Treatment device for domestic sewage and treatment method thereof

Abstract

The present invention relates to a treatment device for domestic sewage and a treatment method thereof. The treatment device includes a sewage regulating tank, a hydrolysis reactor, a first aerobic reactor, an oxygenator, a gas-liquid mixer, N second aerobic reactors, and a flotation device. The hydrolysis reactor is connected to the sewage regulating tank via a first pipe, and the hydrolysis reactor is filled with biological fillers. The first aerobic reactor is connected to the first hydrolysis reactor via a second pipe, and the first aerobic reactor is filled with biological fillers. The first second aerobic reactor is connected to the first aerobic reactor via a third pipe, and the second aerobic reactor is filled with biological fillers. The flotation device is connected to the last second aerobic reactor via a fourth pipe. The above-mentioned treatment device has a good effect on treating domestic sewage and saves water to reduce operating costs. In addition, the utilization rate of oxygen is high, further reducing operating costs.

Description

Technical Field

[0001] The present invention relates to the technical field of wastewater treatment, and in particular to a wastewater treatment device and a wastewater treatment method. Background Art

[0002] Domestic sewage mainly comes from residential buildings and public buildings, such as houses, government offices, schools, hospitals, shops, public places, etc. The pollutants contained in domestic sewage are mainly organic matter (such as protein, carbohydrates, fat, urea, ammonia nitrogen, etc.) and suspended solids. Among them, since the organic matter present in domestic sewage is extremely unstable, it is easy to decompose and produce odor. Therefore, in the field of sewage treatment, indicators such as COD and chromaticity are often used to indicate the types of pollutants in sewage. Among them, COD, also known as chemical oxygen demand, is the amount of oxygen consumed when chemical oxidants (such as potassium permanganate and potassium dichromate) are used to oxidize oxygen-demanding pollutants in water. It is one of the important comprehensive indicators for assessing the degree of water pollution. The larger the COD value, the more serious the water pollution.

[0003] However, traditional sewage treatment methods have low oxygen utilization efficiency, resulting in high treatment costs. Summary of the Invention

[0004] The purpose of the present invention is to provide a treatment device and a treatment method for domestic sewage, so as to solve the problem of low oxygen utilization rate in the prior art resulting in high treatment costs.

[0005] To achieve the above object, the present invention adopts the following technical solutions:

[0006] In a first aspect, an embodiment of the present invention provides a device for treating domestic sewage, the device comprising:

[0007] Sewage regulating tank, used to reduce fluctuations in domestic sewage discharge;

[0008] a hydrolysis reactor, connected to the sewage regulating tank via a first pipeline, wherein the hydrolysis reactor is filled with biological fillers to hydrolyze and ferment organic matter in the sewage;

[0009] a first aerobic reactor, connected to the hydrolysis reactor via a second pipe, and the first aerobic reactor is filled with biological fillers;

[0010] an aerator, installed on the second pipeline;

[0011] a gas-liquid mixer installed on the second pipeline and located downstream of the oxygenator;

[0012] N second aerobic reactors are connected to the first first aerobic reactor via a third pipe, and the second aerobic reactors are filled with biological fillers, wherein 2≤N≤8;

[0013] The flotation device is connected to the last of the second aerobic reactors through a fourth pipeline.

[0014] In combination with the first aspect, in a first possible implementation scheme, the number of the second aerobic reactors is 3, the three second aerobic reactors are connected in series, and the gas-liquid mixer is installed between adjacent second aerobic reactors.

[0015] In combination with the first possible implementation scheme of the first aspect, in a second possible implementation scheme, the third second aerobic reactor connected in series is connected to the sewage regulating tank via a pump.

[0016] In combination with the first aspect, in a third possible implementation scheme, a bag filter is installed on the first pipeline.

[0017] In combination with the first aspect, in a fourth possible implementation, the treatment device further includes a first tank body connected to the flotation device, and the first tank body contains a flocculant.

