JP3480904B2 - Method and apparatus for recovering phosphorus from sludge - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to the treatment of sewage in a sewage treatment plant by using activated sludge or the like, in which an excess sludge generated from this water treatment system and a sludge mixed with the first settling tank are treated in an anaerobic atmosphere. And a device for recovering the phosphorus content contained in this solution by releasing the phosphorus content contained in the excess sludge into the solution.

[0002]

BACKGROUND ART In order to prevent water pollution in rivers, lakes and marshes and closed coastal waters, factories and sewage treatment plants for treating urban sewage have been constructed in various places. At these sewage treatment plants, one example of conventional treatment methods for sewage, etc.
As shown in FIG. The sewage received at the treatment plant is first cleared of sand and coarse debris in the sand basin. Next, suspended solids and the like are first settled in the first settling tank and separated into sludge and settling sewage in the first settling tank. The precipitated sewage separated in this pretreatment step is treated in the reaction tank using activated sludge under an aerobic atmosphere, and the organic matter in the precipitated sewage is mainly removed. Next, in the final settling tank, the activated sludge treated in the reaction tank and the treated water are separated, the activated sludge is sent to the next step, and the separated treated water is discharged to the outside of the treatment plant. The activated sludge separated in this treatment process is divided into return sludge and excess sludge, and the returned sludge is returned to the reaction tank and reused as activated sludge, and the excess sludge is discharged out of the system.

Excess sludge generated in this water treatment system and the first settling tank sludge (raw sludge) settled in the first settling tank are concentrated in the sludge processing system alone or in a mixture of both, and concentrated sludge is obtained. The concentrated separated liquid is separated into the concentrated separated liquid and returned to the water treatment system. The separated concentrated sludge is
It is dehydrated and separated into dehydrated separated liquid and dehydrated sludge, and the dehydrated separated liquid is returned to the water treatment system. Further, the separated dehydrated sludge is treated by a treatment method such as landfill or incineration.

[0004]

Since the treated water contains eutrophication-causing substances such as phosphorus and nitrogen, it is difficult to solve the problem in closed water areas such as lakes and closed coastal waters.
It is a cause of the occurrence of red tides due to eutrophication of water quality. As a countermeasure against this, in the above water treatment system, by making the front stage of the biological reaction tank anaerobic, activated sludge accumulates phosphorus (orthophosphate ion) as polyphosphoric acid, and reduces the phosphorus concentration of the treated water. Treatment methods are becoming popular. However, after the activated sludge accumulating this polyphosphoric acid is drawn as excess sludge into the sludge treatment system, depending on the method of concentrating in the sludge treatment system, the phosphorus content is eluted from the excess sludge,
The phosphorus concentration of the concentrated separated liquid or the dehydrated separated liquid increases. The concentrated separated liquid and the dehydrated separated liquid with the increased phosphorus content concentration are returned to the water treatment system as return water, and as a result, the effect of reducing the phosphorus concentration of the treated water is weakened. It is a problem in sewage treatment. Further, when an anaerobic digester is provided, when the digested sludge digested in this anaerobic digester is transported to the dehydration separation device, the phosphorus content, magnesium content and ammonia content released to the solution side by the anaerobic digestion are The reaction caused the precipitation of crystals of magnesium ammonium phosphate in the transport pipe, which grew and caused a clogging accident of the transport pipe.

In order to solve the above problems and blockage accidents,
At present, flocculants such as lime, aluminum sulfate, ferric sulfate and polyaluminum chloride are used in the sludge treatment process. When these coagulants are used, sludge increases in proportion to the amount of the coagulant added, which causes a problem of increasing the final disposal cost of sludge associated with sewage treatment. In addition, the product produced by the reaction of the aggregating agent and the phosphorus content is chemically stable, and thus has a form having no reusability for fertilizers and the like. In addition, since these products are finally contained in the dehydrated sludge, when the dehydrated sludge is used as a cement raw material, which is attracting attention as the final technology of the sewage treatment that occurs with the treatment of urban sewage, the deterioration of cement quality due to phosphorus content As a result, the situation in which this processing technology is hard to utilize is created.

