JP2618164B2 - Conditioning and propagation of sulfur oxidizing bacteria by addition of inorganic coagulant and biological treatment of wastewater containing reducing sulfur compounds - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to biological treatment of wastewater,
More particularly, the present invention relates to a method of rapidly acclimating and growing a sulfur-oxidizing bacterium suitable for treating wastewater containing a reducing sulfur compound, and a biological treatment method of wastewater containing a reducing sulfur compound.

[0002]

2. Description of the Related Art Wastewater containing reducing sulfur compounds is generated from the photographic industry, petroleum refining industry, chemical industry, metal refining industry, mines, etc., and the reducing sulfur compounds contained in these wastewaters are sulfides. (S ²⁻ ), thiosulfate compound (S
₂ O ₃ ²⁻ ), polythionic acid compound (S ₃ O ₆ ²⁻ ), etc., and the wastewater containing these reducing sulfur compounds has a COD (chemical oxygen demand) due to the reducing sulfur compounds. It is expensive and cannot be released to public water bodies.

[0003] As a method of treating wastewater containing this reducing sulfur compound, a method of oxidizing the reducing sulfur compound using an oxidizing agent such as sodium hypochlorite is known.

[0004] Instead of chemical methods, reducing sulfur compounds are oxidized by microorganisms, so-called sulfur-oxidizing bacteria, to reduce CO2.
There is a method of removing D.

[0005] For example, there are methods described in JP-A-56-67589, JP-A-57-4296, and JP-A-3-296497.

[0006] The method described in JP-A-56-67589 is
Factory wastewater containing S ₂ O ₃ ²⁻ , S ₃ O ₆ ²⁻ , S ₄ O ₈ ²⁻ or similar polythionic acid, household septic tank drainage, sewage treatment plant aeration tank water, or metal mine This is a method in which one or more of wastewater is added and oxygen is blown in to oxidize the sulfur compound to sulfuric acid to remove COD in the wastewater.

The method described in JP-A-57-4296 is
Gypsum generated when removing COD in various wastewaters caused by thiosulfuric acid, polythionic acid, dithionic acid or similar sulfur oxides is used as a carrier substance for sulfur-oxidizing bacteria, and bacteria grown and cultured at the same time are treated with the gypsum. This is a method of removing COD in wastewater biologically by repeatedly using it after adsorbing it and concentrating it.

It is well known that there are many types of sulfur-oxidizing bacteria which decompose thiocyanate and thiosulfate in sewage or human waste sludge, metal mine wastewater, etc., as disclosed in JP-A-56-67589. As described in the Examples and the like of these specifications, the sulfur-oxidizing bacteria described in Japanese Utility Model Laid-Open No. 57-4296 have thiosulfate, polythioic acid, Dithionic acid or a similar sulfur oxide is oxidized to sulfuric acid to remove COD from wastewater. Sulfur-oxidizing bacteria living or active at such a low pH are described in a compendium (for example, “Autotrophic Bacteria” published by Kazunori Imai, pages 63 to 67), and are sulfur-oxidizing bacteria belonging to the genus Thiobacillus. It is estimated to be.

In the method described in JP-A-3-296497, blast furnace slag immersion water is supplied into a tank containing activated sludge containing sulfur bacteria, and at this time, the pH of the tank containing activated sludge containing sulfur bacteria is adjusted. This is a method of biologically treating COD of blast furnace slag immersion water under aerobic conditions while maintaining the COD at 4 to 5.

Next, an oxidation-reduction potential (OR) is used as an index for blowing oxygen gas when treating wastewater containing sulfur compounds.
A method using P) is known from JP-A-58-122093.

That is, this method comprises contacting a wastewater containing sulfides such as sodium sulfide and / or sodium hydrosulfide with a gas containing molecular oxygen or hydrogen peroxide to form sodium sulfide and / or hydrosulfide in wastewater. After soda is converted to sodium thiosulfate and then subjected to microbial treatment with white sulfur bacteria, the sodium sulfide and / or sodium hydrosulfide in the wastewater is brought into contact with a gas containing molecular oxygen or hydrogen peroxide, and the sulfuric acid in the wastewater is removed. In the process of chemically oxidizing soda and / or sodium hydrosulfide to sodium thiosulfate, contains molecular oxygen until the ORP becomes -550 mV or more (reference electrode unknown), preferably -500 mV (reference electrode unknown) or more. To supply gas or hydrogen peroxide.

In this method, air or the like is not aerated using ORP as an index at the stage of biological treatment using white sulfur bacteria as in the present invention.

