JP2009142744A - Sludge concentration method and sludge concentration apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a sludge concentration method by which the volume of sludge produced in a water treatment using an aluminum based flocculant can be reduced and concentration of the sludge in a highly concentrated state is adjusted. <P>SOLUTION: The concentration method of the sludge produced in the water treatment using the aluminum based flocculant includes: an acid treating step of treating the sludge with an acid; and an alkali treating step of treating the sludge to which the acid is added with at least one of a calcium agent and a magnesium agent being an alkali agent. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to a method and apparatus for concentrating sludge generated in water treatment using an aluminum flocculant.

  A water treatment method for performing water treatment such as coagulation precipitation using an aluminum-based flocculant is widely used in general industries, waterworks, sewerage, and the like. Although this treatment is a very good method for removing contaminants in water, aluminum flocculant is used as the flocculant. A large amount of metal compound is contained.

  As a method for treating sludge, for example, as described in Patent Document 1, a method of concentrating and dewatering sludge using a polymer flocculant is known. In addition, as a method that does not use chemicals, a method is known in which sludge is concentrated by gravity sedimentation and solidified by dehydration by pressure dehydration or the like.

  However, sludge containing aluminum hydroxide or the like as described above has very poor sedimentation and concentration of the sludge because the metal hydroxide compound contained in the sludge swells, and the generated sludge has a high water content. It is difficult to dehydrate. Therefore, since concentration by sludge is low in concentration by gravity sedimentation, it takes time to dehydrate to solidification by pressure dehydration or the like, and a large pressure dehydration apparatus is required. Moreover, it was difficult to reduce the moisture content, and the amount of sludge as industrial waste was very large.

  There is also a method of adding slaked lime directly to sludge and performing a dehydration treatment. However, since a large amount of alkaline wastewater is generated and the alkali is dissolved in the wastewater, neutralization treatment and removal of its impurities are possible. It was necessary (see, for example, Non-Patent Document 1). In addition, there is a problem that calcium carbonate generated by the reaction of slaked lime and carbon dioxide in the air precipitates on the filter cloth during the dehydration treatment, causing clogging of the filter cloth, frequent washing of the filter cloth, Chemical cleaning with hydrochloric acid was required.

  Therefore, in Patent Document 2, in order to reduce the volume of sludge by improving the settling concentration of sludge, the precipitated sludge generated when coagulating sedimentation is performed using an aluminum-based and / or iron-based flocculant. In the concentration of the above, it is described that after adding sulfuric acid to sludge, an alkaline agent is added in the presence of calcium ions.

Japanese Patent No. 3709825 JP 2007-196086 A Water Supply Facility Design Guidelines 2000 Japan Waterworks Association, p377

  The method of Patent Document 2 improves the sedimentation and concentration of sludge and can reduce the volume of sludge, but the volume reduction of sludge is insufficient and further reduction of the sludge is required. In addition, adjustment of the sludge concentration in a high-concentration state of sludge after volume reduction is required in order to perform stable treatment in the subsequent dewatering treatment.

  The present invention is a sludge concentration method capable of reducing the volume of sludge generated in water treatment using an aluminum flocculant, and capable of adjusting the sludge concentration in a high concentration state of the sludge after volume reduction, and This is a sludge concentrator.

  The present invention is a method for concentrating sludge generated in water treatment using an aluminum flocculant, an acid treatment step for treating the sludge with an acid, a calcium agent as an alkaline agent for the sludge treated with the acid, and And an alkali treatment step of treating with at least one of the magnesium agents.

  Moreover, in the said sludge concentration method, it is preferable to change the usage-amount of the said calcium agent and the said magnesium agent, and to adjust the density | concentration of the sludge obtained by the said alkali treatment process.

  Moreover, in the said sludge concentration method, it is preferable that the said calcium agent is calcium hydroxide.

  Moreover, in the said sludge concentration method, it is preferable that the said magnesium agent is magnesium hydroxide.

  Moreover, in the said sludge concentration method, it is preferable that the said acid is a sulfuric acid.

  Moreover, in the said sludge concentration method, it is preferable that the chemical equivalent ratio of the said alkali agent with respect to the said acid is the range of 1.2-2.

  Moreover, in the said sludge concentration method, it is preferable that the mixing ratio of the said magnesium agent with respect to the said calcium agent is the range of 0 to 100%.

