JP2006255499A - Fluorine-containing wastewater treatment method and apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a fluorine-containing wastewater treatment method and apparatus which efficiently treat fluorine-containing wastewater to obtain treated water of good quality with a low concentration of residual fluorine, and can reduce the moisture content of sludge generated by the treatment to reduce the amount of the generated sludge. <P>SOLUTION: The fluorine-containing wastewater treatment method comprises a reaction process for adding a calcium compound, and phosphoric acid or its water-soluble salt to the fluorine-containing wastewater to react them at pH of 5-10, a coagulation process for adding a polymer coagulant to the wastewater after the reaction process, a process for performing the solid-liquid separation of coagulated flocs-containing wastewater after the coagulation process, and a sludge return process for returning a part of the sludge subjected to the solid-liquid separation to the reaction process. The calcium compound and an alkali are added beforehand to the return sludge in the sludge return process, and then the sludge is returned to the reaction process. The fluorine-containing wastewater treatment apparatus comprises a reaction tank, a phosphorus supply means, a coagulation tank, a solid-liquid separator, a mixing tank, and a sludge return passage. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a method and apparatus for treating fluorine-containing wastewater. More specifically, the present invention can efficiently treat fluorine-containing wastewater to obtain water with good residual water quality with low residual fluorine concentration, and low moisture content of sludge generated during treatment, and generation of sludge. The present invention relates to a method and apparatus for treating fluorine-containing wastewater that can reduce the amount.

  Fluorine is contained in wastewater from semiconductor manufacturing processes using hydrofluoric acid-containing cleaning solutions and buffered hydrofluoric acid-containing etching agents, wastewater from metal refining, glass, ceramics, chemical factories, flue gas desulfurization wastewater, and groundwater. Since hydrofluoric acid is highly corrosive and damages pipes, and fluorine impairs the biological treatment function at the final treatment plant, it is required to remove fluorine in the wastewater to a low concentration.

  As a method for removing fluorine in water, a calcium compound such as calcium hydroxide or calcium chloride is added to water to produce calcium fluoride and separated by precipitation. An aluminum compound such as polyaluminum chloride or aluminum sulfate is added to water. There are known a method in which fluorine is adsorbed and coprecipitated in the gelled aluminum hydroxide produced, a method in which fluorine is adsorbed on a fluorine adsorbing resin, and the like.

  However, it is difficult to sufficiently remove fluorine by fluorine removal by a one-step treatment method using a calcium compound, and about 10 to 30 mg / L of fluorine remains in the treated water. In the method using an aluminum compound, the fluorine concentration of the treated water decreases as the added amount of the aluminum compound increases, and it is possible to obtain treated water with a fluorine concentration of 8 mg / L or less. However, the amount of chemical used and the generation of sludge There is a problem that the amount increases. Furthermore, the method of adsorbing fluorine to the fluorine-adsorbing resin requires pH adjustment, and after adsorbing a certain amount of fluorine, it needs to be regenerated with an alkali, resulting in a complicated process.

In addition, a method of removing fluorine by generating fluoroapatite using phosphorus and calcium is known, and fluorine can be removed to a low concentration, but the use ratio of calcium and phosphorus is large with respect to fluorine, Since water content is taken in at the time of sludge generation and the water content increases, the amount of sludge generated increases as in the case of the above aluminum treatment (Patent Document 1).
Japanese Patent No. 3504248

  The present invention prevents water entrainment in sludge particles and efficiently removes fluorine, thereby efficiently treating fluorine-containing wastewater to obtain water with good residual quality with low residual fluorine concentration. In addition, the present invention has been made for the purpose of providing a treatment method and a treatment apparatus for fluorine-containing wastewater, which can reduce the water content of sludge generated during treatment and reduce the amount of sludge generated.

  As a result of intensive research to solve the above problems, the present inventor previously added a calcium compound and phosphoric acid or a water-soluble salt thereof to a fluorine-containing wastewater, and reacted them at a pH of 5 to 10 for treatment. Based on this finding, it was found that by adding calcium compound and alkali to solid-liquid separated sludge and returning it to the reaction process, the water content of the generated sludge can be reduced and the fluorine concentration of treated water can be reduced. The present invention has been completed.

