JP5660461B2 - Wastewater treatment method and treatment apparatus using membrane separation - Google Patents

Description

  The present invention relates to a wastewater treatment method and treatment apparatus using membrane separation.

  In the treatment of various wastewaters, removal of suspended solids in the wastewater (hereinafter also referred to as “SS” in the present specification) is performed, and sand filtration is generally widely used as a removal device. It has been. However, it is difficult to efficiently remove fine SS by sand filtration, and it is necessary to use a large-scale device or a plurality of sand filtration devices in order to increase the removal rate.

  In addition, as a method of removing such SS, by using a conventional membrane separation apparatus equipped with a microfiltration membrane, it becomes possible to separate SS that cannot be efficiently removed by sand filtration with high efficiency. ing. However, if organic matter is contained in the wastewater to be treated, a so-called fouling phenomenon occurs in which the organic matter etc. clogs the microfiltration membrane, reducing the amount of treated water that can be treated by the membrane separator. The problem arises. In particular, when the coagulation / precipitation treatment is performed on the upstream side of the membrane separation apparatus, the organic component contained in the coagulant to be added causes the fouling phenomenon to occur more easily.

  Conventionally, as a countermeasure against such fouling, for example, as described in Patent Document 1 and Patent Document 2 below, the membrane separation device is back-washed, washed with a chemical solution, or the type of chemical solution is changed. Measures such as various selections are being considered.

JP 2005-169238 A JP 2006-255526 A

  However, the conventional anti-fouling techniques as described above are not complicated in any method, and a more effective and simple method is required.

  The present invention has been made in view of the above-described problems of the prior art, and is a wastewater that can more easily suppress fouling of the membrane separation apparatus while efficiently removing SS by membrane separation. An object is to provide a processing method and a processing apparatus.

In view of the problems as described above, the wastewater treatment method using membrane separation according to the present invention is a wastewater treatment method including a membrane separation step for membrane separation of suspended solids in wastewater, and the membrane separation step An electrolysis process for electrolyzing a treatment liquid containing a chlorine component in wastewater to be treated on the upstream side of the process, and release of treated water electrolyzed in the electrolysis process between the electrolysis process and the membrane separation process A concentration measurement step for measuring the chlorine concentration, and adjusting the applied voltage in the electrolysis step based on the value of the free chlorine concentration measured in the concentration measurement step, thereby allowing the treatment liquid flowing into the membrane separation step The free chlorine concentration is controlled in the range of 50 to 500 mg / L.

  In the treatment method according to the present invention, preferably, hypochlorite is added to the treatment liquid on the upstream side of the membrane separation step, the amount of the hypochlorite added is adjusted, and the applied voltage is adjusted. The free chlorine concentration is controlled within the above range.

Furthermore, the wastewater treatment apparatus using membrane separation according to the present invention is a wastewater treatment apparatus provided with a membrane separation apparatus for membrane separation of suspended solids in wastewater, and is treated on the upstream side of the membrane separation apparatus. An electrolysis apparatus that electrolyzes a treatment liquid containing a chlorine component in the wastewater, a concentration measurement apparatus that measures a value of free chlorine concentration of the treatment liquid treated by the electrolysis apparatus, and a concentration measurement apparatus based on the concentration of free chlorine that, the free chlorine concentration in the processing solution flows into the membrane separation device and a control device that adjusts the voltage applied by the electrolyzer to be in the range of 50 to 500 mg / L It is characterized by.

  The treatment apparatus according to the present invention preferably includes a hypochlorite addition device for adding hypochlorite to the treatment liquid on the upstream side of the membrane separator, and the control device comprises hypochlorous acid. The free chlorine concentration is controlled to be within the above range by adjusting the amount of salt added and the applied voltage.

