JP2010005491A - Electrolytic phosphorus recovery device and sewage treatment system using it - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrolytic phosphorus recovery device which is excellent in resource conservation and excellent as a measure against global warming, and enables reuse of phosphorus resources, and a sewage treatment system using the device. <P>SOLUTION: The sewage treatment system comprises a wastewater treatment facility 1 for cleaning inflow sewage using at least activated sludge, a sludge treatment facility 2 for dewatering and drying surplus sludge discharged from the wastewater treatment facility to separate it into concentrated sludge and desorbed water, the electrolytic phosphorus recovery device 3 for recovering phosphorus components in the desorbed water discharged from the sludge treatment facility, a solar cell 4 for generating electricity using sunlight, a hydrogen gas recovery device 5 for recovering hydrogen gas generated from the electrolytic phosphorus recovery device 3, a hydrogen battery 6 for generating electricity using the hydrogen gas recovered in the hydrogen gas recovery device as a fuel, and a power source switching device 7. A direct-current power source for electrolysis, applied to the electrolytic phosphorus recovery device 3 can be switched to either the solar cell 4 or the hydrogen battery 6 by the power source switching device 7. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an electrolytic phosphorus recovery apparatus and a sewage treatment system using the same.

  In sewage treatment systems that purify sewage (such as domestic wastewater, human wastewater, general industrial wastewater, and mixed water with rainwater) sent through the sewer, etc., purification treatment is usually performed using activated sludge during the treatment process. Is generally performed. In the purification treatment using this activated sludge, it is difficult to completely remove the phosphorus component contained in the sewage, and the phosphorus component is finally discharged to the outside in the form of excess sludge.

  Conventionally, as a method for recovering and removing a phosphorus component contained in sewage or excess sludge, for example, a phosphorus recovery method using chemical addition or a phosphorus recovery method utilizing electrolysis is known. The phosphorus recovery method by adding chemicals is to recover by adding an inorganic flocculant or a polymer flocculant to the water to be treated containing the phosphorus compound, flocking the phosphorus compound, and aggregating and precipitating. When using the phosphorus recovery method by adding this chemical, the pH of the water to be treated is lowered by the added flocculant, so that there is a problem that the pH must be adjusted using a pH adjusting agent such as sodium hydroxide.

  On the other hand, as shown in Patent Documents 1 and 2, for example, the electrolytic phosphorus recovery method dehydrates excess sludge discharged after purification treatment using activated sludge, separates it into concentrated sludge and desorbed water, and removes it. By electrolyzing the water separation using an electrode made of an insoluble phosphate-forming metal (for example, iron or aluminum), the iron ions and aluminum ions eluted in the desorbed water and the phosphorus ions contained in the desorbed water are electrically It is chemically reacted to recover the phosphorus component in the desorbed water in the form of an insoluble phosphate (such as iron phosphate or aluminum phosphate). This electrolytic phosphorus recovery method does not require pH adjustment of treated desorption water, and is an extremely excellent recovery method.

Japanese Patent Laid-Open No. 3-89998 (full text, all figures) JP 2007-330919 A (the whole sentence, all figures)

  When the electrolytic phosphorus recovery method is used, a DC power source for electrolysis is required. Conventionally, a commercial AC power source is generally used as the DC power source for the electrolysis, and this is converted into a direct current. The amount of power to be used is enormous. Also, electrical equipment such as transformers and AC-DC converters are considerably large.

  By the way, in recent years, from the standpoint of global environmental conservation, resource saving and global warming countermeasures are strongly screamed. There is no exception in sewage treatment systems, and there is a demand for the development of sewage treatment systems that are excellent in resource conservation and global warming countermeasures. Accordingly, an object of the present invention is to provide an electrolytic phosphorus recovery apparatus that is excellent in resource saving and global warming countermeasures and that can reuse phosphorus resources, and a sewage treatment system using the same.

  In order to solve the above-mentioned problems, an electrolytic phosphorus recovery apparatus according to claim 1 is arranged to be immersed in an electrolytic tank for storing water to be treated containing a phosphorus component, in the stored water to be treated, and at least the anode electrode is It is characterized by comprising a pair of positive and negative electrodes made of an insoluble phosphate-forming metal and a solar cell for supplying a direct current voltage for electrolysis to the pair of electrodes.