That is, the present invention includes (1) a reaction step in which a calcium compound and phosphoric acid or a water-soluble salt thereof are added to fluorine-containing waste water and reacted at pH 5 to 10, and an aggregation step in which a polymer flocculant is added to water after the reaction step In the method for treating fluorine-containing wastewater having a step of solid-liquid separation of the water containing the coagulated floc after the coagulation step, and a sludge return step of returning a part of the solid-liquid separated sludge to the reaction step, A treatment method for fluorine-containing wastewater, characterized in that a calcium compound and an alkali are added to the return sludge in the return step and returned to the reaction step,
(2) A process of removing fluorine as calcium fluoride by treating fluorine-containing wastewater with a calcium compound, adding calcium compound and phosphoric acid or a water-soluble salt thereof to the primary treated water of the process and reacting at pH 5-10 A reaction step, a coagulation step of adding a polymer flocculant to the water after the reaction step, a step of solid-liquid separation of water containing the coagulation floc after the coagulation step, and a step of reacting a part of the solid-liquid separated sludge In the method for treating fluorine-containing wastewater having a sludge return process to be returned to the wastewater, the fluorine-containing wastewater treatment method is characterized in that a calcium compound and an alkali are added to the return sludge in the sludge return process and returned to the reaction process in advance.
(3) The method for treating fluorine-containing wastewater according to (1) or (2), wherein the sludge concentration in the reaction step is 0.1 to 5% by weight,
(4) The method for treating fluorine-containing wastewater according to any one of (1) to (3), wherein seed crystals are added in advance to the reaction tank,
(5) The method for treating fluorine-containing wastewater according to (4), wherein the seed crystal is a calcium phosphate having an apatite structure, and
(6) Introduction of fluorine-containing wastewater, reaction tank for converting fluorine in the wastewater to fluoroapatite, phosphorus supply means for adding phosphoric acid or its water-soluble salt to the reaction tank, and adding polymer flocculant to reaction tank effluent A coagulation tank for coagulation treatment, a solid-liquid separation device for solid-liquid separation of coagulation tank effluent containing coagulation floc into treated water and sludge, and mixing calcium compound and alkali into a part of the solid-liquid separated sludge A treatment apparatus for fluorine-containing wastewater having a mixing tank and a sludge return path for returning the mixed sludge of the mixing tank to the reaction tank,
Is to provide.

  According to the method and apparatus for treating fluorine-containing wastewater of the present invention, calcium and alkali are adsorbed on the surface of sludge particles by adding calcium compound and alkali to sludge separated into solid and liquid in advance and returning it to the reaction step. Since it reacts with fluorine and phosphorus in the reaction step to produce fluoroapatite and removes fluorine, fluorine can be removed to a low concentration, and water uptake into sludge particles is suppressed and sludge water content is reduced. The rate can be reduced and the amount of sludge generated can be reduced.

  In the first aspect of the method for treating fluorine-containing wastewater according to the present invention, a reaction step in which a calcium compound and phosphoric acid or a water-soluble salt thereof are added to the fluorine-containing wastewater and reacted at pH 5 to 10, water after the reaction step is added. Fluorine having a coagulation step of adding a polymer flocculant, a step of solid-liquid separation of water containing coagulation flocs after the coagulation step, and a sludge return step of returning a part of the solid-liquid separated sludge to the reaction step In the wastewater treatment method, a calcium compound and an alkali are added in advance to the return sludge in the sludge return step and returned to the reaction step.

  FIG. 1 is a process flow diagram of one embodiment of the method for treating fluorine-containing wastewater of the present invention. Fluorine-containing wastewater stored in the raw water tank 1 is sent to the reaction tank 2. In the reaction tank, calcium compound and alkali previously added to the return sludge together with phosphoric acid and the return sludge are added, and the pH is adjusted to 5 to 10 by the pH adjuster, and fluoroapatite is generated on the surface of the sludge particles. , The fluorine concentration in water decreases. It is also possible to provide a second reaction tank between the reaction tank and the coagulation tank and adjust the pH in the second reaction tank. If pH adjustment is performed independently in the second reaction tank, pH adjustment is easy. The water having a reduced fluorine concentration is sent to the agglomeration tank 3 where a polymer flocculant is added and the flocs in the water agglomerate. The water in which the flocs are aggregated is solid-liquid separated in the sedimentation basin 4 and separated into treated water as supernatant water and sedimented sludge. A part of the sludge extracted from the sedimentation basin is returned to the mixing tank 5 as return sludge, and a calcium compound and an alkali are added.