  The present invention is also a device for concentrating sludge generated in water treatment using an aluminum flocculant, wherein the acid is added to the acid treatment tank for treating the sludge with an acid, and the acid treatment tank. Acid addition means, an alkali treatment tank for treating the sludge treated with the acid with at least one of a calcium agent and a magnesium agent as an alkali agent, and an alkali agent addition for adding the alkali agent to the alkali treatment tank And a sludge concentrating device.

  In the present invention, sludge generated in water treatment using an aluminum-based flocculant is treated with an acid, and then treated with at least one of a calcium agent and a magnesium agent, which are alkaline agents, to thereby improve the sediment concentration properties of the sludge. It is possible to improve the volume of sludge and to adjust the sludge concentration in the high-concentration state of the sludge after volume reduction.

  Embodiments of the present invention will be described below. This embodiment is an example for carrying out the present invention, and the present invention is not limited to this embodiment.

  The outline of an example of the sludge concentration apparatus which concerns on embodiment of this invention is shown in FIG. 1, and the structure is demonstrated. The sludge concentrating device 1 includes a sludge concentration adjusting tank 10 for concentrating and adjusting sludge from a water treatment apparatus such as coagulating sediment using an aluminum flocculant, an acid treatment tank 12 for treating sludge with an acid, and an acid. An alkali treatment tank 14 for treating the treated sludge with an alkali agent, an acid storage tank 16 for storing acid, a calcium agent storage tank 18 and a magnesium agent storage tank 20 which are alkali agent storage tanks for storing the alkali agent, The sludge sedimentation tank 22 for sedimentation and concentration of the sludge treated with the alkali agent and a dehydrator 24 are provided.

  In the sludge concentration apparatus 1 of FIG. 1, the sludge pipe 48 from the water treatment apparatus is connected to the sludge concentration adjustment tank 10, and the sludge concentration adjustment tank 10 is connected to the acid treatment tank 12 via the pump 26 by the sludge pipe 50. Yes. The acid treatment tank 12 is connected to the alkali treatment tank 14 via the pump 28 by the acid treatment liquid pipe 52, and the alkali treatment tank 14 is connected to the sludge settling tank 22 via the pump 30 by the alkali treatment liquid pipe 54. The sludge settling tank 22 is connected to the inlet of the dehydrator 24 via a pump 38 by a sludge pipe 56. An acid storage tank 16 is connected to the acid treatment tank 12 through an acid pipe 58 via a pump 32 as an acid addition means, and a stirring device 40 having a motor, stirring blades, and the like is installed. In the alkali treatment tank 14, the calcium agent storage tank 18 is connected to the calcium agent pipe 60 via a pump 34 as an alkali agent addition means, and the magnesium agent storage tank 20 is connected to a magnesium agent pipe 62 via a pump 36 as an alkali agent addition means. A stirrer 42 that is connected to each other and includes a motor, a stirring blade, and the like is installed. In the calcium agent storage tank 18 and the magnesium agent storage tank 20, stirring devices 44 and 46 each having a motor, stirring blades, and the like are installed.

  Operation | movement of the sludge concentration method and the sludge concentration apparatus 1 which concern on this embodiment is demonstrated.

  The sludge from the water treatment apparatus is transferred to the sludge concentration adjusting tank 10 through the sludge pipe 48, where the concentration is adjusted by gravity sedimentation or the like. The acid treatment target sludge whose volume has been reduced by the concentration adjustment is extracted from the sludge concentration adjustment tank 10 by the pump 26 and transferred to the acid treatment tank 12 through the sludge pipe 50, and sent from the acid reservoir 16 through the acid pipe 58 by the pump 32. And acid treatment (acid treatment step). Aluminum hydroxide or the like contained in the acid treatment target sludge is dissolved by the added acid, and is ionized, for example, in the form of aluminum ions and sulfate ions. In order to advance the acid treatment smoothly, the sludge pipe 50 and the acid pipe 58 may be connected before flowing into the acid treatment tank 12, and the acid treatment target sludge and the acid may be mixed in advance. In the acid treatment tank 12, the acid treatment liquid may be stirred by the stirring device 40 to promote the treatment.

