JP2007196086A - Concentration volume reduction process and arrangement of sludge - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To reduce the volume of sludge by improving the sedimentation concentration property of the sludge. <P>SOLUTION: This invention includes the following method in its embodiment. This method for concentrating sedimentation sludge generated when flocculation sedimentation is carried out using an aluminium and/or iron flocculant comprises the loading of an alkaline agent under the presence of calcium ions after the sludge is loaded with sulfuric acid. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for treating precipitated sludge generated in a water treatment operation in which coagulation precipitation is performed using an aluminum or iron type coagulant.

  Water treatment methods for coagulating and precipitating using aluminum or iron are widely used in general industries and in waterworks and sewers. Although this treatment is a very good method for eliminating contaminants in water, agglomeration and sedimentation sludge generated as a result of treatment is generally used as an agglomerating agent because aluminum or iron is used as the aggregating agent. Contains a large amount of a metal hydroxide compound with aluminum or iron, so that they swell and have very poor sedimentation concentration, and have a high water content and are difficult to dehydrate.

  For such sludge, as described in paragraphs 0002 to 0006 of Japanese Patent No. 3709825, a method of concentration and dehydration using a polymer flocculant is known. In addition, in non-chemical injection, concentration was performed by gravity sedimentation, followed by dehydration by pressure dehydration or the like and solidification treatment was performed. The outline of the gravity sedimentation-type sludge treatment facility 100 by a prior art is shown using FIG. The sludge treatment facility 100 includes a gravity sedimentation concentration tank 2 that concentrates and adjusts the coagulated sediment sludge from the water treatment facility, a sludge dewatering facility 22 that dehydrates the sludge drawn from the gravity sedimentation concentration tank 2, and a sludge dewatering facility 22. And a sludge pipe 21 to be transferred to. As depicted in FIG. 1, the sludge drawn out from the gravity sedimentation tank 2 is directly transferred to the sludge dewatering facility 22 and subjected to a dewatering process.

  However, since concentration concentration is low in gravity sedimentation, it takes time to dehydrate to solidification by pressure dehydration, and a large pressure dehydrator is required. Moreover, it was difficult to reduce the moisture content, and the amount of industrial waste dumped was very large.

There is also a method of adding slaked lime directly to sludge and dehydrating it, but since alkaline wastewater is generated and alkali-dissolved material is included in the wastewater, neutralization treatment and removal of its contaminants are necessary. (Water Supply Facility Design Guidelines 2000, Japan Waterworks Association, p377). In addition, slaked lime and carbon dioxide in the air react to cause calcium carbonate to deposit on the filter cloth during the dehydration operation, resulting in serious clogging of the filter cloth. Chemical cleaning by etc. was required.
Japanese Patent No. 3709825 Water Supply Facility Design Guidelines 2000 Japan Waterworks Association, p377

  The present invention has been made in view of such circumstances, and has been made to create a technique capable of achieving volume reduction of sludge by improving the sediment concentration property of sludge.

  The present invention includes the following method in one embodiment thereof. This method is a method for concentrating precipitated sludge generated when coagulating and precipitating using an aluminum-based and iron-based coagulant. In order to increase the concentration of the sludge, after adding sulfuric acid to the sludge, calcium ions It is characterized by adding an alkali agent in the presence of.

  According to the above method, aluminum hydroxide or iron hydroxide contained in the sludge is once dissolved by sulfuric acid. However, by adding a calcium salt and an alkaline agent, or by directly adding slaked lime (calcium hydroxide), calcium sulfate is produced by the reaction of calcium ions and sulfate ions, and aluminum ions and iron ions are water. It precipitates again (reagglomerates) as aluminum oxide or iron hydroxide. The generation of calcium sulfate and the generation of aluminum ions and / or iron ions proceed in parallel, so that calcium sulfate settles while being taken into the aggregated flocs of aluminum hydroxide by the coprecipitation phenomenon. Since calcium sulfate generally has a large density of about 2.9, the sedimentation concentration of sludge is greatly improved. Further, the concentration and reduction of sludge can dramatically increase the efficiency of the subsequent dehydration process, and can greatly improve the capacity of the subsequent dehydration process according to the degree of concentration and volume reduction.

