An apparatus for recovering phosphorus from excess sludge

Abstract

The present invention relates to the technical field of water treatment, and particularly relates to a device for recovering phosphorus from excess sludge, which includes a sludge thickening unit, a sludge cracking unit, a sludge dewatering unit and a phosphorus recovery unit. The sludge thickening unit is provided with a supernatant discharge port; 10%-20% of the thickened sludge is returned to the sludge thickening unit after being cracked by the sludge cracking unit; the sludge dewatering unit is provided with a sludge dewatering liquid output pipe; both the supernatant discharge port and the sludge dewatering liquid output pipe are connected to the phosphorus recovery unit for phosphorus recovery. The overall structure is concise. The present invention performs alkali cracking on 10% to 20% of the thickened sludge, and then uses the carbon source released by its cracking as the carbon source for polyphosphate-accumulating microorganisms in the total amount of excess sludge. Anaerobic phosphorus release occurs in the anaerobic environment of the sludge thickening unit without the need for external carbon sources. Low-cost and efficient phosphorus release and phosphorus recovery of the total amount of excess sludge are achieved through alkali hydrolysis phosphorus release of a small amount of thickened sludge + anaerobic biological phosphorus release of the total amount of excess sludge.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and particularly relates to a device for recovering phosphorus from excess sludge. Background Art

[0002] To effectively recover phosphorus from sludge, it is necessary to release phosphorus in the sludge (solid phase) into the liquid phase as much as possible. The efficient release of phosphorus is a key step in phosphorus recovery.

[0003] The existing phosphorus release technologies mainly include:

[0004] ① Physical cracking method: By means of hydrothermal hydrolysis, ultrasonic waves, mechanical ball milling, etc., the microbial cells in the sludge are broken, and the phosphorus-containing substances inside and outside the cells are released into the liquid phase. Sludge hydrothermal hydrolysis needs to be carried out under high temperature and high pressure conditions (150 - 190°C, 0.7 - 1.1 MPa), and is usually used as a pretreatment process in combination with the anaerobic digestion process. The equipment is complex, the operation and maintenance are difficult, the investment and energy consumption are high, and the treatment of the malodorous gas generated is difficult. At present, there are only a few engineering application cases; although the ultrasonic cracking has high efficiency, short reaction time (10 - 60 min) and simple equipment, due to the too high power consumption, it is mostly in the laboratory research stage at present, and the actual engineering application needs to overcome the defect of too high power consumption.

[0005] ② Chemical cracking method: Adding chemical agents such as acids, alkalis, H2O2, ozone, etc. to the excess sludge to destroy the microbial cell structure and release the phosphorus-containing substances inside and outside the cells into the liquid phase. The acid-base cracking method has the characteristics of simple process and mature technology, but the existing methods of full-scale acid-base cracking of sludge or oxidation by H2O2, ozone, etc. have high chemical consumption costs and are still difficult to realize engineering application.

[0006] ③ Biological phosphorus release method: Phosphorus is released through anaerobic digestion or enzyme-promoted biological enhanced phosphorus release, etc. The enzyme-promoted biological enhanced phosphorus release technology has high chemical agent costs and is currently in the laboratory research stage; anaerobic digestion is the most widely used sludge disposal technology in engineering applications at present, with the advantages of mature technology and low operating costs. However, this method has a slow phosphorus release rate, a long required time (the sludge needs to be anaerobically digested for 20 - 30 days), a large volume of the reaction device, and high construction investment. If it is necessary to increase the anaerobic phosphorus release rate and shorten the anaerobic phosphorus release time, a sufficient amount of carbon source is required, while the available carbon source in the excess sludge discharged from the biochemical system has basically been consumed in the front-end biochemical system, and a large amount of carbon source needs to be added externally to meet the requirements.

[0007] ④Sludge incineration - wet leaching process: The sludge is dehydrated, dried and then incinerated into ash, and then acid and alkali are used to leach phosphorus. The phosphorus in the sludge incineration ash mainly exists in the form of being combined with metals such as Ca, Mg, Fe, and Al in the ash, and cannot be absorbed and utilized by plants. Moreover, the heavy metal substances in the sludge still remain in the ash after incineration, and it is necessary to separate the phosphorus from the heavy metals in the sludge ash and convert the phosphorus into a form that plants can use. The process flow is complex and the cost of phosphorus recovery is high.

[0008] ⑤Combined cracking method: Combined technologies such as hydrothermal hydrolysis - acid leaching, acidification - microwave radiation, ultrasonic - ozone, and ultrasonic - alkali hydrolysis are used to destroy the microbial cell structure in the sludge, and release the phosphorus - containing substances into the liquid phase. Compared with single technologies, the combined technologies can combine the advantages of various technologies, which is the development trend of the technology in this field.

[0009] Due to the high cost of existing sludge phosphorus release and phosphorus recovery technologies and equipment or the complexity of the system, the sludge from sewage treatment plants is mostly disposed of by direct landfill or incineration after being concentrated and dehydrated, and the phosphorus in the sludge is not recycled resourcefully.

[0010] In summary, a device with a simple structure and capable of achieving efficient phosphorus release and recovery is designed to solve the problems existing in the prior art. Summary of the Invention

[0011] The purpose of the present invention is to provide a device for recovering phosphorus from excess sludge with a simple structure and capable of achieving efficient phosphorus release and recovery. The specific technical solutions are as follows:

[0012] A device for recovering phosphorus from excess sludge includes a sludge concentration unit, a sludge cracking unit, a sludge dewatering unit, and a phosphorus recovery unit;

[0013] The sludge concentration unit includes a first body having a first accommodation cavity. A surplus sludge inlet, a concentrated sludge discharge outlet, and a supernatant discharge outlet communicating with the first accommodation cavity are provided on the first body; the surplus sludge inlet is communicated with a surplus sludge conveying pipeline;

[0014] The sludge cracking unit includes a first shell, a first stirring component, a first sludge inlet pipe, and a first sludge outlet pipe. The first stirring component is arranged on the first shell to stir the liquid inside the first shell. The first sludge inlet pipe is communicated with the concentrated sludge discharge outlet through a first connecting pipeline, and the first sludge outlet pipe is communicated with the surplus sludge inlet through a second connecting pipeline; 10% - 20% of the concentrated sludge discharged from the concentrated sludge discharge outlet is cracked through the sludge cracking unit and then returned to the sludge concentration unit;

[0015] The sludge dewatering unit includes a dewatering treatment body having a dewatering accommodation cavity. On the dewatering treatment body, there are provided a dewatering treatment influent sludge pipe, a dewatering treatment effluent sludge pipe, and a sludge dewatering liquid output pipe that are connected to the dewatering accommodation cavity. The dewatering treatment influent sludge pipe is connected to the concentrated sludge discharge outlet through a third connection pipeline, and the dewatering treatment effluent sludge pipe is used to discharge dry sludge.

[0016] Both the supernatant discharge outlet and the sludge dewatering liquid output pipe are connected to the phosphorus recovery unit for phosphorus recovery.

[0017] Preferably, the phosphorus recovery unit includes an outer cylinder body, an inner cylinder body, a water inlet pipe, a water outlet pipe, a discharge pipe, a perforated plate assembly, and an inclined plate assembly; the outer cylinder body includes an outer cylinder main body with an opening at the upper end and a movable cover body, and the movable cover body is detachably arranged at the opening; the inner cylinder body includes an inner cylinder main body with an opening at the lower end, the inner cylinder main body is arranged in the accommodation cavity of the outer cylinder main body, and a water outlet channel connected to the water outlet pipe is provided between the inner wall of the outer cylinder main body and the outer wall of the inner cylinder main body. Both the water outlet channel and the water outlet pipe are located in the upper part of the outer cylinder main body; a water flow descending channel is formed inside the inner cylinder main body, the water inlet pipe is connected to the water flow descending channel and the water outlet end surface of the water inlet pipe is higher than the upper end surface of the water outlet channel; the perforated plate assembly is arranged in the water flow descending channel; a water flow ascending channel is enclosed by the inner wall of the outer cylinder main body, the water outlet channel, and the outer wall of the inner cylinder main body, and the inclined plate assembly is arranged in the water flow ascending channel; the part of the accommodation cavity in the outer cylinder main body below the inner cylinder main body forms a crystal aggregation area, and the discharge pipe is connected to the crystal aggregation area.

