JP2022185956A - Organic waste water treatment system - Google Patents

Abstract

To provide a waste water treatment system suitable for treatment of organic waste water containing food product derivation sugars, with low energy consumption and formation of undesired by-products.SOLUTION: An organic waste water condensation part condenses saccharides in waste water containing sugars from food product derivation. A hydrothermal treatment part converts the saccharide contained in the condensed waste water to at least 1 of furfural and 5-hydroxymethyl furfural by hydrothermal treatment. A recovery part recovers at least 1 species selected from furfural and 5-hydroxymethyl furfural obtained by hydrothermal treatment. The wastewater treatment system has a methane fermentation part that decomposes organic matter remaining in waste water from which at least 1 of furfural and 5-hydroxymethyl furfural is recovered in the recovery part into biogas by methane fermentation.SELECTED DRAWING: Figure 1

Description

The present disclosure relates to organic wastewater treatment systems.

Food-derived organic wastewater containing sugars discharged from food factories, waste food processing facilities, etc., has a high biochemical oxygen demand (BOD value), and from the viewpoint of water pollution prevention, it is environmentally friendly. Treatment is required to remove organic matter before discharge.
Among them, organic wastewater containing sugars derived from food is generated in large quantities and has a low concentration of organic components, so compared to general organic wastewater, for example, anaerobic treatment There is a problem that the introduction of such methane fermentation is limited. For example, the concentration of saccharides contained in organic wastewater discharged from a noodle factory, which is a food factory that manufactures noodles, is about 5% by mass.

BACKGROUND ART In recent years, in the treatment of organic wastewater, reductions in energy consumption, the amount of residual waste, and costs have been demanded from the viewpoint of improving treatment efficiency.
As a treatment method for organic wastewater, a part of organic matter is separated as solid matter by aeration treatment, that is, a pressure flotation method, and removed as sludge, and the remaining wastewater is aerobicly treated and converted to _CO2 . and discharge it into the sewage system. Aeration treatment has the problem of consuming a large amount of energy during the treatment process, and also produces solid by-products such as scum and sludge, which must be treated separately as waste.
Other methods for treating organic wastewater include anaerobic treatment using methanogenic bacteria using an upflow anaerobic sludge blanket digestion (UASB reactor) or the like. .
Anaerobic treatment consumes less energy than aerobic treatment, but from the perspective of recovering valuables for the purpose of reducing treatment costs, methane gas recovered as valuables is inexpensive, so it is cost effective. still has room for improvement.

From the viewpoint of effective utilization of organic wastewater, attempts have been made to reduce wastewater treatment costs by extracting valuable substances from organic substances in biomass. A technique for extracting furfural from hemicellulose in lignocellulosic biomass by pressurized hot water treatment in the presence of an aqueous solution of phosphoric acid has been proposed (see Patent Document 1).
Ethanol is extracted by subjecting the pre-hydrolyzed liquid generated in the pulp manufacturing process to ethanol fermentation, the remaining treated liquid is subjected to acid treatment and dehydration reaction to produce furfural, and the remaining treated liquid is subjected to methane fermentation to methane and methane fermentation. A method for obtaining drainage has been proposed (see Patent Document 2).
In addition, as a technology focusing on raw sugar, a method for producing 5-hydroxymethyl-2-furfural suitable for industrial-scale production is proposed, in which a sugar containing hexose as a constituent sugar or a derivative thereof is subjected to a dehydration reaction using activated carbon as a catalyst. It is It is disclosed that 5-hydroxymethyl-2-furfural obtained by using activated carbon as a catalyst can also be easily recovered (see Patent Document 3).

JP 2014-214086 A JP 2014-166172 A Japanese Patent Application Laid-Open No. 2018-2701

Both of the techniques described in Patent Document 1 and Patent Document 2 have the problem of recovering valuables from waste liquid, but they are technologies related to waste liquid treatment for the purpose of effective use of cellulosic biomass. There is no focus on application to treatment of organic wastewater that is generated in large quantities and has a low concentration, such as organic wastewater.
Patent Document 3 relates to a technology for industrially producing 5-hydroxymethyl-2-furfural from limited raw sugars with high efficiency, and is suitable for application to the treatment of organic wastewater containing a mixture of various organic substances. do not have.

Even for food-derived organic wastewater that is generated in large quantities and contains low-concentration organic components, it suppresses the generation of unwanted by-products, efficiently recovers valuables with low energy, and organic components in wastewater. It is desired to construct a wastewater treatment system that reduces the wastewater treatment cost and reduces the environmental load by reducing the wastewater treatment cost.

An object of one embodiment of the present invention is to provide a wastewater treatment system that consumes less energy and produces less unwanted by-products and is suitable for treating organic wastewater containing food-derived sugars.

Means for solving the above problems include the following embodiments.
<1> An organic wastewater concentration unit that concentrates sugars in wastewater containing food-derived sugars, and a hydrothermal treatment of sugars contained in the concentrated wastewater to hydrothermally treat furfural and 5-hydroxymethylfurfural (hereinafter referred to as 5-HMF a hydrothermal treatment unit that converts into at least one selected from the hydrothermal treatment, a recovery unit that recovers at least one selected from furfural and 5-hydroxymethylfurfural converted from the wastewater that has undergone the hydrothermal treatment, and the hydrothermal treatment a wastewater treatment system comprising: a methane fermentation unit that decomposes organic matter remaining in wastewater that has passed through methane fermentation to convert it into biogas containing methane gas, and recovers the biogas.

