A wastewater treatment method and apparatus

Abstract

This invention provides a wastewater treatment method and apparatus, belonging to the field of water treatment technology. The invention sequentially treats the wastewater to be treated through anaerobic treatment, anoxic treatment, aerobic DBR treatment, and a first sedimentation treatment, obtaining pre-denitrified wastewater and activated sludge respectively. The activated sludge from the first portion is returned to the anaerobic treatment step, and the activated sludge from the second portion undergoes dominant microbial screening to obtain sludge containing dominant microbial species, which is then returned to the anaerobic treatment step. The pre-denitrified wastewater is mixed with a flocculant and subjected to a second sedimentation treatment to obtain effluent. Using this method to treat wastewater can significantly reduce carbon source consumption in wastewater treatment processes, thus helping to reduce treatment costs.

Description

Technical Field

[0001] This invention relates to the field of water treatment technology, and in particular to a wastewater treatment method and apparatus. Background Technology

[0002] Most existing municipal wastewater treatment plants use the activated sludge process, with the most typical treatment technology being A2O, which utilizes microorganisms for nitrogen removal. With rapid economic development and accelerated urbanization, the volume of urban wastewater is increasing daily, and local governments are imposing stricter requirements on total nitrogen and total phosphorus in the effluent from wastewater treatment plants. However, insufficient carbon sources in the influent result in less than ideal biological nitrogen removal. Therefore, it is necessary to increase the carbon source dosage at the influent to achieve a carbon-to-nitrogen ratio (C / N) close to 5:1 to meet the effluent requirements for biological nitrogen removal. Simultaneously, excessive aeration in the aerobic tank is required, with dissolved oxygen concentrations reaching above 5 mg / L, enabling microorganisms to carry out nitrification to remove ammonia nitrogen. The large addition of carbon sources and excessive aeration lead to increased treatment costs for wastewater treatment plants. Meanwhile, when using the above process, a large amount of flocculant needs to be added to the high-efficiency sedimentation tank for chemical phosphorus removal to meet the requirements of total phosphorus in the effluent, and at the same time remove suspended solids (SS) in the wastewater. The consumption of a large amount of flocculant not only wastes resources, but also generates a large amount of high water content sludge that needs to be disposed of, which brings huge economic pressure to the operation of the wastewater treatment plant. Summary of the Invention

[0003] The purpose of this invention is to provide a wastewater treatment method and apparatus. By using the method of this invention to treat wastewater, the consumption of carbon sources and flocculants in the wastewater treatment process can be significantly reduced, which is beneficial to reducing treatment costs.

[0004] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0005] This invention provides a wastewater treatment method, comprising the following steps:

[0006] The wastewater to be treated was subjected to anaerobic treatment, anoxic treatment, aerobic DBR treatment and first sedimentation treatment in sequence to obtain pre-denitrified wastewater and activated sludge, respectively.

[0007] The activated sludge in the first part is returned to the anaerobic treatment process, and the activated sludge in the second part is subjected to dominant strain screening to obtain sludge containing dominant strains, and the sludge containing dominant strains is returned to the anaerobic treatment process.

[0008] The pre-denitrified wastewater is mixed with flocculant and subjected to a second sedimentation treatment to obtain effluent.

[0009] Preferably, the anaerobic treatment further includes phosphorus removal treatment; the second sedimentation treatment further yields chemical sludge, and the process after obtaining the chemical sludge further includes:

[0010] The chemical sludge is subjected to flocculant extraction and solid-liquid separation treatment in sequence to obtain a light extraction liquid, which is then returned to the phosphorus removal treatment process.

[0011] Preferably, the aerobic DBR treatment further includes: partially recirculating the obtained aerobic DBR effluent to the anoxic treatment process, wherein the recirculation ratio of the aerobic DBR effluent is 200% to 400%.

[0012] Preferably, the mass of the activated sludge in the first part is 80-96% of the total mass of the activated sludge.

[0013] Preferably, the screening treatment of the dominant strain further yields heavy sludge containing mud and sand and light sludge, the total mass of the heavy sludge containing mud and sand and the light sludge being 10-50% of the mass of the activated sludge in the second part. After obtaining the heavy sludge containing mud and sand and the light sludge, the treatment further includes: subjecting the heavy sludge containing mud and sand and the light sludge to a first dewatering treatment before discharging them.

[0014] This invention provides a wastewater treatment device, including an anaerobic tank, an anoxic tank, an aerobic DBR tank, a secondary sedimentation tank, a flocculation sedimentation tank, and a dominant microbial strain screener. The anaerobic tank, anoxic tank, aerobic DBR tank, and secondary sedimentation tank are connected sequentially. The secondary sedimentation tank is provided with a first discharge port, a second discharge port, and a third discharge port. The first discharge port is connected to the inlet of the anaerobic tank, the second discharge port is connected to the inlet of the anaerobic tank via the dominant microbial strain screener, and the third discharge port is connected to the inlet of the flocculation sedimentation tank.

[0015] Preferably, it further includes a first dewatering device; the dominant microbial strain sieve is provided with a sludge discharge port containing dominant microbial strains, a light sludge discharge port and a heavy sludge discharge port containing silt, the sludge discharge port containing dominant microbial strains is connected to the feed inlet of the anaerobic tank, and the light sludge discharge port and the heavy sludge discharge port containing silt are connected to the first dewatering device.

