JPS588315B2 - Biological treatment method for wastewater containing dithionic acid and polythionic acid - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for the biological treatment of wastewater containing dithionic and polythionic acids.

A typical example of wastewater containing dithionic acid and polythionic acid is wet flue gas desulfurization wastewater, which contains dithionic acid as the main ingredient, as well as trithionic acid, tetrathionic acid, pentathionic acid, and hexathionic acid. Contains polythionic acids such as and heavy metals.

Conventionally, coagulation-sedimentation methods, activated carbon adsorption methods, ion-exchange resin methods, etc. have been investigated as methods for treating the above-mentioned wet flue gas desulfurization wastewater. The ion exchange resin method requires post-treatment and has the drawback of being extremely expensive.

On the other hand, the present inventors have already filed a patent application in 1983-799.
No. 37, he discovered a ``biological treatment method for wastewater containing polythionic acid'' and showed that it was a cheaper and more effective method than physical-chemical treatment.

The above invention biooxidizes polythionic acid using activated sludge, and uses thiocyanate or thiosulfate as the main nutrient source of activated sludge. The disadvantage was that it accounted for a fairly large proportion.

Furthermore, in the above invention, a group of sulfur bacteria (Thiobacillus spp.
Activated sludge containing priority species such as Thioparas, Thiobacillus novellas, Thiobacillus neapolitanius, etc. has a property that makes it difficult to form sludge flocs with good sedimentation properties, so it is easy to flow out with treated water, making it difficult to retain sludge in the biological reaction tank. This has the disadvantage that it may be difficult to obtain stable operating performance.

Therefore, the inventors of the present invention have proposed
No. 2273 “Biological treatment method for wastewater containing dithionic acid”
discovered a method that could both stabilize and improve processing performance, and in Japanese Patent Application No. 116114/1989, inexpensive sulfur particles ( We proposed that by-products from pollution control processes (hereinafter referred to as S°) could be used.

To summarize the above, the wastewater treatment of wet flue gas desulfurization process (
(mainly coagulation and sedimentation treatment), the COD in the treated water sometimes became high and the processability became unstable.

When we investigated the cause of this, we found that the polythionic acid contained in the wastewater was hardly removed.

Therefore, we investigated a method for stably treating polythionic acid, and as a result, we obtained the above-mentioned Japanese Patent Application No. 52-79937 method and Japanese Patent Application No. 52-142273 method, and we also developed the above-mentioned Japanese Patent Application No. 1987-142273, which aims to further reduce costs. This method was obtained using the method No. 53-116114.

The present invention has been made for the purpose of making the equipment more compact, reducing the cost of treatment, and stably retaining sludge, in order to make the treatment methods of these earlier applications more complete.

By the way, as described in the specification of the above-mentioned earlier application, the present inventors conducted repeated biological treatment tests for treating dithionic acid and polythionic acid, and discovered that thiocyanine (SCN-)
found that excellent dithionic acid and polythionic acid degrading bacteria exist in activated sludge that decomposes sulfur compounds such as thiosulfuric acid (S2O32-) and sulfur (S°), and furthermore, they found that bacteria that degrade sulfur compounds such as thiosulfuric acid (S2O32-) and sulfur (S°) exist. , Thiobacillus thiopalas (T
hiobacillus thioparus), Thiobacillus neapolitanius
us neapolitanus), Thiobacillus novellus (Thiobacillus novellus)
) and other groups of sulfur-oxidizing bacteria account for the priority species.

Therefore, the present inventors further investigated particulate iron sulfide (hereinafter F
We conducted the following experiment, focusing on polythionic acid (denoted as eS) and believing that there are excellent polythionic acid-degrading bacteria even in activated sludge that decomposes FeS.

Experiment 1 The experimental equipment was four (A, B, C, D) as shown in Figure 1.
Using.

