JPH1133561A - Flocculation and sedimentation treatment equipment - Google Patents

Abstract

PROBLEM TO BE SOLVED: To efficiently decompose and remove a TOC component, iron, manganese or the like in return sludge by providing the way of a sludge return system with a sludge crushing means, a means adding an oxidizing agent to chemically oxidize return sludge to modify the same and an acid adding means ionizing flocs of an inorg. metal flocculant. SOLUTION: Sludge of a flocculation sedimentation tank 3 in purified water making equipment is conc. in a flocculated sludge concn. tank 5 and a part of conc. and flocculated sludge is sent to an aeration tank 8. Next, the sludge subjected to aeration treatment in the aeration tank 8 is aerated by ozone supplied to an ozone reaction tank 102 from an ozone generator 103. Return sludge is crushed and dispersed by the ultrasonic crusher attached to the ozone reaction tank 102 and oxidation is perfectly performed by aerated ozone to oxidize and decompose TOC or the like in flocculated sludge. An acid is added to the sludge aerated by ozone from an acid storage tank 12 on the way through a sludge return pipe 19 and the inorg. metal flocculant in sludge is ionized by a stirring device 13 to be returned to a stirring tank 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to a process for coagulating and sedimenting raw water to produce purified water such as tap water and industrial water and industrial water. The present invention relates to a coagulation / sedimentation treatment facility used for reducing sludge and modifying the generated sludge properties.

[0002]

2. Description of the Related Art As a method for producing purified water by treating raw water, an aluminum-based flocculant is added, the raw water and the flocculant are stirred and mixed by a stirrer, and collected by a floc that generates a turbid component. There is a coagulation-sedimentation method in which the solution is introduced into a sedimentation facility for solid-liquid separation, and the supernatant water is treated and purified. The solid that has been separated into solid and liquid at that time is settled and then withdrawn from a sedimentation facility, concentrated, dehydrated by mechanical or natural drying, and disposed of or reused. However, this method is known to have a problem that although the processing operation is simple, a large amount of coagulant is used.

[0003] In order to reduce the amount of coagulant used in the above method, the separated and recovered sludge is adjusted to about pH 2, aluminum hydroxide (Al (OH) ₃ ) contained therein is dissolved, and aluminum is removed from the supernatant. A method of collecting ionic Al ³⁺ and reusing it as a flocculant has also been proposed. This is generally called a regeneration band method, and has an excellent advantage that the operation cost of the equipment is reduced because the amount of the coagulant used is reduced by recycling.

[0004] However, in this regeneration band system, although the amount of aluminum-based flocculant can be reduced because aluminum in sludge can be used effectively, acidic sludge after aluminum recovery is dehydrated by adding slaked lime or the like. The disadvantage is that the amount of sludge must be increased. In addition, a sedimentation tank for separating the supernatant liquid containing aluminum from the sludge is required, and the high-concentration sludge collected at the bottom of the sedimentation tank must be cleaned once or twice a year. There is also.

[0005] To overcome these drawbacks of the regenerative band system, the Applicant has proposed that instead of returning only the reactivated aluminum ions to the stirring system for coagulating the suspended matter,
A method in which a part of the sludge collected by settling is returned, and an acid is added during the return of the sludge to ionize aluminum hydroxide contained therein (Japanese Patent Laid-Open No. 2-157005).
Oxidizing means (air aeration) for maintaining the returned sludge in an optimal environment of the aerobic microorganisms contained therein for a predetermined time in the middle of the sludge return system as an improved method of this method; An acid addition means for ionizing Al (OH) 3 contained therein is provided in this order to prevent generation of offensive odor of returned sludge and coagulation / sedimentation treatment equipment (JP-A-7-328327).
No.).

[0006]

However, TOC (Total Organic C) taken into sludge is not suitable.
Since the arbon component cannot be decomposed and removed by air aeration, the TOC removal efficiency is poor in the conventional method. Further, when pathogenic microorganisms such as Cryptosporidium are mixed into river water as raw water, most of the mixed water is concentrated into flocculated sludge by the flocculation and sedimentation treatment. Most pathogenic microorganisms are inactivated by ozone, but ozone is ineffective against pathogenic microorganisms trapped in sludge and may not be completely inactivated. There is.