[0013] As in the present invention, an inorganic coagulant is added to improve the cohesiveness and sedimentation of sulfur oxidizing bacteria, suppress the outflow into treated water, and reduce the concentration of sulfur oxidizing bacteria in the aeration tank. There is no known way to enhance it.

[0014]

The conventional method of oxidizing a reducing sulfur compound using an oxidizing agent such as sodium hypochlorite and treating it is not stable because the treatment technology is not sufficiently established. And a fatal disadvantage of high processing cost.

Further, the conventional biological treatment method for wastewater containing sulfur compounds uses a low-pH living or active sulfur-oxidizing bacterium, which complicates the treatment process.
There is a disadvantage that the running cost and the equipment cost of the processing are increased because the processing equipment is also made to have the acid resistance specification.

When treating an alkaline wastewater containing a reducing sulfur compound with a sulfur oxidizing bacterium which lives or is active at such a low pH, for example, a method described in JP-A-57-4296 is used. When treating blast furnace slag immersion water having a high pH, it is necessary to maintain the pH of the aeration tank where low-pH live or active sulfur-oxidizing bacteria are present, at a pH suitable for the sulfur-oxidizing bacteria. Adjust pH of alkaline wastewater to pH suitable for sulfur oxidizing bacteria
If the pH of the treated water is as low as 1.9 to 2.0, it is necessary to adjust the pH again in order to discharge this into public waters. There is a problem that the cost of chemicals and the like is considerably high.

Furthermore, when sulfur-oxidizing bacteria living or active at such a low pH are used for wastewater treatment, it is necessary to make the wastewater treatment equipment acid-resistant, and the construction cost of the wastewater treatment equipment is extremely high. There are fatal drawbacks.

Even if wastewater treatment with sulfur-oxidizing bacteria is carried out at a pH around neutrality, since the index of the amount of aeration in the biological treatment process is not clear, the treatment time becomes extremely long, and the treatment equipment becomes large. There are drawbacks.

For example, in the method described in JP-A-3-296497, as described in the examples, an index of the amount of air to be blown into the biological reaction tank in which sulfur bacteria are present is determined without any measure, and is only 5 m ³ /. Minutes and constant.

For this reason, there is a problem that the processing time is extremely long, about 40 hours, the processing equipment becomes extremely large, and the construction cost of the processing equipment is enormous.

In the case of biologically treating wastewater containing a reducing sulfur compound using conventional sulfur-oxidizing bacteria, an index of the amount of air to be blown into the biological reaction tank is not determined at all. There is a problem.

For example, when the amount of aeration is insufficient, there is a concern that the oxidation of the reducing sulfur compound is insufficient, and the unreacted reducing sulfur compound flows into the treated water, thereby increasing the COD of the treated water.

If the amount of aeration is excessive, the flocs of the sulfur-oxidizing bacteria in the aeration tank are mechanically destroyed, so that the sulfur-oxidizing bacteria flow into the treated water, and the concentration of the sulfur-oxidizing bacteria in the aeration tank decreases. There is a problem that the treatment water quality is deteriorated.

Further, since the sulfur-oxidizing bacteria have a low growth rate and are poor in cohesiveness, the sulfur-oxidizing bacteria in the aeration tank cannot be maintained at a high concentration, so that a treatment with high efficiency and excellent treatment performance can be performed. There is a problem that can not be.

That is, as a specific problem of the sulfur oxidizing bacteria, the sulfur oxidizing bacteria oxidize the reducing sulfur compound and fix the carbon dioxide in the air used for the aeration using the oxidation energy. Cell synthesis and proliferation
The growth rate is extremely slow, and autotrophic bacteria such as sulfur-oxidizing bacteria do not produce high molecular compounds such as sugars and proteins that have aggregating action because they do not use organic matter as a nutrient source. There is little nature.

Sulfur-oxidizing bacteria have a low growth rate and poor cohesiveness, so they are easily fragmented by aeration in an aeration tank.
For this reason, the sulfur oxidizing bacteria easily flow into the treated water in the sludge sedimentation tank, the sulfur oxidizing bacteria in the aeration tank cannot be maintained at a high concentration, and it is difficult to perform high-efficiency treatment or excellent treatment of the treated water quality.