  Subsequently, the acid treatment liquid containing the acid-treated sludge is transferred from the acid treatment tank 12 to the alkali treatment tank 14 through the acid treatment liquid pipe 52 by the pump 28, and from the calcium agent storage tank 18 through the calcium agent pipe 60 by the pump 34. A calcium agent such as calcium hydroxide is alkali-treated by adding a magnesium agent such as magnesium hydroxide from the magnesium agent storage tank 20 through the magnesium agent pipe 62 by the pump 36 (alkali treatment step). In the alkaline treatment tank 14, the treatment may be promoted by stirring the alkaline treatment liquid with the stirring device 42.

  The alkali treatment liquid containing the alkali-treated sludge is transferred from the alkali treatment tank 14 to the sludge settling tank 22 through the alkali treatment liquid pipe 54 by the pump 30, and is settled, concentrated, and reduced in volume by gravity settling or the like. The separated water (supernatant water) separated from the sludge in the sludge settling tank 22 is discharged or reused. On the other hand, the sludge whose volume has been reduced in the sludge settling tank 22 may be further solidified by reducing moisture, and disposed of as industrial waste, or may be reused after further dehydration if necessary. Also good. For example, the sludge whose volume has been reduced in the sludge settling tank 22 is sent to the dehydrator 24 through the sludge pipe 56 by the pump 38, and is discharged as waste or the like through the dehydration process.

  In this embodiment, at least one of a calcium agent and a magnesium agent is used as an alkaline agent, and preferably, the sedimentation and concentration properties of sludge can be improved by using a calcium agent and a magnesium agent in combination. As a result, the volume of sludge can be significantly reduced and the dewaterability and moisture content in the sludge dewatering process can be improved, thus greatly reducing the amount of industrial waste generated at the final stage of the treatment. can do. Hereinafter, the mechanism of volume reduction of sludge estimated by taking as an example the case of using sulfuric acid as the acid, calcium hydroxide as the calcium agent, and magnesium hydroxide as the magnesium agent will be described.

  First, aluminum hydroxide or the like contained in the acid treatment target sludge is dissolved and ionized by the sulfuric acid added in the acid treatment tank 12. Next, by adding calcium hydroxide and magnesium hydroxide in the alkali treatment tank 14, the aluminum ions in the sludge dissolved with sulfuric acid are neutralized with calcium hydroxide and magnesium hydroxide, and at the same time, again as aluminum hydroxide. Precipitate (reaggregate). And this aluminum hydroxide, magnesium hydroxide remaining in an insoluble state, calcium sulfate produced by the reaction of calcium ions and sulfate ions generated from calcium hydroxide, turbid components in sludge, etc. It is thought that coprecipitation occurs due to coexisting substances.

(1) Dissolution of aluminum hydroxide with sulfuric acid 3H ₂ SO ₄ + 2Al (OH) ₃ → 6H ₂ O + 2Al ³⁺ + 3SO ₄ ^2-
(2) Alkali treatment 3Ca (OH) ₂ → 3Ca ²⁺ + 6OH ⁻
3Mg (OH) ₂ → 3Mg ²⁺ + 6OH ⁻
2Al ³⁺ + 6OH ⁻ → 2Al (OH) ₃ ↓
^{_{3Ca 2+ + 3SO 4 2- → 3CaSO}} 4 ↓
3Mg ²⁺ + 3SO ₄ ²⁻ → 3MgSO ₄

That is, under sulfuric acid acidity, the added calcium hydroxide becomes calcium sulfate (gypsum) having low solubility. On the other hand, some of the added magnesium hydroxide becomes magnesium sulfate, but exists as Mg ²⁺ ions because of its high solubility. Therefore, the neutralization reaction can be performed without generating a large amount of calcium sulfate as in the case of using calcium hydroxide alone, and the amount of solid matter involved in aggregation can be reduced. The added magnesium hydroxide has very poor solubility in the vicinity of the neutral where the neutralization reaction has progressed due to the addition of the alkaline agent, and exists as an insoluble state as magnesium hydroxide. This insoluble magnesium hydroxide itself has an aggregating action and is presumed to form an aggregated floc. At this time, the insoluble magnesium hydroxide, the aluminum hydroxide reaggregated as described above, calcium sulfate, and the like co-precipitate. Due to this phenomenon, the sedimentation concentration of sludge is greatly improved compared to when calcium hydroxide is used alone as an alkaline agent, and the sludge can be greatly reduced in volume. Sludge volume reduction can dramatically increase the efficiency of the subsequent dehydration process. Although calcium sulfate is also called gypsum, there are three types of gypsum, and it is unclear what form the generated calcium sulfate is, but since it is mainly a reaction at room temperature, CaSO ₄ without crystal water Presumed to be in shape.

