JP2015000389A - Sludge treatment method and device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a sludge treatment method and a device therefor in which sludge is flocculated by two-stage stirring steps with different rotary speeds using a polymer flocculant, and the content of a dewatering cake is reduced, thus the amount of waste can be more reduced, and further, the using amount of a polymer flocculant can be reduced.SOLUTION: Provided is a sludge treatment method comprising: a first stirring step A in which a first polymer flocculant is added to sludge as the object to be treated, high speed stirring is performed to mix the same; a second stirring step B in which a second polymer flocculant is added thereto, and slow speed stirring is performed to form a flocculated flock; and a dewatering step C in which the sludge including the flocculated flock is dewatered, and in which a pH adjustor is added in at least on of the first stirring step, the second stirring step and the dewatering step.

Description

  The present invention relates to a sludge treatment method and apparatus, and more particularly, to a sludge treatment method and apparatus for reducing the moisture content of a dewatered cake while reducing the amount of flocculant added to agglomerate sludge.

  While it is required to reduce the amount of waste and reduce the environmental load, dewatering technology to reduce the volume of sludge discharged from wastewater treatment facilities and water purification facilities is extremely important and more efficient. Sludge dewatering technology is desired.

  The sludge dehydration treatment is generally composed of a coagulation step of coagulating sludge using a coagulant and a dehydration step of dehydrating the coagulated sludge using a dehydrator. The success or failure of sludge dehydration depends largely on how effectively it can be agglomerated by a flocculant.

  Among the methods of coagulating sludge using a coagulant, a method of coagulating sludge by using a polymer coagulant and a two-stage agitation process with different rotational speeds when stirring the sludge is known. .

  For example, in Japanese Patent Application Laid-Open No. 57-130599 (Patent Document 1), a first polymer flocculant having a charge opposite to the charge of sludge is added to sludge and the first stirring is performed. In the method of adding a second polymer flocculant having a charge opposite to that of the polymer flocculant and performing the second stirring, and dehydrating the generated floc, the first stirring does not generate the floc or has been generated. A sludge dewatering method is disclosed, which is characterized by strong stirring so that the floc diameter is 2 mm or less. The method described in Patent Document 1 intends to form flocs with good dewaterability by neutralizing sludge charges.

  In JP-A-62-277200 (Patent Document 2), in coagulating organic sludge using an amphoteric polymer flocculant, the sludge and the amphoteric polymer flocculant are mixed in the first stage treatment. A part is brought into contact under relatively strong stirring, and the first-stage treated sludge and the remainder of the amphoteric polymer flocculant are brought into contact under relatively weak stirring in the second-stage treatment. And a method for coagulating sludge is disclosed. The method described in Patent Document 2 requires that the cationic active portion and the anionic active portion act independently of each other. In order to make them free from each other, an acidic substance is allowed to coexist, and the pH is 3 .5 or less. Further, the amount of the flocculant added to the first stage is 50 to 90% of the total amount used so that the aggregation in the first stage does not become incomplete.

  In JP-A-11-57800 (patent document 3), an inorganic flocculant and an amphoteric polymer as a first polymer are added to organic sludge and vigorously stirred. Further, an amphoteric polymer is added as a second polymer. There is disclosed a sludge dewatering method characterized by performing pressure dehydration after slow stirring. In Patent Document 3, the strong stirring conditions are 300 to 500 m / min as the peripheral speed to release moisture in the flock to form a strong flock, and the slow stirring conditions are refined to 20 to 100 m / min. By gathering the flocs to produce small granular flocs, it is said to be excellent in filtration and dewatering and not clogged even when high pressure is applied.

  In JP-A-2002-192199 (Patent Document 4), sludge, a first flocculant and a pH adjuster are added to perform primary flocculation, and the primary flocculation floc is introduced into a primary dehydrator. Filled dehydrated cake with a low water content, performing secondary dehydration, adding a second flocculant to the primary dehydrated cake, performing secondary agglomeration, and introducing secondary agglomerated floc into the dehydrator occasionally A method and apparatus for dewatering sludge is disclosed. In Patent Document 4, since the process proceeds with a combination of agglomeration and dehydration as one unit, a plurality of dehydration apparatuses are required, the apparatus becomes large, and maintenance becomes complicated.

Japanese Patent Laid-Open No. 57-130599 JP-A-62-277200 JP-A-11-57800 JP 2002-132199 A

  The object of the present invention is to agglomerate sludge by a two-stage stirring process using a polymer flocculant and different rotation speeds, to reduce the water content of the dehydrated cake, and to further reduce the amount of waste, An object of the present invention is to provide a sludge treatment method and apparatus capable of reducing the amount of the polymer flocculant used.

According to the present invention, the first polymer flocculant is added to the sludge as an object to be treated, and the first stirring step of mixing by stirring at high speed;
A second agitation step of adding a second polymer flocculant and slowly stirring to form an agglomerate floc;
A dehydration step of dewatering the sludge containing the aggregated floc,
The pH of the sludge is measured in at least one of the first stirring step, the second stirring step, and the dehydrating step, and based on the measured pH value, the pH adjuster is added to at least one of the first stirring step, the second stirring step, and the dehydrating step. The sludge treatment method characterized by adding in is provided.

