JPS638840B2 - - Google Patents

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 studied for a long time, no energy-saving or cost-saving method has yet been technically perfected. this is,
This is because sulfur oxides such as dithionic acid are extremely stable compounds and are not easily decomposed even by strong oxidative decomposition methods such as chlorine decomposition and ozonolysis. Therefore, the currently commonly used treatment method for these 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 problems of the above-mentioned conventional methods, the present invention proposes a method of decomposing and removing persistent COD components such as dithionic acid by utilizing the biochemical decomposition ability of microorganisms, that is, using anaerobic microorganisms. The object of the present invention is to provide a method for increasing the decomposition efficiency when proceeding with anaerobic decomposition of wastewater containing dithionic acid or dithionate.

The present invention is a method for treating wastewater containing dithionic acid, which comprises adding a BOD source and halogenated 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 its effects will be described in detail below based on Examples.

Thiobacillus is an aerobic bacterium.
It is well known from previous studies that anaerobic bacteria such as sulfate ring bacteria (genus Desulfovibrio, etc.) and other microorganisms can biodegrade incomplete sulfur oxides such as dithionic 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, for example, in anaerobic biodegradation of dithionic acid in wastewater with low organic matter content, such as flue gas desulfurization wastewater, the decomposition reaction is allowed to proceed by adding organic wastewater, waste sludge, commercially available organic matter, etc. There is. 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 dithionic acid, ammonium salts, phosphates, and other nutrients is prepared and fed continuously into a mixed culture tank of anaerobic bacteria preincubated with dithionic acid, while glucose ( When a solution containing (other sugars) was continuously supplied and the temperature of the mixed culture tank was maintained at 15℃ and the residence time was maintained for 6 to 8 days, dithionic acid gradually began to be decomposed and removed, and after 30 days elapsed. Since then, results have been obtained in which more than 95% of dithionic acid is almost constantly 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 3.0 days, but we found that dithionic acid could be decomposed even if the residence time was reduced to 3.0 days. The decomposition rate of dithionic acid never exceeded 55%.

Next, in this experimental culture tank at 30℃, the concentration in the tank was approximately
When chloroform was added to the concentration of 0.05 to 3.0 mM and the synthetic wastewater was subsequently cultured, the decomposition rate of dithionic acid immediately increased, and a dithionic acid removal rate of 95% or more was obtained even at a residence time of 2.0 days.
The COD concentration in the treated water also decreased and the treatment performance was stable. A similar effect of adding chloroform
This can also be confirmed in experiments at temperatures of 25°C to 40°C and 45°C to 65°C.
Methane difluoride, methane trifluoride, carbon tetrafluoride, chloromethane, dichloromethane, carbon tetrachloride, methane bromide, methane dibromide, methane tribromide,
It was found that the same effect can be seen even if carbon tetrabromide is used instead. Further, the type of organic substance to be added is not limited to the above-mentioned glucose, and conventionally used organic substances such as various organic wastewaters, alcohols, and organic acids can be used alone or in an appropriate combination.

As mentioned above, from the phenomenon discovered in the research leading to the present invention, the addition of halogenated methane was able to improve the decomposition and removal performance 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. especially 20
In contrast, in the method of the present invention, dithionic acid Under these temperature conditions, which are also suitable for decomposition by anaerobic organisms, almost all of the added organic matter is effectively utilized for the reductive decomposition of sulfur oxides such as dithionic acid. This makes it possible to significantly reduce the amount of organic matter. Therefore, the cost of treating water containing dithionic acid (salt) can be significantly reduced, and even relatively expensive commercially available organic substances, such as methanol, lactic acid, etc., are particularly effective for decomposing dithionic acid. This makes it economically possible to carry out the treatment while adding a suitable organic substance.

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

Wastewater 8 containing dithionic acid (salt) is mixed in a storage tank 1
, organic matter 9 and other additives such as nutrient salts and halogenated methane 10 are added and mixed to form mixed water 11, which is then mixed into anaerobic biological reactor 2. (hereinafter abbreviated as reactor).

This reactor 2 is provided with a temperature adjustment device 20, a PH sensor 21, and a PH adjustment chemical inlet 22. The temperature adjustment device 20 may be of an internal heating type as shown in the figure, but it can also be heated by an external heat exchanger type to heat the inflowing wastewater itself, or by externally circulating the reaction liquid. In addition, it is also possible to heat the reaction liquid directly by blowing steam, etc., using any method used in conventional anaerobic digestion to maintain the temperature of the reaction liquid at 20 to 45°C.
Alternatively, it can be maintained at a constant temperature of 45°C to 70°C. Also, 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 is also incorporated into conventional anaerobic digestion such as gas stirring. Any method can be used as long as it can exhibit a stirring effect desirable for decomposing dithionic acid (salt). The pH of the liquid in the reactor 2 can decompose dithionic acid within the range of 5.0 to 8.5, but preferably 6.0 to 7.5.
It is desirable to keep the temperature near neutrality in order to improve the decomposition efficiency.

