JPH0232952B2 - HOSOGANJUSUINOSHORIHOHO - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a boron treatment method for boron-containing wastewater such as discharged wastewater from a coal-fired boiler using an ion exchange resin that selectively adsorbs boron. Boron selective adsorption ion exchange resin (hereinafter simply referred to as resin) was developed in the United States around 1957 and is said to be "the only one that can treat boron in wastewater containing a large amount of coexisting salts to less than 1 mg/kg", but conventionally magnesium brine It has only been applied to purification, and has not gone beyond laboratory trials for irrigation water, incinerator smoke wastewater, etc. Further, in principle, the resin has the effect of concentrating so-called boron, similar to the normal ion exchange method, and is accompanied by recycled waste liquid enriched with boron. Although boron is considered to be an essential element for plants, it is known that excessive amounts have a negative effect on their growth, and even in Japan, extremely strict allowable concentrations in wastewater of less than 1 mg or less than 2 mg have already been established. Some places have enacted them. On the other hand, coal is being reconsidered as an energy source, and there is a trend in the electric power industry in particular to switch from heavy oil-fired to coal-fired thermal power plants, but coal contains tens to hundreds of mg of boron per kg. This must be treated as it migrates and dissolves in waste water and ash dump wastewater. However, due to its characteristics, boron is an extremely poorly soluble substance, and it is impossible to clear the above wastewater regulation value by precipitating it and separating it from water. The ion exchange/adsorption method using an exchange resin is the only one, but this resin has the disadvantage of a small exchange capacity and a low concentration rate of boron in the recycled waste liquid. The present invention provides a method for treating boron in waste water using the resin, which compensates for these drawbacks. As mentioned above, the inventors of the present invention were faced with the need to treat boron in the discharged wastewater of coal-fired boilers, and as a result of various studies, found that the resin method was used especially under the condition that boron in the treated water was 1 mg/or less or 2 mg/or less. It was determined that there is no other practical method, but in this case, the key to this method is to minimize the amount of boron-concentrated recycled waste liquid and extract the boron from the system in a highly concentrated state. I thought it was a thing. From the above point of view, we conducted a column water flow test on drainage and wastewater (simulated water) and learned that the boron concentration in the treated water has a special relationship with the PH of the treated water.
Understand the elution pattern of boron in the recycled waste liquid,
It became clear that the intended purpose could be realized. The results of the column water flow test are shown below. Raw water with the following water quality, which simulates drainage and drainage, is treated with boron selective adsorption ion exchange resin, Amberlite IRA-
Figure 1 shows an example of a boron breakthrough curve obtained by passing water through a small column packed with 743 (Rohm & Haas).

[Table] From Figure 1, it can be seen that there is a clear correlation between the PH of treated water and the leaked boron concentration. In this figure, at the inflection point where the pH starts to decrease from about 10.5 to about 7, the leaked boron reaches approximately 1 mg/, and then the pH drops to about 7.
At the point where the boron concentration in the treated water reaches the same level as the boron concentration in the raw water. In this case, PH
The absolute value of is not a problem. Therefore, if the pH of the water at the outlet of the resin tower is monitored continuously or periodically, the leakage of boron can be detected. In practical terms, the PH of the outlet water of each resin tower is continuously measured, the PH set value as described above is detected, and the towers can be automatically switched as a merry-go-round under the condition that the boron concentration in the treated water is 1 mg/or less. be. In this case, rather than the one-tower water flow system in Figure 2a, the second
The merry-go-round method shown in Figure b has a higher resin utilization rate, and the amount of boron adsorbed per unit amount of resin is approximately 30.
% more. In the figure, W is raw water, W′ is treated water,
The shaded area in the column is an adsorbed area, the plain area is an unadsorbed area, and C is a regenerated column. To explain the merry-go-round method in b in more detail, two resin cylinders are connected in series to perform water flow treatment, and when the resin cylinder on the raw water side reaches the breakthrough point, it is removed and the recycled resin cylinder is processed. This method is placed on the water side, and the removed resin cylinder is recycled and prepared for replacement. The explanation regarding FIG. 2b is as follows.

[Table] On the other hand, an example of the elution pattern of boron in the regeneration process is shown in FIG. In this figure, FIG. 1 is expressed as the ratio (%) of the amount of eluted boron in each fraction to the total amount of boron eluted in the regeneration step after the completion of the adsorption operation. From the data in Figure 3, we can determine the fraction taken out of the system, the average concentration of boron, the concentration ratio expressed as the ratio of the average concentration to the concentration in the raw water of 107 mg/
Furthermore, if the ratio of the eluted boron in the fraction to the total eluted boron amount in the regeneration step is summarized as an exclusion rate, it will be as follows.

