JPH04310296A - Acclimation and propagation of bacteria oxidizing and decomposing reducible sulfur compound, and biological treatment of waste water containing the same compound - Google Patents

Abstract

PURPOSE:To biologically treat waste water containing a reducible sulfur compound with high efficiency by acclimating and propagating bacteria suitable for the treatment of the waste water. CONSTITUTION:Activated sludge for treating sewage or industrial waste water is introduced into an aeration tank to be subjected to aeration. A soluble calcium salt is added to waste water containing a reducible sulfur compound before introducing the waste water into the aeration tank.

Description

[Detailed description of the invention]

0001

[Industrial Application Field] The present invention relates to biological treatment of wastewater, more specifically, a method for acclimating and growing microorganisms suitable for the treatment of wastewater containing reducing sulfur compounds, and Concerning biological treatment methods.

0002

BACKGROUND OF THE INVENTION Methods for biologically treating pollutants contained in municipal sewage, underground water, industrial wastewater, etc. are already known. For example, in JP-A No. 63-126599, a biological reaction tank in which activated sludge exists is divided into four: 1 anaerobic tank, 1 aerobic tank, 2 anaerobic tanks, and 2 aerobic tanks, and each tank has its own preferred method. A method for managing air temperature and anaerobic degree using oxidation-reduction potential (ORP) as an index is described.

By the way, some wastewater contains reducing sulfur compounds, such as wastewater from the photographic industry, oil refining industry, and chemical industry, and these compounds increase the chemical oxygen demand (COD) of the wastewater. COD of wastewater
In order to reduce these compounds, it is necessary to remove them by some method.

[0004] As a method for treating wastewater containing reducible sulfur compounds, a method of chemically oxidizing the wastewater using sodium hypochlorite or the like is known.

[0005]

However, the above-mentioned treatment method has problems in that the treatment cost is high and it is difficult to sufficiently oxidize and decompose these compounds to lower the COD of the wastewater.

The present invention provides a method for rapidly acclimating and multiplying microorganisms suitable for biological treatment of wastewater containing reducing sulfur compounds, and for biologically treating wastewater containing reducing sulfur compounds with high efficiency. provide.

[0007]

[Means for Solving the Problems] The gist of the present invention is that sewage,
When cultivating and growing microorganisms that oxidize and decompose reducing sulfur compounds from activated sludge used to treat industrial wastewater, soluble calcium compounds are added to the wastewater containing reducing sulfur compounds before supplying it to the aeration tank where the activated sludge is present. At the same time, the oxidation-reduction potential of the aeration tank is maintained at the ORP value calculated from the free reaction energy change of the oxidation reaction of the reducing sulfur compound. , a growth method, and a method in which soluble calcium compounds are added to wastewater containing reducing sulfur compounds and then supplied to an aeration tank in which microorganisms that oxidize and decompose reducing sulfur compounds are present, and reducing sulfur is removed in the aeration tank. By attaching and immobilizing these microorganisms to insoluble calcium sulfate particles, which are produced by sulfate ions and calcium ions produced when compounds are oxidized and decomposed by microorganisms, the sedimentation properties of microorganisms are improved, and these particles in the aeration tank are This is a biological treatment method for wastewater containing reducing sulfur compounds, which is characterized by maintaining a high concentration of microorganisms and treating wastewater with high efficiency.

[0008]

[Operation] FIG. 1 is a diagram showing the method of the present invention.

The present inventors have discovered that microorganisms that oxidize and decompose reducing sulfur compounds exist in activated sludge used to treat sewage and industrial wastewater.

That is, the microorganisms preferentially cultured and multiplied from activated sludge used to treat sewage and industrial wastewater by the microorganism acclimatization and multiplication method of the present invention, which will be described later, oxidize reducing sulfur compounds and produce sulfuric acid. It has been revealed that it has the ability to generate.

[0011] Next, a method for acclimating and growing microorganisms that oxidize and decompose reducing sulfur compounds according to the present invention, and a method for biologically treating wastewater containing these compounds using these microorganisms will be explained. .

First, a method for acclimating and growing microorganisms that oxidize and decompose reducible sulfur compounds will be explained.

