A method for treating excess sludge

Abstract

The present invention relates to the field of water treatment technology, and in particular to a method for treating excess sludge, the method comprising a phosphorus release step: excess sludge rich in phosphorus is sent to a sludge concentration unit for concentration treatment to obtain concentrated sludge; a small portion of concentrated sludge is sent to a sludge cracking unit for cracking treatment to obtain cracked sludge; the remaining concentrated sludge is sent to a sludge dewatering unit for sludge dewatering treatment; the obtained cracked sludge is circulated to the sludge concentration unit. The present invention adds alkali to 10%-20% of the concentrated sludge for cracking, and then utilizes the carbon source released by the cracking as a carbon source for polyphosphate microorganisms (polyphosphate bacteria) in the full amount of excess sludge entering a concentration tank, and anaerobic phosphorus release occurs in the anaerobic environment of the sludge concentration tank without the need for an external carbon source. The new scheme of anaerobic biological phosphorus release of a small amount of concentrated sludge alkali-explained phosphorus + full amount of excess sludge achieves low-cost and efficient phosphorus release of the full amount of excess sludge.

Description

Technical Field

[0001] The present invention relates to the technical field of water treatment, and in particular to a method for treating excess sludge. Background Art

[0002] To achieve effective recovery of phosphorus from sludge, it is necessary to release as much phosphorus in the sludge (solid phase) as possible into the liquid phase. Efficient release of phosphorus is a key step in phosphorus recovery. The existing phosphorus release technologies mainly include:

[0003] ① Physical decomposition method: Use thermal hydrolysis, ultrasound, mechanical ball milling and other methods to rupture microbial cells in sludge and release phosphorus-containing substances inside and outside the cells into the liquid phase. Sludge thermal hydrolysis needs to be carried out under high temperature and high pressure conditions (150-190℃, 0.7-1.1MPa). It is usually used as a pretreatment process in conjunction with anaerobic digestion process. The equipment is complex, operation and maintenance are difficult, and the investment and energy consumption are high. In addition, the odorous gas generated is difficult to treat. Currently, there are only a few engineering application cases. Although ultrasonic decomposition is highly efficient, has a short reaction time (10-60min) and simple equipment, it is currently mostly in the laboratory research stage due to its high power consumption. Actual engineering application needs to overcome the defect of high power consumption.

[0004] ② Chemical breakdown: Acids, alkalis, or chemical agents such as H2O2 and ozone are added to the excess sludge to disrupt the microbial cell structure, releasing intracellular and extracellular phosphorus into the liquid phase. Acid-base breakdown offers simple processes and mature technology, but existing methods such as full-scale acid-base breakdown of sludge or H2O2 and ozone oxidation are costly and difficult to implement on a commercial scale.

[0005] ③ Biological phosphorus release method: release phosphorus through anaerobic digestion or enzymatic bioenhanced phosphorus release. Enzymatic bioenhanced phosphorus release technology has high reagent costs and is currently in the laboratory research stage. Anaerobic digestion is the most widely used sludge disposal technology in engineering projects. It has the advantages of mature technology and low operating costs. However, this method has a slow phosphorus release rate, a long time (the sludge needs to be anaerobic digested for 20-30 days), a large reaction device volume, and high construction investment. If the anaerobic phosphorus release rate needs to be increased or the anaerobic phosphorus release time needs to be shortened, a sufficient carbon source is required. However, the available carbon source in the residual sludge discharged from the biochemical system has basically been consumed by the front-end biochemical system, and a large amount of external carbon source is required to meet the requirements.

[0006] ④ Sludge incineration-wet leaching process: After dehydration and drying, the sludge is incinerated into ash, and then acid and alkali leaching is used to extract phosphorus. The phosphorus in the sludge incineration ash mainly exists in the form of metals such as Ca, Mg, Fe, and Al in the ash, making it unavailable for plant absorption and utilization. Furthermore, heavy metals in the sludge remain in the ash after incineration. It is necessary to separate the phosphorus in the sludge ash from the heavy metals and convert the phosphorus into a form that can be used by plants. This process is complex and the phosphorus recovery cost is high.

[0007] ⑤Combination cracking method: Use combined technologies such as thermal hydrolysis-acid leaching, acidification-microwave radiation, ultrasound-ozone, and ultrasound-alkaline hydrolysis to destroy the microbial cell structure in the sludge and release phosphorus-containing substances into the liquid phase. Compared with a single technology, the combination technology can combine the advantages of various technologies and is the trend of technological development in this field.

[0008] Among the existing sludge phosphorus release methods, part of the phosphorus released into the liquid phase by physical breakdown, chemical breakdown and some combined breakdown processes exists in the form of organic phosphorus compounds (organophosphorus). Organic phosphorus compounds are difficult to remove by coagulation and precipitation, and phosphorus cannot be recovered by crystallization and precipitation. If it is necessary to improve the recovery rate of phosphorus resources in sludge, it is also necessary to further increase the content of orthophosphate in the residual sludge phosphorus release liquid phase.