[0018] Preferably, along the water flow direction in the water flow descending channel, the perforated plate assembly includes a first perforated single piece, a second perforated single piece, and a third perforated single piece arranged in sequence. The first perforated single piece includes one or more than two spaced first perforated plates, the second perforated single piece includes one or more than two spaced second perforated plates, and the third perforated single piece includes one or more than two spaced third perforated plates; the ratio of the total area of the through holes to the plate area in the first perforated plate is P1, the ratio of the total area of the through holes to the plate area in the second perforated plate is P2, and the ratio of the total area of the through holes to the plate area in the third perforated plate is P3, and P1 < P2 < P3; P1 ranges from 2.5% to 3%; P2 ranges from 3.5% to 4.5%; P3 ranges from 5.0% to 6.0%.

[0019] Preferably, the inclined plate assembly is arranged on the inner wall of the outer cylinder main body and the outer wall of the inner cylinder main body through an inclined plate support frame; the inclined plate assembly includes multiple settling inclined plates arranged at intervals and offset, and the gaps between the multiple settling inclined plates form a flow channel.

[0020] Preferably, along the water flow direction, the water inlet pipe includes a horizontally arranged pipe section, an arc-shaped transition pipe section, and a vertically arranged pipe section that are sequentially arranged. The water outlet end surface of the vertically arranged pipe section is 5-20 cm higher than the upper end surface of the water outlet channel.

[0021] Preferably, the first housing includes a first body having a first accommodation cavity. The first sludge inlet pipe and the first sludge outlet pipe are both arranged on the first body and are both communicated with the first accommodation cavity. A first chemical addition pipe communicated with the first accommodation cavity is provided on the first body. The first stirring assembly includes a first driving power source, a first stirring shaft, and first stirring blades. The first driving power source is arranged on the first housing. The connecting end of the first stirring shaft is connected to the output end of the first driving power source. The free end of the first stirring shaft is arranged in the first accommodation cavity and the first stirring blades are provided thereon.

[0022] Preferably, it further includes a first pH controller. A measuring hole communicated with the first accommodation cavity is provided on the first body. The first pH controller is arranged at the measuring hole for measuring the pH value of the sludge. The first pH controller is connected to an external PLC control system, and the first pH controller measures the pH value of the sludge through a first measuring electrode. The first measuring electrode is arranged at the measuring hole and a protective net is provided outside the first measuring electrode.

[0023] A plurality of protrusions facing the center of the first accommodation cavity are further provided on the inner wall of the first accommodation cavity. The protrusions are hemispherical protrusions with a radius of 40-80 mm. The plurality of protrusions are evenly distributed on the inner wall of the first accommodation cavity. Multiple layers of the first stirring blades are arranged at intervals along the axial direction of the first stirring shaft. A first odor collection pipe for collecting the odor generated in the first accommodation cavity is further provided on the first body. The first housing further includes an opening communicated with the first accommodation cavity. A first detachable cover plate is provided at the opening. The first driving power source, the first chemical addition pipe, the first pH controller, and the first odor collection pipe are all arranged on the first detachable cover plate.

[0024] Preferably, it further includes a pH value adjustment unit connected in series with the sludge cracking unit. The pH value adjustment unit includes a second housing, a second stirring component, a second sludge inlet pipe, and a second sludge outlet pipe. The second housing includes a second body having a second accommodation cavity. The second sludge inlet pipe and the second sludge outlet pipe are both arranged on the second body and are both communicated with the second accommodation cavity. The second body is provided with a second chemical addition pipe communicated with the second accommodation cavity. The second stirring component includes a second driving power source, a second stirring shaft, and second stirring blades. The second driving power source is arranged on the second housing. The connecting end of the second stirring shaft is connected to the output end of the second driving power source. The free end of the second stirring shaft is arranged in the second accommodation cavity and the second stirring blades are arranged thereon. The first sludge outlet pipe is communicated with the second sludge inlet pipe through a second connecting pipe, and the second sludge outlet pipe is communicated with the excess sludge inlet through a fourth connecting pipe.

[0025] Preferably, it further includes a second pH controller. The second body is provided with a measuring hole communicated with the second accommodation cavity. The second pH controller is arranged at the measuring hole for measuring the pH value of the sludge. The second pH controller is connected to an external PLC control system, and the second pH controller measures the pH value of the sludge through a second measuring electrode. The second measuring electrode is arranged at the measuring hole and a protective net is arranged outside the second measuring electrode.

[0026] The second body is further provided with a second odor collection pipe for collecting the odor generated in the second accommodation cavity. The second housing further includes an opening communicated with the second accommodation cavity. A second detachable cover plate is arranged at the opening. The second driving power source, the second chemical addition pipe, the second pH controller, and the second odor collection pipe are all arranged on the second detachable cover plate.

[0027] Preferably, the pH value control range in the sludge cracking unit is 10.8 - 11.5; the pH value control range in the pH value adjustment unit is 9 - 10; after the sludge whose pH value is adjusted by the pH value adjustment unit meets the excess sludge conveying pipeline, the flowing time of the mixed sludge from the meeting point to the outlet of the excess sludge inlet is not less than 3 seconds; the pH value control range in the phosphorus recovery unit is 9.5 - 10.

[0028] Applying the technical solution of the present invention has the following beneficial effects:

[0029] 1. The device for recovering phosphorus from excess sludge of the present invention comprises a sludge thickening unit, a sludge cracking unit, a sludge dewatering unit and a phosphorus recovery unit. The sludge thickening unit comprises a first body having a first accommodation cavity, and the first body is provided with an excess sludge inlet, a thickened sludge discharge outlet and a supernatant discharge outlet; the sludge cracking unit comprises a first housing, a first stirring assembly, a first sludge inlet pipe and a first sludge outlet pipe, and 10%-20% of the thickened sludge discharged from the thickened sludge discharge outlet is subjected to cracking treatment by the sludge cracking unit and then returned to the sludge thickening unit; the sludge dewatering unit comprises a second body having a second accommodation cavity, and the second body is provided with a second sludge inlet pipe, a second sludge outlet pipe and a sludge dewatering liquid output pipe; both the supernatant discharge outlet and the sludge dewatering liquid output pipe are connected to the phosphorus recovery unit for phosphorus recovery. The overall structure is concise. The present invention performs alkali cracking on 10%-20% of the thickened sludge, and then uses the COD (carbon source) released by the cracking as the carbon source for the polyphosphorus microorganisms (polyphosphorus bacteria) in the total amount of excess sludge entering the thickening tank. Anaerobic phosphorus release occurs in the anaerobic environment of the sludge thickening tank without adding an external carbon source. Through the new scheme of phosphorus release by alkali cracking of a small amount of thickened sludge + anaerobic biological phosphorus release of the total amount of excess sludge, low-cost and high-efficiency phosphorus release of the total amount of excess sludge is achieved.

[0030] 2. In the present invention, the sludge thickening unit is a gravity thickening tank, adopting a conventional gravity thickening tank in the prior art. When recovering phosphorus from the excess sludge of an existing sewage treatment plant, only a sludge cracking component (only cracking 10%-20% of the total amount of thickened sludge), a phosphorus recovery unit and a supporting control system need to be added, and the pipelines are correspondingly modified, then the high-efficiency phosphorus release of the sludge and the high-efficiency recovery of phosphorus resources of the existing sewage treatment plant can be achieved economically and conveniently.

[0031] 3. In the present invention, the sludge cracking unit comprises a first housing, a first stirring assembly, a first sludge inlet pipe and a first sludge outlet pipe, with a concise structure. Moreover, the equipment investment and operation cost (agent consumption, power consumption) of the sludge cracking unit are only equivalent to 10%-20% of the existing alkali cracking process for the total amount of sludge. The occupied area of the equipment can also be saved; the addition of the carbon source in the cracked sludge enables the anaerobic biological phosphorus release time of the sludge in the gravity thickening tank to be shortened to 6 hours, which is only 1 / 80 of the time required for the traditional sludge anaerobic digestion process (anaerobic digestion time is 20-30 days), greatly reducing the equipment investment and operation cost for sludge phosphorus release and phosphorus recovery.