[0018] In combination with the fourth possible implementation scheme of the first aspect, in a fifth possible implementation scheme, the treatment device further includes a second tank body connected to the flotation device, and the second tank body contains a phosphorus removal agent.

[0019] In combination with the first aspect, in a sixth possible implementation scheme, the processing device further includes an air compressor connected to the oxygenator.

[0020] In combination with the first aspect, in a seventh possible implementation scheme, the processing device further includes a sterilizer connected to the liquid outlet of the flotation device.

[0021] In combination with the first aspect, in an eighth possible implementation scheme, the treatment device further includes a sludge tank, and the sludge tank is connected to the bottom of the hydrolysis reactor, the first aerobic reactor, the second aerobic reactor, and the flotation device respectively.

[0022] In a second aspect, an embodiment of the present invention further provides a method for treating domestic sewage, wherein the method uses the treatment device described in any of the above embodiments, and the method comprises the following steps:

[0023] 1) The pre-treated domestic sewage is passed into the sewage regulating tank to reduce the fluctuation of domestic sewage discharge;

[0024] 2) The uniformly mixed domestic sewage flows into the hydrolysis reactor through the first pipe for hydrolysis and fermentation;

[0025] 3) The domestic sewage after hydrolysis and fermentation passes through the second pipeline and the oxygen is mixed with the domestic sewage in the gas-liquid mixer;

[0026] 4) The mixed sewage flows into the first aerobic reactor and then flows into the second aerobic reactor through the third pipe for biochemical degradation;

[0027] 5) The domestic sewage after biochemical degradation flows into the flotation device through the fourth pipeline for flotation treatment and is then discharged.

[0028] The present invention provides a treatment device for domestic sewage, which includes a sewage regulating tank, a hydrolysis reactor, a first aerobic reactor, an oxygenator, a gas-liquid mixer, N second aerobic reactors, and an air flotation device; wherein the hydrolysis reactor is connected to the sewage regulating tank via a first pipe, and the hydrolysis reactor is filled with biological fillers to hydrolyze and ferment organic matter in the sewage; the first aerobic reactor is connected to the hydrolysis reactor via a second pipe, and the first aerobic reactor is filled with biological fillers; the oxygenator is installed on the second pipe; the gas-liquid mixer is installed on the second pipe and is located downstream of the oxygenator; the first second aerobic reactor is connected to the first aerobic reactor via a third pipe, and the second aerobic reactor is filled with biological fillers; the air flotation device is connected to the last second aerobic reactor via a fourth pipe. The above-mentioned treatment device has a good effect on the treatment of domestic sewage and saves water to reduce operating costs; in addition, the utilization rate of oxygen is high, further reducing operating costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following is a brief introduction to the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative labor.

[0030] Figure 1 A schematic structural diagram of a domestic sewage treatment device provided in an embodiment of the present invention.

[0031] Description of reference numerals;

[0032] 10- Treatment plant for domestic sewage;

[0033] 11-Sewage regulating tank;

[0034] 12-hydrolysis reactor;

[0035] 13-first aerobic reactor;

[0036] 14-Aerator;

[0037] 15-gas-liquid mixer;

[0038] 16-second aerobic reactor;

[0039] 17- air flotation device;

[0040] 18-Filter bag;

[0041] 19- first tank body;

[0042] 21- second tank body;

[0043] 22-Air compressor. Specific implementation plan

[0044] In this specification, each embodiment or implementation scheme is described in a progressive manner. Each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referenced to each other.

[0045] Throughout this specification, references to terms such as "one embodiment," "some embodiments," "illustrative embodiments," "example," "specific example," or "some examples" indicate that a particular feature, structure, material, or characteristic described in connection with the embodiment or example is included in at least one embodiment or example of the fuel tank of the present invention. In this specification, exemplary uses of these terms do not necessarily refer to the same embodiment or example. Furthermore, the described particular features, structures, materials, or characteristics may be combined in any suitable manner in any one or more embodiments or examples.