  According to the wastewater treatment method and treatment apparatus using membrane separation according to the present invention, the concentration of free chlorine is set to the above range by electrolyzing the wastewater in a state where the chlorine component is contained. As a result, the amount of organic matter adhering to the membrane of the membrane separator can be reduced, and the fouling phenomenon can be suppressed more easily than in the past. Further, by providing an electrolysis step, it is possible to deposit a metal such as thallium (TI) dissolved in the waste water as an oxide, and it is possible to simultaneously remove heavy metals from the waste water.

  Further, according to the above preferred embodiment of the present invention, since the concentration of hypochlorous acid is controlled by adding hypochlorous acid in addition to electrolysis, the control of the free chlorine concentration is further facilitated. There is an effect of becoming.

  As described above, according to the wastewater treatment method and treatment apparatus using membrane separation according to the present invention, it is possible to efficiently remove SS in the wastewater by membrane separation, and at the same time, It is also possible to suppress fouling.

It is the figure which showed typically the processing apparatus which enforces the processing method of the waste_water | drain using the membrane separation of this invention.

  Hereinafter, a wastewater treatment method and treatment apparatus using membrane separation, which is an embodiment of the present invention, will be described with reference to the drawings. FIG. 1 is a diagram schematically showing a wastewater treatment apparatus using membrane separation according to the present embodiment. The treatment apparatus of this embodiment is applied when desalted dust discharged in a cement production facility is received as chlorine-containing waste D, and the desalted treated product is used as a cement raw material.

  Specifically, the treatment apparatus includes a dissolution tank 1 in which water W is added to a chlorine-containing desalted waste D to fluidize the waste D to dissolve chlorine, and a slurry generated in the dissolution tank 1. Filter device 2 that separates S1 into solid cake C2 and filtrate F2 used as a cement raw material by solid-liquid separation, adjusts the filtrate F2 from the filter device 2 to pH 5-6, and adds a reducing agent to add selenium. Reducing agent by adjusting the reaction tank 3 to be precipitated, the coagulating tank 4 for precipitating selenium from the slurry S3 containing selenium discharged and precipitated from the reaction tank 3, and the supernatant liquid F4 from the coagulating tank 24 to pH 9-10. And a reaction tank 5 for precipitating heavy metals, and a coagulation tank 6 for adding a polymer flocculant F to the slurry S5 discharged from the reaction tank 5 and containing heavy metal precipitates to agglomerate heavy metals and sediment flocs. The floc and said The precipitate produced in the collection tank 4 is separated into a solid cake C7 as a cement raw material and separated into a supernatant liquid F7 to be circulated to the reaction tank 25, and a supernatant F6 from the coagulation tank 6 An electrolytic bath 8 for applying a direct current to the electrode to deposit metal oxide by electrolysis, and a slurry S8 containing the metal oxide produced in the electrolytic bath 8 are filtered by solid-liquid separation and circulated in the agglomeration tank 6 A filtration apparatus 10 that separates the solid content M10 into a filtrate F10 and an activated carbon adsorption tower 11 that filters the filtrate F10 again are provided.

  Specifically, the wastewater treatment method according to the embodiment using the treatment apparatus having such a configuration dissolves chlorine by adding water W to the chlorine-containing waste D and fluidizing the waste D. The slurry S1 was filtered, and the slurry S1 was filtered to perform solid-liquid separation into a filtrate F2 and a solid cake C2, and the filtrate F2 was adjusted to pH 5-6 and a reducing agent was added to precipitate selenium. The selenium removal step of aggregating the precipitated selenium-containing slurry S3 to settle and separate the selenium-containing material S4, and adjusting the supernatant liquid F4 separated in the selenium removal step to pH 9 to 10 and adding a reducing agent A heavy metal removing step of depositing heavy metal, adding a polymer flocculant F to the slurry S5 containing the heavy metal precipitate to agglomerate and settle flocs containing heavy metal, and containing selenium separated in the selenium removing step The fallout S4 and the floc S6 coagulated and settled in the heavy metal removal step are separated into a solid cake C7 and a supernatant F7 as a cement raw material, and the separated supernatant F7 is returned to the heavy metal removal step. A solid-liquid separation step, an electrolysis step in which a direct current is applied to the supernatant F6 separated in the heavy metal agglomeration step for electrolysis to deposit a metal oxide, and a metal oxide produced in the electrolysis step is included. A membrane separation step of filtering the slurry S8 to separate it into a filtrate F10 and a solid content M10, and an activated carbon treatment step of treating the filtrate F10 with activated carbon and discharging it.

