JPS5919595A - Treatment of dithonic acid-contg. waste water - Google Patents

Abstract

PURPOSE:To improve the decomposition efficiency of anaerobically decomposing dithionic acid, etc. in waste water, by adding a BOD source and a methane halide to waste water containing at least dithionic acid or dithionate, and performing anaerobic biotreatment. CONSTITUTION:Waste water 8 containing dithionic acid (or its salt) is introduced into a mixing reservoir tank 1, wherein additives such as organic substance 9 or other nutritive salts and at least one of methane halides 10 are added to and mixed in it to prepare an aqueous mixture 11. The aqueous mixture 11 is introduced into a vessel 2 for anaerobic bioreaction equipped with a temp. regulator 20, a pH sensor 21 and an opening 22 for the injection of a pH-adjusting chemical liquid. In the reactor vessel 2, the temp. of a reaction liquid is held at 20-45 deg.C, a pH is made at 5.0-8.5, and decomposing reaction is continued for 4hr-5 days. Thereafter, the liquid is let flow out as anaerobically biotreated water 12 from the reactor vessel 2 and solid-liquid separated into a separated liquid 15 and a sludge fraction by a solid-liquid separator 3.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for biological treatment of wastewater containing persistent COD components such as dithionic acid.

Although various methods for removing COD from wastewater containing dithionic acid (salt), such as flue gas desulfurization wastewater, have been proposed for a long time, no energy-saving or cost-saving method has yet been technically perfected. This is because sulfur oxides such as dithionic acid are extremely stable compounds, and chlorine decomposition is a powerful oxidative decomposition method.

This is because it is not easily decomposed by ozone decomposition or the like. Therefore, the only treatment method commonly used at present is thermal decomposition such as a wet combustion method. However, this method has drawbacks such as the consumption of fuel for incineration and the need for large-scale facilities, which prevent it from being an efficient method.

In view of the above-mentioned problems of the conventional method, the present invention proposes a method for decomposing and removing refractory COD components such as dithionic acid by utilizing the biochemical decomposition ability of microorganisms. Another object of the present invention is to provide a method for increasing the decomposition efficiency when proceeding with anaerobic decomposition of wastewater containing dithionate.

The present invention is a method for treating wastewater containing dithionic acid, which comprises adding a BOD source and norogenated methane to wastewater containing at least dithionic acid or a dithionate salt, and subjecting the wastewater to anaerobic biological treatment.

The method of the present invention and the effective pressure resulting therefrom will be explained in detail below based on Examples.

Sulfur-oxidizing bacteria (Tb1obacii), which are aerobic bacteria
lus, etc.) and anaerobic bacteria such as sulfate-reducing bacteria (Desu
lfovibri.

It is well known from previous studies that other microorganisms (genus, etc.) can biodegrade incomplete sulfur oxides such as dithimenic acid. The method according to the present invention utilizes the ability of anaerobic bacteria to decompose substances such as dithionic acid. The presence of organic matter is essential for this decomposition by anaerobic bacteria, and dithionic acid and the like are reductively decomposed by the reducing power of the organic matter. For this reason, in the anaerobic biodegradation of dithionic acid in wastewater with a low organic matter content, such as flue gas desulfurization wastewater, the decomposition reaction is progressed by adding organic wastewater, waste sludge, commercially available organic matter, etc.

However, these added organic substances are also fermented and decomposed by coexisting anaerobic heterotrophic microorganisms other than dithionate-degrading microorganisms.

The present invention was completed by successfully discovering a method for preferentially utilizing such added organic substances for the reductive decomposition of sulfur oxides such as dithionic acid. Experimental examples are shown below to clarify the effects of the present invention.

Synthetic wastewater containing monoammonium dithionate, phosphate, and other nutrients is prepared and fed continuously into a mixed culture tank of anaerobic bacteria preincubated with dithionate, while glucose (and other A solution containing saccharides) was continuously supplied, the temperature of the mixing culture tank was kept at 15℃, and the residence time was 6 days.
When kept for 8 days to 8 days, the decomposition and removal of dithionic acid gradually began, and from around the 30th day, 95%
% or more of dithionic acid was removed. Next, when we conducted a similar experiment while keeping the temperature at 30°C, we were able to decompose dithionic acid even if we reduced the residence time to 30 days. However, the decomposition rate of dithionic acid never exceeded 55%.

Next, this experimental culture at 30°C! The concentration in the tank is approximately 0.0.
When the synthetic wastewater was subsequently cultured after adding chloroporum to a concentration of 5 to 3.0 mM, the decomposition rate of dithionic acid immediately increased, and even at a residence time of 2.0 days, a dithionic acid removal rate of 95 coefficients or higher was obtained. The COD concentration of the treated water was reduced, and the treatment performance was stable. The same effect of adding chloroform is 25℃~40℃, 45℃~65℃
It was also confirmed in experiments that chloroporum was detected in similar concentrations of fluorinated methane, difluorided methane, trifluorided methane, carbon tetrafluoride, chloromethane, nichloromethane, carbon tetrachloride, bromated methane, tribromated methane, and trifluorinated methane. It has been found that the same effect can be obtained even if methane or carbon tetrabromide is used instead. However, the types of organic substances added are not limited to the above-mentioned glucose, but may also include various organic wastewaters.