First, assuming an oxidative decomposition reaction of a reducing sulfur compound, the amount of free energy change in this reaction is determined from handbooks, books, literature, etc., and then these are calculated from this amount of free energy change. Find the oxidation-reduction potential (ORP) for the oxidative decomposition reaction to occur.

Next, the ORP sensor 10 shown in FIG.
Activated sludge in which sewage or industrial wastewater is being treated is placed in the aeration tank 3 of an ORP-controlled activated sludge treatment device, which consists of an aeration tank 3 and a sludge settling tank 5, which are equipped with an RP control device 11, a pH sensor 8, a pH control device 9, etc. Add the mixed solution and ORP the aeration tank 3.
is set to the ORP value obtained from the free energy change amount of the chemical reaction assumed previously.

When setting this ORP value, if a plurality of reducing sulfur compounds are present in the wastewater to be treated, the amount of free energy change in the oxidative decomposition reaction of each compound is different, so the ORP value is also different. For example, when sodium thiosulfate and sodium sulfide coexist as reducing sulfur compounds in wastewater, the calculated ORP value is approximately +150 mV (based on Ag/AgCl electrode) for sodium thiosulfate;
Further, that of hydrogen sulfide is about -80 mV (based on Ag/AgCl electrode). If the ORP values are different like this,
When the ORP value of the aeration tank is set to be more oxidizing than +150 mV, an oxidation reaction or decomposition reaction of both compounds occurs.

From this fact, when cultivating and multiplying microorganisms suitable for wastewater in which sodium thiosulfate and sodium sulfide coexist as reducing sulfur compounds, a mixed solution of activated sludge used to treat sewage or industrial wastewater should be added. ORP of aeration tank
If the value is maintained above +150 mV (Ag/AgCl electrode reference) and wastewater containing these compounds is gradually supplied, it is thought that microorganisms that oxidize these compounds will easily grow from the activated sludge.

Based on this idea, microorganisms that oxidize these compounds were cultivated and grown. The method will be explained in detail.

The activated sludge mixed liquid undergoing sewage treatment is put into the aeration tank 3 of the ORP controlled activated sludge treatment equipment shown in FIG. 2, and the ORP value of this aeration tank 3 is set to +150 mV. Wastewater containing sodium thiosulfate and sodium sulfide as sulfur compounds is supplied so that the treatment time is 8 hours. At the beginning of wastewater supply, ORP does not rise to the set value, but gradually rises to +150 mV in about 10 to 15 days. Once the ORP reaches +150 mV, the wastewater supply is increased for 6 treatment times every 7-10 days.
The time is gradually increased as follows: time → 4 hours → 3 hours → 2 hours to increase the growth of these microorganisms. After that, if the wastewater is continuously treated by setting the amount of wastewater supplied so that the treatment time is 2 to 3 hours, the oxidative decomposition of these compounds will be carried out well and they will not be detected in the treated water, resulting in COD. Good quality treated water with low oxidation can be obtained.

Next, a method of the present invention will be described in which microorganisms that oxidize and decompose reducible sulfur compounds are maintained at a high concentration in an aeration tank for highly efficient treatment.

In the biological treatment of wastewater such as sewage, the treatment time is shorter than the conventional 6 to 8 hours, for example, 2 to 8 hours.
If the processing can be carried out in 3 hours, there are advantages such as making the processing equipment more compact and saving space. However, with the traditional method,
There were problems such as deterioration of treated water quality.

[0021] In other words, since conventional activated sludge has insufficient sedimentation properties, bulking tends to occur when the treatment time is shortened.
The activated sludge does not settle sufficiently in the sludge settling tank and flows out into the treated water, making it impossible to maintain a high concentration of activated sludge in the aeration tank. Moreover, a fatal drawback is that it causes deterioration of the quality of treated water. High-efficiency treatment includes activated sludge's pollutant decomposition function,
This is possible by maintaining highly active activated sludge at a high concentration in the aeration tank by improving its activity, sedimentation, etc.