[0009] In summary, a waste sludge treatment method that is easy to operate and can achieve efficient phosphorus release and phosphorus recovery is designed to solve the problems existing in the existing technology. Summary of the Invention

[0010] The present invention aims to provide a method for treating excess sludge that is easy to operate and can achieve efficient phosphorus release and phosphorus recovery. The specific technical solution is as follows:

[0011] A method for treating excess sludge, comprising a phosphorus release step;

[0012] The phosphorus releasing step comprises the steps:

[0013] Step S1: sending the phosphorus-rich excess sludge to a sludge concentration unit for concentration treatment to obtain concentrated sludge and supernatant;

[0014] Step S2: sending the concentrated sludge with a mass or flow ratio of 10% to 20% to the sludge decomposition unit for decomposition treatment to obtain decomposition-treated sludge; sending the remaining concentrated sludge to the sludge dehydration unit for dehydration treatment to obtain dry sludge and sludge dehydrated liquid;

[0015] Step S3: circulating the cracked sludge obtained in step S2 to the sludge concentration unit in step S1.

[0016] Preferably, step S3 also includes a pH adjustment step, specifically: the sludge after the cracking treatment in step S2 is sent to the pH adjustment unit for pH adjustment to obtain pH-adjusted sludge, and then the pH-adjusted sludge is circulated to the sludge concentration unit in step S1; the pH value control range in the pH adjustment unit is 9-10; the pH value control range in the sludge cracking unit is 10.8-11.5; the sludge after the cracking treatment in step S3 is mixed with the phosphorus-rich residual sludge and transported to the sludge concentration unit through a pipeline for a flow time of not less than 3 seconds.

[0017] Preferably, the concentration time of the phosphorus-rich excess sludge in the sludge concentration unit is 6-24 hours; the reaction time of the sludge cracking unit for cracking treatment is 20-100 minutes; the control range of the pH value in the pH adjustment unit is 9-9.5; the pH value of the cracked sludge and the phosphorus-rich excess sludge after mixing in step S3 is 8-9.

[0018] Preferably, the method further includes a phosphorus recovery step, specifically comprising:

[0019] The supernatant obtained in step S1 is input into a phosphorus recovery unit for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water; or the supernatant obtained in step S1 and the sludge dehydrated liquid obtained in step S2 are input into a phosphorus recovery unit for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water.

[0020] When the sludge dehydration unit does not use agents such as aluminum salts, iron salts, and magnesium salts that can form precipitates with phosphate ions, the supernatant obtained in step S1 and the sludge dehydrated liquid obtained in step S2 are input into the phosphorus recovery unit for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water; when the sludge dehydration unit uses agents such as aluminum salts, iron salts, and magnesium salts that can form precipitates with phosphate ions, the sludge dehydrated liquid obtained in step S2 does not enter the phosphorus recovery unit.

[0021] Preferably, the sludge concentration unit is a gravity concentration tank; the sludge concentration unit is provided with a residual sludge feed port, a concentrated sludge discharge port and a supernatant discharge port; the residual sludge feed port is connected to the residual sludge conveying pipeline;

[0022] The sludge breaking unit includes a first shell, a first stirring assembly, a first sludge inlet pipe and a first sludge outlet pipe;

[0023] The first shell includes a first body having a first accommodating cavity, the first mud inlet pipe and the first mud outlet pipe are both provided on the first body and are both connected to the first accommodating cavity; the first mud inlet pipe is connected to the concentrated sludge discharge port of the sludge concentration unit through a first pipe; the first mud outlet pipe is connected to the pH value adjustment unit through a fourth pipe;

[0024] The first body is provided with a first dosing tube communicating with the first accommodating cavity;

[0025] The first stirring assembly includes a first driving power source, a first stirring shaft and a first stirring blade. The first driving power source is arranged on the first shell; the connecting end of the first stirring shaft is connected to the output end of the first driving power source, and the free end of the first stirring shaft is arranged in the first accommodating cavity and is provided with the first stirring blade.

[0026] Preferably, it also includes a first pH controller, the first body is provided with a measuring hole connected to the first accommodating cavity, 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 on the outside of the measuring electrode.

[0027] Preferably, the inner wall of the first accommodating cavity is further provided with a plurality of protrusions facing the center of the first accommodating 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 accommodating cavity;

[0028] The first stirring shaft is provided with multiple layers of the first stirring blades spaced apart along its axial direction;

[0029] The first body is also provided with a first odor collection pipe for collecting odor generated in the first accommodating chamber; the first shell also includes an opening connected to the first accommodating chamber, and a detachable cover is provided at the opening. The first driving power source, the first dosing pipe, the first pH controller and the first odor collection pipe are all arranged on the detachable cover.

[0030] Preferably, the pH value adjusting unit includes a second shell, a second stirring assembly, a second mud inlet pipe and a second mud outlet pipe;

[0031] The second shell includes a second body having a second accommodating cavity, the second mud inlet pipe and the second mud outlet pipe are both provided on the second body and are both communicated with the second accommodating cavity; the second mud inlet pipe is communicated with the first mud outlet pipe through a fourth pipe, and the second mud outlet pipe is communicated with the residual sludge inlet through a third pipe;

[0032] The second body is provided with a second dosing tube communicating with the second accommodating cavity;

[0033] The second stirring assembly includes a second driving power source, a second stirring shaft and a second stirring blade. The second driving power source is arranged on the second shell; the connecting end of the second stirring shaft is connected to the output end of the second driving power source, and the free end of the second stirring shaft is arranged in the second accommodating cavity and is provided with the second stirring blade.

