JP2024088297A - Wastewater treatment/water production system using fo membrane - Google Patents

Abstract

To provide a wastewater treatment/water production system, capable of realizing wastewater treatment cost reduction, water production cost reduction, improvement of wastewater treatment efficiency, and improvement of energy recovery efficiency.SOLUTION: A wastewater treatment/water production system 1 comprises: means 9 for carrying out a FO treatment process comprising a wastewater section 19 introducing domestic wastewater flowing into the system and a seawater section 28 introducing seawater; means 10 for carrying out a RO treatment process of subjecting seawater to a desalination treatment; an anaerobic treatment unit 21 for forming bacterial cell granules to generate biogas 25; and an aerobic treatment unit 27 for treating the anaerobic treatment water using microbes present in active sludge or the like. The means for carrying out the FO treatment process moves water present in the wastewater from the wastewater section to the seawater section via a semipermeable membrane 20 to concentrate the wastewater, subsequently feeds the concentrated wastewater to the anaerobic treatment unit to generate biogas to recover energy, and concurrently feeds introduced seawater and low concentration seawater 22 diluted with water moving from the wastewater section to the RO membrane 14, to reduce energy required to pressurize a pump, and thereby seawater-desalination efficiency can be improved.SELECTED DRAWING: Figure 1

Description

The present invention relates to a wastewater treatment and water production system using FO membranes.

For example, the activated sludge process has been known as a method for treating domestic wastewater (see Patent Document 1 below). Domestic wastewater is generally treated using aerobic treatment, which is more efficient (removing 80-95% of COD (Chemical Oxygen Demand)) than anaerobic treatment (removing 60-80% of COD).

The above-mentioned aerobic treatment system has a primary sedimentation tank 129 that sediments the inflowing wastewater, a reaction tank 127, and a final sedimentation tank 131 that sediments the wastewater from the reaction tank 127, as shown in Figure 2. The primary sedimentation tank 129 sediments the wastewater 125, and the water in the primary sedimentation tank 129 is separated into supernatant water (sedimented wastewater) 136 and sediment (sludge) 141. The supernatant water 136 is sent to the reaction tank 127. Air is sent to the reaction tank 127 by a blower (not shown).

Here, the reaction tank suspends a high concentration of flocs (cotton-like floating matter: activated sludge), and then supernatant water 136 is poured in (flowed into) the tank, aerated, and mixed with the activated sludge containing microorganisms for aerobic treatment. The mixture of supernatant water 136 and activated sludge is sent to the final settling tank 131, where it is settled, the supernatant water is separated, and after disinfection, it is discharged as treated water 143. Meanwhile, part 137 of the settled activated sludge 134 is fed back to the reaction tank 127 (see arrow 137) and reused, and the remainder is sent to a thickening tank (not shown) together with the sediment (sludge) 141 in the primary settling tank 129, where the solids are either put to effective use or treated and disposed of.

Patent No. 7102706

By the way, aerobic treatment can produce stable and good treated water, but it requires a huge amount of energy for aeration, so it is also possible to use it in combination with anaerobic treatment, which allows energy recovery through methane fermentation, etc. Here, when combining anaerobic treatment in the first stage and aerobic treatment in the second stage, for example, the anaerobic UASB (Upflow Anaerobic Sludge Blanket) system used for anaerobic treatment is generally used to treat high-concentration wastewater, but the treatment efficiency is poor when treating low-concentration wastewater because the organic matter decomposition rate is slow. Therefore, it is thought that it is possible to obtain stable and good treated water quality by concentrating low-concentration wastewater to improve the treatment efficiency and then performing anaerobic treatment, and decomposing the remaining organic matter in the second stage of aerobic treatment.

As a method for concentrating liquids such as wastewater, there is a method that utilizes the FO (Forward Osmosis) phenomenon, as shown in prior art documents, which also makes it possible to reduce the amount of wastewater.

The present invention aims to utilize the FO phenomenon, in which seawater and domestic wastewater are used as the input liquid, and the RO (Reverse Osmosis) phenomenon, in which seawater is used as the input liquid, to reduce wastewater treatment costs, improve wastewater treatment efficiency, improve energy recovery efficiency, and reduce the energy required to desalinate seawater.

The present invention has a FO treatment process that draws in wastewater from which solids have been removed from the inflowing wastewater and seawater, a means for performing an RO treatment process that desalinates seawater, a means for performing an anaerobic treatment process, and a means for performing an aerobic treatment process, and is characterized in that the FO treatment process supplies concentrated wastewater from which water has been removed from the drawn-in wastewater to the anaerobic treatment process.