[0006]

[Means for Solving the Problems] The present inventors have solved the above-mentioned problems and efficiently collect phosphorus in mixed sludge and also recover phosphorus in a form that can be effectively used as fertilizer. As a result of researching, the inventors have invented the following method. The invention according to claim 1 treats, in an anaerobic atmosphere, a mixed sludge in which surplus sludge discharged from a water treatment system at a sewage treatment plant and first settling tank sludge are mixed at a ratio of 1: 1 on a dry weight basis. Release the phosphorus content in the sludge, separate the treated sludge into concentrated sludge and concentrated separation liquid, digest this concentrated sludge in an anaerobic digestion tank, and then dehydrate this digested sludge to dehydrate sludge and dehydration separation This liquid is separated into
And the above concentrated separated liquid are mixed, and this mixture is mixed with calcium silicate.
For contacting dephosphorization material mainly composed of hydrated um
Is a method of recovering phosphorus from sludge in a mixed solution . In the invention according to claim 2, the method for recovering phosphorus from the dehydrated separated liquid and the concentrated separated liquid adjusts the calcium concentration in these liquids to 90 to 160 mg / l, and adjusts the pH value of the adjusted liquid. Is adjusted to 8 to 9 and treated with a dephosphorizing material. The invention according to claim 3 is that, in a sewage treatment plant, excess sludge discharged from the water treatment system and the first settling tank sludge are mixed in a ratio of 1: 1 on a dry weight basis to treat the mixed sludge under an anaerobic atmosphere. To release a phosphorus content into the solution by means of a phosphorus releasing means, a concentration means for concentrating the sludge releasing the phosphorus content by the phosphorus releasing means, and separating it into a concentrated separation liquid and a concentrated sludge, and a concentration separated by this concentration means. and anaerobic digestion means digesting with an anaerobic atmosphere sludge, and dewatering means for separating the digested sludge that had been digested with the anaerobic digestion unit to dehydration separated liquid and dewatered sludge, the concentrate separated liquid and dehydrating the separated liquid same
Mix in one water tank and add water-soluble calcium compound to this mixed solution to adjust the calcium concentration in these solutions to 90%.
˜160 mg / l, a pH value adjusting means for adjusting the pH value to 8 to 9 by adding an alkaline substance to the solution in which the calcium content concentration is adjusted, and calcium silicate water from the solution in which the pH value is adjusted. An apparatus for recovering phosphorus in sludge, comprising: a reaction tank for producing a phosphorus compound by using a dephosphorizing agent containing a hydrate as a main component .

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION When sewage is treated by an anaerobic-aerobic method, which is a modified method for removing phosphorus in the activated sludge method, excess sludge contains a high concentration of phosphorus. In the present invention, before concentrating this excess sludge, first, it is mixed with a settling tank sludge, this mixed sludge is treated under an anaerobic atmosphere, and after the phosphorus content in the sludge is released into the solution, The present invention relates to a method and an apparatus for crystallizing the phosphorus component (orthophosphate ion) of hydroxyapatite as hydroxyapatite and recovering it. Moreover, the method and apparatus of the present invention can be applied to a usual activated sludge method. In the present invention, the mixed sludge of the excess sludge generated in the water treatment system and the raw sludge (first settling tank sludge) is treated under an anaerobic atmosphere to remove phosphorus (polyphosphoric acid) in the mixed sludge. It is hydrolyzed and released as orthophosphoric acid into the solution to reduce the phosphorus concentration in the sludge. The sludge is treated with a concentrating device such as gravity concentrating, floating concentrating, centrifugal concentrating or the like to reduce the water content in the sludge, thereby reducing the phosphorus content in the concentrated sludge.

