JP4428696B2 - Excess sludge treatment method - Google Patents

Description

  The present invention relates to a method for dewatering excess sludge generated from an activated sludge treatment process. In particular, the present invention is suitable for dewatering excess sludge generated by the oxidation ditch method having low dewaterability.

  In general, surplus sludge generated from activated sludge treatment steps such as wastewater treatment, sewage treatment, sewage treatment, and the like is concentrated in some cases, then aggregated by addition of a polymer flocculant, and dehydrated by mechanical dehydration treatment. In recent years, surplus sludge generated from the activated sludge treatment process due to changes in the quality of sewage such as factory effluent and domestic effluent due to diversification of production items at various manufacturing factories and lifestyles of residents Is difficult to agglomerate, and the water content of the sludge after dehydration is difficult to decrease.

  In particular, the excess sludge generated when the oxidation ditch treatment method is used for sewage treatment is very poor in dehydration compared to mixed raw sludge, standard activated sludge, digested sludge, and the like. This is because the oxidation ditch treatment method is a treatment method in which mechanical agitation and aeration are performed simultaneously, and the aeration time is prolonged compared to other treatment methods. This is considered to be because the fiber content in the sludge that becomes the core of aggregation is decomposed and consumed.

  Until now, in the treatment process of organic wastewater, attempts have been made to improve the dewatering efficiency of surplus sludge by mixing the initial sludge of the organic wastewater settled in the first sedimentation basin with the surplus sludge. Since it contains a lot of readily decomposable organic matter, the method of mixing the whole amount with excess sludge and dehydrating was not very effective.

  On the other hand, in the water purification process, advanced treatment is performed in which activated carbon is used to decompose and remove residual substances such as trihalomethane and humic substances from raw water. The concentration of substances to be removed in raw water subjected to advanced treatment is very low, 1 mg / l or less. However, the used activated carbon is disposed of once every 5 to 7 years. It needs to be replaced. Water treatment plants that require advanced treatment are large-scale water treatment plants that treat surface water and underground water from rivers that have been contaminated in urban areas and suburban areas as raw water sources (the number of treatments per day is several hundred thousand to several The amount of used activated carbon discarded per time is very large. These used activated carbons were once regenerated and reused as activated carbon, but now the price of activated carbon has fallen, so recycling is no longer an economical method of reuse. Furthermore, there is a problem that it is difficult to secure a space for temporary storage until reuse. In addition, the used activated carbon has a high water content of about 50%, and in order to reuse it as a raw material for combustion in a coke oven or as a sintering material, it is necessary to dry it in advance, and the process and equipment become complicated, and the equipment There is a problem of excessive investment. Furthermore, if the used activated carbon is pulverized, there is a problem that it is difficult to transport the used activated carbon to a place where it is reused.

JP2001-219186

  The object of the present invention is to provide a method for improving the cohesiveness of excess sludge generated from an activated sludge treatment step, particularly an activated sludge treatment step using an oxidation ditch treatment method, and reducing the moisture content of the sludge after dehydration treatment. There is.

  In order to solve the above-mentioned problems, the present inventors have conducted intensive research and found that coagulation can be improved by supplying a substance that becomes the core of aggregation to surplus sludge having low coagulation. .

  According to the present invention, surplus sludge generated from the activated sludge treatment step is mixed with coagulated sediment sludge generated from the water purification treatment step and / or used activated carbon used in the water purification treatment step to form a sludge mixture. And a polymer flocculant addition step for adding a polymer flocculant to the obtained sludge mixture to form a floc floc, and a dehydration step for forcibly dehydrating the obtained floc floc. A method is provided.

  The surplus sludge to be treated in the present invention is not particularly limited as long as it is surplus sludge generated from an activated sludge treatment process such as general wastewater treatment, human waste treatment, sewage treatment, etc. Surplus sludge generated from an activated sludge treatment process including an oxidation ditch treatment in which the moisture content of the treated sludge is unlikely to decrease is optimal. In the activated sludge treatment step including the oxidation ditch treatment, generally, the concentrated sludge obtained through the concentration step is often subjected to dehydration. Such a concentrated sludge can also be treated in the present invention.