  The high speed stirring in the first stirring step is preferably a peripheral speed of 600 rpm or more, and more preferably a peripheral speed of 1000 rpm or more. The stirring time is preferably within 1 minute, more preferably 20 seconds or less. In the first stirring step, it is desirable to form a dense aggregated floc that becomes the core of the aggregated floc in the second stirring step. Since the polymer flocculant is generally high in viscosity, it is difficult to distribute the flocculant uniformly to the sludge details. In the present invention, the polymer flocculant can be uniformly dispersed to the sludge details by high-speed stirring in the first stirring step, and the surface charge of the sludge is neutralized and the polymer is agglomerated by adsorption or crosslinking action. Can be performed simultaneously.

  The slow stirring in the second stirring step is preferably a peripheral speed in the range of 10 to 500 rpm, and more preferably in the range of 20 to 400 rpm. The stirring time is preferably within 20 minutes, and more preferably in the range of 1 to 20 minutes. In the second stirring step, it is desirable to form a large aggregated floc that is easy to dehydrate by stirring slowly. In the second stirring step, agglomerated sludge having good filterability is formed, and then the agglomerated sludge is dehydrated, so that the moisture content of the dewatered cake can be effectively reduced, and the amount of the polymer flocculant used Can also be reduced.

  The pH adjuster can be added together with the polymer flocculant in any one or more of the first stirring step, the second stirring step, and the dehydrating step. The pH adjuster is added in order to reduce the polymer flocculant consumed for neutralizing the surface charge of the sludge as the optimum pH range in which the flocculant action of the polymer flocculant on the sludge is expressed. In order to exert the action of the polymer flocculant, it is preferable that the pH of the sludge is adjusted to the optimum range at the stage where the sludge and the polymer flocculant come into contact with each other. It is more preferable to add a pH adjusting agent in the first stirring step in which the agent is consumed or before the first stirring step.

  The pH adjuster can be appropriately selected depending on the type of sludge and polymer flocculant. For example, when an anionic polymer flocculant is used, the pH is adjusted to 3-12, preferably 3-8, and when a nonionic polymer flocculant is used, the pH is 3-12, preferably 3-8. In order to adjust the pH to 3 to 11, preferably 3 to 8 when using a cationic polymer flocculant, and to adjust the pH to 4 to 8 when using an amphoteric polymer flocculant. Measure the sludge pH and add an appropriate pH adjuster. As the pH adjuster, sulfuric acid, hydrochloric acid or sodium hydroxide can be used. The pH adjuster is added while measuring the pH of the sludge. For example, when the pH is adjusted to 4 to 8, if the pH of the sludge is 8 or more, sulfuric acid or hydrochloric acid is added to the sludge, and the addition of the pH adjuster is stopped when the pH drops to 7. When the pH of the sludge is 4 or less, sodium hydroxide is added and the addition of the pH adjuster is stopped when the pH rises to 5.

According to the present invention, the first stirring device for mixing the sludge and the first polymer flocculant at high speed, and
A second agitation device that further mixes the second polymer flocculant with the sludge containing the first polymer flocculant mixed in the first agitation device, and forms an agglomerated floc by stirring slowly;
A dehydrating device for dewatering sludge containing the aggregated floc formed by the second stirring device,
Provided on the upstream side of the first stirring device is a sludge treatment apparatus comprising a pH meter for measuring the pH of the sludge and a pH adjuster adding means for adding a pH adjuster based on the pH value of the sludge.

According to the present invention, the first stirring device for mixing the sludge and the first polymer flocculant;
A second agitation device that further mixes the second polymer flocculant with the sludge containing the first polymer flocculant mixed in the first agitation device to form an agglomeration floc;
A dehydrating device for dewatering sludge containing the aggregated floc formed by the second stirring device,
The first stirring device is a stirring device having a stirring speed faster than the second stirring device,
A pH meter for measuring the pH of sludge and a pH adjuster addition means for adding a pH adjuster based on the pH value of the sludge to at least one of the first stirrer, the second stirrer, and the dehydrator A sludge treatment apparatus is provided.

  According to the present invention, it is possible to reduce the water content of the dewatered cake while reducing the amount of the polymer flocculant consumed for neutralizing the surface charge of the sludge, and achieve a volume reduction of the sludge dewatering treatment. can do.

It is a schematic flow which shows an example of the sludge processing method of this invention. It is a schematic flow which shows an example of the sludge processing apparatus of this invention. It is a schematic flow which shows another example of the sludge processing apparatus of this invention. It is a schematic flow which shows another example of the sludge processing apparatus of this invention. It is a schematic flow which shows another example of the sludge processing apparatus of this invention. It is a schematic flow which shows another example of the sludge processing apparatus of this invention. It is the schematic which shows an example of a sludge concentrator. It is the schematic which shows another example of a sludge concentrator. It is the schematic which shows an example of a slit formation apparatus. It is a graph which shows the relationship between the addition ratio of a 1st polymer flocculent and a 2nd polymer flocculant, and SS recovery.

Preferred embodiment

  Hereinafter, the present invention will be described in detail with reference to the accompanying drawings, but the present invention is not limited thereto.