[0034] Preferably, the phosphorus recovery unit comprises an outer shell, a middle shell, an inner shell, a water inlet pipe, a drain pipe, a discharge port, a plug-flow stirring assembly, a folded plate vortex assembly, a modular vortex assembly and a slanted plate assembly;

[0035] The outer shell includes a first cylindrical body arranged in series from top to bottom and a first conical body which is wide at the top and narrow at the bottom and closed at the lower end; a receiving chamber a is provided in the first cylindrical body, and a receiving chamber b communicating with the receiving chamber a is provided in the first conical body; a water collecting tank is provided at the upper part of the receiving chamber a; the middle shell includes a second cylindrical body arranged in series from top to bottom and a second conical body which is wide at the top and narrow at the bottom and provided with an opening at the lower end; a receiving chamber c is provided in the second cylindrical body, and a receiving chamber d communicating with the receiving chamber c is provided in the second conical body; the upper end of the second conical body is located in the receiving chamber a and the lower end thereof is located in the receiving chamber b; the inner shell includes a third cylindrical body arranged in the receiving chamber c, the third cylindrical body including a receiving chamber e with openings at both upper and lower ends;

[0036] The e accommodating chamber forms a first water flow ascending channel; a water flow descending channel is formed between the inner wall of the second cylindrical cylinder and the outer wall of the third cylindrical cylinder; the annular area between the inner wall of the first cylindrical cylinder and the first conical cylinder, the outer wall of the second cylindrical cylinder and the second conical cylinder, and the water collecting tank form a second water flow ascending channel; the propelling stirring assembly and the folded plate vortex assembly are arranged from top to bottom in the first water flow ascending channel; the modular vortex assembly is arranged in the water flow descending channel; the inclined plate assembly is arranged in the second water flow ascending channel; the lower part of the accommodating chamber forms a crystal aggregation area;

[0037] The water inlet pipe is connected to the supernatant discharge port, and the water inlet pipe passes through the side wall of the first cylindrical barrel and the side wall of the second cylindrical barrel and is inserted into the upper part of the first water flow rising channel, and the water outlet end of the water inlet pipe is lower than the water collecting tank position; the drain pipe is connected to the water collecting tank; the discharge port is connected to the crystal aggregation area.

[0038] Preferably, the plug-flow stirring assembly includes a third driving power source, a third stirring shaft and a third stirring blade, the connecting end of the third stirring shaft is connected to the output end of the third driving power source, and the third stirring blade is arranged on the free end of the third stirring shaft; the water outlet end of the water inlet pipe is located 20-50 cm above the third stirring blade;

[0039] The folded plate vortex assembly is located directly below the plug-flow stirring assembly, and the folded plate vortex assembly includes a first folded plate and a second folded plate arranged in parallel, the first folded plate includes a plurality of connecting plates connected in sequence, and the angle α between two adjacent connecting plates is 80°-100°; the first folded plate and the second folded plate are in a mirror-image structure;

[0040] The modular vortex assembly includes a plurality of vortex units stacked or spaced apart, each of which is a hollow cylindrical body formed by a first vertical plate, a second vertical plate, an upper arc-shaped outer frame, an upper arc-shaped inner frame, a lower arc-shaped outer frame, and a lower arc-shaped inner frame; a vortex sheet is installed in the vortex unit, and the cross-section of the vortex sheet is at least one of a triangle, a semicircle, and a rectangle;

[0041] The inclined plate assembly includes a plurality of sedimentation inclined plates arranged in parallel, and the sedimentation inclined plates are arranged at an angle to the inner wall of the a-accommodation chamber; and the inclined plate assembly is located in the middle and lower part of the a-accommodation chamber.

[0042] The application of the technical solution of the present invention has the following beneficial effects:

[0043] 1. The excess sludge treatment method of the present invention includes a phosphorus release step, which includes the following steps: sending the excess sludge rich in phosphorus to a sludge concentration unit for concentration treatment to obtain concentrated sludge and supernatant; sending the concentrated sludge with a mass or flow ratio of 10-20% to a sludge cracking unit for cracking treatment to obtain cracked sludge; sending the remaining concentrated sludge to a sludge dewatering unit for sludge dewatering treatment to obtain dry sludge and sludge dewatered liquid; and recycling the cracked sludge to the sludge concentration unit. The present invention adds alkali to crack 10%-20% of the concentrated sludge, and then uses the COD (carbon source) released by the cracking as a carbon source for the polyphosphate microorganisms (polyphosphate bacteria) in the entire excess sludge entering the concentration tank. Anaerobic phosphorus release occurs in the anaerobic environment of the sludge concentration tank without the need for an external carbon source. The new scheme of alkali phosphorus excretion of a small amount of concentrated sludge + anaerobic biological phosphorus release of the entire excess sludge achieves low-cost and efficient phosphorus release from the entire excess sludge.