  Examples of the calcium compound used in the method of the present invention include calcium chloride and calcium hydroxide. Examples of the alkali used in the method of the present invention include sodium hydroxide, potassium hydroxide and calcium hydroxide. Calcium hydroxide is inexpensive and can be suitably used because calcium hydroxide and alkali can be used together by using calcium hydroxide as the calcium compound. Examples of phosphoric acid or a water-soluble salt thereof used in the method of the present invention include phosphoric acid, polyphosphoric acid, metaphosphoric acid, pyrophosphoric acid, and their water-soluble salts. Among these, phosphoric acid can be suitably used because it is easy to handle. Examples of the pH adjuster that adjusts the pH in the reaction step to 5 to 10 include hydrochloric acid, sulfuric acid, sodium hydroxide, potassium hydroxide, and the like. When alkali is used as a pH adjuster, it is added to the mixing tank, but a part can be added to the reaction tank.

  In the method of the present invention, the calcium compound and alkali added to the return sludge are adsorbed on the surface of suspended solid particles in the sludge, sent to the reaction tank, adjusted to pH 5-10, and contained in the fluorine-containing wastewater. Fluorapatite reacts with fluorine and phosphoric acid added in the reaction vessel. Since this reaction occurs when calcium is adsorbed on the surface of the sludge particles and localized, the local concentration of calcium is higher than when the calcium compound is uniformly distributed throughout the reaction vessel. Since the surface of the sludge particles has a locally high calcium concentration, when fluoroapatite is formed, there is little entrainment of water molecules, and high density floc (HDS: High Density) with good sedimentation and dehydration properties. Solid) is formed, the moisture content of the sludge is lowered, and the amount of sludge generated can be reduced.

  In the second aspect of the method for treating fluorine-containing wastewater of the present invention, a step of treating fluorine-containing wastewater with a calcium compound to remove fluorine as calcium fluoride, a calcium compound and phosphoric acid or primary treatment water in the step A reaction step of adding the water-soluble salt and reacting at pH 5 to 10, a coagulation step of adding a polymer flocculant to the water after the reaction step, a step of solid-liquid separation of water containing the coagulation floc after the aggregation step, In addition, in a method for treating fluorine-containing wastewater having a sludge return step for returning a part of the solid-liquid separated sludge to the reaction step, a calcium compound and an alkali are added to the return sludge in the sludge return step and returned to the reaction step. .

  In the method of the present invention, there is no particular limitation on the process of removing fluorine as calcium fluoride by treating fluorine-containing wastewater with a calcium compound. For example, after adding a calcium compound to the coagulation sedimentation method, crystallization method, return sludge, fluorine Examples thereof include a method of supplying to the contained waste water. In the method of the present invention, the calcium compound used for removing fluorine as calcium fluoride is not particularly limited, and examples thereof include calcium hydroxide and calcium chloride.

  FIG. 2 is a process flow diagram of another embodiment of the method for treating fluorine-containing wastewater of the present invention. In this embodiment, in the former stage, the fluorine-containing wastewater is treated with a calcium compound to remove a part of the fluorine as calcium fluoride, and in the latter stage, the primary obtained in the former stage is the same as the embodiment shown in FIG. Fluorine remaining in the treated water is removed as fluoroapatite. The fluorine-containing wastewater stored in the raw water tank 6 is sent to the reaction tank 7, the pH is adjusted to 5-9 by adding a pH adjuster, and the calcium compound supplied to the reaction tank together with the return sludge reacts with fluorine. It precipitates as calcium fluoride, and the fluorine concentration in water decreases. The water having a reduced fluorine concentration is sent to the coagulation tank 8 and a polymer flocculant is added to aggregate the flocs in the water. The water in which flocs are condensed is solid-liquid separated in the sedimentation basin 9 and separated into primary treated water as supernatant water and sedimented sludge. A part of the sludge extracted from the sedimentation basin is returned to the mixing tank 10 as return sludge, and a calcium compound is added. By returning the sludge, calcium ions in the returned sludge are used to fix fluorine, and the calcium fluoride in the returned sludge serves as the core of crystallization, and suspended matter with good sedimentation and dehydration properties. Particles can be formed.

  The primary treated water obtained by the previous treatment is temporarily stored in the primary treated water tank 11 and then sent to the reaction tank 12. In the reaction tank, calcium compound and alkali previously added to the return sludge together with phosphoric acid and the return sludge are added, and the pH is adjusted to 5 to 10 by the pH adjuster, and fluoroapatite is generated on the surface of the sludge particles. , The fluorine concentration in water decreases. It is also possible to provide a second reaction tank between the reaction tank and the coagulation tank and adjust the pH in the second reaction tank. The water having a reduced fluorine concentration is sent to the coagulation tank 13 and a polymer coagulant is added to aggregate the flocs in the water. The water in which the flocs are agglomerated is solid-liquid separated in the sedimentation basin 14 and separated into treated water as supernatant water and sedimented sludge. A part of the sludge extracted from the sedimentation basin is returned to the mixing tank 15 as return sludge, and a calcium compound and an alkali are added.