  The coagulation sedimentation sludge used in the present invention may be any sludge generated in a process of purifying raw water at a general water purification plant. In a general water purification process, raw water such as river water, lake water, and groundwater is first mixed with an inorganic flocculant or an organic flocculant and optionally an organic flocculant in a rapid stirring tank to form agglomerates. The formed agglomerates are sent to a floc forming tank and grow as flocs. Grown flocs are solid-liquid separated in the sedimentation basin and settle at the bottom of the sedimentation basin. The flocs that have settled at the bottom of the sedimentation basin are collected at the center of the sedimentation basin by a sludge scraper to form sedimentation sludge. Usually, an extraction line for extracting the precipitated sludge as sludge is provided at the bottom of the settling basin, and the precipitated sludge extracted through this extraction line is concentrated to a concentration of about 2 to 4% as SS. After coagulation with an inorganic coagulant, an organic coagulant is further added to increase the size of the floc and improve the sedimentation property. However, coagulated sediment sludge derived from such a large floc is also preferably used. be able to.

  The used activated carbon used in the present invention may be a waste of activated carbon used in a process of purifying raw water at a general water purification plant. In general water purification treatment, raw water is coagulated and settled or sand-filtered, and then residue of trihalomethane, which is a mold odor-causing substance and a carcinogenic substance, and humic substances, which are precursors of trihalomethane, are granular activated carbon Advanced treatments for decomposition and adsorption removal are performed using a single or a combination of granular activated carbon and ozone. In the present invention, it is preferable to use the used activated carbon used in this advanced treatment as the core of aggregation. The used activated carbon obtained from the water purification treatment has a high water content, and even if it is sufficiently drained, the water content does not become 50% or less. However, in the present invention, when it is mixed with surplus sludge as the core of aggregation, this large amount of water content does not matter.

  The shape of the used activated carbon may be various shapes such as a granular shape, a crushed shape, a cylindrical shape, etc., but it is more preferable to be finely divided to improve the mixing into the excess sludge to be agglomerated and the dewaterability. . The particle size of the used activated carbon that has been pulverized is preferably about several μm to 1 mm. If it is smaller than this range, the pulverization cost increases, which is not preferable. Micronization can be performed using a commercially available grinder. As a pulverizer, a container containing rod balls as a pulverizing medium is driven, centrifugal force is applied to the pulverizing medium, and impact force, shearing force and friction are applied to the used activated carbon between the media and between the medium and the container wall. A ball mill, a tube mill, a disc-shaped table, a roll mill that rotates while pressing a roller against the cylindrical wall surface with hydraulic pressure and centrifugal force, or an underwater mill that pulverizes in a slurry state can be preferably used. In the case of using an underwater mill, it is particularly preferable because it can be pulverized in a state containing a large amount of water that has been discarded from advanced treatment without draining used activated carbon having a high water content.

  Since the used activated carbon discharged | emitted from the water purification process used in this invention is obtained as a slurry, it can be transferred to a use place as it is, or can be transferred to a storage tank and stored. When the used activated carbon is obtained from the water purification process as a slurry having a high concentration of used activated carbon such that it is difficult to transfer the piping as a slurry, tap water or industrial water is used as a diluent in the slurry. It is preferable to increase the fluidity by setting the used activated carbon concentration to about 20% or less. Further, when the used activated carbon in a slurry state obtained from the water purification treatment step is pulverized using an underwater mill, the higher the used activated carbon concentration, the better the pulverization efficiency. Therefore, it is preferable to dilute after pulverization.

  In the present invention, the step of mixing the excess sludge with the coagulated sediment sludge generated from the water purification treatment step and / or the used activated carbon used in the water purification treatment step is preferably performed before the excess sludge is dehydrated. In a water treatment facility having a sludge storage tank, when the excess sludge is stored in the sludge storage tank, the coagulated sediment sludge and / or the used activated carbon can be introduced into the sludge storage tank. In a water treatment facility without a sludge storage tank, the coagulated sediment sludge and / or the used activated carbon can be put into any place in the pipe where surplus sludge is sent from the concentration tank to the dehydrator. In the present invention, either or both of agglomerated sedimentation sludge and used activated carbon may be added. However, when both are introduced, agglomerated sedimentation sludge is introduced first from the viewpoint of workability and effect. After mixing, it is preferable to add used activated carbon.