According to the first embodiment of the present disclosure, first, the organic wastewater concentrating part concentrates sugars and reduces the water content in the wastewater, so that the subsequent hydrothermal treatment part consumes less energy and produces by-products. Production is suppressed, and valuable resources such as furfural and biogas can be obtained efficiently.
Furthermore, since the residual waste liquid from which organic matter such as furfural has been collected in advance in the collection unit has a reduced content of organic matter, the volumetric load on the fermenter in the methane fermentation unit performed downstream of the collection unit is improved. and the fermenter can be made smaller.
Also, the residual wastewater treated by methane fermentation and the wastewater separated in the organic wastewater concentrator have a low content of organic matter. Therefore, it is possible to further reduce the load on the wastewater treatment equipment such as the aerobic treatment section provided as desired downstream of the methane fermentation section.

<2> The wastewater treatment system according to <1>, wherein the organic wastewater concentration unit includes a reverse osmosis membrane (hereinafter also referred to as RO membrane).

According to the second embodiment of the present disclosure, in the first embodiment of the present disclosure, by applying membrane technology to separate organic matter and water in the organic wastewater concentrating section, with lower energy consumption, Organic substances can be efficiently concentrated. Moreover, since the waste liquid separated by the RO membrane contains almost no organic components, it can be discharged as it is as treated water.

<3> The method according to <1> or <2>, further comprising an aerobic treatment unit that aerobically treats at least one of the wastewater separated in the organic wastewater concentration unit and the wastewater separated in the methane fermentation unit. wastewater treatment system.

According to the third embodiment of the present disclosure, in the first embodiment or the second embodiment of the present disclosure, by further providing an aerobic treatment section, the wastewater separated in the organic wastewater concentration section and Further aerobic treatment of at least one of the wastewater separated in the methane fermentation section enables sewage discharge with less environmental load.
The wastewater supplied to the aerobic treatment section in the third embodiment has the organic component content reduced in the organic wastewater concentration section or the methane fermentation section in advance. Therefore, the energy consumption in the aerobic treatment section is further reduced.

According to one embodiment of the present invention, it is possible to provide a wastewater treatment system that consumes less energy and produces less unwanted by-products and is suitable for treating organic wastewater containing food-derived sugars.

1 is a system configuration diagram showing a wastewater treatment system according to an embodiment of the present disclosure; FIG. FIG. 2 is a system configuration diagram showing a wastewater treatment system according to another embodiment of the present disclosure; FIG. 1 is a system configuration diagram showing one embodiment of a conventional wastewater treatment system to which aerobic treatment is applied; FIG.

The wastewater treatment system of the present disclosure will now be described in detail.
The description of the constituent elements described below may be made based on representative embodiments of the present disclosure, but the present disclosure is not limited to such embodiments.
In addition, in the present disclosure, "to" indicating a numerical range is used to include the numerical values described before and after it as a lower limit and an upper limit.
In the numerical ranges described step by step in the present disclosure, the upper limit value or lower limit value described in one numerical range may be replaced with the upper limit value or lower limit value of another numerical range described step by step. Also, in the numerical ranges described in the present disclosure, the upper or lower limits of the numerical ranges may be replaced with the values shown in the examples.
In the present disclosure, a combination of two or more preferred aspects is a more preferred aspect.
In this disclosure, 5-hydroxymethyl-2-furfural and 5-hydroxymethylfurfural are sometimes referred to as "5-HMF." At least one selected from the group consisting of furfural and 5-HMF may be collectively referred to as "furfurals".
In the present disclosure, "room temperature" refers to 25°C unless otherwise specified.
In the present disclosure, the term "process" includes not only an independent process but also a process that cannot be clearly distinguished from other processes as long as the intended purpose of the process is achieved.
Components shown using the same reference numerals in each drawing mean the same components.
The dimensional ratios in the drawings do not necessarily represent the actual dimensional ratios.

A wastewater treatment system according to an embodiment of the present disclosure will be described below with reference to the drawings.

(Wastewater treatment system: first embodiment)
FIG. 1 shows a system configuration diagram of a wastewater treatment system 10 according to the first embodiment of the present disclosure.

The wastewater treatment system 10 includes an organic wastewater concentration unit 12 for concentrating the organic components of wastewater containing food-derived organic components, a hydrothermal treatment unit 14 for hydrothermally treating the concentrated wastewater, and an organic It comprises a recovery unit 16 that recovers furfurals converted from components, a methane fermentation unit 18 that performs methane fermentation treatment of wastewater from which furfurals have been recovered, and conveying equipment 30A to 30G including pumps (not shown). there is

Conveying facilities 30A-30G are configured with piping provided with pumps (not shown) useful for conveying waste water as needed.

As shown in FIG. 1, wastewater containing organic components including food-derived sugars (described as “organic wastewater” in FIG. 1) is conveyed to organic wastewater concentrating section 12, where , a concentrate in which organic components are concentrated, and a separated waste water containing a large amount of water.
The concentrated liquid concentrated in the organic wastewater concentration unit 12 is transported to the hydrothermal treatment unit 14 through a pipe 30A, which is transport equipment.
The separated wastewater containing a large amount of water separated by concentration is discharged to the sewage through the pipe 30B, or transported to an aerobic treatment section (not shown) as necessary.