[Table] In Case 1, the exclusion rate is 100%, but the concentration factor is only 6.7. On the other hand, in case 4, although the rejection rate decreases to about 88%, the concentration ratio reaches 30.7, and it is clear that the subsequent operation, the treatment of recycled waste liquid, will be much more economically advantageous. To put it simply, when 100 m ³ of wastewater is treated, in case 1 it is necessary to treat about 15 m ³ of recycled waste liquid, but in case 4 it is only necessary to treat about 3 m ³ of recycled waste liquid. Fractionation of the fraction F ₁ thus selected is carried out as shown in FIG. 4, and can be easily carried out on an industrial scale using a combination of an extremely common timer and valve. The remaining fraction _F2 is recycled together with the raw wastewater. The present invention is based on the above test results and relates to a method for deboronizing boron-containing wastewater, and is characterized by the following points. (1) Fully utilize resin exchange capacity by adopting a merry-go-round system. (2) Check the pH of the resin tower outlet water to prevent boron leakage into the treated water.
to monitor. (3) Without removing all of the recycled waste liquid from the system,
Only the fraction with a high concentration of boron is taken out of the system, and the remaining recycled waste liquid is returned to the raw water side for circulation treatment. (4) The recycled waste liquid taken out of the system is treated by volume reduction through evaporation drying or solidification with cement, and then disposed of. Note that a weakly basic anion exchange resin is used as the boron selective adsorption ion exchange resin in the present invention. A case in which the method of the present invention is carried out in a three-tower system will be specifically explained using FIG. 5. After filling a predetermined amount of boron selective adsorption ion exchange resin 1 (Amberlite IRA-743) into at least two resin towers 2 and 3 and regenerating each separately with, for example, 10% sulfuric acid and 4% sodium hydroxide aqueous solution. ,
The resin towers 2 and 3 are connected in series, and boron-containing waste water W such as discharged water is passed through at a specified flow rate. In this case, even if the first column 2 reaches breakthrough, water continues to flow and the leaked boron is adsorbed in the second column 3. In the figure, hatched areas indicate adsorbed areas, and plain areas indicate non-adsorbed areas. In this system, the resin in the first column is adsorbed to a state substantially close to the equilibrium capacity, so that the resin is effectively utilized, and the amount of boron adsorbed per unit amount of resin increases. In addition, the boron adsorption status of the resin in each tower during water flow, that is, the leakage status of boron in the effluent water W′ or treated water W″, is determined by the PH of the water at the outlet of each tower.
It can be detected by continuous or periodic monitoring using the PH detector 4. In the regeneration process, the waste liquid from all processes is not discharged outside the system, but only a fraction with a high boron concentration, such as extruded water after passing through sulfuric acid, or a part of it, is discharged outside the system, and the remaining waste liquid is returned to the raw water side. do. In this case, the fraction can be freely selected by timer control or by detecting the pH of the regenerated waste liquid. The recycled waste liquid taken out of the system is evaporated to dryness to reduce its volume, or treated with cement solidification, and then disposed of. In the figure, 5 indicates regenerated adsorption, etc. The method of the present invention can be applied to equipment for treating boron-containing water, such as drainage and drainage from coal-fired boilers, ash dump wastewater from coal-fired boilers, smoke wastewater from garbage incinerators, and leachate from garbage landfills.

[Brief explanation of drawings]

Figure 1 is a boron breakthrough curve in the present invention, which is a graph showing the relationship between boron concentration in treated water and PH of treated water, Figure 2 is a diagram comparing the adsorption status by water flow method, and Figure 3 is a graph showing the relationship between boron concentration in treated water and PH of treated water. FIG. 4 is a graph showing the state of boron elution in the process; FIG. 4 is a diagram showing the situation in which part of the treated water is returned to the waste liquid treatment process and the other part is returned to the raw water side; FIG. FIG. 2 is a diagram illustrating one embodiment.

Claims (1)

[Claims] 1 In a method for treating boron-containing water using an ion exchange resin that selectively adsorbs boron, the adsorption operation is performed in a merry-go-round manner, and the boron adsorption status of the resin is detected by monitoring the pH of the water at the outlet of the resin tower during water flow. A treatment of boron-containing water that is characterized by switching the resin cylinder and taking out only a part of the fraction with a high boron concentration from the waste liquid generated in the regeneration process, and returning the other fractions to the raw water side. Method.