[0044] 2. The present invention also includes a phosphorus recovery step, specifically comprising: feeding the resulting supernatant, or the supernatant and sludge dewatered liquid, into a phosphorus recovery unit for phosphorus recovery treatment to produce phosphorus crystals and low-phosphorus water. The present invention returns the sludge after alkaline decomposition to the sludge concentration unit. The organic phosphorus and organic nitrogen released during the decomposition process are converted into orthophosphate and ammonia nitrogen by the anaerobic environment of the concentration tank and the anaerobic microorganisms in the excess sludge, which can be recovered by the subsequent phosphorus recovery unit. This further improves the phosphorus recovery rate and reduces the cost of ammonia nitrogen reagents added to the phosphorus recovery unit.

[0045] 3. The sludge thickening unit in the present invention is a gravity thickening tank, which adopts the conventional gravity thickening tank in the prior art. When it is necessary to recover phosphorus from the residual sludge of an existing sewage treatment plant, it is only necessary to add a sludge breaking component (only 10%-20% of the total concentrated sludge needs to be broken), a phosphorus recovery unit and a supporting control system, and to make corresponding modifications to the pipelines, so as to economically and conveniently achieve efficient phosphorus release from sludge and efficient recovery of phosphorus resources in the existing sewage treatment plant.

[0046] 4. The sludge breakdown unit of the present invention includes a first shell, a first stirring assembly, a first sludge inlet pipe and a first sludge outlet pipe, with a streamlined structure. The equipment investment and operating costs (drug consumption, power consumption) of the sludge breakdown unit are only equivalent to 10%-20% of the existing full-scale sludge alkaline phosphorus digestion process, and the equipment footprint can also be saved. The addition of carbon source to the broken sludge shortens the anaerobic biological phosphorus release time of the sludge in the gravity thickening tank to 6 hours, which is only 1 / 80 of the time required for the traditional sludge anaerobic digestion process (anaerobic digestion time 20-30 days), greatly reducing the equipment investment and operating costs of sludge phosphorus release and phosphorus recovery.

[0047] 5. The phosphorus recovery unit of the present invention adopts a three-layer shell structure of an outer shell, a middle shell, and an inner shell to form a circulating flow channel formed by a first water flow rising channel, a water flow descending channel, and a second water flow rising channel. The plug flow stirring component and the folded plate vortex component are arranged from top to bottom in the first water flow rising channel and combined with the modular vortex component in the water flow descending channel to form a mechanical stirring mixed crystallization + hydraulic vortex crystallization composite system. Due to its special structure, hydraulic classification is achieved during operation, so that the solution is fully mixed with materials and the crystal particles are fluidized, and self-induction is achieved without the need for external crystal seeds. Crystallization, the particle size of the crystal particles is larger than that of traditional stirred crystallization; the first water flow rising channel and the water flow descending channel form a water flow circulation flow channel to automatically sort the crystal particles, and the particles with large size and mass will automatically separate from the circulating water flow under the action of gravity and be discharged into the crystal gathering area, and the crystal particles with small particle size and mass continue to crystallize in the water flow circulation channel. The crystal particles collected in the crystal gathering area have larger particle size and higher purity than those of traditional stirred crystallization; the inclined plate component is arranged in the second water flow rising channel, which can perform secondary separation on the fine crystal particles entrained in the water flow, thereby further improving the recovery efficiency of the phosphorus crystal particles.

[0048] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention will be further described in detail below with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0050] Figure 1 Schematic diagram of the process of treating excess sludge in a preferred embodiment of the present invention;

[0051] Figure 2 It is the plan layout of each device in the figure;

[0052] Figure 3 yes Figure 2 Schematic diagram of the facade structure;

[0053] Figure 4 yes Figure 3 Schematic diagram of the structure of the sludge cracking component;

[0054] Figure 5 yes Figure 3 Schematic diagram of the structure of the medium phosphorus recovery unit;

[0055] Figure 6 yes Figure 5 A top view of the center fold plate vortex assembly mounted on the inner casing;

[0056] Figure 7 yes Figure 6 MM cross-section diagram;

[0057] Figure 8 yes Figure 5 Schematic diagram of the structure of the vortex monomer of the modular vortex assembly;

[0058] Figure 9 yes Figure 8 A top view of

[0059] Figure 10 yes Figure 9 NN cross-section diagram.