[0032] 4. The phosphorus recovery unit in the present invention includes an outer cylinder, an inner cylinder, a water inlet pipe, a water outlet pipe, a discharge pipe, a perforated plate assembly, and an inclined plate assembly. The effects are as follows: ①. This phosphorus recovery unit makes full use of the kinetic energy and potential energy of the wastewater itself to achieve efficient hydraulic vortex crystallization, which is more energy-saving and has lower operating costs than conventional mechanical mixing crystallization; the integration of crystallization and precipitation separation makes the device structure compact and saves floor space. ②. An inclined plate assembly is provided in the water rising channel B, which increases the precipitation area of fine phosphorus crystal particles in the wastewater, shortens the precipitation time, and at the same time changes the water flow of the plate from a turbulent state to a laminar state, improving the recovery efficiency of phosphorus crystal particles in the wastewater.

[0033] In addition to the purposes, features, and advantages described above, the present invention has other purposes, features, and advantages. The following will refer to the drawings to further elaborate on the present invention in detail. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] The drawings forming a part of this application are used to provide a further understanding of the present invention. The schematic embodiments and descriptions of the present invention are used to explain the present invention and do not constitute an improper limitation to the present invention. In the drawings:

[0035] Figure 1 is the plan layout diagram of the excess sludge phosphorus recovery device in the preferred embodiment of the present invention;

[0036] Figure 2 is Figure 1 the elevation structure schematic diagram of

[0037] Figure 3 is Figure 2 the connection structure schematic diagram of the sludge cracking unit and the pH value adjustment unit in

[0038] Figure 4 is Figure 2 the structure schematic diagram of the phosphorus recovery unit in

[0039] Figure 5 is Figure 4 the structure schematic diagram of the first perforated plate in

[0040] Figure 6 is Figure 4 the structure schematic diagram of the second perforated plate of

[0041] Figure 7 is Figure 4 the structure schematic diagram of the third perforated plate in

[0042] Among them, 1. Sludge thickening unit, 1.1. Excess sludge inlet, 1.2. Thickened sludge discharge outlet, 1.3. Supernatant discharge outlet, 1.4. Thickening cavity;

[0043] 2. Sludge cracking unit, A1. First housing, A1.1. First accommodation chamber, A1.2. First body, A1.3. Protrusion, A1.4. First detachable cover plate, A2. First stirring assembly, A2.1. First driving power source, A2.2. First stirring shaft, A2.3. First stirring blades, A3. First sludge inlet pipe, A4. First sludge outlet pipe, A5. First chemical dosing pipe, A6. First pH controller, A6.1. First measuring electrode, A7. First odor collection pipe;

[0044] 3. Sludge dewatering unit, 3.1. Dewatering accommodation chamber, 3.2. Dewatering treatment sludge inlet pipe, 3.3. Dewatering treatment sludge outlet pipe, 3.4. Sludge dewatering liquid output pipe;

[0045] 4. Phosphorus recovery unit, 4.1. Outer cylinder, 4.1.1. Outer cylinder body, 4.1.2. Movable cover body; 4.2. Inner cylinder, 4.2.1. Inner cylinder body; 4.3. Water inlet pipe; 4.4. Water outlet pipe; 4.5. Discharge pipe; 4.6. Perforated plate assembly, 4.6.1. First perforated plate, 4.6.2. Second perforated plate, 4.6.3. Third perforated plate; 4.7. Inclined plate assembly; 4.8. Water outlet channel; 4.9. Support; 4.10. Inclined plate support frame; 4.11. Inner cylinder support frame; A. Water flow down channel, B. Water flow up channel, C. Crystal aggregation area, D. Through hole;

[0046] 5. pH value adjustment unit, B1. Second housing, B1.1. Second accommodation chamber, B1.2. Second body, B1.3. Second detachable cover plate, B2. Second stirring assembly, B2.1. Second driving power source, B2.2. Second stirring shaft, B2.3. Second stirring blades, B3. Second sludge inlet pipe, B4. Second sludge outlet pipe, B5. Second chemical dosing pipe, B6. Second pH controller, B6.1. Second measuring electrode, B7. Second odor collection pipe;

[0047] 6. Surplus sludge conveying pipeline;

[0048] G1. First connecting pipeline, G2. Second connecting pipeline, G3. Third connecting pipeline, G4. Fourth connecting pipeline;

[0049] H. Pipe mixer, H1. Magnesium salt dosing pipe, H2. Ammonium salt dosing pipe, H3. Alkali dosing pipe, F1. First electric valve, F2. Second electric valve; L1. First flowmeter, L2. Second flowmeter, L3. Third flowmeter, L4. Fourth flowmeter; T. Lift pump; P1. Orthophosphate online detector, P2. pH value online detector. Detailed implementation manners

[0050] The embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings. However, the present invention can be implemented in many different ways defined and covered by the claims.

[0051] Embodiment:

[0052] Refer to Figures 1-2 , a device for recovering phosphorus from excess sludge, which includes a sludge thickening unit 1, a sludge cracking unit 2, a sludge dewatering unit 3, a phosphorus recovery unit 4, and a pH value adjustment unit 5. The detailed structure is as follows:

[0053] The sludge thickening unit 1 includes a thickening tank body having a thickening accommodation cavity 1.4. A surplus sludge inlet 1.1, a thickened sludge discharge port 1.2, and a supernatant discharge port 1.3 that are communicated with the thickening accommodation cavity 1.4 are provided on the thickening tank body. The surplus sludge inlet 1.1 is communicated with a surplus sludge conveying pipeline 6. The surplus sludge from an urban sewage treatment plant enters the sludge thickening unit 1 through the surplus sludge inlet 1.1 via the surplus sludge conveying pipeline 6 for sludge thickening treatment. In this embodiment, the sludge thickening unit 1 adopts a circular gravity thickening tank in the prior art. The tank body is built with reinforced concrete or made of a steel anti-corrosion device. The thickening time of the sludge in the tank (calculated by hydraulic retention time) is 14 - 24h. The surplus sludge inlet 1.1 is communicated with the surplus sludge conveying pipeline 6 (a first flowmeter L1 is provided on this pipeline), and the surplus sludge conveying pipeline 6 is communicated with an external sludge conveying pump. The supernatant discharge port 1.3 is communicated with the phosphorus recovery unit 4.

[0054] The sludge cracking unit 2 includes a first housing A1, a first stirring component A2, a first sludge inlet pipe A3, and a first sludge outlet pipe A4. See Figure 3 , the first stirring component A2 is arranged on the first housing A1 to stir the liquid inside the first housing. The first sludge inlet pipe A3 is communicated with the thickened sludge discharge port 1.2 through a first connecting pipeline G1. The cracked sludge from the first sludge outlet pipe A4 enters the pH value adjustment unit 5 through a second connecting pipeline G2 for pH value adjustment and then enters the surplus sludge inlet 1.1; 10% - 20% of the thickened sludge discharged from the thickened sludge discharge port 1.2 is cracked by the sludge cracking unit and then returned to the sludge thickening unit 1.

[0055] Preferably, in this embodiment, the first housing A1 includes a first body A1.2 having a first accommodation chamber A1.1. The first sludge inlet pipe A3 and the first sludge outlet pipe A4 are both provided on the first body A1.2 and are both connected to the first accommodation chamber A1.1. A first chemical addition pipe A5 communicating with the first accommodation chamber A1.1 is provided on the first body A1.2. The first stirring assembly A2 includes a first driving power source A2.1, a first stirring shaft A2.2, and first stirring blades A2.3. The first driving power source A2.1 is provided on the first housing A1. The connecting end of the first stirring shaft A2.2 is connected to the output end of the first driving power source A2.1, and the free end of the first stirring shaft A2.2 is arranged in the first accommodation chamber A1.1 and the first stirring blades A2.3 are provided thereon. The first housing A1 is a cylindrical housing, made of carbon steel anti-corrosion material. Sodium hydroxide is added to crack the sludge. In this embodiment, the pH control range in the sludge cracking assembly is 10.8 - 11.5, and more preferably the pH control range is 10.8 - 11. The reaction time for sludge cracking is: 40 - 60 min.

