TWI523816B - Wastewater treatment method and system for containing fluoride ion and iron ion - Google Patents

Description

Treatment method and system for wastewater containing fluoride ion and iron ion

The invention relates to a method for treating wastewater and a system thereof, in particular to a method for treating wastewater containing fluoride ions and iron ions and a system thereof.

With the advancement and development of industry, although life has become more and more convenient, the relative environmental pollution has become more and more serious. The environmental pollution is far-reaching. In addition to the air pollution caused by the exhaust gas emitted by the factory, it is the factory. Water pollution caused by discharged wastewater.

Among the wastewater discharged from the factory, the water pollution caused by the pickling wastewater of the steelmaking industry and the stainless steel industry is the most serious, because the acid washing wastewater of the steelmaking industry and the stainless steel industry are often mixed with extremely high concentrations of various mixed acids. Among them, hydrofluoric acid with high toxicity and strong corrosivity is the most serious.

In order to treat hydrofluoric acid in pickling wastewater, the related art has developed an invention patent such as U.S. Patent No. 5,106,509, which is characterized in that calcium chloride (CaCl ₂ ) is added to a fluidized bed, and fluoride ions in the pickling wastewater are used. The reaction produces calcium fluoride crystals for the purpose of removing fluoride ions from the pickling wastewater. However, in practical applications, it is necessary to add an additional water source to dilute the pickling wastewater to below 500 mgF ^- /1, which not only forms an additional burden on the processing equipment. In addition, the manufacturing cost of the processing equipment is increased.

In order to improve the above shortcomings, the Republic of China Announcement No. 495487 invention patent first adds sodium hydroxide (NaOH) to the pH adjustment tank to adjust the fluorine waste. The pH of the water is then added to the fluidized bed crystallization tank (FBC) by adding calcium (or magnesium), sodium or aluminum to remove most of the fluoride ions, and then adding sodium hydroxide (NaOH) to adsorb the coagulation. The co-precipitation method further removes fluoride ions, making the fluorine-containing wastewater a standard discharge water. However, the addition of sodium hydroxide (NaOH) and calcium (or magnesium), sodium or aluminum agents will not only increase the cost, but also make the composition of the discharged water more complicated, which will cause difficulties in subsequent treatment, and will cause calcium ( Or magnesium, sodium or aluminum agents impose an additional burden on the fluidized bed crystallization tank (FBC).

Accordingly, it is an object of the present invention to provide a treatment method for wastewater containing fluoride ions and iron ions which can reduce sludge volume and reduce treatment cost.

Another object of the present invention is to provide a treatment system for wastewater containing fluoride ions and iron ions which can reduce sludge volume and reduce processing costs.

Thus, the method for treating wastewater of the present invention comprises a first processing step and a second processing step.

The first processing step is to input the wastewater into a fluidized bed crystallization tank for reaction, and define that the water discharged from the fluidized bed crystallization tank is the outflow water, wherein the outflow water can be divided into direct crystallization from the fluidized bed. The system discharged from the tank discharges water and the circulating water that flows into a reaction tank.

The second treatment step is to add calcium hydroxide to the reaction tank, and the hydroxide in the calcium hydroxide reacts with the circulating water to form a precipitate, and the circulating water is formed into the fluidized bed crystallization tank and is re-run. Reflow of reaction water.

The wastewater treatment system of the present invention comprises a raw water unit capable of discharging waste water, a processing unit for treating the wastewater, and a dosing unit connected to the processing unit.

The processing unit includes a fluidized bed crystallization tank for receiving wastewater, and a reaction tank in communication with the fluidized bed crystallization tank. The medicinating unit can add calcium hydroxide to the reaction tank to react with the wastewater to form a precipitate, and the waste water becomes a reflux water flowing into the crystallization tank of the fluidized bed.