[0016] Preferably, the dominant strain sieve is a hydrocyclone, which includes a first-stage hydrocyclone and a second-stage hydrocyclone. The first-stage hydrocyclone and the second-stage hydrocyclone are respectively provided with a feed inlet, an upper outlet and a lower outlet. The first-stage hydrocyclone and the second-stage hydrocyclone are connected in series or in parallel.

[0017] When the first-stage hydrocyclone and the second-stage hydrocyclone are connected in series, the second outlet of the secondary sedimentation tank is connected to the inlet of the first-stage hydrocyclone, the downstream outlet of the first-stage hydrocyclone is connected to the inlet of the second-stage hydrocyclone, and the upstream outlet of the second-stage hydrocyclone is connected to the inlet of the anaerobic tank; both the upstream outlet of the first-stage hydrocyclone and the downstream outlet of the second-stage hydrocyclone are connected to the inlet of the first dewatering device.

[0018] When the first-stage hydrocyclone and the second-stage hydrocyclone are connected in parallel, the second discharge port of the secondary sedimentation tank is connected to the inlet of the first-stage hydrocyclone and the inlet of the second-stage hydrocyclone. The downstream outlet of the first-stage hydrocyclone and the upstream outlet of the second-stage hydrocyclone are connected to the inlet of the anaerobic tank. The upstream outlet of the first-stage hydrocyclone and the downstream outlet of the second-stage hydrocyclone are connected to the inlet of the first dewatering device.

[0019] Preferably, the aerobic DBR tank is an aerobic tank equipped with a DBR reactor, and the aerobic DBR tank is provided with a reflux liquid outlet, which is connected to the feed inlet of the anoxic tank.

[0020] Preferably, it further includes a phosphorus removal device, a flocculant extraction device, and a solid-liquid separator; the outlet of the phosphorus removal device is connected to the inlet of the anaerobic tank; the outlet of the flocculation sedimentation tank is connected to the inlet of the phosphorus removal device sequentially via the flocculant extraction device and the solid-liquid separator.

[0021] This invention provides a wastewater treatment method comprising the following steps: sequentially subjecting the wastewater to anaerobic treatment, anoxic treatment, aerobic DBR treatment, and a first sedimentation treatment to obtain pre-denitrified wastewater and activated sludge, respectively; recirculating the first portion of the activated sludge back to the anaerobic treatment step; performing dominant microbial screening on the second portion of the activated sludge to obtain sludge containing dominant microbial species, and recirculating the sludge containing dominant microbial species back to the anaerobic treatment step; mixing the pre-denitrified wastewater with a flocculant and performing a second sedimentation treatment to obtain effluent. Using this method to treat wastewater can significantly reduce carbon source consumption in wastewater treatment processes, thus helping to reduce treatment costs. Specifically, this invention simultaneously achieves nitrification and denitrification reactions in the aerobic DBR treatment of wastewater. Compared with ordinary aerobic tanks, the aeration rate is reduced, and the dissolved oxygen is lowered. At the same time, a process of screening dominant bacteria is added after the first settling treatment, which can return high-quality sludge bacteria to the anaerobic treatment process, which is conducive to improving the activity of nitrifying and denitrifying bacteria, thereby improving the efficiency of nitrification and denitrification reactions (i.e., biological nitrogen removal efficiency), and can reduce the carbon source added in the biological stage by 10-80%.

[0022] Furthermore, using the method of this invention to treat wastewater can significantly reduce the consumption of flocculants in the wastewater treatment process, which is beneficial for further reducing treatment costs. Specifically, the second sedimentation treatment of this invention requires the use of flocculants (such as polyaluminum chloride, polyferric sulfate, etc.). The chemical sludge produced after the second sedimentation treatment has low phosphorus content and high aluminum and iron content. By using flocculant extraction treatment, aluminum and iron can be dissolved, and after solid-liquid separation treatment, a high-purity aluminum-iron solution (i.e., light extraction liquid) can be obtained, which can be recycled to the phosphorus removal process of wastewater treatment (the total phosphorus removal rate can reach 10-60%). This enables the recycling of flocculants, which is beneficial for reducing the amount of flocculant added (the amount of flocculant added during the second sedimentation treatment can be reduced by 30-50%), saving reagent costs, and at the same time, it is beneficial for reducing the sludge production of the entire wastewater treatment plant.

[0023] The results of the embodiments show that the wastewater treatment method provided by the present invention can effectively reduce the amount of carbon source and flocculant added, and can also effectively reduce the aeration power consumption and sludge treatment cost, and can ensure that the total nitrogen and total phosphorus in the effluent meet the index requirements, wherein ammonia nitrogen ≤1.0mg / L, total nitrogen ≤10(15)mg / L, and total phosphorus ≤0.2mg / L. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the wastewater treatment device in an embodiment of the present invention, wherein 1 is a phosphorus removal device, 2 is an anaerobic tank, 3 is an anoxic tank, 4 is a DBR reaction tank, 5 is a secondary sedimentation tank, 6 is a flocculation sedimentation tank, 7 is a dominant bacteria screening device, 8 is a flocculant extraction device, 9 is a solid-liquid separator, 10 is a first dewatering device, and 11 is a second dewatering device.