[0056] Preferably, in this embodiment, a first pH controller A6 is further included. A measuring hole communicating with the first accommodation chamber A1.1 is provided on the first body A1.2. The first pH controller is arranged at the measuring hole for measuring the pH value of the sludge. The first pH controller is connected to an external PLC control system, and the first pH controller measures the pH value of the sludge through a first measuring electrode A6.1. The first measuring electrode is arranged at the measuring hole and a protective net is provided outside the first measuring electrode. A plurality of protrusions A1.3 facing the center of the first accommodation chamber are further provided on the inner wall of the first accommodation chamber A1.1. The protrusions A1.3 are hemispherical protrusions with a radius of 40 - 80 mm. The plurality of protrusions A1.3 are evenly distributed on the inner wall of the first accommodation chamber. Here, the radii of the hemispherical protrusions are the same, and the plurality of protrusions are evenly distributed on the vertical inner side wall of the first accommodation chamber. The distance between the edges of two adjacent protrusions is 1.5 times their diameter. A plurality of layers of the first stirring blades A2.3 are provided at intervals along the axial direction of the first stirring shaft A2.2 (preferably two layers of first stirring blades arranged in the up and down direction here, and upward thrusts are generated when the stirring blades rotate). A first odor collection pipe A7 for collecting the odor generated in the first accommodation chamber is further provided on the first body A1.2. The first housing A1 further includes an opening communicating with the first accommodation chamber A1.1, and a first detachable cover plate A1.4 is provided at the opening. The first driving power source A2.1, the first chemical addition pipe A5, the first pH controller A6, and the first odor collection pipe A7 are all provided on the first detachable cover plate A1.4.

[0057] The sludge dewatering unit 3 includes a dewatering treatment body having a dewatering accommodation chamber 3.1. A dewatering treatment feed sludge pipe 3.2, a dewatering treatment discharged sludge pipe 3.3, and a sludge dewatering liquid output pipe 3.4 are provided on the dewatering treatment body and are communicated with the dewatering accommodation chamber 3.1. The dewatering treatment feed sludge pipe 3.2 is communicated with the concentrated sludge discharge port 1.2 through a third connecting pipe G3. The dewatering treatment discharged sludge pipe 3.3 is used to discharge dry sludge, and subsequent transportation can be carried out by means of pipelines, belt conveyors, etc. In this embodiment, the sludge dewatering unit 3 adopts an existing horizontal screw centrifugal dewatering complete set of equipment.

[0058] Both the supernatant discharge port 1.3 and the sludge dewatering liquid output pipe 3.4 are communicated with the phosphorus recovery unit 4 for phosphorus recovery. For the structure of the phosphorus recovery unit 4, see Figure 4, which includes an outer cylinder body 4.1, an inner cylinder body 4.2, a water inlet pipe 4.3, a water outlet pipe 4.4, a discharge pipe 4.5, a perforated plate assembly 4.6 and an inclined plate assembly 4.7; the outer cylinder body 4.1 includes an outer cylinder main body 4.1.1 with an opening at the upper end and a movable cover body 4.1.2, and the movable cover body 4.1.2 is detachably arranged at the opening (preferably, the opening is arranged at the top of the outer cylinder main body). In this embodiment, the outer cylinder main body is composed of a hollow cylindrical vertical cylinder and a hollow frustum cylinder with a wider upper part and a narrower lower part. The hollow frustum cylinder is located at the lower end, that is, the bottom of the outer cylinder body is a frustum structure; the inner cylinder body 4.2 includes an inner cylinder main body 4.2.1 with an opening at the lower end. In this embodiment, the inner cylinder main body adopts a hollow cylindrical vertical cylinder, and the height of the inner cylinder main body is 60% - 80% of the height of the outer cylinder main body. And the inner cylinder main body is supported by an inner cylinder support frame 4.11 located at the bottom of the outer cylinder main body, and the upper end surface of the inner cylinder main body can be abutted against the lower surface of the movable cover body on the cover or arranged with a gap. The inner cylinder main body 4.2.1 is arranged in the accommodation cavity of the outer cylinder main body 4.1.1, and a water outlet channel 4.8 communicated with the water outlet pipe 4.4 is arranged between the inner wall of the outer cylinder main body 4.1.1 and the outer wall of the inner cylinder main body 4.2.1. Here, the water outlet channel is an annular water outlet channel. Both the water outlet channel 4.8 and the water outlet pipe 4.4 are located in the upper part of the outer cylinder main body 4.1.1; a water flow descending channel A (forming a crystallization reaction area) is formed inside the inner cylinder main body 4.2.1, the water inlet pipe 4.3 is communicated with the water flow descending channel A and the water outlet end face of the water inlet pipe 4.3 is higher than the upper end face of the water outlet channel 4.8; the perforated plate assembly 4.6 is arranged in the water flow descending channel A; a water flow ascending channel B is surrounded by the inner wall of the outer cylinder main body 4.1.1, the water outlet channel 4.8 and the outer wall of the inner cylinder main body 4.2.1, and the inclined plate assembly 4.7 is arranged in the water flow ascending channel B; the part of the accommodation cavity in the outer cylinder main body 4.1.1 below the inner cylinder main body 4.2.1 forms a crystal aggregation area C, and the discharge pipe 4.5 is communicated with the crystal aggregation area C. In this embodiment, the hollow frustum cylinder of the outer cylinder main body 4.1.1 is the crystal aggregation area, and the frustum structure is beneficial to the aggregation and compression precipitation of phosphorus crystal particles. The discharge pipe 4.5 is communicated with the crystal aggregation area C. In this embodiment, the discharge pipe 4.5 is communicated with the lower side of the frustum structure. A pH value on-line detector P2 is also arranged in the phosphorus recovery unit 4.

[0059] Preferably, in this embodiment, along the water flow direction in the water flow down channel A, the perforated plate assembly 4.6 includes a first perforated single piece, a second perforated single piece, and a third perforated single piece arranged in sequence. The first perforated single piece includes one or more than two first perforated plates 4.6.1 arranged at intervals. The second perforated single piece includes one or more than two second perforated plates 4.6.2 arranged at intervals. The third perforated single piece includes one or more than two third perforated plates 4.6.3 arranged at intervals. The first perforated plate 4.6.1, the second perforated plate 4.6.2, and the third perforated plate 4.6.3 are all detachably arranged by the support member 4.9. Here, the support member is composed of a first plate and a second plate arranged at a right angle. The first plate is connected to the perforated plate, and the second plate is connected to the inner wall of the inner cylinder body (i.e., the inner wall forming the water flow down channel A). The ratio of the total area of the through holes D in the first perforated plate to the plate area is P1. The ratio of the total area of the through holes D in the second perforated plate to the plate area is P2. The ratio of the total area of the through holes D in the third perforated plate to the plate area is P3, and P1 < P2 < P3. Further preferably, the value of P1 is 2.5% - 3%; the value of P2 is 3.5% - 4.5%; the value of P3 is 5.0% - 6.0%. Further preferably, the support member 4.9 can be a horizontal straight plate and a vertical straight plate arranged at a 90° angle. The vertical straight plate is used to be fixed to the inner wall of the inner cylinder body 4.2.1, and the horizontal straight plate is used to be connected or clamped to the perforated plate in the perforated plate assembly. The first perforated single piece includes two first perforated plates arranged at intervals. The second perforated single piece includes two second perforated plates arranged at intervals. The third perforated single piece includes two third perforated plates arranged at intervals. In this embodiment, the first perforated plate, the second perforated plate, and the third perforated plate are all circular plates. Preferably, the diameter of the circular plate is slightly smaller than the inner diameter of the inner cylinder body, such as 20 mm smaller. Circular through holes are provided on the first perforated plate, the second perforated plate, and the third perforated plate. The central axis of the circular through hole is the same as the water flow direction in the water flow down channel A. The value of P1 is 2.5%. Refer to Figure 5 , four layers of hole groups are arranged on the first perforated plate from the center to the periphery, that is, water passing round holes with a radius of 15 - 20 mm (shown as through holes D in the figure) are equally spaced at the center of the circle and on three concentric circles; the value of P2 is 4%. Refer to Figure 6 , five layers of hole groups are arranged on the second perforated plate from the center to the periphery, that is, water passing round holes with a radius of 15 - 20 mm (shown as through holes D in the figure) are equally spaced at the center of the circle and on four concentric circles; the value of P3 is 5.5%. Refer to Figure 7, six layers of hole groups are arranged on the third perforated plate from the center to the periphery, that is, water-passing round holes with a radius of 15-20 mm are equally spaced at the center of the circle and on five concentric circles (shown as through holes D in the figure). By adopting a perforated plate assembly with a unique structure, when the liquid flows through the perforated plate assembly, micro-vortices can be formed, enabling the orthophosphate that has not yet formed crystals in the wastewater and the crystal-forming ions (magnesium ions, ammonium ions) in the reagent to contact and mix under the action of the vortices to form magnesium ammonium phosphate crystals.