The concentrated sludge having a reduced phosphorus content is further treated in an anaerobic digestion tank and then dehydrated to be separated into dehydrated sludge and dehydrated separated liquid. At this time, the digested sludge treated in the anaerobic digestion tank has a lower phosphorus content in advance, so even if phosphorus is released from this digested sludge, ammonium magnesium phosphate is transported into the transport pipe. The possibility that the crystals will precipitate will be reduced. The phosphorus content recovery apparatus of the present invention treats the mixed sludge generated in the sewage treatment plant with the sludge mixed with the raw sludge in the anaerobic phosphorus release tank before the concentration apparatus, and removes the phosphorus content in the excess sludge. To a solution for releasing phosphorus in the solution. In the process, as shown in FIG. 1, the mixed sludge is treated in an phosphorus release tank under an anaerobic atmosphere to release the phosphorus content in the mixed sludge to the solution side. Next, this sludge is separated into a concentrated sludge and a concentrated separation liquid by a concentrating means such as a gravity concentrating device, a centrifugal concentrating device, or a flotation concentrating device, and the phosphorus concentration in the concentrated sludge is reduced. This concentrated sludge is separated into a dehydrated sludge and a dehydrated separated liquid by a dehydrator.

After the concentrated sludge is digested in the anaerobic digestion tank, it is separated into dehydrated sludge and dehydrated separated liquid by a dehydrator. Both the concentrated separation liquid and the dehydrated separation liquid dissolve the phosphorus content (orthophosphate ion) released from the sludge, and the phosphorus content (orthophosphate ion) in this solution (hereinafter referred to as raw water) is removed. It is recovered by using a phosphorus material, for example, a dephosphorization material disclosed in Japanese Patent Application Laid-Open No. 10-34167 previously disclosed by the present applicant. As another recovery method, a crystallization method in which phosphate rock or bone charcoal is used as a seed crystal, or a method in which it is recovered as a magnesium ammonium phosphate crystal product can also be used. The method using the above dephosphorizing agent is a dephosphorizing agent for ALC or calcium hydrate hydrate, which is mainly produced from a calcareous raw material and a siliceous raw material, to which water and a foaming agent are added and cured at high temperature and high pressure. Is the method used as.

As shown in FIG. 1, the phosphorus content recovery method of the present invention comprises adding slaked lime or calcium chloride as a calcium ion source to raw water to adjust the calcium ion concentration in the raw water to 90 to 160 mg / l, and The pH of the adjusted solution and / or the reaction tank is adjusted to 8 to 9 with an alkaline agent such as calcium hydroxide or caustic soda, and a dephosphorization material composed of ALC and / or calcium silicate hydrate is stored. The hydroxyapatite crystals are formed on the surface of the dephosphorization material by contacting the dephosphorization material in the reaction tank. This is a method of using the dephosphorization material that has produced the hydroxyapatite crystals for a predetermined period of time, and then exchanging the dephosphorization material to recover the phosphorus content. The time to replace the dephosphorization material is to replace the dephosphorization material when the concentration of phosphorus in the treated water discharged outside the sewage treatment plant exceeds the discharge target value. As one of the methods, there can be mentioned a method in which the dephosphorization efficiency of the dephosphorizing agent in use is 70 to 90% lower than the usual value as a guide.

If the mixed sludge is treated in an anaerobic atmosphere, phosphate ions can be released from the excess sludge in a short time, unlike anaerobic digestion. The release treatment time depends on the properties of the sludge, but in the case of mixed sludge, for example, it is about 1 to 2 hours. If it is less than 1 hour, the treatment time is too short, the release of phosphorus is not sufficient, and there is no particular problem if the treatment time is more than 2 hours, but the increase in the release amount of phosphorus becomes gradual, so the overall treatment efficiency Becomes worse,
The capacity of this processing tank becomes too large. In addition, when the excess sludge is treated alone in an anaerobic atmosphere, the release of phosphorus is delayed as compared with the mixed sludge, and it is necessary to treat the sludge for a longer time than the above time. Therefore, it is effective to treat the mixed sludge of the excess sludge and the raw sludge as described above, because the rise of phosphorus content is accelerated and the treatment efficiency is improved.