[0025] Figure 2 This is a flowchart of the dominant bacterial strain screening process when the first-stage hydrocyclone and the second-stage hydrocyclone are connected in series in an embodiment of the present invention.

[0026] Figure 3 This is a flowchart of the dominant bacterial strain screening process when the first-stage hydrocyclone and the second-stage hydrocyclone are connected in parallel in an embodiment of the present invention. Detailed Implementation

[0027] This invention provides a wastewater treatment method, comprising the following steps:

[0028] The wastewater to be treated was subjected to anaerobic treatment, anoxic treatment, aerobic DBR treatment and first sedimentation treatment in sequence to obtain pre-denitrified wastewater and activated sludge, respectively.

[0029] The activated sludge in the first part is returned to the anaerobic treatment process, and the activated sludge in the second part is subjected to dominant strain screening to obtain sludge containing dominant strains, and the sludge containing dominant strains is returned to the anaerobic treatment process.

[0030] The pre-denitrified wastewater is mixed with flocculant and subjected to a second sedimentation treatment to obtain effluent.

[0031] This invention effectively reduces the amount of carbon source added through aerobic DBR treatment and screening of dominant bacterial strains, which helps to reduce treatment costs. Furthermore, this invention effectively reduces the amount of flocculant added through flocculant extraction treatment, which helps to further reduce treatment costs. Figure 1 The flowchart below shows the wastewater treatment method of the present invention. The method of the present invention will be described in detail below.

[0032] This invention involves anaerobic treatment of wastewater to obtain anaerobic effluent. In this invention, depending on the indicators of the wastewater to be treated, phosphorus removal treatment may be included before the anaerobic treatment. That is, this invention can directly subject the wastewater to anaerobic treatment, or it can sequentially undergo phosphorus removal treatment followed by anaerobic treatment. In this invention, the wastewater to be treated is preferably municipal wastewater. In embodiments of this invention, the indicators of the wastewater to be treated preferably include: COD 98–150 mg / L, TP 5.45–6.37 mg / L, TN 50–75 mg / L, ammonia nitrogen 45–62.35 mg / L, and pH 7.21–7.44. In this invention, the conditions for phosphorus removal treatment preferably include: total phosphorus in the influent <10 mg / L, specifically 5.45–6.37 mg / L. In this invention, the anaerobic treatment conditions preferably include a dissolved oxygen concentration of 0.1 to 0.5 mg / L, specifically 0.1 mg / L, 0.2 mg / L, 0.3 mg / L, 0.4 mg / L, or 0.5 mg / L.

[0033] After obtaining the anaerobic effluent, the present invention subjectes the anaerobic effluent to anoxic treatment to obtain anoxic effluent. In the present invention, a carbon source is preferably added during the anoxic treatment process, and the preferred dosage of the carbon source is 50–70 mg / L, specifically 50 mg / L, 55 mg / L, 60 mg / L, 65 mg / L, or 70 mg / L. In the present invention, the preferred conditions for the anoxic treatment include a dissolved oxygen concentration of 0.3–1.0 mg / L, specifically 0.3 mg / L, 0.4 mg / L, 0.5 mg / L, 0.6 mg / L, 0.7 mg / L, 0.8 mg / L, 0.9 mg / L, or 1.0 mg / L.

[0034] After obtaining the anoxic effluent, the present invention performs aerobic DBR treatment on the anoxic effluent to obtain aerobic DBR effluent. In the present invention, the preferred conditions for the aerobic DBR treatment include: a hydraulic retention time of 8-9 hours and a dissolved oxygen concentration of 1.0-1.5 mg / L in the DBR reaction zone, specifically 1.0 mg / L, 1.1 mg / L, 1.2 mg / L, 1.3 mg / L, 1.4 mg / L, or 1.5 mg / L.

[0035] After obtaining the aerobic DBR effluent, this invention subjectes the aerobic DBR effluent to a first sedimentation treatment, yielding preliminarily denitrified wastewater and activated sludge. Preferably, this invention recirculates a portion of the aerobic DBR effluent to the anoxic treatment process, and performs the remaining aerobic DBR effluent under a first sedimentation treatment. In this invention, the recirculation ratio (denoted as the internal recirculation ratio) of the aerobic DBR effluent is preferably 200%–400%. In this invention, the conditions for the first sedimentation treatment preferably include a residence time of 4–6 hours, specifically 4 hours, 5 hours, or 6 hours.

[0036] After obtaining the activated sludge, the present invention divides the activated sludge into two parts for separate treatment. Specifically, the first part of the activated sludge is returned to the anaerobic treatment process; the second part of the activated sludge is subjected to dominant bacterial strain screening to obtain sludge containing dominant bacterial strains, light sludge, and heavy sludge containing silt and sand. The sludge containing dominant bacterial strains is returned to the anaerobic treatment process, and the heavy sludge containing silt and sand and the light sludge are discharged after a first dewatering treatment, which will be described in detail later.

[0037] In this invention, the mass of the activated sludge in the first part is preferably 80-96% of the total mass of the activated sludge, more preferably 85-95%, specifically 85%, 90% or 95%.

[0038] In this invention, the preferred conditions for the dominant microbial strain screening treatment include an influent pressure of 0.5–1.0 MPa, specifically 0.5 MPa, 0.6 MPa, 0.7 MPa, 0.8 MPa, 0.9 MPa, or 1.0 MPa. This invention preferably utilizes dominant microbial strain screening treatment to separate sludge with higher activity and better aggregation, which is beneficial for constructing a more efficient denitrification system within the biological system.

