of MLSS develops on the particle surface of the carbonate, MLSS can be maintained at a high level in the biological treatment process, and as a result, high-load operation of organic matter is possible. Furthermore, since it has excellent sedimentation properties, it does not cause swelling phenomena such as bulking even with high concentration MLSS, and the treated water can be separated with high efficiency in the solid-liquid separation process.

In addition, by adding and mixing excess sludge after solid-liquid separation to acid component-containing wastewater, Ca or ? Since 1 g is dissolved as a soluble salt and transferred to the liquid phase side, surplus MLSS corresponding to proliferated bone can be removed by solid-liquid separation after this dissolution. Since the above-mentioned soluble salts are automatically converted into carbonates in the biological treatment process, the Ca or Mg content can be recycled and reused except for a small amount that is eluted and lost in the effluent treatment water due to its solubility. Ru.

Ca or Mg carbonate in the initial biological treatment process is automatically produced as a by-product during biological treatment from Ca or Mg by using Ca or Mg hydroxide as a neutralizing agent for wastewater containing acid components. . Therefore, after the ratio of carbonate to MLSS reaches equilibrium in the biological treatment process, the amount of neutralizing agent used will be reduced by the amount of Ca escaping into the effluent treated water.
Alternatively, a small amount of addition corresponding to the Mg content is sufficient. In addition, in this treatment method, even if the acid concentration of the wastewater is high, that is, the pH is low, when it is introduced into the biological treatment process, it is neutralized by the carbonates that are present in large quantities in the process, so there is no problem with the treatment. There is no problem.

Here, the concentration ratio of the carbonate and MLSS at equilibrium in the biological treatment process is regulated by the sludge conversion rate of the carbonate and organic matter. : CaCO3#1:
10 (weight ratio). In the case of this concentration ratio, the MLSS is 10,000 to 13. OOO+w/
1 When operating at 2, the total solid content <SS> is 110.0
Although the concentration reached 00 to 143.000 ■/l, no swelling of the sludge was observed, and it was found that the SvI was always below 0.00 - 143.000 ■/l, indicating that CaCO3 functions very effectively as a biological carrier. This has been proven.

The wastewater to be treated in this invention is HNO3 wastewater,
Acid wastewater containing other acid components along with HNO3, organic acid wastewater,
Various types of wastewater such as general organic wastewater can be mentioned, but in the case of organic wastewater that does not contain acid components, excess sludge containing Ca or M
What is necessary is to combine the wastewater with acid component-containing wastewater that dissolves the acid component.

As biological treatment, existing treatment methods such as denitrification treatment, nitrification-denitrification treatment, aerobic biological treatment, and combinations thereof can be selected depending on the type of wastewater, but treatment means that include denitrification treatment are particularly useful. It is. In other words, denitrification treatment has the advantage of higher organic matter decomposition ability than aerobic biological treatment, and this advantage is further enhanced by increasing the concentration of MLSS using carbonate as a biological carrier. Even in the case of organic acid wastewater or general organic wastewater that does not contain HNO3, highly efficient BOD removal is possible by combining it with HNO3 wastewater and subjecting it to denitration treatment. In addition,
After this denitrification treatment, it is preferable to perform aerobic biological treatment to decompose residual organic matter such as residual hydrogen donors.
Since the residual organic matter in this case is extremely small, the amount of aeration may be small.

(Example) Hereinafter, an example of the present invention will be described based on process diagrams shown in FIGS. 1 and 2. In addition, in the following, the carbonate in the biological treatment process may be a force side gco3 represented by CaCO3.