[0027]

SUMMARY OF THE INVENTION The gist of the present invention is to provide (1) a mixed liquid of activated sludge such as sewage and industrial wastewater in an aeration tank of an apparatus for biologically treating wastewater containing a reducing sulfur compound. And a wastewater containing a reducing sulfur compound and an inorganic coagulant are supplied to the aeration tank, and the amount of change in free energy when the reducing sulfur compound contained in the wastewater is chemically oxidized to a sulfuric acid compound (ΔG ₀ ) to control and control the aeration of the aeration tank using the oxidation-reduction potential (ORP) obtained by calculation as an index, and to control and control the pH of the aeration tank within a range of 4.0 to 7.5. Characterized by the sewage and industrial wastewater activated sludge oxidizing reducible sulfur compounds in the sludge oxidizing bacteria acclimation and propagation method,

(2) Acclimation according to the method described in the above (1)
A wastewater containing a reducing sulfur compound is supplied to an aeration tank in which microorganisms that oxidize the grown reducing sulfur compound are present, and the aeration of the aeration tank is controlled so that the ORP value obtained by the method (1) can be maintained. A biological treatment method for wastewater containing a reducing sulfur compound, wherein the method comprises controlling and controlling and controlling the pH of the aeration tank within a range of 4.0 to 7.5;

(3) The method according to (1) or (2), wherein iron chloride is supplied as an inorganic coagulant. Biological treatment of wastewater,

(4) The wastewater containing a reducing sulfur compound as described in the above (1), (2) or (3) is a wastewater resulting from slag generated when refining metal from ore. Biological treatment method of wastewater containing the method of acclimation and propagation of sulfur oxidizing bacteria or reducing sulfur compounds,

(5) The wastewater containing a reducing sulfur compound according to (1), (2) or (3) is wastewater originating from blast furnace slag generated from a blast furnace at a steelworks. Biological treatment method of wastewater containing a method of acclimation and propagation of sulfur-oxidizing bacteria or reducing sulfur compounds,

(6) In the method according to the above (5),
Iron chloride is supplied as an inorganic coagulant, aeration is performed so that the ORP of the aeration tank becomes 0 to +150 mV (based on silver / silver chloride electrode), and the pH of the aeration tank is adjusted to 5.0 to 7.0. A method of acclimating and growing sulfur-oxidizing bacteria or a method of biologically treating wastewater containing a reducing sulfur compound, characterized by being controlled and controlled within a range.

[0033]

The present inventors have found that activated sludge treating sewage and industrial wastewater inhabits sulfur-oxidizing bacteria that oxidize reducible sulfur compounds at pH 4.0 to 7.5. .

That is, as shown in the treatment flow of the present invention in FIG. 1, according to the present invention, the activated sludge is pH 4.0 from these activated sludges by the method of acclimating and growing the sulfur-oxidizing bacteria of the present invention described below.
-7.5, sulfur oxidizing bacteria are preferentially adapted and proliferated, and waste water containing a reducing sulfur compound is continuously treated using the sulfur oxidizing bacteria.

First, a method for promoting the adaptation and growth of sulfur-oxidizing bacteria which oxidize reducing sulfur compounds at pH 4.0 to 7.5 will be described.

First, assuming a reaction in which a reducing sulfur compound is chemically oxidized to a sulfuric acid compound, the amount of change in free energy in this reaction is determined from a handbook, a textbook, a literature, and the like.
Next, an oxidation-reduction potential (ORP) for causing these reactions is obtained by calculation from the amount of change in free energy.

Next, the activated sludge mixed solution collected from the aeration tank of the activated sludge treatment apparatus for treating sewage or industrial wastewater is put into the aeration tank (3) of the ORP control activated sludge treatment apparatus shown in FIG. The ORP value of the aeration tank (3) is changed from 0 mV to the range of the ORP value calculated from the amount of change in free energy when it is assumed that the reducing sulfur compound contained in the wastewater has caused an oxidation reaction, for example, When the reducing sulfur compound is a thiosulfate compound, 0 to +150 mV (Ag / Ag
(Based on Cl electrode).

According to the research by the inventors, this is not to say that in the case of a biological reaction, for example, a reaction in which a reducible sulfur compound is oxidized to sulfuric acid does not occur unless a calculated ORP value is obtained. Although the reducing sulfur compound is not completely oxidized in a place lower than the calculated ORP value, the oxidation reaction occurs at a considerably high oxidation rate, and the closer to the calculated ORP value, the higher the oxidation rate becomes. It is based on the observation that the oxidation rate reaches 100% when calculated.

For example, when treating wastewater containing a thiosulfate compound, the calculated ORP value is about +150 mV, but the lower limit of the ORP functioning as wastewater treatment is about 0 mV experimentally.

Therefore, when biologically treating wastewater containing a thiosulfate compound, the ORP control of the aeration tank requires 0 to +
A range of 150 mV is preferred.

When biologically treating wastewater containing a plurality of reducing sulfur compounds, the ORP control value of the aeration tank is:
What is necessary is just to set to the ORP in which an oxidation reaction occurs highest among the reducing sulfur compounds.