－Organic Wastewater Concentrator－
The organic wastewater concentrator 12 in the wastewater treatment system 10 of the present disclosure concentrates organic wastewater containing food-derived sugars.
Organic wastewater containing sugar discharged from food factories, etc. is discharged in large quantities from food manufacturing processes, food washing processes, etc. The concentration of is low and the content of liquid components is high.
Organic wastewater containing food-derived sugars contains organic components other than sugars, such as proteins and lipids. There are various types and contents.
If the organic wastewater containing food-derived sugars contains proteins in addition to sugars, the proteins are decomposed in the hydrothermal treatment section described later and converted to methane in the methane fermentation section, so there is no particular need for separation. It can be treated with the wastewater treatment system of the present disclosure. On the other hand, since lipids are difficult to decompose in the hydrothermal treatment part, it is preferable to consider separation and removal of lipids prior to applying the lipid-rich organic wastewater to the wastewater treatment system of the present disclosure.

When converting sugars contained in food-derived organic wastewater into furfurals, it is necessary to heat the organic wastewater. Here, a lot of energy is required to raise the temperature of the wastewater containing a large amount of solvent.
In the wastewater treatment system of the present disclosure, an organic wastewater concentrating unit is provided to concentrate organic wastewater containing sugars, thereby obtaining a concentrated liquid having a higher concentration of organic components, especially sugars, in the organic wastewater. be able to. In addition, the separated waste water containing a large amount of the solvent, which is mainly water, separated from the concentrate becomes the separated waste water with extremely little remaining organic components such as sugars.
By increasing the concentration of saccharides in the organic waste water concentrating part and obtaining a concentrated liquid with a reduced amount of solvent such as water, in the hydrothermal treatment to obtain valuable components such as furfurals from the concentrated liquid, energy consumption required for heating is reduced. can be lower.

There is no particular limitation on the concentration rate of the organic wastewater in the organic wastewater concentration section, and the effect is achieved as long as the amount of solvent is reduced compared to the organic wastewater introduced into the organic wastewater concentration section.
Among them, from the viewpoint of efficiency of the treatment in the hydrothermal treatment part, it is preferable to concentrate the saccharide content in the obtained concentrated liquid in the range of 1% to 20% by mass, and 3% to 10% by mass. It is more preferable to concentrate in the range of mass %.

There are no particular restrictions on the concentration method in the organic wastewater concentration section, and known methods can be applied.
Concentration methods include a method of concentrating organic wastewater by filtration using a membrane such as a reverse osmosis membrane (RO membrane), a boiling concentration method of heating organic wastewater at a high temperature to evaporate the water content, and concentrating the organic wastewater. Vacuum concentration method in which organic wastewater is decompressed at low temperature to evaporate water content, freeze concentration method in which water contained in organic wastewater is frozen and ice crystals are separated and extracted, and concentration methods that combine these methods arbitrarily, etc. is mentioned.

Among them, the concentration method using an RO membrane is preferable from the viewpoints that energy consumption is low, efficient concentration can be achieved, and the separated waste water is clean. RO membranes are generally membranes with pores of 2 nm or less, and in order to continuously obtain a concentrate containing a large amount of sugars, it is necessary to apply a pressure exceeding the osmotic pressure of sugars.
In the present disclosure, "RO membrane" refers not only to general reverse osmosis membranes (RO membranes), but also to nanofilters (nanofiltration membranes: NF membranes) having relatively larger pore sizes than RO membranes, such as , the diameter of the opening is 1 nm to 2 nm, and the separation efficiency of ions and the like is 70% or less, which is lower than that of the RO membrane.
Separation of the concentrated liquid and the separated wastewater by the RO membrane can be carried out by a known method. Since the amount of water permeated through the RO membrane is temperature dependent, the pressurization conditions above the osmotic pressure required for separation can be appropriately adjusted in consideration of the temperature of the organic wastewater and the type of sugars contained in the organic wastewater. good.

－Hydrothermal treatment department－
The concentrated liquid obtained in the organic wastewater concentrating section 12 is conveyed to the hydrothermal treatment section 14 through a pipe 30A, which is a conveying facility.
In the hydrothermal treatment section, the concentrated liquid is treated at high temperature and high pressure in a closed system, and sugars in the organic wastewater can be converted into furfurals.
According to the hydrothermal treatment, since the system becomes high temperature and high pressure, water maintains a liquid state in a subcritical state and is considered to have a high hydrolytic capacity.
The concentrated liquid treated in the hydrothermal treatment section is not particularly limited as long as it contains sugars and water as a solvent.
Apparatuses such as an autoclave, a tubular reactor, a flow reactor, etc. can be applied to the hydrothermal treatment section.
The concentrated liquid is put into the reaction apparatus of the hydrothermal treatment section and subjected to hydrothermal treatment at the temperature and pressure shown below, whereby the reaction proceeds and the saccharides in the concentrated liquid are converted to furfurals.

The temperature of the hydrothermal treatment section can be 100°C to 400°C, preferably 140°C to 260°C, more preferably 140°C to 230°C. By heating to the above temperature range, furfurals can be efficiently obtained from the concentrate.