  In this method, the desalted dust which is chlorine-containing waste D is discharged as solid cakes C2 and C7 and used as a cement raw material.

Hereinafter, each step will be described more specifically.
(Washing / filtration process)
In the water washing / filtration step, desalted dust that is chlorine-containing waste D is put into the dissolution tank 1, and water W is added to the extent that the desalted dust is fluidized and stirred to form a slurry. Soluble components such as chlorine compounds contained in the desalted dust are eluted and repulped. The amount of water W to be added is preferably 2 to 10 times the amount of demineralized dust D, and as the water W, secondary water discharged from industrial water, manufacturing processes, etc. or waterworks Etc. are used. When the amount of water added is 2 to 10 times the chlorine-containing waste D, soluble components in the chlorine-containing waste D are sufficiently eluted to reduce the chlorine components remaining in the desalted cake C2. And the slurry can have a viscosity that is easy to pump.

  In said repulp, in order to raise the melt | dissolution rate of a soluble component, you may raise the temperature in the dissolution tank 1 to 40 degreeC or more. The stirring time is preferably within 10 hours.

Further, in the water washing / filtering step, the slurry S21 produced by repulping is put into the filter 22 and pressed to perform solid-liquid separation to separate the dehydrated cake C2 and the filtrate F2. As the filter 2, a filter press or a belt filter is used.
Further, if necessary, water W may be introduced into the filter 2 to wash away soluble components remaining in the solid content C2. The water W used for washing is preferably 0.5 to 2.0 times the amount of waste to be subjected to desalting washing.

  The obtained dewatered cake C2 is effectively used as a cement raw material. Specifically, the solid content C2 is sent directly to the cement production facility, mixed with other cement raw materials, then supplied to the cement firing process as a powder cement raw material through steps such as drying and grinding, and fired as a cement clinker The

(Selenium removal process)
In the filtrate F2 discharged from the filter 2, chlorine in the desalted dust D is eluted, and selenium, heavy metals and the like are contained. Therefore, in the selenium removal step, selenium contained in the filtrate F2 is selectively removed. Specifically, first, the filtrate F2 is sent to the reaction tank 3, and the pH adjuster A1 is added to the filtrate F2 to adjust the pH to about 5-6. As the pH adjuster A1, inorganic acids such as carbonic acid, hydrochloric acid, nitric acid, and sulfuric acid are preferably used.

In the reaction vessel 3, the pH adjusting agent A1 is added to adjust the pH to the above range, and a reducing agent A2 such as iron powder or ferrous chloride is further added to the filtrate F2 in the reaction vessel 3, A slurry S3 is obtained by stirring and mixing.
When the pH of the filtrate F2 is in the above range, when a reducing agent A2 such as iron powder or ferrous chloride is added, a reduction reaction of selenium occurs, and selenium can be precipitated and removed.

  The addition amount of the reducing agent A2 such as iron powder or ferrous chloride may be an amount capable of reducing and precipitating selenium contained in the filtrate F2, and is, for example, 0.5% by mass relative to the filtrate F2. The content is preferably 4% by mass or less and more preferably 1% by mass or more and 2% by mass or less. The slurry S3 may be heated, and the temperature during the heating is preferably 45 ° C to 60 ° C.

  In the selenium removal step, selenium is reduced and precipitated by a reducing agent A2 such as iron powder or ferrous chloride, while iron powder or ferrous chloride is partially ionized by selenium and slurried as ferric ions. It will elute during S3.

(Heavy metal removal process)
In the supernatant liquid F4 separated in the coagulation tank 4, the chlorine in the desalted dust D is eluted, and also contains heavy metals and the like. Therefore, the pH adjusting agent B1 is added to the supernatant liquid F4, and the polymer flocculant F is further added to precipitate heavy metals contained in the supernatant liquid F4, and the precipitate is separated by filtration.

Specifically, the supernatant liquid F4 of the coagulation tank 4 is transferred to the reaction tank 5, and a reducing agent B2 such as ferrous sulfate (FeSO ₄ ) or ferrous chloride (FeCl ₂ ) is added to the supernatant liquid F4. And react to form slurry S5.

  For example, heavy metals can be efficiently removed by precipitating heavy metal hydroxide by setting the pH of the supernatant liquid F4 to about 9 to 10.5. As pH adjuster B1 used in this case, what is necessary is just alkaline, and NaOH is especially preferable.

  Next, in the agglomeration tank 6, by adding the polymer flocculant F to the slurry S5 from the reaction tank 5, the heavy metal in the slurry S5, the heavy metal finely divided, or the heavy metal of hydroxide is agglomerated and settled. Let

(Solid-liquid separation process)
The precipitate S6 in the agglomeration tank 6 and the precipitate S4 in the agglomeration tank 4 are solid-liquid separated using, for example, a filter 7 such as a filter press and discharged as a dehydrated cake C7. Here, if necessary, water may be introduced into the filter 7 and the precipitate may be washed with water.

  The dewatered cake C7 obtained by the filtration device 7 can be effectively used as a cement raw material. The usage method is the same as the dehydrated cake C2 obtained by the water washing / filtration process. In addition, the dewatered cake C7 obtained by the filtration device 7 can be repeatedly used as a part of iron powder or the like added to the slurry of the reaction tank 3, and the filtrate F7 is circulated to the reaction tank 5. Can be used.

(Electrolysis process)
The supernatant water F6 discharged from the coagulation tank 6 is sent to the electrolysis tank 8 and is energized through the electrodes of the electrolysis tank 8 to be electrolyzed. By electrolyzing the supernatant liquid F6, the metal dissolved in the supernatant liquid F6 can be precipitated as an oxide and changed into a fine suspended substance. In the electrolysis step, it is preferable to add sodium hypochlorite G as shown in FIG. By adding sodium hypochlorite, the precipitation reaction of the dissolved metal by the electrolysis can be promoted, and the fouling phenomenon in the subsequent membrane separation step can be easily suppressed.

  When the metal dissolved in the supernatant water F26 is thallium (Tl), the thallium can be removed by providing a thallium treatment step because it is easily suspended in the electrolysis step. Specifically, the slurry S8 containing the suspended matter generated in the electrolytic cell 8 is allowed to stand in a decanter 9, and the suspended matter is settled to recover thallium (Tl). When a thiosulfate such as sodium thiosulfate is added to the decanter 9, excess sodium hypochlorite is removed, and thallium can be recovered.

(Membrane separation process)
The treatment liquid F8 containing the suspended substance from the electrolytic cell 28 is sent to the membrane separation apparatus 10, and the fine suspended substance containing the metal oxide is removed by membrane separation. Examples of the membrane separation device 10 include a membrane filtration device using a membrane such as a microfiltration (MF) membrane and an ultrafiltration (UF) membrane.
The filtrate F10 treated by the membrane separation step has a suspended suspended solids (SS) content of 1 mg / L or less, so there is no environmental problem and can be discharged to sewers. It is also possible to introduce the filtrate F10 into the activated carbon adsorption tower 11 as in the form and remove the contained trace components. On the other hand, the solid content M10 obtained by the membrane separator 10 is circulated to the agglomeration tank 6 and reprocessed.