[0022] As a method of maintaining activated sludge in the aeration tank at a high concentration, silica sand, zeolite, activated carbon, granulated blast furnace slag, etc. are added to the aeration tank, and activated sludge is attached and immobilized to this to improve sedimentation. There are known methods for improving activated sludge in an aeration tank and maintaining it at a high concentration.

[0023] The inventors have discovered that the above-mentioned method can be used to culture, without adding the above-mentioned activated sludge immobilization carrier to the aeration tank from the outside.
We have invented a method for producing activated sludge immobilization carriers in an aeration tank using sulfate ions produced by the oxidative decomposition of reducing sulfur compounds by grown microorganisms.

[0024] When the microorganisms cultured and propagated by the method described above treat wastewater containing reducing sulfur compounds, the pH of the aeration tank is significantly lowered. From this phenomenon, it was assumed that reducing sulfur compounds are biologically oxidized and decomposed to produce sulfuric acid. The inventors studied a method of producing an activated sludge immobilization carrier using this sulfuric acid, and found that after adding a water-soluble calcium compound to wastewater containing reducing sulfur compounds in advance, the wastewater was aerated. It was discovered that when supplied to the aeration tank, immobilized carriers are generated in the aeration tank, making it possible to increase the concentration of microorganisms. That is, in the aeration tank, this water-soluble calcium compound reacts with biologically produced sulfuric acid to produce insoluble calcium sulfate (gypsum). Since this gypsum is a fine particle of about 20 to 200 μm, microorganisms easily adhere to it, and the microorganisms are immobilized on the gypsum, improving its sedimentation properties. As a result, the microorganisms cultured by the above-described method can be maintained at a high concentration in the aeration tank, making it possible to perform highly efficient treatment with a treatment time of 2 to 3 hours. Further, it is optimal to use calcium hydroxide as the water-soluble calcium compound because it can suppress a decrease in the pH of the aeration tank. Note that if calcium compounds already exist in wastewater containing reducing sulfur compounds at an amount of approximately 100 mg/l or more as calcium ions, the above-mentioned effect will be achieved, so there is no need to add water-soluble calcium compounds from outside. .

Next, biological treatment of wastewater containing reducing sulfur compounds by the method of the present invention will be specifically explained.

[0026] The activated sludge mixture used for treating sewage or industrial wastewater is put into the aeration tank 3 in FIG.
is calculated from the amount of free energy change in the assumed oxidative decomposition reaction of reducing sulfur compounds contained in wastewater.
P value is set, microorganisms that oxidize and decompose these compounds are cultured and multiplied by the method described above, and after acclimatization is completed, the wastewater is continuously supplied to the aeration tank 3 for a processing time of 2 to 3 hours. do.

In this wastewater treatment, aeration to the aeration tank 3 is preferably managed and controlled using the ORP of the aeration tank 3 as an index. That is, when the ORP of the aeration tank 3 falls below the set value, the ORP sensor (gold-silver/silver chloride composite electrode) 10 detects this, and the ORP control device 11 causes the roots blower 12 to
This is ORP control using a proportional control method in which the rotation speed of the roots blower 12 is increased to increase the amount of aeration, and when the rotation speed of the roots blower 12 is restored to the set value, the rotation speed of the Roots blower 12 is lowered to reduce the amount of aeration.

The pH of the aeration tank 3 is preferably in the range of 5 to 8 depending on the material of the device, etc., and the pH sensor 8 and the control device 9
The pH is controlled within this range by adding acid or alkali. In addition, the activated sludge concentration in aeration tank 3 is 20
The optimum concentration is about 00 to 5000 mg/l, and if the activated sludge concentration is higher than this, there is a concern that activated sludge separated from the immobilization carrier will flow into the treated water, leading to deterioration of the quality of the treated water.

In the case of the present invention, the sludge return rate from the sludge settling tank 5 to the aeration tank 3 may be about 20 to 30% because the activated sludge has excellent settling properties. Additionally, as the process progresses,
These microorganisms increase, but this is caused by excess sludge 14 as appropriate.
Remove and dispose of. For example, gypsum can be recovered and used effectively by incineration. In principle, this biological treatment is carried out regularly, but good treated water quality can be obtained even if the operational treatment is restarted after stopping the operational treatment for about 20 to 30 days. Furthermore, even during the low water temperature period in winter, for example, when the water temperature drops to about 5°C, it oxidizes reducing sulfur compounds in wastewater and shows the same treatment performance as in summer.

