JPS5919594A - Treatment of dithionic acid-contg. waste water - Google Patents

Abstract

PURPOSE:To improve the speed of biodecomposing dithionic acid or the like, by adding organic substance to waste water containing at least dithionic acid or dithionate, and performing anaerobic biotreatment while formed hydrogen sulfide. CONSTITUTION:An outflow liquid mixture 2 from a decomposition tank 4 is degasified by circulating it through a decompression chamber 5 decompressed by a decompression pump 10 and then introduced into a precipitation-separating tank 6. Said liquid is separated into the fraction 12 of precipitating (living) sludge and the fraction 3 of a supernatant liquid in the precipitation-separating tank 6. The fraction 3 of a supernatant liquid is introduced as water for the treatment of decomposing dithionic acid into the process of aerobic treatment to remove BOD components. A part of the fraction 12 of precipitating sludge is returned to a decomposition tank 4 by a pump 11, while the remainder is disposed as excess sludge 13. The removal of gaseous hydrogen sulfide from an inner liquid inside the decomposition tank 4 can be performed by a method such as adding a metal salt, e.g. a ferric one, to the inner liquid to remove it as an insoluble sulfide.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a biological treatment method for wastewater containing persistent COD, such as flue gas desulfurization wastewater.

Flue gas emitted from boilers and other combustion equipment using fossil fuels contains high concentrations of sulfur oxides and nitrogen oxides. If these are discharged into the atmosphere without treatment, they will cause many problems in terms of environmental conservation, both because of their own toxicity and because they change into even more harmful substances through photochemical reactions in the atmosphere. Therefore, in accordance with legal regulations, flue gas containing these substances is desulfurized and denitrated before being discharged into the atmosphere.

One of the most commonly used flue gas desulfurization and denitrification methods today is a method in which sulfur oxides and nitrogen oxides in flue gas are absorbed and removed by an alkaline solution. In this method, most of the sulfur oxides are removed as sulfates such as calcium sulfate and magnesium sulfate, but compounds that are difficult to be oxidized and decomposed such as dithionates are also produced as by-products. Among sulfur oxides that are difficult to decompose by oxidation, dithionic acid in particular cannot be effectively decomposed by chlorine or ozone, and physicochemical methods are limited to wet combustion methods.

In view of the current situation, the present invention proposes a method for degrading the above-mentioned persistent COD components, which are sulfur oxides, by utilizing the biodegradability of microorganisms. The object is to provide a method that can accelerate the biodegradation rate during decomposition.

The present invention is a method for treating wastewater containing dithionic acid, which is characterized by adding organic matter to wastewater containing at least dithionic acid or a dithionate salt, and performing anaerobic biological treatment while removing generated hydrogen sulfide.

The basic structure of the present invention will be explained in detail below based on the research history that led to the present invention.

Sulfur-oxidizing bacteria (genus Th1obaci 11us, etc.) and sulfur-reducing bacteria (Desulfoviburio JfA, etc.)
It is well known that these compounds biodegrade dithionic acid, etc. As an energy-saving treatment method for decomposing persistent COD components of sulfur oxides containing dithionic acid, replacing the wet combustion method, the horizontal side was initially started using a simple continuous fermentation treatment method using anaerobic bacteria. The sample flue gas desulfurization wastewater was concentrated by dilution or physicochemical treatment such as ion exchange treatment, and the dithionic acid concentration was reduced to 10.
0m9/las S20'b + 3001ffi7/
las 5206 + 500m9/L as S 2
06+ 1 (100m9/l as 5206 4 stages 1
lactic acid was added as a BOD source so that the concentration was 100 my/l (lactic acid).

The inoculum used was a mixed bacteria cultured from digested sludge taken from an anaerobic sewage sludge digester in an enrichment medium containing 1 sodium dithionate, and the actual concentration in the experimental reaction tank was 7513000+.
It was planted to become '19A-MLSS. As a result,
In the case of the sample wastewater with a dithionic acid concentration of 1oom9/L, the decomposition and removal of dithionic acid was almost completely achieved, but when the dithionic acid concentration in the sample wastewater was 75x 300 m9/L.
1, the removal rate of dithionic acid decreased to about 60 ml, and when the dithionic acid concentration was 5 oomy/1 or more, dithionate fermentation occurred. Decomposition of this dithionic acid! As a result of investigating the H harmful factor, it was found that the hydrogen sulfide concentration in the treated water at the time when the inhibition phenomenon was observed changes as shown in Table 1, depending on the dithionic acid concentration in the test wastewater75 (known).