  Calcium compounds and alkali added to the return sludge are adsorbed on the surface of suspended solid particles in the sludge, sent to the reaction tank, adjusted to pH 5-10, and added in the reaction tank with fluorine in the primary treated water Reacts with the formed phosphorus to produce fluoroapatite. Since this reaction occurs when calcium is adsorbed on the surface of the sludge particles and localized, the local concentration of calcium is higher than when the calcium compound is uniformly distributed throughout the reaction vessel. Since the surface of the sludge particles has a locally high calcium concentration, when fluoroapatite is formed, there is little entrainment of water molecules, and high density floc (HDS: High Density) with good sedimentation and dehydration properties. Solid) is formed, the moisture content of the sludge is lowered, and the amount of sludge generated can be reduced.

In the method of the present invention, the embodiment shown in FIG. 2 can be suitably applied to fluorine-containing wastewater having a high fluorine concentration, for example, fluorine-containing wastewater having a fluorine concentration of 30 mg F ⁻ / L or more. The treatment of fluorine-containing wastewater is divided into two stages, fluorine-containing wastewater with a high fluorine concentration is treated with a calcium compound to remove fluorine as calcium fluoride, and the remaining fluorine in the primary treated water is phosphoric acid or its By removing it as fluoroapatite with the water-soluble salt and calcium compound and alkali added to the returned sludge in advance, the amount of chemicals used can be reduced, the moisture content of the sludge can be reduced, and the total amount of generated sludge can be reduced. it can.

  In the method of the present invention, the pH in the reaction step is 5 to 10, more preferably 7 to 8.5. When the pH is less than 5, fluoroapatite is hardly generated, and the phosphorus concentration of the treated water may not be sufficiently lowered. When pH exceeds 10, there exists a possibility that the removal of a fluorine may become inadequate. By setting the pH of the reaction step to 7 to 8.5, both the fluorine concentration and the phosphorus concentration of the treated water can be reduced.

In the method of the present invention, the sludge concentration in the reaction step in which fluoroapatite is produced is preferably 0.1 to 5% by weight, and more preferably 1 to 4% by weight. The sludge concentration in the reaction process can be controlled by selecting the sludge return ratio. Usually, the sludge density | concentration of a reaction process can be 0.1-5 weight% by making sludge return ratio 15-900. The sludge return ratio can be obtained by the following equation.
Sludge return ratio = (Amount of returned sludge) / (Amount of sludge extracted from sedimentation tank-Amount of returned sludge)
When the sludge concentration in the reaction process is less than 0.1% by weight, the amount of suspended solid particles adsorbed on the surface is small, and the reaction that produces fluoroapatite does not occur locally on the sludge particle surface. There is a risk that water will be entrained in the gel. When the sludge concentration in the reaction process exceeds 5% by weight, the crystallinity proceeds too much and the sludge particles become small, so that the number of fine crystals that cannot be sufficiently solid-liquid separated in the sedimentation basin increases, and the sludge There is a possibility that the power consumption for returning will be excessive.

  In the method of the present invention, seed crystals can be added to the reaction vessel in advance. By adding seed crystals to the reaction tank, fluoroapatite is generated on the surface of the seed crystals from the initial stage of fluorine-containing wastewater treatment, forming sludge with good dehydration with little water uptake, and fluorine-containing wastewater. The processing can reach a steady state in a short time.

In the method of the present invention, the seed crystal added to the reaction vessel is preferably a calcium phosphate having an apatite structure. Examples of the phosphate of calcium having an apatite structure include fluoroapatite, chloroapatite, hydroxyapatite, and carbonate apatite. Among these, fluoroapatite is the same substance as that produced in the method of the present invention, and has a large effect as a seed crystal, so that it can be particularly preferably used. Fluoroapatite is a hexagonal crystal having a composition of approximately Ca ₅ (PO ₄ ) ₃ F.

In the method for treating fluorine-containing wastewater of the present invention, the amount of calcium compound added is preferably 5 to 20 times the amount of fluorine to be removed as calcium. For example, the fluorine concentration 10 mgf ^- a / L fluorine-containing waste water, the fluorine concentration 0.1MgF ^- / L to below the treated water, it is preferable to 50～200MgCa ²⁺ / L adding calcium compound as calcium.