  Examples of the acid used in the acid treatment of this embodiment include sulfuric acid and hydrochloric acid, and sulfuric acid is preferred. In order to control the volume reduction by adjusting the amount of calcium sulfate produced, sulfuric acid and hydrochloric acid may be used in combination as the acid for dissolving the acid treatment target sludge. However, it is possible to adjust the amount of calcium sulfate produced by using sulfuric acid and hydrochloric acid together, but magnesium hydroxide and calcium hydroxide both produce magnesium chloride and calcium chloride that are very soluble in hydrochloric acid, Since the amount of coagulation reaction product necessary for the expression of the coprecipitation phenomenon is reduced, the degree of volume reduction may be low even when sulfuric acid and hydrochloric acid are used in combination. Furthermore, the addition management of hydrochloric acid chemicals becomes complicated. For this reason, sulfuric acid is preferred as the acid.

  Since ionization of aluminum hydroxide or the like contained in the acid treatment target sludge is effective even if it is limited to a part, it is preferable to conduct a reaction test in advance and set the acid addition amount as economical as possible.

  The reaction solution in the acid treatment tank 12 is preferably adjusted to have a pH of less than 5, more preferably adjusted to have a pH of 4 or less, and adjusted to have a pH of 3 or less. Further preferred. From the viewpoint of running cost and the like, it is preferable to adjust the pH to 2.5 to 3, but the reaction time can be shortened by adjusting the pH to 1.5 to 2.5. The apparatus can be reduced in size.

  The calcium agent is not particularly limited as long as it is an alkaline agent containing calcium and dissolves to generate calcium ions, but calcium hydroxide (slaked lime), calcium oxide (quick lime), calcium chloride, carbonic acid There may be mentioned at least one of calcium salts such as calcium. Of these, calcium hydroxide and calcium oxide are preferable, and calcium hydroxide is more preferable.

  Since calcium hydroxide and calcium oxide have low solubility in water, it is considered that agglomeration and crystal formation reactions proceed mainly around calcium hydroxide particles and calcium oxide particles while limiting local reactions in the bulk. It is done. Therefore, reaggregation of aluminum hydroxide or the like occurs using the particles as nuclei, and it is considered that calcium sulfate or the like can be smoothly taken in during the reaggregation, and sludge having good dewaterability can be obtained. In addition, when calcium oxide is used, the above reaction and sludge settling acceleration effect can be expected due to the heating effect due to the exothermic reaction when calcium oxide is dissolved in water.

  The magnesium agent is not particularly limited as long as it is an alkaline agent containing magnesium and can be dissolved to produce magnesium ions, but magnesium salts such as magnesium hydroxide, magnesium oxide, magnesium chloride, magnesium carbonate, etc. At least one of them is mentioned. Of these, magnesium hydroxide and magnesium oxide are preferable from the viewpoints of neutralizing ability against acid and cohesive strength, and magnesium hydroxide is more preferable.

  The calcium agent and the magnesium agent can be used in a powder form or a slurry form mixed with a solvent such as water. In terms of ease of handling, it is often better to use it as a slurry. In addition, when using as a slurry, in the calcium agent storage tank 18 and the magnesium agent storage tank 20, it is preferable to stir with the stirring apparatuses 44 and 46 so that a calcium agent and a magnesium agent may not settle.

  The calcium agent and the magnesium agent can be added together with the addition of the acid or after the addition of the acid. Moreover, as an alkaline agent added to sludge, the form which adds alkaline agents, such as caustic soda and sodium carbonate in presence of calcium ion or magnesium ion, may be sufficient.

  The calcium agent and the magnesium agent may be added in the order of adding the calcium agent and then adding the magnesium agent, adding the magnesium agent and then adding the calcium agent, or adding the calcium agent together with the magnesium agent. For example, when magnesium hydroxide is used as the magnesium agent, magnesium hydroxide has low solubility in water in the neutral region as described above. Therefore, it is desirable to add and dissolve in the acidic region. It is preferable to add the calcium agent after adding the agent.

  In this embodiment, when adding a calcium agent and a magnesium agent, you may use the mixing agent containing a calcium agent and a magnesium agent. In this case, the calcium agent storage tank 18 and the magnesium agent storage tank 20 of FIG. 1 may be one alkaline agent storage tank.