  In the above method, calcium ions can be supplied by adding a calcium salt to sludge before or after adding sulfuric acid, or after adding sulfuric acid. Moreover, you may supply a calcium ion by using an alkaline agent containing calcium, such as calcium hydroxide, as an alkaline agent added to sludge. In the case where sufficient calcium ions are already contained in the sludge to be treated, an embodiment in which no additional calcium ions are intentionally supplied to the sludge is also possible.

In the above method, it is preferable to stir the sludge when adding sulfuric acid. The stronger the stirring strength, the faster the acid diffuses and the faster the dissolution, so the stronger the stirring strength is, and the G value (an index indicating the strength of stirring) is preferably 100 s ⁻¹ or more. . In the above method, it is preferable to stir the reaction solution also in the addition of the alkaline agent. In this case, the sludge may be agitated at a speed slower than the agitation speed at the time of the addition of sulfuric acid so as not to destroy the flocs of the hydroxide reaggregated by the addition of the alkali agent. When the object to be treated is sludge slurry, it is preferable that the stirring strength is increased more than usual and the G value is about 50 to 120 s ⁻¹ .

  In a more specific embodiment of the above method, when the sludge is a precipitated sludge generated by a coagulation precipitation process using an aluminum-based coagulant, after adjusting the pH to less than 5 by adding the sulfuric acid, You may adjust pH to 4.5-9 by adding an alkaline agent in presence of a calcium ion.

  In addition, when the sludge is a precipitated sludge generated by a coagulating sedimentation process using an aluminum-based coagulant, sulfuric acid may be added in the presence of calcium ions after adding an alkali agent to the sludge. Good. In a more specific embodiment of this method, the pH may be adjusted to 5 to 8 by adding sulfuric acid in the presence of calcium ions after adjusting the pH to exceed 8 by adding the alkaline agent. Good.

  Furthermore, the sludge may be stirred at the time of adding the sulfuric acid, and the sludge may be stirred at a speed slower than the stirring speed at the time of adding the sulfuric acid at the time of adding the alkaline agent.

  The present invention includes the following apparatus in another embodiment thereof. This apparatus is a concentration treatment apparatus for precipitation sludge generated when coagulation precipitation treatment is performed using an aluminum-based and iron-based flocculant, and a first reaction tank for reacting sulfuric acid with sulfuric acid, and the sludge And a second reaction tank for reacting an alkaline agent in the presence of calcium ions.

The present invention includes the following apparatus in yet another embodiment thereof. This device is a concentration treatment device for precipitation sludge that is generated when agglomeration and precipitation treatment is performed using an aluminum-based and iron-based flocculant,
A gravity sedimentation concentration tank for concentrating the precipitated sludge by gravity sedimentation;
A sludge dewatering device for dewatering the concentrated sludge concentrated by the gravity sedimentation tank;
A first sludge pipe for transferring the concentrated sludge from the gravity sedimentation tank to the sludge dewatering device;
A branch pipe provided in the middle of the first sludge pipe to branch the flow of the concentrated sludge in the first sludge pipe;
A first reaction tank for reacting sulfuric acid with the concentrated sludge supplied through the branch pipe;
A second reaction tank for reacting an alkaline agent in the presence of calcium ions with the concentrated sludge supplied through the branch pipe;
A second sludge pipe for transferring the treated concentrated sludge processed by the first reaction tank and the second reaction tank to the gravity sedimentation tank;
It is characterized by providing.

  In this apparatus, a branch pipe is provided in a pipe for transferring concentrated sludge from the gravity sedimentation tank to the sludge dewatering apparatus, thereby extracting a part of the sludge transferred to the sludge dewatering apparatus and using the method according to the present invention. Since the configuration of concentrating and returning to the gravity sedimentation concentration tank is employed, the present invention can be easily incorporated into a conventional sludge reforming apparatus having a gravity sedimentation concentration tank and a sludge dewatering device.

