JPS6344036B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for biological treatment of wastewater containing dithionic acid and polythionic acid. A typical example of wastewater containing dithionic acid and polythionic acid is wet flue gas desulfurization wastewater, which mainly contains dithionic acid but also trithionic acid, tetrathionic acid, pentathionic acid, hexathionic acid, etc. Contains polythionic acid. Conventionally, coagulation-sedimentation method and activated carbon adsorption method have been attempted as treatment methods for the above-mentioned wet flue gas desulfurization wastewater, but
The above-mentioned thionic acids are hardly removed, and the ion exchange resin method requires post-treatment, which is economically disadvantageous. In contrast, Japanese Patent Application No. 79937 (1983)
No. 49638) "Biological treatment method for wastewater containing polythionic acid", Patent Application No. 142273 (1983)
No.) and Special Patent Application No. 116114 (Sho 53-116114)
“Biological treatment method for wastewater containing dithionic acid”, Tokkun Sho
No. 54-36235 (Japanese Patent Publication No. 58-8315) ``Method for treating wastewater containing dithionic acid and polythionic acid'' was proposed, and it was discovered that the treatment technology and economic efficiency could be dramatically improved compared to the conventional methods. Among the above proposals, in Japanese Patent Application No. 79937/1987, thiocyanate or thiosulfate was used as the main nutrient source when biooxidizing polythionic acid, but the proportion of the chemical cost in the treatment cost was Its large size was a drawback. In addition, activated sludge, which is dominated by sulfur bacteria that contribute to the biological oxidation of dithionic acid and polythionic acid, is difficult to form sludge floes with good settling properties.
The drawback was that it was difficult to maintain the minimum required amount of sludge in the tank, making it difficult to obtain stable performance. Therefore, Japanese Patent Application No. 142273 and Patent Application No. 53-
No. 116114 proposed a method for stabilizing the processing performance and improving the processing performance at the same time, and Japanese Patent Application No. 54-36235 proposed a method for making the device more compact and at lower cost. That is, in place of thiocyanate and thiosulfate, which are the main nutritional sources for living things that have been used in the past, the three applications mentioned above use sulfur particles or particulate iron sulfide to produce suspended biological activated sludge or biofilm-based biological filters. Alternatively, the immersed bed method was used to downsize the processing equipment and reduce processing costs. As mentioned above, in the previous application, thiocyanate (SCN'), thiosulfate (S ₂ O ₃ ^2- ), sulfur particles (S゜), and iron sulfide (Fes) particles are decomposed in activated sludge. A method has been proposed for the biological treatment of dithionic acid and polythionic acid by effectively utilizing a group of sulfur-oxidizing bacteria that are present as the dominant species. In addition to the above-mentioned series of sulfur compounds, the present invention uses iron sesquisulfide (Fe ₂ S ₃ ) and iron disulfide (FeS ₂ ) as the main nutritional sources, which is equivalent to the above-mentioned case of sulfur and iron sulfide. This was done after confirming that at least a better effect could be obtained. That is, the present invention provides iron sesquisulfide in the form of particles,
This invention relates to a method for treating wastewater containing dithionic acid and polythionic acid, which comprises biologically oxidizing dithionic acid and polythionic acid to sulfuric acid under aerobic conditions using at least one kind of iron disulfide as a main nutrient source. be. In the method of the present invention, the above-mentioned main nutritional sources
In addition to Fe ₂ S ₃ and FeS ₂ , supplementary nutritional sources include thiosulfate (S ₂ O ₃ ^2- ), thiocyanate (SCN ^- ), sulfite (SO ₃ ^2- ), and sulfide (S ^2- ). These supplemental nutritional sources can also be reduced stepwise after the dithionic and polythionic acids have been sufficiently biooxidized to sulfuric acid. In addition, in the method of the present invention, for example, the above-mentioned particulate main nutrient source is fixedly held in a container, and a biological (sulfur-oxidizing bacteria group) film is formed on the surface of the particles, or the above-mentioned particulate main nutrient source is The main nutrient source and the fluid medium are formed on the surface of the particles, and the particles are allowed to flow in a container to aerobically biooxidize dithionic acid and polythionic acid to sulfuric acid. This biological oxidation is shown by the following reaction formula. Dithionic acid: S ₂ O ₆ ^2- +O ₂ →2SO ₄ ^2- Trithionic acid: S ₃ O ₆ ^2- +3O ₂ →3SO ₄ ² -Tetrathionic acid: S ₄ O ₆ ^2- +5O ₂ →4SO ₄ ^2- Pentathionic acid: S ₅ O ₆ ^2- +7O ₂ →5SO ₄ ^2- Sixthionic acid: S ₆ O ₆ ^2- +9O ₂ →6SO ₄ ^2- In addition, the reactions of the main nutrient source and supplementary nutrient source in this case are as follows. It is shown as follows. Iron sesquisulfide: Fe ₂ S ₃ +6O ₂ →2Fe ²⁺ +3SO ₄ ^2- Iron disulfide: FeS ₂ +4O ₂ →Fe ²⁺ +2SO ₄ ^2- Thiosulfate: S ₂ O ₃ ^2- +5/2O ₂ →2SO ₄ ^2- Hereinafter, the method of the present invention will be explained in detail using specific examples. Specific example 1 Using a fixed bed apparatus as shown in Figure 1, sand, particulate iron sesquisulfide (Fe ₂ S ₃ ),
Three types of iron disulfide (FeS ₂ ) were each used as the filler 6, and each was filled and fixed in a separate device. At that time, activated sludge containing sulfur bacteria as the dominant species was charged into each device as seed sludge. The pH inside each device was set at 7 to 8, and air was supplied by an aeration blower 5 to maintain aerobic conditions. The temperature was kept at 25°C. As raw water 7, we used wastewater containing dithionic acid at a concentration of 100ppm to which 50ppm thiosulfuric acid was added as a supplementary nutrient source, and wastewater containing only dithionic acid at a concentration of 100ppm. Supply mode (in the same column, , indicates 1st stage,
(means the second stage carried out following this first stage)). In addition, in FIG. 1, 2 is an oxygen supply section, 3 is a packing material support bed, 4 is a diffuser plate, and 8
indicates treated water. The above results were as shown in Table 1.