The concentration of calcium in the raw water to be treated is 90 to 160 mg / l.
Is. When it is 90 mg / l or less, the calcium concentration is insufficient and the dephosphorization efficiency is lowered. When the concentration is adjusted to 160 mg / l or higher, a calcium-aggregation reaction product is produced,
This aggregated product may adhere to the surface of the dephosphorization material, which may reduce the efficiency of the dephosphorization material and the efficiency of phosphorus content recovery.

[0013]

[Example] [Example 1] Raw sludge and excess sludge (phosphorus content:
4.0%) of both sludges on a dry weight basis,
Mixed sludge (phosphorus content: 2.5%) in which raw sludge and excess sludge were mixed at a ratio of 1: 1 and excess sludge were used as samples, and this was filled in a 500 ml Erlenmeyer flask, and the lid was placed on the Erlenmeyer flask. After filling the mouth with a lab stirrer, the mixture was stirred for 30, 60, 90, 150 and 240 minutes so that the sludge was not separated, and then filtered, and the concentration of orthophosphate ions in the filtrate was measured to calculate the phosphorus release rate. The results are shown in Table 1. From the above results, as for the time for treating the mixed sludge in the anaerobic atmosphere, from the results shown in Table 1, the treatment rate of 30 minutes, the release rate of orthophosphate ions was insufficient,
If treated for more than a minute, the positive phosphate ion in the sludge will be 50 to 8
About 0% can be released. Further, when treating the excess sludge alone, it is estimated that the treatment time is about 10 times longer than that of the mixed sludge.

[0014]

[Table 1]

[Example 2] A gravity concentrated separation liquid of a mixed sludge of excess sludge and raw sludge was used as raw water. This raw water was treated with the test apparatus shown in FIG. The concentration of orthophosphate (PO ₄ -P) in the raw water at this time was 4
It is about 0 mg / l, and calcium chloride hydrated while adjusting calcium ion concentration and pH in this solution by adding calcium chloride and a caustic soda aqueous solution to the levels of B to H as shown in FIG. Thing (average particle size 1.2m
m) Superficial velocity of 100 ml in a reaction tank filled with 100 ml
The phosphorus concentration in the treated water was measured every predetermined number of days by passing it at a speed of / hr. The result is as shown in FIG. From this result, the calcium ion concentration in the raw water was 90-160 m.
It was found that by adjusting g / l and further adjusting the pH value to 8 to 9, positive phosphate ions can be recovered by about 75 to 95%. At the test levels G and H,
Aggregation reaction products were confirmed in the calcium adjusting tank. Therefore, it is clear that the G and H level calcium ion concentrations are excessive additions.

[0016]

EFFECT OF THE INVENTION The phosphorus recovery method and the apparatus thereof according to the present invention, when the sludge mixed with the excess sludge and the raw sludge generated when the sewage is treated is digested in the anaerobic digester, the phosphorus in the sludge is preliminarily obtained. Since the concentration is reduced, the digestion sludge generated in the digestion tank is transported to the next dehydrator, and magnesium ammonium phosphate crystals are generated in the pipe, which reduces the possibility of clogging this transport pipe. , The stable operation can be secured, and the treatment efficiency of the whole sludge treatment can be improved. Further, in the present invention, since the phosphorus content is released from the activated sludge without digesting the mixed sludge, the phosphorus content is released within a short time, so that it is possible to reduce the installation area of the release tank. I can. Therefore, it is possible to easily add to existing equipment. Further, when recovering phosphorus in the concentrated separated liquid and the dehydrated separated liquid, by controlling the amount of calcium ions added to the liquid and the pH value to predetermined values, the dephosphorizing material can be used with high efficiency for a long period of time. You can The dephosphorized material after use can be reused as siliceous fertilizer and phosphate fertilizer without being discarded as industrial waste. Further, since the dehydrated sludge treated by using the method and the apparatus thereof of the present invention has a low phosphorus content, it is possible to prevent the deterioration of cement quality due to harmful phosphorus when it is effectively used as a raw material fuel for cement. .