For example, in the case of wastewater containing a thiosulfate compound, a sulfide, a sulfite compound, etc., ORP in which an oxidation reaction occurs
Is the highest for the thiosulfate compound, so the ORP of the thiosulfate compound, specifically 0 to +150 mV, may be set.

Since the oxidation rate of the reducing sulfur compound at this time is the highest, there is no point in setting the upper limit of the ORP to a higher value.

Wastewater containing a reducing sulfur compound such as a thiosulfate compound or a sulfide as a reducing sulfur compound is supplied to the aeration tank in which the ORP is set such that the treatment time is 8 hours.

At the beginning of the wastewater supply, the ORP does not rise to the set value, but gradually rises and rises to the set value in about 3 to 5 days, and the ORP control is performed.

The reducing sulfur compound of the treated water is OR
When P becomes about 0 mV or more, it is hardly detected, and the COD of the treated water is significantly reduced.

When ORP reaches 0 to +150 mV, 7
Processing time every 6 to 10 days → 6 hours → 3 hours → 3 hours → 2
Gradually increase the supply of wastewater so that it is time.

At this time, as the acclimation and growth of the sulfur-oxidizing bacteria progress, the oxidation of the reducing sulfur compound progresses to generate sulfuric acid, so that the pH of the aeration tank decreases, and if no measures are taken, Japanese Patent Application Laid-Open No. 56-59589. , As described in JP-A-57-4296.

The sulfur-oxidizing bacteria acclimated and grown in the state where the pH is lowered as described above are strongly acidic and active Thiobacs.
The genus illus becomes the priority species, causing the problems described above.

If the pH is 7.5 or more,
The ability of the grown sulfur oxidizing bacteria to oxidize reducing sulfur compounds such as thiosulfate compounds and sulfides is reduced, and these reducing sulfur compounds are detected in the treated water.

For this reason, the pH of the aeration tank is 4.0 to 7.0.
5, preferably controlled and controlled by an alkali agent so as to be in the range of 5.5 to 6.5.

When the pH of the aeration tank is controlled and controlled in this manner, sulfur-oxidizing bacteria that are active in the pH range of 4.0 to 7.5 and oxidize reducible sulfur compounds can be adapted and propagated.

At the same time, an inorganic coagulant, for example, iron chloride, polyaluminum chloride or the like, preferably iron chloride, is added to the aeration tank.

As described above, the sulfur-oxidizing bacteria oxidize the reducing sulfur compounds and use the oxidizing energy to immobilize the carbon dioxide in the air used for aeration and to synthesize and grow. , The growth rate is extremely slow,
Since no organic matter is used as a nutrient source, the production of high molecular weight saccharides and proteins having an aggregation effect is small.

Therefore, it is difficult to maintain the sulfur-oxidizing bacteria in the aeration tank at a high concentration by a usual method, and it is necessary to promote the adaptation and growth of the sulfur-oxidizing bacteria and to improve the cohesiveness.

The addition of an inorganic coagulant is effective for improving the cohesion of the sulfur-oxidizing bacteria. That is, when an inorganic coagulant, such as iron chloride, polyaluminum chloride (PAC), or polyiron, is added during the acclimation and growth of the sulfur-oxidizing bacteria, the flocculation of the sulfur-oxidizing bacteria is improved, and the flocculence of the large sulfur-oxidizing bacteria is improved. To form

As a result, the flocs of sulfur oxidizing bacteria in the aeration tank become less susceptible to breakage due to the aeration, and the sedimentation is improved, and the floating of the sulfur oxidizing bacteria into the treated water in the sludge settling tank is suppressed. For this reason, the sulfur-oxidizing bacteria can be maintained at a high concentration in a short period of time, and the quality of the treated water is improved because the sulfur-oxidizing bacteria do not flow into the treated water.

The inorganic coagulant to be added has a coagulation effect,
Considering costs and the like, iron chloride is optimal. In particular, iron chloride acts as an inorganic nutrient for sulfur-oxidizing bacteria, and the addition of iron chloride promotes the adaptation and growth of sulfur-oxidizing bacteria.

The amount of iron chloride to be added is optimally about 5 to 200 mg / l as iron per day in a warm air tank, and if it is less than this, there is almost no effect. Can not.

An organic polymer flocculant may be used in place of the inorganic flocculant. However, some of the polymer flocculants have toxicity that inhibits the function of sulfur-oxidizing bacteria. Therefore, it is necessary to select a non-toxic polymer-based flocculant.

Next, an aeration method which is an important element of the present invention will be described. In this wastewater treatment, the aeration to the aeration tank (3) is performed by an ORP sensor (gold-silver / silver chloride composite electrode) when the ORP of the warming tank (3) falls below a set value.
(10) is caught, the rotation speed of the roots blower (12) is increased by the ORP control device (11) to increase the amount of aeration, and when the set value is restored, the rotation speed of the roots blower (12) is reduced and the aeration amount is reduced. Is an ORP control by a proportional control method for reducing the power consumption.