The problem to be solved by the present invention is the TOC
An object of the present invention is to provide a coagulation-sedimentation treatment facility which is excellent in removal efficiency and capable of killing and removing pathogenic microorganisms even when raw water is contaminated with pathogenic microorganisms such as cryptosporidium.

[0008]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that the above problems can be solved by crushing the returned sludge and reforming the sludge, and have completed the present invention. Reached.

That is, the present invention provides a stirring system for aggregating suspended substances in raw water by adding an inorganic metal flocculant, and a flocculating suspended substance to be coagulated and precipitated to be separated from treated water. In a coagulated sedimentation treatment system having a sludge separation treatment system for collecting and recovering the settled sludge and a sludge return system for returning at least a part of the collected sludge to the stirring system. Sludge crushing means for crushing the sludge, and means for adding an oxidizing agent to the returned sludge and chemically oxidizing the returned sludge to improve the returned sludge, and further comprising a floc of inorganic metal coagulant contained in the returned sludge And an acid addition means for ionizing the compound.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The inorganic metal coagulant used in the coagulation / sedimentation treatment equipment of the present invention according to claims 1 to 5 is not particularly limited as long as the coagulated floc is ionized by an acid. Examples thereof include aluminum-based coagulants such as aluminum sulfate and polyaluminum chloride (PAC), and iron-based coagulants such as ferric sulfate, ferric chloride and polyiron sulfate.

In the coagulation and sedimentation treatment apparatus according to the first aspect, the sludge is crushed and dispersed by the sludge crushing means, so that the TOC component taken in the coagulated sludge is released into the medium. Is efficiently oxidized and can be removed. When the raw water is contaminated by pathogenic microorganisms, the pathogenic microorganisms are incorporated into the aggregated sludge, but the aggregated sludge is crushed and dispersed by the sludge crushing means. , Can inactivate pathogenic microorganisms.

The sludge crushing means is not particularly limited as long as it can crush and disperse the aggregated sludge, and examples thereof include an ultrasonic crusher and a high-speed mixer.

The sludge crushing by the sludge crushing means may be performed continuously or intermittently. Further, sludge crushing may be performed separately from the oxidation treatment, but it is more efficient to perform the sludge crushing simultaneously with the oxidation treatment. When the sludge crushing is performed separately from the oxidation treatment, the sludge crushing may be performed before the oxidation treatment.

Further, by subjecting the returned sludge to crushing for a predetermined time by a sludge crushing means such as an ultrasonic crusher, components such as iron and manganese are released to the solution side together with the TOC component. Since all of these components consume the oxidizing agent, the returned sludge after the crushing treatment is centrifugally concentrated, and if the supernatant water is separately treated, the returned sludge is concentrated and reduced in volume, so that the sludge reforming process is Equipment can be reduced,
The use amount of the oxidizing agent can be reduced. Furthermore, the biological treatment of the supernatant water after centrifugal concentration can remove most of iron and some manganese and TOC components. In order to remove TOC and manganese in the supernatant water more efficiently, the TOC component may be modified to a biodegradable material with an oxidizing agent or the like, and then subjected to biological treatment. In that case, to save the oxidizer, before adding the oxidizer,
The supernatant may be aerated with air, exhausted ozone gas or the like to oxidize the iron component in advance. When the sludge is concentrated by the centrifugal concentrator, the TS (Tot) of the concentrated sludge is used due to the operability of the sludge.
al Solid) concentration is preferably 1 to 5%.

According to a third aspect of the present invention, the returned sludge is aerated with an oxygen-containing gas for a predetermined time to oxidize iron in the returned sludge,
Further, the present invention is characterized in that sludge is prevented from becoming anaerobic to generate an odor, and manganese which cannot be completely oxidized by aeration with an oxygen-containing gas is chemically oxidized by adding an oxidizing agent. Thereby, the addition of the oxidizing agent can be reduced as compared with the case where both iron and manganese are oxidized only by the oxidizing agent.

The reason for adding activated carbon in the invention according to claim 4 is that, for example, when ozone is used as an oxidizing agent, it is usually difficult to remove TOC with ozone alone. The oxidation is performed, and the remaining TOC is removed with powdered activated carbon. Further, when activated carbon is added after treatment with ozone and hydrogen peroxide, TOC can be more efficiently removed. The amount of activated carbon added is 1L of sludge.
50 to 2000 mg, preferably 200 to 100
What is necessary is just to select suitably in the range of 0 mg.

