JP2020151672A - Treatment method and apparatus for waste water containing calcium - Google Patents

Abstract

To provide a treatment method and a treatment apparatus which enable stable treatment operations of treatment by eliminating waste of added amount of chemicals and eliminating defects of the conventional technology to prevent scale formation and adhesion which are in question in a treatment of raw water containing calcium such as leachate.SOLUTION: A treatment apparatus for waste water containing calcium includes a conditioning tank 1 in which a scale inhibitor is added to calcium-containing wastewater to homogenize, scale inhibitor feeding means 6 and 61 connected to the conditioning tank 1, a mixing tank 2 in which a carbonate is added to the adjusted waste water to produce calcium carbonate, a flocculation tank 3 in which a flocculant is added to the waste water containing calcium carbonate and produce coagulation flock, a dehydrator 4 which dehydrates waste water containing coagulation flock, a neutralization tank 5 which neutralizes the dehydrated filtrate produced by the dehydration process, and a line 35 which feeds waste water containing coagulation flock directly from the coagulation tank 3 to the dehydrator 4. The apparatus does not include a solid-liquid separator such as a setting tank and a membrane separator which were essential in conventional treatment apparatus and a sludge storage tank which stores separated sludge prior to dehydration.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method and a treatment device for treating calcium-containing wastewater such as leachate generated at a controlled final disposal site.

In general, of the waste generated in industry and general life, waste that cannot be reused or recycled is landfilled at a final disposal site such as a controlled final disposal site. At the controlled final disposal site, organic waste such as garbage was often landfilled directly, but there are environmental hygiene issues such as the breeding of flies, rats and crows, and combustible gas is generated due to the decomposition of organic matter. In recent years, incineration ash and incineration flying ash that have undergone incineration have been mainly landfilled due to safety issues such as the problem of reducing the amount of waste carried in to prolong the life of landfill sites. Since acidic components such as SO _X , NO _X , and HCl that can be contained in the exhaust gas discharged from the incineration facility cause acid rain, the incineration facility sprays alkaline slaked lime powder on the flue to neutralize and remove it. are doing. Therefore, since the incinerated fly ash contains a large amount of calcium salt and unreacted slaked lime, the leachate generated at the controlled final disposal site also has a high calcium concentration and a high pH, which is the leachate. It is a cause of scale adhesion failure in piping, pumps, biological treatment tanks, etc. of treatment facilities.

The purpose and function of the leachate treatment facility is to treat the leachate collected by the leachate collection and drainage facility in the landfill so as not to contaminate the public water area and groundwater at the discharge destination. The quality of leachate is high at the beginning of landfill, but not only becomes low over time, but also fluctuates greatly depending on the amount of precipitation, so maintenance is important for stable treatment.

The conventional leachate treatment flow is shown in FIG. The leachate (raw water) is homogenized in the adjusting tank 10 and then sent to the mixing tank 20, so sodium carbonate is added to generate calcium carbonate, an alkaline agent and a coagulant are added, and then the coagulating tank 30 is added. After being sent to the settling tank 40 and solidified by adding a polymer flocculant, the sludge containing calcium carbonate is solid-liquid separated, and the supernatant whose calcium concentration is reduced is the neutralization tank 50. After being neutralized by adding acid or alkali, it is subjected to post-treatment such as biological treatment, coagulation-precipitation treatment, advanced treatment equipment, and desalting treatment. The solid-liquid separated sludge containing calcium carbonate is sent to the sludge storage tank 60 and then subjected to dehydration treatment in the dehydrator 70 for a certain period of the day to prepare a dehydrated cake containing calcium carbonate and a dehydrated filtrate. The dehydrated filtrate having been separated into the water and having a reduced calcium concentration is returned to the adjusting tank 10.

Since the amount of the chemical added to the mixing tank 20, the coagulation tank 30, and the neutralization tank 50 depends on the concentration of calcium contained in the leaching water, it is difficult to adjust and the chemical cost is high. In addition, the properties of the raw water and the dehydrated filtrate are significantly different, and in particular, the calcium concentration in the raw water is diluted by adding the dehydrated filtrate, so there are times when the dehydrated filtrate is returned to the adjusting tank 10 and times when it is not returned. The properties of raw water will fluctuate greatly. As described above, since the amount of the drug added depends on the calcium concentration, it becomes more difficult to adjust the amount of the drug added, which not only increases the drug cost but also makes the treatment unstable. Further, there are many necessary facilities such as a adjusting tank, a mixing tank, a coagulation tank, a settling tank, a neutralization tank, a sludge storage tank and a dehydrator, and there is a problem that the scale of the equipment becomes large because the settling tank is large.