[0060] Preferably in this embodiment, the inclined plate assembly 4.7 is arranged on the inner wall of the outer cylinder body 4.1.1 and the outer wall of the inner cylinder body 4.2.1 through the inclined plate support frame 4.10; the inclined plate assembly 4.7 includes multiple sedimentation inclined plates arranged at intervals and offset, and the gaps between the multiple sedimentation inclined plates form a flow channel. By increasing the sedimentation area, shortening the sedimentation time, and changing the water flow from a turbulent state to a laminar state, the sedimentation efficiency of fine phosphorus crystal particles is improved.

[0061] In this embodiment, the water outlet at the upper part of the water flow rising channel B is adjusted by the water outlet channel 4.8 and then discharged by the water outlet pipe 4.4, which can eliminate the short-circuit phenomenon of the water outlet, is beneficial to the stable operation state, improves the sedimentation effect of the mud and water separation, reduces other pollutants carried in the water outlet, and thus improves the pollutant removal rate.

[0062] The structure of the pH value adjustment unit 5 is shown in detail in Figure 3, which includes a second housing B1, a second stirring component B2, a second sludge inlet pipe B3, and a second sludge outlet pipe B4; the second housing B1 includes a second body B1.2 having a second accommodation cavity B1.1, where the second housing B1 is a cylindrical housing. The second sludge inlet pipe B3 and the second sludge outlet pipe B4 are both arranged on the second body B1.2 and are both connected to the second accommodation cavity B1.1; a second chemical addition pipe B5 connected to the second accommodation cavity B1.1 is provided on the second body B1.2; the second stirring component B2 includes a second driving power source B2.1, a second stirring shaft B2.2, and second stirring blades B2.3, and the second driving power source B2.1 is arranged on the second housing B1; the connecting end of the second stirring shaft B2.2 is connected to the output end of the second driving power source B2.1, the free end of the second stirring shaft B2.2 is arranged in the second accommodation cavity B1.1 and the second stirring blades B2.3 are provided thereon; the first sludge outlet pipe A4 is connected to the second sludge inlet pipe B3 through a second connecting pipe G2, and the second sludge outlet pipe B4 is connected to the excess sludge inlet 1.1 through a fourth connecting pipe G4. In this embodiment, the control range of the pH value in the pH adjustment unit is 9-10, and further preferably the control range of the pH value is 9-9.5. The effective volume of the second accommodation cavity B1.1 in the pH adjustment unit is half of the volume of the first accommodation cavity A1.1 in the sludge cracking unit, and the height of the pH adjustment unit is lower than that of the sludge cracking unit, which can ensure that the sludge in the sludge cracking unit flows into the pH adjustment unit by gravity.

[0063] In this embodiment, preferably, the pH adjustment unit 5 further includes a second pH controller B6. A measurement hole connected to the second accommodation cavity B1.1 is provided on the second body B1.2. The second pH controller is arranged at the measurement hole for measuring the pH value of the sludge; the second pH controller is connected to an external PLC control system, and the second pH controller measures the pH value of the sludge through a second measurement electrode B6.1; the second measurement electrode is arranged at the measurement hole and a protective net is provided outside the second measurement electrode; a second odor collection pipe B7 for collecting the odor generated in the second accommodation cavity is further provided on the second body B1.2; the second housing B1 further includes an opening connected to the second accommodation cavity B1.1, and a second detachable cover plate B1.3 is provided at the opening. The second driving power source B2.1, the second chemical addition pipe B5, the second pH controller B6, and the second odor collection pipe B7 are all arranged on the second detachable cover plate B1.3.

[0064] Preferably, in this embodiment, the pH value in the sludge cracking unit 2 is controlled within the range of 10.8 to 11.5; the pH value in the pH adjustment unit 5 is controlled within the range of 9 to 10; after the sludge whose pH value is adjusted by the pH adjustment unit 5 meets with the excess sludge conveying pipeline 6, the flow-through time of the mixed sludge from the meeting point to the outlet of the excess sludge inlet 1.1 is not less than 3 seconds; the pH value in the phosphorus recovery unit 4 is controlled within the range of 9.5 to 10.

[0065] Applying the technical solution of this embodiment, the excess sludge is conveyed by the excess sludge conveying pipeline 6 to the excess sludge inlet 1.1 and enters the sludge thickening unit 1 for thickening treatment; the supernatant after thickening treatment is discharged through the supernatant discharge port 1.3 and enters the phosphorus recovery unit 4 for phosphorus recovery; the thickened sludge after thickening treatment is discharged through the thickened sludge discharge port 1.2, and a part of the thickened sludge enters the sludge cracking unit 2 through the first connecting pipeline G1 (a second flowmeter L2 and a first electric valve F1 are provided on this pipeline) for sludge cracking treatment, and further undergoes pH adjustment by the pH adjustment unit 5, and after being lifted by the lift pump T, it returns to the excess sludge conveying pipeline 6 through the fourth connecting pipeline G4 to be mixed with the excess sludge and then circulates to the sludge thickening unit 1; another part of the thickened sludge enters the sludge dewatering unit 3 through the third connecting pipeline G3 (a fourth flowmeter L4 and a second electric valve F2 are provided on this pipeline) for sludge dewatering treatment, and the flow rate ratio of the sludge in the two pipelines can be adjusted by controlling the first electric valve F1 and the second electric valve F2. The supernatant discharged from the supernatant discharge port 1.3 and the sludge dewatering liquid output from the sludge dewatering liquid output pipe 3.4 are mixed in the pipeline. A third flowmeter L3 and a pipeline mixer H are provided on the pipeline. The magnesium salt dosing pipe H1, the ammonium salt dosing pipe H2 and the alkali dosing pipe H3 are all connected to the pipeline mixer H, and the liquid after mixing enters the water inlet pipe 4.3 in the phosphorus recovery unit 4.

[0066] Apply the phosphorus recovery unit 4 of the invention. Its working process is as follows: Magnesium ammonium phosphate crystallization (struvite) is used to recover phosphorus in the liquid phase. In continuous flow operation, the pH in the phosphorus recovery unit 4 is controlled at 9.5 - 10. The supernatant from the supernatant discharge port 1.3 of the sludge thickening unit 1 and the sludge dewatering liquid output from the sludge dewatering liquid output pipe 3.4 of the sludge dewatering unit 3 are mixed to form wastewater containing orthophosphate. After being mixed with the medicaments (the medicaments are magnesium salts, ammonium salts, and alkalis) in the pipeline mixer H, it enters the cylinder body 4.2 of the phosphorus recovery unit 4 through the water inlet pipe 4.3 (specifically: it overflows from the end of the water inlet pipe 4.3 to form a hydraulic jump and mixes into the upper part of the water flow descending channel A in the inner cylinder body 4.2.1). The orthophosphate in the influent water and the crystal-forming ions (magnesium ions, ammonium ions) in the medicaments contact and mix under the action of the hydraulic jump to form magnesium ammonium phosphate crystals (crystal nuclei). The wastewater flows through the perforated plate assembly 4.6 in sequence in the water flow descending channel A under the action of gravity to reach the bottom of the water flow descending channel A. When flowing through the perforated plate, micro-vortices are formed at both ends of the round hole channel. The orthophosphate that has not formed crystals in the wastewater and the crystal-forming ions (magnesium ions, ammonium ions) in the medicaments contact and mix under the action of the vortices to continue forming magnesium ammonium phosphate crystals. The fine crystals further grow. The water flow and the tiny crystal particles slowly flow upward from the bottom outlet of the water flow descending channel A into the water flow ascending channel B under the action of gravity. The crystal particles with larger particle sizes sink into the crystal aggregation area C under the action of gravity. The wastewater flowing into the wastewater ascending channel flows through the inclined plate assembly 4.7 during the ascending process. The tiny crystal particles precipitate on the inclined plate assembly and sink to the crystal aggregation area C. The clarified wastewater overflows to the water outlet channel 4.8 located in the upper part of the outer cylinder body 4.1.1, and then flows out through the water outlet pipe 4.4 to the next sewage treatment unit. The struvite crystals precipitated in the crystal aggregation area are regularly discharged to a separately provided dehydration and separation device through the discharge pipe 4.5.

[0067] Apply the phosphorus recovery unit 4 of this embodiment. The effects are as follows: ① The invention makes full use of the kinetic energy and potential energy of the wastewater itself to achieve efficient hydraulic vortex crystallization, which is more energy-saving and has lower operating costs than conventional mechanical mixing crystallization; the crystallization and precipitation separation are integrated, and the device structure is compact, saving floor space. ② The inclined plate assembly is provided in the water flow ascending channel B, increasing the precipitation area of the fine phosphorus crystal particles in the wastewater, shortening the precipitation time, and at the same time, the water flow of the plate changes from a turbulent state to a laminar state, improving the recovery efficiency of the phosphorus crystal particles in the wastewater.