[0046] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0047] Domestic sewage mainly comes from residential buildings and public buildings, such as houses, government agencies, schools, hospitals, shops, public places, etc. The pollutants contained in domestic sewage are mainly organic matter (such as protein, carbohydrates, fat, urea, ammonia nitrogen, etc.) and suspended solids. Among them, since the organic matter present in domestic sewage is extremely unstable, it is easy to decompose and produce odor. Therefore, in the field of sewage treatment, indicators such as COD and chromaticity are often used to indicate the types of pollutants in sewage. Among them, COD, also known as chemical oxygen demand, is the amount of oxygen consumed when chemical oxidants (such as potassium permanganate and potassium dichromate) are used to oxidize oxygen-demanding pollutants in water. It is one of the important comprehensive indicators for assessing the degree of water pollution. The larger the COD value, the more serious the water pollution. However, traditional sewage treatment methods have a low utilization rate of oxygen, resulting in high treatment costs.

[0048] Refer to Figure 1, Figure 1 Schematic diagram of the structure of a domestic sewage treatment device provided in an embodiment of the present invention. The domestic sewage treatment device provided in an embodiment of the present invention, the treatment device 10, includes: a sewage regulating tank 11, a hydrolysis reactor 12, a first aerobic reactor 13, an aerator 14, a gas-liquid mixer 15, a second aerobic reactor 16, and a flotation device 17.

[0049] Domestic sewage discharge fluctuates significantly, which can lead to significant variations in the quality of the sewage each time it is discharged. This variation makes it difficult to control the process parameters, hindering the effectiveness of the treatment device and even damaging it. Therefore, in the embodiments provided by the present invention, the sewage regulating tank 11 can reduce the fluctuations in domestic sewage discharge.

[0050] Specifically, first, the sewage regulating tank 11 can provide buffering capacity for the treatment device to prevent sudden changes in the device load; second, the sewage regulating tank 11 can control the pH of the sewage so that the inflowing sewage can achieve acid-base neutralization to reduce the amount of chemicals used in the neutralization process; third, it can reduce flow fluctuations so that the chemical addition rate is suitable for the quota of the feeding equipment; finally, the sewage regulating tank 11 can control the discharge of sewage to alleviate changes in the sewage load distribution.

[0051] In the embodiment provided by the present invention, the maximum treatment capacity of the sewage regulating tank 11 can reach 50m 3 / d, which can greatly improve the processing efficiency of the processing device and maximize the utilization of the device.

[0052] It should be noted here that domestic sewage will be pretreated before entering the sewage regulating tank 11, that is, domestic sewage flows into the septic tank to remove most of the solid suspended matter, then flows through the screen to remove debris, and finally flows into the sewage regulating tank 11.

[0053] Furthermore, to better remove impurities from domestic sewage, in one possible embodiment, after domestic sewage flows out of the sewage regulating tank 11, it flows through a bag filter 18. The bag filter 18 herein refers to a bag filter. The bag filter 18 intercepts impurities in the water to prevent them from affecting subsequent treatment. In the embodiment provided by the present invention, the bag filter 18 is a bag filter well known to those skilled in the art and will not be further elaborated upon herein.

[0054] The domestic sewage flowing through the filter bag 18 will flow into the hydrolysis reactor 12. It can be understood that the hydrolysis reactor 12 is connected to the sewage regulating tank 11 through a first pipe, and a delivery pump is installed on the first pipe. The sewage in the sewage regulating tank 11 is transported to the filter bag 18 and the hydrolysis reactor 12 in sequence through the delivery pump. In addition, the filter bag 18 is also installed on the first pipe. The hydrolysis reactor 12 is also filled with biological fillers. Therefore, the hydrolysis reactor 12 can be understood as a primary biochemical treatment. The organic matter in the sewage can be hydrolyzed and fermented by the biological fillers in the hydrolysis reactor 12. The biological fillers used here are the biofilm filler balls disclosed in application number CN201620455598.8.