  The mixing ratio of the coagulated sediment sludge to the excess sludge can vary depending on the concentration of various sludges, but the volume ratio of surplus sludge: coagulated sediment sludge is preferably 8: 2 to 2: 8, and the surplus More preferably, the ratio of sludge: coagulated sediment sludge = 7: 3 to 3: 7. Moreover, the mixing ratio of the used activated carbon with respect to the excess sludge may vary depending on the concentration of various sludges, but is preferably set to a ratio of 100 to 3000 mg / l with respect to the excess sludge, A ratio is more preferable.

  In the present invention, a polymer flocculant is added to a mixture of surplus sludge, coagulated sediment sludge and / or used activated carbon. By the addition of the polymer flocculant, the excess sludge aggregates around the aggregated sludge and / or the used activated carbon that becomes the core of aggregation, forming aggregated flocs.

  Preferred examples of the polymer flocculant used in the present invention include anionic polymer flocculants, nonionic polymer flocculants, and cationic polymer flocculants, and in particular, cationic polymer flocculants and amphoteric polymers. Flocculants are preferred.

  As the cationic polymer flocculant, a cationic polymer flocculant having a cationic monomer as an essential component and comprising a copolymer of a cationic monomer or a copolymer of a cationic monomer and a nonionic monomer, and a molecule A cationic polymer flocculant having an amidine unit therein can be preferably used. Preferred examples of the cationic monomer include dimethylaminoethyl acrylate, dimethylaminoethyl methacrylate, diethylaminoethyl acrylate, diethylaminoethyl methacrylate, neutralized salts, quaternary salts thereof, and combinations thereof. Preferred examples of the nonionic monomer include acrylamide, methacrylamide, methacrylonitrile, vinyl acetate, and combinations thereof. Examples of the cationic polymer flocculant composed of a copolymer of a cationic monomer and a nonionic monomer that can be used in the present invention include dimethylaminoethyl acrylate and / or methyl chloride quaternized product of dimethylaminoethyl methacrylate / An acrylamide copolymer can be preferably mentioned. Moreover, as a cationic high molecular flocculant which has an amidine unit in the molecule | numerator which can be used in this invention, the amidine thing of an N-vinylformamide / acrylonitrile copolymer can be mentioned preferably, for example.

  As the amphoteric polymer flocculant, a copolymer of a cationic monomer unit, an anionic monomer unit and a nonionic monomer unit can be preferably used. Preferred examples of the amphoteric polymer flocculant that can be used in the present invention include dimethylaminoethyl acrylate and / or dimethylaminoethyl methacrylate methyl chloride quaternized / acrylamide / acrylic acid copolymer.

  Preferable examples of the anionic polymer flocculant include a polyacrylamide partial hydrolyzate, a copolymer of an anionic monomer, and a copolymer of an anionic monomer and a nonionic monomer. As an anionic monomer, acrylic acid, methacrylic acid, itaconic acid, maleic acid, fumaric acid, vinyl sulfonic acid, allyl sulfonic acid, methallyl sulfonic acid, styrene sulfonic acid, 2-allylamide ethane sulfonic acid, 2-acrylamide- 2-methylpropanesulfonic acid, 2-methacrylamideamidoethanesulfonic acid, 2-methacrylamide-2-methylpropanesulfonic acid, 2-acryloyloxyethanesulfonic acid, 3-acryloyloxypropanesulfonic acid, 4-acryloyloxybutanesulfonic acid 2-methacryloyloxyethanesulfonic acid, 3-methacryloyloxypropanesulfonic acid, 4-methacryloyloxybutanesulfonic acid, and metal salts or ammonium salts of these alkali metals and alkaline earth metals are preferred. It can be mentioned. Preferable examples of the copolymer of the anionic monomer and the nonionic monomer include acrylamide / acrylic acid copolymer and acrylamide / 2-acrylamido-2-methylpropanesulfonic acid copolymer.

