Carbon-neutral wastewater treatment system that improves energy efficiency and accelerates the granulation of microalgae

Abstract

A sewage treatment device and method using microalgae granules is disclosed. [Solution] According to one aspect of the present invention, there is provided a sewage treatment device characterized by a microalgae granule culture tank in which microalgae are cultured in a preset environment to form seeds, which are aggregates of microalgae and sludge, and in which the microalgae-sludge seeds produced in the microalgae granule culture tank are introduced to produce microalgae granules, which are then used to remove organic matter and nitrogen from the sewage.

Description

[Technical Field]

[0001] The present invention relates to a carbon-neutral sewage treatment system that improves energy consumption efficiency by accelerating the production of microalgae granules used to remove organic matter and nitrogen from sewage. [Background technology]

[0002] The content of this section is merely intended to provide background information for the present embodiment and does not constitute prior art.

[0003] Biological treatment processes for treating sewage wastewater require an appropriate concentration of dissolved oxygen to treat organic matter and induce nitrification reactions. For example, in the case of activated sludge processes, the energy used to supply oxygen accounts for approximately 60% of the total energy consumption of the sewage treatment process. In addition, because suspended microorganisms are used, problems with solid-liquid separation and treatment efficiency, such as bulking and foaming, can occur depending on the influent water properties and operating method.

[0004] As an alternative to the activated sludge process, aerobic granular sludge (AGS) has been proposed, which treats sewage by granulating suspended sludge. Aerobic granular sludge (AGS) can simultaneously remove carbon, nitrogen, phosphorus, and other pollutants in a single sludge system, and has the advantage of being superior in treatment efficiency while shortening settling time compared to the general activated sludge process.

[0005] However, sewage treatment using aerobic granular sludge (AGS) still has the same energy consumption problem as the activated sludge process, because it requires artificial aeration to maintain aerobic conditions and release CO2 into the atmosphere. Therefore, a sewage treatment method using microalgae has been proposed as an alternative to the traditional activated sludge process.

[0006] Sewage treatment methods using microalgae are a method of removing organic matter, nitrogen components, and other substances from sewage using microalgae. The microalgae can be autotrophic microalgae that absorb light and perform photosynthesis. Photoautotrophic microalgae produce oxygen through photosynthesis, allowing sewage to be treated under aerobic conditions without a separate oxygen supply, and the microalgae used can be used as biomass. Sewage treatment methods using microalgae can be applied by treating water by coexisting activated sludge and microalgae in a single reaction tank, or by forming sludge and microalgae into granules consisting of biological aggregates.

[0007] However, the sewage treatment method that uses granulated sludge and microalgae has the problem that it takes a considerable amount of time to granulate the sludge and microalgae and form granules. In conventional methods, it takes at least three months or more for the microalgae and sludge to form granules. Because it takes such a long time, it is difficult to completely solve the problems of activated sludge treatment methods in a short period of time, even with conventional methods. Summary of the Invention [Problem to be solved by the invention]

[0008] One embodiment of the present invention aims to provide a sewage treatment device including a culture tank and a granule reaction tank that can accelerate the production of microalgae granules so that they can be utilized as biomass with high energy productivity while reducing energy consumption in the sewage treatment process. [Means for solving the problem]

[0009] According to one aspect of the present invention, a sewage treatment device is provided, comprising: a primary treatment tank into which sewage flows and precipitates and separates suspended matter or solids in the sewage; a microalgae granule culture tank into which the sewage that has passed through the primary treatment tank flows and cultures microalgae in a predetermined environment to form seeds, which are aggregates of microalgae and sludge; a microalgae granule reaction tank into which the sewage that has passed through the primary treatment tank and the microalgae-sludge seeds produced in the microalgae granule culture tank flow and produce microalgae granules, and which uses the produced microalgae granules to remove organic matter and nitrogen from the sewage; and a settling tank into which the sewage that has passed through the microalgae granule reaction tank flows and separates residual suspended algae or residual microalgae granules.

[0010] According to one aspect of the present invention, the microalgae are photoautotrophic microalgae that perform photosynthesis.

[0011] According to one aspect of the present invention, the microalgae are selected from the group consisting of filamentous cyanobacteria or cyanobacteria.

[0012] According to one aspect of the present invention, the microalgae granules are characterized in that when light is incident on the microalgae granule reaction tank, a photosynthetic reaction by the microalgae and a nitrification reaction by the sludge occur, and when light is not incident on the microalgae granule reaction tank, a denitrification reaction by the sludge occurs.

[0013] According to one aspect of the present invention, the microalgae granule culture tank is characterized by forming seeds, which are mat-like aggregates of microalgae and sludge.

[0014] According to one aspect of the present invention, the preset environment of the microalgae granule culture tank is an anaerobic environment or an anoxic environment, and light is incident on the inside of the culture tank.

[0015] According to one aspect of the present invention, the microalgae granule reaction tank includes a reaction tank that stores inflowing sewage and produces granules from the inflowing microalgae-sludge seeds, an agitation unit that circulates and agitates the sewage and the microalgae granules inside the reaction tank, a light source unit that irradiates light into the inside of the reaction tank, and a control unit that controls the operation of the agitation unit and the light source unit.

[0016] According to one aspect of the present invention, the agitation unit is a hyperboloid agitator that generates a vertical water flow inside the reaction tank.

[0017] According to one aspect of the present invention, the system further includes an anaerobic digestion tank into which biomass flows from the primary treatment tank, the microalgae granule reaction tank, or the sedimentation tank and undergoes anaerobic digestion. [Effects of the Invention]

[0018] As described above, according to one aspect of the present invention, in order to prioritize photoautotrophic microalgae, seeds, which are aggregates of microalgae and sludge, are formed to accelerate the production of microalgae granules, and when applied to sewage treatment, there is an advantage in that the dominant species and sedimentation characteristics of microalgae can be maintained even during long-term operation.