[0068] In addition, a control system is provided in this embodiment. The control system consists of on-line detection instruments, cables, and an electric control cabinet containing a programmable logic controller (PLC). The on-line detection instruments include a first flowmeter L1 arranged on the surplus sludge conveying pipeline 6, a second flowmeter L2 arranged on the first connecting pipeline G1, a third flowmeter L3 arranged on the pipeline connected to the supernatant discharge port 1.3, a fourth flowmeter L4 arranged on the third connecting pipeline G3, an orthophosphate on-line detector P1 arranged near the supernatant discharge pipe, a pH value on-line detector P2 arranged in the phosphorus recovery unit, a first pH controller A6 and a second pH controller B6 arranged in the sludge cracking component; the cables and the electric control cabinet containing a programmable logic controller (PLC) both adopt existing mature equipment, which can supply power to the on-line detection instruments and communicate with the on-line detection instruments. The PLC controls the operation of external dosing equipment and other equipment according to the data detected by the on-line monitoring instruments and the preset control logic.

[0069] Applying the technical solution of this embodiment specifically is as follows:

[0070] The surplus sludge rich in phosphorus (Q_surplus, water content 99.2%) discharged from the sewage treatment biochemical system is mixed with the cracked sludge (Q_cracked after) whose pH has been adjusted by the pH adjustment unit 5 and discharged from the sludge cracking unit 2 through the surplus sludge conveying pipeline 6 and then enters the sludge thickening unit 1. The surplus sludge rich in phosphorus undergoes sludge thickening in the sludge thickening unit 1 under the action of the carbon source provided by the cracked sludge and simultaneously undergoes anaerobic biological phosphorus release effect, releasing the phosphorus in the solid phase into the liquid phase. The low-phosphorus sludge after thickening and biological phosphorus release is discharged from the bottom of the gravity thickening tank. A part of the thickened sludge (Q_cracked) enters the sludge cracking unit 2 through the first connecting pipeline G1 for sludge cracking, and the sludge (Q_cracked after) after cracking enters the pH adjustment unit 5 for pH adjustment and then all returns to the sludge thickening unit 1; another part of the thickened sludge (Q_dewatering) is discharged into the sludge dewatering unit 3 through the third connecting pipeline G3 for dewatering treatment. In this embodiment, the flow rate or mass ratio of the total amount of sludge entering the sludge cracking unit to the thickened sludge is Q_cracked:(Q_cracked + Q_dewatering)=0.2; the high-concentration phosphorus-containing supernatant generated by the sludge thickening unit 1 is discharged into the phosphorus recovery unit 4 to recover phosphorus; the sludge dewatering liquid generated by the sludge dewatering unit is mixed with the supernatant of the sludge thickening unit and then discharged into the phosphorus recovery unit 4 together for phosphorus recovery, and the dry sludge is transported out for disposal; the low-phosphorus water discharged from the phosphorus recovery unit can be returned to the biochemical tank at the front end of the sewage treatment system.

[0071] In this embodiment, after the sludge is cracked by alkali, substances such as COD (carbon source), ammonia nitrogen, organic nitrogen, orthophosphate, and organic phosphorus are released into the aqueous phase and converted into cracked sludge (Q after cracking). The test data of the main components of the sludge before concentration (Q remaining) and after cracking (Q after cracking) are shown in Table 1. The mass of the cracked sludge (Q after cracking) is equal to the sum of the mass of the concentrated sludge (Q cracked) and the masses of the alkali and acid reagents added during the cracking process. The cracked sludge (Q after cracking) is discharged into the inlet of the gravity thickening tank. The sludge cracking step in this embodiment simultaneously achieves five technical effects:

[0072] ① It realizes the phosphorus release from the sludge during cracking for the residual phosphorus in the sludge, releases orthophosphate from the solid phase to the liquid phase, and creates conditions for the subsequent phosphorus recovery unit to recover phosphorus;

[0073] ② The high-concentration COD (carbon source) released by the sludge cracking returns to the sludge thickening tank and serves as the carbon source for the anaerobic biological phosphorus release of the excess sludge, eliminating the need for additional external carbon source, achieving "treating waste with waste", and saving the cost of sludge phosphorus release;

[0074] ③ The sludge cracking releases ammonia nitrogen, reducing the dosage of reagents such as ammonium salts (such as ammonium chloride) added in the subsequent phosphorus recovery unit to recover struvite, and further saving the cost of phosphorus recovery;

[0075] ④ After the sludge is cracked, its dewatering performance can be improved, reducing the dosage of sludge dewatering agents in the subsequent sludge dewatering unit, which is beneficial to enhancing the treatment efficiency of the subsequent sludge dewatering unit and reducing the cost of sludge dewatering;

[0076] ⑤ The cracked sludge is adjusted to a pH of 9 - 9.5 by adding acid in the pH adjustment unit 5. After mixing with the excess sludge (Q remaining), in this solution, the pH of the mixed sludge entering the sludge thickening tank can be between 8 - 8.5, forming a suitable pH condition for anaerobic biological phosphorus release in the sludge thickening tank.

[0077] Table 1 Main components of the sludge before and after concentration

[0078]

[0079] Note: In the table, the concentration of the sludge before concentration (Q remaining, referring to the excess sludge entering the sludge thickening unit through the excess sludge conveying pipeline 6) MLSS = 8 g / L, and the concentration of the sludge after concentration and cracking (Q after cracking) MLSS = 20 g / L. In this embodiment, the volume of the sludge after concentration and cracking (Q after cracking) is only about 8% of the volume of the excess sludge Q remaining entering the sludge thickening tank. The component data of the sludge are all measured by centrifuging the sludge and taking the supernatant.

[0080] The surplus sludge before concentration (Q_surplus) and the cracked sludge (Q_cracked) are mixed before entering the sludge thickening unit 1 and then enter the sludge thickening unit 1. Compared with the conventional gravity thickening process, in addition to achieving the physical thickening effect of sludge in the sludge thickening unit 1, the following technical effects are also achieved in this embodiment:

[0081] ① The surplus sludge (Q_surplus) and the cracked sludge (Q_cracked) are mixed before entering the sludge thickening unit. The mixing process and the pipeline transportation process enable the microorganisms in the surplus sludge (Q_surplus) to rapidly adsorb the organic components in the cracked sludge (Q_cracked), creating conditions for the microorganisms to further absorb the adsorbed organic matter into the microbial cells in the thickening tank, overcoming the defect of low mass transfer efficiency between the organic matter and the microbial cells caused by small fluid disturbance in the sludge thickening tank, and enabling more organic components in the cracked sludge to enter the microbial cells in the surplus sludge to achieve anaerobic phosphorus release;

[0082] ② The phosphorus-rich microorganisms in the surplus sludge (such as polyphosphate-accumulating organisms) release the phosphorus in the cells into the water (in the form of orthophosphate, PO4 3- ) under the anaerobic conditions in the sludge thickening unit 1 under the action of the COD (carbon source) provided by the cracked sludge, achieving anaerobic biological phosphorus release from all the surplus sludge. The concentration of orthophosphate (PO4 3- , calculated as phosphorus) in the supernatant after thickening treatment can reach 50 - 60 mg / L, creating conditions for subsequent phosphorus recovery;

[0083] ③ The organic nitrogen and organic phosphorus contained in the cracked sludge are converted into ammonia nitrogen and orthophosphate (PO4 3- ) under the action of the anaerobic environment in the sludge thickening tank and the anaerobic microorganisms in the surplus sludge. The conversion of organic nitrogen into ammonia nitrogen can save the dosage of ammonia nitrogen agents in the subsequent phosphorus recovery unit, and the conversion of organic phosphorus into orthophosphate can further improve the phosphorus recovery efficiency (organic phosphorus cannot be recovered by struvite crystallization).

[0084] The test data of the main components of the sludge before thickening, the inlet of the sludge thickening unit, and the supernatant of the outlet of the sludge thickening unit are shown in Table 2. This embodiment has a significant effect on sludge phosphorus release, and most of the phosphorus exists in the form of orthophosphate and can be recovered by the subsequent phosphorus recovery unit 4.