FIG. 1 is a schematic flow diagram of the sludge treatment method of the present invention.
In the sludge treatment method of the present invention, the first polymer flocculant is added to the sludge as an object to be treated, the first stirring step A in which the first polymer flocculant is mixed by stirring at high speed, and the second polymer flocculant is further added. A first agitation step A, a second agitation step B, and a dehydration step C for dehydrating sludge containing the agglomeration floc; It is added in at least one of the steps C.

  The sludge that can be treated in this method may be either organic sludge or inorganic sludge. Organic sludge means that the main component of sludge contains an organic component, but does not exclude the inclusion of an inorganic component. Similarly, inorganic sludge is one in which the main component of the sludge contains an inorganic component, but does not exclude the inclusion of an organic component.

  Examples of the organic sludge include organic sludge generated in sewage treatment, human waste treatment, and various industrial wastewater treatment. More specifically, first sedimentation basin sludge, excess sludge, anaerobic digested sludge, aerobic digested sludge, manure, septic tank sludge, digested and desorbed liquid, and the like can be mentioned.

  Examples of the inorganic sludge include inorganic sludge generated in water purification treatment, construction wastewater treatment, and various industrial wastewater treatment. Here, the sludge generated in the water purification treatment is sludge discharged from a settling pond, a waste mud pond, a concentration tank, or the like in the water purification treatment facility.

  In the sludge treatment method of the present invention, both organic sludge and inorganic sludge can be treated, but from the viewpoint that the effect of the present invention of improving dewatering efficiency can be expressed better, organic sludge. Among them, the application to the treatment of hardly dewatering anaerobic digested sludge is preferred.

  The sludge treatment method of the present invention includes a two-stage stirring process with different stirring speeds. First, at a 1st stirring process, sludge and a polymer flocculent are stirred at high speed, a polymer flocculant is uniformly disperse | distributed in sludge, and it spreads to the detail of sludge. Next, in the second stirring step, a polymer flocculant is further added and stirred gently to form a floc floc suitable for dehydration.

  In the first stirring step, 600 rpm or more, preferably 1000 rpm or more, more preferably 2000 rpm or more, more preferably 3000 rpm or more at a peripheral speed of 20 seconds or less, preferably 1 to 20 seconds, more preferably 1 to 15 seconds, Stirring is preferably performed in the range of 1 to 10 seconds. In the second stirring step, the peripheral speed is in the range of 10 to 500 rpm, preferably in the range of 20 to 400 rpm, more preferably in the range of 30 to 300 rpm, 1 to 20 minutes, preferably 2 to 15 minutes, more preferably 3 to 3. Stir for 10 minutes.

  Since the stirring speed applied in the first stirring step is very high, if the stirring is performed for a long time, the molecular chain of the polymer flocculant is cut and the cohesive force is reduced. It has been found that, as the stirring speed becomes higher, the reduction of the cohesive force can be suppressed by shortening the stirring time. On the other hand, in the second stirring step, it is desirable to form a large aggregated floc slowly under mild conditions.

  The first and second polymer flocculants added in the first stirring step and the second stirring step may be the same type or different types, but the same type of polymer flocculant from the viewpoint of selection of the pH adjuster and operation management. Is preferably used.

  As the polymer flocculant, any of anionic polymer flocculants, nonionic polymer flocculants, cationic polymer flocculants and amphoteric polymer flocculants can be used. When treating organic sludge, it is particularly preferable to use a cationic polymer flocculant or an amphoteric polymer flocculant.

  Examples of the anionic polymer flocculant include sodium polyacrylate, a copolymer of sodium acrylate and acrylamide, polysodium methacrylate, a copolymer of sodium methacrylate and acrylamide, and the like.

  Examples of nonionic polymer flocculants include polyacrylamide and polyethylene oxide.

Examples of cationic polymer flocculants include acrylate polymer flocculants (also referred to as “DAA polymer flocculants”), methacrylate polymer flocculants (also referred to as “DAM polymer flocculants”), and amide groups. , Nitrile groups, amine hydrochlorides, formamide groups, and the like, and polyvinylamidines (also referred to as “amidine polymer flocculants”), polyacrylamide Mannich modified products, and the like.
Examples of the DAA polymer flocculant include a polymer of a quaternized product of dimethylaminoethyl acrylate, a copolymer of a quaternized product of dimethylaminoethyl acrylate and acrylamide, and the like.
Examples of the DAM polymer flocculant include a polymer of a quaternized product of dimethylaminoethyl methacrylate and a copolymer of a quaternized product of dimethylaminoethyl methacrylate and acrylamide.

Examples of amphoteric polymer flocculants include, for example, dimethylaminomethyl acrylate quaternized products of acrylamide and acrylic acid, dimethylaminomethyl methacrylate quaternized products of acrylamide and acrylic acid, and the like. Can do.
However, the above is an example and is not limited thereto.