  As the nonionic polymer flocculant, a polymer or copolymer of a nonionic monomer can be preferably used. For example, acrylamide, methacrylamide, methacrylonitrile, vinyl acetate and the like, and combinations thereof can be used, and more preferably. Can be polyacrylamide.

In the step of adding the polymer flocculant of the present invention, a two-agent method in which the above-mentioned anionic polymer flocculant is further added after the aforementioned cationic polymer flocculant can be added.
Furthermore, in this invention, before adding a polymer flocculent, an inorganic flocculant and / or an organic polymer coagulant can also be added to the mixed sludge. As the inorganic flocculant, a sulfuric acid band, polyaluminum chloride (PAC), polyferric sulfate (polyiron), ferric chloride and a mixture thereof can be preferably used. Organic polymer coagulants include condensed polyamines, dicyandiamide / formalin condensates, polyethyleneimine, polyvinylimidazoline, polyvinylpyridine, diallylamine salts / sulfur dioxide copolymers, polydimethyldiallylammonium salts, polydimethyldiallylammonium salts / dioxides Sulfur copolymers, polydimethyldiallylammonium salt / acrylamide copolymers, polydimethylasialylammonium salt / diallylamine hydrochloride derivative copolymers, acrylamine salt copolymers and the like can be preferably used. Preferred examples of the condensed polyamine include a condensate of alkylene dichloride and alkylene polyamine, a condensate of aniline and formalin, a condensate of alkylene diamine and epichlorohydrin, a condensate of ammonia and epichlorohydrin, and the like. Preferred examples of the alkylene diamine that condenses with epichlorohydrin include dimethylamine, diethylamine, methylpropylamine, methylbutylamine, and dibutylamine.

  In the present invention, excess sludge is mixed with agglomerated sedimentation sludge and / or spent activated carbon to form a sludge mixture, and then a polymer flocculant and optionally an inorganic flocculant and / or an organic polymer coagulant are added. Thus, agglomerated floc is formed, and the obtained agglomerated floc is forcibly dehydrated. The forced dehydration process in the dehydration step of the present invention can be performed using a normal pressure dehydrator, vacuum dehydrator, belt press dehydrator, centrifugal dehydrator, screw press dehydrator, or the like.

DESCRIPTION OF PREFERRED EMBODIMENTS

Preferred embodiments of the present invention will be described with reference to the accompanying drawings.
FIG. 1 is a schematic apparatus configuration diagram showing a preferred embodiment of the present invention. The surplus sludge treatment apparatus 1 of the present invention mixes the sludge mixture by mixing the coagulated sediment sludge generated from the water purification process and / or the used activated carbon used in the water purification process with the surplus sludge generated from the activated sludge treatment process. A sludge mixing tank 2 to be formed; a coagulation tank 3 for adding a polymer flocculant to the obtained sludge mixture to form a coagulated floc; and a dehydrator 4 for forcibly dehydrating the obtained coagulated floc. .

  The sludge mixing tank 2 is provided with an excess sludge supply line 21, a coagulated sediment sludge supply line 22 and / or a used activated carbon supply line 23. Between the sludge mixing tank 2 and the coagulation tank 3, a sludge mixture transfer line L1 for sending the sludge mixture obtained by mixing in the sludge mixing tank 2 to the coagulation tank 3 is connected. A pump for pumping up the sludge mixture is disposed in the sludge mixture transfer line L1. The coagulation tank 3 is provided with a polymer coagulant supply line 31 and an agitation device 32. A coagulation floc transfer line L2 is connected to the upper part of the coagulation tank 3, and the coagulation floc formed in the coagulation tank 3 is sent to the dehydrator 4. In the illustrated apparatus, the dehydrating device 4 is a belt press dehydrator.

The illustrated apparatus further includes a concentration tank 5 that concentrates excess sludge disposed upstream of the sludge mixing tank 2. An excess sludge supply line 21 is connected to the concentration tank 5. In addition, the polymer flocculant dissolution tank 6 is connected to the polymer flocculant supply line 31 in order to dissolve the polymer flocculant supplied to the flocculant tank 3 and supply the polymer flocculant as a polymer flocculant solution to the flocculant tank 3. .
A procedure for treating surplus sludge generated from the activated sludge treatment step will be described using the illustrated apparatus.