The activated carbon may be added at the same time as the acid is added to the sludge and the acid is added to the reaction tank for dissolving the floc of the inorganic metal coagulant in the sludge, or the activated carbon is added after the acid is added to the sludge. It is preferred to add.

The reason is that by adding an acid to the sludge to adjust the acidity, the TOC component is eluted from the solid matter in the sludge, the TOC concentration of the sludge increases, and the adsorption efficiency of activated carbon to organic matter generally increases. This is because the acid side is higher than the neutral side.

In the first to sixth aspects of the present invention, the stirring system for coagulating the suspended matter in the raw water refers to a reaction for binding the suspended substance in the raw water to fine particles by adding a coagulant. (Coagulation reaction), and is generally provided as a tank with a stirrer (stirring tank) for adding a flocculant to raw water introduced into an open-type tank and mixing rapidly. In some cases, a stirring tank of a type that is stirred by a relatively strong water flow is also used. Chlorine may be added to the raw water in the stirring tank (and / or the coagulating sedimentation tank described below) as in the conventional method.

The sludge separation treatment system, which is provided at the next stage of the stirring system and grows coagulated suspended matter as flocculated floc and separates and recovers sludge precipitated from treated water, is, for example, a moderately slow sludge. While stirring, it can be provided as a coagulation sedimentation tank consisting of a region in which the coagulated suspended matter is grown as coagulated flocs, and a region in which the grown flocs are separated from treated water by settling to solid-liquid separation. The method is not limited, and any known method may be used. In addition, a coagulation settling tank in which the above-described stirring system and sludge separation treatment system are integrally formed may be used. Further, it is preferable to provide a thickening means such as a thickener (sedimentation type thickening tank) for adjusting the concentration of the extracted sludge to a concentration suitable for returning to the raw water side, at the next stage of the sludge pulling system of the coagulating sedimentation tank.

A sludge return system for returning the collected sludge to the agitation system is provided as a path for continuously or intermittently returning sludge from the coagulation settling tank, the thickening tank, etc., and is provided with a pump for returning sludge. Is done. The return is usually a part of the sludge collected in the coagulating sedimentation tank, the thickening tank, etc., but it can be all if necessary. Returning sludge,
It may be returned to the above-described stirring system tank, or may be returned to the path for introducing raw water into the stirring tank, and is not particularly limited.

The method of aerating the returned sludge with oxygen-containing gas for a predetermined time is not particularly limited. For example, the returned sludge is introduced into an aeration tank, and the amount of air (1 atm) per hour is generally equal to the amount of sludge. By performing the same amount of aeration for about 0.5 to 24 hours, iron in the sludge is oxidized, and the sludge further becomes aerobic, thereby preventing odor generation due to the returned sludge becoming anaerobic. be able to. When the main purpose is to oxidize iron or remove odor, depending on the amount of aeration, aeration for 1 hour to 12 hours is usually sufficient. The oxidizing agent added after the returned sludge is aerated with an oxygen-containing gas for a predetermined time includes ozone, hydrogen peroxide, sodium hypochlorite, liquefied chlorine, chlorine dioxide, and the like. Ozone or a combination of ozone and hydrogen peroxide is preferred from the viewpoint that chlorine-resistant pathogens can be killed and removed.

When ozone is used as the oxidizing agent, it is preferable to supply ozone by aeration.

Ozone as an oxidizing agent is also preferable in that it can kill chlorine-resistant pathogens such as Cryptosporidium. The inactivation (death) rate of Cryptosporidium by ozone is 99% under the conditions of c × t = 10 mg · min / L (c: dissolved ozone concentration (mg / L), t: reaction time (min)). is there.

Therefore, when treating with ozone, c
× t value is 15 mg · min / L or more, preferably 20 to
Cryptosporidium can be almost completely killed by performing the ozone treatment under the condition of 60 mg · min / L.

On the other hand, the sludge contains TOC adsorbed on the flocculant.
(Total Organic Carbon) component is contained at about several tens mg / L. Since this TOC component becomes trihalomethane by chlorination, it is preferable to remove as much as possible from sludge. The TOC component in sludge can hardly be reduced by ozone alone, but can be significantly reduced by using ozone and hydrogen peroxide together. Therefore, by the treatment with ozone and hydrogen peroxide, not only the oxidation of manganese in the sludge but also the TOC component can be removed, and thus the manganese in the coagulated sedimentation-treated water and the TOC component which is a source of trihalomethane can be reduced.