The molecular weight of the polymer flocculant is preferably 4.5 million or more. A more preferable molecular weight is 5 million or more. The molecular weight here is an average molecular weight determined by a viscosity method.
The viscosity of the polymer flocculant is preferably 150 mPa · s or more, particularly 175 mPa · s or more, and more preferably 200 mPa · s or more.
The viscosity at this time is a value measured by dissolving the polymer flocculant in pure water at 2 g / L and using a B-type viscometer at a rotation speed of 25 ° C. and 60 rpm.
In the present invention, since high-speed stirring is performed in the first stirring step, it is necessary that the cohesive force does not decrease even if the molecular chain is cut by high-speed stirring. If it is the above-mentioned molecular weight and viscosity range, even if a molecular chain is partially cut | disconnected, cohesion force can be maintained.

  When the molecular weight of the first polymer flocculant is 4.5 million or more, the injection amount of the first polymer flocculant is 45 to 95% by mass of the total injection amount of the first polymer flocculant and the second polymer flocculant. It is preferable to adjust and add so that it may become, It is preferable to adjust and add so that it may occupy 50-95 mass% especially, and 55-90 mass% especially among them.

  If the ratio of the polymer flocculant injection amount in the first stirring step is too high, the polymer flocculant injection amount added in the second stirring step is too small, and the aggregation flocs may not grow. As a result, the filterability deteriorates in the concentration process and the dehydration process. On the other hand, if the ratio of the amount of the polymer flocculant injected in the first stirring step is too low, the proportion of the polymer flocculant uniformly dispersed in the sludge by the high-speed stirring decreases in the first stirring step. The effect may be reduced. By controlling the injection amount of the polymer flocculant in the first stirring step to 45 to 95% of the total injection amount, the polymer flocculant can be uniformly dispersed in the sludge and the aggregated floc can be grown.

  The polymer flocculant can be added in a liquid state or a solid state, but is preferably in a liquid state from the viewpoint of being uniformly dispersed in sludge. The solvent used for bringing the polymer flocculant into a liquid state preferably does not contain other ionic components in order not to reduce the cohesive force, and pure water is preferred. However, pure water is expensive from the viewpoint of economy. In this invention, since it adjusts to a suitable pH range by adding a pH adjuster, it is not limited to a pure water, Tap water, industrial water, ground water, and the treated water of various waste water treatment can be used.

  The concentration of the polymer flocculant in the aqueous solution state may be 1 to 3 g / L, but is preferably 3 g / L or more, more preferably 5 g / L or more, and even more preferably 10 g / L. L or more.

  In the coagulation of sludge with a polymer flocculant, the polymer flocculant solution is generally prepared at 1 to 3 g / L, and usually a polymer flocculant solution of 3 g / L or more is used. Absent. When the concentration of the polymer flocculant becomes 3 g / L or more, the polymer flocculant solution becomes highly viscous. Therefore, at the rotational speed of the stirrer (about 10 to 500 rpm) used in the conventional flocculant, the polymer flocculant It is difficult to disperse the agent uniformly in the sludge. However, in the present invention, even when a high-concentration solution of 3 g / L or more is used, the polymer flocculant can be uniformly dispersed in the sludge by high-speed stirring in the first stirring step. As a result, the amount of water dissolved in the polymer flocculant can be reduced, and the water content of the dehydrated cake after the dehydration treatment can be reduced. Moreover, since the density | concentration of the polymer flocculant in the sludge which added the polymer flocculent can be raised, the injection amount of a polymer flocculant can also be reduced. For example, when 200 mL of a 2 g / L polymer flocculant solution is injected into 1 L of sludge (0.4 g as a polymer flocculant), the concentration of the polymer flocculant in the sludge is 333 mg / L. On the other hand, when 40 mL of 10 g / L of polymer flocculant is injected into 1 L of sludge (0.4 g of polymer flocculant is injected), the concentration of the polymer flocculant in the sludge is 385 mg / L. Thus, even when the same 0.4 g of polymer flocculant is added, it is more sludge to use 10 g / L of polymer flocculant than to use 2 g / L of polymer flocculant solution. The concentration of the polymer flocculant therein can be increased, the amount of the polymer flocculant injected can be reduced, and the water content of the dehydrated cake after the dehydration treatment can be reduced.

  Furthermore, in the present invention, the cohesive force of the polymer flocculant can be exhibited and maintained to the maximum by adding a pH adjuster before the first stirring step or in the first stirring step. The addition of the pH adjuster is less effective than in the first stirring step, but may be performed in the second stirring step or the dehydration step.

  As the pH adjuster, an acid such as sulfuric acid or hydrochloric acid or an alkali such as sodium hydroxide can be used. The pH of the sludge is measured, and the acid or alkali may be selected so that it is in a pH range where the coagulant action of the polymer flocculant is exhibited.

  The addition amount of the pH adjuster varies depending on the type of sludge, alkalinity, and type of polymer flocculant. For example, it is preferable to use sodium hydroxide as a pH adjuster for excess sludge generated from human waste processing facilities. Moreover, it is preferable to use sulfuric acid as a pH adjuster for human waste and septic tank sludge. The pH adjusting agent is 5.0 with respect to the sludge evaporation residue (referred to as “TS”. TS is the concentration of the substance remaining when the sludge is evaporated to dryness at 105 to 110 ° C.). It is desirable to add at a ratio of less than mass% (in terms of pure content).

  The sludge containing the aggregated floc formed in the second stirring step is then dehydrated in the dehydration step and separated into a dehydrated cake and a dehydrated filtrate. A dehydration process can be performed using a normal dehydration apparatus.