The invention has the advantages of utilizing the design of the fluidized bed crystallization tank and the reaction tank, not only can directly treat the high concentration of wastewater, but also can increase the density of the precipitate by reducing the water content of the precipitate by high-density sludge reaction. Reduce the load on the dehydrator and reduce the overall volume of the sediment to improve the treatment efficiency of the wastewater, and at the same time, the harmful substances in the wastewater can be greatly removed.

Calcium hydroxide is added to the reaction tank to react with the circulating water in the reaction tank to form a precipitate having a higher density and a lower water content, thereby reducing the load of the dehydrator, thereby improving the efficiency of wastewater treatment and reducing the treatment cost.

The above and other technical contents, features and advantages of the present invention will be apparent from the following detailed description of the preferred embodiments.

Referring to Figure 1, a preferred embodiment of a treatment system 1 for treating wastewater containing fluoride ions and iron ions comprises a raw water unit 11 capable of outputting wastewater 100, a processing unit 12 for treating the wastewater 100, and a The dosing unit 13 to which the processing unit 12 is connected.

The raw water unit 11 includes a raw water tank 111 that can store the wastewater 100, and a first pump 112 that can transport the wastewater 100 in the raw water tank 111 to the processing unit 12. By the manner in which the raw water tank 111 stores the wastewater 100, the process of transporting the wastewater 100 to the processing unit 12 can be made more stable.

In the preferred embodiment, the raw water tank 111 is used to store wastewater 100 containing fluoride ions (F ^- ) and iron ions (Fe ²⁺ ) after a steelmaking process in a steelmaking plant.

The processing unit 12 includes a fluidized bed crystallization tank 121 connected to the raw water tank 111, a reaction tank 122 communicating with the fluidized bed crystallization tank 121, and a circulation pump 123. In the preferred embodiment, the fluidized bed crystallization tank 121 is filled with a cerium oxide (SiO ₂ ) support.

The medicating unit 13 includes a lime tank 131 for storing calcium hydroxide (Ca(OH) ₂ ) 101, and a _second tank capable of transporting calcium hydroxide 101 in the lime tank 131 to the reaction tank 122. Pump 132. By using the lime tank 131 to store the calcium hydroxide 101, the transportation process of the calcium hydroxide 101 can be made more stable. The calcium hydroxide 101 in the preferred embodiment is stored in the lime tank 131 in the form of a milk of lime.

Referring to Figures 1 and 2, a preferred embodiment of the method of treating wastewater 100 of the present invention comprises a first processing step 21 and a second processing step 22.

The present embodiment is a preferred embodiment of the wastewater treatment system 1 described above. Therefore, the device structure described in the present embodiment is a preferred embodiment of the wastewater treatment system 1, and therefore is not Repeat them.

Before the treatment of the wastewater 100, an appropriate amount of the support is filled in the fluidized bed crystallization tank 121, and water is filled to fluidize the support.

The first processing step 21 is to use the first pump 112 to input the wastewater 100 stored in the raw water tank 111 into the fluidized bed crystallization tank 121 of the processing unit 12 for reaction, and define the fluidized bed crystallization tank. The water discharged from 121 is the outflow water 102, wherein the outflow water 102 can be divided into system discharge water 103 directly discharged from the fluidized bed crystallization tank 121, and circulating water 104 containing iron ions which flows into the reaction tank 122 again. .

The second processing step 22 uses the second pump 132 to continuously transport the calcium hydroxide 101 stored in the lime tank 131 into the reaction tank 122, and recycle the circulating water 104 and the hydroxide into the reaction tank 122. The calcium 101 is aerated and agitated so that the divalent iron ions (Fe ²⁺ ) in the circulating water 104 can be oxidized to ferric ions (Fe ³⁺ ) via the aeration reaction, and the hydrogen hydroxide of the calcium hydroxide 101 The root generates high density sludge (HDS) to form iron hydroxide (FeOOH) precipitate, and then the circulating water 104 forms reflux water 105 containing calcium ions (Ca ²⁺ ), and the pump is pumped by the circulation. 123, the reflux water 105 is introduced into the fluidized bed crystallization tank 121 to carry out the reaction.

