JP2002177966A - Dephosphorizing agent and dephosphorization method as well as dewatering treatment method for sludge - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dephosphorizing agent and dephosphorization method with which dephosphorization treatment of waste water is cost effectively carried out and which contribute to an improvement in dewaterability of sludge as well as a dewatering treatment method for the sludge. SOLUTION: This dephosphorizing agent 10 contains at least hydraulic cement. The dephosphorizing agent 10 is added to the prescribed points in waste water treatment systems S1 and S2 to react the component of the hydraulic cement and the phosphorus in a sludge liquid to form a calcium phosphate salt, by which the phosphorus is removed from the sludge liquid. Sludge dewatering treatment process steps 5a and 5b are provided with a tempering process step of adding a prescribed high-polymer flocculating agent 13 to the separated sludge liquids 9, 15a and 17 obtained by separation of a solid from the sludge liquid subjected to the dephosphorization treatment, by which the moisture content of dewatered cake C is surely lowered.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a technology for dephosphorizing sludge liquid and a technology for dewatering sludge in a wastewater treatment system. More specifically, the present invention relates to a dephosphorization technique in which a hydraulic cement component reacts with phosphorus contained in a sludge liquid, and a sludge dewatering method for improving sludge dewaterability using the phosphorus removal technique.

[0002]

2. Description of the Related Art In recent years, in order to prevent eutrophication of water bodies and the occurrence of blue-green algae and red tide due to eutrophication, there is an increasing demand for removal of phosphorus in wastewater in wastewater treatment technology.

[0003] Phosphorus in wastewater (mainly orthophosphoric acid, P
As a so-called phosphorus removal technique for removing O ₄ -P), a coagulant such as an aluminum salt or an iron salt is added to inflow wastewater or secondary treatment water to remove phosphorus as an insoluble salt by precipitation. And a simultaneous coagulation method in which a coagulant is directly injected into an aeration tank for biological treatment of wastewater to remove phosphorus together with sludge in a final sedimentation basin.

[0004]

However, the conventional coagulation-sedimentation method and simultaneous coagulation method have an economic problem that the cost of the coagulant and the equipment cost increase.

Further, sludge generated from a wastewater treatment system has poor dewatering properties, and has a water content of 80% or more even after dewatering treatment.
Its disposal has been a major technical challenge.

Accordingly, the present invention provides a dephosphorizing agent, a dephosphorizing method, and a sludge dewatering method which can economically perform the dephosphorization treatment of the wastewater and contribute to the improvement of the dewatering property of the sludge. The purpose is to provide.

[0007]

In order to achieve the above object, the present invention employs the following means.

[0008] The present invention finds the reactivity of phosphorus and a component contained in cement which shows curability when kneaded with water, so-called hydraulic cement, and determines the reaction between the two from the inflow of wastewater to the final sludge treatment. To be applied to the phosphorus removal means (phosphorus removal means) for sludge liquid present in the "wastewater treatment system" including all wastewater treatment processes up to and contributing to the improvement of sludge dewatering properties It is an ingenious means.

Specifically, first, in claim 1, a phosphorus removal agent containing at least hydraulic cement is employed as an additive for removing phosphorus contained in sludge liquid in a wastewater treatment system. In Item 2, the phosphorus is removed from the sludge liquid by adding the dephosphorizing agent to the wastewater treatment system and reacting a component derived from hydraulic cement contained in the dephosphorizing agent with phosphorus contained in the sludge liquid. Adopt dephosphorization method.

A hydraulic cement is used as the phosphorus removing agent according to the present invention. This hydraulic cement includes, for example, ordinary Portland cement, early strength Portland cement,
In addition to ultra-high strength Portland cement, moderate heat Portland cement, sulfate resistant Portland cement, plain cement such as hydraulic lime, Roman cement, natural cement, alumina cement, and mixed cement such as lime mixed cement and mixed Portland cement Can be widely adopted.

The above-mentioned hydraulic cement includes calcium silicate (tricalcium silicate, dicalcium silicate), calcium aluminate (tricalcium aluminate), tetracalcium iron aluminate, calcium sulfate, Many calcium salts such as calcium oxide are complexly contained as components.

Therefore, when the dephosphorizing agent according to the present invention is added to the sludge liquid in the wastewater treatment system at a predetermined location, the calcium ion group derived from the hydraulic cement is multi-staged with calcium ions. , Iron ions, aluminum ions, etc. are eluted and react with phosphorus (mainly orthophosphoric acid) in the sludge solution to form calcium phosphate (Ca ₃ (PO ₄ ) ₂ ) and phosphoric acid which are hardly soluble under neutral or basic conditions. Iron (Fe ₂ (P
O ₄ ) ₃ , FePO ₄ ), aluminum phosphate (AlP)
O ₄ ) and the like. Therefore, phosphorus can be efficiently removed from the sludge solution for a long period of time.