In the hydrothermal treatment section, furfurals are produced by treating the concentrated liquid in the above temperature range, so no particular catalyst is required.
From the viewpoint of improving the production efficiency of furfurals, the hydrothermal treatment may be performed in the presence of a catalyst. When a catalyst is used, a known catalyst can be appropriately selected and used. Examples of catalysts that can be used in the hydrothermal treatment unit include modified or unmodified activated carbon, organic acids such as citric acid, inorganic acids such as sulfuric acid, solid acid catalysts such as ion exchange resins, and catalysts with controlled active points. A zeolite catalyst etc. are mentioned.
The pressure in the hydrothermal treatment section may be normal pressure, but from the viewpoint of reaction efficiency, pressurization is also a preferred embodiment.
The pressurizing condition for pressurizing the hydrothermal treatment section is preferably 0.15 MPa to 10 MPa, more preferably 1.0 MPa to 3.5 MPa.
The reaction time is preferably 0.2 hours to 3.0 hours, more preferably 0.5 hours to 1.5 hours.
After completion of the reaction, it is preferable to cool the temperature inside the apparatus in the hydrothermal treatment section to room temperature (25° C.).

In general, various attempts have been made to efficiently produce furfurals from saccharides, celluloses and the like. However, the wastewater treatment system of the present disclosure is intended to consume less energy and produce less undesirable by-products in the treatment of organic wastewater containing sugars. According to the wastewater treatment system of the present disclosure, furfurals as valuables can be obtained in the hydrothermal treatment unit, so that the cost of the entire wastewater treatment system can be suppressed. Furthermore, biogas as a valuable resource can be recovered in the subsequent methane fermentation section. Therefore, extremely efficient furfurals production in the hydrothermal treatment section is not important in the wastewater treatment system of the present disclosure.

The concentrated liquid hydrothermally treated in the hydrothermal treatment unit 14 contains furfurals produced by the hydrothermal treatment, organic acids that are organic components derived from organic wastewater and have not been converted to furfurals, and solvents. and at least water. The concentrated liquid hydrothermally treated in the hydrothermal treatment unit 14 is cooled to room temperature and then conveyed to the recovery unit 16 through the pipe 30C, which is a conveying facility.

-Recovery Department-
In the recovery unit 16, furfurals produced in the concentrate are recovered.
A known method can be applied to recover furfurals in the concentrate in the recovery section.
As a recovery method, a method of introducing the concentrate into a container impermeable to the concentrate and allowing the furfurals to be adsorbed by an adsorbent such as activated carbon or ion exchange resin, or a method of extraction with an organic solvent such as a mixed solvent of hexane/acetone. etc.
It is also preferable to subject the concentrate to solid-liquid separation, remove fine solid components, and then bring only the separated liquid component into contact with the adsorbent before contacting the concentrate with the adsorbent. By removing the solid components from the concentrated liquid in advance, it is possible to prevent the solid components from adhering to the pores of the adsorbent such as activated carbon and lowering the adsorption efficiency.
In the case of adopting a method of adsorbing furfurals on an adsorbent, the adsorbent is washed with an organic solvent so that the furfurals are eluted into the organic solvent and highly pure furfurals are recovered. The collected furfurals are collected and stored as valuables through a pipe 30D, which is a transportation facility.

Furfurals are attracting attention as biomass-derived chemical raw materials that can replace fossil resources.
Furfural is useful as a solvent, a raw material for synthetic rubber, a raw material for producing furan resin, and a raw material for producing adipic acid, which is a raw material for polyamide. In addition, 5-HMF is useful as a raw material for biofuels and a raw material for synthetic resins, and is also used as a physiologically active substance.
Therefore, furfural and furfurals such as 5-HMF recovered by the recovery unit 16 can be sold as valuables. Therefore, it can be expected that the operating cost of the wastewater treatment system will be reduced.
The wastewater treatment system of the present disclosure has the advantage of being able to continuously recover furfurals at a constant yield.

The remaining wastewater from which furfurals have been recovered in the recovering unit 16 is conveyed to the methane fermentation unit 18 as a purification processing unit through a pipe 30E as a conveying facility. In the residual wastewater, organic components other than furfurals such as organic acids remain, and it is difficult to discharge the wastewater as it is as treated water. Therefore, the organic matter is further recovered in the methane fermentation section 18 as a purification processing section.

－Methane Fermentation Division－
In the methane fermentation unit 18, methane fermentation is performed using waste water remaining after the furfurals are taken out in the recovery unit 16 as a raw material to generate and recover biogas containing methane gas.

The waste liquid after the furfurals are taken out contains fine food-derived organic substances and organic substances such as organic acids.
Examples of the organic components in the wastewater include soluble components such as organic acids dissolved in the wastewater and insoluble organic components contained in the wastewater.

In the methane fermentation section, anaerobic treatment, that is, under anaerobic conditions, anaerobic microorganisms such as acid-producing bacteria and methanogenic bacteria are used to decompose the organic components of the remaining wastewater to produce methane gas, carbon dioxide, etc. get biogas.
A known fermenter can be applied to the methane fermentation unit. As the fermenter, for example, a UASB reactor, a fluidized bed reactor, a fixed bed reactor, or the like is preferably used.
As the anaerobic bacteria used in the methane fermentation section, known anaerobic bacteria capable of decomposing organic components under anaerobic conditions can be applied.

Since methanogens have a low growth rate, there is a concern that they may be washed away together with the treated water, resulting in a decrease in treatment capacity. Therefore, in order to maintain the treatment capacity, it is preferred that the anaerobes are self-granulated or immobilized on a carrier and placed in the fermenter. For example, in the method using a UASB reactor, good reactivity is achieved by forming granulated sludge with excellent sedimentation properties of about 0.5 mm to 2 mm, which is formed by self-granulation of methanogens. .
Fermentation conditions are not particularly limited, and are appropriately selected in consideration of the residual amount of organic components, the amount of wastewater to be treated, and the like.

Anaerobic microorganisms such as methanogens are placed in the fermenter. The organic components in the organic acid-containing wastewater supplied through the pipe 30E through the recovery unit 16 are decomposed by methane fermentation in the methane fermentation unit.
Conditions for the anaerobic treatment in the methane fermentation section include a medium temperature method with a reaction temperature of around 37° C. and a high temperature method with a reaction temperature around 55° C., both of which can be applied.
From the viewpoint of fermentation efficiency, the high-temperature method is more efficient, but requires energy for heating. Heating is not necessary in the case of the medium temperature method. Since the wastewater treatment system of the present disclosure treats wastewater from which valuables as organic components have been removed in advance, stable treatment efficiency can be expected even with the intermediate temperature method. If desired, two mesophilic fermenters may be provided to carry out two-step fermentation.
Since the preferred conditions for anaerobic microorganisms are near neutrality, the pH in the fermenter is preferably 6.0 to 8.5, more preferably 7.0 to 8.0. If desired, the pH of the waste liquid introduced into the methane fermentation section may be adjusted.
In order to maintain the treatment conditions for the anaerobic microorganisms within a suitable range, the anaerobic state of the fermenter can be controlled by measuring, for example, the oxidation-reduction potential.

In the methane fermentation section, the contact time between the wastewater to be treated and the anaerobic microorganisms in the fermenter, that is, the residence time of the wastewater in the fermenter is not particularly limited. For example, the retention time of the wastewater in the fermenter can be 5 hours to 30 days, preferably 6 hours to 20 days, more preferably 6 hours to 3 days.

The fermenter has an anaerobic atmosphere, and heating is not required when the mesophilic method is used, and aeration energy such as in aerobic treatment is not required.
The biogas produced in the methane fermentation section is mainly composed of methane gas and carbon dioxide, and is a valuable substance that can be applied as fuel or the like. Depending on the conditions, hydrogen sulfide may be produced as a by-product, and in such a case, treatment is performed to remove hydrogen sulfide from the biogas.
The biogas may be effectively used by supplying it to the outside as a fuel, for example, it can also be used as a heating fuel in the hydrothermal treatment section.
The wastewater treatment system of the present disclosure produces biogas as well as furfurals. Biogas can be provided as a commodity or used as an energy source for heating the wastewater treatment system, thus achieving the goal of cost reduction in the overall wastewater treatment system.

The biogas produced in the methane fermentation section 18 is recovered outside the system via the pipe 30G. The separated waste water after recovering the biogas is directly discharged to the sewage system through the pipe 30F when the remaining amount of the organic component is small. Even after the treatment in the methane fermentation unit 18, insoluble organic components such as components not decomposed by fermentation may remain in the separated wastewater. In such a case, it is preferable to remove the insoluble organic component by solid-liquid separation and then discharge it into sewage. The insoluble organic components separated by solid-liquid separation may be treated separately as waste.
The solid-liquid separation method is not particularly limited, and can be carried out by known methods such as filtration, centrifugation, and standing to precipitate solids.

In the wastewater treatment system of the present disclosure, organic matter such as furfural is previously collected in the recovery unit from the separated wastewater supplied to the methane fermentation unit, and the organic matter content in the wastewater is reduced. Therefore, the fermenter in the methane fermentation section that is performed downstream of the collection section can be made more compact.
Also, the residual wastewater treated by methane fermentation and the wastewater separated in the organic wastewater concentrator have a low content of organic matter. Therefore, when the content of the organic component is less than the predetermined amount, it can be directly discharged into the sewage. In addition, it is possible to reduce the processing load in the wastewater treatment facility such as the aerobic treatment section provided as desired downstream of the methane fermentation section.

(Wastewater treatment system: Second embodiment)
FIG. 2 shows a system configuration diagram of a wastewater treatment system 20 according to the second embodiment of the present disclosure.

The wastewater treatment system 20 includes an organic wastewater concentration unit 12 for concentrating the organic components of wastewater containing food-derived organic components, a hydrothermal treatment unit 14 for hydrothermally treating the concentrated wastewater, and an organic A recovery unit 16 that recovers furfurals converted from components, a methane fermentation unit 18 that performs methane fermentation treatment of wastewater from which furfurals have been recovered, and an aerobic treatment unit that performs aerobic treatment of separated wastewater separated from the methane fermentation unit 18. 22 and transfer facilities 30A to 30H including pumps (not shown).

Conveying facilities 30A-30H are configured with piping provided with pumps (not shown) useful for conveying waste water as needed.
The wastewater treatment system 20 has the same configuration as the wastewater treatment system 10 according to the first embodiment, except that an aerobic treatment section 22 is provided downstream of the methane fermentation section 18 . Therefore, descriptions of the organic wastewater concentration unit 12, the hydrothermal treatment unit 14, the recovery unit 16, and the methane fermentation unit 18 are omitted.