Conventionally used alcohols, organic acids, and the like can be used alone or in appropriate combinations.

As mentioned above, from the phenomenon discovered in the research that led to the present invention, it was found that adding halogenated methane can improve the decomposition and removal properties of dithionic acid. This is presumed to be because it has the effect of inhibiting the decomposition and fermentation of other coexisting organic substances without inhibiting reductive decomposition.

In this way, when conventional anaerobic biological treatment of wastewater containing dithionic acid is performed by adding organic matter, the reducing power of the added organic matter is consumed not for the decomposition of dithionic acid but for other fermentative decomposition processes. is especially 20℃~45℃, 45℃~70℃
In contrast, in the method of the present invention, it was necessary to add an excessive amount of organic matter because it was significant under medium-temperature treatment conditions or high-temperature treatment conditions of about By effectively utilizing almost the entire area of the added organic matter for reductive decomposition of sulfur oxides such as dithionic acid under temperature conditions of . Therefore, the cost of treating wastewater containing dithionic acid (salt) can be significantly reduced, and even relatively expensive commercially available organic substances, such as methanol and lactic acid, can be decomposed, especially dithionic acid. This makes it economically possible to carry out the treatment while adding organic substances suitable for the treatment.

Next, an example of an embodiment of the present invention will be described in detail based on the drawings.

Wastewater containing sinaonic acid (salt) is introduced into a mixing storage tank containing 8 containers of sinaonic acid (salt), and any one of additives such as organic matter 9 and other nutrient salts and halogenated methane 10 (multiple types may be combined) is added. The water is mixed to form mixed water 11, which is led to an anaerobic biological reactor 2 (hereinafter abbreviated as reactor).

This reactor 2 includes a temperature adjustment device 20 and a pH sensor 21.
Also, a spout 22 for pH adjustment is provided. Although the temperature adjustment device 20 may be an internal heating system as shown in the figure,
It is possible to heat the inflowing wastewater itself using an external heat exchanger method, to heat it by circulating the reaction liquid externally, and to heat it directly by blowing steam, etc. Using the same method used in anaerobic digestion, the temperature of the reaction solution was kept at 20°C.
The temperature can be maintained at a constant temperature of 45°C or 45°C to 70°C. In addition, depending on the type of reactor 2, it may be necessary to provide a stirring device 6 in this reactor 2, but this stirring method can also be adapted to any method that has been incorporated into conventional anaerobic digestion, such as gas stirring. Any method can be adopted as long as it can exhibit a stirring effect desirable for decomposing dithionic acid (salt). Liquid rlH in reactor 2 is 5.0
Although it is possible to decompose dithionic acid within the range of 85 to 85, it is preferable to set it at around neutrality of 6.0 to 7.5 in order to improve the decomposition efficiency.

Under reaction conditions as described above, depending on their settings and dithionate (salt) loading conditions, the influent effluent is usually 4
It stays in this reactor 2 for about 5 days to undergo a decomposition reaction. Thereafter, it flows out from this reactor 2 as (Iti, temperament) biologically treated water 12, but this biologically treated water 12 contains halogenated methane, albeit at a low concentration, and the permissible values of these in the discharge area are The next stage of processing is required except in satisfactory special cases. In addition, regardless of whether or not this next stage treatment is necessary, the water flowing out from the reactor 2 is separated into solid and liquid by the solid-liquid separator 3, separated into a separated liquid 15 and a sludge fraction, and one of the sludge fractions is separated. Returning the sludge to the reactor 2 as return sludge 13 is effective in operating the reactor 2 at a high efficiency. The remaining sludge is treated as surplus sludge 14.
It will be disposed of.

In the method of the present invention, the method for removing halogenated methane contained in the anaerobic biologically treated wastewater 12 containing dithio/acid salts is heat expulsion.

Any method and conditions may be used as long as it is a conventional method for removing halogenated methane, such as stripping with steam or air, A-sin decomposition treatment, adsorption treatment with activated carbon, and combination treatments thereof. can be used as is, and many of these can also be applied for the purpose of removing residual COD.

However, as a treatment method for halogenated methane, a method in which an aerobic biological reactor 4 equipped with a special aeration device as shown in the figure is installed in the next stage to treat the halogenated methane is particularly important because of the anaerobic biological reaction in the previous stage as in this method. This is effective in systems where there is a high possibility that organic substances will remain in addition to halogenated methane, such as when organic substances and halogenated methane are added at the same time. In physical-chemical methods such as stripping methods, adsorption methods, and ozonolysis methods, when the COD concentration due to residual organic matter is high, VCFiI energy consumption, chemical usage, etc. rapidly increase, making them extremely uneconomical. The above aerobic biological treatments can be selected. Normally, air 23 is forcibly blown into this aerobic biological reactor 4 from a blower 7, but the aeration method is not limited to this, and may include a surface aeration method, an underwater aerator method, a 9-rotation disk method, etc. Even if there is, it can be adopted as long as it has sufficient oxygen supply capacity to meet the biodecomposition pressure of halogenated methane.