Since the water content of the iron hydroxide hydroxide precipitate is small, the structure of the iron hydroxide hydroxide precipitate is relatively tight and the density is high, so that the load of the dewatering machine of the subsequent dewatering treatment can be effectively reduced, thereby improving the treatment efficiency, and utilizing The high density of the oxidized iron hydroxide precipitate also reduces the volume occupied by the precipitate.

In the preferred embodiment, calcium ions in the reflux water 105 are reacted with fluoride ions (F ^- ) input into the wastewater 100 in the fluidized bed crystallization tank 121 to form calcium fluoride (CaF ₂ ) crystals, and again The outflow water 102 discharged from the fluidized bed crystallization tank 121 is formed. Moreover, since the second pump 132 continuously transports the calcium hydroxide 101 into the reaction tank 122 to increase the pH value of the circulating water 104, it is not necessary to additionally adjust the pH value of the wastewater 100, and the reaction tank 122 can continue. The pair of circulating water 104 and the calcium hydroxide 101 are aerated and agitated to oxidize the divalent iron ions in the circulating water 104 to ferric ions to continuously generate a high-density sludge reaction with the hydroxide in the calcium hydroxide 101. An iron hydroxide hydroxide precipitate is formed to continuously carry out the treatment of the wastewater 100.

It should be particularly noted that since the preferred embodiment is to remove fluorine and iron from the wastewater 100 and add calcium hydroxide, the reflux water 105 will contain calcium ions and can be combined with wastewater 100. The fluoride ion reacts to form calcium fluoride. In practical applications, in addition to removing iron ions from the wastewater 100, the calcium hydroxide 101 can also remove, for example, aluminum or other heavy metal harmful substances in the wastewater 100.

Moreover, since the calcium hydroxide 101 is added to the reaction tank 122, the structure and operation of the fluidized bed crystallization tank 121 are not affected, and only one type of calcium hydroxide 101 can be added to effectively remove fluorine and iron. The treatment cost can be effectively reduced. By the circulation treatment step 24, the reflux water 105 containing calcium ions can be continuously input into the fluidized bed crystallization tank 121, which can not only effectively improve the use efficiency of calcium ions, but also can be used with wastewater. The fluoride ion in 100 is sufficiently reacted to greatly reduce the concentration of fluoride ions in the system discharge water 103.

The inventors found that the average iron concentration of the system discharge water 103 after treatment with the treatment system 1 was 10.3 mg/L, with the circulating water 104 containing an average iron concentration of 6968 mg/L and an average fluorine concentration of 9000 mg/L. average The fluoride ion concentration is between 13 and 14 mg/L, and the density of the precipitate produced by the treatment system 1 is about twice that of the prior treatment. Thus, it can be seen that the fluidization bed crystallization tank 121 and the reaction tank 122 are combined with the fluidized bed. The design can significantly reduce the concentration of iron ions and fluoride ions, and can effectively reduce the water content in the precipitate and increase the density of the precipitate to effectively reduce the volume of the precipitate.

It should be particularly noted that in the preferred embodiment, the reflux water 105 is mixed with the wastewater 100 in the fluidized bed crystallization tank 121, thereby continuously treating the wastewater 100, but in practical applications, The treatment system 1 of the wastewater 100 can also be controlled to circulate the reflux water 105 between the fluidized bed crystallization tank 121 and the reaction tank 122, and then treat the wastewater 100 batch by batch, and the control method The prior art is generally known to those skilled in the art and will not be further described herein.