  The electrolytic phosphorus recovery apparatus according to claim 2 is the electrolytic phosphorus recovery apparatus according to claim 1, wherein the hydrogen gas recovery apparatus recovers hydrogen gas generated from the cathode electrodes of the pair of electrodes, and the hydrogen gas recovery A hydrogen battery using hydrogen gas recovered by the device as fuel and a power source switching device capable of switching the direct current power source for electrolysis applied to the pair of electrodes to either the solar cell or the hydrogen cell. However, it is characterized in that it is switched to the solar cell side in a time zone in which solar power generation can be used, and to the hydrogen battery side in a time zone in which solar power generation cannot be used.

  The electrolytic phosphorus recovery apparatus according to claim 3 is the electrolytic phosphorus recovery apparatus according to claim 2, wherein an iron electrode is used as an anode electrode of the pair of electrodes for electrolysis and a titanium electrode is used as a cathode electrode. It is what.

  According to a fourth aspect of the present invention, there is provided a sewage treatment system for purifying incoming sewage using at least activated sludge, and dewatering and drying excess sludge discharged from the sewage treatment facility to remove concentrated sludge. A sludge treatment facility that separates into dewatered water, and a phosphorus recovery device that collects phosphorus components in the desorbed water discharged from the sludge treatment facility, and returns the desorbed water after dephosphorization to the sewage treatment facility. In the sewage treatment system, the electrolytic phosphorus recovery apparatus according to any one of claims 1 to 3 is used as the phosphorus recovery apparatus.

According to the electrolytic phosphorus recovery apparatus of the present invention and the sewage treatment system using the same, the solar cell is employed as the direct current power source for electrolysis used in the electrolytic phosphorus recovery apparatus. An AC power supply can be eliminated, and cost reduction and resource saving of sewage treatment can be achieved. For example, the amount of processing eliminated water 5,000 m ³ / day, total phosphorus concentration _(PO 4 -P) 64mg / L of phosphorus compound in the eliminated water, _PO 4 -P inflow 320 kg / day, phosphorus removal of 90% As an example, the daily power for electrolysis requires about 97 to 98 kWh (DC3V, 32,400A), all of which are solar cells (for example, 153W panel × about 635 sheets, approximately 732 m ² ), cost reduction and resource saving can be achieved. In addition, since thermal power generation using fossil fuels such as oil, coal, and LNG is not used, the amount of carbon dioxide emission can be reduced, which contributes to prevention of environmental destruction. Further, by recycling the collected phosphorus, it is possible to recycle the phosphorus. Furthermore, since a commercial AC power supply is not used, a large-capacity transformer, an AC-DC converter, and the like are not required, and facility costs and management costs can be reduced.

  In addition, a hydrogen gas recovery device that recovers hydrogen gas generated from the cathode electrode of the electrolytic phosphorus recovery device, a hydrogen battery that uses the recovered hydrogen gas as fuel, and a power source switching device can be added to use solar power generation. Electrolysis is performed by solar cells during time periods (for example, daytime), and electrolysis is performed by hydrogen batteries during times when solar power generation cannot be used (for example, at night or in the rain). It is possible to continue the recovery of the phosphorus component by electrolysis even when it is not available, and it is possible to realize an inexpensive and efficient phosphorus recovery.

In addition, since the iron electrode is used as the anode electrode of the pair of electrodes for electrolysis, the phosphorus component in the desorbed water can be efficiently recovered in the form of iron phosphate (FePO ₄ ) that is insoluble in water. In addition, since the anode electrode is eluted into the desorbed water by electrolysis and consumed, it must be replaced at regular intervals. However, since the iron electrode is inexpensive, it can contribute to cost reduction. Furthermore, since a titanium electrode excellent in strength, hardness and corrosion resistance is used as the cathode electrode, electrolysis can be continued stably over a long period of time, and efficient phosphorus recovery can be performed.

Hereinafter, an embodiment of a sewage treatment system constructed using the electrolytic phosphorus recovery apparatus of the present invention will be described with reference to the drawings.
As shown in FIG. 1, the sewage treatment system according to the present embodiment includes a sewage treatment facility 1 that purifies incoming sewage using at least activated sludge, and surplus discharged from the sewage treatment facility 1. Sludge treatment facility 2 for dewatering and drying sludge to separate concentrated sludge and desorbed water, electrolytic phosphorus recovery device 3 for collecting phosphorus components in desorbed water discharged from sludge treatment facility 2, solar light The solar cell 4 that supplies the generated DC power to the electrolytic phosphorus recovery device 3 as a DC power source for electrolysis and the hydrogen gas generated from the cathode electrode of the electrolytic phosphorus recovery device 3 is recovered. A hydrogen gas recovery device 5 and a hydrogen battery 6 that generates power using the hydrogen gas recovered by the hydrogen gas recovery device 5 as fuel and supplies the obtained DC power to the electrolytic phosphorus recovery device 3 as a DC power source for electrolysis , And a power supply switching device 7 for switching a DC power supply for electrolysis is supplied to the electrolytic phosphorus recovery device 3 in any of the solar cell 4 or hydrogen batteries 6.

  As shown in FIG. 2, the electrolytic phosphorus recovery device 3 stores the desorbed water from the sludge treatment facility 2 sent through the inflow port 35 and treats the desorbed water after dephosphorization through the outflow port 36. An electrolysis tank 31 for returning to the facility 1 is provided, and a pair of positive and negative electrodes 32 and 33 for electrolysis are opposed to each other in a state of being immersed in desorption water at a predetermined interval. In this embodiment, of the pair of positive and negative electrodes 32 and 33, an iron (Fe) electrode is used for the anode electrode (anode) 32 and a titanium (Ti) electrode is used for the cathode electrode (cathode) 33.

  In the illustrated example, the bottom surface of the electrolytic cell 31 has a mortar shape, and a phosphorus recovery valve 34 is provided at the center of the mortar-shaped bottom surface. It is configured so that the iron phosphate accumulated and precipitated can be recovered.

On the other hand, on the upper side of the cathode electrode 33 in the electrolytic cell 31, a hydrogen gas recovery tower 51 for collecting and recovering hydrogen (H ₂ ) gas generated from the cathode electrode 33 by electrolysis, a compression pump 52, A hydrogen gas recovery device 5 including a hydrogen gas storage tank 53 and a pressure adjusting regulator 54 is provided, and the recovered and stored hydrogen gas can be supplied to the hydrogen cell 6 as a fuel for hydrogen power generation.

  The power supply switching device 7 receives direct current power from the solar battery 4 and the hydrogen battery 6 and applies direct current power to the pair of electrodes 32 and 33 according to instructions from a controller (not shown). It is configured to be able to freely switch to either side of the.

  In the sewage treatment system having the above-described configuration, when sewage flows in through a sewer or the like, the sewage is sent to the sewage treatment facility 1 and purified using activated sludge.

  For example, first, sediment and sediment are removed by sedimentation in the sand basin, and large garbage is removed by a screen. Send to aeration tank. In the aeration tank, the sent sewage is agitated and mixed with the activated sludge while aerated, and the purification treatment using the activated sludge is performed. The sewage after the purification treatment with activated sludge is sent to the second settling basin, where flocs and other garbage generated in the aeration tank are slowly settled and removed over time. Then, the supernatant water after removal of sedimentation is taken out, sterilized with chlorine, and then discharged into a river.

  On the other hand, in the sewage treatment facility 1, a large amount of activated sludge is generated in the treatment system as the purification treatment using activated sludge proceeds. A part of the sludge is returned to the aeration tank as seed sludge. It is sent to the sludge treatment facility 2 as surplus sludge.

  The excess sludge sent to the sludge treatment facility 2 is dehydrated and dried using a concentration tank, a dehydrator, etc., and separated into concentrated sludge and desorbed water. The concentrated sludge is digested in a digestion tank, then sent to an incinerator for incineration, and the incinerated ash is disposed of by landfill. The desorbed water separated from the excess sludge is sent to the electrolytic phosphorus recovery device 3 and stored in the electrolytic bath 31 (see FIG. 2).

  A pair of electrodes 32 and 33 immersed in the electrolytic cell is supplied with, for example, a DC power source for electrolysis from the solar cell 4 via the power source switching device 7. That is, a positive voltage is applied to the anode electrode 32 made of an iron electrode, and a negative voltage is applied to the cathode electrode 33 made of a titanium electrode.

When a DC voltage is applied to the electrodes 32 and 33, divalent iron ions Fe ²⁺ are eluted from the iron electrode constituting the anode electrode 32 into the desorbed water by electrolysis. The divalent iron ions react with dissolved oxygen in the desorbed water to become trivalent iron ions Fe ³⁺ . On the other hand, the phosphorus component is present in the form of trivalent phosphate ions PO ₄ ^{3− in} the desorbed water. As a result, the iron ions ^{Fe 3+} and phosphate ions _PO ^{4 3-} is bound to water becomes iron phosphate insoluble (FePO ₄₎ aggregate sedimentation on the bottom of the electrolytic cell 31. Therefore, if the iron phosphate stored in the bottom of the electrolytic cell 31 is recovered by opening the phosphorus recovery valve 34 at regular intervals or when necessary, it can be reused as phosphorus resources. The desorbed water after phosphorus recovery is returned to the sewage treatment facility 1 through the outlet 36 (see FIG. 1).

When the recovery of the phosphorus component by the electrolysis is started, hydrogen (H ₂ ) gas is generated from the cathode electrode 33. The hydrogen gas recovery tower 51 (see FIG. 2) collects this hydrogen gas, sends it to the hydrogen gas storage tank 53 via the compression pump 52, and stores it as fuel for hydrogen power generation. The stored hydrogen gas is sent to the hydrogen battery 6 through a pressure adjusting regulator 54 under the control of a controller (not shown), and hydrogen gas power generation is performed by reacting with oxygen. The DC power generated by the hydrogen battery 6 is sent to the power supply switching device 7 and used as a DC power source for electrolysis together with the solar battery 4 as follows.

  That is, the solar cell 4 can generate power only during the daytime when the sun is out. Therefore, the solar cell 4 is used as a DC power source for electrolysis by switching to the solar cell 4 side in a time zone in which solar power generation at daytime can be used by the power source switching device 7. On the other hand, in a time zone such as nighttime when the solar battery 4 cannot be used, the hydrogen battery 6 is used as a DC power source for electrolysis by switching to the hydrogen battery 6 side. As a result, the phosphorus component can be collected continuously day and night. In order to perform such switching, for example, an illuminance sensor used in a night-time automatic lighting street light or the like may be used, and switching may be performed by the power supply switching device 7 according to the output of the illuminance sensor. Of course, it may be switched manually or by a timer.

The sewage treatment system according to the above embodiment has the following excellent effects.
(1) Recycling of phosphorus Phosphorus, the maximum nutrient of fertilizer, is used as a fertilizer by most farmers, but in Japan there is no phosphorus ore and 100% import is relied on. Recently, the price of phosphorus ore has soared due to the tight demand in the world. According to this system, since phosphorus ore is artificially made from phosphorus contained in sewage instead of phosphorus ore, it can be supplied and sold stably, and phosphorus can be recycled. .

(2) Reduction of sewage treatment costs Sludge generated during the sewage treatment process contains a large amount of phosphorus. In the process of incinerating this sludge, the water contained in the sludge is dehydrated, and the desorbed water obtained at that time contains a large amount of phosphorus. Therefore, this desorbed water cannot be discharged into the river as it is, but is returned and treated again at the sewage treatment plant. The influence of the phosphorus load due to this desorbed water has reached 20% or more of the total phosphorus load in the sewage treatment plant, requiring enormous energy in the treatment process, leading to an increase in the cost of sewage treatment costs. According to the present system, almost all the phosphorus in the desorbed water can be recovered, so that the energy and cost in the phosphorus treatment can be reduced by about 20%.

(3) Global warming countermeasures Normally, greenhouse gas such as carbon dioxide (CO ₂ ) is emitted in the process of digging phosphorus ore, and ships carrying phosphorus ore are also greenhouse gas in the process of transporting to Japan from abroad. Is discharged. Since this system uses solar cells and hydrogen batteries as energy sources required for the production of phosphate ore, it can be an environment-friendly system that does not generate any greenhouse gases.