[0039] In this invention, the total mass of the heavy sludge containing mud and sand and the light sludge is preferably 10-50% of the mass of the activated sludge in the second part, more preferably 15-25%, specifically 15%, 20% or 25%. This invention does not have any particular limitation on the first dewatering treatment; methods well known to those skilled in the art can be used.

[0040] After obtaining the initially denitrified wastewater, this invention mixes the initially denitrified wastewater with a flocculant and performs a second sedimentation treatment to obtain effluent. In this invention, the flocculant preferably includes one or more of polyaluminum chloride, polyferric sulfate, and polyaluminum ferric sulfate, more preferably polyaluminum chloride or polyferric sulfate; the dosage of the flocculant is preferably 35–64 mg / L, specifically 35 mg / L, 40 mg / L, 45 mg / L, 50 mg / L, 55 mg / L, 60 mg / L, or 64 mg / L. In this invention, the conditions for the second sedimentation treatment preferably include a retention time of 4–6 hours, specifically 4 hours, 5 hours, or 6 hours. The effluent indicators obtained after the second sedimentation treatment of this invention preferably include: total nitrogen (TN) ≤ 10 mg / L, and total phosphorus (TP) ≤ 0.2 mg / L.

[0041] In this invention, the second sedimentation treatment also yields chemical sludge. Preferably, after obtaining the chemical sludge, the process further includes: sequentially subjecting the chemical sludge to flocculant extraction and solid-liquid separation to obtain a light extraction liquid, which is then returned to the phosphorus removal treatment step. In this invention, the extraction reagent used in the flocculant extraction is preferably an acidic reagent, preferably including one or more of sulfuric acid, hydrochloric acid, acetic acid, and citric acid; the mass of the extraction reagent is preferably 0.1-5% of the mass of the chemical sludge, specifically based on ensuring that the pH value requirement for flocculant extraction is met; the conditions for flocculant extraction are preferably: a pH value of 1.0-3.5, preferably 1.5-2.2; a time of 30-120 min, preferably 45-60 min; and the flocculant extraction is preferably carried out under stirring conditions. This invention preferably performs flocculant extraction under the above conditions, which can recover 70-80% of aluminum and iron ions, facilitating the recycling of flocculants, reducing the chemical costs of wastewater treatment plants, reducing carbon emissions, and belonging to a green circular economy. This invention involves solid-liquid separation of the effluent obtained after flocculant extraction to obtain a light extract, which is then recycled to the phosphorus removal process. Preferably, the solid-liquid separation conditions include a gravity settling time of 3–5 hours, specifically 3, 4, or 5 hours. Furthermore, a heavy residual effluent is obtained after the solid-liquid separation. Preferably, the heavy residual effluent is then subjected to a second dehydration treatment before being discharged. This invention does not impose any specific limitations on the second dehydration treatment; methods well-known to those skilled in the art can be used.

[0042] This invention provides a wastewater treatment device, including an anaerobic tank, an anoxic tank, an aerobic DBR tank, a secondary sedimentation tank, a flocculation sedimentation tank, and a dominant microbial strain screener. The anaerobic tank, anoxic tank, aerobic DBR tank, and secondary sedimentation tank are connected sequentially. The secondary sedimentation tank is provided with a first discharge port, a second discharge port, and a third discharge port. The first discharge port is connected to the inlet of the anaerobic tank, the second discharge port is connected to the inlet of the anaerobic tank via the dominant microbial strain screener, and the third discharge port is connected to the inlet of the flocculation sedimentation tank.

[0043] The wastewater treatment device provided by this invention includes an anaerobic tank, an anoxic tank, an aerobic DBR tank, and a secondary sedimentation tank connected in sequence, respectively used for anaerobic treatment, anoxic treatment, aerobic DBR treatment, and a first sedimentation treatment. The secondary sedimentation tank is provided with a first outlet, a second outlet, and a third outlet. The first outlet is connected to the inlet of the anaerobic tank, the second outlet is connected to the inlet of the anaerobic tank via a dominant bacteria separator, and the third outlet is connected to the inlet of the flocculation sedimentation tank. As an embodiment of this invention, the aerobic DBR tank is an aerobic tank equipped with a DBR reactor, and the aerobic DBR tank is provided with a reflux outlet, which is connected to the inlet of the anoxic tank. As an embodiment of this invention, the aerobic DBR tank is the aerobic DBR tank described in patent application number 201810106057.8.

[0044] As an embodiment of the present invention, the DBR reactor consists of three parts: a frame body, denitrification packing, and an aeration system. As an embodiment of the present invention, the DBR reactor is the DBR reactor described in patent application number 201810104982.7. Specifically, the frame body is made of S304 stainless steel, which is durable and the frame is independent, facilitating installation and maintenance. The denitrification packing is made of a special material with microbial affinity and hydrophilicity, a large specific surface area, and a fast biofilm formation rate. A separate aeration system is configured at the bottom of the DBR reactor, a guide plate is configured at the top, and a fixed denitrification packing is configured in the middle. In practical applications, when the bottom aeration system aerates, the upflow velocity in the frame body area will be higher than in other areas. Combined with the effect of the guide plate, the water in the frame body area will have more opportunities to contact the packing than the water in other areas, thereby increasing the media exchange capacity and promoting the capture of pollutants by the biofilm activated sludge. Meanwhile, due to the combined effect of the aeration system within the aerobic tank and the aeration system configured at the bottom of the DBR reactor, the dissolved oxygen in the main frame area is higher than in other areas, which increases the oxygen partial pressure, thereby improving the activity of the biofilm sludge, accelerating the decomposition of organic matter, and the proportion of the anoxic and anaerobic zones of the biofilm can be controlled through aeration control.