[0019] In addition, according to one aspect of the present invention, the sewage treatment device uses microalgae granules, which allows for the creation of an aerobic environment in the sewage treatment process without the need for a separate oxygen supply, thereby reducing energy consumption. Furthermore, the high sedimentation properties of the microalgae granules have the advantage of increasing the biomass recovery rate. [Brief explanation of the drawings]

[0020] [Figure 1] 1 is a diagram showing the configuration of a sewage treatment device according to an embodiment of the present invention; [Figure 2] FIG. 1 is a diagram showing a cross section of a microalgae granule according to an embodiment of the present invention. [Figure 3]1 is a diagram illustrating the chemical action of microalgae granules in sewage according to an embodiment of the present invention. FIG. [Figure 4] FIG. 1 is a diagram showing the configuration of a microalgae granule culture tank according to an embodiment of the present invention. [Figure 5] FIG. 1 is a cross-sectional view of a microalgae granule reactor according to an embodiment of the present invention. [Figure 6] FIG. 2 is a diagram showing microalgae-sludge seeds cultured in a microalgae granule culture tank according to an embodiment of the present invention. [Figure 7A] 1 is an image showing a process of forming microalgae-sludge seeds in a microalgae granule culture tank according to an embodiment of the present invention. [Figure 7B] 1 is an image showing a process of forming microalgae-sludge seeds in a microalgae granule culture tank according to an embodiment of the present invention. [Figure 7C] 1 is an image showing a process of forming microalgae-sludge seeds in a microalgae granule culture tank according to an embodiment of the present invention. [Figure 8] 1 is an image showing microalgae-sludge seeds cultured in a microalgae granule culture tank according to an embodiment of the present invention and a non-microalgae culture tank. [Figure 9] 1 is an image showing the sedimentation properties of microalgae granules and the morphology of microalgae cultured using microalgae-sludge seeds according to an embodiment of the present invention. [Figure 10] 1 is an image showing the sedimentation of granules and the morphology of microalgae from seeds cultured in a culture tank of another type other than the culture tank of one embodiment of the present invention. [Figure 11] FIG. 2 is a diagram showing the shape of an agitation unit provided in a microalgae granule reaction tank according to an embodiment of the present invention. [Figure 12] FIG. 1 is a diagram showing the water flow pattern in the agitation unit of a microalgae granule reactor according to one embodiment of the present invention and in the reactor for a non-agitation unit. [Figure 13]10 is a photograph comparing the state of microalgae granules produced in a microalgae granule reactor according to an embodiment of the present invention with that of microalgae granules produced in a non-existent granule reactor. [Figure 14] 10 is a photograph comparing the sedimentation properties of microalgae granules produced in a microalgae granule reactor according to an embodiment of the present invention and microalgae granules produced in a non-existent granule reactor. [Figure 15] 3 is a flowchart illustrating a method for treating sewage by a sewage treatment device according to an embodiment of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0021] Although the present invention can be implemented in various forms and in various embodiments, specific embodiments will be illustrated in the drawings and described in detail. However, it should be understood that this is not intended to limit the present invention to the specific embodiments, but rather to include all modifications, equivalents, or alternatives that fall within the spirit and technical scope of the present invention. In describing the various drawings, like reference numerals are used to refer to like components.

[0022] Terms such as "first," "second," "A," and "B" may be used to describe various components, but the components should not be limited by these terms. These terms are used only to distinguish one component from another. For example, a first component may be referred to as a "second component," and similarly, a second component may be referred to as a "first component," without departing from the scope of the present invention. The term "and / or" includes a combination of multiple related listed items or any one of multiple related listed items.

[0023] When a component is said to be "coupled" or "connected" to another component, it should be understood that it may be directly coupled or connected to the other component, but that there may be other components in between. Conversely, when a component is said to be "directly coupled" or "directly connected" to another component, it should be understood that there are no other components in between.

[0024] The terms used in this application are merely used to describe specific embodiments and are not intended to limit the present invention. A singular expression includes a plural expression unless the context clearly indicates otherwise. In this application, it should be understood that terms such as "comprise" or "have" do not preclude the possibility of the presence or addition of features, numbers, steps, operations, components, parts, or combinations thereof described in the specification.

[0025] Unless otherwise defined, all terms used herein, including technical or scientific terms, have the same meaning as commonly understood by one of ordinary skill in the art to which this invention belongs.

[0026] Terms defined in commonly used dictionaries should be construed to have a meaning consistent with the meaning they have in the context of the relevant art, and should not be construed in an idealized or overly formal sense unless expressly defined in this application.

[0027] Furthermore, the configurations, processes, steps, or methods included in the embodiments of the present invention may be shared within the scope of not being technically inconsistent with each other.

[0028] FIG. 1 is a diagram showing the configuration of a sewage treatment device according to an embodiment of the present invention.

[0029] Referring to FIG. 1, a sewage treatment apparatus 100 according to one embodiment of the present invention includes a primary treatment tank 110, a microalgae granule culture tank 120, a microalgae granule reaction tank 130, a sedimentation tank 140, and an anaerobic digestion tank 150.

[0030] The sewage treatment device 100 uses microalgae granules to remove sources of contamination in sewage, such as organic matter and nitrogen.

[0031] Sewage treatment plants use various types of microorganisms to remove contaminants from sewage. After removing contaminants, the microorganisms present in each reactor of the plant must not be discharged along with the sewage. Therefore, after the reactor has completed the process of removing contaminants, it waits for the microorganisms to settle and then discharges only the supernatant.

[0032] This process significantly reduces the settling time of the granules containing microorganisms, thereby increasing the number of sewage treatments per unit period and improving treatment capacity. The sewage treatment device 100 includes a microalgae granule culture tank 120 and a microalgae granule reaction tank 130, and dramatically improves the production rate of granules, which are a combination of microalgae and sludge. As a result, the sewage treatment device 100 uses microalgae granules to remove organic matter and nitrogen from sewage, and can achieve the target water treatment efficiency using relatively little energy.

[0033] The primary treatment tank 110 receives sewage from the outside and removes suspended matter or solids from the sewage. The primary treatment tank 110 can remove suspended matter or solids by settling the suspended matter or solids by gravity or by using a filtration method that passes the sewage through a floating filter material. The sewage from which suspended matter or solids have been removed in the primary treatment tank 110 is separated and discharged to the microalgae granule culture tank 120 and the microalgae granule reaction tank 130.