(4) Reduction of sludge incineration ash This system can also reduce the phosphorus contained in sewage sludge incineration ash, resulting in a reduction in the amount of incineration ash and the processing costs required for landfill and transportation. be able to. By the way, when recovering 218kg of phosphorus per day, it leads to a reduction of about 80 tons of incineration ash in one year.

  As mentioned above, although embodiment of this invention was described, this invention is not limited to the said embodiment. For example, in the above-described embodiment, the case where an iron electrode and a titanium electrode are used as a pair of positive and negative electrodes for electrolysis is exemplified, but the anode side electrode is a metal that can form an insoluble phosphate by electrolysis. What is necessary is just to have, and besides iron, an aluminum electrode, an iron-aluminum alloy electrode, etc. can be used, for example. Further, the cathode side electrode is not limited to the titanium electrode, and an electrode made of the same metal as the carbon electrode or the anode side can be used.

  In the above embodiment, the electric power generated by the hydrogen power generation using the hydrogen gas generated from the electrolytic phosphorus recovery apparatus is used as the direct current power source for the electrolysis. In addition to this, the gas power generation using the digestion gas (methane gas). It is also possible to use the electric power from the above as a direct current power source for electrolysis.

  That is, in the sludge treatment facility 2, a digestion treatment using a digestion tank is adopted as one of the sludge treatment steps, and digestion gas (methane gas) is generated from the sludge decomposed in this digestion treatment. Therefore, if gas power generation is performed using this digestion gas, this generated power can also be used as a DC power source for electrolysis. If digestion gas power generation is also used, three of the solar battery, hydrogen battery, and digestion gas power generation can be used as a direct current power source for electrolysis, and further cost reduction can be achieved.

It is a figure which shows one Embodiment of the sewage treatment system comprised using the electrolytic phosphorus collection | recovery apparatus of this invention. It is a figure which shows the example of a specific example of the electrolytic phosphorus collection | recovery apparatus in FIG.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Sewage treatment facility 2 Sludge treatment facility 3 Electrolytic phosphorus recovery device 4 Solar cell 5 Hydrogen gas recovery device 6 Hydrogen battery 7 Power supply switching device 31 Electrolysis tank 32 Anode electrode 33 Cathode electrode 34 Phosphorus recovery valve 35 Desorption water inlet 36 Desorption Water separation outlet 51 Hydrogen gas recovery tower 52 Compression pump 53 Hydrogen gas storage tank 54 Regulator for pressure adjustment

Claims (4)

An electrolytic cell for storing water to be treated containing a phosphorus component;
While being immersed in the stored water to be treated, at least the anode electrode is a pair of positive and negative electrodes made of an insoluble phosphate forming metal,
An electrolytic phosphorus recovery apparatus comprising a solar cell that supplies a direct current voltage for electrolysis to the pair of electrodes. The electrolytic phosphorus recovery apparatus according to claim 1,
A hydrogen gas recovery device for recovering hydrogen gas generated from the cathode electrode of the pair of electrodes;
A hydrogen battery using hydrogen gas recovered by the hydrogen gas recovery device as a fuel;
A power switching device capable of switching a direct current power source for electrolysis applied to the pair of electrodes to either the solar cell or the hydrogen cell; and
An electrolytic phosphorus recovery apparatus characterized by switching to a solar cell side during a time zone in which solar power generation can be used, and switching to a hydrogen battery side in a time zone in which solar power generation cannot be used. The electrolytic phosphorus recovery apparatus according to claim 2,
An electrolytic phosphorus recovery apparatus using an iron electrode as an anode electrode of a pair of electrodes for electrolysis and a titanium electrode as a cathode electrode. A sewage treatment facility that purifies inflowing sewage using at least activated sludge, and a sludge treatment facility that separates excess sludge discharged from the sewage treatment facility into concentrated sludge and desorbed water by dehydration and drying. A sewage treatment system comprising a phosphorus recovery device for recovering phosphorus components in the desorbed water discharged from the sludge treatment facility, and returning the desorbed water after dephosphorization to the sewage treatment facility,
A sewage treatment system using the electrolytic phosphorus recovery apparatus according to any one of claims 1 to 3 as the phosphorus recovery apparatus.

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