  According to the present invention, the sediment concentration of sludge is dramatically improved. As a result, the volume of sludge can be significantly reduced, and the dewaterability and moisture content in the dewatering and solidification of the sludge can be improved. Therefore, the amount of industrial waste generated at the final stage of treatment is greatly reduced. can do.

  In the most preferred embodiment of the present invention, a part of sludge is dissolved with sulfuric acid in order to treat the precipitated sludge generated when the coagulating precipitation treatment is performed using an aluminum-based and / or iron-based flocculant. Then, slaked lime is added and neutralized.

  By first adding acid to the sludge, the aluminum hydroxide in the sludge is dissolved. In this dissolution, sulfuric acid is preferably used, and aluminum sulfate is preferably dissolved in the form of aluminum ions and sulfate ions. At this time, the pH is preferably adjusted to be less than 5, more preferably adjusted to 4 or less, and further preferably adjusted to 3 or less. From the viewpoint of running cost, 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.

  After dissolving aluminum hydroxide by adding sulfuric acid, slaked lime is added. When an aluminum-based flocculant is used, the pH is preferably adjusted to 4 or more, more preferably adjusted to 4.5 to 9, and still more preferably, the pH is It is desirable to adjust to 5.6-8. When an iron-based flocculant is used, the pH is preferably adjusted to 4 or more, more preferably adjusted to 4.5 to 9, and still more preferably pH It is desirable to adjust so that it may become 5-6.

  In this operation, by injection of slaked lime, aluminum ions are insolubilized as aluminum hydroxide, and at the same time, calcium sulfate is generated by the reaction between calcium ions and sulfate ions. As this reaction proceeds in parallel, calcium sulfate and aluminum hydroxide are generated in parallel, and at the same time, calcium sulfate is incorporated into the flocs of aluminum hydroxide together with turbid components in the sludge by the coprecipitation phenomenon. It settles down. This greatly improves the sedimentation and concentration of sludge. Further, the concentration and reduction of sludge can dramatically increase the efficiency of the subsequent dehydration process, and can greatly improve the capacity of the subsequent dehydration process according to the degree of concentration and volume reduction.

  According to the present invention, since the specific gravity of the sludge increases, sufficient sedimentation can be obtained without adding a polymer flocculant. However, the addition of a polymer flocculant can further improve the sedimentation. it can.

  In the above description, when the coagulant used first is an iron-based coagulant, it goes without saying that the aluminum hydroxide and aluminum ions in the above description can be read as iron hydroxide and iron ions.

  If the sedimentation and concentration of sludge and the dewaterability of sludge are improved, it is possible to reduce the capacity of expensive dewatering equipment and the amount of industrial waste dumped. In particular, sludge generated from coagulation sedimentation treatment using polyaluminum chloride or sulfuric acid band as an aluminum-based coagulant as in waterworks has a very significant concentration and volume reduction effect. It can be a very useful technique in water purification plants that suffer from the treatment of water. Even in the case of using a sun-dried bed, if the concentration increases, it becomes possible to reduce the penetration depth, the progress of drying becomes faster, the operation becomes easier, and the area of the dry bed can be reduced. This leads to effects such as

  Here, as the calcium salt, any calcium salt such as calcium chloride, calcium carbonate, quick lime and slaked lime can be used, but quick lime and slaked lime are preferably used.

  That is, since quick lime and slaked lime have low solubility in water, it is considered that the agglomeration reaction and the crystal formation reaction proceed around the periphery of quick lime particles and slaked lime particles while limiting local reactions in the bulk. Therefore, reaggregation of aluminum ions and / or iron ions occurs using the particles as nuclei, and calcium sulfate can be smoothly taken in during the reaggregation, and sludge having good dewaterability can be obtained.