[0060] Among them, 1. Sludge concentration unit, 1.1. Residual sludge inlet, 1.2. Concentrated sludge outlet, 1.3. Supernatant outlet; 2. Sludge breaking component, 2.1. Sludge breaking unit, A1. First shell, A1.1. First accommodating chamber, A1.2. First body, A1.3. Protrusion, A1.4. Removable cover, A2. First stirring component, A2.1. First driving power source, A2.2. First stirring shaft, A2.3. First stirring blade, A3. First mud inlet pipe, A4. First mud outlet pipe, A5. First dosing pipe, A6. First pH controller , A6.1, first measuring electrode, A7, first odor collection pipe; 2.2, pH value adjustment unit, B1, second shell, B1.1, second accommodating chamber, B1.2, second body, B2, second stirring assembly, B2.1, second driving power source, B2.2, second stirring shaft, B2.3, second stirring blade, B3, second mud inlet pipe, B4, second mud outlet pipe, B5, second dosing pipe, B6, second pH controller, B6.1, second measuring electrode, B7, second odor collection pipe; 3, sludge dehydration unit; 4, first pipeline; 5, second pipeline; 6, first Three pipelines; 7. Fourth pipeline; 8. Phosphorus recovery unit, 8.1. Outer shell, 8.1.1. First cylindrical cylinder, 8.1.2. First conical cylinder, 8.1.3. Accommodation chamber a, 8.1.4. Accommodation chamber b, 8.2. Middle shell, 8.2.1. Second cylindrical cylinder, 8.2.2. Second conical cylinder, 8.2.3. Accommodation chamber c, 8.2.4. Accommodation chamber d, 8.3. Inner shell, 8.3.1. Third cylindrical cylinder, 8.3.2. Accommodation chamber e, 8.4. Water collecting tank, 8.5. Water inlet pipe, 8.6. Drain pipe, 8.7. Discharge port, 8.8 , plug flow stirring assembly, 8.8.1, third driving power source, 8.8.2, third stirring shaft, 8.8.3, third stirring blade; 8.9, folded plate vortex assembly, 8.9.1, first folded plate, 8.9.2, second folded plate, 8.10, modular vortex assembly, 8.10.1, first vertical plate, 8.10.2, second vertical plate, 8.10.3, upper arc-shaped outer frame, 8.10.4, upper arc-shaped inner frame, 8.10.5, lower arc-shaped outer frame, 8.10.6, lower arc-shaped inner frame, Y, semicircular shell vortex sheet, S, isosceles right triangle vortex sheet; 8.11. Inclined plate assembly; A. First water flow ascending channel; B. Water flow descending channel; C. Second water flow ascending channel; D. Crystal accumulation area; 9. Fifth pipeline; 10. Dry sludge conveying element; 11. Sixth pipeline; 12. Residual sludge conveying pipeline; 13. Seventh pipeline; 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; K1. First flowmeter; K2. Second flowmeter; K3. Third flowmeter; K4. Fourth flowmeter; C4. Lifting pump; P1. Orthophosphate online detector; P2. pH online detector. DETAILED DESCRIPTION

[0061] The embodiments of the present invention are described in detail below with reference to the accompanying drawings. However, the present invention can be implemented in many different ways as defined and covered by the claims.

[0062] Example:

[0063] See also Figure 1 , a method for treating excess sludge, including a phosphorus release step and a phosphorus recovery step, the details of which are as follows:

[0064] The phosphorus releasing step comprises the steps:

[0065] Step S1: sending the phosphorus-rich excess sludge Q1 discharged from the sewage treatment biochemical system to a sludge concentration unit for concentration treatment to obtain concentrated sludge Q3 and supernatant Q2;

[0066] Step S2: sending the concentrated sludge Q4 accounting for 10%-20% by mass or flow into the sludge cracking unit for cracking treatment to obtain cracked sludge; sending the remaining concentrated sludge Q5 into the sludge dehydration unit for sludge dehydration treatment to obtain dry sludge and sludge dehydrated liquid;

[0067] Step S3: circulating the cracked sludge obtained in step S2 to the sludge concentration unit 1 in step S1.

[0068] In this embodiment, step S3 also includes a pH adjustment step, specifically: the sludge after the cracking treatment in step S2 is sent to the pH adjustment unit for pH adjustment to obtain pH-adjusted sludge, and then the pH-adjusted sludge Q6 is circulated to the sludge concentration unit in step S1; the pH control range of the pH adjustment unit is 9-10, and the preferred pH control range is 9-9.5.

[0069] The phosphorus recovery step specifically comprises:

[0070] The supernatant obtained in step S1 is fed into the phosphorus recovery unit 8 for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water. This situation is applicable when the sludge dehydration unit uses agents such as aluminum salts, iron salts, and magnesium salts that can form precipitates with phosphate ions. The sludge dehydrated liquid obtained in step S2 does not enter the phosphorus recovery unit, and only the supernatant obtained in step S1 enters the phosphorus recovery unit for phosphorus recovery treatment.

[0071] Alternatively, the supernatant obtained in step S1 and the sludge dewatering liquid obtained in step S2 are fed to a phosphorus recovery unit 8 for phosphorus recovery to produce phosphorus crystals and low-phosphorus water. This method is applicable when the sludge dewatering unit does not use agents such as aluminum salts, iron salts, and magnesium salts that can form precipitates with phosphate ions.

[0072] See also Figure 2-Figure 3 A method for treating excess sludge includes a device for releasing phosphorus and a phosphorus recovery unit 8. The excess sludge from a municipal sewage treatment plant is subjected to phosphorus release treatment by the phosphorus release device, and then phosphorus is recovered by the phosphorus recovery unit 8 as follows:

[0073] In this embodiment, the phosphorus release mechanism includes a sludge concentration unit 1, a sludge breaking component 2 and a sludge dewatering unit 3. The sludge concentration unit 1 is provided with a residual sludge inlet 1.1, a concentrated sludge discharge outlet 1.2 and a supernatant discharge outlet 1.3; the sludge breaking component 2 includes a sludge breaking unit 2.1 and a pH value adjustment unit 2.2 arranged in series.