[0045] The wastewater treatment device provided by this invention includes a dominant microbial strain sieve for screening dominant microbial strains. As an embodiment of this invention, the wastewater treatment device further includes a first dewatering device; the dominant microbial strain sieve is provided with a sludge outlet containing dominant microbial strains, a light sludge outlet, and a heavy sludge outlet containing silt and sand. The sludge outlet containing dominant microbial strains is connected to the inlet of the anaerobic tank, and the light sludge outlet and the heavy sludge outlet containing silt and sand are connected to the first dewatering device.

[0046] As an embodiment of the present invention, the dominant microbial strain sieving device is a hydrocyclone. The present invention does not specifically limit the type of hydrocyclone; any hydrocyclone well-known to those skilled in the art can be used. In this invention, a hydrocyclone is used. Pressurized sludge (i.e., the activated sludge described in the second part) enters the cyclone chamber tangentially from the inlet of the hydrocyclone, generating high-speed rotational motion. Due to the constraints of the inner and outer cylinders and the top cover, the sludge forms a downward-flowing external vortex within the sludge. During the vortex process, denser solid particles carrying adhering water are subjected to centrifugal force, and most are thrown against the cylinder wall, losing energy and sliding down the wall. Thus, the concentrated phase sludge is discharged from the bottom outlet; while the less dense particles move towards the axis and form an upward-flowing internal vortex at the center of the axis, which is discharged outward through the overflow pipe, thereby achieving the effect of two-phase separation.

[0047] As an embodiment of the present invention, the hydrocyclone includes a first-stage hydrocyclone and a second-stage hydrocyclone. The first-stage hydrocyclone and the second-stage hydrocyclone are respectively provided with a feed inlet, an upper outlet and a lower outlet. The first-stage hydrocyclone and the second-stage hydrocyclone are connected in series or in parallel.

[0048] As an embodiment of the present invention, when the first-stage hydrocyclone and the second-stage hydrocyclone are connected in series (e.g.) Figure 2As shown in the figure, the second discharge port of the secondary sedimentation tank is connected to the inlet of the first-stage hydrocyclone, the downstream outlet of the first-stage hydrocyclone is connected to the inlet of the second-stage hydrocyclone, and the upstream outlet of the second-stage hydrocyclone is connected to the inlet of the anaerobic tank; the upstream outlet of the first-stage hydrocyclone and the downstream outlet of the second-stage hydrocyclone are both connected to the inlet of the first dewatering device. Specifically, in actual operation, the first-stage hydrocyclone discharges the heavy sludge carrying dominant bacteria from the downstream outlet. Sludge with a longer sludge age carries bacteria with lower activity, smaller particle size, and lower specific gravity, overflowing from the upstream outlet (i.e., the light sludge discharge outlet). Then, the heavy sludge carrying dominant bacteria enters the second-stage hydrocyclone. Large particles of heavy sludge containing silt are discharged from the downstream outlet (i.e., the heavy sludge containing silt discharge outlet), while the sludge carrying dominant bacteria, relatively lighter than silt, overflows from the upstream outlet (i.e., the sludge containing dominant bacteria discharge outlet). After treatment by the first and second-stage hydrocyclones, the final sludge carrying dominant bacteria (i.e., sludge containing dominant bacteria) is returned to the anaerobic tank to participate in nitrification and denitrification reactions, improving nitrogen removal efficiency and reducing carbon source dosage.

[0049] As an embodiment of the present invention, when the first-stage hydrocyclone and the second-stage hydrocyclone are connected in parallel (e.g.) Figure 3 As shown in the diagram, the second discharge outlet of the secondary sedimentation tank is connected to the inlet of both the first-stage hydrocyclone and the second-stage hydrocyclone. The downstream outlet of the first-stage hydrocyclone and the upstream outlet of the second-stage hydrocyclone are both connected to the inlet of the anaerobic tank. The upstream outlet of the first-stage hydrocyclone and the downstream outlet of the second-stage hydrocyclone are both connected to the inlet of the first dewatering device. When the first-stage hydrocyclone and the second-stage hydrocyclone are connected in parallel, the preferred mass ratio of activated sludge entering the first-stage hydrocyclone to the second-stage hydrocyclone is 1 to 3:1, more preferably 1 to 2:1. Specifically, taking a 1:1 mass ratio of activated sludge entering the Stage I hydrocyclone to the Stage II hydrocyclone as an example, 50% of the activated sludge enters the Stage I hydrocyclone. The Stage I hydrocyclone discharges the heavy sludge carrying the dominant bacterial species from the downstream outlet (i.e., the discharge outlet for sludge containing the dominant bacterial species) to the anaerobic tank. The sludge with a longer sludge age carries bacteria with lower activity, smaller particle size, and lower specific gravity, overflowing from the upstream outlet (i.e., the discharge outlet for light sludge) of the Stage I hydrocyclone. The activated sludge enters the first dewatering device; 50% of the activated sludge enters the second-stage hydrocyclone. The second-stage hydrocyclone separates large particles such as silt from the dominant bacteria in the sludge. Because the dominant bacteria are smaller and lighter than the silt particles, they overflow from the upper outlet of the second-stage hydrocyclone (i.e., the sludge discharge outlet containing dominant bacteria) and enter the anaerobic tank. The heavier silt particles overflow from the lower outlet of the second-stage hydrocyclone (i.e., the heavy sludge discharge outlet containing silt) and enter the first dewatering device.