In this reaction process, it is conceivable that calcium silicate or the like as a hydraulic cement component serves as a seed crystal and also contributes to a crystallization mechanism in which calcium phosphate precipitates on the surface.

Here, the sludge liquid to be added with the dephosphorizing agent of the present invention or to be used in the dephosphorization method is a liquid containing biological sludge existing in the wastewater treatment system, or sludge before the dewatering treatment.

[0015] Specifically, 1) "pulled-out sludge" liquid (SS (suspended substance) concentration of 1,500 to 4,000 from the aeration tank)
0mg / L) 2) "Excess sludge" liquid (SS concentration 4,000-15,000m) withdrawn from the final sedimentation basin
g / L) 3) "Return sludge" returned to the aeration tank
Liquid, 4) "Concentrated sludge" liquid (SS concentration of about 6,000 to 30,000 mg / L) extracted from the sludge concentration step,
5) Dewatered desorbed liquid obtained in the sludge dewatering step (SS concentration of about 100 to 200 mg / L), 6) Desorbed liquid from anaerobic digestion tank when anaerobic digestion treatment is adopted (supernatant), 7) Anaerobic digestion Includes all sludge liquids treated in the tank, at least phosphoric acid (mainly orthophosphoric acid) and SS
Sludge liquid containing biological sludge having a concentration of 50 mg / L or more can be treated. After the addition of the dephosphorizing agent according to the present invention, it is necessary to increase the degree of contact between the dephosphorizing agent and the sludge liquid by means of appropriate stirring or the like in the vicinity of the addition point.

According to a third aspect of the present invention, the sludge liquid dephosphorized by the dephosphorization method according to the present invention is obtained by solid-liquid separation by means such as sedimentation, centrifugation, and membrane separation. A sludge dewatering method devised so as to include at least a tempering step of adding a predetermined polymer flocculant to the separated sludge liquid to promote separation of water is adopted.

The sludge liquid separated from the sludge liquid that has been subjected to the dephosphorization treatment before the final sludge treatment step has already been increased in cohesiveness by the action of the hydraulic cement component in the phosphorus removal treatment step. Add a polymer flocculant there,
The dewatering property of the sludge is greatly improved by promoting the separation of water and conditioning the sludge.

This is because the dephosphorizing agent or method according to the present invention is not only effective as a phosphorus removing means, but also functions effectively as a pretreatment step (coagulation promoting step) of sludge dewatering treatment. Means

Therefore, according to the third aspect of the present invention,
The technical problem of generation of hardly dewaterable sludge in the biological treatment system for wastewater described above can be solved.

The polymer flocculant that can be used in the present invention includes an anionic polymer flocculant, a cationic polymer flocculant and an amphoteric polymer flocculant. Is preferred.

[0021] As described above, the present invention improves the dephosphorization treatment technology of the wastewater treatment system and prevents eutrophication of the water area, and also improves the dewatering property of the sludge generated from the wastewater treatment system to perform sludge treatment. It has the technical significance of facilitating.

[0022]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS First, a preferred embodiment of the present invention will be described with reference to FIGS.
Figure 1 is a diagram showing in simplified general activated sludge wastewater treatment system S ₁ configuration using as purification treatment technologies of the organic waste water.

_First , the overall configuration of the wastewater treatment system S1 utilizing the activated sludge method will be briefly described with reference to FIG. 1. The wastewater D rich in organic components discharged from a sewage treatment plant, a food factory, a livestock barn, etc. Is first stored in the sedimentation tank 1 after dust and the like are removed by a screen device (not shown).

Then, in the aeration tank 2 provided with a stirring device and an aeration device 6 (not shown),
Air (air) sent from the aeration device 6 is brought into contact with the activated sludge introduced into the wastewater D to decompose the organic matter in the wastewater D, reduce the BOD, and solidify the sludge and treated water in the final sedimentation basin 3. Separation is performed, and the treated water T overflowing from above the final sedimentation basin 3 is discharged out of the system.
And returning the sludge liquid 7 precipitated to the aeration tank 2 via a pipe.