In the case where ozone and hydrogen peroxide are used in combination, the sterilizing power is weaker when ozone and hydrogen peroxide are used at the same time than when ozone is used alone. To oxidize manganese in the sludge and kill chlorine-resistant pathogens, then add hydrogen peroxide to the sludge after ozone treatment, and then blow ozone again to decompose the TOC. . Therefore, when both ozone and hydrogen peroxide are used, two ozone treatment tanks, a first-stage ozone treatment tank and a second-stage ozone treatment tank after adding hydrogen peroxide, are required.

After the returned sludge is chemically treated with an oxidizing agent,
In order to recover and reuse the inorganic metal coagulant, an acid addition means for ionizing floc is provided. As the acid addition means, a mineral acid such as sulfuric acid or hydrochloric acid, preferably sulfuric acid is added, and the returned sludge is pH 4 or less. The pH is preferably adjusted to about 2 to 3. Specifically, there are various methods such as a method of adding acid to a storage tank having a stirrer, a method of injecting acid into a sludge return path and stirring in the path, and a method of injecting acid into a sludge return path and stirring with a stirrer. Can be adopted. It is also preferable to provide a pH meter or the like in the acid addition means to control the addition amount. The floc of the inorganic metal coagulant can be ionized by the acid addition means, and the ionized inorganic metal coagulant is returned to the coagulation step, so that the amount of the inorganic metal coagulant used in the coagulation step can be reduced. it can.

[0029]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a water purification plant will be further described below with reference to the drawings.

Example 1 In FIG. 1, reference numeral 2 denotes a flocculant mixing and stirring tank, which is provided with a rotary blade type stirring device. In the stirring tank 2, the raw water introduced from the raw water introduction pipe 1 and the inorganic metal coagulant injected by the coagulant injection device 15 such as a pump from the coagulant storage tank 16 are stirred and mixed, and contained in the raw water. The coagulation reaction of the suspended material is carried out.

A flocculating sedimentation tank 3 is disposed downstream of the flocculating agent mixing and stirring tank 2. The flocculated suspended fine particles are flocculated by moderate slow stirring and further grown. Then, the sludge is settled at the bottom of the tank 3 by sedimentation and separation, while the treated water 18 flows out to an unillustrated downstream water purification treatment system via an unillustrated overflow channel.

The sludge collected at the bottom of the coagulating sedimentation tank 3 is
The coagulated sludge is drawn into the coagulated sludge thickening tank 5 by the coagulated sludge withdrawal pipe 4 and concentrated in the thickening tank 5 to a concentration suitable for returning to the raw water side as returned sludge (for example, about 2 to 10 times). From the bottom of the thickening tank 5, a concentrated thickened sludge transfer pump 7 is passed through a first thickened concentrated sludge drawing pipe 61.
1 is provided such that the sludge is appropriately and intermittently sent to a concentrated coagulation sludge treatment device 17 such as a dehydration device, and excess sludge can be dewatered and disposed of. Further, another second concentrated coagulated sludge withdrawal pipe 62 is connected to the bottom of the concentrating tank 5, through which a part of the sludge is sent to the aeration tank 8 by the condensed coagulated sludge transfer pump 72. Have been.

The aeration tank 8 of the present embodiment is an open horizontal flow tank, and is used until the sludge introduced through the second concentrated coagulated sludge withdrawing pipe 62 is sent out by the first-stage first sludge feed pump 101. In the above, the air blown by the blower 9 from the air diffuser 91 at the bottom of the tank is aerated,
It is provided to be held in this aeration tank for a period of time. The aeration tank 8 may be omitted. The degree of aeration can be controlled by time as described above. However, as an industrial-scale device, the oxidation-reduction potential of sludge is monitored at the outlet of the aeration tank, and aeration control or sludge flow control of the aeration tank 8 is performed. It is also preferable to provide feedback so that reliable oxidation control is performed. By this aeration treatment, iron and odor-causing substances contained in the sludge are mainly oxidized.