[0050] The present invention preferably achieves the screening treatment of dominant bacterial species by adjusting the diameter and height of the first-stage hydrocyclone and the second-stage hydrocyclone. That is, the first-stage hydrocyclone and the second-stage hydrocyclone separate some of the less active microbial species and separate the heaviest sediment, thereby improving the efficiency of nitrification and denitrification in the biological treatment stage and reducing the amount of carbon source added.

[0051] The wastewater treatment device provided by the present invention includes a flocculation sedimentation tank for performing a second sedimentation treatment.

[0052] As an embodiment of the present invention, the wastewater treatment device further includes a phosphorus removal device, a flocculant extraction device, and a solid-liquid separator, which are used for phosphorus removal treatment, flocculant extraction treatment, and solid-liquid separation treatment, respectively; the outlet of the phosphorus removal device is connected to the inlet of the anaerobic tank; the outlet of the flocculation sedimentation tank is connected to the inlet of the phosphorus removal device in sequence via the flocculant extraction device and the solid-liquid separator.

[0053] As an embodiment of the present invention, the wastewater treatment device further includes a second dewatering device; the solid-liquid separator is provided with a light extract liquid outlet and a heavy residual liquid outlet, the light extract liquid outlet is connected to the feed inlet of the phosphorus removal device, and the heavy residual liquid outlet is connected to the second dewatering device.

[0054] Figure 1 This is a schematic diagram of the wastewater treatment device in an embodiment of the present invention, wherein 1 is a phosphorus removal device, 2 is an anaerobic tank, 3 is an anoxic tank, 4 is a DBR reaction tank, 5 is a secondary sedimentation tank, 6 is a flocculation sedimentation tank, 7 is a dominant bacteria screening device, 8 is a flocculant extraction device, 9 is a solid-liquid separator, 10 is a first dewatering device, and 11 is a second dewatering device. Figure 2 This is a flowchart of the dominant bacterial strain screening process when a Class I hydrocyclone and a Class II hydrocyclone are connected in series in Embodiment 1 of the present invention. Figure 3 This is a flowchart illustrating the dominant bacterial strain screening process when a stage I hydrocyclone and a stage II hydrocyclone are connected in parallel in Embodiment 2 of the present invention. The technical solutions of the present invention will be clearly and completely described below in conjunction with the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0055] Comparative Example 1

[0056] The original process of a wastewater treatment plant was as follows: the wastewater to be treated was sequentially subjected to anaerobic treatment in an anaerobic tank, anoxic treatment in an anoxic tank, aerobic treatment in an aerobic tank (without a DBR reactor), and first sedimentation treatment in a secondary sedimentation tank, to obtain preliminarily denitrified wastewater and activated sludge respectively; wherein the aerobic effluent obtained after the aerobic treatment was partially recycled to the anoxic treatment process.

[0057] The pre-denitrified wastewater is transported to a flocculation sedimentation tank, where a flocculant (specifically polyaluminum chloride, abbreviated as PAC) is added for a second sedimentation treatment, yielding effluent and chemical sludge respectively.

[0058] The activated sludge is mixed with chemical sludge and then transported to a thickening tank for concentration. The resulting concentrated material is then transported to a dewatering device for dewatering and then discharged.

[0059] Example 1

[0060] Improvements were made to Comparative Example 1, primarily by converting the aerobic tank into a DBR reactor and introducing a dominant microbial strain sieve and a flocculant extraction device. The specific process is as follows:

[0061] The wastewater to be treated is sequentially subjected to phosphorus removal in a phosphorus removal device, anaerobic treatment in an anaerobic tank, anoxic treatment in an anoxic tank, aerobic DBR treatment in an aerobic DBR tank (i.e., an aerobic tank equipped with a DBR reactor), and first sedimentation treatment in a secondary sedimentation tank to obtain pre-denitrified wastewater and activated sludge, respectively; wherein the aerobic effluent obtained after the aerobic treatment is partially recycled to the anoxic treatment process.

[0062] The activated sludge in the first part is returned to the anaerobic treatment process. The activated sludge in the second part is screened for dominant bacteria in a dominant bacteria sieve to obtain sludge containing dominant bacteria, light sludge, and heavy sludge containing silt. The sludge containing dominant bacteria is returned to the anaerobic treatment process. The light sludge and the heavy sludge containing silt are dewatered in a first dewatering device and then discharged.

[0063] The pre-denitrified wastewater is transported to a flocculation sedimentation tank, where a flocculant (specifically polyaluminum chloride, abbreviated as PAC) is added for a second sedimentation treatment, yielding effluent and chemical sludge respectively.