  Since slaked lime is effective in either powder or slurry, a convenient one can be used. Slurry slaked lime is often excellent in terms of ease of handling. Moreover, when quicklime is utilized, the acceleration of the reaction and the sedimentation acceleration effect of sludge can be expected by the heating effect due to the exothermic reaction when quicklime is dissolved. Calcium sulfate is also called gypsum, but there are three types of gypsum, and it is unclear which form it is, but generally the density is as large as about 2.9. It is considered that the sedimentation concentration of sludge swollen with aluminum is greatly improved.

The reaction formula with sulfuric acid and slaked lime is shown below.
(1) First dissolution of aluminum hydroxide with sulfuric acid
3H ₂ SO ₄ + 2Al (OH) ₃ → 6H ₂ O + 2Al ³⁺ + 3SO ₄ ^2-
(2) Neutralization reaction with second-stage reaction slaked lime
3Ca (OH) ₂ → 3Ca ²⁺
+ 6OH ^over
2Al ³⁺ ＋ 6OH ⁻ → 2Al (OH) ₃ ↓
3Ca ²⁺ + 3SO ₄ ²⁻
→ 3CaSO ₄ ↓

Test example 1

  Hereinafter, the example which improved the sludge of a certain water purification plant using one embodiment of the present invention is shown. 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 0.59%. When the sludge concentration is low, a large amount of sludge is treated, and the sludge treatment facility becomes a very large facility, and at the same time, a large facility is required for dehydration and solidification.

  Therefore, in this test, sulfuric acid with a concentration of 65% was added to the sludge generated at the water purification plant in various amounts as shown in Table 1, and slaked lime was added 15 minutes after the addition, and another 30 minutes passed. After and after 24 hours, the sludge concentration and pH were examined. The results are shown in Table 1.

表１に示す如く、３０分沈降後の汚泥濃度は初期汚泥濃度の４〜４.５倍に達し、２４時間沈降後の汚泥濃度は初期濃度のおよそ５倍に達する。また全ての硫酸添加範囲で濃縮効果が確認される。硫酸添加量を多くすると初期の３０分沈降が良い為沈降濃縮槽の容量を小さく出来るメリットが見られる。また硫酸の添加量の低い方が消石灰による中和量が少なくて済むというメリットがある。そこで硫酸及び消石灰の添加量を変化させ、汚泥の濃縮濃度を調査し、硫酸、消石灰の少ない添加量を選択すれば良い。表１に示すごとく、最も少ない硫酸添加量でも作用は殆ど変わらず２４時間沈降後約５倍濃縮に達し、大幅な濃度の向上を達成している。最終ｐＨは鉄及びＡｌ濃度に影響を与えるため、返送先もしくは放流先の必要とする値により、消石灰の量を増減し調整すれば良い。ｐＨを中性とすれば、鉄及びアルミの濃度を減少させることができる。試験例で見る如く溶解に際しては溶解後のｐＨが３.７程度おいても効果があり、このｐＨでは水酸化アルミニウム必ずしも全量溶解しているわけではなく、一部が溶解しアルミイオンと硫酸イオンが存在していると推察される。従って、原汚泥中の水酸化アルミニウムが全量溶解される必要はないと考えられる。

As shown in Table 1, the sludge concentration after settling for 30 minutes reaches 4 to 4.5 times the initial sludge concentration, and the sludge concentration after settling for 24 hours reaches about 5 times the initial concentration. In addition, the concentration effect is confirmed in all sulfuric acid addition ranges. If the amount of sulfuric acid added is increased, the initial 30-minute sedimentation is good, so there is an advantage that the capacity of the sedimentation tank can be reduced. Further, the lower the amount of sulfuric acid added, there is a merit that the amount of neutralization by slaked lime is less. Therefore, the addition amount of sulfuric acid and slaked lime may be changed, the concentrated concentration of sludge may be investigated, and the addition amount of sulfuric acid and slaked lime may be selected. As shown in Table 1, even with the smallest amount of sulfuric acid added, the action hardly changed, and the concentration reached about 5 times after sedimentation for 24 hours, and the concentration was greatly improved. Since the final pH affects the iron and Al concentrations, the amount of slaked lime may be adjusted by adjusting the value required by the return destination or discharge destination. If the pH is neutral, the concentrations of iron and aluminum can be reduced. As seen in the test examples, the dissolution is effective even when the pH after dissolution is about 3.7. At this pH, the total amount of aluminum hydroxide is not necessarily dissolved, but part of the aluminum hydroxide and sulfate ions are dissolved. Is presumed to exist. Therefore, it is considered that the entire amount of aluminum hydroxide in the raw sludge need not be dissolved.