－Aerobic treatment part－
The aerobic treatment unit 22 shown in FIG. 2 is provided downstream of the methane fermentation unit 18, and treats the separated wastewater from which the biogas has been recovered in the methane fermentation unit 18, further treats the wastewater under aerobic conditions, and discharges it to sewage. It is a processing unit that performs a suitable purification process.
The aerobic treatment unit 22 is a treatment unit that applies an activated sludge method or a carrier fluidized bed method in which organic components in wastewater are decomposed by aerobic microorganisms.
The aerobic treatment section 22 generally includes an aeration tank and a sedimentation tank.

The aeration tank includes water in which agglomerates (flocs) of aerobic microorganisms float, and an exhaust pipe for sending air into the water to activate the aerobic microorganisms. The exhaust pipe is usually located at or near the bottom of the aeration tank.
The aeration tank is filled with water in which flocs enriched with aerobic microorganisms are suspended. Air is jetted into the aeration tank as fine bubbles from an air diffuser placed near the bottom of the aeration tank. The supply of air activates aerobic microorganisms and decomposes organic components in the wastewater.
The sedimentation tank connected to the aeration tank has the function of separating the treated water from which the organic components have been decomposed and removed from the flocs as activated sludge by sedimentation.
The supernatant liquid in the sedimentation tank can be discharged into the sewage system as treated water. The floc as activated sludge precipitated in the sedimentation tank may be recovered from the bottom of the sedimentation tank and supplied to the aeration tank again. In addition, in order to improve the volume load, a carrier for retaining the cells may be added to the aeration tank.
The aerobic treatment unit 22 is supplied with the separated wastewater separated from the concentrate in the organic wastewater concentrating unit 12 and the separated wastewater after the biogas is recovered in the methane fermentation unit 18, and is subjected to aerobic treatment. be.
The supernatant liquid in the sedimentation tank, which has been treated by the aerobic treatment unit 22 and the content of organic components has been reduced, is discharged to sewage through the pipe 30H.

In the wastewater treatment system 20 according to the second embodiment, the wastewater separated from the organic wastewater concentrator 12 and the methane fermentation unit 18 is further subjected to aerobic treatment, thereby further improving the water quality of the wastewater discharged into sewage.
The separated wastewater from the organic wastewater concentrating unit 12 is preferably water separated by an RO membrane and contains almost no organic components, and the separated wastewater from the methane fermentation unit 18 is also water treated by the hydrothermal treatment unit 14 and the methane fermentation. This is water from which organic components have been previously removed in the section 18 . Therefore, according to the wastewater treatment system of the present disclosure, it is possible to improve the water quality of wastewater with less energy than general aerobic treatment.

FIG. 3 shows a system configuration diagram showing an example of a conventional wastewater treatment system. A conventional wastewater treatment system 40 as an example is a system using aerobic treatment, and has an aerobic treatment section 22 and a pressurized flotation treatment section 24 for pressurized flotation performed prior to aerobic treatment. .
The pressurized flotation processing unit 24 floats and separates sludge contained in the organic wastewater by a pressurized flotation method. Specifically, air is compressed and dissolved in the organic wastewater of the pressurized flotation treatment unit 24 by a pressurization pump (not shown), and sludge in the wastewater adheres to fine bubbles to float them. This method is also called aeration treatment. The scum separated by the aeration treatment is sucked by a suction pump (not shown), collected through the pipe 30I, and treated as waste.
The wastewater remaining in the pressurized flotation treatment section 24 is sent to the aerobic treatment section 22 via the pipe 30J. The aerobic treatment unit 22 holds a carrier to which microorganisms are attached, and organic components in the wastewater are biologically treated. Solids in the treated organic wastewater are collected via a pipe 30K equipped with a discharge valve (not shown) and treated as sludge.
The configuration of the aerobic treatment unit 22 is the same as in the wastewater treatment system 20 according to the second embodiment of the present disclosure.
The separated wastewater whose organic components have been reduced in the aerobic treatment section 22 is discharged to sewage through a pipe 30L provided with a discharge valve (not shown).
The conventional wastewater treatment system 40 has the problem that energy is required to compress and dissolve the air in the aeration process, and waste such as scum and sludge is generated.

The wastewater treatment system of the present disclosure may have other configurations as necessary in addition to the above treatment units, ie, the organic wastewater concentration unit, the hydrothermal treatment unit, the recovery unit, and the methane fermentation unit.
Other configurations include a foreign matter removal device that removes solid foreign substances other than organic components from organic wastewater containing food-derived sugars, and an oil-water separation device that removes oil such as lipids from organic wastewater. Alternatively, a pressurized levitation device or the like may be used.
Another configuration includes a pressurized flotation treatment section that floats and separates sludge generated in the aerobic treatment section described above by a pressurized flotation method.

[Example 1]
A wastewater treatment system 20 having an aerobic treatment section 22 shown in FIG. 2 was used as the wastewater treatment system.