The excess sludge liquid 8 withdrawn from the final sedimentation basin 3 is settled and concentrated (or centrifuged by a centrifuge) in a sludge thickening tank (thickener) 8. The separated water (supernatant water) 11 is returned to the aeration tank 2, and the separated sludge liquid 9 settled and concentrated at the bottom of the tank is subjected to vacuum dehydration, centrifugal dehydration, pressure dehydration,
The sludge is dewatered by being transferred to a sludge dewatering apparatus 5a using a roll dehydrator (such as a belt press).

The dewatering / desorbing liquid 12 separated and generated in the sludge dewatering treatment apparatus 5a is returned to the aeration tank 2, and one dewatering cake (dewatered sludge) C is generally dried or incinerated.
It is dried and reused as fertilizer and soil conditioner.

Here, the waste water D flowing into the waste water treatment system S ₁
Medium is, if a P / BOD> 0.01, is subjected to some sort of dephosphorization treatment at a predetermined position of the waste water treatment system S _1, it is necessary to reduce the phosphorus concentration in treated water T occurs.

Therefore, first, the dephosphorizing agent 10 according to the present invention is used.
Generates a hardly soluble calcium salt by the reaction between the hydraulic cement component and phosphorus, and removes phosphorus from the wastewater D. At the same time, the present dephosphorizing agent 10 promotes the aggregation of sludge by the hydraulic cement, and also contributes to improving the dewatering property of the sludge.

The dephosphorizing agent 10 is an additive containing at least a hydraulic cement component such as ordinary Portland cement, and may be composed of only the hydraulic cement component or various additives (eg, a flocculant). May be used in combination. For example, inorganic flocculants such as iron salts and aluminum salts,
Salts such as Ca, Al, Si, and Fe may be used in combination. By using the phosphorus removing agent 10 and an inorganic flocculant in combination, the compressive strength of the precipitate can be further increased, which also contributes to the improvement of the dewatering property of the final sludge.

The amount of the hydraulic cement to be added is preferably at least 1 times, preferably 2 to 20 times, as dry weight of the cement in terms of molar ratio with respect to phosphorus in the treated water. If less than one time,
The degree of contact between the cement component and phosphorus is so small that an effective dephosphorizing action is not exhibited. If it exceeds 20 times, the microbial activity in the sludge may be adversely affected.

Further, the pH of the treated water should just satisfy the alkaline condition of 7 or more, and preferably pH 7 to 9. Therefore, it is not necessary to adjust the pH to a strong alkaline condition of 10 or more, so that handling is easy.

The preferred place for adding the dephosphorizing agent 10 in the wastewater treatment system S ₁ is to add it to the aeration tank 2 (arrow 1 in FIG. 1).
0a), addition to the transfer pipe from the aeration tank 2 to the final sedimentation basin 3 (see arrow 10b in the figure), addition to the final sedimentation basin 3 (see arrow 10c in the figure), excess sludge liquid (sludge concentration tank 4). )
(See arrow 10d in the figure), addition to the returned sludge liquid 7 (see the arrow 10e in the figure), addition to the desorbed liquid 12 from the sludge dewatering apparatus 5a (see the arrow 10f in the figure), and the like. .

In order to ensure that the dephosphorizing agent 10 contributes not only to the dephosphorization function but also to the improvement of the dewatering property of sludge, it is necessary to consider the reaction time between phosphorus and the cement component at least in the final precipitation. Excess sludge liquid 8 drawn from pond 3 etc.
It is desirable to add it before.

Subsequently, when the concentration of organic matter, BOD, SS, etc. in the wastewater D is high, a so-called “anaerobic digestion treatment” in which the organic matter is decomposed by the anaerobic bacteria group may be employed. It is practical for treating organic matter such as raw sludge and excess sludge liquid 8 for activated sludge treatment. FIG. 2 is a diagram schematically illustrating the configuration of the anaerobic digestion process.

[0035] Also in this waste water treatment system (anaerobic digestion treatment system) in S _2, it is possible to use a dephosphorization agent 10 according to the present invention.

Specifically, addition to the anaerobic digestion tank 14, addition to a transfer pipe for directly transferring the sludge liquid 15a drawn from the anaerobic digestion tank 14 to the sludge dewatering apparatus 5 (see arrow 10h in FIG. 2), Sludge liquid extracted from anaerobic digestion layer 1
5b is added to the sludge thickening tank 4b (arrow 1 in the figure).
0i), and addition to the sludge liquid 16 returned from the sludge concentration tank 4b or the wastewater sludge liquid 17 (see arrows 10j and 10k in the figure).

Next, the dephosphorizing agent 10 according to the present invention is added, dephosphorized and concentrated, and the separated sludge liquids 9, 15 transferred to the sludge dewatering devices 5a, 5b.
1 and 17, a polymer flocculant 13 is further added (arrow 13a in FIG. 1 and arrow 13 in FIG. 2).
b, 13c), it has been found that sludge can be subjected to so-called "conditioning" to improve the dewatering property of the sludge.