Table 1 The above experiment revealed that anaerobic biodegradation of dithionic acid cannot be continued by simple anaerobic biodegradation method when the concentration of dithionic acid in the sample wastewater exceeds ]oomp/j. It is known that the concentration of hydrogen sulfide in the reaction solution is relatively high when an inhibition phenomenon occurs. Next, the concentration of dithionic acid was 3 oomp/l and 500 μ/1.

Similar biological treatment experiments were conducted on wastewater of 1000 m9/l while desulfurizing the hydrogen sulfide concentration in the reaction solution to below 8 m9/l. Complete decomposition treatment of dithionic acid was achieved. From the above results, it is known that in the anaerobic biodegradation treatment of dithionic acid, a high concentration of hydrogen sulfide is generated, which inhibits the decomposition of dithionic acid. The effectiveness of decomposition treatment while removing hydrogen has been demonstrated.

As described above, the method according to the present invention is particularly effective for wastewater with a high concentration of dithionic acid, so it is preferable to use ion exchange resin,
It is preferable to use a membrane in which at least dithionic acid is concentrated with K, such as an electrodialysis membrane or a reverse osmosis membrane.

Next, an example of an embodiment of the present invention will be described in detail based on the drawings. Although the illustrated process belongs to the anaerobic contact method, other types of processes are also possible as described below.

In the figure, dithionic acid-containing wastewater discharged from a flue gas desulfurization process or the like or from its concentration process is input as an inflow liquid 1 into an anaerobic biodecomposition tank 4 (hereinafter abbreviated as a decomposition tank). The residence time in the decomposition tank at this time is often set in the range of 05 to 10 days in the anaerobic contact method such as this embodiment, and the residence time of this wastewater is the amount of organic matter 15 added to the decomposition tank 4. The decision can be made depending on the type of immigration.

When methanol is used as the added organic substance, the residence time can be particularly shortened to a range of 0.3 to 2.0 days; on the other hand, sewage sludge and industrial wastewater sludge.

When using fresh human urine, etc., the residence time must be slightly longer, from 4 days to 0 days.

Other organic wastewaters that were effective in decomposing dithionic acid include urban sewage, pit garbage juice from garbage treatment plants, sewage sludge, leachate from municipal waste composting plants, and garbage from landfills. leachate, leachate from manure, including livestock manure from pig pens and cattle pens, and stable cleaning wastewater;
Examples include molasses from sugar mills, steam drain from pulp mills, brewing wastewater and distillation wastewater from brewing plants, and factory wastewater from food processing plants. When these are used, the residence time in the reactor is It is necessary to take a slightly longer period of time, from 0.8 days to 5.0 days, than when methanol is used as the added organic substance.

The only commercially available organic substance other than methanol that has been shown to have an additive effect is glopanol among alcohols.

Butanol, glycerol, and ethanol can be mentioned, but among these, ethanol had a slightly lower addition effect.

Organic acids include formic acid, pyruvic acid, lactic acid, propionic acid,
Additive effects were seen for butyric acid, succinic acid, citric acid, and acetic acid. Particularly in the case of acetic acid, the addition effect was high when mixed with other organic acids. When these organic acids are added, the residence time in the reactor needs to be about 0.6 to 40 days, which is slightly longer than when methanol is added. It has been found that the time required is shorter than in the case of addition. , it's maltose.

Cellobiose, glucose, etc., and R elements also require approximately the same residence time.

Depending on the amount of organic matter added and the n degree of dithionic acid (salt) and other persistent COD substances in the wastewater to be treated, the amount of organic matter to be added ranges from the same concentration as dithionic acid to 7% in terms of BOD. It is preferable to add twice as much. If the amount of added organic matter is less than this, dithionic acid cannot be fully decomposed, and undecomposed dithionic acid will remain in the treated water, and if more organic matter is added, the residual BOD concentration in the treated water will decrease. 130 due to high oxidation, aerobic treatment, etc.
D Removal costs are high.