In the present invention, the means for carrying out the FO treatment process preferably transfers the water in the drawn-in wastewater to the drawn-in seawater via a semipermeable membrane, and supplies the diluted drawn-in seawater to the RO treatment process.

In the present invention, it is preferable that the means for carrying out the anaerobic treatment process includes a concentrated wastewater inlet portion into which the concentrated wastewater flows, and that biogas is generated by anaerobic fermentation of the concentrated wastewater.

In the present invention, it is preferable to further have a pretreatment unit that is connected to a first settling tank for receiving the inflowing wastewater, physically removes solids from the supernatant water after settling, and discharges the filtered wastewater, and supplies the filtered wastewater to a means for carrying out the FO treatment process.

The present invention makes it possible to reduce wastewater treatment costs, improve wastewater treatment efficiency, improve energy recovery, and reduce the energy required for desalinating seawater.

1 is a diagram showing a configuration of a wastewater treatment and fresh water production system according to an embodiment of the present invention. FIG. 1 is a diagram for explaining conventional aerobic treatment. FIG. 2 is a diagram for explaining the function of an RO membrane.

Below, an example of an embodiment (example) of the present invention will be described in detail with reference to the drawings. This embodiment is merely one example for realizing the present invention, and does not limit the technical scope of the present invention. For example, in this embodiment, the subject of water treatment is described as domestic wastewater, but it can also be applied to industrial wastewater (e.g., factory wastewater) without being limited to domestic wastewater.

The configuration of the wastewater treatment and freshwater production system 1 according to this embodiment will be described below with reference to FIG. 1. FIG. 1 shows a schematic diagram of the wastewater treatment and freshwater production system according to the embodiment. The wastewater treatment and freshwater production system 1 is configured to have a primary sedimentation tank 2, a pretreatment facility 3, a means 9 for performing an FO treatment process, a means 10 for performing an RO treatment process, an anaerobic treatment unit 21, an aerobic treatment unit 27, and a final sedimentation tank 31. The primary sedimentation tank 2, the pretreatment facility 3, the means 9 for performing an FO treatment process, the anaerobic treatment unit 21, the aerobic treatment unit 27, and the final sedimentation tank 31 are connected in order in the direction in which the domestic wastewater flows. The means 9 for performing an FO treatment process and the means 10 for performing an RO treatment process are connected in order in the direction in which the seawater flows.

[First settling tank]
The primary sedimentation tank 2 is a tank for sedimentation treatment of the inflowing domestic wastewater 4, and has the main function of separating (sedimentation separation) into supernatant water 8 and sediment 6. The supernatant water 8 is discharged to a pretreatment facility 3 described below. The sediment 6 is discharged together with a portion of the activated sludge discharged from a final sedimentation tank 31 described below, and sent to a thickening tank (not shown), and the solid content is effectively utilized or subjected to sludge treatment and disposal.

[Pretreatment facility]
The pretreatment facility 3 is a filtration device connected to the primary sedimentation tank 2, which physically removes solids in the supernatant water 8 that flows in and discharges the filtered domestic wastewater 5. The pretreatment facility 3 supplies the prefiltered domestic wastewater 5 to a means 9 for carrying out an FO treatment process. The pretreatment facility 3 may be, for example, a filtration device equipped with a plurality of filters that separates and removes floatable matter from the supernatant water 8. This filtration device has the same floatable matter removal performance and treatment speed as conventional rapid filtration.

This filtration device is realized in the following way. It is equipped with a filter function and a cleaning function at the front end of the FO treatment process, and has the function of preventing clogging of the forward osmosis membrane (FO membrane) 20 by removing solid particles with large particle sizes.

[FO processing step]
The means 9 for performing the FO treatment process has a high osmotic pressure solution region and a low osmotic pressure solution region sandwiched between the FO membrane 20, and has the function of moving water from the low osmotic pressure solution side to the high osmotic pressure solution side using osmotic pressure as a driving force. In this embodiment, the means 9 for performing the FO treatment process has two regions (compartments) sandwiched between the FO membrane 20: a drainage region 19 as a low osmotic pressure solution region and a seawater region 28 as a high osmotic pressure solution region. In the drainage region 19, the water of the domestic wastewater 5 drawn in through the FO membrane 20 is moved to the seawater region 28, so that the concentration increases and the amount of water decreases at the same time and flows out as concentrated wastewater 24, and in the seawater region 28, the drawn in seawater 7 is diluted with the water moved from the drainage region 19, so that the concentration decreases and the amount of water increases at the same time and flows out as low-concentration seawater 22.

The concentrated wastewater 24 flowing out from the drainage area 19 of the means 9 that performs the FO membrane treatment process is supplied to the anaerobic treatment section 21, and the low-concentration seawater 22 flowing out from the seawater area 28 is supplied to the means 10 that performs the RO treatment process.

[RO treatment process]
The means 10 for performing the RO treatment process has a function common to a general seawater desalination device in which a high osmotic pressure solution region and a low osmotic pressure solution region are present on either side of the reverse osmosis membrane 14, and water is moved from the high osmotic pressure solution side to the low osmotic pressure solution side using pump pressure as a driving force. The means 10 for performing the RO treatment process in this embodiment has two regions (compartments) on either side of the reverse osmosis membrane 14: a low concentration seawater region 12 as a high osmotic pressure solution region and a freshwater region 11 as a low osmotic pressure solution region. In the low concentration seawater region 12, water is moved from the low concentration seawater 22 drawn in through the reverse osmosis membrane 14 to the freshwater region 11, so that the concentration of the low concentration seawater 22 becomes high and flows out as normal concentration seawater 17, and in the freshwater region 11, water moves from the low concentration seawater region and flows out as freshwater 15.

The low-concentration seawater 22 supplied to the means 10 for carrying out the RO treatment process is a solution with a lower osmotic pressure than normal seawater, so the pump pressure required as a driving force is lower than when normal seawater is supplied, and power consumption can be reduced, making it possible to reduce energy consumption compared to a conventional seawater desalination device that supplies normal seawater. In addition, the discharged normal-concentration seawater 17 can be discharged directly to the coast, eliminating the need for special discharge equipment such as offshore discharge of high-concentration seawater discharged from a conventional seawater desalination device that supplies normal seawater, and making it possible to reduce the construction costs of seawater discharge equipment from the means 10 for carrying out the RO treatment process.

[Anaerobic treatment section]
The anaerobic treatment unit 21 is, for example, a reactor using the UASB method, and forms granulated bacterial cells (granules) by utilizing the self-granulating property of microorganisms. It is possible to hold high-concentration microorganisms in the reaction tank of the anaerobic treatment unit 21, and it is possible to treat a very high organic matter load. In the reaction tank of the anaerobic treatment unit 21, concentrated wastewater 24 is introduced into the lower part, and concentrated wastewater is introduced in an upward flow, and sludge is expanded, so that organic matter and microorganisms are efficiently contacted. A gas solid liquid separation unit (GSS: Gas Solid Separator) 23 is provided at the upper part of the reaction tank of the anaerobic treatment unit 21. The generated biogas (e.g., methane gas (CH ₄ ) 25 is collected by a gas collection pipe 30 located at the upper part of the anaerobic treatment unit 21, and suspended solids (SS) are separated at the lower part (sedimentation part) of the reaction tank of the anaerobic treatment unit 21.

Compared to aerobic treatment, anaerobic treatment does not require aeration, so it consumes less electricity, produces less excess sludge, and can collect the methane gas and other wastewater generated for use in power generation and boilers, making it an energy-saving treatment system. In conventional anaerobic treatment, the objects to be treated are sludge and high-concentration wastewater, but in this embodiment, the domestic wastewater 5 is concentrated by the FO membrane 20 in the front stage and supplied to the anaerobic treatment unit 21 as concentrated wastewater 24 with a high concentration and reduced volume, making it possible to recover energy such as methane gas directly from domestic wastewater, etc.

[Aerobic treatment section]
The aerobic treatment unit 27 is a wastewater treatment plant, and sends aerobically treated wastewater 29 treated in the wastewater treatment plant to a final sedimentation tank 31. The aerobic treatment unit 27 is supplied with anaerobically treated water 26 discharged from the anaerobic treatment unit 21, and the supplied anaerobically treated water 26 is sent to a reaction tank inside the wastewater treatment plant. Air is sent to the reaction tank by a blower (not shown).

Here, the reaction tank is used to suspend activated sludge in high concentration, and then anaerobically treated water 26 is introduced into the reaction tank, which is aerated to mix the activated sludge containing microorganisms, and aerobic treatment is performed. However, an aerobic treatment method in which microorganisms are fixed on a carrier instead of activated sludge may also be used. The mixture of anaerobically treated water 26 and activated sludge (aerobic treatment wastewater 29) is subjected to microbial purification by air agitation in the reaction tank and then sent to the final settling tank 31, where solid-liquid separation is performed, the supernatant water is separated, and the mixture is disinfected and discharged as effluent 33. On the other hand, part of the settled excess sludge 35 is sent to the aerobic treatment unit 27 as returned sludge 37, and the remainder is sent to a thickening tank (not shown) and a digestion tank (not shown) together with the sediment 6 in the primary settling tank 2, where the solids are effectively utilized or treated and disposed of.