  First, surplus sludge generated from the activated sludge treatment step is supplied to the concentration tank 5, becomes concentrated sludge, and is sent to the sludge mixing tank 2 via the excess sludge supply line L1. On the other hand, the coagulated sediment sludge generated from the water purification treatment process is sent to the sludge mixing tank 2 via the coagulation sedimentation sludge supply line 22 and / or the used activated carbon used in the water purification treatment process is sent to the used activated carbon supply line 23. Sent. The concentrated sludge, the coagulated sedimented sludge and / or the used activated carbon supplied to the sludge mixing tank 2 are mixed to form a sludge mixture. The formed sludge mixture is sent to the coagulation tank 3 through the sludge mixture transfer line L1. The coagulation tank 3 is supplied with the polymer coagulant via the polymer coagulant supply line 31 and mixed with the sludge mixture to form coagulation flocs. The formed agglomeration floc rides on the stirring ascending flow by the agitator 32 and rises to the upper part of the agglomeration tank 3 and overflows to the agglomeration flock transfer line L2 provided at the upper part of the agglomeration tank 3. The agglomerated floc sent to the dewatering device 4 via the agglomerated floc transfer line L2 is forcibly dehydrated by a belt press to form a dehydrated cake.

The operation of this apparatus can be performed either continuously or intermittently. After the sludge mixture is formed in the sludge mixing tank 3, the pump disposed in the sludge mixture transfer line L1 is operated to send the sludge mixture to the coagulation tank 3, and at the same time or slightly behind, the polymer coagulant supply line 31 The polymer flocculant may be supplied to the agglomeration tank 3 by operating the pump arranged in the system. In addition, an inorganic flocculant and / or an organic polymer flocculant may be added to the flocculant 3 before supplying the polymer flocculant to the flocculant 3. In addition, used activated carbon can use what was grind | pulverized to the desired particle size using arbitrary grinders before supplying to this apparatus as needed.
[The invention's effect]

  According to the present invention, surplus sludge, in particular, oxidation sludge treated surplus sludge with low dewaterability is mixed with agglomerated sedimentation sludge and / or used activated carbon as a core of agglomeration to form a sludge mixture, A sludge having a low water content can be obtained by adding a polymer flocculant to the sludge mixture to form a floc floc and then forcibly dehydrating the obtained floc floc. When the used activated carbon is used, it also has an economical effect of reusing waste from the water treatment plant and an effect of reducing waste from the water treatment plant.

EXAMPLES Hereinafter, although this invention is demonstrated further in detail using an Example, this invention is not limited to these.
The polymer flocculants used in the following examples are shown in Table 1 below, and the properties of excess sludge and coagulated sediment sludge are shown in Table 2 below.

[Example 1]
In a 300 ml beaker, sewage surplus sludge A and purified water coagulated sediment sludge C were mixed at a volume ratio of 7: 3 to obtain a 200 ml sludge mixture. Subsequently, the polymer flocculent a was added to the sludge mixture so that it might become 1.0% per SS, and it moved to the prepared empty 300 ml beaker. This transfer was repeated 10 times to agglomerate the sludge mixture to form agglomerated floc. After measuring the size of the obtained floc floc with a measure, the floc floc formed in the beaker was dehydrated by gravity with a 60 mesh nylon filter cloth for 30 seconds, and filtered water was received in a graduated cylinder. The amount of filtered water was measured. The sludge after gravity filtration is sandwiched between two filter cloths and squeezed for 1 minute at a pressure of ² kg / cm ² using a piston-type dehydrator. After measuring the mass of the dehydrated sludge obtained, It dried for 4 hours or more at the temperature of 0 degreeC, measured the mass after drying, and calculated | required the moisture content from the difference of both. The results are shown in Table 3.

[Examples 2 to 10 and Comparative Examples 1 to 17]
The procedure of Example 1 was repeated while changing the mixing ratio of excess sludge and coagulated sediment sludge, the type of polymer flocculant and the addition rate. The results are shown in Table 3.