In the method for treating fluorine-containing wastewater according to the present invention, the addition amount of phosphoric acid or a water-soluble salt thereof is preferably a reaction equivalent to produce fluoroapatite as PO ₄ ^3- or 3 equivalents thereof. For example, the fluorine concentration 10 mgf ^- / L fluorine-containing waste water of, fluorine concentration 0.1mgF ^- / L to below the treated water, 150~450mgPO ₄ ³ phosphoric acid or its water-soluble salts as PO ₄ ^{3- -} / L is preferably added.

  The apparatus for treating fluorine-containing wastewater of the present invention is a reaction tank that introduces fluorine-containing wastewater and converts fluorine in the wastewater to fluoroapatite, phosphorus supply means for adding phosphoric acid or its water-soluble salt to the reaction tank, reaction tank outflow Coagulation tank for adding a polymer coagulant to water for coagulation treatment, coagulation tank outflow water containing coagulation flocs for solid-liquid separation into treated water and sludge, part of sludge separated from solid and liquid And a mixing tank for mixing the calcium compound and the alkali, and a sludge return path for returning the mixed sludge of the mixing tank to the reaction tank.

  FIG. 3 is a process flow diagram of one embodiment of the fluorine-containing wastewater treatment apparatus of the present invention. The fluorine-containing wastewater stored in the raw water tank 16 is sent to the reaction tank 17, and the fluorine in the wastewater reacts with calcium hydroxide and phosphoric acid to produce fluoroapatite. To the reaction tank, phosphoric acid is added from the phosphoric acid storage tank 18, the return sludge to which calcium hydroxide is added from the mixing tank 19 via the sludge return path 20, and hydrochloric acid from the pH adjuster tank 21. The treated water in which fluoroapatite is generated on the surface of the sludge particles and the fluorine concentration in the water is lowered is sent to the agglomeration tank 22, and the polymer flocculant is added from the aggregating agent tank 23, so that the flocs in the water are aggregated. . The water in which the flocs are aggregated is solid-liquid separated by the solid-liquid separator 24 and separated into treated water as supernatant water and sedimented sludge. Part of the sludge extracted from the solid-liquid separator is returned to the mixing tank 19 as return sludge, and calcium hydroxide is added from the calcium hydroxide tank 25. There is no restriction | limiting in particular in the solid-liquid separator used for this invention, For example, a sedimentation separator, a centrifuge, a filtration separator, a membrane separator etc. can be mentioned.

Hereinafter, the present invention will be described in more detail with reference to examples, but the present invention is not limited to these examples.
In Examples and Comparative Examples, the fluoride ion concentration was measured using an ion meter [Horiba, F-23] according to JIS K 0102 34.2. The phosphorus concentration was measured by the potassium peroxodisulfate decomposition method according to JIS K 0102 46.3.1. The sludge moisture content was measured by weighing about 10 g of sludge, using a centrifuge [Kokusan Co., Ltd., H-103N], dewatering at 3,000 rpm for 60 seconds to remove the supernatant water, and removing the cake from the sludge. It dried for 1 hour at 110 degreeC using drying machine [Kurita industry Co., Ltd., cricket], and calculated by measuring dry weight.
The sludge return ratio R was calculated by (SS amount of returned sludge) / (Original SS amount). The SS amount of returned sludge is (returned sludge amount) × (SS concentration of returned sludge). The raw SS amount is the amount of SS generated without returning sludge, and is (the SS concentration at the outlet of the reaction tank) × (raw water flow rate) when there is no returning sludge.

Example 1
The apparatus shown in FIG. 1 was used to treat fluorine-containing wastewater having a fluoride ion concentration of 15.0 mg F ⁻ / L, pH 6.4, and electrical conductivity of 30 mS / m discharged from a semiconductor manufacturing factory. The fluorine-containing wastewater was supplied to the apparatus at a flow rate of 3 L / h. The liquid amount in each tank was 1 L for the reaction tank, 1 L for the aggregation tank, and 0.3 L for the mixing tank, and the water area load of the sedimentation tank was 1 m.
To 1 L of fluorine-containing wastewater to be supplied, 320 mg / L of phosphoric acid was added in a reaction tank, and 3 mg / L of a polymer flocculant [Kurita Kogyo Co., Ltd., anion polymer PA311] was added in a coagulation tank. The treatment was performed at a sludge return ratio of 2, and 350 mg / L of calcium hydroxide was added and mixed with the returned sludge in a mixing tank. In addition, hydrochloric acid was added to the reaction tank and pH was adjusted to 8.0. When steady state was reached, the sludge concentration in the reaction vessel is 0.10 wt%, the fluoride ion concentration in the treated water 0.3mgF ^- / L, the phosphorus concentration was 0.4mgP / L, the sludge moisture content Was 55% by weight.
Example 2
The fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge return ratio was 20 and the pH of the reaction tank was adjusted to 8.1. When steady state was reached, the sludge concentration in the reaction vessel is 0.96 wt%, the fluoride ion concentration in the treated water 0.1mgF ^- / less than L, the phosphorus concentration was 0.2mgP / L, the sludge water The rate was 48% by weight.
Example 3
The fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge return ratio was 50 and the pH of the reaction tank was adjusted to 8.2. When steady state was reached, the sludge concentration in the reaction vessel is 2.40 wt%, the fluoride ion concentration in the treated water 0.1mgF ^- / less than L, the phosphorus concentration was 0.2mgP / L, the sludge water The rate was 50% by weight.