The sludge that has been subjected to the predetermined aeration treatment in the aeration tank 8 is subjected to the first sludge pump 101 for sludge feeding.
The ozone is introduced into the hermetically sealed ozone reaction tank 102 and aerated by ozone supplied by the ozone generator 103.
The ozone after the treatment is discharged through the exhaust gas discharge pipe 104. Although not shown, the discharged waste ozone is subjected to an exhaust gas treatment and discharged outside the system. The exhausted ozone gas can be introduced into the aeration tank 8 and used as oxygen-containing gas for sludge aeration.

An ultrasonic crusher 106 is attached to the ozone reaction tank 102 as sludge crushing means. The returned sludge is crushed and dispersed by the ultrasonic waves generated by the ultrasonic crusher, and is oxidized by the aerated ozone. Done more completely. Therefore, pathogenic microorganisms, TOC, and the like, which are taken into the coagulated sludge, are more completely oxidatively decomposed.

The sludge aerated with ozone is supplied to the intermediate tank 1
05 and temporarily stored therein, the acid from the acid storage tank 12 is added on the way through the sludge return pipe 19 by the second sludge pump 10, and then introduced into the stirring device 13, where the inorganic metal contained in the sludge is added. After the flocculant is ionized, it is returned to the stirring tank 2. Reference numeral 11 denotes an acid injection pump for injecting the acid in the acid storage tank 12 into the sludge return pipe 19. 14 is the pH of the sludge at the outlet from the stirring device 13
Is used to control the amount of acid added to, for example, maintain the pH of the outlet sludge at 3 or less by feeding back the measurement information to the acid injection pump 11.

According to the coagulating sedimentation treatment equipment of the present embodiment 1 constructed as described above, in the middle of the returned sludge system, the aggregated returned sludge is crushed and dispersed by an ultrasonic crusher, and is returned to an oxidizing agent such as ozone. Since chemical oxidation treatment is performed, and then acid addition for reusing the flocculant is performed, TOC components and pathogenic microorganisms incorporated in the flocculated sludge can be efficiently oxidatively decomposed, and less. The oxidation treatment can be more completely performed with the oxidizing agent.

The suspended solids contained in the sludge returned to the stirring tank function as a coagulation aid by being added back to the raw water, and when the raw water has a low turbidity, a conventional coagulant is added. This improves the difficulty of controlling the amount of sludge and also contributes to the growth of high-density flocculent flocs, thereby providing the advantage of improving the separation of sludge.

Further, effects such as a reduction in the amount of coagulant used, a reduction in the total amount of waste sludge generated, a reduction in operation costs, and the like can be obtained without complicating the operation and introducing new adverse effects.

Test Example 1 One liter (raw sludge) of a water purification plant having a TS concentration of 0.7% was irradiated with ultrasonic waves of 20 kHz for 5 minutes to perform a crushing treatment of the sludge. After the crushing treatment, the sludge is filtered, and the TOC in the filtrate,
Table 1 shows the concentrations of iron and manganese. For comparison, one liter of raw sludge was aerated with 2 L / L / min air for 10 minutes and then filtered to measure the filtrate, and the filtrate was measured after simply filtering the raw sludge without any treatment. Are also shown in Table 1.

[0041]

[Table 1]

As can be seen from Table 1, the amount of TO in the filtrate is higher than that in the case where the raw sludge is directly filtered by ultrasonication.
C concentration increased. This is because the TOC component taken into the sludge began to dissolve into the solution from the sludge crushed by the ultrasonic treatment. In the air aeration process,
The concentration of the TOC component in the filtrate is hardly changed as compared with that of the raw sludge, because the TOC component is hardly decomposed by such a short-time air aeration treatment. On the other hand, the iron component in the filtrate after the air aeration was almost eliminated, because divalent iron was reduced to trivalent iron by oxygen in the air. In addition, manganese slightly increased after the ultrasonic treatment, because divalent manganese incorporated in the condensed sludge began to melt into the solution side by the sludge crushing by the ultrasonic treatment.

Test Example 2 Cryptosporidium oocysts were added to the sludge of the water purification plant with a TS concentration of 0.7% used in Test Example 1 at a rate of 100 / ml (as the number of fluorescent emission detectors), and crushed and dispersed by ultrasonic waves. The effect and the inactive effect by ozone were confirmed.
Table 2 shows the test results. The ultrasonic treatment is 20k
The ultrasonic treatment was performed by irradiating an ultrasonic wave of Hz for 5 minutes, and the ozone treatment was performed under the condition of a ct value of 30 mg · min / L.