[0034] The microalgae granule culture tank 120 receives sewage from which suspended matter or solids have been removed in the primary treatment tank 110, cultivates microalgae in a preset environment, and generates microalgae-sludge seeds, which are aggregates of microalgae combined with sludge contained in the sewage, and then transfers these to the microalgae granule reaction tank 130.

[0035] The sewage that flows in after the suspended matter or solids are removed in the primary treatment tank 110 contains mostly ungranulated bacteria and a small amount of microalgae. These bacteria aggregate together in the microalgae granule culture tank 120 to form seeds, which are aggregates for the production of granules.

[0036] A microalgae seed culture can be added to the microalgae granule culture tank 120 in order to accelerate seed formation.

[0037] The concentration of the sludge flowing into the microalgae granule culture tank 120 is preferably in the range of 3,000 to 5,000 mg / L based on MLSS. Sludge with a high concentration of more than 5,000 mg / L cannot receive light all the way to the bottom of the microalgae granule culture tank 120, making it difficult for microalgae to grow throughout the microalgae granule culture tank 120.

[0038] In addition, when seed culture of microalgae is added from outside, the amount of microalgae added to the microalgae granule culture tank 120 can be added at a ratio of 0.001 to 0.1 relative to the amount of sludge.

[0039] In the microalgae granule culture tank 120, the microalgae grow by receiving light incident into the microalgae granule culture tank 120. At this time, the light incident into the microalgae granule culture tank 120 may be sunlight or artificial light from another light source.

[0040] The microalgae granule culture tank 120 is created in an anaerobic or anoxic environment, and no external carbon sources or compounds containing cationic substances are supplied. The microalgae granule culture tank 120 is maintained in a static state without shaking for 1 to 14 days to promote the growth of microalgae and the aggregation of sludge. Here, a static state refers to a state in which there is no mechanical agitation and no intentional application of heat or density gradients that would cause fluid flow inside.

[0041] When microalgae seed culture is added from outside, the microalgae granule culture tank 120 can produce seeds by statically culturing for about 1 to 7 days in a preset environment. Also, when culturing microalgae using only activated sludge, seeds can be produced by statically culturing for about 7 to 14 days in the same environment as when the seed culture is added.

[0042] When a predetermined environment is maintained in the microalgae granule culture tank 120, a specific type of microalgae can grow preferentially. Here, the microalgae that grow preferentially are cyanobacteria or blue-green algae that have a high coagulation force and are excellent at coagulating with sludge granules, such as Aphanizomenon sp., Oscillatoria sp., or Phormidium sp.

[0043] Meanwhile, the microalgae granule culture tank 120 is a reaction tank having a predetermined shape, and forms a mat-like microalgae-sludge seed, thereby improving the cohesive force between the microalgae and the sludge. The microalgae granule culture tank 120 will be described in detail with reference to FIG. 4.

[0044] The microalgae granule reaction tank 130 receives sewage from which suspended matter or solids have been removed from the primary treatment tank 110 and mat-like microalgae-sludge seeds from the microalgae granule culture tank 120 to produce microalgae granules, which are then used to remove organic matter and nitrogen from the sewage.

[0045] The microalgae granule reactor 130 forms granules from microalgae-sludge seeds and grows them to a preset size range. The microalgae granule reactor 130 provides a preset environment necessary to accelerate granule production. The preset environment may include the temperature within the reactor 130, the amount of light incident at a constant level and period, and shear force due to up / down flow applied to the granules.

[0046] More specifically, the microalgae granule reaction tank 130 accelerates the formation and growth of granules by flowing the introduced seeds upward and downward. To this end, the microalgae granule reaction tank 130 may include a stirring means. Furthermore, to improve the settling of the microalgae granules and maintain the microalgae, light is also allowed to enter the granule reaction tank 130. The incident light may be sunlight or artificial light from another light source. In this way, the microalgae granule reaction tank 130 provides optimal conditions for the formation of microalgae granules, thereby producing microalgae granules in which microalgae are attached to sludge granules. The produced granules are shown in detail in FIG. 2.

[0047] FIG. 2 is a diagram showing a cross section of a microalgae granule according to one embodiment of the present invention.

[0048] The microalgae granules 200 are formed when microalgae 220 adhere to the outside of the sludge granules 210. As the microorganisms form aggregates, seeds, which are mat-like microalgae-sludge aggregates, are produced in the microalgae granule culture tank 120, and these are produced as granules 200 in the microalgae granule reaction tank 130.

[0049] That is, the mat-like microalgae-sludge seeds flow vertically in the microalgae granule reaction tank 130 and are formed into granules 200 consisting of a structure of microalgae 220 surrounding the outside of sludge granules 210.

[0050] Figure 3 shows the process by which organic matter and nitrogen are removed from wastewater using the microalgae granules produced through the above process.

[0051] FIG. 3 is a diagram illustrating the chemical reaction that microalgae granules produced according to an embodiment of the present invention perform in sewage.

[0052] Referring to Figure 3, the microalgae on the surface of the microalgae granules consume carbon dioxide (CO2), organic matter, and nutrients such as nitrogen and phosphorus in the sewage to produce oxygen (O2) for photosynthesis. Meanwhile, the bacteria inside the microalgae consume the oxygen (O2) produced by the microalgae, consuming the remaining organic matter and nutrients.

[0053] In this way, the microalgae granules 200 produced can remove organic matter and nitrogen from the sludge granules 210 using oxygen produced by the microalgae without the need for a separate oxygen supply device, and because the sludge granules 210 and the microalgae 220 exist in a combined state, the granules 200 from which the organic matter and nitrogen have been removed have a high settling speed. As a result, the treatment speed increases, and the time required for subsequent treatment of the sewage from which the organic matter and nitrogen have been removed can be significantly reduced.

[0054] 1 again, the microalgae granule reaction tank 130 performs a denitrification reaction, a photosynthesis reaction, and a nitrification reaction using the generated microalgae granules depending on whether light is incident on the reaction tank. That is, the microalgae granules undergo different reactions depending on whether light is incident on the reaction tank.