[0030]

[Example 1] Activated sludge from sewage and industrial wastewater was introduced into an aeration tank for ORP controlled activated sludge treatment. Thiosulfate compound (S2 O3 2-
) is approximately 500 mg/l (S2 O3 2- ), C
Wastewater with an OD of about 250 mg/l is adjusted to pH 13-14 by adding calcium hydroxide, and the residence time in the aeration tank is 8 hours, and the pH of the aeration tank is 5-8. It was continuously supplied while controlling the pH. After starting to supply wastewater, it takes about 10 to 15 days for the ORP of the aeration tank to rise to +150 to 200 mV (ref
Ag/AgCl electrode standard) was reached, thiosulfate compounds were no longer detected in the treated water, and the COD of the treated water was 20.
It became below mg/l. In this state, the acclimatization of the microorganisms that oxidize and decompose reducing sulfur compounds was completed.

[0031]

[Example 2] The same wastewater as in Example 1 was introduced into the activated sludge that had been acclimatized in Example 1, and the treatment time was successively shortened from 6 hours → 4 hours → 3 hours → 2 hours every week, and then The treatment took 2 hours. As a result, no thiosulfate compounds were detected, and clear treated water was obtained with COD of 20 mg/l or less, transparency of 100 cm or more, and SS of 10 mg/l or less.

[0032]

Effects of the Invention According to the present invention, the acclimatization and proliferation of microorganisms that oxidize and decompose reducing sulfur compounds are significantly promoted, and acclimatization can be achieved in a short period of time. Furthermore, since the same microorganisms can be maintained at a high concentration in the biochemical reaction tank, it becomes possible to treat wastewater containing reducing sulfur compounds with high efficiency.

[Brief explanation of drawings]

FIG. 1 is a diagram illustrating the method of the present invention.

FIG. 2 is a diagram showing an example of automatic operation of the method of the present invention.

[Explanation of symbols]

1 Waste water tank 2 Wastewater supply pump 3 Aeration tank ４　　　　Air diffuser pipe 5 Sludge settling tank 6 Rake 7. Treated water 8. pH sensor 9. pH control device 10 ORP sensor 11 ORP control device 12 Roots blower 13 Return sludge pump 14 Surplus sludge

Claims (3)

[Claims] Claim 1: When acclimating and growing microorganisms that oxidize and decompose reducing sulfur compounds from activated sludge used to treat sewage and industrial wastewater, a soluble calcium compound is added to the wastewater containing reducing sulfur compounds before the activated sludge is grown. At the same time, the oxidation-reduction potential (ORP) of the aeration tank is
A method for acclimating and growing microorganisms that oxidize and decompose reducing sulfur compounds, characterized by maintaining an ORP value calculated from the amount of free reaction energy change in the oxidation reaction of reducing sulfur compounds. 2. A soluble calcium compound is added to the wastewater containing the reducing sulfur compound and then supplied to the aeration tank in which the microorganisms that oxidize and decompose the reducing sulfur compound, which have been acclimatized and multiplied by the method according to claim 1, are present. In the aeration tank, the reducing sulfur compound is oxidized and decomposed by the microorganisms that have been acclimatized and cultured according to the method of claim 1, and these microorganisms are added to the insoluble calcium sulfate particles produced by the sulfate ions and calcium ions. A wastewater organism containing reducing sulfur compounds that improves the settling properties of microorganisms by adhering and immobilizing them, maintains these microorganisms at a high concentration in the aeration tank, and performs wastewater treatment with high efficiency. Scientific processing method. 3. In the wastewater treatment according to claim 2, the oxidation-reduction potential (ORP) of the aeration tank is controlled to an ORP value calculated from the free reaction energy change amount of the oxidative decomposition reaction of the reducing sulfur compound. , a biological treatment method for wastewater containing reducing sulfur compounds, characterized in that: