JP2019055346A - Ammonia separation method, water treatment method, ammonia separation device, and water treatment device - Google Patents

Abstract

To improve efficiency of energy by enabling gas containing ammonia to be separated from ammonia-containing water.SOLUTION: An ammonia separation method is an ammonia separation method of separating ammonia from ammonia-containing water and includes: a step of separating gas containing ammonia from the ammonia-containing water using a membrane separator having a gas separation membrane separating water and gas; and a step of transferring the gas separated from the ammonia-containing water using a pump.SELECTED DRAWING: Figure 1

Description

  Embodiments described herein relate generally to an ammonia separation method, a water treatment method, an ammonia separation apparatus, and a water treatment apparatus.

  In sewage treatment plant water treatment and sludge treatment, industrial wastewater treatment, etc., the received treated water is subjected to bioreduction treatment to gasify or sludge suspended matter and dissolved matter in water, Purify treated water. Sludge is generally subjected to sludge treatment after being separated in a sedimentation tank.

  In recent years, energy recovery from such sewage treatment plants has attracted technical attention, and digests sludge produced by water treatment in a digestion tank, ferments methane, and purifies methane after purification with a gas engine. A process of burning and recovering energy as electric power with a generator is being promoted. Since the exhaust heat recovery by hot water can be performed from the gas engine, the heat efficiency is as high as 60% or more.

  By installing a digestion tank, energy can be recovered from sludge. On the other hand, since digestion is an anaerobic reaction, digested sludge contains a lot of ammonia components and phosphoric acid in the liquid phase. Among these, phosphoric acid is solidified by a flocculant containing iron / aluminum added before dewatering the sludge and removed through a dehydration step. However, the ammonia component remains in the dehydrated separation liquid, mixed with the return water, and returned to the water treatment step. The dehydrated separation liquid containing the returned ammonia component is again aerated, nitrified and denitrified, and gasified by the bioreduction treatment in the water treatment apparatus.

  In this way, energy recovery is promoted at sewage treatment plants, etc., and energy self-sufficiency is promoted by covering part of the power used, but dehydration separation containing ammonia components generated by installing a digestion tank Since the liquid is processed again by the water treatment device, a problem arises that the required aeration power increases. For this reason, in particular, in a sewage treatment plant where the facility capacity is not sufficient, there is a restriction that it is impossible even if a digester is to be introduced.

Japanese Patent No. 5521922

  Energy efficiency is achieved by making it possible to separate ammonia-containing gas from ammonia-containing water.

  The ammonia separation method according to the present embodiment is an ammonia separation method for separating ammonia from ammonia-containing water, and using a membrane separation device having a gas separation membrane for separating water and gas, the ammonia is separated from the ammonia-containing water. And a step of transferring the gas separated from the ammonia-containing water using a pump.

  The ammonia separation device according to the present embodiment is an ammonia separation device that separates ammonia from ammonia-containing water, and is a membrane separation device that includes a gas separation membrane that separates water and gas, and uses the gas separation membrane. A membrane separation device that separates the gas containing ammonia from the ammonia-containing water, and a pump that transfers the gas separated from the ammonia-containing water by the membrane separation device.

The block diagram explaining the structure of the water treatment apparatus which concerns on one Embodiment. The graph which shows the time change of pH and electrical conductivity at the time of making ammonia containing water contact air. The graph which shows the time change of the removal rate of inorganic carbon at the time of making ammonia containing water contact air, and the removal rate of ammonia nitrogen.

  Hereinafter, an ammonia separation method according to an embodiment will be described with reference to the drawings. In the following description, components having substantially the same functions and configurations are denoted by the same reference numerals, and redundant description will be provided only when necessary.

(Basic concept of ammonia separation method)
First, the basic concept of the ammonia separation method in this embodiment will be described. The ammonia component generated in the digestion tank that performs the bioreduction treatment is contained in the dehydrated separation liquid obtained when the digested sludge is dehydrated. When this dehydrated separation liquid is returned to the water treatment process and mixed, ammonia is mixed. The concentration of the component will decrease. For this reason, in this embodiment, ammonia is separated from the dehydrated separation liquid having a high concentration of the ammonia component. Here, the term “ammonia component” is used to mean not only pure ammonia (NH ₃ ) but also various ammonium compounds such as NH ₄ ⁺ ammonia ions and ammonia nitrogen (NH ₃ —N).

The dehydrated separation liquid contains about several hundred mg / L to several hundreds mg / L of ammonia nitrogen as an ammonia component. Moreover, since it is after digestion, pH is weakly alkaline. Ammonia nitrogen in water, have a relationship of dissociation equilibrium in the form of NH ₄ ⁺ ion form of ammonia molecules NH _3, further gas-liquid equilibrium between NH ₃ and NH ₃ in the gas phase in the liquid Are in a relationship. In order to advance the dissociation equilibrium in the direction of NH ₃ , means such as raising the pH, raising the water temperature, or removing NH ₃ from the liquid can be used. To move the vapor-liquid equilibrium from NH ₃ in a liquid phase to move to the NH ₃ in the gas phase increases the NH ₃ concentration in the liquid phase, raising the water temperature, replace the gas in the gas phase, such means Can be used.

  In this embodiment, the water temperature is increased to move the dissociation equilibrium, the pH is adjusted to the alkali side using an alkali agent as necessary, and ammonia is extracted into the gas phase by gas-liquid contact. The extracted ammonia is a corrosive substance and needs to be detoxified by some means, but is detoxified by burning using a combustor. A purification device for purifying the gas may be provided in the front stage of the combustor as necessary, and impurities such as water, carbon dioxide gas, and hydrogen sulfide accompanying the ammonia are removed. Here, a power generator may be connected to the combustor, and in that case, energy recovery using ammonia as fuel can be performed, so not only aeration power reduction of the water treatment system but also energy self-sufficiency Can be promoted.

(One embodiment)
Next, an example of a specific configuration of the water treatment apparatus of the present embodiment will be described based on the drawings. FIG. 1 is a block diagram illustrating the overall configuration of a water treatment apparatus 1 according to the present embodiment. As shown in FIG. 1, the water treatment device 1 according to this embodiment includes a pretreatment device 10, a heating device 12, a surplus heat source 14, a membrane separation device 16, an aeration device 18, and a pump 20. The refining device 22, the combustor 24, and the energy recovery device 26 are provided.

  The pretreatment device 10 is supplied with ammonia-containing water containing an ammonia component as raw water. In particular, in this embodiment, a dehydrated separation liquid obtained by dewatering digested sludge is supplied as raw water. A dehydration separation liquid may contain many solid substances according to the state of dehydration. For this reason, if this raw water is treated as it is in the subsequent stage, solid matter may adhere to the pipes at various places in the water treatment apparatus 1 and cause pipe blockage. Therefore, a pretreatment device 10 is additionally provided to remove solids from the raw water that is ammonia-containing water. As the pretreatment device 10, for example, a sand filtration device or a membrane treatment device can be used in addition to a staying sedimentation tank provided with an inclined plate.

  The warming device 12 is supplied with ammonia-containing water that has been pretreated by the pretreatment device 10 and from which solids have been removed. The warming device 12 warms the ammonia-containing water from which the solid matter has been removed. In the present embodiment, the surplus heat source 14 is used as a heat source for heating. As the surplus heat source 14, heat generated by burning methane gas burned and discarded for convenience such as capacity adjustment of the gas engine with a biogas boiler, or hot water recovered from the gas engine may be used. it can. These were originally generated in the treatment plant where the water treatment apparatus 1 is installed, and are energy that may be discarded due to the generation of surplus. It can be used effectively by using it for ammonia separation.

  The dehydrated separation liquid that is raw water is often about 30 ° C., but it is preferably about 60 ° C. or higher by heating with the heating device 12. Although the amount of heat of the surplus heat source 14 varies depending on the design concept of the treatment plant where the water treatment apparatus 1 is installed, according to the results of the investigation, the total amount of the dehydrated separation liquid is 30 ° C to 40 ° C at a certain treatment plant. There is surplus energy that can be increased. If the total amount of the dehydrated separation liquid cannot be raised to 60 ° C. or higher, only a part of the dehydrated separation liquid is supplied to the pretreatment device 10 to separate ammonia from the part of the dehydrated separation liquid. You may do it. Even in that case, since the amount of ammonia in the return water is decreased, it is possible to obtain an effect of reducing aeration power and an effect of recovering energy from power generation using ammonia as fuel. For heat exchange in the heating device 12, a shell and tube or a plate-type heat exchanger can be used.

  Here, in the heating device 12, it is desirable to adjust the pH by adding an alkaline agent as necessary. When ammonia is removed from the ammonia-containing water at the subsequent stage of the heating device 12, the pH of the ammonia-containing water decreases. When the pH is lowered, the movement of ammonia into the gas phase becomes slow, which takes time and the desired removal rate cannot be achieved. Therefore, the reaction time of ammonia extraction and the extraction / removal rate can be controlled by adjusting to a predetermined pH using an alkali agent in advance. For example, in order to set the ammonia removal rate from the ammonia-containing water to about 80%, it is necessary to set the pH to about 8 or more, and it is possible to shorten the time by setting the pH to 9 or more. Further, when the amount of the flocculant used for dewatering the digested sludge is known in advance by measurement, set values, or the like, the amount of the alkali agent may be set from the amount of acid contained in the flocculant.

  Membrane separation device 16 is supplied with ammonia-containing water that has been heated by heating device 12 and adjusted in pH as necessary. In the membrane separator 16, the ammonia-containing water ammonia moves to the gas phase by gas-liquid equilibrium using the gas separation membrane provided in the membrane separator 16. Further, in the membrane separation device 16, bubbling is performed by blowing air with a pump and a diffuser plate, or by using a gas separation membrane for deaeration, a dehydrated separation liquid is allowed to flow on the primary side and air is allowed to flow on the secondary side. Thus, the transition of the ammonia from the liquid phase to the gas phase may be promoted. The air blown into the membrane separation device 16 is preferably heated in advance to a temperature equivalent to the supplied ammonia-containing water, for example, using an excess heat source 14 or a heat source (not shown).

  FIG. 2 is a graph showing temporal changes in pH and conductivity when ammonia-containing water simulating a dehydrated separation liquid is brought to 60 ° C. and brought into contact with air. In FIG. 2, the horizontal axis represents time T, the left vertical axis represents pH, and the right vertical axis represents conductivity (mS / cm). Moreover, FIG. 3 is a graph which shows the time change of the removal rate behavior of inorganic carbon and the removal rate behavior of ammonia nitrogen under the same conditions as FIG. In FIG. 3, the horizontal axis represents time T, and the vertical axis represents the removal rate (%) of inorganic carbon and ammonia nitrogen.

  According to the graphs of FIG. 2 and FIG. 3, the inorganic carbon is a carbonic acid component. First, carbon dioxide is released into the gas phase, so that the pH of water rises. It can be seen that the ammonia removal rate increases accordingly. The conductivity is lowered due to a decrease in carbonic acid and ammonium ions, which are ionic components. In this way, the membrane separation device 16 can separate ammonia from the dehydrated separation liquid that is ammonia-containing water.

  As shown in FIG. 1 again, the liquid from which ammonia has been separated from the ammonia-containing water in the membrane separation device 16 is returned to the upstream process of the water treatment device 1 as return water. In this embodiment, the return water is returned to the aeration device 18 and aerated. At this time, as shown in the graph of FIG. 3, the aeration power of the aeration apparatus 18 is reduced by several% to 10% due to the reduction of ammonia nitrogen. In the present embodiment, the solid matter that has been subjected to solid-liquid separation in the above-described pretreatment device 10 is also returned to the upstream process as return water. In this embodiment, the return water from the pretreatment device 10 is also aerated by the aeration device 18.

  The gas containing ammonia separated by the membrane separation device 16 is sucked by the pump 20 and transferred to the purification device 22. Here, the pump 20 is a general term for mechanical devices for transferring a gas containing ammonia from the membrane separation device 16, and includes various mechanical devices having the ability to carry gas from one to the other.

The gas transferred by the pump 20 may contain impurities such as carbon dioxide (CO ₂ ) and water vapor (H ₂ O) in addition to ammonia (NH ₃ ). Depending on the combustor 24, the reaction may be hindered by impurities, so a purification device 22 as a pretreatment is installed as necessary. For example, when the combustor 24 is a fuel cell or a catalytic combustion device, it is necessary to remove hydrogen sulfide, and therefore, it is removed using a desulfurizing agent containing an iron component or the like. When the combustor 24 is a gas turbine or a gas engine, an air dryer using a gas separation membrane is installed to remove water.

In the present embodiment, a carbon dioxide absorbing solution is supplied to the purifier 22, and the carbon dioxide absorbing solution absorbs carbon dioxide (CO ₂ ) contained in the gas transferred by the pump 20. The solution in which carbon dioxide has been absorbed is sent from the purifier 22 to the carbon dioxide absorbing solution recovery tank.

  It should be noted that when the gas containing ammonia separated by the membrane separation device 16 does not contain impurities, it does not cause any problem even if impurities are contained, or there is a problem with the combustion of the combustor 24 at the subsequent stage. If this does not occur, the refining device 22 can be omitted.

  The combustor 24 is supplied with a gas containing ammonia from which impurities have been removed by the purifier 22. As the combustor 24, a fuel cell, a gas turbine, a gas engine, a catalytic combustion apparatus, or the like can be used. Among these, in a fuel cell, a gas turbine, and a gas engine, a generator can be used as the energy recovery device 26 that recovers combustion energy, and the amount of energy recovered is increased by the power generation function of the generator. Can do. Although the catalytic combustion device is an exothermic reaction that burns at several hundred degrees Celsius, although it depends on the catalyst used, a heat recovery device can be used as the energy recovery device. Since the heat recovered by the heat recovery device can be used as, for example, the surplus heat source 14 of the heating device 12 described above, the energy efficiency of the ammonia separation process itself in the water treatment device 1 according to the present embodiment can be increased. it can.

  Further, in the combustion in the combustor 24, the amount of ammonia that can be extracted is as small as about several to 20% of methane on a calorie basis, and it is easier in terms of combustion technology than ammonia-only firing, so that digestion gas And may be mixed and fired.

  As can be seen from the above, in the water treatment apparatus 1 according to this embodiment shown in FIG. 1, the pretreatment apparatus 10, the heating apparatus 12, the membrane separation apparatus 16, the pump 20, and the purification apparatus 22. Thus, the ammonia separation device in the present embodiment is configured. That is, the gas containing ammonia separated by the ammonia separation device is burned by the combustor 24, and the combustion energy is recovered by the energy recovery device 26. Further, the liquid obtained by separating the ammonia-containing gas from the ammonia-containing water by the ammonia separation device is sent to the aeration device 18 as return water.

  As described above, according to the water treatment device 1 according to the present embodiment, in the membrane separation device 16 supplied with ammonia-containing water, ammonia is separated from the ammonia-containing water by the gas separation membrane, and the separated gas Therefore, the ammonia component contained in the return water from the membrane separation device 16 can be reduced. For this reason, the load of the aeration apparatus 18 that performs aeration of the return water can be reduced, the air volume of the aeration apparatus 18 can be suppressed, and the energy consumption can be reduced. In addition, since the load on the aeration device 18 can be reduced in this way, a digester can be newly introduced even in a sewage treatment plant with insufficient facility capacity.