(Preparation of model wastewater and measurement of TOC)
A 1% by weight starch aqueous solution was prepared as a model of food-derived wastewater.
The treatment is carried out with a processing amount of 50 tons per day.
Unless otherwise specified, the amount of wastewater, power consumption, thermal energy, etc., all indicate amounts per day.
The amount of organic carbon contained in 50 tons of 1% by weight starch aqueous solution is about 222 kg, and the total organic carbon (TOC) present in water is about 4 g/L (liter).
TOC in wastewater can be measured, for example, by the combustion oxidation method described below. In this example, model wastewater containing no inorganic carbon is used, and thus the usual step of removing inorganic carbon is omitted.
(Combustion oxidation method)
Model water is filled with air and an oxidation catalyst such as cobalt oxide, platinum, or palladium, and supplied to a combustion tube heated to 900° C. to 950° C. to oxidize organic matter to carbon dioxide.
The amount of carbon dioxide generated is measured by an infrared analyzer, specifically, a non-dispersive infrared gas detector (NDIR) to determine the total carbon amount.

(Organic wastewater concentrator: hereinafter abbreviated as "wastewater concentrator")
The model wastewater is input to the wastewater concentration unit 12, where the wastewater is concentrated. Concentration is performed using a reverse osmosis membrane (RO membrane) concentrator equipped with an ultrafiltration membrane (UF membrane: MWCO 1,000) (manufactured by Alfa Laval, RO98pHt).
By the treatment in the wastewater concentrating unit 12, the wastewater is separated into 5.0t, that is, a concentrate containing 10-fold concentrated starch (organic carbon content: 211kg) and 45t of separated wastewater (residual carbon content: 11kg). be.
In the wastewater concentration unit 12, the energy consumption used for concentration such as pressurization necessary for the reverse osmosis membrane method is 600 kWh.
The concentrated liquid is conveyed to the hydrothermal treatment section 14 from the pipe 30A. The separated waste water is conveyed to the aerobic treatment section 22 through the pipe 30B.

(Hydrothermal treatment department)
The hydrothermal treatment unit 14 heats the concentrated liquid conveyed from the wastewater concentration unit 12 to obtain furfurals. The temperature in the hydrothermal treatment section 14 is 230° C., and the pressure is 3.0 MPa.
The heat energy for heating for processing 5.0 t of the concentrated liquid was 3780 MJ, and the power consumption used in the hydrothermal treatment section 14 was 200 kWh.
As a result of analysis, 89 kg of furfural was produced in the concentrate by the treatment in the hydrothermal treatment unit 14 . The concentrated liquid that has been hydrothermally treated and contains furfural is transported to the recovery section via the pipe 30C.

(Recovery Department)
The concentrated liquid containing furfural is collected in the collection unit 16 by allowing activated carbon to adsorb the furfural contained in the concentrated liquid. Furfural and the like adsorbed on activated carbon are recovered with an organic solvent, and the organic solvent is evaporated to increase the purity of furfural and the like.
The thermal energy for heating the organic solvent is 500 MJ, and the power consumption used in the recovery unit 16 is 100 kWh.
The total amount of the remaining concentrated liquid from which furfural was recovered in the recovery unit 16 remained almost unchanged after the recovery of furfural, and was about 5.0 t. The organic carbon converted to furfural was 40.6 kg, and the remaining concentration The amount of organic carbon in the liquid is 144 kg.
The remaining concentrated liquid is conveyed to the methane fermentation section 18 via the pipe 30E.

The furfural adsorbed by the activated carbon in the recovery unit 16 is recovered by washing the activated carbon with acetone, which is an organic solvent, to remove the organic solvent. The amount of furfural produced is 71.2 kg. The price of furfural converted at the market price in March 2021 is estimated at 50,000 yen.

(Methane Fermentation Department)
A UASB reactor is used for the fermentation tank in the methane fermentation section 18 . The fermenter is provided with a carrier on which methanogens are carried.
The separated wastewater separated by the collection unit 16 is carried into the fermentation tank. The fermenter is equipped with an agitator and the separated wastewater is brought into contact with the methanogens while being agitated. The temperature in the fermenter is maintained at around 37°C and the pH at around 7.5. The separated wastewater remains in the fermenter for about 24 hours, and biogas is produced by decomposing the organic components in the wastewater by the action of methanogenic bacteria. The produced biogas is collected from the top of the fermenter through the pipe 30G.
The separated wastewater from which the biogas has been recovered is transported to the aerobic treatment section 22 via the pipe 30F.
In the methane fermentation section 18, power consumption used for temperature maintenance and agitation of the fermenter is 164 kWh.
Of the recovered biogas, methane gas is 102 kg. The amount of heat that can be generated by 102 kg of methane gas is estimated at 5125 MJ.

(Aerobic treatment section)
The separated wastewater carried into the aerobic treatment section 22 is introduced into an aeration tank in the aerobic treatment section 22 . The aeration tank is equipped with water in which aggregates (flocs) of aerobic microorganisms are suspended, and an exhaust pipe that sends air into the water to activate the aerobic microorganisms, and is located near the bottom of the aeration tank. Air is jetted into the aeration tank as fine bubbles from the aeration pipe, and aeration treatment is performed. Aeration treatment activates aerobic microorganisms to further decompose organic components in the wastewater.
The wastewater aerated in the aeration tank is conveyed to a sedimentation tank connected to the aeration tank. In the sedimentation tank, the treated water in which organic components have been decomposed and removed in the aeration tank and flocs as activated sludge are separated by sedimentation.
The supernatant liquid in the sedimentation tank is discharged to the sewage through the pipe 30H as treated water having a reduced content of organic components.
Flocs as activated sludge precipitated in the sedimentation tank are collected from the bottom of the sedimentation tank and supplied to the aeration tank again. Here, the sludge whose activity has decreased is treated as sludge after being separated by sedimentation in a sedimentation tank.
The power consumption used for the aeration treatment in the aerobic treatment unit 22 is 471 kWh.