The pH of the aeration tank (3) is adjusted to 4.0 to 4.0 by a pH sensor (8) and a pH controller (9).
It is controlled and controlled with an alkali agent and an acid so that the pH is in the range of 7.5, preferably 5.5 to 6.5.

In the present invention, if the sludge return rate from the sludge settling tank (5) to the aeration tank (3) is less than 20%, the sludge in the sludge settling tank cannot be sufficiently returned. Since the sludge concentration is low, the sludge return rate is optimally about 20 to 30% for efficient sludge return, and reducing sulfur compounds grow with the progress of continuous treatment of wastewater. Extract and dispose of the excess sludge as appropriate (14).

Next, the properties of the sulfur-oxidizing bacteria acclimated and grown by such a method will be described.

By the above method, sewage, industrial wastewater, gas wastewater generated from a coke oven of a steelworks, activated sludge of wastewater from each factory such as a fish processing factory, a photographic film factory, and an oil refinery factory, or Sulfur-oxidizing bacteria were acclimated and cultivated based on the above-mentioned method from sludge accumulated in a blast furnace slag storage site of a steelworks and sludge of wastewater of an old sulfur mine.

The activated sludge of this sulfur-oxidizing bacterium is inoculated in a liquid Starkey medium having a different pH, and the thiosulfate ion concentration of the Starkey medium is 2200 mg / l to 50 mg / l or less at 20 ° C. using a shaking incubator. Days were measured. FIG. 3 shows the result. The liquid S
The composition of the starkey medium is as follows.

Sodium thiosulfate: 5000 mg / l magnesium chloride: 100 mg / l potassium monophosphate: 3000 mg / l ammonium chloride: 100 mg / l calcium chloride: 250 mg / l pH: 2.0 to 10 .0

The above reagent was dissolved in 1 liter of a buffer solution of each pH to prepare a Starkey liquid medium having a different pH.

From the results shown in FIG. 3, p of the Starkey medium was
When H is in the range of 2 to 3.5 and 8.0 to 10, thiosulfate ions hardly decrease even after shaking for 20 days or more.
In the range of 4.0 to 7.5, the number of thiosulfate ions became 50 mg / l or less in 10 days or less at pH 5.0 to 6.5, especially at pH 5.0 to 6.5.

Therefore, the sulfur-oxidizing bacteria acclimated and cultured from the activated sludge of various wastewaters by the method of the present invention have a pH of 4.0.
It was found that the compound has the ability to oxidize reducible sulfur compounds in the range of -7.5.

This is the same as the D.C. shown in FIG. P. Kell
y and A. P. It is also evident by the Harrison classification, that is, according to their classification, the sulfur oxidizing bacteria active in the pH range of 4.0 to 7.5 that have been adapted and grown by the method of the present invention are classified into Group-2 and especially Kaisho 53-5
9254 and JP-A-56-67589 are active at pH 1.9 to 2.0.
(Title: Bergey '
s Manual of Systematic Ba
teriology Vol. 3, Author: James
T. Staley, Publisher: Williams &
Wilkins, description: page 1843, FIG. 2
0.47).

On the other hand, a conventional method of treating wastewater containing a reducing sulfur compound using a sulfur-oxidizing bacterium by a biological method, for example, JP-A-53-59254 and JP-A-56-59254
The sulfur-oxidizing bacteria used in the method described in -67589 oxidize reducing sulfur compounds at pH 1.9 to 2.0.

The sulfur-oxidizing bacteria acclimated and cultured by the method of the present invention do not have the ability to oxidize reducing sulfur compounds at such a low pH.

From this, it became clear that the sulfur oxidizing bacteria acclimated and cultured by the method of the present invention are different from the sulfur oxidizing bacteria used in the conventional wastewater treatment.

Next, promotion of adaptation and growth of sulfur oxidizing bacteria by addition of the inorganic coagulant of the present invention, for example, iron chloride, and increase in the concentration of sulfur oxidizing bacteria in the aeration tank will be described.

Without adding an inorganic coagulant such as iron chloride, PAC, or polyiron, or a carrier for immobilizing sulfur-oxidizing bacteria, and without controlling and controlling the ORP in the aeration tank,
Only control and management were performed to acclimate and multiply sulfur-oxidizing bacteria from activated sludge from sewage and industrial wastewater.