  Next, Table 2 shows the experimental results of examining the difference in sludge dewatering capacity between the sludge concentrated by the above test example and the conventional sludge to which the present example is not applied.

脱水機の能力は濾過速度とケーキ含水率により評価される。本実験例によれば、上記試験例によって濃縮された汚泥は、従来汚泥に対して濾過速度は約３倍、脱水ケーキで８〜９％程度改善され、特に脱水速度は顕著な効果があることが示されている。本発明では汚泥中に硫酸カルシウムが増加するが、乾燥固形分としての増加量は汚泥の２０％程度であり、濾過速度を補正しても脱水機能力の増加は２倍以上になり汚泥の脱水性を大幅に改善されている。このため、本試験例によって濃縮された汚泥に対しては、脱水設備を約５０％以上削減することが可能であり、設備の大幅なコスト削減もしくは運転時間の削減ができる。

The capacity of the dehydrator is evaluated by the filtration rate and cake moisture content. According to this experimental example, the sludge concentrated in the above test example has a filtration rate about 3 times that of the conventional sludge and is improved by about 8 to 9% with the dehydrated cake, and the dehydration rate is particularly effective. It is shown. In the present invention, calcium sulfate is increased in the sludge, but the increase in dry solid content is about 20% of the sludge, and even if the filtration rate is corrected, the increase in the dewatering function is more than doubled and the sludge is dehydrated. The sex has been greatly improved. For this reason, with respect to the sludge concentrated by this test example, it is possible to reduce the dehydration equipment by about 50% or more, and it is possible to greatly reduce the cost of the equipment or the operation time.

  Thus, this test shows that even when the pH after the sulfuric acid reaction is 3.7, a sufficient sludge concentration effect and improvement of the sludge dewatering ability can be seen, and there is no problem with good results for the treatment liquid after neutralization. There was found. For this reason, at the time of this application, in the said water purification plant, examination is advanced in the direction which actually applies this test example on these conditions.

  Embodiments of the present invention will be described below with reference to the accompanying drawings. FIG. 2 is a diagram for explaining an outline and an operation flow of the apparatus configuration of the sludge treatment facility 200 according to an embodiment of the present invention.

  The sludge treatment facility 200 is composed of a gravity sedimentation concentration tank 2 for concentrating and adjusting the coagulated sediment sludge from a water treatment facility that performs coagulation precipitation using an aluminum or iron type coagulant, and a sulfuric acid reaction tank 4 for reacting sludge and sulfuric acid. Sulfuric acid reservoir 10 for storing sulfuric acid, slaked lime reaction tank 12 for reacting with slaked lime, slaked lime slurry tank 16 for storing slaked lime slurry, neutralized sludge settling tank 19 for settling and separating sludge neutralized by slaked lime, sludge dewatering equipment 22 Etc.