Example 4
Fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge return ratio was set to 100. When steady state was reached, the sludge concentration in the reaction vessel is 4.80 wt%, the fluoride ion concentration in the treated water 0.2mgF ^- / L, the phosphorus concentration was 0.2mgP / L, the sludge moisture content Was 50% by weight.
Example 5
The fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge return ratio was 150 and the pH of the reaction tank was adjusted to 8.2. When steady state was reached, the sludge concentration in the reaction vessel is 7.20 wt%, the fluoride ion concentration in the treated water 0.6mgF ^- / L, the phosphorus concentration was 0.5mgP / L, the sludge moisture content Was 50% by weight.
Example 6
Fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge return ratio was 50 and the pH of the reaction tank was adjusted to 5.2. When steady state was reached, the sludge concentration in the reaction vessel is 2.40 wt%, the fluoride ion concentration in the treated water 0.1mgF ^- / less than L, the phosphorus concentration was 9.8mgP / L, the sludge water The rate was 48% by weight.
Example 7
The fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge return ratio was 50 and the pH of the reaction tank was adjusted to 9.8. When steady state was reached, the sludge concentration in the reaction vessel is 2.40 wt%, the fluoride ion concentration in the treated water 0.5mgF ^- / L, the phosphorus concentration is less than 0.1mgP / L, the sludge water The rate was 56% by weight.

Comparative Example 1
The fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge was not returned and 350 mg / L of calcium hydroxide was added to the reaction tank. When steady state was reached, the sludge concentration in the reaction vessel is 0.05 wt%, the fluoride ion concentration in the treated water 1.0mgF ^- / L, the phosphorus concentration was 0.2mgP / L, the sludge moisture content Was 62% by weight.
Comparative Example 2
The fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge return ratio was 50 and the pH of the reaction tank was adjusted to 4.8. When steady state was reached, the sludge concentration in the reaction vessel is 2.40 wt%, the fluoride ion concentration in the treated water 0.3mgF ^- / L, the phosphorus concentration was 13.0mgP / L, the sludge moisture content Was 52% by weight.
Comparative Example 3
The fluorine-containing wastewater was treated in the same manner as in Example 1 except that the sludge return ratio was 50 and the pH of the reaction tank was adjusted to 10.1. When steady state was reached, the sludge concentration in the reaction vessel is 2.40 wt%, the fluoride ion concentration in the treated water 0.8mgF ^- / L, the phosphorus concentration is less than 0.1mgP / L, the sludge water The rate was 60% by weight.
Comparative Example 4
Using the apparatus shown in FIG. 4, fluorine-containing wastewater discharged from the same semiconductor manufacturing factory as in Example 1 was treated. Fluorine-containing wastewater is supplied from the raw water tank 26 to the apparatus at a flow rate of 3 L / h. The liquid volume in each tank is 1 L for the first reaction tank 27, 1 L for the second reaction tank 28, and 1 L for the coagulation tank 29. The water area load of the pond 30 was 1 m.
To 1 L of fluorine-containing wastewater to be supplied, 350 mg / L of calcium hydroxide is added to the first reaction tank, and 1,060 mg / L of phosphoric acid is added to the second reaction tank. ), Anionic polymer PA311] 3 mg / L was added. Moreover, hydrochloric acid was added to the 2nd reaction tank, pH was adjusted to 8.1, and the sludge from a sedimentation tank was returned to the 1st reaction tank by the sludge return ratio 20. When steady state was reached, the sludge concentration in the reaction vessel is 1.02 wt%, the fluoride ion concentration in the treated water 0.2mgF ^- / L, the phosphorus concentration was 0.2mgP / L, the sludge moisture content Was 63% by weight.
The results of Examples 1 to 7 and Comparative Examples 1 to 4 are shown in Table 1.