As a result, the pH 4 obtained by the method of the present invention was
Although active sulfur-oxidizing bacteria can be obtained at 7.5 to 7.5, it takes a long time of 10 to 30 days or more to acclimate and grow the sulfur-oxidizing bacteria, and wastewater containing a reducing sulfur compound is treated. In this case, the activated sludge concentration of sulfur oxidizing bacteria in the aeration tank gradually decreases, and after 3 to 6 months, it becomes 500 mg / l or less,
Oxidation of the reducing sulfur compound does not proceed, and eventually activated sludge treatment becomes impossible.

As described above, it took a long time to acclimate and multiply the sulfur-oxidizing bacteria because the inorganic flocculant such as iron chloride was not added, so that the flocs of the sulfur-oxidizing bacteria were broken as described above. This is because the water was divided into small pieces and discharged into treated water.

On the other hand, the method of the present invention, that is, the addition and addition of an inorganic coagulant, controls the ORP of the aeration tank and the pH control / management while acclimating and growing sulfur-oxidizing bacteria from activated sludge from sewage and industrial wastewater. By doing so, the period of acclimation and growth of sulfur oxidizing bacteria is significantly shortened as described in the examples, and the floc of activated sludge of sulfur oxidizing bacteria is less likely to be broken by aeration and sedimentation is improved. Therefore, there is no outflow to the treated water from the sludge settling tank.

As a result, the activated sludge of sulfur-oxidizing bacteria in the aeration tank can be maintained at a high concentration, and it is possible to treat wastewater containing a reducing sulfur compound with high efficiency and excellent treatment performance.

In particular, iron chloride acts as a nutrient salt for sulfur oxidizing bacteria in addition to the aggregating action, and the synergistic action thereof significantly shortens the period of acclimation and growth, and the concentration of sulfur oxidizing bacteria in the aeration tank. Is not expected to decrease.

[0082]

EXAMPLE 1 Next, the method of the present invention was carried out at a high concentration of a reducing sulfur compound such as a thiosulfate compound or a sulfide generated from a slag aging yard of a steelworks and a pH of 12-14. With high alkalinity and COD of 300-600
Drainage as high as mg / l (hereinafter referred to as blast furnace slag drainage)
An embodiment applied to the processing of (1) will be described.

Activated sludge mixture (activated sludge concentration: 1524 mg / l) in which the aeration tank (3) and the sludge settling tank (5) of the ORP control activated sludge treatment apparatus of FIG.
Insert

The ORP of the aeration tank (3) is increased by about +150 mV.
(Ag / AgCl electrode standard), and while controlling the pH to 6.0 to 6.5, aerated blast furnace slag drainage having a high pH of 13 to 14 showing one example of properties in Table 1. It supplies so that the residence time in tank (3) may be 8 hours.

At this time, a 38% aqueous solution of iron chloride was simultaneously added to the aeration tank as ferric ion in an amount of 50 mg / day to the aeration tank.
/ L. The sludge return rate from the sludge settling tank (5) to the aeration tank (3) is about 25%.

About 3 to 5 days after supplying the blast furnace slag wastewater, no thiosulfate compound or sulfide is detected in the treated water, and the COD decreases to about 50 mg / l.

Next, the processing time is set to 8 hours every 7 to 10 days →
When the time is reduced from 6 hours to 4 hours to 3 hours to 2 hours, the COD of the treated water is reduced to 10 mg / l or less, and the adaptation of the sulfur-oxidizing bacteria is completed in a short time.

Incidentally, reducing sulfur compounds such as thiosulfate compounds and sulfides are not detected in the treated water.

After the acclimatization of the sulfur-oxidizing bacteria is completed, the blast furnace slag wastewater can be supplied so that the treatment time is 2-3 hours, and the continuous treatment can be performed.

Sulfuric acid (10% sulfuric acid) used for controlling the pH of the aeration tank decreases in consumption as the acclimation of the sulfur-oxidizing bacteria progresses, and the acclimation of the sulfur-oxidizing bacteria is completed. At the stage of continuous processing, it is hardly consumed.

This is because reducing sulfur compounds such as thiosulfuric acid compounds and sulfides are oxidized to sulfuric acid, and the sulfuric acid can maintain the pH of the aeration tank at an appropriate value without adding an acid from outside. It is.

Table 1 shows examples of the water quality of the treated blast furnace slag wastewater, the treatment time during the acclimatization period of the sulfur-oxidizing bacteria, and the treated water quality when the continuous treatment was performed for 2 to 3 hours. Table 2 shows an example of the activated sludge concentration in the aeration tank.

As a result, in the treated water of the continuous treatment, reducing sulfur compounds such as thiosulfate compounds and sulfides were not detected,
Since the COD is 10 mg / l or less and the pH is 6.0 to 6.5, it can be discharged into public water bodies.