In summary, the method for treating wastewater containing fluoride ion and iron ion and the system thereof are designed by combining the fluidized bed crystallization tank 121 and the reaction tank 122, and directly processing the pH value of the wastewater 100 without additionally adjusting the pH value of the wastewater 100. High-concentration wastewater 100 can also increase the density of sediment by reducing the water content of the sediment by high-density sludge reaction, thereby reducing the load of the dehydrator and reducing the overall volume of the sediment, thereby improving the treatment efficiency of the wastewater 100, and at the same time The fluorine ion and the iron ion in the wastewater 100 can be largely removed, so that the object of the present invention can be achieved.

The above is only the preferred embodiment of the present invention, and the scope of the invention is not limited thereto, that is, the simple equivalent changes and modifications made by the scope of the invention and the description of the invention are All remain within the scope of the invention patent.

1‧‧‧Wastewater treatment system

100‧‧‧ Wastewater

101‧‧‧calcium hydroxide

102‧‧‧Outflow

103‧‧‧System discharge water

104‧‧‧Circulating water

105‧‧‧Return water

11‧‧‧ raw water unit

111‧‧‧ original sink

112‧‧‧First pump

12‧‧‧Processing unit

121‧‧‧ Fluidized bed crystallization tank

122‧‧‧Reaction tank

123‧‧‧Circulating pump

13‧‧‧Dosing unit

131‧‧‧ Lime trough

132‧‧‧Second pump

21‧‧‧First processing steps

22‧‧‧Second processing steps

BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1 is a schematic view showing a preferred embodiment of a treatment system for wastewater according to the present invention; and Fig. 2 is a flow chart showing a preferred embodiment of a treatment method for wastewater according to the present invention.

1‧‧‧Wastewater treatment system

100‧‧‧ Wastewater

101‧‧‧calcium hydroxide

102‧‧‧Outflow

103‧‧‧System discharge water

104‧‧‧Circulating water

105‧‧‧Return water

11‧‧‧ raw water unit

111‧‧‧ original sink

112‧‧‧First pump

12‧‧‧Processing unit

121‧‧‧ Fluidized bed crystallization tank

122‧‧‧Reaction tank

123‧‧‧Circulating pump

13‧‧‧Dosing unit

131‧‧‧ Lime trough

132‧‧‧Second pump

Claims (5)

A method for treating wastewater containing fluoride ions and iron ions, comprising: a first treatment step of introducing wastewater into a fluidized bed crystallization tank for reaction, and defining water discharged from the fluidized bed crystallization tank as outflow water, Wherein, the outflow water can be divided into system discharge water directly discharged from the fluidized bed crystallization tank, and circulating water re-injected into a reaction tank; and a second treatment step, adding calcium hydroxide to the reaction tank, Hydrogen peroxide in the calcium hydroxide is reacted with the circulating water to form a precipitate, and the circulating water is formed into reflux water which is re-introduced into the fluidized bed crystallization tank and re-reacted. The method for treating wastewater containing fluoride ions and iron ions according to claim 1, wherein the reaction tank of the second treatment step can be used for aeration reaction of wastewater to oxidize divalent iron ions in the wastewater into Ferric iron ions react with hydroxide in calcium hydroxide to form iron hydroxide precipitate. The method for treating wastewater containing fluoride ions and iron ions according to claim 2, wherein the calcium hydroxide in the second treatment step can cause calcium ions in the reflux water to react with fluoride ions to form calcium fluoride. Precipitate. The method for treating wastewater containing fluoride ions and iron ions according to any one of claims 2 or 3, wherein the reaction tank is agitated by aeration in the second treatment step to make ferrous iron Ions are oxidized to ferric ions. A treatment system for wastewater containing fluoride ions and iron ions, comprising: a raw water unit capable of outputting waste water; a treatment unit comprising a fluidized bed crystallization tank for receiving waste water, and a fluidized bed crystallization tank connected thereto a reaction tank; and a dosing unit capable of adding calcium hydroxide to the reaction tank to react with the waste water to form a precipitate, and the waste water becomes a return water flowing into the fluidized bed crystallization tank.