In the treatment of raw water containing calcium such as leachate, the generation of scale derived from calcium in the raw water and the adhesion to the inner wall of the facility become problems. In order to prevent scale formation and adhesion, it is allowed to flow into a fluid bed type crystallization reaction tank filled with pellets of calcium carbonate having an average particle size of 0.5 mm, and in the crystallization reaction tank, 0.1 mol / mol / mol of sodium carbonate as an alkaline agent. By adding L and circulating 4 times the amount of inflow water, treatment is performed at a flow rate of 100 m ³ / m ² / hr in the tank, and biological treatment, acidic aggregation treatment, filtration treatment, activated carbon treatment, and sterilization treatment are performed in the subsequent stage. As a result, the calcium concentration of the final treated water became 20 mg / L, and a technique was reported in which the problem of clogging of the sludge extraction pipe of the coagulation sedimentation tank and clogging of the sludge transfer pipe and pumps was solved (Patent Documents). 1). However, this report does not show that the calcium concentration in the raw water is as low as 100 mg / L, and that the same effect can be obtained in the recent treatment of leachate containing a high concentration of calcium. In addition, when applied to the treatment of leachate containing a high concentration of calcium, it is difficult to stably generate crystals by using the calcium carbonate crystallization method, and the amount of chemicals added may be large. The problem of high drug costs, which is expected, cannot be solved.

Calcium carbonate roots are added to raw water containing 50 to 2000 mg / L of calcium and magnesium, respectively, to precipitate calcium carbonate and magnesium hydroxide under alkaline conditions of pH 11 or higher, and a reaction solution containing the precipitate is placed in a circulation tank. Upon receipt, the effluent from the circulation tank is solid-liquid separated by a microfiltration membrane separation device, and a part of the concentrated water of the microfiltration membrane separation device is returned to the reaction tank as circulating water and mixed with raw water for processing. A processing method for returning the balance to the circulation tank has been proposed (Patent Document 2). However, since a part of the concentrated water is mixed with the raw water as circulating water for treatment, the calcium concentration in the raw water fluctuates, it is difficult to adjust the amount of the drug added, and the problem that the treatment becomes unstable cannot be solved.

Japanese Unexamined Patent Publication No. 2001-47062 Japanese Patent No. 5906892

The present invention eliminates the drawbacks of the prior art that prevents scale formation and adhesion, which is a problem in the treatment of calcium-containing raw water such as leachate, reduces waste of the amount of chemicals added, and enables stable treatment operation. It is an object of the present invention to provide a processing method and a processing apparatus.

The present invention provides a high concentration of calcium without returning the solid-liquid separation and dehydration filtrate using the settling tank or microfiltration membrane separator used in the conventional treatment method and treatment device and mixing with raw water. It is characterized in that the raw water contained therein is aggregated, directly dehydrated, the dehydrated filtrate is neutralized, and then subjected to the subsequent treatment.

Specific embodiments of the present invention are as follows.
[1] A step of adding a scale inhibitor to the wastewater containing calcium to homogenize the wastewater.
The process of adding carbonate to the wastewater after the homogenization treatment to generate calcium carbonate,
A process of adding a coagulant to the wastewater after calcium carbonate is generated to generate coagulated flocs,
A step of directly dehydrating wastewater containing agglomerated flocs without solid-liquid separation to obtain a dehydrated cake containing calcium carbonate and a dehydrated filtrate.
The step of neutralizing the dehydrated filtrate and
A method for treating calcium-containing wastewater, which comprises.
[2] The feature is that when a flocculant is added to the wastewater after calcium carbonate formation and / or before the wastewater containing the aggregated flocs is dehydrated, an antiscale agent is additionally added to the wastewater. The method for treating calcium-containing wastewater according to the above [1].
[3] The method for treating calcium-containing wastewater according to the above [1] or [2], wherein the scale inhibitor contains a (meth) acrylic polymer.
[4] An adjusting tank that adds a scale inhibitor to wastewater containing calcium to homogenize it.
The anti-scale agent supply means connected to the adjustment tank,
A mixing tank that adds carbonate to the adjusted wastewater to generate calcium carbonate,
A coagulation tank that produces coagulation flocs by adding a coagulant to wastewater containing calcium carbonate,
A dehydrator that directly dehydrates wastewater containing aggregated flocs without solid-liquid separation.
A neutralization tank that neutralizes the dehydrated filtrate obtained by the dehydration treatment,
A line that directly sends wastewater containing coagulated flocs from the coagulation tank to the dehydrator,
A calcium-containing wastewater treatment apparatus comprising the above.
[5] The antiscale agent supply means connected to a line for directly sending wastewater containing the agglomerated flocs from the mixing tank and / or the coagulation tank to the dehydrator is further provided. 5] The calcium-containing wastewater treatment apparatus according to.
[6] The calcium-containing wastewater treatment apparatus according to the above [4] or [5], wherein the dehydrator includes a vibrometer for detecting a change in vibration during the dehydration treatment.