  In this embodiment, sufficient sedimentation can be obtained without using a polymer flocculant, but a polymer flocculant may be used to further improve the sedimentation.

  The reaction solution in the alkali treatment tank 14 is preferably adjusted to have a pH of 4 or more, and more preferably adjusted to have a pH of 4.5 to 9, from the viewpoint of releasing or reusing the separated water. Preferably, it is more preferable to adjust so that pH may be 6.0-8.5.

  By changing the mixing ratio of the calcium agent and the magnesium agent, the concentration of the sludge after volume reduction can be adjusted to the target degree of volume reduction according to the treatment in the subsequent stage. Moreover, the clarity of the supernatant water (separated water) can be adjusted by changing the mixing ratio of the calcium agent and the magnesium agent.

  For example, by changing the amount of calcium hydroxide and magnesium hydroxide added, that is, by changing the mixing ratio of calcium hydroxide and magnesium hydroxide, the amount of calcium sulfate produced and the amount of insoluble magnesium hydroxide are adjusted. Thus, the concentration of sludge volume reduction can be adjusted while improving the quality of the separated water. Therefore, since the sludge concentration can be adjusted to be constant, for example, the operation management of the subsequent dehydration process can be smoothly advanced.

  When adjusting the volume reduction sludge concentration, for example, to increase the concentration of volume reduction sludge, increase the ratio of magnesium hydroxide to calcium hydroxide, and to decrease it, increase the ratio of calcium hydroxide to magnesium hydroxide. be able to.

  When magnesium hydroxide is used alone as the alkaline agent, the concentration of the volume-reducing sludge is the highest, but there is a lot of suspended solids in the separation water generated by the separation operation such as gravity sedimentation of the latter stage sludge. In addition, the chromaticity associated therewith may occur and it may be difficult to see the situation in which volume reduction is progressing (such as the interface between the settled sludge and separated water). In addition, the separated water containing a large amount of suspended matter may become an obstacle in the discharge or reuse. In order to improve this situation, when calcium hydroxide is used in addition to magnesium hydroxide as an alkaline agent, the volume is reduced while reducing suspended solids and reducing chromaticity without impairing volume reduction. Can be adjusted.

  As described above, the addition of calcium hydroxide causes the calcium sulfate formation reaction and the neutralization reaction to occur in parallel. The calcium sulfate crystals and the aluminum hydroxide produced by the neutralization reaction cause an agglomeration reaction, and the sludge volume is reduced by coprecipitation while calcium sulfate and insoluble magnesium hydroxide are taken in. Becomes clear. The clarity of the separated water increases as the ratio of calcium hydroxide to magnesium hydroxide increases, and at the same time, the amount of calcium sulfate produced increases, the total amount of solid substances increases, and the degree of volume reduction decreases.

  The mixing ratio of magnesium agent to calcium agent ((magnesium agent weight / (magnesium agent weight + calcium agent weight)) × 100) is appropriately determined in the range of 0 to 100%, and the volume of sludge after volume reduction is determined. The sludge concentration in the high concentration state may be adjusted, but it is preferably in the range of 35 to 65% from the viewpoint of reducing the sludge volume and the clarification of separated water.

  As an index of the clarity of separated water, for example, it can be expressed by SS (Suspended Solid), and SS can be, for example, 10 (mg / L) or less.

  The chemical equivalent ratio of the alkali agent to the acid (alkali agent / acid) is preferably in the range of 1.2 to 2 from the viewpoint of formation of a stirring and mixing device, particle size characteristics of the powder, and the like. In the present specification, “chemical equivalent” means “molar equivalent”.

  As described above, in this embodiment, the sludge from the water treatment apparatus is acidified using an acid, and then the sludge is reduced in volume by adding a calcium agent. By doing so, compared with the case of using calcium agent alone, for example, volume reduction of about 1.1 to 3 times and adjustment of sludge concentration in the high concentration state of sludge after volume reduction can be performed. Moreover, the separated water generated by volume reduction by the combined treatment of the magnesium agent and the calcium agent can be clarified, for example, as a neutral liquid by changing the addition ratio of both alkali agents.