[0055] When sunlight or artificial light is incident on the reaction tank 130, the microalgae 220 in the microalgae granules 200 undergo photosynthesis, and the nitrifying microorganisms in the sludge granules 210 undergo a nitrification reaction. In contrast, when light is not incident on the reaction tank 130 or is blocked, the denitrifying microorganisms in the sludge granules 210 undergo a denitrification reaction. In this way, the microalgae granules remove organic matter and nitrogen depending on whether or not light is incident, and the microalgae granules from which the organic matter and nitrogen have been removed can be transported to the anaerobic digestion tank 150 to be used as biomass. A detailed description of the microalgae granule reaction tank 130 will be provided with reference to FIG. 5.

[0056] The sedimentation tank 140 receives the sewage that has passed through the microalgae granule reaction tank 130, settles and removes floating algae or microalgae granules remaining in the sewage, and discharges supernatant water.

[0057] In the microalgae granule reaction tank 130, microalgae become entangled on the surface of the sludge granules to form granules. However, some microalgae may not adhere to the surface of the granules and remain floating in the water, and microalgae granules that do not settle in the microalgae granule reaction tank 130 may still remain floating in the sewage. If the remaining floating microalgae or microalgae granules were to be discharged as is, it could have a negative impact on rivers and oceans. Therefore, the sedimentation tank 140 induces the floating microalgae and granules to settle by gravity, thereby removing them from the effluent.

[0058] The anaerobic digestion tank 150 receives the biomass generated in the primary treatment tank 110, the microalgae granule reaction tank 130, and the settling tank 140, and anaerobically digests it to generate methane (CH4). The methane generated in the anaerobic digestion tank 150 can be used as energy.

[0059] The microalgae granules and microalgae that have been settled and separated in the microalgae granule reaction tank 130 and the settling tank 140 flow into the anaerobic digestion tank 150. At this time, because the microalgae granules have a high energy potential during anaerobic digestion, methane production can be increased compared to a conventional activated sludge process.

[0060] Specifically, when the same amount of organic matter flows into a wastewater treatment plant, the amount of biomass increases when using microalgae granules compared to activated sludge. Moreover, considering the higher energy potential of biomass, including microalgae, the total methane production can increase by approximately 30% compared to conventional wastewater treatment plants.

[0061] [Table 1]

[0062] FIG. 4 is a diagram showing the configuration of a microalgae granule culture tank 120 according to one embodiment of the present invention.

[0063] FIG. 4(a) is a cross-sectional view of the microalgae granule culture vessel 120, and FIG. 4(b) is a view showing the microalgae granule culture vessel 120 from above.

[0064] The microalgae granule culture tank 120 may be configured as a single reaction tank using the culture tank 120 shown in Fig. 4, or may be configured to include a plurality of the culture tanks 120 shown in Fig. 4. When including a plurality of culture tanks 120, the plurality of unit culture tanks 120 may be arranged on the same plane or may be arranged in a vertically stacked form, but is not limited thereto.

[0065] The microalgae granule culture tank 120 includes a reaction tank 410 , an upper surface 420 , and a light source unit 430 .

[0066] The reaction tank 410 receives sewage containing microorganisms, i.e., activated sludge, and cultivates microalgae by keeping it stationary and undisturbed in a predetermined environment for a predetermined time, forming microalgae-sludge seeds, and supplies the seeds to the microalgae granule reaction tank 130.

[0067] Reactor 410 may be a rectangular or cylindrical reactor.

[0068] When the light source unit 430 is located above the reaction vessel, the reaction vessel 410 is preferably a rectangular plate-shaped reaction vessel with a large bottom area and a relatively shallow depth so that light can be incident on the entire area of ​​the reaction vessel 410. However, the shape is not limited thereto as long as light can be received on the entire surface of the reaction vessel depending on the position of the light source.

[0069] The upper surface 420 of the reaction vessel 410 is preferably made of a light-transmitting material so that light from the light source can enter the reaction vessel 410. The upper surface 420 may be a cover that can be separated from the reaction vessel 410, and must be able to maintain an anaerobic or anoxic environment within the reaction vessel 410 during the culture period.

[0070] The light source unit 430 is located on the upper surface of the reaction vessel 410 so that light is evenly incident on the entire area of ​​the reaction vessel 410. The light source unit 430 can receive power from a separate power supply (not shown) to irradiate light. The light source can be sunlight or artificial light, or a combination of sunlight and artificial light. An LED can be used as the artificial light.

[0071] When artificial light is used, the light intensity can be in the range of about 7,000 lux or less, and more preferably 5,000 lux or less. The light irradiation time to the microalgae granule culture tank 120 may be 24 hours per day. At this time, the temperature inside the reaction tank 410 can be maintained in the range of 15°C to 30°C, and more preferably 22°C to 28°C.

[0072] When the culture tank 120 is a plate-shaped rectangular reaction tank, the sludge and microalgae produced through static culture in a preset environment aggregate, eventually forming a mat-like microalgae-sludge seed, which can be seen in Figures 6 and 7.

[0073] FIG. 6 is a diagram showing microalgae-sludge seeds cultured in a microalgae granule culture tank 120 according to one embodiment of the present invention, and FIG. 7 is an image showing the process of forming microalgae-sludge seeds in a microalgae granule culture tank according to one embodiment of the present invention.

[0074] Referring to FIG. 6, a microalgae-sludge seed 600 formed in a microalgae granule culture tank according to one embodiment of the present invention includes a top microalgae layer 610, a bottom microalgae layer 610', and a sludge layer 620 interposed between these microalgae layers 610, 610'.

[0075] While static cultivation is carried out in a preset environment in the plate-shaped reaction vessel 410, the sludge flowing into the reaction vessel 410 undergoes aggregation and sedimentation to form a sludge layer 620. Microalgae that grow due to light irradiated from the light source 430 grow on the surface of the sludge layer 620, forming microalgae layers 610 and 610' that surround the upper and lower surfaces of the sludge, as shown in FIG.

[0076] At this time, the microalgae attached to the upper and lower surfaces of the sludge layer 620 are filamentous cyanobacteria, and the filamentous structures of the microalgae are intertwined to form microalgae layers 610, 610' on the surface of the sludge layer 620, resulting in the formation of aggregates of sludge and microalgae. The process of the formation of mat-like microalgae-sludge seeds during the cultivation period is shown in Figure 7.