According to the present invention, the entire amount of calcium-containing wastewater (hereinafter, also referred to as “raw water”) to be treated is subjected to dehydration treatment without precipitation separation, and the entire amount is treated in the subsequent stage without returning the dehydrated filtrate to raw water. The properties of the raw water are stable, an appropriate amount of chemicals can be added, and stable treatment is possible.

Further, since the processing apparatus of the present invention does not use a solid-liquid separation apparatus such as a conventional settling separation tank or a microfiltration membrane apparatus, the entire apparatus can be miniaturized.

It is the schematic explanatory drawing of the processing apparatus which carries out the processing method of this invention. It is the schematic explanatory drawing of the processing apparatus which carries out the conventional processing method.

Preferred embodiment

The present invention will be described in detail with reference to the accompanying drawings.
FIG. 1 is a schematic explanatory view of a processing apparatus for carrying out the processing method of the present invention. The treatment apparatus shown in FIG. 1 includes an adjusting tank 1 for homogenizing the wastewater containing calcium by adding an anti-scale agent, and anti-scale agent supplying means 6 and 61 connected to the adjusting tank 1, after adjustment. The mixing tank 2 that adds carbonate to the wastewater to generate calcium carbonate, the coagulation tank 3 that adds a coagulant to the wastewater containing calcium carbonate to generate coagulated flocs, and the wastewater containing coagulated flocs are dehydrated. It includes a dehydrator 4, a neutralizing tank 5 for neutralizing the dehydrated filtrate obtained by the dehydration treatment, and a line 35 for directly sending wastewater containing agglomerated flocs from the coagulation tank 3 to the dehydrator 4. It does not include solid-liquid separation equipment such as settling tanks and membrane separation equipment, which were indispensable in the equipment, and sludge storage tanks that store solid-liquid separated sludge before dehydration.

In the processing apparatus shown in FIG. 1, the scale inhibitor supply means 6 supplies the scale inhibitor to the mixing tank 2, the scale inhibitor supply means 62, and the scale inhibitor to the aggregated flocs in the line 35. Although the supply means 63 is included, these may not be added depending on the properties of the calcium-containing wastewater.

In the processing apparatus shown in FIG. 1, a vibration meter 7 is provided in the dehydrator 4. The vibrometer 7 is connected to a control means (not shown) that stops the operation of the dehydrator 4 when it detects an abnormal vibration of the dehydrator 4 that occurs when the load of the dehydrator 4 becomes too large due to scale generation or the like. Is preferable. In the present invention, although scale generation is suppressed, it is inevitable that scale is generated by long-term operation. Therefore, a vibrometer 7 is provided in the dehydrator 4, and normal operation or abnormal operation is determined based on the vibration of the dehydrator 4, and maintenance such as scale removal and adjustment of injection conditions of the scale inhibitor is performed. Abnormal vibration can be discriminated by relative comparison with normal vibration using general factors such as acceleration (m / s ² ), velocity (mm / s), and displacement (μmP-P).

In the treatment apparatus shown in FIG. 1, the scale inhibitor is added to the calcium-containing wastewater in the adjusting tank 1 from the scale inhibitor supply means 6 and 61 to perform a uniform treatment. The wastewater after the homogenization treatment is sent to the mixing tank 2, and carbonate is added to generate calcium carbonate. An alkali may be added to the mixing tank 2 for pH adjustment, or an inorganic flocculant may be added to the mixing tank 2. Further, the scale inhibitor may be added to the drainage in the mixing tank 2 via the scale inhibitor supply means 62. The wastewater after calcium carbonate is produced is sent to the coagulation tank 3, and a coagulant is added to generate coagulated flocs. The flocculant added to the flocculation tank 3 is preferably a polymer flocculant. The wastewater containing the coagulated flocs is directly sent from the coagulation tank 3 to the dehydrator 4 via the line 35 and dehydrated by the dehydrator 4, to obtain a dehydrated cake containing calcium carbonate and a dehydrated filtrate. The anti-scale agent may be added to the waste water containing the agglomerated flocs immediately before being sent to the dehydrator 4 in the line 35 via the anti-scale agent supply means 63. The dehydrated filtrate is sent to the neutralization tank 5, and an acid or alkali is added to neutralize the filtrate. The treated water after the neutralization treatment is subjected to post-treatment such as biological treatment, coagulation sedimentation treatment, sand filtration, membrane treatment, desalting treatment, etc., and then discharged into public water areas. In the treatment method of the present invention, solid-liquid separation before dehydrating the aggregated flocs, which is required in the conventional method, is not performed, and the entire amount of wastewater containing the aggregated flocs is dehydrated without generating a separation liquid. Unlike the conventional method, the dehydrated filtrate is not returned to the adjusting tank to dilute the raw water, and the properties of the raw water do not fluctuate much.