【table】

[Table] When dithionic acid treatment was started in Experiments B to F, a biological (sulfur oxidizing bacteria group) film was formed on the surface of each filler. It can be seen from Table 1 that the treatment cannot be performed when dithionic acid coexists only with sand, and dithionic acid decomposition is possible only in the coexistence of thiosulfuric acid, Fe ₂ S ₃ , or FeS ₂ . When dithionic acid was biooxidized in the coexistence of only Fe ₂ S ₃ (experiment C), it took more time to achieve a dithionate removal rate of 95% or more than in the case of coexistence of thiosulfuric acid alone (experiment B). It took about 30 days, but this is thought to be because thiosulfuric acid is easily soluble in water, whereas Fe ₂ O ₃ is poorly soluble, making it difficult to use in biological oxidation reactions, which delayed the growth of sulfur-oxidizing bacteria. . Furthermore, when dithionic acid and thiosulfuric acid were first supplied into a reaction vessel filled with Fe ₂ S ₃ to allow sufficient growth of sulfur-oxidizing bacteria, only dithionic acid was supplied (Experiment D). The treatment of dithionic acid continued to be stable, and compared to the case where dithionic acid was biooxidized in the presence of only Fe ₂ S ₃ (Experiment C), it took 30 days to achieve a dithionic acid removal rate of more than 95%. The period has been shortened. When only FeS ₂ was used (experiment E) instead of only Fe ₂ S ₃ (experiment C), as in experiment C above, the dithionate removal rate was lower than when only thiosulfate was used (experiment B). It took about 30 days to achieve over 95%. The reason for this is thought to be the same as in Experiment C. In addition, when dithionic acid and thiosulfuric acid were first supplied into a reaction vessel filled with _FeS2 instead of _Fe2S3 to allow sufficient growth of sulfur bacteria, only dithionic acid was supplied (Experiment F ₎ . ), the same results as in Experiment D were obtained. In addition, thiosulfate (S ₂ O ₃ ^2- ) is used as a supplementary nutritional source.
It has also been confirmed that the same results can be obtained when thiocyanate (SCN ^- ), sulfite (SO ₃ ^2- ), or sulfide (S ^2- ) is used instead. The above treatment target is dithionic acid, but
Similar results have been obtained with polythionic acid. Specific example 2: Using a fluidized bed apparatus as shown in Figure 2,
The same experiment as in Example 1 was conducted except that sand, particulate iron sesquisulfide (Fe ₂ S ₃ ), and iron disulfide (FeS ₂ ) were used as fluid media. In Fig. 2, the same symbols as in Fig. 1 indicate the same functional parts as in Fig. 1, 11 is a fluidized bed column, 12 is a reaction section, 13 is a separator, 14 is an air lift pipe, 15 is a buttful plate, 1
6 is a treated water trough, 17 is an aeration pipe, and the above-mentioned fluid media are put into the reaction section 12 and the separation section 13, and flow together with the raw water in the direction of the arrow. The above results were as shown in Table 2.

[Table] In the above experiments b to f, it was confirmed that when the dithionic acid treatment was sufficient, a biological (sulfur oxidizing bacteria group) film was formed on the surface of each fluid medium. Furthermore, it was confirmed that the amount of dithionic acid treated per unit volume was increased compared to the fixed bed biofilm method of Example 1. This is thought to be because the amount of sulfur-oxidizing bacteria is larger than that in the fixed bed. From Table 2, the same things as Table 1 of Example 1 can be considered. In addition, thiocyanate (SCN ^{- )} , sulfite ( _{SO 3 2-} ⁾ _,
The same results were obtained when sulfide (S ^2- ) was used;
Similar results were also obtained when polythionic acid was used as the treatment target. The effects of the method of the present invention detailed above are summarized as follows. (1) The treatment of dithionic acid and polythionic acid, which has been difficult or extremely expensive with conventional physicochemical treatments, can be biologically oxidized and decomposed, making the treatment easy and cost-effective. (2) Processing costs can be significantly reduced by using inexpensive Fe ₂ S ₃ or FeS as a nutrient source instead of expensive thiocyanate or thiosulfate. (3) Sludge can be stably maintained by growing sulfur-oxidizing bacteria on particulate main nutrients. (4) By using particulate Fe ₂ S ₃ and FeS ₂ , it is possible to use the fixed bed method (adopted in Example 1) and the fluidized bed method (adopted in Example 2) among biofilm methods, and According to the fluidized bed method, the amount of sludge retained can be increased, and the treatment capacity can be dramatically improved.

[Brief explanation of the drawing]

FIGS. 1 and 2 are diagrams schematically showing the apparatus used in Examples 1 and 2 of the present invention.

Claims (1)

[Claims] 1. Dithionic acid and polythionic acid, which are characterized by biooxidizing dithionic acid and polythionic acid to sulfuric acid under aerobic conditions using at least one of particulate iron sesulfide and iron disulfide as a main nutrient source. A method for treating wastewater containing polythionic acid.