[0077] FIG. 7A shows the shape of microalgae-sludge seeds formed in a microalgae granule culture tank according to one embodiment of the present invention, FIG. 7B is a photograph showing the process of microalgae attaching and growing on the surface of the sludge layer 620 during the culture period, and FIG. 7C is a diagram showing mat-shaped seeds at the early (a), middle (b) and completed (c) stages of culture, respectively.

[0078] In the process of forming microalgae-sludge seeds in the culture tank 120 according to one embodiment of the present invention, light irradiation was performed 24 hours a day at a light intensity of 5,000 lux, and the inside of the culture tank 120 was maintained in a static state in an anaerobic or anoxic environment, and the temperature was maintained at 26°C within a preset tolerance range.

[0079] 7A, it can be seen that the microalgae-sludge (Seed) formed in the microalgae granule culture tank 120 is formed in a mat shape. Also, referring to FIG. 7B, it can be seen that microalgae are growing on the surface of the sludge (brown part).

[0080] Referring to Figure 7C, in the early stages of cultivation, microalgae (cyanobacteria) begin to grow on the surface of the sludge (the black dots are cyanobacteria, Figures (a) and (b)). After a predetermined cultivation period, a mat-like microalgae covering the entire surface - a sludge seed (Figure (c)) - can be seen.

[0081] The mat-like microalgae-sludge seeds formed in this way have a certain level of cohesive force between the sludge and the microalgae, so there is almost no disintegration of these aggregates during the process of growing them into granules in the microalgae granule reaction tank 130.

[0082] In this case, in order to form a mat-like microalgae-sludge seed, it is most advantageous for the reaction vessel 410 of the microalgae granule culture vessel 120 to be a plate-shaped rectangular reaction vessel. During seed culture of microalgae and sludge, the settling properties of granules and the morphology of microalgae depending on the shape of the reaction vessel are shown in Figures 8 to 10.

[0083] FIG. 8 is an image showing microalgae-sludge seeds cultured in a culture tank having a shape according to one embodiment of the present invention and a culture tank having a different shape. FIG. 9 is an image showing the sedimentation property and morphology of microalgae granules from microalgae-sludge seeds cultured in a culture tank according to one embodiment of the present invention. FIG. 10 is an image showing the sedimentation property of granules and the morphology of microalgae from seeds cultured in a culture tank having a shape other than that of the culture tank according to one embodiment of the present invention.

[0084] Figure 8 shows microalgae-sludge seeds according to the shape of the culture tank, which are microalgae granule culture tanks according to one embodiment of the present invention: a square plate-shaped culture tank (Figure (a)), a cylindrical culture tank (Figures (b) and (c)), and a spherical culture tank (Figure (d)).

[0085] The same ratio of sludge and microalgae was added to each culture tank in Figure 8, and the internal environment including light intensity and temperature (anaerobic or anoxic, static state) was all controlled to the same conditions.

[0086] Referring to Figure 8, it can be seen that in the square plate-shaped culture tank (Figure (a)), the microalgae-sludge seeds formed in a shape similar to a mat. In contrast, in all other reactors, seeds consisting of a single mass were formed, and it can be seen that there is a difference in physical shape between the seeds formed in the square plate-shaped reactor. The seeds formed in the cylindrical and spherical reactors also consist of microalgae aggregates on the outside of the sludge, similar to the mat-shaped seeds.

[0087] Meanwhile, the square plate-shaped culture tank according to one embodiment of the present invention can also shorten the period for forming microalgae-sludge seeds.

[0088] Table 2 below summarizes the cultivation period required for the formation of seeds, which are aggregates of microalgae and sludge, in each reactor.

[0089] When seeds are formed using a square plate-shaped microalgae granule culture tank 120, it takes 1 to 5 days for mat-shaped seeds to form, and it can be seen that the culture period can be shortened by at least 2 days (30% or more) compared to when seeds are cultured using a cylindrical or spherical reaction tank under the same environment.

[0090] [Table 2]

[0091] FIG. 9 is an image showing the sedimentation properties of microalgae granules formed by introducing mat-shaped seeds formed in a square plate-shaped culture tank according to one embodiment of the present invention into a microalgae granule reaction tank 130 and the dominant species of the granules.

[0092] Referring to FIG. 9, FIG. 9(a) shows the state of granules within 7 days after the seeds were introduced into the granule reactor, and FIG. 9(b) shows the state of granules about 60 days after the seeds were introduced into the granule reactor.

[0093] It can be seen that the sedimentation properties of the granules shown in Figures 9(a) and (b) remain excellent and remain almost unchanged from the initial operation of the granule reactor until about 60 days later. In addition, Figure 9(a) shows that, although the granules are relatively small in size at the initial stage of operation, filamentous cyanobacteria are proliferating, and in Figure 9(b) it can be seen that, after 60 days, the granules have grown and the filamentous cyanobacteria have become dominant.

[0094] FIG. 10 is a diagram showing the results of introducing seeds cultured in a cylindrical reactor into a microalgae granule reactor, which is not an embodiment of the present invention.

[0095] Figure 10 (a) shows the results within 7 days after the microalgae granules were added to the reactor, Figure 10 (b) shows the state of the granules after about 15 days, and Figure 10 (c) shows the state of the granules after 30 days. The granules in Figure 10 were grown under the same conditions as the granules of the example shown in Figure 9.

[0096] Referring to Figure 10, it can be seen that, in the initial stage of addition of the microalgae granules to the reactor, filamentous cyanobacteria were dominant, similar to the result of adding mat-like seeds (Figure 9). Judging from the state of the supernatant liquid during sedimentation, it was also confirmed that there was no significant difference in sedimentation properties.

[0097] Furthermore, it was confirmed that filamentous cyanobacteria were still present after approximately 15 days had passed, but after 30 days had passed since the microalgae granules were added to the reactor (Figure (c)), it was confirmed that filamentous fungi and green algae, which are not cyanobacteria, had proliferated, and the settling properties of the granules had also deteriorated significantly.

[0098] Therefore, when culturing microalgae in the microalgae granule culture tank 120 and forming aggregates with sludge, it can be confirmed that the shape of the culture tank affects the cohesive strength of the formed aggregates, i.e., seeds, and the sedimentation properties of the granules.