By adding an anti-scale agent, the scale formed from calcium carbonate is maintained in a softened state and adheres to the mixing tank 2, the coagulation tank 3, the dehydrator 4, and the inner wall of the piping between them. To prevent this, the scale in the wastewater containing the aggregated flocs to be subjected to the dehydration treatment can be taken into the dehydrated cake and discharged from the dehydrator. Depending on the calcium concentration in the wastewater, it is preferable to add the anti-scale agent not only in the adjusting tank 1 but also in the mixing tank 2 and in the line 5 immediately before the dehydrator 4.

The anti-scale agent is an agent that produces scale to prevent it from adhering to dehydrators and pipes. Among them, a "scale softening agent" that softens the generated scale and prevents it from adhering to equipment is particularly preferable. Can be used. As the scale softening agent, a (meth) acrylic acid-based polymer can be preferably used. The molecular weight of the (meth) acrylic acid-based polymer is not particularly limited, but it is desirable that the (meth) acrylic acid-based polymer has a relatively low molecular weight, for example, a weight average molecular weight of 2000 to 12000, preferably about 3000 to 9000. Examples of the (meth) acrylic acid-based polymer include polyacrylic acid, polymethacrylic acid, (meth) acrylic acid-maleic acid copolymer, (meth) acrylic acid-sulfonic acid-based monomer copolymer, and acrylic acid-methacrylic acid. Preferred examples thereof include polymers, (meth) acrylic acid-hydroxyaryloxypropanesulfonic acid copolymers, and salts thereof (sodium salt, potassium salt, etc.). (Meta) Acrylic acid-sulfonic acid-based monomer The sulfonic acid-based monomer (sulfonic acid group-containing monomer) of the copolymer includes 2-acrylamide-2-methylpropanesulfonic acid, metharylsulfonic acid, styrenesulfonic acid, and allylsulfone. Acid, vinyl sulfonic acid, 2-hydroxy-3-allyloxy-1-propanesulfonic acid, 2-hydroxy-3-butenesulfonic acid, 2-hydroxyethylmethacrylate (HEMA), bis (poly-2-carboxyethyl) phosphon Examples thereof include acids, nitrilotrimethylenephosphonic acid (NTMP), hydroxyethylidene disulfonic acid (HEDP), ethylenediaminetetramethylenephosphonic acid (EDTP) and the like. Among these, sodium polyacrylate, potassium polyacrylate, sodium polymethacrylate, potassium polymethacrylate, sodium salt or potassium salt of acrylic acid-methacrylic acid copolymer, sodium salt of acrylic acid-maleic acid copolymer. Alternatively, sodium salts or potassium salts of potassium, acrylic acid-sulfonic acid-based monomer copolymers are particularly preferable. These scale softeners can be used alone or in any combination of two or more.

Further, the scale softening agent is an acrylic acid-based two-component system containing polyacrylamide and its hydrolyzate, maleic acid-based polymer, itaconic acid-based polymer, acrylamide-2-methylpropanesulfonic acid, isoprene sulfonic acid and the like. Includes copolymers or three-component copolymers, iron salts such as ferric chloride and ferric sulfate (polyiron), and inorganic salts such as aluminum salts such as aluminum sulfate and polyaluminum chloride (PAC). Is preferable. Specifically, a combination of a (meth) acrylic acid-sulfonic acid-based monomer copolymer and an iron salt, a combination of sodium polyacrylate and an iron salt, and a combination of sodium polyacrylate and an aluminum salt are preferable.

The amount of the anti-scale agent added can be appropriately set according to the calcium concentration and the salt concentration of the wastewater, but when the wastewater contains 1000 mg / L of calcium, 10 to 1000 mg / L, preferably 10 to 500 mg / L. It is desirable to add L, more preferably 10 to 300 mg / L of anti-scale agent (in the case of containing an inorganic salt or other polymer-based anti-scale agent, the total amount including these). When an inorganic salt is used in combination, 100 to 200 parts by mass, preferably 130 to 190 parts by mass, and more preferably 150 to 180 parts by mass of the inorganic salt is used with respect to 100 parts by mass of the (meth) acrylic acid-based polymer. It is desirable to add.