This is because the dephosphorizing agent 10 and the polymer flocculant 13
The dewatered cake C dehydrated through such a sludge refining treatment has a low water content and is easy to dispose.

[0039]

EXAMPLES The present inventors conducted the following experiments. <Example> First, in this example, the phosphorus concentration was 15 mg /
L excess sewage sludge (SS concentration is 12,000mg /
L) 270m of "ordinary Portland cement"
g / L (18 times by mole relative to phosphorus) was added.

After the precipitation concentration (gravity concentration),
The cationic polymer (Crifix CP604, manufactured by Kurita Kogyo Co., Ltd.) was added in an amount of 0.1 to the total solid weight (dry weight).
5% was added and dewatered by a belt press dehydrator.

As a result, the SS concentration of the concentrated sludge subjected to sedimentation concentration (gravity concentration) was 27,000 mg / L, the phosphorus concentration of the concentrated separated liquid was 1.2 mg / L, and the phosphorus concentration of the desorbed liquid by the dehydration treatment was 0.8mg / L, water content of dehydrated cake is 7
3%.

<Comparative Example> A comparative experiment was performed under the same conditions as in the above example, except that cement was not added before the precipitation concentration (gravity concentration).

As a result, the SS concentration of the concentrated sludge subjected to sedimentation concentration (gravity concentration) was 25,000 mg / L, the phosphorus concentration of the concentrated separated liquid was 14.5 mg / L, and the phosphorus concentration of the desorbed liquid by the dehydration treatment was 15 mg / L, water content of dehydrated cake is 8
2%. Table 1 summarizes the data of the above Examples and Comparative Examples.

[0044]

[Table 1]

As is clear from Table 1 above, by employing the dephosphorizing agent 10 according to the present invention, the phosphorus concentration can be greatly reduced and the synergistic effect with the polymer coagulant 13 is obtained. It was proved that the sludge dewaterability was improved.

[0046]

The main effects achieved by the present invention are as follows.

(1) The dephosphorizing agent according to the present invention containing a hydraulic cement containing a calcium salt such as calcium silicate or calcium aluminate and the method for dephosphorizing using the dephosphorizing agent can be used for drainage even under weak alkaline conditions. Since it reacts efficiently with phosphorus in the treatment system to form a calcium phosphate salt, phosphorus can be reliably removed from the sludge solution.

(2) The dephosphorizing agent according to the present invention can handle the pH of the treated water under neutral to weakly alkaline conditions.
Easy to handle.

(3) According to the dephosphorizing agent of the present invention and the dephosphorizing method using the dephosphorizing agent, the effect of increasing the cohesiveness of sludge is effectively exhibited. For this reason, sludge with improved dewaterability (easily dewatered) can be supplied to the subsequent sludge dewatering treatment step, so that the water content of the dewatered cake can be reliably reduced.

[Brief description of the drawings]

FIG. 1 is a simplified view of a configuration of a wastewater treatment system using a general activated sludge method as a purification treatment technology for organic wastewater, showing a place where a dephosphorizing agent according to the present invention is added.

FIG. 2 is a diagram schematically showing the configuration of an anaerobic digestion treatment step, in which an addition place of a dephosphorizing agent according to the present invention is shown.

[Explanation of symbols]

9,15a, 17 separated sludge liquid 10 (10a-10j) dephosphorization agent 13 (13 a to 13 c) polymer coagulant S _1, S ₂ waste water treatment system

Continued on front page F term (reference) 4D028 AA08 AC03 AC09 BD11 4D038 AA08 AB45 BB18 BB19 4D059 AA03 AA19 BE08 BE15 BE31 BE38 BE49 BE56 BF14 BK30 CA28 CC01 CC10 DA66

Claims (3)

[Claims] 1. An additive for removing phosphorus contained in a sludge liquid in a wastewater treatment system, which comprises at least a hydraulic cement component. 2. The phosphorus removal agent according to claim 1 is added to a wastewater treatment system, and the hydraulic cement component contained in the phosphorus removal agent reacts with phosphorus contained in the sludge solution, whereby phosphorus is removed from the sludge solution. A dephosphorization method, comprising removing phosphorus. 3. A polymer coagulant is added to a liquid containing a separated sludge obtained by solid-liquid separation of a sludge liquid dephosphorized by the method for dephosphorization according to claim 2. A sludge dewatering method comprising at least a tempering step for promoting separation.