  Further, the gas containing ammonia transferred by the pump 20 is burned by the combustor 24 through the purifier 22 or directly, and the combustion energy can be recovered by the energy recovery device 26. For this reason, the energy efficiency of this water treatment apparatus 1 can also be improved. Furthermore, if the combustion energy recovered by the energy recovery device 26 is used as a heat source of the heating device 12, the energy cycle of the water treatment device 1 can be made independent.

  Although several embodiments have been described above, these embodiments are presented as examples only and are not intended to limit the scope of the invention. The novel apparatus and methods described herein can be implemented in a variety of other forms. In addition, various omissions, substitutions, and changes can be made to the forms of the apparatus and method described in the present specification without departing from the spirit of the invention. The appended claims and their equivalents are intended to include such forms and modifications as fall within the scope and spirit of the invention.

1: water treatment device, 10: pretreatment device, 12: heating device, 14: surplus heat source, 16: membrane separation device, 18: aeration device, 20: pump, 22: purification device, 24: combustor, 26: Energy recovery equipment

Claims (14)

An ammonia separation method for separating ammonia from ammonia-containing water,
Separating a gas containing ammonia from the ammonia-containing water using a membrane separation device having a gas separation membrane for separating water and gas;
Transferring a gas separated from the ammonia-containing water using a pump;
A method for separating ammonia.   The ammonia separation method according to claim 1, wherein the ammonia-containing water is a dehydrated separation liquid obtained when dehydrated digested sludge produced by bioreduction treatment.   The ammonia separation method according to claim 1, further comprising a step of purifying the gas containing ammonia transferred using the pump using a purifier to remove impurities.   The method according to claim 1, further comprising a step of heating the ammonia-containing water using a heating device before separating the gas containing ammonia from the ammonia-containing water using the membrane separation device. The ammonia separation method according to any one of the above.   Using the ammonia separation method according to any one of claims 1 to 4, the liquid after separation of the gas containing ammonia from the ammonia-containing water is returned to the water treatment step as return water, and the air is removed. A water treatment method further comprising the step of performing aeration with a supplied aeration apparatus.   A water treatment method, further comprising a step of combusting, using a combustor, a gas containing ammonia separated by using the ammonia separation method according to claim 1.   The water treatment method according to claim 6, further comprising a step of recovering combustion energy generated by the combustor using an energy recovery device. An ammonia separation device for separating ammonia from ammonia-containing water,
A membrane separation device comprising a gas separation membrane for separating water and gas, wherein the gas separation membrane is used to separate a gas containing ammonia from the ammonia-containing water; and
A pump for transferring a gas separated from the ammonia-containing water in the membrane separator;
An ammonia separator comprising:   The ammonia separation apparatus according to claim 8, wherein the ammonia-containing water is a dehydrated separation liquid obtained when dehydrated digested sludge produced by bioreduction treatment.   The ammonia separation device according to claim 8 or 9, further comprising a purification device for purifying a gas containing ammonia transferred using the pump to remove impurities.   11. The heating apparatus according to claim 8, further comprising a heating device that heats the ammonia-containing water before separating the gas containing ammonia from the ammonia-containing water using the membrane separation device. Ammonia separation equipment.   Using the ammonia separator according to any one of claims 8 to 11, the liquid after the gas containing ammonia is separated from the ammonia-containing water is returned to the water treatment step as return water, and air is supplied. The water treatment apparatus further provided with the aeration apparatus which performs the aeration to supply.   A water treatment device, further comprising a combustor that burns a gas containing ammonia separated from the ammonia-containing water using the ammonia separation device according to any one of claims 8 to 11.   The water treatment device according to claim 13, further comprising an energy recovery device that recovers combustion energy generated by the combustor.

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