[0055] Specifically, within the hydrolysis reactor 12, wastewater releases phosphorus, increasing the concentration of phosphorus in the water. Simultaneously, during the anaerobic process, organic matter undergoes hydrolysis and fermentation under the action of microorganisms (e.g., fermentative bacteria). Specifically, polysaccharides are first hydrolyzed into monosaccharides, which are then further fermented through glycolysis into intermediate products such as ethanol and fatty acids. Furthermore, proteins in the water can be first hydrolyzed into amino acids, which are then deaminated to produce intermediate products of fatty acids and ammonia. Lipid organic matter in the water can also be first converted into fatty acids and glycerol, and then into intermediate products of fatty acids and alcohols.

[0056] Furthermore, the intermediate products produced in the above stages can be further converted into valuable products under the action of microorganisms (such as hydrogen-producing acetogenic bacteria and methanogens). For example, under the action of hydrogen-producing acetogenic bacteria, intermediate products other than formic acid, acetic acid, methylamine and methanol, such as water-soluble small molecule compounds such as fatty acids (such as propionic acid, butyric acid) and alcohols (such as ethanol) can be converted into acetic acid, hydrogen and carbon dioxide. Methanogens can convert intermediate products such as formic acid, acetic acid, methylamine and methanol into methane through different pathways. This methane can be used as a fuel, such as natural gas and coal gas, and is widely used in civil and industrial applications.

[0057] In order to improve the hydrolysis and fermentation effects of domestic sewage, in a possible embodiment, more than two hydrolysis reactors 12 can be designed. In a specific embodiment, as Figure 1 As shown, two hydrolysis reactors 12 are designed in the treatment device.

[0058] The domestic sewage after the primary biochemical treatment will flow into the first aerobic reactor 13 through the second pipe. The first aerobic reactor 13 is filled with the above-mentioned biological filler. It can be understood that the first aerobic reactor 13 can perform secondary biochemical treatment, that is, a combination of aerobic and anaerobic methods to treat domestic sewage.

[0059] Specifically, in the first aerobic reactor 13, the interior of the biological filler is an anoxic environment, and the denitrifying bacteria therein use the organic matter in the sewage as a carbon source to reduce the nitrate and nitrite in the sewage into nitrogen gas and release it into the air, thereby reducing the concentration of BOD5 (BOD5: the amount of free oxygen consumed by aerobic microorganisms to oxidize and decompose organic matter per unit volume of water within 5 days, expressed in milligrams of oxygen per liter (O2, mg / l)), and the concentration of nitrate will also drop significantly, while the concentration of P will change very little. In an aerobic environment, organic matter will be biochemically degraded by microorganisms, and BOD5 will continue to drop. In addition, after the organic nitrogen is ammonified, it can be nitrified by denitrifying bacteria, which will significantly reduce the concentration of ammonium. In this process, the concentration of nitrate will increase accordingly, and the concentration of P will drop rapidly due to the filtration and uptake by polyphosphate bacteria.

[0060] In the embodiment provided by the present invention, the treatment device further includes an oxygenator 14 installed on the second pipeline. The oxygenator 14 can provide oxygen to the first aerobic reactor 13 and the second aerobic reactor 16 to form an aerobic environment.

[0061] Furthermore, in order to enable air to flow into the aerator 14 quickly, in a possible embodiment, the processing device further includes an air compressor 22 connected to the aerator 14 .

[0062] In order to improve the contact between oxygen and sewage, a gas-liquid mixer 15 is installed downstream of the oxygenator 14 to fully mix the oxygen and sewage.

[0063] The oxygen provided by the oxygenator 14 flows through the first aerobic reactor 13 and then into the second aerobic reactor 16, further improving the oxygen utilization rate. The biochemical degradation in the second aerobic reactor 16 is the same as that in the first aerobic reactor 13 and will not be repeated here.