[0085] Table 2 Main components of the sludge before thickening, the inlet of the sludge thickening tank, and the outlet of the sludge thickening tank

[0086]

[0087] Note: In the table, the sludge concentration MLSS before sludge thickening (Q remaining, referring to the excess sludge entering the sludge thickening unit through the excess sludge conveying pipeline 6) is 8 g / L. The data before sludge thickening are the data measured by centrifuging the sludge and taking the supernatant; the sludge concentration of the mixed liquid at the inlet of the sludge thickening tank is approximately 8.8 g / L. In this embodiment, the volume of the thickened sludge is 40% of the volume of the sludge before thickening (Q remaining). The proportion of the thickened sludge (Q cracking) entering the cracking unit in the total volume of the thickened sludge (Q cracking + Q dewatering) is 20%. The reagent NaOH added to the sludge cracking unit is added in solid form. The density of the sludge after cracking is similar to the density of the sludge before cracking (Q cracking). The volume of the sludge after cracking (Q after cracking) accounts for 8% of the volume of the sludge before sludge thickening (Q remaining); the composition of the mixed liquid at the inlet of the sludge thickening tank is measured by taking the supernatant obtained by centrifuging the mixed liquid.

[0088] In this embodiment, the phosphorus recovery unit 4 uses magnesium ammonium phosphate crystallization (struvite) to recover phosphorus in the liquid phase. The wastewater containing orthophosphate from the sludge thickening unit 1 and the sludge dewatering unit 3 is mixed with reagents (the reagents are magnesium chloride, ammonium chloride, and sodium hydroxide) in the pipeline mixer H and then enters the phosphorus recovery unit 4. The dosing amounts of the magnesium chloride and ammonium chloride reagents are determined according to Mg:NH 4+ :P = 1.3:1.3:1 (molar ratio), and the pH of the crystallization reaction is controlled at 9.5 - 10. In this embodiment, the recovery rate of orthophosphate by the phosphorus recovery unit is greater than 80%, and the recovered product is struvite. The low-phosphorus liquid discharged from the phosphorus recovery unit can be returned to the biochemical tank at the front end of the sewage treatment system.

[0089] Applying the technical solution of this embodiment has the following beneficial effects:

[0090] First, all existing sludge cracking and phosphorus release technologies use cracking of the total amount of excess sludge. In this embodiment, only 10% - 20% of the thickened sludge needs to be cracked with alkali, and then the COD (carbon source) released by its cracking is used as the carbon source for the polyphosphorus microorganisms (polyphosphorus bacteria) in the total amount of excess sludge entering the thickening tank. Anaerobic phosphorus release occurs in the anaerobic environment of the sludge thickening tank without adding an external carbon source. Through the new scheme of a small amount of thickened sludge alkali hydrolysis and phosphorus release + anaerobic biological phosphorus release of the total amount of excess sludge, low-cost and high-efficiency phosphorus release of the total amount of excess sludge is achieved. In this embodiment, the equipment investment and operating costs (reagent consumption, power consumption) of the sludge cracking unit are only equivalent to 10% - 20% of the existing total sludge alkali hydrolysis and phosphorus release process, and the equipment floor area can also be saved; the addition of the carbon source in the cracked sludge enables the anaerobic biological phosphorus release time of the sludge in the gravity thickening tank to be shortened to 6 h, which is only 1 / 80 of the time required for the traditional sludge anaerobic digestion process (anaerobic digestion time 20 - 30 d), greatly reducing the equipment investment and operating costs for sludge phosphorus release and phosphorus recovery.

[0091] II. In the existing physical phosphorus release by cracking (ultrasonic wave, hydrothermal hydrolysis, mechanical ball milling) and chemical phosphorus release by cracking (acid, alkali) technologies, a part of the phosphorus and nitrogen elements released into the liquid phase exist in the forms of organic phosphorus and organic nitrogen. It is difficult to recycle organic phosphorus. In this embodiment, the sludge after chemical cracking is returned to the thickening tank. Under the action of the anaerobic environment in the thickening tank and anaerobic bacteria in the excess sludge, the organic phosphorus and organic nitrogen released during the cracking process are converted into orthophosphate and ammonia nitrogen that can be recycled by the subsequent phosphorus recovery unit, which can further improve the phosphorus recovery rate and reduce the chemical cost of adding ammonia nitrogen to the phosphorus recovery unit.

[0092] III. At present, most urban sewage treatment plants in China adopt the technical route of sludge gravity thickening + sludge dewatering for excess sludge, and sludge thickening tanks and sludge dewatering facilities have been built. In this embodiment, the sludge thickening unit adopts an existing conventional gravity thickening tank. When recovering phosphorus from the excess sludge of an existing sewage treatment plant, only a sludge cracking unit, a pH value adjustment unit, a phosphorus recovery unit, and a control system need to be added, and the pipeline needs to be correspondingly modified, then the sludge phosphorus resource recovery of the existing sewage treatment plant can be economically and conveniently realized.

[0093] IV. The phosphorus recovery unit in this embodiment includes an outer cylinder, an inner cylinder, an inlet pipe, an outlet pipe, a discharge pipe, a perforated plate assembly, and an inclined plate assembly. The effects are as follows: ①. This phosphorus recovery unit makes full use of the kinetic energy and potential energy of the wastewater itself to achieve efficient hydraulic vortex crystallization, which is more energy-saving and has a lower operating cost than conventional mechanical stirring crystallization; crystallization and precipitation are integrated, and the device structure is compact, saving floor area; ②. There are multiple perforated plate assemblies with different porosities in the water flow descending channel A. The perforated plates with different porosities can form micro-vortices with different intensities when the wastewater flows through, so that the wastewater realizes hydraulic classification during the flow process, enabling the orthophosphate in the solution to fully contact and mix with the crystal-forming ions (Mg 2+ , NH4 + ions) and making the crystal particles present a fluidized state, and self-induced crystallization can be achieved without adding external crystal seeds; ③. There is an inclined plate assembly in the water flow ascending channel B, which increases the precipitation area of fine phosphorus crystal particles in the wastewater, shortens the precipitation time, and at the same time the water flow of the plate changes from a turbulent state to a laminar state, improving the recovery efficiency of phosphorus crystal particles in the wastewater.

[0094] The above are only the preferred embodiments of the present invention and are not used to limit the present invention. For those skilled in the art, the present invention can have various changes and modifications. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included within the protection scope of the present invention.

Claims

1. A residual sludge phosphorus recovery device, characterized in that: It includes a sludge concentration unit (1), a sludge cracking unit (2), a sludge dewatering unit (3) and a phosphorus recovery unit (4); The sludge concentration unit (1) comprises a concentration tank body having a concentration accommodating chamber (1.4); the concentration tank body is provided with a residual sludge inlet (1.1), a concentrated sludge outlet (1.2), and a supernatant outlet (1.3) that are connected to the concentration accommodating chamber (1.4); the residual sludge inlet (1.1) is connected to a residual sludge conveying pipeline (6); The sludge decomposition unit (2) comprises a first shell (A1), a first stirring assembly (A2), a first sludge inlet pipe (A3) and a first sludge outlet pipe (A4); the first stirring assembly (A2) is arranged on the first shell (A1) for stirring the liquid inside the first shell; the first sludge inlet pipe (A3) is connected to the concentrated sludge outlet (1.2) via a first connecting pipe (G1); the first sludge outlet pipe (A4) is connected to the residual sludge inlet (1.1) via a second connecting pipe (G2); 10%-20% concentrated sludge discharged from the concentrated sludge outlet (1.2) is decomposed by the sludge decomposition unit and then returned to the sludge concentration unit (1); The sludge dewatering unit (3) comprises a dewatering treatment body having a dewatering accommodating chamber (3.1); a dewatering treatment mud inlet pipe (3.2), a dewatering treatment mud outlet pipe (3.3), and a sludge dewatering liquid outlet pipe (3.4) connected to the dewatering accommodating chamber (3.1) are provided on the dewatering treatment body; the dewatering treatment mud inlet pipe (3.2) is connected to the concentrated sludge outlet (1.2) via a third connecting pipe (G3); and the dewatering treatment mud outlet pipe (3.3) is used to discharge dry mud; The supernatant liquid outlet (1.3) and the sludge dewatering liquid output pipe (3.4) are both connected to the phosphorus recovery unit (4) for phosphorus recovery; The phosphorus recovery unit (4) comprises an outer cylinder (4.1), an inner cylinder (4.2), a water inlet pipe (4.3), a water outlet pipe (4.4), a discharge pipe (4.5), a perforated plate assembly (4.6), and an inclined plate assembly (4.7); The outer cylinder (4.1) comprises an outer cylinder body (4.1.1) having an opening at the upper end and a movable cover (4.1.2), wherein the movable cover (4.1.2) is detachably arranged at the opening; The inner cylinder (4.2) comprises an inner cylinder body (4.2.1) with an opening at the lower end, the inner cylinder body (4.2.1) is arranged in the accommodating cavity of the outer cylinder body (4.1.1), and the outer cylinder body ( A water outlet channel (4.8) connected to the water outlet pipe (4.4) is provided between the inner wall of the inner tube body (4.1.1) and the outer wall of the inner tube body (4.2.1). The water outlet channel (4.8) and the water outlet pipe (4.4) are both located in the outer tube body ( 4.1.1); a water flow descending channel (A) is formed inside the inner cylinder body (4.2.1); the water inlet pipe (4.3) is connected to the water flow descending channel (A), and the water outlet end surface of the water inlet pipe (4.3) is higher than the upper end surface of the outlet channel (4.8); the perforated plate assembly (4.6) is arranged in the water flow descending channel (A); The inner wall of the outer cylinder body (4.1.1), the outlet channel (4.8) and the outer wall of the inner cylinder body (4.2.1) enclose a water flow rising channel (B), and the inclined plate assembly (4.7) is arranged in the water flow rising channel (B); The accommodating cavity in the outer cylinder body (4.1.1) is located below the inner cylinder body (4.2.1) to form a crystal gathering area (C), and the discharge pipe (4.5) is connected to the crystal gathering area (C).