[0074] Excess sludge is transported via excess sludge conveying pipeline 12 (equipped with a first flowmeter K1) and enters sludge concentration unit 1 through excess sludge inlet 1.1 for concentration. The supernatant after concentration is discharged through supernatant outlet 1.3 to phosphorus recovery unit 8 for phosphorus recovery. The concentrated sludge is discharged through concentrated sludge outlet 1.2. A portion of the concentrated sludge enters sludge disintegration unit 2.1 through first pipeline 4 (equipped with a second flowmeter K2 and a first electric valve F1) for disintegration. The remaining portion enters sludge dewatering unit 3 through second pipeline 5 (equipped with a third flowmeter K3 and a second electric valve F2) for dewatering. The flow ratio of the sludge in these two pipelines can be adjusted by controlling the first and second electric valves F1 and F2. The disintegrated sludge enters pH adjustment unit 2.2 for pH adjustment. It is then lifted by lift pump C4 and transported through third pipeline 6 to excess sludge inlet 1.1 for circulation back to sludge concentration unit 1. The detailed structure is as follows:

[0075] The sludge concentration unit 1 adopts a circular gravity concentration tank in the prior art. In this embodiment, the tank body is constructed of reinforced concrete or steel anti-corrosion equipment. Sludge is concentrated in an anaerobic environment without stirring in the sludge concentration tank, and an anaerobic biological phosphorus release effect occurs simultaneously, releasing phosphorus into the liquid phase. The sludge concentration time in the tank (calculated by hydraulic retention time) is 6-24 hours (preferably 14-24 hours). The residual sludge inlet 1.1 is connected to the residual sludge conveying pipe 12, and the residual sludge conveying pipe 12 is connected to the external sludge conveying pump. The sludge flows from the intersection of the residual sludge conveying pipe 12 and the outlet pipe of the lifting pump C4 to the residual sludge inlet 1.1 in the sludge concentration unit 1 for no less than 3 seconds; the supernatant discharge port 1.3 provided at the upper part of the sludge concentration unit 1 is connected to the phosphorus recovery unit 8, and the supernatant (i.e., the high-concentration phosphorus-containing supernatant produced by the sludge concentration tank) is transported to the phosphorus recovery unit for phosphorus recovery treatment; a concentrated sludge discharge port 1.2 is provided at the bottom of the sludge concentration unit 1, and the concentrated sludge discharge port 1.2 is respectively connected to the sludge breaking component 2 and the sludge dewatering unit 3. When the sludge dewatering unit 3 does not use aluminum salts, iron salts, magnesium salts and other agents that can form precipitates with phosphate ions, the sludge dewatering liquid generated by the sludge dewatering unit and the supernatant discharged from the sludge concentration unit enter the phosphorus recovery unit together for phosphorus recovery treatment to obtain phosphorus crystal products and low-phosphorus water; when the sludge dewatering unit 3 uses aluminum salts, iron salts, magnesium salts and other agents that can form precipitates with phosphate ions, the sludge dewatering liquid generated by the sludge dewatering unit does not enter the phosphorus recovery unit, but directly returns to the biochemical pool at the front end of the sewage treatment system; the low-phosphorus water discharged from the phosphorus recovery unit returns to the biochemical pool at the front end of the sewage treatment system.

[0076] The sludge decomposition component 2 includes a sludge decomposition unit 2.1 and a pH value adjustment unit 2.2 arranged in series. Figure 4 , this embodiment is preferred:

[0077] The sludge decomposition unit 2.1 includes a first shell A1, a first stirring assembly A2, a first mud inlet pipe A3, a first mud outlet pipe A4 and a first pH controller A6; the first shell A1 includes 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 connected to the first accommodating cavity A1.1; the first mud inlet pipe A3 is connected to the concentrated sludge outlet 1.2 of the sludge thickening unit through a first pipe 4; the first mud outlet pipe A4 is connected to the pH value adjustment unit through a fourth pipe 7 2.2 is connected; the first body A1.2 is provided with a first dosing tube A5 connected to the first accommodating chamber 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, and 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 chamber A1.1 and is provided with the first stirring blade A2.3. The first body A1.2 is provided with a measuring hole connected to the first accommodating chamber A1.1, and the first pH controller A6 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 pH controller measures the pH value of the sludge through a first measuring electrode A6.1; the measuring electrode is arranged at the measuring hole and a protective net is provided on the outside of the measuring electrode.

[0078] Further preferably, the first shell A1 is a cylindrical shell made of carbon steel anti-corrosion material, and sodium hydroxide is added to break down the sludge. In this embodiment, the pH control range of the sludge breaking component is: 10.8-11, and the sludge breaking reaction time is: 40-60 minutes. The inner wall of the first accommodating chamber A1.1 is also provided with multiple protrusions A1.3 facing the center of the first accommodating chamber; the protrusions A1.3 are hemispherical protrusions with a radius of 40-80mm; the multiple protrusions A1.3 are evenly distributed on the inner wall of the first accommodating chamber, where the radius of the hemispherical protrusions is the same, and the multiple protrusions are evenly distributed on the vertical inner wall of the first accommodating chamber, and the distance between the edges of two adjacent protrusions is 1.5 times their diameters. The first stirring shaft A2.2 is provided with multiple layers of the first stirring blades A2.3 at intervals along its axial direction (here, preferably two layers of first stirring blades are arranged in the up and down directions, and the stirring blades generate upward thrust when rotating); the first body A1.2 is also provided with a first odor collection pipe A7 for collecting the odor generated in the first accommodating cavity; the first shell A1 also includes an opening connected to the first accommodating cavity A1.1, and a removable cover A1.4 is provided at the opening, and the first driving power source A2.1, the first dosing tube A5, the first pH controller A6 and the first odor collection pipe A7 are all arranged on the removable cover A1.4.