In the wastewater treatment system 20 of Example 1, the total power consumption is 1535 kWh per day, and the total amount of heat consumed by the hydrothermal treatment unit 14 and the like is 4413 MJ per day.
As described above, the retained heat quantity of the biogas obtained in the methane fermentation section 18 was 5125 MJ per day. Therefore, in the wastewater treatment system 20 of Example 1, it is a trial calculation that the amount of heat for heating the system can be supplemented by the amount of heat obtained by treating the wastewater.
The amount of sludge discharged is 86 kg per day. The discharged sludge is further subjected to solid-liquid separation, and the separated water has a low content of organic components like the supernatant, and can be discharged to sewage. In the case of solid-liquid separation, it is estimated that 30 kg of water per day can be discharged into sewage, and the amount of sludge generated can be reduced to 56 kg.
Therefore, according to the wastewater treatment system of Example 1, the valuable furfural can be continuously recovered. Furthermore, there is the advantage that the power consumption can be kept low, and the energy required for heating the system can be covered by the amount of heat stored in the valuable biogas.
According to the wastewater treatment system of Example 1, when treating organic wastewater containing food-derived sugars, less energy is consumed and less undesirable by-products are produced.

[Control Example 1]
In Comparative Example 1, power consumption and the like are estimated when a wastewater treatment system is used in which aerobic treatment is applied as a wastewater treatment system, and wastewater is aerated to separate sludge and treated water.
In Control Example 1, as in Example 1, a 1% by mass starch aqueous solution was used as a model of food-derived wastewater, and treatment was carried out with a treatment amount of 50 tons per day.
Similar to Example 1, the amount of organic carbon contained in 50 t of 1% by weight starch aqueous solution is about 222 kg, and the total amount of organic carbon (TOC) present in water is about 4 g/L.

The wastewater treatment system of Comparative Example 1 uses an aerobic treatment section similar to the apparatus applied to Example 1, which includes an aeration tank and a sedimentation tank. A 1% by mass starch aqueous solution is put into an aeration tank provided in the aerobic treatment section.
Assuming that the treatment amount is 50 tons per day, the total power consumption for heating and aerating the wastewater in the aeration tank is estimated to be 2919 kWh per day.
The wastewater aerated in the aeration tank is conveyed to a sedimentation tank connected to the aeration tank. In the sedimentation tank, the treated water in which organic components have been decomposed and removed in the aeration tank and flocs as activated sludge are separated by sedimentation.
In the sedimentation tank, 921 kg of sludge is collected. The supernatant in the sedimentation tank is discharged into sewage.
The sludge collected in the sedimentation tank may be further subjected to solid-liquid separation. Since the water separated by solid-liquid separation has a low content of organic components, it can be discharged into sewage. In the case of solid-liquid separation, it is estimated that 30 kg of water can be discharged into sewage per day, and the amount of sludge generated can be reduced to 186 kg.

In the wastewater treatment system of Control Example 1, no valuables are recovered. Further, in the wastewater treatment system of Comparative Example 1, heating such as in the hydrothermal treatment section and recovery section in Example 1 is unnecessary, and no heat is consumed.
On the other hand, in the wastewater treatment system of Comparative Example 1, the power consumption required for aeration treatment was 2919 kWh, which is 1.9 times the power consumption in the wastewater treatment system of Example 1. The amount of sludge generated is 10.7 times the mass.
In the wastewater treatment system of Comparative Example 1, valuables are not recovered, and the power consumption and the amount of sludge generated are higher than those of the wastewater treatment system of Example 1, so the wastewater treatment system of Example 1 The superiority of Example 1 over the wastewater treatment system is clear.

10, 20, 40 wastewater treatment system 12 organic wastewater concentration unit 14 hydrothermal treatment unit 18 methane fermentation unit 22 aerobic treatment unit 24 pressure flotation treatment units 30A, 30B, 30C, 30D, 30E, 30F, 30G, 30H, 30I , 30J, 30K, 30L Piping (conveyance equipment)

Claims (3)

an organic wastewater concentrator for concentrating sugars in wastewater containing food-derived sugars;
a hydrothermal treatment unit for hydrothermally treating sugars contained in the concentrated wastewater to convert them into at least one selected from furfural and 5-hydroxymethylfurfural;
a recovery unit for recovering at least one selected from furfural and 5-hydroxymethylfurfural obtained through the hydrothermal treatment;
a methane fermentation unit that decomposes organic matter remaining in the wastewater from which at least one selected from furfural and 5-hydroxymethylfurfural has been recovered in the recovery unit and converts it into biogas by methane fermentation, and recovers the biogas;
A wastewater treatment system with 2. The wastewater treatment system of claim 1, wherein said organic wastewater concentrator comprises a reverse osmosis membrane. 3. The wastewater treatment according to claim 1, further comprising an aerobic treatment section that performs aerobic treatment of at least one of the wastewater separated in the organic wastewater concentration section and the wastewater separated in the methane fermentation section. system.

Images