Under the above-mentioned reaction conditions, the inflow wastewater usually remains in the reactor 2 for about 4 hours to 5 days and undergoes a decomposition reaction, depending on the setting conditions and the loading conditions of dithionic acid (salt). Thereafter, it flows out from this reactor 2 as (anaerobic) biologically treated water 12, but this biologically treated water 12 contains halogenated methane, albeit at a low concentration, and these permissible values for the discharge area are satisfied. The next stage of processing is required except in special cases where it is possible. In addition, regardless of whether or not this next stage treatment is necessary, the effluent water from the reactor 2 is separated into solid and liquid by the solid-liquid separator 3 and separated into a separated liquid 15 and a sludge fraction. Part of the sludge returned 13
Returning the reactor 2 to the reactor 2 is effective in operating the reactor 2 at high efficiency. The remaining sludge is used as surplus sludge 14 for sludge treatment and disposal.

In the method of the present invention, methods for removing halogenated methane contained in the anaerobic biologically treated water 12 of wastewater containing dithionic acid (salt) include heating expulsion, stripping with steam or air, ozone decomposition treatment, and activated carbon treatment. Any treatment method and conditions adopted for conventional halogenated methane removal methods, such as adsorption treatment and combination treatments, can be used as is, and many of these methods are effective for removing residual COD. It can also be applied as a purpose.

However, as a treatment method for halogenated methane, a method in which an aerobic biological reactor 4 equipped with an aeration device as shown in the figure is installed in the next stage for treatment is particularly important in the anaerobic biological reaction in the first stage as in this method. This is effective in systems where there is a high possibility that organic substances will remain in addition to the halogenated methane, such as when organic substances and halogenated methane are added at the same time. Physicochemical methods such as stripping, adsorption, and ozonolysis methods are extremely uneconomical due to rapid increase in energy consumption and chemical consumption in areas where the COD concentration due to residual organic matter is high. Aerobic biological treatment can be selected. Normally, air 23 is forcibly blown into this aerobic bioreactor 4 from a blower 7, but the aeration method is not limited to this, and the surface aeration method,
Submersible aerator systems, rotating disk systems, etc. may be used as long as they have sufficient oxygen supply capacity for biodegradation of halogenated methane.

The effluent water 16 from the aerobic biological reactor 4 is normally separated into solid and liquid by the solid-liquid separator 5, and the separated liquid 1
9 is discharged into water bodies either 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 processed 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 it is often a type reactor, 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 shown in the diagram is 2
For the solid-liquid separators 3 and 5, it is cheapest to use a simple sedimentation tank system, but depending on constraints such as construction costs, operating costs, and required land area, conventional solid-liquid separation systems such as centrifugal separation and flotation separation may be used. Although a liquid separation method may be used, methods that would inactivate the 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 dithionic acid (salt) progresses, a particularly large amount of hydrogen sulfide accumulates, which has a significant adverse effect on the reductive decomposition of dithionic acid and the like by anaerobic organisms. This can be prevented by hydrogen desulfurization, so
The effect of performing hydrogen desulfurization is extremely high compared to conventional methods.

It is sufficient to adopt conventionally reported methods for desulfurizing hydrogen, such as the absorption method using liquid or solid absorbents, the Takahatsu method and the Silotsu method used for desulfurization of digestion gas, as they are. The fact that the method of the present invention does not require any special system is advantageous in terms of manufacturing and operation management since the device configuration does not become more complicated than before.

Moreover, the effect of such hydrogen desulfurization is particularly large when the concentration of dithionic acid in the waste water is high.
Therefore, dithionic acid (salt) in the incoming wastewater
If the concentration of
As described above, it is effective to concentrate dithionic acid (salt) in advance through a concentration step using ion exchange treatment or other physicochemical methods.

As described above, according to the present invention, a simple process and a simple device 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 flow sheet showing one embodiment of the invention. 1... Mixing storage tank, 2... Reactor, 3, 5...
Solid-liquid separator, 4...Aerobic biological reactor, 6...
Stirring device, 7...Blower, 8...Drainage, 9...
Organic matter, 10... Halogenated methane, 11... Mixed water, 12... Biologically treated water, 13, 17... Returned sludge, 14, 18... Excess sludge, 15... Separated liquid, 16... Runoff water, 19...Separated liquid, 20...
Temperature adjustment device, 21...PH sensor, 22...PH
Adjustment medicine spout, 23...Air.

Claims (1)

[Scope of Claims] 1. A method for treating dithionic acid-containing wastewater, which comprises adding a BOD source and halogenated methane to wastewater containing at least dithionic acid or a dithionate salt, and subjecting the wastewater 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. 3. 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, dichloromethane, chloroform, carbon tetrachloride, methane fluoride, methane difluoride, methane trifluoride, carbon tetrafluoride, methane bromide, methane dibromide, 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. The method according to claim 1, 2, or 3, wherein the anaerobic biological treatment is performed while removing hydrogen sulfide generated during the treatment process. 6. Claims 1, 2, 3, or 6, 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 Section 5. 7 Perform the anaerobic biological treatment at a pH of 6.0 to 6.0.
7.5. 8. The method according to claim 1, wherein the BOD source is arbitrarily selected from the group consisting of sugars, organic wastewater, alcohols, and organic acids.