  In at least one of the first stirring step, the second stirring step, and the dehydration step, an inorganic flocculant may be added to the sludge. Examples of the inorganic flocculant include ferric chloride, aluminum sulfate, aluminum chloride, polyaluminum chloride, and polyferric sulfate. The inorganic flocculant is preferably added after diluting with diluting water from the viewpoint of decreasing the viscosity to facilitate dispersion in the sludge and diluting to increase the volume and facilitate uniform dispersion. The dilution factor of the inorganic flocculant is 2 to 5 times, preferably 3 to 4 times. As the diluting liquid, pure water, tap water, industrial water, ground water, treated water for various wastewater treatment, seawater, etc. can be used, but from the economical viewpoint, industrial water, groundwater, treated water for various wastewater treatment are preferable. .

  If the inorganic flocculant is added in an amount of 1.0% by mass (converted to Fe) or more with respect to the evaporation residue (TS) of the sludge, the dehydration effect can be improved, but added exceeding 10% by mass (converted to Fe). Even so, the inorganic flocculant is wasted. Therefore, from this point of view, it is preferable to add the inorganic flocculant in an amount of 1.0 to 10% by mass (converted to Fe) with respect to the sludge. It is even more preferable to add at a ratio of 0% by mass (Fe conversion) or less, of which 2% by mass (Fe conversion) or more or 6.0% by mass (Fe conversion) or less.

Sludge containing agglomerated flocs may be concentrated before dehydration. When the inorganic flocculant is added before the dehydration treatment, it is preferably added after the concentration. Concentration is preferably carried out until TS in the sludge containing agglomerated floc is in the range of 50 g / L to 150 g / L, preferably 80 g / L to 140 g / L. When the sludge TS is less than 50 g / L, the inorganic flocculant flows out into the concentrated filtrate. When the sludge TS is higher than 150 g / L, the sludge becomes close to solid and the inorganic flocculant is dispersed inside the sludge. The effect of the inorganic flocculant cannot be exhibited sufficiently.
Concentration of sludge containing coagulated flocs is preferably performed while applying pressure in order to achieve the TS. The applied pressure is 0.5 to 50 kPa, preferably 1 to 40 kPa, more preferably 3 to 30 kPa.

  When an inorganic flocculant is added after concentration and before dehydration, the sludge is concentrated and the fluidity is low, and it is difficult to uniformly penetrate and disperse the inorganic flocculant. On the other hand, when the concentrated sludge is stirred or kneaded, the flocculent flocs due to the polymer flocculant are broken, and the water content of the dewatered cake cannot be reduced. Therefore, it is preferable to form slits in the concentrated sludge to permeate and disperse the inorganic flocculant. By forming the slit and infiltrating the inorganic flocculant, the effect of the inorganic flocculant can be enhanced and the amount used can be reduced.

Next, the sludge treatment apparatus of the present invention will be described with reference to FIGS.
The sludge treatment apparatus shown in FIG. 2 includes a sludge storage tank 1 that stores sludge to be treated, a first agitation apparatus 2 that performs high-speed agitation, a second agitation apparatus 3 that performs a slow agitation, and a dehydration apparatus that performs a dehydration process. 4, first polymer flocculant addition means 5 for adding the first polymer flocculant to the first stirring device 2, and second polymer flocculant for adding the second polymer flocculant to the second stirring device 3 The addition means 6, the pH meter which measures the pH of the sludge supplied to a 1st stirring apparatus, and the pH adjuster addition means 7 which adds a pH adjuster to a 1st stirring apparatus are included. The sludge from the sludge storage tank 1 is added with the first polymer flocculant and the pH adjuster, and is stirred at high speed by the first stirring device 2. Next, in the second stirring device 3, the second polymer flocculant is added and gently stirred to form an aggregated floc. The sludge containing the aggregated floc is dehydrated by the dehydrator 4 and separated into a dehydrated filtrate and a dehydrated cake.

  In the sludge treatment apparatus shown in FIG. 2, the pH adjusting agent adding means 7 may be configured to add a pH adjusting agent to the second stirring device 3 and / or the dehydrating device 4 as indicated by a dotted line. In this case, the pH meter can be provided at a position where the pH adjusting agent adding means 7 measures sludge in the apparatus to which the pH adjusting agent is added.

  In the sludge treatment apparatus shown in FIG. 3, the polymer flocculant added to the first stirring apparatus 2 and the second stirring apparatus 3 is supplied from the same storage tank, and the supply lines are supplied to the first stirring apparatus 2 and the second stirring apparatus 3, respectively. Is a mode in which is provided. Moreover, the concentration apparatus 8 which concentrates the sludge containing the aggregation floc formed in the 2nd stirring apparatus 3 is included. The sludge from the sludge storage tank 1 is added with the first polymer flocculant and the pH adjuster, and is stirred at high speed by the first stirring device 2. Next, in the second stirring device 3, the second polymer flocculant and the pH adjuster are added and stirred gently to form a flocculent floc. The sludge containing the aggregated floc is concentrated by the concentrating device 8 and then dehydrated by the dehydrating device 4 and separated into a dehydrated filtrate and a dehydrated cake.