The activated sludge concentration of the sulfur oxidizing bacteria in the aeration tank was:
The initial activated sludge of the sewage is 1524 mg / l, and the acclimation period of the sulfur oxidizing bacteria, that is, 1280 mg when treated for 8 hours.
/ L, but then the growth period of sulfur oxidizing bacteria,
That is, during the period in which the treatment time is reduced from 8 hours to 6 hours to 4 hours to 3 hours to 2 hours every 7 to 10 days, the activated sludge concentration gradually increases, and sometimes increases to 2680 mg / l for 3 hours. Even if the blast furnace slag wastewater is continuously treated for 2 to 3 hours, the activated sludge concentration of the sulfur oxidizing bacteria does not decrease, and the excess sludge is extracted so that the activated sludge concentration in the aeration tank can be maintained at 2800 to 3200 mg / l. And managed.

[0095]

[Table 1]

[0096]

[Table 2]

In the method of the present invention, the acclimation of sulfur-oxidizing bacteria was completed in 3 to 5 days using blast-furnace slag wastewater from activated sludge which is treating sewage.

That is, it is considered that the acclimation of the sulfur oxidizing bacterium is completed when no reducing sulfur compounds such as thiosulfate compounds and sulfides are detected in the treated water. , Ie, the processing time is increased by 6
Every 7 days, the proliferation of sulfur-oxidizing bacteria was measured by sequentially shortening from 8 hours to 6 hours to 4 hours to 3 hours.

No reducing sulfur compound was detected in the treated water even during the growth period of the sulfur-oxidizing bacteria, and the COD was 10 mg / l.
The following conditions were favorable, and the activated sludge of sulfur-oxidizing bacteria in the aeration tank also grew smoothly.

After the completion of the growth of the sulfur-oxidizing bacteria, the blast furnace slag wastewater can be treated with a high efficiency treatment for a treatment time of 2 to 3 hours.
No reducing sulfur compounds were detected in the treated water, the COD of the treated water was as good as 10 mg / l or less, there was almost no outflow of the activated sludge of the sulfur-oxidizing bacteria, and the SS concentration of the treated water was all. It was 10-20 mg / l or less throughout the period.

Incidentally, without adding an inorganic coagulant such as iron chloride or an immobilizing carrier for sulfur-oxidizing bacteria,
When ORP control / management of the aeration tank was not performed and only pH control / management was performed, and the acclimation and propagation of the sulfur oxidizing bacteria from the activated sludge of the sewage were performed in the above-described manner, the pH 4 to 4 obtained by the method of the present invention was obtained. At 7.5 active sulfur-oxidizing bacteria were obtained.

However, it takes 10 to 30 days or more to acclimatize and multiply the sulfur-oxidizing bacteria, and when the wastewater containing the reducing sulfur compound is treated, the activity of the sulfur-oxidizing bacteria in the aeration tank is reduced. The sludge concentration gradually decreases and becomes 500 mg / l or less after 3 to 6 months, the oxidation of the reducing sulfur compound does not proceed, and finally the activated sludge treatment becomes impossible.

[0103]

EXAMPLE 2 The method of the present invention was carried out using sodium sulfite at a high concentration, an alkaline pH of 10 to 11, and COD.
An example in which the present invention is applied to the treatment of chemical plant wastewater as high as 500 to 800 mg / l will be described.

The activated sludge mixture (sludge concentration: 2000 to 3200 mg / l) collected from the aeration tank of the activated sludge treatment facility for treating the wastewater of this chemical factory is put into the aeration tank shown in FIG.

The ORP of the aeration tank (3) is set to about 0 to +50 mV.
(Ag / AgCl electrode standard), and after adjusting the pH of this wastewater to 8 to 8.5 in advance with sulfuric acid, while controlling the pH of the aeration tank to 6.0 to 6.5, Is supplied such that the residence time in the aeration tank is 8 hours.

At this time, polyaluminum chloride (P
200 mg of aqueous solution of AC) as aluminum ion
/ L to the aeration tank.

The sludge settling tank (5) to the aeration tank (3)
The return rate of sludge to the wastewater is about 25%.

About three to five days after supplying this wastewater,
Sodium sulfite is no longer detected in the treated water, and the COD drops to about 25 mg / l.

At this stage, the ORP of the aeration tank should be 0 to
It reached 50 mV, and ORP control became possible.

Next, the processing time is set to 8 hours every 7 to 10 days →
When the time is reduced from 6 hours to 4 hours to 3 hours to 2 hours, the COD of the treated water is reduced to 10 mg / l or less, and the adaptation of the sulfur-oxidizing bacteria is completed in a short time.