The treatment liquid F8 transferred from the electrolytic cell 8 is controlled so that the free chlorine concentration is 50 to 500 mg / L, and preferably 50 to 200 mg / L. Specifically, a concentration measuring device (not shown) that measures the free chlorine concentration of the treatment liquid F8 between the electrolytic cell 8 and the membrane separation device 10 and the value of the free chlorine concentration measured by the measuring device. And a control device (not shown) for controlling the applied voltage in the electrolytic cell 8, and the control device controls the concentration of free chlorine to be in the above range. Free chlorine is generated in the treatment liquid by electrolyzing the treatment liquid containing chlorine, that is, in the above-described embodiment, the supernatant liquid F6 containing chlorine derived from the chlorine-containing waste D in the embodiment. By adjusting the applied voltage in the electrolytic cell 8 (electrolysis step), the free chlorine concentration can be controlled within the above range. By adjusting the free chlorine concentration within the above range, fouling of the membrane separation device can be suppressed, and a reduction in the amount of treated water can be prevented.
The free chlorine concentration can be easily measured, for example, by measuring the redox potential of the liquid.

  From the viewpoint of controlling the concentration of free chlorine within the above range, the chlorine concentration in the supernatant F6 is preferably 1000 mg / L or more, and more preferably 10,000 to 50,000 mg / L.

  Further, as described above, hypochlorite such as sodium hypochlorite may be separately added in the electrolytic cell 8 (electrolysis step). By separately adding hypochlorite in the electrolytic cell 8 (electrolysis step), the precipitation reaction of dissolved metal is promoted, and at the same time, the free chlorine concentration of the treated water in the membrane separation step is increased to prevent fouling. There is an effect that it can be planned.

  Note that the processing method and the processing apparatus according to the present invention are not limited to the above-described embodiment, and it goes without saying that various modifications can be made without departing from the scope of the present invention. For example, in the above-described embodiment, the case where the chlorine-containing waste is applied in a treatment facility for use as a cement raw material has been described. However, it can also be applied in a general wastewater treatment process or a sludge treatment process. is there.

DESCRIPTION OF SYMBOLS 1 Dissolution tank 2 Filtration apparatus 3 Reaction tank 4 Coagulation tank 5 Reaction tank 6 Coagulation tank 7 Filtration apparatus 8 Electrolysis tank 9 Decanter 10 Membrane separation apparatus 11 Activated carbon adsorption tower

Claims (4)

A wastewater treatment method comprising a membrane separation process for membrane separation of suspended solids in wastewater,
An electrolysis process for electrolyzing a treatment liquid containing a chlorine component in wastewater to be treated on the upstream side of the membrane separation process ;
A concentration measuring step for measuring the free chlorine concentration of the treatment liquid electrolyzed in the electrolysis step between the electrolysis step and the membrane separation step ;
Based on the value of the free chlorine concentration measured by the concentration measurement step, the free chlorine concentration in the treatment liquid flowing into the membrane separation step is adjusted in the range of 50 to 500 mg / L by adjusting the applied voltage in the electrolysis step. A wastewater treatment method using membrane separation, characterized in that the control is performed.   Hypochlorite is added to the treatment liquid upstream of the membrane separation step, and the free chlorine concentration is controlled within the above range by adjusting the amount of hypochlorite added and adjusting the applied voltage. The wastewater treatment method using membrane separation according to claim 1. A wastewater treatment device equipped with a membrane separation device for membrane separation of suspended solids in wastewater,
And electrolysis of the electrolytic apparatus the processing liquid moistened chlorine component be processed wastewater upstream of the membrane separation device,
A concentration measuring device for measuring the value of the free chlorine concentration of the treatment liquid treated by the electrolytic device ;
Control for adjusting the voltage applied by the electrolysis device based on the free chlorine concentration measured by the concentration measuring device so that the free chlorine concentration in the treatment liquid flowing into the membrane separation device is in the range of 50 to 500 mg / L. Equipment ,
An apparatus for treating waste water using membrane separation. Provided with a hypochlorite addition device for adding hypochlorite to the treatment liquid upstream of the membrane separation device, the control device adjusts the amount of hypochlorite added and the applied voltage 4. The apparatus for treating wastewater using membrane separation according to claim 3, wherein the free chlorine concentration is controlled to be within the above range.

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