[0064] It should be noted that the specific surface area of these filler balls is several times greater than conventional fillers in the prior art, for example, six times greater. They also create turbulent flow within the wastewater and enable both aerobic and anoxic conditions to coexist. Specifically, biofilm forms from the surface to the interior of the filler balls, controlling the surface oxygen concentration at 0.5-1.5 mg / L, creating an aerobic environment. The filler balls rotate with the turbulent air-water flow, ensuring uniform oxygenation across the surface. The outer biofilm envelops the inner biofilm, controlling the internal oxygen concentration at 0.1-0.3 mg / L, creating an anoxic environment. These filler balls can further enhance wastewater treatment efficiency and increase load-bearing capacity.

[0065] In the embodiment provided by the present invention, the number of the second aerobic reactors 16 can be adjusted according to the amount of domestic sewage to be treated, and is generally 2-8. Figure 1 As shown, the treatment device is designed with three second aerobic reactors 16 , wherein each second aerobic reactor 16 has a height of 3-10 m and a diameter of 0.6-3 m, and a gas-liquid mixer 15 is installed between the second aerobic reactors 16 .

[0066] Furthermore, in a possible embodiment, the third second aerobic reactor 16 is connected to the sewage regulating tank 11 via a pump, which can significantly improve the treatment effect and prevent the discharged water from secondary pollution.

[0067] In the embodiment provided herein, flotation device 17 is connected to second aerobic reactor 16 via a fourth conduit. After biochemical degradation, wastewater flows into flotation device 17 for flotation treatment. Specifically, a high-pressure water pump pressurizes water to several atmospheres and injects it into the tank, causing the air and water to mix and form dissolved air water. This dissolved air water then flows through a dissolved air releaser into the wastewater. Due to the sudden decompression, the air in the dissolved air water forms numerous tiny bubbles, which attract impurities, causing them to float upwards for separation and removal. These impurities are typically detached biofilm, phosphates, and other suspended matter.

[0068] In one possible embodiment, the treatment device further includes a first tank 19 in communication with the flotation device 17, and a flocculant is contained in the first tank 19. When treating electroplating wastewater, the flocculant is usually polyacrylamide.

[0069] In addition, in a possible embodiment, the treatment device further includes a second tank body 21 connected to the flotation device 17 , and the second tank body 21 contains a phosphorus removal agent.

[0070] In one possible embodiment, the treatment device further includes a sterilizer connected to the liquid outlet of the flotation device 17. Specifically, the sterilizer can be a UV sterilizer. Since the sewage passing through the flotation device 17 may contain microorganisms and viruses, to prevent secondary contamination, the microorganisms and viruses are killed by UV light before being discharged into the environment.

[0071] Since sludge may be generated in the hydrolysis reactor 12, the first aerobic reactor 13, the second aerobic reactor 16, and the flotation device 17, the treatment device also includes a sludge pool, which is connected to the bottom of the hydrolysis reactor 12, the first aerobic reactor 13, the second aerobic reactor 16, and the flotation device 17 respectively, and the sludge therein will be discharged into the sludge pool and then regularly transported out for treatment by a septic tank truck.

[0072] An embodiment of the present invention further provides a method for treating domestic sewage, which uses the treatment device described in any of the above embodiments and includes the following steps:

[0073] 1) The pre-treated domestic sewage is passed into the sewage regulating tank to reduce the fluctuation of domestic sewage discharge;

[0074] 2) The uniformly mixed domestic sewage flows into the hydrolysis reactor through the first pipe for hydrolysis and fermentation;

[0075] 3) The domestic sewage after hydrolysis and fermentation passes through the second pipeline and the oxygen is mixed with the domestic sewage in the gas-liquid mixer;

[0076] 4) The mixed sewage flows into the first aerobic reactor and then flows into the second aerobic reactor through the third pipe for biochemical degradation;

[0077] 5) The domestic sewage after biochemical degradation flows into the flotation device through the fourth pipeline for flotation treatment and is then discharged.