In Figure 1, 1 is a dithionic acid tank (20l), 2
is an oxygen supply column (1l), 3 is a biological reaction column (0.
5l), 4 is a nutrient source tank (5l) (However, equipment A, C
5 is a packed filter medium (0.3 l), 6 is a dithionic acid supply pump, 7 is an oxygen supply blower, and 8 is a nutrient source supply pump (however, none is provided in apparatuses A and C).

In addition, in the four devices A, B, C, and D, devices A, B
In this case, sand with a particle size of 1 mmφ was used as the filling filter medium 5, and the apparatus C
, D has a particle diameter of 2 mmφ that also serves as a nutrient source as a packed filter medium 5.
of FeS was used.

In addition, 50 thiocyanine was added to the nutrient tank 4 of devices B and D.
It was adjusted to ppm and added.

Furthermore, in the four apparatuses A, B, C, and D, in addition to the packed filter medium 5, coke wastewater treatment activated sludge was preliminarily placed in the biological reaction column 3 at a concentration of 3000 to 4000 ppmM.
The sludge was introduced as a seed sludge to obtain LSS, and the pH in the biological reaction column 3 was controlled to 7 to 8 and the water temperature to 25°C.

To supply oxygen, air or air + pure oxygen is sent from the blower 7 into the oxygen supply column 2 through a differential user.
By coming into contact with the raw water flowing downward from the dithionic acid tank 1, the dissolved oxygen in the raw water reached almost the saturation point, and this was carried out by sending this to the biological reaction force ram 3 using the dithionic acid supply pump 6. .

The method of supplying raw water to the biological reaction column 3 was changed for each of the four devices as follows.

Apparatus A: Dithionic acid with a concentration of 100 ppm was fed to the bioreaction force ram 3 at a flow rate of 1 l/day.

Apparatus B: Dithionic acid at a concentration of 100 ppm was simultaneously supplied to the biological reaction column 3 at a flow rate of 1 l/day, and thiocyanate at a concentration of 50 ppm was supplied at a flow rate of 0.2 l/day.

Apparatus C: The feeding method was the same as apparatus A.

Apparatus D: Dithionic acid at a concentration of 100 ppm was simultaneously supplied to the biological reaction column 3 at a flow rate of 1 l/day and thiocyanate at a concentration of 50 ppm at a flow rate of 0.2 l/day.

After the treatment of the dithionic acid was confirmed, the supply of thiocyanate was stopped, and only dithionic acid with a concentration of 100 ppm was supplied to the biological reaction column 3 at a flow rate of 1 l/day.

The above experimental results were summarized as follows.

From the above results, treatment cannot be achieved by passing water through only dithionic acid, but treatment is possible when thiocyanide or FeS is supplied, and activated sludge that decomposes FeS contains dithionic acid as well as activated sludge that decomposes thiocyanide. The presence of degrading bacteria was confirmed.

In devices B and C, dithionic acid (
It was found that S2O62-), thiocyanine (SCN-), and FeS were biooxidized as follows.

S2O62-+O2→2SO42- SCN-+3O2→SO42-+NH4++CO2Fe
S+2O2→Fe2++SO42− These reactions are carried out in the Thiobacillus thioparus shown above.
This reaction is unique to sulfur-oxidizing bacteria such as Thiobacillus neapolitanius and Thiobacillus novellas.

When FeS was supplied to dithionic acid (apparatus C), it took about 30 days longer to achieve a dithionic acid removal rate of 95% or more compared to when thiocyanate was supplied (apparatus B). While thiocyanide easily dissolves in water, FeS hardly dissolves in water, so the reaction was slow and the growth of the sulfur-oxidizing bacteria was delayed.

In addition, when dithionic acid and thiocyanate were supplied into a reaction vessel filled with FeS in advance, and the sulfur-oxidizing bacteria were sufficiently grown, only dithionic acid was supplied (apparatus D
), the treatment of dithionic acid continues to be stable, and it takes about 30 days to achieve a dithionic acid removal rate of 95% or more compared to the case where only FeS is supplied to the dithionic acid described above (apparatus C). was shortened.