It should be noted that sodium sulfite is not detected in the treated water. When the acclimation of the sulfur-oxidizing bacteria is completed, the treatment time
The wastewater is supplied so that the treatment time is 3 hours, and the continuous treatment is performed.

According to the method of the present invention, sulfur-oxidizing bacteria which oxidize sodium sulfite can be adapted and propagated from activated sludge which is treating industrial wastewater using industrial wastewater containing sodium sulfite. The factory wastewater could be easily treated using oxidizing bacteria.

[0113]

According to the present invention, a reducing sulfur compound having a pH of 4.0 to 4.0 is obtained from activated sludge which is treating sewage and industrial wastewater.
The adaptation and growth of sulfur-oxidizing bacteria that oxidize around 7.5 were remarkably promoted, and the adaptation and growth of the sulfur-oxidizing bacteria could be performed in a short period of time.

Further, by using this sulfur-oxidizing bacterium, wastewater containing a reducing sulfur compound can be easily treated, and treatment equipment and treatment costs can be reduced.

[Brief description of the drawings]

FIG. 1 is a diagram showing a processing flow of the present invention.

FIG. 2 is an explanatory diagram of an example of an ORP-controlled activated sludge treatment apparatus used for treating wastewater containing a reducing sulfur compound using sulfur-oxidizing bacteria.

FIG. 3 is a graph showing the relationship between the thiosulfate ion oxidation rate (activity) and pH of sulfur-oxidizing bacteria acclimated by the method of the present invention.

FIG. 4 is a diagram showing classification of sulfur-oxidizing bacteria.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Wastewater tank 2 Wastewater supply pump 3 Aeration tank 4 Aerator tube 5 Sludge settling tank 6 Rake 7 Treated water 8 pH sensor 9 pH controller 10 ORP sensor 11 ORP controller 12 Roots blower 13 Sludge return pump 14 Excess sludge 15 Inorganic system coagulation Storage tank 16 Inorganic coagulant supply pump

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Kazuhisa Fukunaga 20-1 Shintomi, Futtsu City Nippon Steel Corporation Technology Development Division (56) References JP-A-2-268896 (JP, A) JP-A-4 −310296 (JP, A)

Claims (6)

(57) [Claims] 1. An activated sludge mixture such as sewage and industrial wastewater is put into an aeration tank of an apparatus for biologically treating wastewater containing a reducing sulfur compound, and the wastewater containing a reducing sulfur compound and inorganic waste are put into the aeration tank. An oxidation-reduction potential (ORP) calculated from the free energy change (ΔG ₀ ) when a reducing sulfur compound contained in wastewater is chemically oxidized to a sulfuric acid compound by supplying a system flocculant is used as an index. Reducing sulfur in the activated sludge of sewage and industrial effluent, characterized in that the aeration of the aeration tank is controlled and controlled, and the pH of the aeration tank is controlled and controlled within the range of 4.0 to 7.5. A method of acclimating and growing sulfur-oxidizing bacteria that oxidize compounds. 2. A wastewater containing a reducing sulfur compound is supplied to an aeration tank in which microorganisms that oxidize a reducing sulfur compound acclimated and grown by the method according to claim 1 are present, and obtained by the method according to claim 1. The aeration of the aeration tank is controlled and controlled so that the ORP value can be maintained, and the pH of the aeration tank is set to 4.0 to 4.0.
A biological treatment method for wastewater containing a reducing sulfur compound, which is controlled and controlled within a range of 7.5. 3. The method according to claim 1 or 2, wherein iron chloride is supplied as an inorganic coagulant, and a method of acclimating and growing sulfur-oxidizing bacteria or a wastewater organism containing a reducing sulfur compound. Treatment method. 4. The wastewater containing a reducing sulfur compound according to claim 1, 2 or 3, wherein the wastewater is wastewater caused by slag generated when refining metal from ore. A method for acclimatizing and growing oxidizing bacteria or a method for biologically treating wastewater containing a reducing sulfur compound. 5. Sulfur oxidation characterized in that the wastewater containing a reducing sulfur compound according to claim 1, 2, or 3 is wastewater originating from blast furnace slag generated from a blast furnace of a steelworks. A method for acclimating and growing bacteria or a biological treatment method for wastewater containing a reducing sulfur compound. 6. The method according to claim 5, wherein iron chloride is supplied as an inorganic coagulant, and the ORP of the aeration tank is 0 to +
Aeration and breeding of sulfur oxidizing bacteria, characterized by aeration to 150 mV (based on silver / silver chloride electrode) and controlling and controlling the pH of the aeration tank in the range of 5.0 to 7.0. Or biological treatment of wastewater containing reducing sulfur compounds.