The effluent water 16 from the aerobic biological reactor 4 is usually separated into solid and liquid by a solid-liquid separator 5, and the separated liquid 19 is discharged into a water body directly or after further detoxification treatment. A part of the settled sludge fraction is returned to the aerobic biological reactor 4 as return sludge 17, and the rest is separately treated and disposed of as surplus sludge 18.

As shown above, one embodiment of the present invention is provided with an anaerobic biological treatment reactor 2 and an aerobic biological reactor 4 following it, but the type of these reactors is generally a simple mixing tank. Although a type reactor is often used, it is also possible to adopt a packed bed fixed bed system, a fluidized bed system containing a fluidized medium, etc. If it is a conventionally reported bioreactor, it is possible to set the operating conditions. By selecting appropriately, almost all of them can be adopted. Also, the two solid-liquid separators 3 and 5 shown in the figure may be of a simple sedimentation tank type at the lowest cost, but depending on constraints such as construction costs, operating costs, and required land area, centrifugal separation may be preferable.

Any conventional solid-liquid separation method such as flotation separation may be used, but methods that inactivate microorganisms cannot be used because the living organisms must be returned.

The present invention incorporates into the anaerobic biological reactor according to the present invention a method for performing biodegradation while removing hydrogen sulfide generated during the decomposition process of sulfur compounds such as dithionic acid (salt) in the reactor. This is effective in further enhancing the effects of

This is because, as is known, a large amount of hydrogen sulfide is produced in the decomposition pathway of sulfur oxides, which particularly inhibits the decomposition of dithionic acid. When the decomposition of (salt) progresses, a particularly large amount of hydrogen sulfide accumulates, which has a significant negative effect on the reductive decomposition of dithionic acid and the like by anaerobic organisms. Since this can be prevented by hydrogen desulfurization, the effect of hydrogen desulfurization is much higher than that of conventional cleaning methods.

Conventionally reported methods for desulfurizing hydrogen, such as liquid absorbent absorption methods, solid absorbent absorption methods, and the Takahax method and Silotsuk method used for desulfurization of digestion gas, can be used as is. The fact that the method of the present invention does not require any special method is advantageous in terms of manufacturing and operation management since the device configuration does not become more complicated than before.

Also, the effect of such desulfurization is particularly dog when the concentration of dithionic acid in the wastewater is high.

Therefore, if the concentration of dithionic acid (salt) in the inflowing wastewater is low, the dithionic acid (salt) concentration should be at least 300 to 500 w/1 or more by a concentration process using ion exchange treatment or other physicochemical methods. ) is effective.

As described above, according to the present invention, the simple process and simple equipment result in extremely energy saving.

This method brings many benefits, such as being able to decompose and remove dithionic acid (salt) economically and with high efficiency, and making operation management easy.

[Brief explanation of the drawing]

The drawing is a flowchart showing one embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Mixing storage tank, 2... Reactor, 3, 5... Solid-liquid separation device, 4... Aerobic biological reactor, 6... Stirring device, 7... Blower 38 ...Drainage, 9...Organic matter, 1o...Halogenated methane, 11...Mixed water, 12
... Biologically treated water, 13, 17... Returned sludge, 14
, 18... Surplus sludge, ]5... Separated liquid, J6...
Effluent water, 19...Separated liquid, 20...Temperature adjustment device,
21...pH sensor~, 22.1) H adjustment medicine spout, 2
3...Air. Patent applicant: Patent attorney representing Ebara Infilco Co., Ltd.
Go Hayama - Patent Attorney Sen 1) Neji

Claims (1)

[Claims] A method for treating dithionic acid-containing wastewater, which comprises subjecting it to anaerobic biological treatment. 2. The method according to claim 1, wherein the anaerobic biological treatment is performed by returning microbial sludge obtained by subjecting the biologically treated water to solid-liquid separation treatment. 6. The method according to claim 2, wherein the separated water obtained by the solid-liquid separation treatment is subjected to aerobic biological treatment. 4. The halogenated methane is chloromethane, dilormethane, chloroform, or carbon tetrachloride. Methane fluoride, methane difluoride, methane trifluoride, carbon tetrafluoride, methane bromide, methane tribromide, methane tribromide,
The method according to claim 1, 2 or 3, wherein the carbon tetrabromide is selected arbitrarily from the group consisting of carbon tetrabromide. 5. Claim 1, wherein the anaerobic biological treatment is performed while removing hydrogen sulfide generated during the treatment process.
3. The method described in Section 2, Section 2, or Section 3. 6. Claims 1 and 2, wherein the wastewater has been concentrated in advance by a physicochemical method such as ion exchange treatment to increase the concentration of dithionic acid or dithionate salt.
The method described in paragraph 3 or paragraph 5. l The above-mentioned anaerobic biological treatment is carried out by adjusting the pH of the reaction solution to 6.0 to 7.
．． 5. The method according to claim 1, wherein the method is carried out while maintaining a The BOD source is sugars, organic wastewater, alcohols,
The method according to claim 1, wherein the acid is arbitrarily selected from a group consisting of organic acids.