Once the removal rate exceeds 95%, thiocyanide, FeS
No matter which one was supplied, the processability was similarly stable thereafter.

Regarding the clarity of the treated water, extremely clear treated water was obtained with a suspended solids concentration of 10 ppm or less.

Through the above experiment, the present inventors confirmed that the biological treatment of dithionic acid can be performed by simultaneously supplying FeS, and thus arrived at the first aspect of the present invention.

That is, in the first aspect of the present invention, after growing microorganisms under aerobic conditions using FeS as a main nutrient source, the microorganisms and F
wastewater containing at least one type of dithionic acid is introduced into a container holding eS, and the dithionic acid and/or polythionic acid is biooxidized to sulfuric acid under aerobic conditions. and a biological treatment method for wastewater containing polythionic acid.

A second aspect of the present invention described below is provided as a method for more effectively carrying out the first aspect.

That is, the second aspect of the present invention is to grow microorganisms under aerobic conditions using FeS as a main nutrient source and at least one of thiosulfate, thiocyanate, and S° as an auxiliary nutrient source, and then grow the microorganisms under aerobic conditions. A wastewater containing at least one of dithionic acid and polythionic acid is introduced into a container holding FeS and FeS, and at least one of thiosulfate, thiocyanate, and S° is added as a supplementary nutrient source while maintaining aerobic conditions. After the dithionic acid and/or polythionic acid is biooxidized to sulfuric acid and the treatment of the dithionic acid and/or polythionic acid is confirmed, the supply amount of the supplementary nutrient source is gradually reduced. The present invention relates to a biological treatment method for wastewater containing dithionic acid and polythionic acid.

The process of the second invention will be explained as follows.

1) First, in addition to FeS, at least one of thiosulfate, thiocyanate, and S° is added, and activated sludge is acclimatized using this as a supplementary nutrient source.

(During this period, sulfur-oxidizing bacteria that decompose dithionic acid are sufficiently grown and increased.

)2) When the growth of sulfur-oxidizing bacteria has increased sufficiently according to 1) above, supply of raw water containing at least one of dithionic acid and polythionic acid is started.

(At this point, sulfur-oxidizing bacteria are the dominant species in the activated sludge, and it can be expected that the treatment of dithionic acid and/or polythionic acid will be carried out quickly.

)3) Once treatment with dithionic and/or polythionic acids is confirmed, the supply of one or more of thiosulfate, thiocyanate and S° as supplementary nutritional sources can be reduced until finally: The supply of the supplementary nutrient source is stopped and the Fe
Only support S.

The first and second aspects of the present invention can be implemented along the flow shown in FIG. 1 described above.

The biological reaction columns 3 in apparatuses C and D in FIG. 1 are of a biological filtration type, which not only uses FeS as a main nutrient source but also has the function of an attached biofilm type packing 5. However, in addition to this, a submerged filter type wastewater treatment apparatus shown in FIG. 2 can also be used.

In Fig. 2, 1 is the main body of the submerged filter type wastewater treatment equipment, 2
3 is a filling part (10 l), 3 is an air lift circulation part, 4 is an aeration blower, 5 is a raw water supply line, and 6 is a treated water extraction line.

The following experiment was conducted using the apparatus shown in FIG.

Experiment 2 FeS crushed into a 2 to 3 cm opening was placed in the filling part 2 shown in Figure 2.
Filled with a small amount of S° and a small amount of soil, and the pH of the filled part 2 was
The water temperature was controlled at 7-8 and the water temperature at 25°C.

Air was supplied from blower 4 at 5 l/min.

The raw water is 10 l/d of dithionic acid-containing wastewater from line 5.
Water was passed at a flow rate of .

As a result, it became possible to treat dithionic acid about 30 days after water flow, and thereafter the removal rate of dithionic acid was good and stable treatment performance was obtained.