  The sludge treatment apparatus shown in FIG. 4 is a mode in which the polymer flocculant is supplied from the same storage tank and a line to be supplied to the first stirring device 2 and a line to be supplied to the second stirring device 3 are selected by valve control. .

The sludge treatment device shown in FIG. 5 is the same as the embodiment shown in FIG. 2 except that the first stirring device 2 is an inline mixer.
In the sludge treatment apparatus shown in FIG. 6, except that the first stirring device 2 is an in-line mixer, and an inorganic flocculant addition means 9 for adding an inorganic flocculant to the sludge concentrated by the concentration device 8 is provided. This is the same as the embodiment shown in FIG. In addition, as shown with a dotted line in FIG. 6, the structure added to the sludge supplied to the 1st stirring apparatus 2 may be sufficient as an inorganic flocculant.

  The combination of each component of the apparatus shown in FIGS. 2-6 is not limited to the aspect shown in figure, You may substitute suitably.

The first stirrer may be any stirrer capable of high-speed stirring, and may be a stirrer composed of a stirring blade, a shaft and a motor, a stirrer composed of a rotor, a stator and a motor, and an inline provided in a supply pipe. A mixer or the like can be used. An in-line mixer is also called a line mixer. The merit of the in-line mixer is that the mixer is hermetically sealed, so if there are two pumps for the sludge and the polymer flocculant upstream, the liquid can be sent downstream. On the other hand, when a stirrer is installed in the container, the upper part of the container is open, so there is no other pump or equivalent to the pump in addition to the upstream sludge pump and polymer flocculant pump. The liquid cannot be sent downstream. For this reason, it is common to send a liquid downstream with a height difference without installing a pump.
The second stirring device may be any stirring device that enables slow stirring, and various stirring devices can be used in the same manner as the first stirring device.

  The dehydrating apparatus may be a dehydrating apparatus used for ordinary dehydration treatment, and for example, a screw press dehydrator, a belt press dehydrator, a centrifugal dehydrator, a vacuum dehydrator, a filter press dehydrator, a multiple disk dehydrator, or the like may be used. it can. The dehydrator may have a concentration mechanism.

  As the concentrating device, a centrifugal concentrator, a screw concentrator, an elliptical plate concentrator, a sieve, a pressure concentrator, a belt type filter concentrator, etc., which are used for ordinary dehydration treatment can be used. Examples of the concentrating device are shown in FIGS.

  7 includes a sludge charging hopper 21, a sludge moving means 22, and a water catching means 23 provided below the sludge moving means 22, and the sludge moving means 22 includes a belt 24 and a belt drive. The apparatus 25 is comprised. The entire upper surface (conveying surface) of the belt 24 is horizontally moved by the belt driving device 25, and the sludge can be moved to the horizontal sludge discharge port side, and the sludge containing the aggregated floc is filtered while moving on the belt 24. Then, the filtrate is configured to fall into the lower water capturing means 23. The water catching means 23 is provided below the sludge moving means 22 and is configured to catch water falling from the sludge moving means 22 and drain it from the waste water outlet.

  The concentration apparatus shown in FIG. 8 includes a sludge charging hopper 21, a sludge moving means 22, a pressurizing means 28 provided above the sludge moving means 22, and a water trapping means provided below the sludge moving means 22. 23, and the pressurizing means 28 is provided with the pressurizing plate 28A obliquely so as to provide a gap with the belt 24 in front of the sludge discharge port 26 of the sludge moving means 22, so that the sludge is sludge moving means. When moved to the horizontal sludge discharge port side by 22, it is configured to be pressurized from above when passing through the gap between the pressure plate 28 </ b> A and the belt 24. At this time, one or two or more pressure plates 28A may be provided, and the pressure plate 28A may be provided so that the installation angle is fixed, or provided so that the installation angle can be changed as needed. Further, it can be pivotally supported so as to be swingable up and down. By changing the angle of the pressure plate 28A and the size of the gap with the belt 24, the pressure applied to the sludge containing the aggregated floc can be adjusted, and the concentration ratio can be adjusted. Further, instead of the pressure plate 28A, for example, a roller may be installed.

  An example of a slit forming apparatus for forming slits in the concentrated sludge is shown in FIG. The slit forming machine 30 can be configured so that the comb-shaped cutting blade 31 is disposed in the sludge discharge port 26 of the sludge concentrator 20 at an appropriate interval in the horizontal direction so that the blade is in the vertical direction. . With such a comb-shaped cutting blade, a vertical slit can be formed in the concentrated sludge extruded from the sludge concentrator 20. However, the slit forming machine 30 is not limited to the above configuration. For example, a cutting blade assembled in a lattice shape when viewed from the top, or a cutting blade assembled at an appropriate interval in the length direction or width direction of the concentrated sludge when viewed from above, is raised and lowered from above with respect to the concentrated sludge. It is also possible to use devices that can.

[Example 1]
According to the flow shown in FIG. 3, the sludge collected from the manure treatment plant was dehydrated. Table 1 shows the properties of the sludge used as a sample. TS was measured according to JIS K 0101.