  Sludge from the water treatment facility is transferred from the sludge pipe 1 to the gravity settling tank 2 where it is concentrated by gravity settling. The sulfuric acid reaction target sludge whose volume has been reduced by the concentration adjustment is extracted from the gravity sedimentation concentration tank 2 by the sludge transfer pump 3, transferred to the sulfuric acid reaction tank 4, and mixed with the sulfuric acid sent from the sulfuric acid reservoir 10. Before the reaction in the sulfuric acid reaction tank 4, the sludge pipe 6 and the sulfuric acid pipe 7 are connected to the mixing pipe 8 before flowing into the tank 4, and the reaction can proceed smoothly by mixing with sulfuric acid in advance. it can. A sulfuric acid reaction tank stirrer 5 is installed in the sulfuric acid reaction tank 4 to promote the reaction. Aluminum hydroxide and iron hydroxide are dissolved and ionized by sulfuric acid. This ionization is effective even if it is limited to a part, and a reaction test is performed in advance to set the addition amount as economical as possible.

  Subsequently, the reaction liquid is transferred from the sulfuric acid reaction tank 4 to the slaked lime reaction tank 12 by the sulfuric acid sludge transfer pump 11, and the slaked lime slurry is further transferred from the tank 16 using the slaked lime slurry injection pump 15 and the slaked lime slurry pipe 14. Inject. Since calcium sulfate is produced in the reaction vessel 12, the injection point needs attention. That is, when calcium sulfate is produced, scales such as calcium sulfate accumulate on the walls in the tank, impellers such as a stirrer, and shafts, so that the injection point that minimizes contact with the produced high-concentration calcium sulfate is minimized. Is desirable. For example, it is desirable to arrange the inflow point of the liquid to be treated transferred from the sulfuric acid reaction tank 4 and the injection point of slaked lime at symmetrical positions around the center of the slaked lime reaction tank 12.

Here, the production reaction of aluminum hydroxide, iron hydroxide and calcium sulfate is performed, and the coagulation reaction proceeds at the same time, and the sludge having improved sedimentation is reformed. A stirrer 13 is also installed in the slaked lime reaction tank 12 to promote the reaction. In addition, a stirrer 17 is also installed in the slaked lime slurry tank 16 so that the slurry does not settle.

At this time, it is necessary to select the stirrer 17 of the slaked lime reaction tank 12 so as not to break the flocs, and it is preferable to stir at a speed slower than the stirring speed of the sulfuric acid reaction tank stirrer 5. Specifically, it is preferable to select so that the so-called G value is 10 to 150 s ^−1, and it is more preferable to select the G value to be 50 to 120 s ⁻¹ .

  The sludge modified in the slaked lime reaction tank 12 is transferred to the neutralized sludge settling tank 19 by the neutralized sludge transfer pump 18, and is concentrated and settled by gravity settling. The concentrated and reduced sludge is sent to the sludge dewatering facility 22 through the concentrated sludge pump 20 and the concentrated sludge pipe 21, and is carried out as waste through the dewatering process.

  In this embodiment, the liquid to be treated is pumped to a sulfuric acid reaction tank, a slaked lime reaction tank, and a neutralized sludge settling tank, but may be transferred by piping or trough without using a pump.

  FIG. 3 is a diagram for explaining an outline of an apparatus configuration and an operation flow of a sludge treatment facility 300 according to another embodiment of the present invention. In FIG. 2, the same components as those in the sludge treatment facility 200 according to Example 1 described above are denoted by the same reference numerals, and description thereof is omitted.

  The sludge treatment facility 300 is provided with a branch pipe 23 in the middle of the sludge pipe 21 from the gravity sedimentation concentration tank 2 to the sludge dewatering facility 22, and is provided with a sulfuric acid and slaked lime reaction tank similar to the sludge treatment facility 200 according to the first embodiment. Thus, a reforming reaction is performed, and the reformed sludge is returned to the gravity sedimentation tank 2 using the neutralized sludge transfer pump 18 and the sludge circulation pipe 24. By circulating the modified sludge, concentration and volume reduction of the sludge can be achieved. In this circulation method, it takes time until the volume reduction and concentration of sludge reaches an equilibrium state and the concentration is stabilized, and the final sludge concentration is often slightly lower than that of the sludge treatment apparatus 200. However, in the case of an iron-based coagulant, crystals grow by circulation and an increase in the sludge concentration may be observed.