As seen in Table 1, in Comparative Example 1 in which sludge is not returned, the fluoride ion concentration of the treated water and the moisture content of the sludge are higher than in Examples 1-7. In Comparative Example 2 in which the pH was adjusted to 4.8, the phosphate ion concentration of the treated water was high. In Comparative Example 3 in which the pH was adjusted to 10.1, the fluoride ion concentration of the treated water and the water content of sludge The rate is high. In Comparative Example 4 in which calcium hydroxide was added to the reaction tank, the quality of the treated water was good, but the moisture content of the sludge was high.
Among Examples 1 to 7, particularly good results were obtained in Examples 2 to 3 treated at a sludge concentration of 0.96 to 2.40% by weight. In Example 5 where the sludge return ratio is large and the sludge concentration is 7.20% by weight, both the fluoride ion concentration and the phosphate ion concentration are slightly high. In Example 6 treated at pH 5.2, the fluoride ion concentration is low and the phosphate ion concentration is high. In Example 7 treated at pH 9.8, the fluoride ion concentration is slightly high and the phosphate ion concentration is low. Therefore, it can be seen that the optimum pH can be selected according to the quality of the treated water to be obtained.

Example 8
The apparatus shown in FIG. 1 was used to treat fluorine-containing wastewater having a fluoride ion concentration of 50.0 mg F ⁻ / L, pH 2.8, and electrical conductivity of 380 mS / m discharged from a semiconductor manufacturing factory. The fluorine-containing wastewater was supplied to the apparatus at a flow rate of 3 L / h. The liquid amount in each tank was 1 L for the reaction tank, 1 L for the aggregation layer, 0.3 L for the mixing tank, and the water area load of the sedimentation tank was 1 m.
To 1 L of fluorine-containing wastewater to be supplied, 1,060 mg / L of phosphoric acid was added in a reaction tank, and 3 mg / L of a polymer flocculant [Kurita Kogyo Co., Ltd., anion polymer PA311] was added in a coagulation tank. The treatment was performed at a sludge return ratio of 10, and 1,330 mg / L of calcium hydroxide was added and mixed with the returned sludge in a mixing tank. In addition, hydrochloric acid was added to the reaction tank and pH was adjusted to 8.0. When steady state was reached, the sludge concentration in the reaction vessel is 1.33 wt%, the fluoride ion concentration in the treated water 0.2mgF ^- / L, the phosphorus concentration was 0.2mgP / L, the sludge water The rate was 50% by weight, and the amount of sludge generated was 2,600 mg per liter of fluorine-containing wastewater.
Example 9
The same treatment of fluorine-containing wastewater as in Example 8 was performed using the apparatus shown in FIG. Fluorine-containing wastewater is supplied to the apparatus at a flow rate of 3 L / h, and the liquid volume in each tank is set to 1 L in the previous stage, 1 L in the coagulation tank, and 0.3 L in the mixing tank, 1 L in the subsequent stage, 1 L in the coagulation tank, The tank was 0.3 L, and the water area load of the two sedimentation basins was 1 m.
In the first stage treatment, the sludge return ratio is set to 300, and 400 mg / L of calcium hydroxide is added in the mixing tank to 1 L of fluorine-containing wastewater to be supplied. In the coagulation tank, the polymer flocculant [Kurita Kogyo Co., Ltd., Anion polymer PA311] 3 mg / L was added. Moreover, hydrochloric acid was added to the reaction tank and pH was adjusted to 6.5. When the steady state was reached, the fluoride ion concentration of the primary treated water flowing out from the sedimentation basin as supernatant water was 12.5 mg F ⁻ / L.
In the latter stage treatment, 280 mg / L of phosphoric acid is added to 1 L of fluorine-containing wastewater supplied to the former stage, and 3 mg of polymer flocculant [Kurita Kogyo Co., Ltd., anion polymer PA311] is added in the coagulation tank. / L was added. The treatment was performed at a sludge return ratio of 40, and 300 mg / L of calcium hydroxide was added and mixed with the returned sludge in a mixing tank. In addition, hydrochloric acid was added to the reaction tank and pH was adjusted to 8.0. When the steady state was reached, the sludge concentration in the reaction vessel was 1.35% by weight, the fluoride ion concentration in the treated water was 0.1 mg F ⁻ / L, and the phosphorus concentration was 0.2 mg P / L.
Sludge generated in the first settling basin and sludge generated in the second settling pond were mixed, and the amount of sludge generated and the water content were measured. The amount of sludge generated per liter of fluorine-containing wastewater was 785 mg, and the moisture content of the sludge was 48% by weight.
The results of Examples 8-9 are shown in Table 2.