  For each 250 ml of sludge A and B shown in Table 1, an inorganic flocculant (polyferric sulfate) and a pH adjuster (sodium hydroxide) were added, and the first polymer flocculant adjusted to 2 g / L (“ Ebagulose LEB-250 "trade name (manufactured by Mizuing Co., Ltd.), amphoteric polymer flocculant, molecular weight 3 million) aqueous solution was added and stirred with a high-speed stirring device at a stirring speed of 11000 rpm (first stirring step). Next, a second polymer flocculant (“Ebagulose LEB-250” trade name (manufactured by Mizuing Co., Ltd.), amphoteric polymer flocculant, molecular weight 3 million) aqueous solution adjusted to 2 g / L with a slow stirring device. The mixture was added and stirred at a stirring speed of 150 rpm (second stirring step). The moisture content of the dewatered cake obtained by dewatering the sludge containing the aggregated floc obtained in the second stirring step with a screw press dehydrator was measured. Table 2 shows the addition amount of the inorganic flocculant, the pH adjuster, the first and second polymer flocculants, and the moisture content of the dehydrated cake.

  Since sludge A and B are excess sludge, when an inorganic flocculant is added, pH will fall and a polymer flocculant will not act. In this example, by adding a pH adjuster and increasing the pH of the sludge to the pH range where the polymer flocculant acts, the amount of inorganic flocculant added was increased and the flocculant action was able to be exhibited. . From Table 2, it can be seen that by adding the pH adjuster, the amount of the inorganic flocculant is increased and the dehydration rate can be reduced when the amount of the polymer flocculant added is the same.

[Example 2]
In accordance with the flow shown in FIG. 2, the sludge collected from the manure treatment plant was dehydrated. Table 3 shows the properties of the sludge used as a sample.

  The first polymer flocculant ("Ebagulose LEC-512" trade name (manufactured by Mizuing Co., Ltd.) was adjusted to 2 g / L by adding a pH adjuster (sulfuric acid) to each 250 ml of sludge C to E shown in Table 3. ), Cationic polymer flocculant, molecular weight 9 million) aqueous solution was added and stirred with a high-speed stirring device at a stirring speed of 11000 rpm (first stirring step). Next, a second polymer flocculant (“Ebagulose LEC-512” trade name (manufactured by Mizuing Co., Ltd.), cationic polymer flocculant, molecular weight 9 million) aqueous solution adjusted to 2 g / L with a slow stirring device Was added and stirred at a stirring speed of 150 rpm (second stirring step). The moisture content of the dewatered cake obtained by dewatering the sludge containing the aggregated floc obtained in the second stirring step with a belt press dehydrator was measured. Table 4 shows the addition amount of the pH adjuster, the first and second polymer flocculants, and the moisture content of the dehydrated cake.

  From Table 4, it can be seen that the addition amount of the polymer flocculant and the moisture content of the dehydrated cake can be reduced by the high-speed stirring and the addition of the pH adjusting agent.

[Example 3]
The anaerobic digested sludge collected from different wastewater treatment facilities was dehydrated according to the flow shown in FIG. Table 5 shows the properties of the sludge as a sample.

  To each 250 ml of sludge F to G shown in Table 5, a pH adjuster (sulfuric acid) is added, and the first polymer flocculant aqueous solution adjusted to a concentration of 10 g / L is added, and sludge and polymer flocculant are added by a high-speed stirrer. The solution was mixed and stirred for 10 seconds to prepare mixed sludge. Next, the second polymer flocculant aqueous solution adjusted to a concentration of 10 g / L is added to the mixed sludge, and the mixed sludge and polymer flocculant are mixed and stirred for 2 minutes with a slow agitator with a stirring speed of 150 rpm. Aggregated to form aggregated floc. Finally, the aggregated floc was dehydrated with a belt press dehydrator, and the moisture content (%) of the obtained dehydrated cake was measured.

  Table 6 shows the pH adjuster, the types of the first and second polymer flocculants (both are cationic polymer flocculants) and the amount added, and the moisture content of the dehydrated cake (when the stirring speed is 3000 rpm during high-speed stirring). .

  Table 7 shows the water content of the dehydrated cake when the stirring speed during high-speed stirring was changed.

[Reference Example 1]
After the first polymer flocculant solution is added to the sludge and the first stirring is performed, the second polymer flocculant solution is added and the second stirring is performed, and the obtained flocculent sludge is removed by a belt press dehydrator. Dehydrated to obtain a dehydrated cake.

Sludge T was used for the experiment. Sludge T is anaerobic digested sludge. The TS of the sludge T is 20.9 g / L.
As the polymer flocculant, polymer flocculants (q, r, s, t) having different molecular weights were used.
The polymer flocculants q, r, and t are cationic polymer flocculants, and the polymer flocculant s is an amphoteric polymer flocculant.
The molecular weights (viscosity mPa · s) of the polymer flocculants q, r, s, and t are 5 million (147 mPa · s), 6 million (225 mPa · s), 7 million (238 mPa · s), and 8 million (280 mPa, respectively). S).
The molecular weight described here is an average molecular weight determined by a viscosity method. The viscosity is a value measured by dissolving the polymer flocculant in water at 2 g / L and using a B-type viscometer at 25 ° C. and 60 rpm.
In the experiment, the same kind of both the first and second polymer flocculants were used, and the solutions of the first and second polymer flocculants were prepared at the same concentration.