In this embodiment of the aerobic treatment unit 27, the amount of water to be treated is significantly reduced compared to the amount of domestic wastewater 5 due to the concentration effect in the upstream FO treatment process, allowing for a significant reduction in the scale of the treatment facility and a significant reduction in the energy required for aeration. In addition, organic matter that cannot be treated in the upstream anaerobic treatment unit 21 can be treated to a low concentration, making it possible to obtain stable effluent quality.

<Summary of effects>
A commonly known concept for the treatment process of domestic wastewater 5 is to obtain good quality treated water through an aerobic water treatment process, while recovering energy from the production of methane gas and the like through an anaerobic sludge treatment process for the sludge generated.
In this embodiment, the domestic wastewater 5 is concentrated by the means 9 performing the FO membrane treatment process to obtain a concentrated wastewater 24 with a high concentration and reduced water volume, and the concentrated wastewater 24 is decomposed in the anaerobic treatment section 21 to generate and recover methane gas, etc., while decomposing organic matter, and the remaining organic matter is decomposed in the subsequent aerobic treatment section 27 to obtain good treated water quality. The anaerobic treatment section 21 has an energy recovery effect, and the aerobic treatment section 27 can obtain an energy reduction effect by reducing the water volume. At the same time, the low-concentration seawater 22 flowing out from the means 9 performing the FO membrane treatment process is supplied to the means 10 performing the RO membrane treatment process, thereby reducing the pump pressure required for seawater desalination, and obtaining an energy reduction effect. Furthermore, since the normal concentration seawater 17 flows out from the means 10 performing the RO membrane treatment process, it is possible to reduce the construction costs of special discharge facilities, such as discharging seawater offshore.
As a result of the above-mentioned effects, it is possible to simultaneously achieve good treated water quality and methane production through energy-saving wastewater treatment, and energy-saving seawater desalination, thereby simultaneously achieving reductions in wastewater treatment costs, reductions in freshwater production costs, improvements in wastewater treatment efficiency, and improvements in energy recovery efficiency.

The present invention is not limited to the above-described embodiment, and various modifications are possible without departing from the spirit of the present invention.

1 Wastewater treatment and water production system 2 Primary sedimentation tank 3 Pretreatment facility (pretreatment section)
4. Domestic wastewater (domestic wastewater supplied to primary sedimentation tank 2)
5 Domestic wastewater (domestic wastewater supplied to the FO membrane 20)
6 Sediment 7 Seawater 8 Supernatant 9 Means for performing FO treatment process (means for performing forward osmosis treatment process)
10 Means for performing RO treatment process (means for performing reverse osmosis treatment process)
11 freshwater area 12 low concentration seawater area 14 reverse osmosis membrane (RO membrane)
15 Fresh water 17 Normal concentration seawater 19 Drainage area 20 Forward osmosis membrane (FO membrane, semipermeable membrane)
21 Anaerobic treatment section 22 Low concentration seawater 23 Gas-solid-liquid separation section 24 Concentrated wastewater 25 Biogas ( _CH4 )
26 Anaerobic treated water 27 Aerobic treatment section 28 Seawater area 29 Aerobic treated water 30 Gas collection pipe 31 Final settling tank 33 Discharge water 35 Excess sludge 37 Return sludge

Claims (4)

a means for carrying out a forward osmosis treatment process in which solid matter-removed domestic wastewater is supplied, and the water in the wastewater is transferred to seawater through a semipermeable membrane to obtain concentrated wastewater, while seawater is supplied and diluted with the water in the wastewater that has transferred through the semipermeable membrane to obtain low-concentration seawater;
A means for carrying out a reverse osmosis treatment process in which diluted seawater is supplied under pressure and passed through a semipermeable membrane to obtain fresh water;
an anaerobic treatment section that generates biogas while decomposing organic matter in the concentrated wastewater using anaerobic microorganisms;
and an aerobic treatment unit that treats organic matter and the like in organic matter-containing wastewater using aerobic microorganisms.
A wastewater treatment and water production system comprising: The means for carrying out the forward osmosis treatment step supplies the concentrated wastewater obtained from the forward osmosis treatment step to the anaerobic treatment unit, and brings organic matter into contact with microorganisms to generate the biogas.
2. The wastewater treatment and freshwater production system according to claim 1 . The reverse osmosis treatment step is to obtain fresh water by pressurizing and supplying the diluted seawater obtained in the forward osmosis treatment step.
2. The wastewater treatment and freshwater production system according to claim 1 . The method further comprises a primary filtration device connected to a storage tank for storing the inflowing wastewater, physically removing solids in the inflowing supernatant water and discharging the filtered wastewater, and a pretreatment device for supplying the prefiltered wastewater to a means for carrying out the forward osmosis treatment step.
2. The wastewater treatment and freshwater production system according to claim 1 .

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