From the above Experiment 2 and the above Experiment 1, the first and second inventions of the present invention use FeS as a filler, and a biofilm mainly consisting of dithionic acid and/or polythionate degrading bacteria is attached to and grows on the filler. It can be seen that biological treatment of dithionic acid and/or polythionic acid can be performed by this attached biofilm method.

Experiments 1 and 2 described above used dithionic acid, but when similar experiments were attempted using polythionic acid, a removal rate of 95% or more was obtained in both cases.

It was found that all polythionic acids were biooxidized to sulfuric acid as shown below.

In the case of trithionic acid, S3O52-+3O2→3SO42- In the case of tetrathionic acid, S4O62-+5O2→4SO42- In the case of pentathionic acid, S5O62-+7O2→5SO42- In the case of hexathionic acid, S6O62-+9O2→&6SO42- 1. The second invention is that even if the raw water contains ammonia or amines in addition to dithionic acid and polythionic acid, nitrification is not possible because both dithionate oxidizing bacteria and nitrifying bacteria are aerobic autotrophic bacteria. By adding bacteria to the filling part of the device shown in FIGS. 1 and 2,
Not only dithionic acid oxidation but also ammonia and amine oxidation can be performed simultaneously in the same tank.

Biological oxidation at this time can be estimated as follows, for example.

NH4+ nitrifying bacteria and O2NO3 The generated NO3- is reduced to N2 gas and removed by using a biological denitrification method as a post-treatment.

The effects of the first and second aspects of the present invention explained above are summarized as follows.

1) The treatment of dithionic acid and polythionic acid, which was conventionally considered to be extremely difficult to perform physicochemical treatment, is now possible through biological treatment, and the processability is also stable.

2) Since dithionic acid and polythionic acid are completely oxidized to sulfuric acid, post-treatment like the ion exchange resin method is not necessary.

3) Instead of thiocyanide and thiosulfuric acid, which are the main nutritional sources of activated sludge, which were used in Japanese Patent Application No. 1982-79937, also filed by the present inventors,
Processing costs are further reduced by using sulfur particles that can be treated in the same way as the thiocyanide and thiosulfuric acid used in 6114 and can be obtained at an extremely low cost, and iron sulfide in the form of particles that can be obtained at the same or lower cost. It is possible (estimated 1/5 to 1/10).

4) Particulate iron sulfide can be used not only as the main nutrient source for activated sludge, but also as a filler for biofilm attachment, making the equipment more compact, tower-type, and sludge can be stably maintained.

5) Various types of equipment can be used, such as the attached biofilm method and the floating activated sludge method.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing a schematic flow of the apparatus used in Experiment 1 of the present invention, and FIG. 2 is a diagram showing a schematic flow of the apparatus used in Experiment 2 of the present invention.

Claims (1)

[Claims] 1. After microorganisms are grown under aerobic conditions using particulate iron sulfide as a main nutrient source, dithionic acid, dithionic acid, Biological treatment of dithionic acid- and polythionic acid-containing wastewater, characterized in that wastewater containing at least one type of polythionic acid is introduced, and the dithionic acid and/or polythionic acid is biooxidized to sulfuric acid under aerobic conditions. Processing method. 2 Particulate iron sulfide is the main nutritional source, thiosulfate,
After microorganisms are grown under aerobic conditions using at least one of thiocyanate and particulate sulfur as supplementary nutritional sources, at least one of dithionic acid and polythionic acid is grown in a container holding the microorganism and particulate iron sulfide. The dithionic acids and/or polythionic acids are biologically purified to sulfuric acid under aerobic conditions, with at least one of thiosulfate, thiocyanate and particulate sulfur added as a supplementary nutrient source. Biological treatment of wastewater containing dithionic acid and polythionic acid, characterized in that after oxidation treatment and treatment of the dithionic acid and/or polythionic acid is confirmed, the supply amount of the supplementary nutrient source is reduced in stages. Method.