As seen in Table 2, the fluoride ion concentration 50.0mgF ^- / L fluorine-containing waste water as compared to Example 8 was treated in one step, fluoride fluoride ions by addition of calcium hydroxide in the previous paragraph In Example 9, which was removed as calcium and made into a primary treatment water with a fluoride ion concentration of 12.5 mg F ⁻ / L, then added with calcium hydroxide and phosphoric acid at the latter stage, the use of calcium hydroxide was performed in Example 9. The amount is about 60%, the amount of phosphoric acid used is reduced to about 25%, and the amount of sludge generated is reduced to about 30%. When the fluoride ion concentration of fluorine-containing wastewater is high, the amount of chemicals used and sludge generation can be reduced as a whole by removing a part of the fluoride ions as calcium fluoride in advance. I understand.

  According to the method and apparatus for treating fluorine-containing wastewater of the present invention, calcium and alkali are adsorbed on the surface of sludge particles by adding calcium compound and alkali to sludge separated into solid and liquid in advance and returning it to the reaction step. Since it reacts with fluorine and phosphorus in the reaction process to produce fluoroapatite and removes fluorine, fluorine can be removed to a low concentration, and water uptake into sludge particles is suppressed and sludge moisture content is reduced. Can be reduced and the amount of sludge generated can be reduced.

It is a process flow diagram of one mode of a processing method of fluorine content drainage of the present invention. It is a process flow diagram of other modes of a processing method of fluorine content drainage of the present invention. It is a process flow diagram of one mode of a processing device of fluorine content drainage of the present invention. 6 is a process flow diagram of a processing apparatus used in Comparative Example 4. FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Raw water tank 2 Reaction tank 3 Coagulation tank 4 Settling tank 5 Mixing tank 6 Raw water tank 7 Reaction tank 8 Coagulation tank 9 Settling tank 10 Mixing tank 11 Primary treatment water tank 12 Reaction tank 13 Coagulation tank 14 Settling tank 15 Mixing tank 16 Raw water tank 17 Reaction tank 18 Phosphoric acid storage tank 19 Mixing tank 20 Sludge return path 21 pH adjuster tank 22 Coagulation tank 23 Coagulant tank 24 Solid-liquid separator 25 Calcium hydroxide tank 26 Raw water tank 27 First reaction tank 28 Second reaction tank 29 Aggregation Tank 30 sedimentation pond

Claims (6)

  A reaction process in which a calcium compound and phosphoric acid or a water-soluble salt thereof are added to fluorine-containing wastewater and reacted at pH 5-10, an aggregation process in which a polymer flocculant is added to water after the reaction process, and an aggregation floc after the aggregation process In the method for treating fluorine-containing wastewater having a step of solid-liquid separation of contained water and a sludge return step of returning a part of the solid-liquid separated sludge to the reaction step, a calcium compound is added to the return sludge of the sludge return step in advance. A method for treating fluorine-containing wastewater, which comprises adding alkali and alkali and returning to the reaction step.   A step of removing fluorine as calcium fluoride by treating fluorine-containing wastewater with a calcium compound, a reaction step of adding a calcium compound and phosphoric acid or a water-soluble salt thereof to the primary treated water and reacting at pH 5 to 10; A coagulation step of adding a polymer flocculant to the water after the reaction step, a step of solid-liquid separation of the water containing the coagulation floc after the coagulation step, and a part of the sludge separated from the solid and liquid is returned to the reaction step A treatment method for fluorine-containing wastewater having a sludge return step, wherein a calcium compound and an alkali are added to the return sludge in the sludge return step in advance and returned to the reaction step.   The method for treating fluorine-containing wastewater according to claim 1 or 2, wherein the sludge concentration in the reaction step is 0.1 to 5% by weight.   The method for treating fluorine-containing wastewater according to any one of claims 1 to 3, wherein seed crystals are added in advance to the reaction tank.   The method for treating fluorine-containing wastewater according to claim 4, wherein the seed crystal is a phosphate of calcium having an apatite structure.   A reaction tank that introduces fluorine-containing wastewater and converts the fluorine in the wastewater to fluoroapatite, a phosphorus supply means that adds phosphoric acid or its water-soluble salt to the reaction tank, and a polymer flocculant added to the reaction tank effluent to agglomerate A coagulation tank to be treated, a solid-liquid separation device for solid-liquid separation of coagulation tank effluent containing coagulation floc into treated water and sludge, a mixing tank for mixing calcium compound and alkali in a part of the solid-liquid separated sludge, And the processing apparatus of the fluorine-containing waste water which has the sludge return path which returns the mixed sludge of a mixing tank to a reaction tank.

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