[Examples 11 to 13]
Used activated carbon (“Evadia LG10S” manufactured by Ebara Manufacturing Co., Ltd.) with a water content of 40% collected from an advanced treatment facility in the water purification treatment process was pulverized for 30 minutes with a ball mill. The water content of the pulverized used activated carbon was about 8%. The obtained used activated carbon pulverized product was mixed with surplus sludge A at the ratio shown in Table 4, and the same procedure as in Example 1 was repeated. The results are shown in Table 4.

[Examples 14 to 16]
In a 300 ml beaker, sewage surplus sludge B and purified water agglomerated sedimentation sludge C were mixed at 5: 5 (volume ratio) to obtain a 200 ml sludge mixture. Subsequently, the used activated carbon used in Example 11 with respect to the sewage surplus sludge B was added to the sludge mixture at the ratio shown in Table 5. Thereafter, the polymer flocculent b was added so as to be 1.0% per SS, and transferred to the prepared empty 300 ml beaker. This transfer was repeated 10 times to agglomerate the sludge mixture to form agglomerated floc. In the same manner as in Example 1, the floc diameter, the filtered water amount after 30 seconds, and the sludge moisture content were measured. The results are shown in Table 5.

  As is clear from the results of the examples, according to the method of the present invention, a good coagulation floc having a floc diameter of about 3 mm or more is formed, the amount of gravity filtration is increased, and the sludge moisture content after dehydration is also about 83. It can be seen that the percentage is reduced to about 79%.

FIG. 1 is a schematic configuration diagram showing an embodiment of a surplus sludge treatment apparatus according to the present invention.

Explanation of symbols

1: Surplus sludge treatment device 2: Sludge mixing tank 21: Surplus sludge supply line 22: Coagulation sediment sludge supply line 23: Used activated carbon supply line 3: Coagulation tank 4: Dehydration apparatus 5: Concentration tank 6: Dissolving polymer flocculant Tank

Claims (11)

A sludge mixing step in which the excess sludge generated from the activated sludge treatment step is mixed with the coagulated sediment sludge generated from the water purification treatment step and the used activated carbon waste from the water purification treatment step to form a sludge mixture;
A polymer flocculant addition step of adding a polymer flocculant to the obtained sludge mixture to form a floc floc;
A dehydration step for forcibly dehydrating the obtained agglomerated floc,
Of excess sludge containing water.   The method according to claim 1, wherein the excess sludge is generated from a sewage treatment plant.   The method according to claim 1, wherein the excess sludge is oxidation ditch treated sludge. The method according to claim 1, wherein the used activated carbon waste is added to the excess sludge after pulverization. The spent activated carbon waste is less pulverized coal particle diameter 1 mm, the method according to any one of claims 1-4. In the sludge mixing step, the coagulation sedimentation sludge to the waste sludge, flocculation sludge: excess sludge = 8: 2 to 2: 8 mixed in a ratio (volume ratio), any one of claims 1 to 5 2. The method according to item 1. The said sludge mixing process WHEREIN: The method of any one of Claims 1-6 which mixes the said used activated carbon waste in the range of 100-30000 mg / L with respect to the said excess sludge. After the sludge mixing step, prior to said polymeric flocculant addition step, further comprising the step of adding an inorganic flocculant and / or an organic polymer coagulant according to any one of claims 1-7 Method. A sludge mixing tank that forms a sludge mixture by mixing surplus sludge generated from the activated sludge treatment process with coagulated sediment sludge generated from the water purification process and spent activated carbon waste from the water purification process;
A coagulation tank in which a polymer flocculant is added to the obtained sludge mixture to form an aggregate floc;
A dehydrating device for forcibly dewatering the obtained agglomerated floc,
An apparatus for treating excess sludge. Furthermore, the apparatus of Claim 9 provided with the concentration tank which concentrates this excess sludge before supplying the excess sludge generated from an activated sludge process process to the said sludge mixing tank. The apparatus according to claim 9 or 10, further comprising means for crushing the used activated carbon waste.

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