In addition, in the present invention, the above-mentioned organic wastewater, organic sludge, and alcohols are used as additive organic substances.

It goes without saying that organic acids and saccharides can be used in appropriate combinations.

Under the above-mentioned added nutrient conditions and retention conditions, dithionic acid in the input wastewater is almost completely reduced and decomposed to hydrogen sulfide, and some remains as dissolved hydrogen sulfide in the tank liquid. The rest moves to 14 in the digestive gas. The dithionic acid decomposition tank 4 of the present invention is operated under the temperature conditions adopted for normal methane fermentation, that is, 20°C to 20°C for decomposition using mesophilic bacteria.
4 (1'c, 45℃ to 70℃ for decomposition using thermophilic bacteria)
Its efficiency can be significantly increased by keeping the temperature at - especially when operating at 45 to 70 °C (dissolution) Lz
Although it is very effective in reducing the S concentration, if decomposition efficiency is not an issue, operation without temperature control may be used.

The mixed liquid 2 flowing out from the decomposition tank 4 is degassed by passing through a vacuum chamber 5 whose pressure is reduced by a vacuum pump 10 and then guided to a precipitation separation tank 6, but the degree of pressure reduction in the vacuum chamber 5 It is appropriate that the pressure should be as strong as or weaker than the conventional anaerobic contact method used for methane fermentation treatment of organic wastewater, etc. Although it is possible to omit the degassing operation in some cases, it is necessary to make this selection after confirming that the solid-liquid separability in the precipitation separation tank 6 will not be extremely deteriorated.

In the sedimentation separation tank 6, the sludge is separated into a sedimentation (biological) sludge fraction 12 and a supernatant fraction 3, and this supernatant fraction 3 is used as dithionic acid decomposition treated water to remove residual BOD components, etc. The waste may be directed to an aerobic treatment process or directly discharged. A part of the settled sludge fraction 12 is returned to the decomposition tank 4 by the sludge transport pump 11, and the rest is the surplus sludge 1.
However, this ratio can be adjusted and determined so that the biological sludge concentration in the decomposition tank 4 is maintained at 500 to 10,000 r&9/l.

Various methods can be used to remove hydrogen sulfide from the liquid in the decomposition tank 4. As shown in the figure, providing a gas circulation path for hydrogen sulfide accumulated in the digestion gas and providing an absorption device 7 therein creates a low-concentration H2S atmosphere in the gas phase of the head space of the decomposition tank, and prevents it from remaining in the liquid in the decomposition tank. It is made for the purpose of expelling H2S' (r. H2S absorption and removal agents include caustic soda solution, ferrous solution, calcium carbonate solution, 1 lime solution,
A liquid absorbent such as ammonia liquid or monoethanolamine may be used, or a solid absorbent such as iron oxide may be used.

In addition, the Takaax method and the Zyrosox method, which have been conventionally used for desulfurization of digestion gas, may also be used depending on the case.

The gas circulation route for absorbing hydrogen sulfide is not necessarily limited to the method shown in the diagram; for example, a circulation pump (gas pump) and nine air supply pipes are placed below the liquid level in the decomposition tank to stir the gas. It is preferable that the hydrogen sulfide concentration dissolved in the liquid can be further reduced by the stripping effect than by gas circulation only in the head space. In addition to the above-mentioned gas absorption method, hydrogen sulfide can be removed by adding metal salts such as iron salts to the decomposition tank liquid to remove the hydrogen sulfide as insoluble sulfide.

In any of these cases, it is preferable to keep the hydrogen sulfide concentration in the decomposition tank liquid below 20m9/, especially from 0 to
It is desirable to keep it within the range of 8■/l.

If the pH in the digester shows extreme fluctuations, reduce the pH to 5.
．． It is preferable to adjust it to a range of 5 to 7.5. This p
H adjustment is effective not only in promoting the anaerobic biodecomposition reaction of dithionic acid but also in removing the hydrogen sulfide through gas circulation and absorption. This is particularly important when the pH in the digester liquid increases above 7.5 in a system without pH adjustment. That is, if the p.

In addition, it is 81-1 stirrer in the figure.