The number of fluorescent light-emitting specimens is the number of all specimens including living specimens and dead specimens.

[0045]

[Table 2]

As can be seen from the results of the number of fluorescent light-emitting specimens in Table 2, when the raw sludge to which oocysts had been added was measured as it was, only about half of the added oocysts were detected, whereas the ultrasonic sonication was not performed. The detection rate of oocysts increased by the sludge crushing treatment, and almost all of the added oocysts were detected. This is because the oocysts taken in the sludge were dispersed in the solution because the sludge was crushed and dispersed. In addition, since the number of living specimens by the DAPI-PI test method (staining method) was not detected by the sludge crushing treatment and the ozone treatment by the ultrasonic wave, the ozone treatment was carried out while the sludge was crushed by the ultrasonic wave. It can be seen that oocysts of Ptosporidium can be almost inactivated.

[0047]

According to the coagulation / sedimentation treatment equipment of the present invention, the TOC component, iron, manganese, etc. in the returned sludge can be efficiently decomposed and removed, and the amount of the oxidizing agent used can be reduced and the size of the oxidation tank can be reduced. it can.

Further, even if the raw water is contaminated with a pathogenic microorganism such as Cryptosporidium, the pathogenic microorganism can be efficiently killed and removed.

[Brief description of the drawings]

FIG. 1 is a diagram illustrating an example of a schematic configuration of a coagulation / sedimentation treatment facility according to a first embodiment of the present invention, which is shown in a flowchart.

[Description of Signs] 1 Raw water introduction pipe 2 Coagulant mixing and stirring tank 3 Coagulation sedimentation tank 4 Coagulation sludge extraction pipe 5 Coagulation sludge concentration tank 61, 62 Concentration coagulation sludge extraction pipe 71, 72 Concentration coagulation sludge transfer pump 8 Aeration tank 9 Blower Reference Signs List 10 Sludge transfer pump 11 Acid injection pump 12 Acid storage tank 13 Stirrer 14 pH meter 15 Coagulant injection device 16 Coagulant storage tank 17 Coagulation sludge treatment device 18 Treated water 19 Sludge return pipe 101 First sludge conveyance pump 102 Ozone reaction Tank 103 Ozone generator 104 Exhaust gas discharge pipe 105 Intermediate tank 106 Ultrasonic crusher

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C02F 1/78 C02F 1/78 11/06 ZAB 11/06 ZABA 11/12 11/12 Z

Claims (6)

[Claims] 1. A stirring system for coagulating a suspended substance in raw water by adding an inorganic metal coagulant, and a coagulated and precipitated substance to be coagulated and precipitated to be separated from treated water. In the coagulated sedimentation treatment facility having a sludge separation treatment system for collecting the settled sludge and a sludge return system for returning at least a part of the collected sludge to the stirring system, the returned sludge is crushed in the middle of the sludge return system. A sludge crushing means, and a means for adding an oxidizing agent to the returned sludge and chemically oxidizing the returned sludge to reform the returned sludge; and an acid for ionizing flocs of the inorganic metal coagulant contained in the returned sludge. Coagulation / sedimentation treatment equipment characterized by comprising an adding means. 2. The coagulation / sedimentation treatment equipment according to claim 1, wherein the sludge crushing means is an ultrasonic crusher. 3. A method of adding an oxidizing agent to the returned sludge to chemically oxidize the returned sludge and providing a means for aerating the returned sludge with an oxygen-containing gas for a predetermined time upstream of the means for reforming the returned sludge. The coagulation / sedimentation treatment equipment according to claim 1 or 2, wherein 4. A means for adding an oxidizing agent to the returned sludge and chemically oxidizing the returned sludge, and a means for adding activated carbon to the returned sludge is provided downstream of the means for reforming the returned sludge. The coagulation sedimentation treatment equipment according to any one of claims 1 to 3. 5. The method according to claim 1, wherein the oxidizing agent is ozone or ozone and hydrogen peroxide.
The coagulation sedimentation treatment equipment according to any one of the above. 6. The coagulation-sedimentation treatment equipment according to claim 1, wherein the inorganic metal coagulant is an aluminum-based coagulant.