[0079] In this embodiment, the pH value adjustment unit 2.2 includes a second shell B1, a second stirring assembly B2, a second mud inlet pipe B3 and a second mud outlet pipe B4; the second shell B1 includes a second body B1.2 with 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 connected to the second accommodating cavity B1.1, the second mud inlet pipe B3 is connected to the first mud outlet pipe A4 through a fourth pipe 7, and the second mud outlet pipe B4 is connected to the residual sludge through a third pipe 6 (a lifting pump C4 is provided on the third pipe). The feed port 1.1 is connected; the second body B1.2 is provided with a second dosing pipe B5 connected to the second accommodating chamber 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, with the second driving power source B2.1 being disposed 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, and the free end of the second stirring shaft B2.2 is disposed within the second accommodating chamber B1.1 and is provided with the second stirring blade B2.3. Further preferably, the second shell B1 is cylindrical; in this embodiment, the pH value in the pH adjustment unit 2.2 is controlled within a range of 9-10, preferably 9-9.5. The effective volume of the second chamber B1.1 in the pH adjustment unit 2.2 is half the volume of the first chamber A1.1 in the sludge breakdown unit 2.1. The pH adjustment unit 2.2 is lower than the sludge breakdown unit 2.1, ensuring that sludge in the sludge breakdown unit 2.1 flows by gravity into the pH adjustment unit 2.2. The sludge discharged from the third pipe 6 has a soluble COD of no less than 2000 mg / L and a pH of 9-9.5. Furthermore, the second body B1.2 is provided with a measuring port connected to the second chamber B1.1. A second pH controller B6 is located at this port to measure the pH of the sludge. The second pH controller is connected to an external PLC control system and measures the pH of the sludge using a second measuring electrode B6.1. This electrode is located at the measuring port and is protected by a protective mesh. The second body B1.2 is also provided with a second odor collection pipe B7 to collect odors generated in the second chamber.

[0080] In this embodiment, the phosphorus recovery unit 8 is connected to the supernatant outlet 1.3 via a fifth pipe 9 (a fourth flowmeter K4 is provided on this pipe). The sludge after sludge dehydration treatment in the sludge dehydration unit 3 is transported via a dry sludge conveying member 10 (preferably a dry sludge conveying pipe, but a conveying device such as a conveyor belt may also be used). The sludge dehydrated liquid after sludge dehydration treatment is connected to the fifth pipe 9 or the phosphorus recovery unit via a sixth pipe 11. Figure 2-3It is shown in FIG. 8 that it is connected to the fifth pipeline 9 and then enters the phosphorus recovery unit 8.

[0081] Further preferably, the phosphorus recovery unit 8 comprises an outer shell 8.1, a middle shell 8.2, an inner shell 8.3, a water inlet pipe 8.5, a drain pipe 8.6, a discharge port 8.7, a plug-flow stirring assembly 8.8, a folded plate vortex assembly 8.9, a modular vortex assembly 8.10 and a slanted plate assembly 8.11, see Figure 5 , the detailed structure is as follows:

[0082] The outer shell 8.1 comprises a first cylindrical body 8.1.1 and a first conical body 8.1.2 which is wide at the top and narrow at the bottom and closed at the bottom, arranged in series from top to bottom. A receiving chamber a 8.1.3 is provided in the first cylindrical body 8.1.1, and a receiving chamber b 8.1.4 communicating with the receiving chamber a 8.1.3 is provided in the first conical body 8.1.2. A water collecting trough 8.4 is provided above the receiving chamber a 8.1.3.

[0083] The middle housing 8.2 comprises a second cylindrical body 8.2.1 and a second conical body 8.2.2, which is wide at the top and narrow at the bottom and has an opening at the lower end, arranged in series from top to bottom. A receiving chamber c 8.2.3 is provided in the second cylindrical body 8.2.1, and a receiving chamber d 8.2.4 communicating with the receiving chamber c 8.2.3 is provided in the second conical body 8.2.2. The upper end of the second conical body 8.2.2 is located in the receiving chamber a 8.1.3 and the lower end is located in the receiving chamber b 8.1.4.

[0084] The inner shell 8.3 includes a third cylindrical barrel 8.3.1 arranged in the c accommodating chamber 8.2.3, and the third cylindrical barrel 8.3.1 includes an e accommodating chamber 8.3.2 with openings at both the upper and lower ends.