  If sludge sedimentation concentration and sludge dewaterability are improved, it is possible to reduce the capacity of expensive dewatering equipment and the amount of industrial waste dumped. Especially for sludge generated from coagulation sedimentation treatment using polyaluminum chloride or sulfuric acid band as an aluminum-based coagulant as in waterworks, there is a very remarkable concentration reduction effect. This can be a very useful technology in water purification plants where sludge treatment is a problem. Even when using a sun-dried bed, if the concentration is increased, it is possible to reduce the depth of penetration, making the drying progress faster and easier to operate, and reducing the area of the dry bed. This leads to effects such as

  In addition, the fact that the separated water is clear as a neutral liquid means that when it is discharged as wastewater, it does not touch the wastewater standards, there is no need for secondary treatment, and the sludge concentrator operation management monitors sludge interface. Can be easily performed.

In this embodiment, it is preferable to stir the liquid containing sludge when adding acid in the acid treatment tank 12. The stronger the stirring strength in the acid treatment tank 12, the faster the acid diffuses and the faster the dissolution proceeds, and the smaller the capacity of the device, the stronger the stirring strength of the stirring device 40. It is preferable to set the strength index) to be 150 s ⁻¹ or more.

Moreover, in this embodiment, it is preferable to stir the liquid containing sludge also at the time of the addition of the alkaline agent in the alkaline treatment tank 14. The stirring strength of the stirring device 42 in the alkali treatment tank 14 is preferably set so as not to destroy the generated flocs, and is preferably set lower than the stirring strength of the stirring device 40 in the acid treatment tank 12. For example, the stirring intensity of the stirring device 42 in the alkali treatment tank 14 is preferably set so that the so-called G value is 10 to 150 s ^−1, and more preferably set so that the G value is 50 to 120 s ^−1. preferable.

  Depending on the temperature conditions, the alkali treatment tank 14 generates insoluble calcium sulfate or the like to which crystal water has been added due to the alkali treatment, so care must be taken in the injection point of the acid treatment solution and the alkali agent. That is, when calcium sulfate or the like is produced, scales such as calcium sulfate may accumulate on the walls in the alkali treatment tank 14 or the stirring blades and shafts of the stirring device 42. It is preferable to set the injection point so as to minimize the contact with. For example, it is preferable to arrange the injection point of the acid treatment liquid transferred from the acid treatment tank 12 and the injection point of the calcium agent and the magnesium agent at symmetrical positions with the central portion of the alkali treatment tank 14 as the center.

  In the present embodiment, sludge and the like are pumped to the acid treatment tank 12, the alkali treatment tank 14, the sludge settling tank 22, and the dehydration device 24. You may transfer by trough. In a small-scale treatment, an alkaline agent is put in the acid treatment tank 12, and in this tank, the effect of the present embodiment can be sufficiently exerted even in a batch-type apparatus form in which sludge is concentrated and supernatant water is separated. Can do.

  As the dehydrator 24, a pressure dehydrator or a dryer is used.

  Hereinafter, although an example and a comparative example are given and the present invention is explained more concretely in detail, the present invention is not limited to the following examples.

(Examples 1-7)
Hereinafter, the example which processed the sludge generated in a certain water purification plant using the sludge concentration apparatus as shown in FIG. This water purification plant uses river water as its water source, has low turbidity, and has humic chromaticity. Therefore, it uses PAC (polyaluminum chloride) as a flocculant and is injected by about 50 mg / L. Then, a floc is generated, and a treatment suitable for water quality as a water supply is performed by a coagulation precipitation treatment and a filtration treatment. Agglomerated flocs become agglomerated sedimentation sludge in the sedimentation basin. The sludge is solidified and discarded as industrial waste. In the solidification process, sludge is first concentrated by gravity sedimentation and sludge is dehydrated by a pressure dehydrator to be solidified (dehydrated cake). The dehydrated cake is disposed of as industrial waste.

  The agglomerated sediment sludge generated in this water purification plant has a high content of aluminum hydroxide due to its high chromaticity, low turbidity, and high PAC injection rate as raw water quality, very poor sedimentation concentration, and a sludge concentration of 48 Even if time sedimentation is performed, the sludge properties reach only 1.6%. When the sludge concentration is low, a large amount of sludge is treated, and the sludge treatment facility becomes a very large facility. At the same time, a large dehydration facility is required for dehydration and solidification.