Figure 1 shows the treatment process for HNO3 wastewater. First, HNO3
In the wastewater dissolution process, surplus sludge consisting of CaCO3 and MLSS and a small amount of Ca (01(
) 2 is added and mixed. At this time, CaC0+ +2H
NO3→Ca (NO3) 2 + N20 +CO2
↑Ca (OH) 2 +2HNO3Ca (NO3
) 2 +2H20 reaction, Ca content is dissolved in the liquid with the generation of CO2, so in the next solid-liquid separation step, only MLSS is separated and removed as a solid content. This separated liquid is then led to the denitrification step of biological treatment to remove CaC.
In the presence of O3, MLSS, and a hydrogen donor a little higher than the theory, the mixture is denitrified by stirring for a required period of time under non-molecular oxygen conditions (closed). The reaction in this case is 8Ca
(NO3) 2 + 5 (CH3COO) 2 C
a -1→13CaCO3+ 15H20+ 7CO2
It is shown as ↑ +8N2↑, and NO3- and organic matter are biologically decomposed to generate CO2 and N2, and Ca content is precipitated as CaCO3.

As this hydrogen donor, in addition to CH3CO0H, CH3
Although 0H etc. are used, other wastewater BOD substances may also be used. That is, by introducing organic acid wastewater or general organic wastewater into the denitration process, the organic substances act as hydrogen donors and are decomposed, making it possible to combine HNO3 wastewater and these wastewaters.

The liquid after the above-mentioned denitrification treatment is led to an aerobic biological treatment step, and the residual hydrogen donor is biologically decomposed by aeration. The liquid after this biological treatment is converted into CaCO in a solid-liquid separation process.
The solid content consisting of 3 and MLSS is separated from the treated water, and the excess sludge corresponding to growth is returned to the dissolution process, and the treated water is almost completely denitrified.

Since it has been desalinated and the BOD is close to O, it can be discharged.

Figure 2 shows the treatment process for organic acid wastewater. First, surplus sludge and a small amount of Ca (OH) 2 are added and mixed to the wastewater in the dissolution process, similar to HNO3 wastewater, and the Ca content is changed to CO2.
It is dissolved as an organic acid Ca salt with the generation of .

In the next solid-liquid separation step, only the MLSS is separated and removed, and the separated liquid is led to the denitrification step of biological treatment. Since HNO3 wastewater is introduced into this denitrification process, Ca
Organic acid radicals and NO
3- is decomposed to generate CO2 and N2, and
Ca content precipitates as CaCO3.

Next, in an aerobic treatment step, the remaining organic acid Ca salt is biologically decomposed and the Ca content is precipitated as CaCO3. The liquid after biological treatment is separated into effluent treated water and solids by solid-liquid separation, and excess sludge is returned to the dissolution process.

In addition, in the treatment of this organic acid wastewater, instead of performing the above-mentioned denitrification treatment as biological treatment, aerobic biological treatment may be performed as shown within the dashed-dotted line in Figure 2. Even in the conventional treatment, the organic acid Ca salt is decomposed and the Ca content is precipitated as CaCO3, and the excess sludge obtained in the subsequent solid-liquid separation is returned to the dissolution step. However, if the organic acid concentration is high, biological treatment including the above-mentioned denitrification treatment is preferable.

(Processing test example) Test example l The treatment effect of HNO3 wastewater was investigated under the following conditions.

Biological treatment tank> A transparent PVC container measuring 30 x 30 x 30 cm with a canopy, a stirrer, and an aeration pipe, and the effective volume is 17 cm.
e0kuhara water) Calcium nitrate (Ca (NO3) 2 ・4H20
.

Special grade product] was dissolved in pure water to give a concentration of 132.250 s/1 as Ca (NOs) 2, and 340 m
j! is separated and CH3C0OH as a hydrogen donor is converted into N
Add in an amount such that the weight ratio with O3- is 1:1, then add nutrients, and finally add pure water to make the total amount 34001a 1
And so.

Activated sludge〉 Using MLSS obtained from a sewage treatment plant, an acclimatization test was conducted over a long period of time, and the concentration of l'1Lss and CaCO3 reached equilibrium (in the measurement results, the weight ratio of SS: CaC0+ = l:10). thing.

<Treatment operation) Approximately 4000ml of the supernatant of the biological treatment tank in which the activated sludge (MLSS + CaCO3) has settled was extracted, and 340ml of raw water was extracted.
0w Il was introduced, and the total amount was made up to ill by adding the supernatant liquid extracted above. In addition, the MLSS concentration is 10,000+w/j! It is. Subsequently, a stirrer was rotated under closed conditions to perform denitrification treatment, followed by aeration to treat undecomposed material under aerobic conditions, and then left to stand to perform solid-liquid separation. Thereafter, the above steps were repeated at a treatment cycle of 24 hours/day.