[0064] The chemical sludge is sequentially subjected to flocculant extraction in a flocculant extraction device and solid-liquid separation in a solid-liquid separator to obtain light extract liquid and heavy residual liquid, respectively. The light extract liquid is returned to the phosphorus removal process, and the heavy residual liquid is subjected to a second dewatering treatment in a second dewatering device before being discharged.

[0065] The activated sludge in the first part accounts for 85% of the total mass of the activated sludge, and the total mass of the heavy sludge containing silt and sand and the light sludge accounts for 25% of the mass of the activated sludge in the second part. The dominant microbial strain screening device includes a first-stage hydrocyclone and a second-stage hydrocyclone arranged in series. Specifically, the second discharge port of the secondary sedimentation tank (i.e., the discharge port of the second part of activated sludge) is connected to the inlet of the first-stage hydrocyclone, the downstream outlet of the first-stage hydrocyclone is connected to the inlet of the second-stage hydrocyclone, the upstream outlet of the second-stage hydrocyclone is connected to the inlet of the anaerobic tank, and the upstream outlet of the first-stage hydrocyclone and the downstream outlet of the second-stage hydrocyclone are both connected to the inlet of the first dewatering device.

[0066] The specific parameters of Comparative Example 1 and Example 1 are listed in Table 1. As can be seen from Table 1, the method of the present invention can make the effluent meet the Class I effluent discharge requirements of the "DB12 / 599-2015 Pollutant Discharge Standard for Urban Wastewater Treatment Plants" issued by Tianjin Municipality in 2015 (total nitrogen content less than 10 mg / L, ammonia nitrogen content less than 1.5 mg / L, and total phosphorus content less than 0.3 mg / L). Furthermore, as shown in Table 1, after introducing the DBR reactor and the dominant bacteria sieve in the process of Example 1, the carbon source dosage was 70 mg / L, which was reduced by 30% compared to the original process. At the same time, the chemical sludge was extracted by the flocculant extraction device and separated by the solid-liquid separator to obtain aluminum-iron recovery liquid. The aluminum-iron recovery liquid was transported to the wastewater inlet for phosphorus removal (total phosphorus removal rate of 30%). Since the phosphorus removal agent was added at the inlet, the dosage of polyaluminum chloride in the flocculation sedimentation tank was reduced to 35 mg / L, which was reduced by 30% compared to the original process.

[0067] Table 1. Index parameters in Comparative Example 1 and Example 1

[0068]

[0069] Comparative Example 2

[0070] The procedure was the same as in Comparative Example 1, except that the flocculant used was polyferric sulfate, and the relevant parameters are shown in Table 2.

[0071] Example 2

[0072] Improvements were made to Example 1, primarily by converting the aerobic tank into a DBR reactor and introducing a dominant microbial strain sieve and a flocculant extraction device. The specific process steps are the same as in Example 1, except that the mass of the activated sludge in the first part is 95% of the total activated sludge mass, and the total mass of the heavy sludge containing silt and sand and the light sludge is 15% of the activated sludge mass in the second part. The dominant microbial strain sieve includes a parallel-connected first-stage hydrocyclone and a second-stage hydrocyclone, specifically located in the second stage of the secondary sedimentation tank. The discharge ports (i.e., the discharge ports of the second part of activated sludge) are all connected to the inlets of the first-stage hydrocyclone and the second-stage hydrocyclone. The downstream outlet of the first-stage hydrocyclone and the upstream outlet of the second-stage hydrocyclone are both connected to the inlet of the anaerobic tank. The upstream outlet of the first-stage hydrocyclone and the downstream outlet of the second-stage hydrocyclone are both connected to the inlet of the first dewatering device. The mass ratio of activated sludge entering the first-stage hydrocyclone to that entering the second-stage hydrocyclone is 1:1. The relevant index parameters are shown in Table 2.

[0073] As shown in Table 2, the method of this invention can ensure that the effluent meets the Class I effluent discharge requirements of the "DB12 / 599-2015 Pollutant Discharge Standard for Urban Wastewater Treatment Plants" issued by Tianjin Municipality in 2015 (total nitrogen content less than 10 mg / L, ammonia nitrogen content less than 1.5 mg / L, and total phosphorus content less than 0.3 mg / L). Furthermore, Table 2 shows that after introducing a DBR reactor and a dominant bacteria sieve in Example 2, the carbon source dosage is 50 mg / L, a 67% reduction compared to the original process. Simultaneously, the chemical sludge is extracted by a flocculant extraction device and separated by a solid-liquid separator to obtain an aluminum-iron recovery liquid. This aluminum-iron recovery liquid is then transported to the wastewater inlet for phosphorus removal (total phosphorus removal rate of 20%). Because a phosphorus removal agent is added at the inlet, the dosage of polyferric sulfate in the flocculation sedimentation tank is reduced to 64 mg / L, a 20% reduction compared to the original process.

[0074] Table 2 shows the index parameters in Comparative Example 2 and Example 2.