  In this embodiment, therefore, sulfuric acid having a concentration of 70% is added to the sludge generated at the water purification plant as shown in Table 1, and as an alkaline agent at an addition amount and ratio as shown in Table 1 15 minutes after the addition. Magnesium hydroxide and calcium hydroxide were added as a mixture in a slurry state, and SS (mg / L) of supernatant water after 1 hour had passed, and the volume-reduced sludge interface after 24 hours and 24 hours later, 24 The SS of the supernatant water after the lapse of time was examined. The results are shown in Table 1. The SS of supernatant water (separated water) was measured by the method of Appendix 8 of Environment Agency Notification No. 59, and the volume-reduced sludge interface was measured visually using a graduated cylinder.

(Comparative Examples 1 and 2)
The treatment was carried out in the same manner as in Examples 1 to 7, except that only magnesium hydroxide (Comparative Example 1) and only calcium hydroxide (Comparative Example 2) were used as the alkaline agent. The results are shown in Table 1.

  As can be seen from the results of Examples 1 to 7, the concentration of sludge volume reduction could be adjusted by adjusting the addition amount of magnesium hydroxide and calcium hydroxide. When the magnesium hydroxide of Comparative Example 1 was used alone, the supernatant suspended in suspension was very large, and the degree of volume reduction was a combination of magnesium hydroxide and calcium hydroxide of Examples 1-3. It was low compared to.

  Although the progress of volume reduction of sludge is seen even when magnesium hydroxide is used alone, the SS value of the supernatant water generated by volume reduction is high, and in Examples 1 to 7, the sludge is seen from the side through the glass of the graduated cylinder. Although the volume reduction could be observed, Comparative Example 1 was not able to be observed from above.

  In the operation of the sludge concentrator, visual observation of the volume-reducing interface is very important in that the performance of the apparatus is extracted and stable operation is possible. Moreover, it is desirable that the supernatant water can be discharged without any treatment even when discharged as surplus water. In this volume reduction treatment, the combined treatment of magnesium hydroxide and calcium hydroxide in Examples 1 to 7 was used to adjust the volume ratio of sludge by adjusting both chemical ratios of magnesium hydroxide and calcium hydroxide. It is shown that it can be adjusted from 5.71 times to 2.70 times of Example 7 and the quality of the supernatant water can be improved.

  By adding magnesium hydroxide, the amount of calcium sulfate produced by the reaction between sulfuric acid and calcium hydroxide can be adjusted as compared with the case of using calcium hydroxide alone, and solids produced in sludge It is presumed that the quantity changes and acts as a factor that controls sludge volume reduction. In addition, the formation of calcium sulfate has an influence on the aggregation reaction prior to the coprecipitation phenomenon, and it is presumed that the coprecipitation phenomenon occurs while taking in suspended suspended solids that are observed when magnesium hydroxide is used alone.

  Magnesium hydroxide dissolves in an acidic solution, but the solubility becomes very small as the pH approaches neutrality. It is presumed that a part of magnesium hydroxide remains in an insoluble state as the neutralization proceeds. It is presumed that the volume reduction occurs most when the amount of alkali agent added is greater than the sulfuric acid equivalent, because partially insoluble magnesium hydroxide is related to the coprecipitation phenomenon.

  The progress of volume reduction by coprecipitation is due to the reaction between sulfate ions and calcium hydroxide while adding aluminum hydroxide and calcium hydroxide to produce aluminum dissolved in acidic sludge in aluminum hydroxide. Due to the coprecipitation phenomenon due to multi-component related substances such as calcium sulfate generated in sewage, insoluble magnesium hydroxide, solids in sludge and substances that are dissolved in sulfuric acid and become solids again by the addition of alkaline agent It is guessed.

  In Examples 2 and 3, it is shown that the addition of calcium hydroxide causes the production of supernatant water with less suspended suspended matter and the stronger sedimentation concentration than using magnesium hydroxide alone (Comparative Example 1). ing.

  In the situation where magnesium hydroxide alone is used in Comparative Example 1 and the amount of calcium hydroxide is low as in Example 1, there is no or almost no calcium sulfate formation, so coprecipitation phenomenon including agglomeration hardly occurs and the volume of sludge is reduced. The magnification is estimated to be low.