  The sludge treatment facility 300 has a structure in which a branch pipe is provided in the middle of the sludge pipe 21 from the gravity sedimentation concentration tank 2 to the sludge dewatering equipment 22, and the sludge reforming equipment according to the present invention is installed at the end thereof. There is an advantage that the sludge reforming facility according to the present invention can be easily incorporated into the existing sludge treatment facility according to the prior art.

  As described above, the present invention has been described by way of examples in order to help understanding of the present invention. However, the present invention is not limited by the above-described examples, and various implementations can be made without departing from the scope of the present invention. It goes without saying that embodiments can be taken.

It is a figure for demonstrating the outline of the sludge treatment facility 100 by a prior art. It is a figure for demonstrating the outline of the sludge treatment facility 200 which concerns on one Example of this invention. It is a figure for demonstrating the outline of the sludge treatment facility 300 which concerns on another Example of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sludge piping 2 Gravity sedimentation concentration tank 4 Sulfuric acid reaction tank 5 Sulfuric acid reaction tank agitator 6 Sludge piping 7 Sulfuric acid piping 10 Sulfuric acid storage tank 11 Sulfuric acid sludge transfer pump 12 Slaked lime reaction tank 14 Slaked lime slurry piping 15 Slaked lime slurry injection pump 16 Slaked lime slurry tank 17 Stirrer 18 Neutralized sludge transfer pump 19 Neutralized sludge settling tank 20 Concentrated sludge pump 21 Concentrated sludge piping 22 Sludge dewatering equipment 23 Branch pipe 24 Sludge circulation piping 100 Sludge treatment facility 200 according to the prior art Sludge treatment facility according to the first embodiment of the present invention 300 Sludge treatment facility according to the second embodiment of the present invention

Claims (7)

  In a method for concentrating precipitated sludge generated when coagulating sedimentation using an aluminum-based and / or iron-based flocculant, after adding sulfuric acid to the sludge, adding an alkali agent in the presence of calcium ions A characteristic method for concentrating sludge.   In a method for concentrating precipitated sludge generated when coagulating sedimentation is performed using an aluminum-based flocculant, an alkaline agent is added to the sludge, and then sulfuric acid is added to the sludge in the presence of calcium ions. To concentrate sludge.   The method according to claim 1, wherein the sludge is stirred at the time of the addition of the sulfuric acid, and the sludge is stirred at a speed slower than the stirring speed at the time of the addition of the sulfuric acid when the alkaline agent is added.   Precipitation sludge concentration treatment apparatus generated when coagulating and precipitating using an aluminum-based and / or iron-based coagulant, a first reaction tank for reacting the sludge with sulfuric acid, and presence of calcium ions And a second reaction tank for reacting an alkaline agent with the sludge. An apparatus for concentrating precipitation sludge generated when coagulating and precipitating using an aluminum-based and / or iron-based coagulant,
A gravity sedimentation concentration tank for concentrating the precipitated sludge by gravity sedimentation;
A sludge dewatering device for dewatering the concentrated sludge concentrated by the gravity sedimentation tank;
A first sludge pipe for transferring the concentrated sludge from the gravity sedimentation tank to the sludge dewatering device;
A branch pipe provided in the middle of the first sludge pipe to branch the flow of the concentrated sludge in the first sludge pipe;
A first reaction tank for reacting sulfuric acid with the concentrated sludge supplied through the branch pipe;
A second reaction tank for reacting the concentrated sludge supplied via the branch pipe with an alkaline agent in the presence of calcium ions;
A second sludge pipe for transferring the treated concentrated sludge processed by the first reaction tank and the second reaction tank to the gravity sedimentation tank;
A device comprising:   6. The apparatus according to claim 4 or 5, wherein the sludge is premixed with the sulfuric acid and configured to flow into the first reaction tank. The stirrer is provided in both the first reaction tank and the second reaction tank, and the stirring speed in the second reaction tank is set slower than the stirring speed in the first reaction tank. The device according to any one of the above.

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