As the carbonate added in the mixing tank 2, any carbonate that can form calcium carbonate by substitution with calcium may be used, and for example, sodium carbonate, potassium carbonate and the like can be used.

The coagulant added in the mixing tank 2 is preferably an inorganic coagulant, for example, iron salts such as ferric chloride and ferric polysulfate (polyiron), and aluminum such as aluminum sulfate and polyaluminum chloride (PAC). Salt and the like can be preferably used.

The alkali added in the mixing tank 2 is a pH adjuster. Calcium ions in the wastewater may be precipitated as calcium carbonate, and the alkaline component and the amount added may be adjusted so that the pH of the inorganic flocculant can be adjusted to 8 to 11 at which the coagulant can exert the coagulation action. As the pH adjuster, for example, sodium hydroxide, potassium hydroxide and the like can be preferably used.

As the flocculant added in the coagulation tank 3, a polymer flocculant is preferable, and for example, one or more of a cationic polymer flocculant, an anionic polymer flocculant, and an amphoteric polymer flocculant are optionally used. Can be used in combination.

As the dehydrator, a general dehydrator used for the dehydration treatment can be used without limitation, and examples thereof include a centrifuge type dehydrator, a belt press type dehydrator, and a screw press type dehydrator.

The dehydrated cake after the dehydration treatment contains precipitated calcium carbonate. Since the dehydrated filtrate contains almost no calcium carbonate that causes scale formation, scale is hardly formed in the post-treatment equipment after the neutralization tank 5. According to the present invention, calcium contained in wastewater can be almost completely removed by the dehydration treatment, and therefore, after the neutralization treatment, general post-treatment such as biological treatment, coagulation sedimentation treatment, sand filtration, membrane treatment, and desalting treatment is performed. Processing can be performed without limitation. In particular, in the method of the present invention, the SS content in the dehydration filtrate may be higher than that of the treated water by the coagulation sedimentation method, so the post-treatment equipment has a solid-liquid separation function (solid-liquid separation function) capable of removing these. It is desirable to have at least one biological treatment, coagulation sedimentation treatment, sand filtration, membrane treatment, etc.).

According to the treatment method and treatment apparatus of the present invention, the calcium concentration is 100 mg / L or more and 6000 mg / L or less, preferably 500 mg / L or more and 3000 mg / L or less, and more preferably 1000 mg / L or more and 3000 mg / L or less. The contained wastewater can be treated stably.

Claims (6)

A process of adding a scale inhibitor to the wastewater containing calcium to homogenize it,
The process of adding carbonate to the wastewater after the homogenization treatment to generate calcium carbonate,
A process of adding a coagulant to the wastewater after calcium carbonate is generated to generate coagulated flocs,
A step of directly dehydrating wastewater containing agglomerated flocs without solid-liquid separation to obtain a dehydrated cake containing calcium carbonate and a dehydrated filtrate.
The step of neutralizing the dehydrated filtrate and
A method for treating calcium-containing wastewater, which comprises. A claim comprising adding an anti-scale agent to the wastewater after adding the coagulant to the wastewater after calcium carbonate formation and / or before dehydrating the wastewater containing the aggregated flocs. The method for treating calcium-containing wastewater according to 1. The method for treating calcium-containing wastewater according to claim 1 or 2, wherein the anti-scale agent contains a (meth) acrylic polymer. A regulating tank that adds a scale inhibitor to the wastewater containing calcium to homogenize it.
The anti-scale agent supply means connected to the adjustment tank,
A mixing tank that adds carbonate to the adjusted wastewater to generate calcium carbonate,
A coagulation tank that produces coagulation flocs by adding a coagulant to wastewater containing calcium carbonate,
A dehydrator that directly dehydrates wastewater containing aggregated flocs without solid-liquid separation.
A neutralization tank that neutralizes the dehydrated filtrate obtained by the dehydration treatment,
A line that directly sends wastewater containing coagulated flocs from the coagulation tank to the dehydrator,
A calcium-containing wastewater treatment apparatus comprising the above. 5. The fifth aspect of the present invention is further comprising an antiscale agent supply means connected to a line for directly sending wastewater containing the agglomerated flocs from the mixing tank and / or the coagulating tank to the dehydrator. Calcium-containing wastewater treatment equipment. The calcium-containing wastewater treatment apparatus according to claim 4 or 5, wherein the dehydrator includes a vibrometer for detecting a change in vibration during the dehydration treatment.

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