  In Examples 1 to 7, sludge generated using PAC (polyaluminum chloride) as a flocculant was used, and in the case of a conventional method, the concentration of sludge is used when pressure dehydration is used as a subsequent dewatering treatment. As a result, the dewatering capacity changed drastically, and the amount of dewatered cake generated after the dehydration process fluctuated greatly. In this example, volume reduction was achieved by adjusting the addition amount of magnesium hydroxide and calcium hydroxide while improving the capacity of the pressure dehydrator while achieving volume reduction exceeding that when using magnesium hydroxide alone as the alkali agent. It was possible to facilitate the operation management of the activated sludge concentration and the subsequent pressure dehydrator.

  The ability to control the amount of cake generated by the pressure dehydrator ensures that the amount handled is constant even during subsequent sludge drying, etc., and can provide a useful means in terms of operation management in the treatment of water sludge with severe sludge generation and property fluctuations. become.

  Examples 1 to 7 are examples of a volume reduction treatment in which the supernatant water after sedimentation is made neutral so that it can be discharged. When considering the discharge of wastewater, it is necessary to make the supernatant water neutral. In Examples 1 to 7, magnesium hydroxide and calcium hydroxide are simultaneously added as a mixture, and the total alkali equivalent used for the acid equivalent is about 1.7 to 1.9 times. It was. Increasing the ratio of calcium hydroxide to magnesium hydroxide tended to increase the total alkali equivalent used relative to the acid equivalent.

  The factor that requires a total alkali equivalent of sulfuric acid or more with respect to sulfuric acid is that the rate of calcium sulfate formation reaction when calcium sulfate is formed is high, so insoluble water with a slow dissolution rate due to the generated calcium sulfate. It is presumed that this is because the surfaces of calcium oxide and magnesium hydroxide are covered to prevent dissolution, and that magnesium hydroxide hardly dissolves in the neutral region and remains in an insoluble state. In addition, it is estimated that this phenomenon is influenced also by the stirring condition.

  However, since it was difficult to improve the total alkali equivalent even when the stirring operation was performed for a long time, it is considered that the total alkali equivalent as in the examples is necessary in a practical apparatus. In addition, since the sludge is comprised with very many substances, the said consideration is only an estimation to the last.

It is a schematic block diagram which shows an example of the sludge concentration apparatus which concerns on embodiment of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Sludge concentration apparatus, 10 Sludge concentration adjustment tank, 12 Acid treatment tank, 14 Alkali treatment tank, 16 Acid storage tank, 18 Calcium agent storage tank, 20 Magnesium agent storage tank, 22 Sludge sedimentation tank, 24 Dehydration apparatus, 26, 28, 30, 32, 34, 36, 38 Pump, 40, 42, 44, 46 Stirrer, 48, 50, 56 Sludge pipe, 58 Acid pipe, 60 Calcium agent pipe, 52 Acid treatment liquid pipe, 54 Alkali treatment liquid pipe, 62 Magnesium Agent piping.

Claims (8)

A method for concentrating sludge generated in water treatment using an aluminum flocculant,
An acid treatment step of treating the sludge with an acid;
An alkali treatment step of treating the sludge treated with the acid with at least one of a calcium agent and a magnesium agent which are alkali agents;
A method for concentrating sludge. It is a sludge concentration method of Claim 1, Comprising:
A method for concentrating sludge, wherein the concentration of sludge obtained by the alkali treatment step is adjusted by changing the amount of calcium agent and magnesium agent used. It is the sludge concentration method of Claim 1 or 2,
The method for concentrating sludge, wherein the calcium agent is calcium hydroxide. It is the sludge concentration method of any one of Claims 1-3,
The method for concentrating sludge, wherein the magnesium agent is magnesium hydroxide. It is the sludge concentration method of any one of Claims 1-4,
The sludge concentration method, wherein the acid is sulfuric acid. It is the sludge concentration method of any one of Claims 1-5,
The chemical equivalent ratio of the alkaline agent to the acid is in the range of 1.2 to 2, wherein the sludge concentration method is characterized. It is the sludge concentration method of any one of Claims 1-6,
The mixing ratio of the magnesium agent to the calcium agent is in the range of 0 to 100%. An apparatus for concentrating sludge generated in water treatment using an aluminum flocculant,
An acid treatment tank for treating the sludge with an acid;
Acid addition means for adding the acid to the acid treatment tank;
An alkali treatment tank for treating the sludge treated with the acid with a calcium agent and a magnesium agent which are alkali agents;
Alkali agent addition means for adding the alkali agent to the alkali treatment tank;
A sludge concentrating device characterized by comprising:

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