[0078] Specifically,

[0079] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0080] In the present invention, unless otherwise expressly provided, the terms "installed," "connected," "connected," "fixed," etc. should be understood in a broad sense. For example, they may refer to fixed connections, detachable connections, or integral molding; they may refer to mechanical connections, electrical connections, or communication with each other; they may refer to direct connections or indirect connections through an intermediate medium; they may refer to internal communication between two components or the interaction between two components, unless otherwise expressly provided. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0081] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or make equivalent replacements for some or all of the technical features therein. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for treating domestic sewage, characterized in that: The processing device comprises: Sewage regulating tank, used to reduce fluctuations in domestic sewage discharge; a hydrolysis reactor connected to the sewage regulating tank via a first pipe, wherein the hydrolysis reactor is filled with biological fillers to hydrolyze and ferment organic matter in the sewage, and a bag filter is installed on the first pipe to intercept impurities in the water; a first aerobic reactor, connected to the hydrolysis reactor via a second pipe, and the first aerobic reactor is filled with biological fillers; an aerator, installed on the second pipeline; a gas-liquid mixer installed on the second pipeline and located downstream of the oxygenator; N second aerobic reactors are connected to the first first aerobic reactor via a third pipe, and the second aerobic reactors are filled with biological fillers, wherein 2≤N≤8; an air flotation device connected to the last of the second aerobic reactors via a fourth pipeline, and a delivery pump installed on the first pipeline, the delivery pump being used to make the pressure inside the hydrolysis reactor, the first aerobic reactor, and the second aerobic reactor greater than that inside the air flotation device, and to mix the air and water in the first aerobic reactor and the second aerobic reactor to form dissolved air water; The interior of each biological filler in the first aerobic reactor and the second aerobic reactor is an anoxic environment, and the surface of the biological filler is an aerobic environment, so that the first aerobic reactor and the second aerobic reactor can achieve a secondary biochemical treatment combining aerobic and anaerobic conditions based on the filled biological filler, and each biological filler is spherical; The treatment device also includes a pre-treatment unit, which includes a sewage regulating tank. The sewage regulating tank is used to pre-treat domestic sewage before entering the sewage regulating tank, that is, domestic sewage flows into the septic tank to remove most of the solid suspended matter, then flows through the screen to remove debris, and finally flows into the sewage regulating tank; The treatment device further comprises a sludge pool, which is connected to the bottom of the hydrolysis reactor, the first aerobic reactor, the second aerobic reactor and the flotation device respectively.

2. The processing device according to claim 1, characterized in that The number of the second aerobic reactors is 3, the three second aerobic reactors are connected in series, and a gas-liquid mixer is installed between adjacent second aerobic reactors.

3. The processing device according to claim 2, characterized in that The third second aerobic reactor connected in series is communicated with the sewage regulating tank via a pump.

4. The processing device according to claim 1, characterized in that The treatment device further includes a first tank body communicated with the flotation device, wherein the first tank body contains a flocculant.

5. The processing device according to claim 4, characterized in that The treatment device further includes a second tank body communicated with the flotation device, wherein the second tank body contains a phosphorus removal agent.

6. The processing device according to claim 1, characterized in that The processing device also includes an air compressor connected to the aerator.

7. The processing device according to claim 1, characterized in that The processing device further comprises a sterilizer connected to the liquid outlet of the air flotation device.

8. A method for treating domestic sewage, characterized in that: The processing method uses the processing device according to any one of claims 1 to 7, and the processing method comprises the following steps: 1) The pre-treated domestic sewage is passed into the sewage regulating tank to reduce the fluctuation of domestic sewage discharge; 2) flowing the uniformly mixed domestic sewage into a hydrolysis reactor through a first pipe for hydrolysis and fermentation, wherein a delivery pump is installed on the first pipe; 3) The domestic sewage after hydrolysis and fermentation passes through the second pipeline and the oxygen is mixed with the domestic sewage in the gas-liquid mixer; 4) The mixed sewage flows into the first aerobic reactor and then flows into the second aerobic reactor through the third pipe for biochemical degradation, and a secondary biochemical treatment combining aerobic and anaerobic treatment is performed in the first aerobic reactor and the second aerobic reactor; 5) The domestic sewage after biochemical degradation flows into the flotation device through the fourth pipeline for flotation treatment and is then discharged.

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