The end point of the denitrification process was detected from the change in the oxidation-reduction potential, and the time required for denitrification was estimated to be 6.
It turned out that it was time.

Also, the SVI was always below Da.

The results of the above treatment are shown in Table 1. Also, NO3-concentration, NO2-concentration, BOD, , Con in each treatment cycle.

The average value of the change in the oxidation-reduction potential (ORP) over time is shown in FIG. Note that t in FIG. 3 is the time point at which aeration starts. Moreover, the BOD of the treated water was almost 0.

Table 1 (*) Electrical conductivity is the value at infinite dilution for raw water, and the actual value for treated water. In addition, N03- and CaCO3 of the treated water
The electrical conductivity calculated from is 255μ37G,
The difference from this theoretical value of 295 μ/mouth is due to the nutritional supplement.

From this test result, it was found that by applying the method of this invention, 1(N
It can be seen that the O3 wastewater is highly denitrified and desalted. Furthermore, since the ability to decompose CH3C001 by denitrification treatment is extremely large, it is clear that a high degree of combined treatment becomes possible by introducing general organic wastewater or organic acid wastewater in place of CH3CO0H.

Test Example 2 Acid wastewater (IF,
At present, HNO3, CH3CO0H) is neutralized with slaked lime, F- ions are removed as poorly soluble CaF2 by solid-liquid separation, and separated liquid (Ca(NO3) 2
, (CH3COO) 2 Ca] is mixed with other wastewater for treatment.

Here, a two-month continuous treatment experiment was conducted in the same manner as in Test Example 1, using the mixed wastewater as the treatment target. The results are shown in Table 2.

Table 2 In addition, in order to increase the applicability in the case of directly treating the acid wastewater, the same activated sludge (MLSS + C
aC03) was added to adjust the pH to 6, and the F- ion in the treated supernatant was measured and found to be 5.7 F/1. As a result, it was demonstrated that there is no problem in directly treating the acid waste water using the method of the present invention.

(Effects of the Invention) According to the wastewater treatment method of the present invention, activated sludge in the biological treatment process maintains a high concentration of Ca or Mg carbonate as a by-product as a biological carrier, so operation with a high load of organic matter is possible. , HNO3 wastewater, organic acid wastewater,
It is possible to efficiently purify various kinds of wastewater, such as general wastewater, and it is also possible to process these wastewaters in combination1.In addition, compared to conventional methods, the above-mentioned high-load operation reduces equipment and electricity/!
! The amount of neutralizing agent used can be greatly reduced, and the amount of neutralizing agent used can be significantly reduced because the above-mentioned by-product carbonate is reused and elution of Ca or Mg into the treated water is extremely small. Excellent denitrification and desalination effects are achieved.

[Brief explanation of drawings]

FIGS. 1 and 2 are process diagrams showing an example of the wastewater treatment method according to the present invention, and FIG. 3 is a characteristic diagram showing changes over time in various treatment indicators in treatment test example 1. Applicant Naigai Chemical Products Co., Ltd. Figure 1

Claims (1)

[Claims] 1. A dissolution step of mixing excess sludge consisting of Ca or Mg carbonate and activated sludge with acid component-containing wastewater to dissolve Ca or Mg as a soluble salt; and after this dissolution, activated sludge is dissolved. a solid-liquid separation step for separating and removing; a biological treatment step for biologically treating the separated liquid in the presence of the carbonate and activated sludge; and a biological treatment step for producing the carbonate as a by-product from the soluble salt; A wastewater treatment method comprising: a solid-liquid separation step for separating treated water from the carbonate and activated sludge; and a return step for sending the separated excess sludge to the dissolution step. 2. The wastewater treatment method according to claim 1, wherein the acid component-containing wastewater is nitric acid-containing wastewater, and the biological treatment step includes biological denitrification treatment.