[0099] In other words, the cultivation process also results in the formation of seeds in the form of microalgae attached to the surface of the sludge, but when the seeds are in the form of a mat, the area of ​​attachment between the sludge and the microalgae is relatively larger than when the seeds are made up of a single mass, and the cohesive bonding strength between them for the microalgae to grow is also stronger.

[0100] As a result, even if the system is operated for a long period of time under conditions where physical agitation is performed to grow the granules, not only can the sedimentation properties of the granules be maintained, but the differentiated microalgae can also be maintained as they are, allowing the photosynthetic reaction by the microalgae to continue.

[0101] By using seeds with enhanced flocculation properties in the microalgae granule culture tank 120, the microalgae granule reaction tank 130 can reduce the time required for conventional microalgae granulation by at least one-third or less.

[0102] FIG. 5 is a cross-sectional view of a microalgae granule reactor according to one embodiment of the present invention.

[0103] Referring to FIG. 5, the microalgae granule reaction vessel 130 includes a reaction vessel 510, an upper surface 520, an agitation unit 530, a light source unit 540, and a control unit (not shown).

[0104] The reaction tank 510 may be a rectangular or cylindrical reaction tank, and may have an inlet (not shown) through which sewage flows and an outlet (not shown) through which settled microalgae granules are discharged. In addition, a sloping haunch 515 may be included at the boundary between the bottom surface and the inner wall of the reaction tank 510, as needed.

[0105] The haunch portion 515 can assist the upward flow of the fluid while the agitator 530 is agitating the fluid and granules in the vertical direction, and can prevent the granules from being deposited in the corner areas of the reaction vessel 510.

[0106] In the reaction vessel 510, seeds are formed into spherical granules by the vertical flow of the seeds. In addition, since light must be incident inside the reaction vessel 510 for photosynthesis of the microalgae, the upper surface 520 of the reaction vessel 510 is preferably made of a light-transmitting material. A driving means (not shown) for the agitator 530 may be provided on the upper surface 520 of the reaction vessel.

[0107] The agitator 530 is installed at a certain position in the reaction tank 510 and agitates the sewage and microalgae-sludge seeds that have flowed into the reaction tank 510 in the vertical direction (y-axis in FIG. 5).

[0108] An appropriate stirring speed must be maintained so that the microalgae-sludge seeds introduced into the microalgae granule reaction tank 130 can grow into granules of a predetermined size. The size of the granules for sewage treatment is preferably about 1 to 5 mm, and therefore the stirring speed of the stirring unit 530 must be maintained at a speed that prevents the granules from being deposited in the corners of the reaction tank 510.

[0109] In this case, the agitator 530 may be implemented by any device capable of generating a water current, such as an impeller agitator or a water motor. When an agitator is used, any one of a propeller-type, paddle-type, or anchor-type impeller agitator or a hyperboloid agitator may be used, but a hyperboloid agitator is preferred because it can circulate the water from the bottom of the reaction vessel 510 to the water surface so that the granules do not settle on the bottom or corners of the reaction vessel 510. A hyperboloid agitator according to one embodiment of the present invention is shown in FIG. 11.

[0110] FIG. 11 is a diagram showing the shape of an agitator provided in a microalgae granule reaction tank according to one embodiment of the present invention.

[0111] FIG. 11(a) is an impeller of a Hyperboloid agitator, and FIG. 11(b) is a cross-sectional view of the Hyperboloid agitator.

[0112] Referring to Figure 11(a), the hyperboloid agitator has a hyperboloid-shaped impeller, which is known to be the most effective shape for creating a very strong water flow at the bottom of a reaction vessel and preventing the formation of sediment at the bottom. Unlike a normal vertical shaft agitator that creates only an axial flow, the hyperboloid agitator has both vertical and horizontal radial flows, and can achieve complete mixing at a relatively low power density.

[0113] That is, the water flow pattern generated inside the reaction tank 510 changes depending on the shape of the impeller of the agitator 530, and this water flow pattern affects the growth of microalgae granules and the efficiency of water treatment.

[0114] FIG. 12 is a diagram showing water flow patterns for an agitation unit of a microalgae granule reaction tank according to one embodiment of the present invention and for a non-agitation unit.

[0115] In Figure 12, (a) shows the circulation region in a reaction vessel formed by a radial impeller, (b) shows the circulation region formed by an axial impeller, and (c) shows the circulation region formed by a hyperboloid impeller.

[0116] Referring to FIG. 12, radial impellers direct the liquid in the reactor against the inner walls of the reactor, creating circulation zones at the top and bottom of the reactor, while axial impellers pump the liquid in the reactor downwards in the reactor, creating a circulation pattern throughout the entire reactor.

[0117] In contrast, the hyperboloid impeller in Figure (c) draws the water in the reactor down the shaft, then pumps it outward, creating micro-vortices along the bottom, which raise particles and sediments inside the reactor to just below the water surface. Because the impeller is located close to the bottom of the reactor, it efficiently suspends the particles inside the reactor and forms a circulation pattern toward the inner wall of the reactor, enabling complete mixing.

[0118] In particular, the hyperboloid impeller can produce the same level of mixture with only 25-50% of the power and rotation speed compared to existing impellers, which reduces energy consumption and makes it suitable for microalgae granule reactors that require microalgae granules to be stirred on the water surface for photosynthesis. Figures 13 and 14 show the difference in microalgae granule growth and performance depending on the type of agitator.

[0119] Figure 13 is a photograph comparing the state of microalgae granules produced in a microalgae granule reaction tank that includes a hyperboloid agitator according to one embodiment of the present invention as an agitation unit with that of microalgae granules produced in a non-hyperboloid agitation unit, and Figure 14 is a photograph comparing the sedimentation properties of each microalgae granule.

[0120] In order to compare the properties and sedimentation performance of granules depending on the shape of the agitation section 530, all detailed configurations, residence times, and operating conditions of the light source section 540 of the microalgae granule reaction tank 130 were maintained the same except for the agitation section 530.

[0121] In addition, a hyperboloid agitator and a radial agitator were used as the agitator 530, and the agitation conditions of each agitator were set to a speed that would prevent microalgae granules from settling near the corners of the reaction vessel 130. The experimental conditions are summarized in Table 3.