The experimental procedure is as follows.
A predetermined amount of the first polymer flocculant solution (concentration 2 g / L) is added to 250 mL of sludge, and the sludge and polymer flocculant solution are mixed and stirred for 10 seconds with a high-speed stirrer with a stirring speed of 5000 rpm to prepare mixed sludge. did. Next, a predetermined amount of a second polymer flocculant solution (concentration 2 g / L) is added to the mixed sludge, and the mixed sludge and the polymer flocculant are mixed and stirred for 5 minutes by a stirrer with a stirring speed of 200 rpm, thereby aggregating the mixed sludge. And agglomerated flocs were formed. Finally, the aggregated floc was dehydrated with a belt press dehydrator to obtain a dehydrated cake, and the SS recovery rate was measured.

In the experiment, the total injection amount of the first and second polymer flocculant solutions was 40 mL, and the first polymer flocculant solution was added in a range of 2.5 to 37.5 mL.
The experimental results are shown in FIG.

FIG. 10 is a graph showing the relationship between the injection amount of the polymer flocculant added during high-speed stirring and the ratio of the average SS recovery rate when the polymer flocculants q, r, s, and t are used. In this figure, the ratio of the average SS recovery rate indicates the ratio when the average SS recovery rate is 100 when the injection amount of the first polymer flocculant is 59%.
From this result, SS was adjusted by adjusting the injection amount of the polymer flocculant added at the time of high-speed stirring to preferably 45 to 95%, more preferably 50 to 95%, still more preferably 55 to 90% of the total injection amount. It has been found that the recovery rate can be increased.

1: Sludge storage tank 2: First stirring device 3: Second stirring device 4: Dehydration device 5: First polymer flocculant addition means 6: Second polymer flocculant addition means 7: pH adjuster addition means 8: Concentration Apparatus 9: Inorganic flocculant addition means 20: Sludge concentrator 21: Sludge hopper 22: Sludge moving means 23: Water trapping means 24: Belt 25: Belt drive device 26: Sludge discharge port 27: Belt cleaning pipe 28: Addition Pressure device 28A: Pressure plate 30: Slit forming machine 31: Cutting blade

Claims (12)

A first stirring step of adding the first polymer flocculant to the sludge as an object to be treated and stirring at high speed;
A second agitation step of adding a second polymer flocculant and slowly stirring to form an agglomerate floc;
A dehydration step of dewatering the sludge containing the aggregated floc,
The pH of the sludge is measured in at least one of the first stirring step, the second stirring step, and the dehydrating step, and based on the measured pH value, the pH adjuster is added to at least one of the first stirring step, the second stirring step, and the dehydrating step. The sludge treatment method characterized by adding in.   The method according to claim 1, wherein the pH adjuster is added in the first stirring step.   The method according to claim 1 or 2, wherein the first polymer flocculant and the second polymer flocculant are the same polymer flocculant.   The sludge treatment method according to any one of claims 1 to 3, further comprising adding an inorganic flocculant in at least one of the second stirring step and the dehydrating step before the first stirring step.   The sludge treatment method according to any one of claims 1 to 4, further comprising a sludge concentration step of concentrating sludge containing aggregated floc before the dehydration step. A first stirrer that stirs and mixes the sludge and the first polymer flocculant;
A second agitation device that further mixes the second polymer flocculant with the sludge containing the first polymer flocculant mixed in the first agitation device, and forms an agglomerated floc by stirring slowly;
A dewatering device for dewatering sludge containing agglomerated floc formed by the second stirring device;
A sludge treatment apparatus comprising a pH meter for measuring the pH of sludge and a pH adjuster addition means for adding a pH adjuster based on the sludge pH value on the upstream side of the first stirring device. A first stirrer that stirs and mixes the sludge and the first polymer flocculant;
A second agitation device that further mixes the second polymer flocculant with the sludge containing the first polymer flocculant mixed in the first agitation device, and forms an agglomerated floc by stirring slowly;
A dewatering device for dewatering sludge containing agglomerated floc formed by the second stirring device;
A pH meter for measuring the pH of sludge and a pH adjuster addition means for adding a pH adjuster based on the pH value of the sludge to at least one of the first stirrer, the second stirrer, and the dehydrator And a sludge treatment apparatus.   The sludge treatment apparatus according to claim 7, wherein the first stirring apparatus includes a pH adjuster addition unit.   The sludge according to any one of claims 6 to 8, further comprising an inorganic flocculant adding means for adding an inorganic flocculant to at least one of the first stirrer, the second stirrer and the dehydrator. Processing equipment.   The sludge treatment apparatus according to any one of claims 6 to 9, further comprising a sludge concentrator for concentrating sludge containing aggregated floc between the second agitator and the dehydrator.   The sludge concentrating device comprises a sludge charging hopper, sludge moving means, pressurizing means provided above the sludge moving means, and water collecting means provided below the sludge moving means. The sludge treatment apparatus according to claim 10, wherein   12. The sludge treatment apparatus according to claim 11, wherein the sludge squeezing apparatus further includes a slit forming machine at a sludge discharge port of the sludge moving means.