In addition to the above-mentioned embodiments, the anaerobic biological treatment apparatus for flue gas desulfurization wastewater according to the present invention includes a semi-batch contact digestion method, an upflow anaerobic digestion apparatus, which is a conventionally known anaerobic digestion apparatus. Most of the equipment belonging to the filter bed method 1 fluidized bed anaerobic reactor method, upflow anaerobic sludge blank °soto method, etc. can be used to improve the water quality of the flue gas desulfurization wastewater to be treated and the amount of added organic matter. This can be cited as an advantage of widening the selection range in configuring the most efficient device.

Note that after treating wastewater containing at least dithionic acid by the method of the present invention, if the water flowing out from the anaerobic reactor (decomposition tank 4) contains unused organic matter, hydrogen desulfurization is incomplete. If it is necessary to remove residual BOI or COD concentration, such as when hydrogen sulfide is present, or when sulfite and ions are contained due to insufficient sulfate reduction, use an aeration tank or biofilm method reactor (immersion). Needless to say, it is preferable to introduce the material into an aerobic biological treatment device (filter bed, fluidized bed, single-rotation disk, trickling filter, etc.) and perform aerobic biological treatment.

As described above, the present invention is applicable to wastewater containing dithionic acid or dithionate, including 1 water, human waste, various industrial wastewater, various agricultural and livestock wastewater, and mausoleum wastewater such as blackstrap molasses, discharged from these treatment processes. waste sludge, commercially available organic substances such as methanol, ethanol 9 propatool, butanol, alcohols such as chrycerol, oligo lees obtained by hydrolysis of polysaccharides such as cellulose and starch, sugars such as reducing sugars, and Formic acid, acetic acid, propionic acid, acetic acid.

A) A method of anaerobic biological treatment by adding any one or a mixture of organic substances such as icosyl acids such as pyruvic acid, lactic acid, succinic acid, and citric acid to the biological treatment step. This method is characterized by the fact that it is carried out while removing the hydrogen sulfide that is generated, and it is possible to decompose difficult-to-decompose COD substances in a short time, efficiently, and in a labor-saving manner through a simple process. It has many advantages such as there is no problem of secondary pollution, and existing equipment can be used as is or with only slight modification.

[Brief explanation of the drawing]

The drawing is a flow/-1. showing an embodiment of the present invention. DESCRIPTION OF SYMBOLS 1... Inflow liquid, 2... Outflow mixed liquid, 3... Supernatant liquid fraction, 4... Decomposition tank, 5... Decompression chamber, 6... Precipitation separation tank, 7... Absorption device, 8... Stirrer, 9... Circulation pump, 10... Decompression pump, 11... Sludge transport pump, 12. Precipitated sludge fraction, 13... Excess sludge, 14.
Digestion gas, 15...Organic matter. Patent applicant: Patent attorney representing Ebara Infilco Co., Ltd.
Edge Mountain Tlj-

Claims (1)

[Scope of Claims] 1. A method for treating wastewater containing dithionic acid, which comprises adding organic matter to wastewater containing at least dithionic acid or a dithionate salt, and performing anaerobic biological treatment while removing generated hydrogen sulfide. 2. The method according to claim 1, wherein the waste water is concentrated water of dithionic acid or dithionate salt, and is obtained by concentrating flue gas desulfurization waste water by physicochemical treatment such as ion exchange treatment. 3. The method according to claim 1 or 2, wherein the organic substance is a substance arbitrarily selected from the group consisting of organic wastewater, organic sludge, alcohols, organic acids, and sugars. 4. The method according to claim 3, wherein equnol is used as the organic substance. 5. The method according to claim 3, wherein acetic acid is used as the organic substance. 6. The amount of the organic substance added is calculated based on the BOD equivalent amount of dithionic acid, dithionate, and other persistent COD* quality C.
The method according to claim 4 or 5, wherein the amount is set to be 1 to 7 times the OD conversion amount. Z. The method according to claim 6, wherein the anaerobic biological treatment is carried out while maintaining the hydrogen sulfide concentration of the biological reaction liquid at 2o''9/ or less, preferably 8 to 1/2 or less. 8. The anaerobic treatment. During biological treatment, the pH of the biological reaction solution was set to 5.
The method according to claim 6 or 7, which is carried out by adjusting the temperature to 5 to 7.5. 9. The anaerobic biological treatment El'! Claim 6, in which the temperature of the biological reaction solution is maintained at 45°C to 70°C;
The method described in paragraph 7 or 8.