[0122] [Table 3]

[0123] Figure 13 (a) shows microalgae granules produced in a microalgae granule reactor 130 using a hyperboloid agitator according to one embodiment of the present invention, and (b) shows microalgae granules produced in the same environment and reactor using a radial agitator.

[0124] Referring to Figure 13, it can be seen that granules produced under the same operating conditions using the same microalgae-sludge seed were predominantly cyanobacteria, regardless of the type of agitator, and the size of the microalgae granules was also formed within a predetermined range.

[0125] On the other hand, when using the hyperboloid agitator, compared to the conventional radial agitator, it was confirmed that the diameter of the microalgae granules grew to 4-5 mm, which was larger than the granules (1.5 mm) produced by the radial agitator, and that the density of the cyanobacteria attached to the granules was also higher.

[0126] In addition, the results of experiments on the growth and settling properties of microalgae granules depending on the type of agitator are shown in Table 4 below.

[0127] When the hyperboloid mixer was used, the size of the microalgae granules grew about twice as large as when the radial mixer was used. It was also confirmed that the stabilization period required for the microalgae granules to grow to the target size and perform normal water treatment was shortened by about half compared to when the radial mixer was used.

[0128] [Table 4]

[0129] Under the same microalgae-sludge seed input and controlled operating conditions, 15 days after the start of operation of the microalgae granule reactor, the MLSS in the reactor was 5,200 mg / L when using a hyperboloid agitator, which was higher than when using a radial agitator, and measurements of sludge settling showed complete granule precipitation within 5 minutes.

[0130] FIG. 14 is a photograph showing the results of measuring the sedimentation properties of microalgae granules for each of the above-mentioned agitators.

[0131] Figure 14 (a) shows the experimental results of the settling property of microalgae granules when a hyperboloid agitator is used, and Figure 14 (b) shows the settling property of granules when a radial agitator is used. From Figure 14, it can be seen that the measurement results of the settling property (SVI) of microalgae granules when a hyperboloid agitator is used achieves superior settling property compared to when using a conventional radial agitator.

[0132] It can be seen from Table 4 that the sedimentation property of microalgae granules when a hyperboloid agitator is used is improved by about 60% compared to when a radial agitator is used, based on SVI5.

[0133] Furthermore, it can be confirmed that when a hyperboloid agitator is used, the suspended solids (SS) removal rate of microalgae granules is significantly improved compared to when a radial agitator is used.

[0134] As mentioned above, this is thought to be because the microalgae granules descend vertically due to the vertical water flow created by the hyperboloid agitator, capturing fine flocs and achieving the removal of fine suspended solids.

[0135] In contrast, when a radial mixer was used, fine flocs remaining in the supernatant water were visible to the naked eye. This is thought to be the result of the shear force generated by the radial impeller becoming very high locally, causing the fine flocs to break.

[0136] [Table 5]

[0137] From the above results, the microalgae granule reaction tank 130 can shorten the growth and stabilization period of microalgae granules with less power consumption than conventional agitators by applying a hyperboloid agitator to the agitation unit 530 and controlling the water flow pattern. As a result, the residence time in the microalgae granule reaction tank 130 is shortened, and process efficiency can be improved in terms of increased processing capacity and reduced energy consumption.

[0138] 5 again, the light source unit 540 is located above the reaction vessel 510 and can irradiate light into the reaction vessel 510. The light source unit 540 may receive power from a separate power supply (not shown) to irradiate light, or may be provided with an energy storage device (not shown) that receives sunlight, generates energy, and stores it to irradiate light using energy stored from sunlight.

[0139] The light irradiated to the microalgae granule reactor 130 may be sunlight or artificial light, or a combination of sunlight and artificial light. When sunlight is used, the granule reactor 130 can be placed and operated in a location where sunlight is incident. In this case, even when the sun is not up, photosynthesis of the microalgae can be induced using the light source unit 540, which is artificial light.

[0140] The light source unit 540 irradiates the microalgae granule reaction tank 130 with light at a preset cycle, allowing light reactions and dark reactions to occur alternately within the reaction tank 510. Since the light incident into the reaction tank 510 by the light source unit 540 can only reach a certain depth, the inside of the reaction tank 510 is divided into an area 550 where light is incident from the water surface to a certain depth, and an area 560 where light is not incident.

[0141] Microalgae undergo photosynthesis when exposed to light, and the photosynthetic process involves light and dark reactions. Microalgae produce NADP + In the presence of light, they carry out light reactions to produce energy (ATP), oxygen (O2), and NADPH. On the other hand, in the absence of light, in the presence of carbon dioxide and NADPH, microalgae consume energy to produce glucose, water, and NADP. + In other words, in order for microalgae to carry out the light reaction and produce oxygen, they need NADP, a product of the dark reaction. + Therefore, it can be seen that the light and dark reactions must occur continuously.

[0142] Therefore, in the reaction tank 510, light and dark reactions can continuously occur in the light-incident region 550 and the other light-blocking region 560. However, if light and dark reactions continuously occur in each region, a problem may occur in which the microalgae cannot smoothly generate oxygen. To this end, the agitator 530 generates a vertical water current and agitates the water so that the microalgae granules are evenly distributed in the light-incident region 550 at the top of the reaction tank 510 and the light-blocking region at the bottom, thereby forming microalgae granules and removing organic matter and nitrogen.

[0143] A control unit (not shown) controls the operation of the microalgae granule reaction tank 130.

[0144] When mat-like microalgae-sludge seeds are supplied to the microalgae granule reaction tank 130, the control unit (not shown) controls the inflow of sewage flowing out from the primary treatment tank 110 into the reaction tank 130 and the operation of the agitation unit 530 and the light source unit 540.

[0145] The control unit (not shown) controls the stirring speed of the stirring unit 530 so that granules can grow inside the microalgae granule reaction tank 130, and determines whether the microalgae granules have grown by determining the concentration and / or turbidity of suspended matter in the microalgae granule reaction tank 130. For this purpose, the microalgae granule reaction tank 130 may further include another measuring unit (not shown).

[0146] The control unit (not shown) monitors the concentration / turbidity of suspended matter, the amount of dissolved oxygen, or the amount of carbon dioxide in water in the microalgae granule reaction tank 130, and if the microalgae granules grow excessively or the granule concentration increases excessively, it suspends the operation of the stirring unit 530.