[Brief description of drawings]

FIG. 1 is a process diagram showing a dephosphorization method of the present invention.

FIG. 2 is a test process diagram of Example 2 of the present invention.

3] Calcium ion addition amount and p in Example 2
It is a relationship diagram between H value and dephosphorization efficiency.

FIG. 4 is a process drawing showing an example of sludge treatment that has been conventionally performed.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI C05B 11/16 C05B 11/16 C05D 9/00 C05D 9/00 (72) Inventor Yuichi Fukushima 1-297 Kitabukuro-cho, Omiya-shi, Saitama Prefecture Mitsubishi Material Co., Ltd. Cement Research Institute (72) Inventor Tadashi Matsumoto 1-297 Kitabukuro-cho, Omiya-shi, Saitama Prefecture Mitsubishi Material Co., Ltd. Cement Research Institute (72) Inventor Yuichiro Abe 1-297 Kitabukuro-cho, Omiya-shi, Saitama Mitsubishi Mate (56) Reference JP-A-8-10791 (JP, A) JP-A-56-150500 (JP, A) JP-A-8-238499 (JP, A) JP-A-7-303889 (JP, A) JP 10-34167 (JP, A) (58) Fields investigated (Int.Cl. ⁷ , DB name) C02F 11 / 00-11 / 12

Claims (3)

(57) [Claims] 1. A mixed sludge in which excess sludge discharged from a water treatment system at a sewage treatment plant and first sludge in a primary sedimentation tank are mixed on a dry weight basis in a ratio of 1: 1 is treated in an anaerobic atmosphere to remove sludge from the sludge. The phosphorus content is released, the treated sludge is separated into a concentrated sludge and a concentrated separation liquid, the concentrated sludge is digested in an anaerobic digestion tank, and then the digested sludge is dehydrated and separated into dehydrated sludge and dehydrated separated liquid. The dehydrated separated liquid and the concentrated separated liquid
And the calcium silicate hydrate is the main component in this mixture.
By contacting the dephosphorizing material to
A method of recovering phosphorus in sludge that recovers phosphorus. 2. The method for recovering phosphorus from the dehydrated separated liquid and the concentrated separated liquid is such that the calcium concentration in these liquids is adjusted to 90 to 160 mg / l, and the pH of the adjusted liquid is adjusted.
The value is adjusted to 8 to 9 and treated with the dephosphorizing material.
The method for recovering phosphorus in sludge as described in. 3. A mixed sludge obtained by mixing the excess sludge discharged from the water treatment system and the first settling tank sludge in a ratio of 1: 1 on a dry weight basis in a sewage treatment plant is treated under an anaerobic atmosphere to remove phosphorus content. Phosphorus releasing means for releasing it into the solution, concentration means for concentrating the sludge that has released the phosphorus content by this phosphorus releasing means and separating it into concentrated separation liquid and concentrated sludge, and the concentrated sludge separated by this concentrating means Anaerobic digestion means for digesting under an atmosphere, dehydration separation means for separating digested sludge digested by this anaerobic digestion means into dehydrated separation liquid and dehydrated sludge, and the concentrated separation liquid and dehydrated separation liquid in the same water tank Mixed
Then, a water-soluble calcium compound was added to this mixed solution to adjust the calcium concentration in these solutions to 90 to 160 mg / l.
And a pH value adjusting means for adjusting the pH value to 8 to 9 by adding an alkaline substance to the calcium content adjusted solution, and calcium silicate hydrate from the pH adjusted solution.
An apparatus for recovering phosphorus in sludge, comprising a reaction tank for producing a phosphorus compound by using a dephosphorizing material as a main component .