[0075]

[0076]

[0077] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A wastewater treatment method, characterized in that, Includes the following steps: The wastewater to be treated is subjected to anaerobic treatment, anoxic treatment, aerobic DBR treatment, and a first sedimentation treatment in sequence to obtain preliminarily denitrified wastewater and activated sludge, respectively. The dissolved oxygen concentration in the anaerobic treatment is 0.1~0.3 mg / L. During the anoxic treatment, a carbon source is added at a dosage of 50~60 mg / L, and the dissolved oxygen concentration in the anoxic treatment is 0.3~0.4 mg / L. During the aerobic DBR treatment, the dissolved oxygen concentration in the DBR reaction zone is 1.3~1.5 mg / L. The activated sludge from the first part is returned to the anaerobic treatment process. The activated sludge from the second part is subjected to dominant microbial screening to obtain sludge containing dominant microbial species, heavy sludge containing silt and sand, and light sludge. The sludge containing dominant microbial species is returned to the anaerobic treatment process. The heavy sludge containing silt and sand and the light sludge are discharged after a first dewatering treatment. The mass of the activated sludge from the first part is 90-96% of the total mass of the activated sludge. The total mass of the heavy sludge containing silt and sand and the light sludge is 10-20% of the mass of the activated sludge from the second part. The pre-denitrified wastewater is mixed with flocculant and subjected to a second sedimentation treatment to obtain effluent; The wastewater treatment method uses an apparatus including an anaerobic tank, an anoxic tank, an aerobic DBR tank, a secondary sedimentation tank, a flocculation sedimentation tank, a dominant microbial strain screener, and a first dewatering device. The anaerobic tank, anoxic tank, aerobic DBR tank, and secondary sedimentation tank are connected sequentially. The secondary sedimentation tank is provided with a first discharge port, a second discharge port, and a third discharge port. The first discharge port is connected to the inlet of the anaerobic tank, the second discharge port is connected to the inlet of the anaerobic tank via the dominant microbial strain screener, and the third discharge port is connected to the inlet of the flocculation sedimentation tank. The dominant microbial strain screening device is a hydrocyclone, which includes a first-stage hydrocyclone and a second-stage hydrocyclone. Each of the first-stage and second-stage hydrocyclones is provided with an inlet, an upstream outlet, and a downstream outlet. The first-stage and second-stage hydrocyclones are connected in parallel. The second outlet of the secondary sedimentation tank is connected to the inlet of both the first-stage and second-stage hydrocyclones. The downstream outlet of the first-stage hydrocyclone and the upstream outlet of the second-stage hydrocyclone are both connected to the inlet of the anaerobic tank. The upstream outlet of the first-stage hydrocyclone and the downstream outlet of the second-stage hydrocyclone are both connected to the inlet of the first dewatering device. The mass ratio of activated sludge entering the stage I hydrocyclone to that entering the stage II hydrocyclone is 1~2:

1.

2. The wastewater treatment method according to claim 1, characterized in that, The anaerobic treatment is preceded by phosphorus removal treatment; the second sedimentation treatment further yields chemical sludge, and the process after obtaining the chemical sludge includes: The chemical sludge is subjected to flocculant extraction and solid-liquid separation treatment in sequence to obtain a light extraction liquid, which is then returned to the phosphorus removal treatment process.

3. The wastewater treatment method according to claim 1 or 2, characterized in that, The aerobic DBR treatment further includes: partially recirculating the resulting aerobic DBR effluent to the anoxic treatment process, wherein the recirculation ratio of the aerobic DBR effluent is 200%~400%.

4. A wastewater treatment device, characterized in that, It includes an anaerobic tank, an anoxic tank, an aerobic DBR tank, a secondary sedimentation tank, a flocculation sedimentation tank, a dominant microbial strain sieve, and a first dewatering device. The anaerobic tank, anoxic tank, aerobic DBR tank, and secondary sedimentation tank are connected in sequence. The secondary sedimentation tank is provided with a first discharge port, a second discharge port, and a third discharge port. The first discharge port is connected to the inlet of the anaerobic tank. The second discharge port is connected to the inlet of the anaerobic tank via the dominant microbial strain sieve. The third discharge port is connected to the inlet of the flocculation sedimentation tank. The dominant strain sieve is a hydrocyclone, which includes a first-stage hydrocyclone and a second-stage hydrocyclone. Both the first-stage and second-stage hydrocyclones are respectively provided with a feed inlet, an upper outlet, and a lower outlet. The first-stage hydrocyclone and the second-stage hydrocyclone are connected in parallel. The second discharge port of the secondary sedimentation tank is connected to the inlet of the first-stage hydrocyclone and the inlet of the second-stage hydrocyclone. The downstream outlet of the first-stage hydrocyclone and the upstream outlet of the second-stage hydrocyclone are connected to the inlet of the anaerobic tank. The upstream outlet of the first-stage hydrocyclone and the downstream outlet of the second-stage hydrocyclone are connected to the inlet of the first dewatering device.

5. The wastewater treatment device according to claim 4, characterized in that, The aerobic DBR tank is an aerobic tank equipped with a DBR reactor. The aerobic DBR tank is equipped with a reflux liquid outlet, which is connected to the feed inlet of the anoxic tank.

6. The wastewater treatment apparatus according to claim 4 or 5, characterized in that, It also includes a phosphorus removal device, a flocculant extraction device, and a solid-liquid separator; the outlet of the phosphorus removal device is connected to the inlet of the anaerobic tank; the outlet of the flocculation sedimentation tank is connected to the inlet of the phosphorus removal device in sequence via the flocculant extraction device and the solid-liquid separator.

Images