2. The excess sludge phosphorus recovery device according to claim 1, characterized in that, along the water flow direction in the water flow descending channel (A), the perforated plate assembly (4.6) comprises a first perforated single piece, a second perforated single piece and a third perforated single piece arranged in sequence, the first perforated single piece comprises one or more first perforated plates ( 4.6.1), the second perforated single piece includes one or more second perforated plates (4.6.2) spaced apart, and the third perforated single piece includes one or more third perforated plates (4.6.3) spaced apart; The ratio of the total area of the through holes in the first perforated plate to the plate area is P1, the ratio of the total area of the through holes in the second perforated plate to the plate area is P2, and the ratio of the total area of the through holes in the third perforated plate to the plate area is P3, and P1<P2<P3; The value of P1 is 2.5%~3%; the value of P2 is 3.5%~4.5%; and the value of P3 is 5.0%~6.0%.

3. The excess sludge phosphorus recovery device according to claim 1, characterized in that: The inclined plate assembly (4.7) is arranged on the outer cylinder body ( 4.1.1) and the outer wall of the inner cylinder body (4.2.1); the inclined plate assembly (4.7) includes a plurality of sedimentation inclined plates arranged at intervals and in a staggered manner, and the gaps between the plurality of sedimentation inclined plates form a flow channel.

4. The excess sludge phosphorus recovery device according to claim 1, characterized in that: Along the water flow direction, the water inlet pipe (4.3) comprises a horizontal pipe section, an arc-shaped transition pipe section and a vertical pipe section arranged in sequence, and the outlet end surface of the vertical pipe section is 5-20 cm higher than the upper end surface of the outlet channel (4.8).

5. The excess sludge phosphorus recovery device according to any one of claims 1 to 4, characterized in that: The first shell (A1) comprises a first body (A1.2) having a first accommodating cavity (A1.1); the first mud inlet pipe (A3) and the first mud outlet pipe (A4) are both arranged on the first body (A1.2) and are both in communication with the first accommodating cavity (A1.1); The first body (A1.2) is provided with a first dosing tube (A5) communicating with the first accommodating cavity (A1.1); The first stirring assembly (A2) includes a first driving power source (A2.1), a first stirring shaft (A2.2) and a first stirring blade (A2.3). The first driving power source (A2.1) is arranged on the first shell (A1); the connecting end of the first stirring shaft (A2.2) is connected to the output end of the first driving power source (A2.1), and the free end of the first stirring shaft (A2.2) is arranged in the first accommodating cavity (A1.1) and is provided with the first stirring blade (A2.3).

6. The excess sludge phosphorus recovery device according to claim 5, characterized in that: The device further comprises a first pH controller (A6); the first body (A1.2) is provided with a measuring hole connected to the first accommodating cavity (A1.1); the first pH controller is arranged at the measuring hole for measuring the pH value of the sludge; the first pH controller is connected to an external PLC control system, and the first pH controller measures the pH value of the sludge via a first measuring electrode (A6.1); the first measuring electrode is arranged at the measuring hole, and a protective net is provided on the outside of the first measuring electrode; The inner wall of the first accommodating cavity (A1.1) is further provided with a plurality of protrusions (A1.3) facing the center of the first accommodating cavity; the protrusions (A1.3) are hemispherical protrusions with a radius of 40-80 mm; the plurality of protrusions (A1.3) are evenly distributed on the inner wall of the first accommodating cavity; The first stirring shaft (A2.2) is provided with multiple layers of the first stirring blades (A2.3) at intervals along its axial direction; The first body (A1.2) is also provided with a first odor collection pipe (A7) for collecting odor generated in the first accommodating chamber; the first shell (A1) also includes an opening connected to the first accommodating chamber (A1.1), and a first detachable cover (A1.4) is provided at the opening. The first driving power source (A2.1), the first dosing pipe (A5), the first pH controller (A6) and the first odor collection pipe (A7) are all arranged on the first detachable cover (A1.4).

7. The excess sludge phosphorus recovery device according to claim 5, characterized in that: It also includes a pH value adjustment unit (5) connected in series with the sludge decomposition unit (2), the pH value adjustment unit (5) including a second shell (B1), a second stirring assembly (B2), a second sludge inlet pipe (B3) and a second sludge outlet pipe (B4); The second shell (B1) comprises a second body (B1.2) having a second accommodating cavity (B1.1); the second mud inlet pipe (B3) and the second mud outlet pipe (B4) are both arranged on the second body (B1.2) and are both in communication with the second accommodating cavity (B1.1); The second body (B1.2) is provided with a second dosing pipe (B5) communicating with the second accommodating cavity (B1.1); The second stirring assembly (B2) includes a second driving power source (B2.1), a second stirring shaft (B2.2), and a second stirring blade (B2.3); the second driving power source (B2.1) is arranged on the second shell (B1); the connecting end of the second stirring shaft (B2.2) is connected to the output end of the second driving power source (B2.1); the free end of the second stirring shaft (B2.2) is arranged in the second accommodating cavity (B1.1) and is provided with the second stirring blade (B2.3); The first mud outlet pipe (A4) is connected to the second mud inlet pipe (B3) through a second connecting pipe (G2), and the second mud outlet pipe (B4) is connected to the excess sludge inlet (1.1) through a fourth connecting pipe (G4).

8. The excess sludge phosphorus recovery device according to claim 7, characterized in that: The device further comprises a second pH controller (B6), wherein the second body (B1.2) is provided with a measuring hole connected to the second accommodating cavity (B1.1), and the second pH controller is arranged at the measuring hole for measuring the pH value of the sludge; the second pH controller is connected to an external PLC control system, and the second pH controller measures the pH value of the sludge via a second measuring electrode (B6.1); the second measuring electrode is arranged at the measuring hole, and a protective net is provided on the outside of the second measuring electrode; The second body (B1.2) is also provided with a second odor collection pipe (B7) for collecting odor generated in the second accommodating chamber; the second shell (B1) also includes an opening connected to the second accommodating chamber (B1.1), and a second detachable cover (B1.3) is provided at the opening. The second driving power source (B2.1), the second dosing pipe (B5), the second pH controller (B6) and the second odor collection pipe (B7) are all arranged on the second detachable cover (B1.3).

9. The excess sludge phosphorus recovery device according to claim 5, characterized in that: The control range of the pH value in the sludge decomposition unit (2) is 10.8 to 11.5; the control range of the pH value in the pH adjustment unit (5) is 9 to 10; After the sludge, which has been pH-adjusted by the pH-adjusting unit (5), intersects with the excess sludge conveying pipeline (6), the flow time of the mixed sludge from the intersection point to the outlet of the excess sludge feed port (1.1) is not less than 3 seconds; The control range of the pH value in the phosphorus recovery unit (4) is 9.5-10.

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