[0147] If the size of the microalgae granules becomes excessively large, the surface area of ​​the granules per unit area of ​​the reaction tank in the sewage treatment process will actually decrease. The decrease in the surface area of ​​the microalgae granules leads to a decrease in the amount of photosynthesis, and insufficient oxygen will be generated. For this reason, a control unit (not shown) determines whether the size of the microalgae granules exceeds a preset range and controls the stirring speed accordingly.

[0148] If the size of the microalgae granules does not fall within a preset range, the control unit (not shown) reduces the stirring speed of the stirring unit 530. By reducing the stirring speed, the time that the microalgae granules remain in the light incident region 550 increases, allowing the granules to grow. Conversely, if the size of the microalgae granules exceeds the preset range, the control unit (not shown) increases the stirring speed to reduce the size of the granules.

[0149] In addition, the control unit (not shown) controls the operation of the light source unit 540 of the microalgae granule reaction tank 130. That is, the light source unit 540 can be controlled by adjusting the ratio of the area 550 where light is incident and the area 560 where light is not incident in the reaction tank 130, so that the microalgae granules can grow to a predetermined size.

[0150] The microalgae granules can most efficiently remove organic matter and nitrogen when the ratio of the light-incident area 550 to the light-non-incident area 560 is 1:1. To this end, a control unit (not shown) controls the light source unit 540 to control the ratio of the light-incident area to the light-non-incident area.

[0151] 15 is a flowchart showing a method for treating sewage by the sewage treatment device according to an embodiment of the present invention. The method for treating sewage by the sewage treatment device 100 has been described in detail with reference to FIG. 1, so a detailed description thereof will be omitted.

[0152] The sewage treatment device 100 uses the primary treatment tank 110 to receive sewage and remove suspended matter or solids (S1510).

[0153] A preset environment is created in the microalgae granule culture tank 120, and microalgae are cultured from the sewage flowing in from the primary treatment tank 110 to form seeds, which are mat-like microalgae-sludge aggregates (S1520).

[0154] The microalgae granule reaction tank 130 produces microalgae granules from the sewage flowing in from the primary treatment tank 110 and the microalgae-sludge seeds flowing in from the microalgae granule culture tank 120 (S1530).

[0155] The intensity of light received in the microalgae granule reaction tank 130, the amount of dissolved oxygen or the amount of carbon dioxide in the water, and the like are monitored to control the stirring speed, and organic matter and nitrogen are removed from the sewage (S1540).

[0156] The sedimentation tank 140 is used to settle and remove the residual floating algae and microalgae granules in the sewage flowing in from the microalgae granule reaction tank 130, and the supernatant water is discharged (S1550).

[0157] The anaerobic digestion tank 150 is used to perform anaerobic digestion on the biomass flowing in from the primary treatment tank 110, the microalgae granule reaction tank 130, and the settling tank 140 (S1560).

[0158] The above description is merely an example of the technical concept of the present embodiment, and various modifications and variations may be made by a person skilled in the art without departing from the essential characteristics of the present embodiment. Therefore, the present embodiment is intended to illustrate, not limit, the technical concept of the present embodiment, and the scope of the technical concept of the present embodiment is not limited by such examples. The scope of protection of the present embodiment should be interpreted according to the following claims, and all technical concepts within the scope equivalent thereto should be interpreted as being included in the scope of the present embodiment.

[0159] CROSS-REFERENCE TO RELATED APPLICATION

[0160] This patent application claims priority under 35 U.S.C. § 119(a) of patent application serial numbers 10-2023-0038352 and 10-2023-0038359, filed in Korea on March 24, 2023, the entire contents of which are incorporated herein by reference. Additionally, if this patent application claims priority from countries other than the United States for the same reasons as above, the entire contents of such countries are incorporated herein by reference.

Claims

1. a primary treatment tank into which sewage flows and which separates suspended matter or solids in the sewage; a microalgae granule culture tank into which the sewage that has passed through the primary treatment tank flows and which cultures microalgae in a predetermined environment to form seeds, which are aggregates of microalgae and sludge; a microalgae granule reaction tank into which the sewage that has passed through the primary treatment tank and the microalgae-sludge seeds generated in the microalgae granule culture tank are introduced to generate microalgae granules, and which removes organic matter and nitrogen from the sewage using the generated microalgae granules; A sedimentation tank into which the sewage that has passed through the microalgae granule reaction tank flows and separates residual floating algae or residual microalgae granules; A sewage treatment device comprising:

2. The microalgae are 2. The sewage treatment device according to claim 1, wherein the microalgae is photoautotrophic microalgae that performs photosynthesis.

3. The microalgae are 3. The sewage treatment device according to claim 2, wherein the bacteria is selected from the group consisting of filamentous cyanobacteria or cyanobacteria.

4. The microalgae granules are When light is incident on the microalgae granule reaction tank, a photosynthetic reaction by the microalgae and a nitrification reaction by the sludge occur, The sewage treatment device according to claim 1, wherein a denitrification reaction is carried out by sludge when light is not incident on the microalgae granule reaction tank.

5. The microalgae granule culture tank is 2. The sewage treatment device according to claim 1, wherein a seed is formed which is a mat-like aggregate of microalgae and sludge.

6. The preset environment of the microalgae granule culture tank is The sewage treatment device according to claim 5, wherein light is incident on the inside of the culture tank in an anaerobic or anoxic environment.

7. The microalgae granule reaction tank is A reactor for storing influent sewage and producing the influent microalgae-sludge seeds as granules; A stirring unit that circulates and stirs the sewage and the microalgae granules inside the reaction tank; a light source unit that irradiates light into the inside of the reaction vessel; The sewage treatment device according to claim 1 , further comprising: a control unit that controls operations of the agitation unit and the light source unit.

8. The stirring unit is 8. The sewage treatment device according to claim 7, wherein the reaction tank is provided with a hyperboloid agitator for generating a vertical water flow inside the reaction tank.

9. The sewage treatment device according to claim 1 , further comprising an anaerobic digestion tank into which biomass is introduced from the primary treatment tank, the microalgae granule reaction tank, or the sedimentation tank and subjected to anaerobic digestion.

Images