[0085] In the phosphorus recovery unit 8: the e accommodating chamber 8.3.2 forms a first water flow rising channel A; a water flow descending channel B is formed between the inner wall of the second cylindrical cylinder 8.2.1 and the outer wall of the third cylindrical cylinder 8.3.1; the annular area between the inner wall of the first cylindrical cylinder 8.1.1 and the first conical cylinder 8.1.2, the outer wall of the second cylindrical cylinder 8.2.1 and the second conical cylinder 8.2.2, and the water collecting trough 8.4 enclose a second water flow rising channel C; the plug-flow stirring assembly 8.8 and the folded plate vortex assembly 8.9 are arranged from top to bottom in the first water flow rising channel A; the modular vortex assembly 8.10 is arranged in the water flow descending channel B; the inclined plate assembly 8.11 is arranged in the second water flow rising channel C; the lower part of the accommodating chamber 8.1.4 forms a crystal aggregation area D, and the discharge port 8.7 is connected to the crystal aggregation area D.

[0086] The water inlet pipe 8.5 is connected to the supernatant discharge outlet 1.3 through the fifth pipe 9. The water outlet end of the water inlet pipe 8.5 passes through the side wall of the first cylindrical barrel 8.1.1 and the side wall of the second cylindrical barrel 8.2.1 and is inserted into the upper part of the first water flow rising channel A, and the water outlet end of the water inlet pipe 8.5 is lower than the position of the water collection tank 8.4; the drain pipe 8.6 is connected to the water collection tank 8.4.

[0087] Further preferably, the plug-flow stirring assembly 8.8 includes a third driving power source 8.8.1, a third stirring shaft 8.8.2, and a third stirring blade 8.8.3, wherein the connection end of the third stirring shaft 8.8.2 is connected to the output end of the third driving power source 8.8.1, and the third stirring blade 8.8.3 is disposed on the free end of the third stirring shaft 8.8.2; the outlet end of the water inlet pipe 8.5 is located 20-50 cm above the third stirring blade 8.8.3. The plug-flow stirring assembly 8.8 lifts the liquid and suspended particles in the first water flow rising channel A from its lower section to its upper section, and provides a driving force for the water to circulate in the first water flow rising channel A.

[0088] The top of the folded plate vortex component 8.9 is 0.5m away from the lower edge of the third stirring blade 8.8.3 and the lower end is flush with the lower end of the inner shell 8.3; see Figure 6 and Figure 7 The folded plate vortex assembly 8.9 includes a first folded plate 8.9.1 and a second folded plate 8.9.2 arranged in parallel. The first folded plate 8.9.1 comprises a plurality of connecting plates connected in series, with the angle α between adjacent connecting plates being 80°-100°. The first folded plate 8.9.1 and the second folded plate 8.9.2 form a mirror image. The angle α between adjacent connecting plates in the folded plate vortex assembly is 90°, and the length Q1 of the connecting plates is 20% of the diameter of the inner shell 8.3. The angle and length of each connecting plate in the same first or second folded plate are identical. The peaks and troughs of the first and second folded plates are horizontally aligned, and the horizontal spacing Q2 is equal and 10% of the diameter of the inner shell 8.3.

[0089] The upper end of the modular vortex component 8.10 is located 0.5m below the liquid level of the inner cavity of the water flow descending channel B, and the lower end is 0.6m away from the plane where the lower end of the inner shell 8.3 is located. Figure 8 、 Figure 9 、 Figure 10As shown, the modular eddy current assembly has the shape of a fan-shaped cylindrical cube, with its horizontal projection forming a fan-shaped ring. It comprises a plurality of stacked or spaced eddy current units, each of which is a hollow cylindrical body formed by a first riser 8.10.1, a second riser 8.10.2, an upper curved outer frame 8.10.3, an upper curved inner frame 8.10.4, a lower curved outer frame 8.10.5, and a lower curved inner frame 8.10.6. The eddy current units are equipped with eddy current blades, each having a cross-section of at least one of triangular, semicircular, and rectangular. The columnar body is made of metal or engineering plastic and can withstand the weight of the frame itself and the eddy current blades installed therein.

[0090] In this embodiment, the vortex unit is further preferably provided with alternating layers of semicircular shell vortex sheets and isosceles right-angled triangle vortex sheets. The semicircular shell vortex sheets have an arc-shaped horizontal projection and a semicircular cross-section with a diameter of 30-40 mm. The horizontal spacing of each semicircular shell vortex sheet Y in the same layer is equal, and the distance between two adjacent semicircular shell vortex sheets is 1.3 times their diameters. The length of the isosceles right-angled triangle vortex sheet S in the same layer is determined by the radius of its own horizontal projection arc and the arc radian of the horizontal projection of the vortex unit frame. The horizontal projection of a single isosceles right-angled triangle vortex sheet is an arc-shaped horizontal projection and an isosceles right-angled triangle cross-section, the height of the triangle being the same as the radius of the semicircular shell vortex sheet. Adjacent layers of semicircular shell vortex sheets and isosceles right-angled triangle vortex sheets are arranged alternately, and the horizontal projections of adjacent layers of semicircular shell vortex sheets and isosceles right-angled triangle vortex sheets do not overlap.

[0091] The inclined plate assembly 8.11 includes a plurality of sedimentation inclined plates arranged in parallel, and the sedimentation inclined plates are arranged at an angle to the inner wall of the a-accommodation chamber; and the inclined plate assembly 8.11 is located in the middle and lower part of the a-accommodation chamber.

[0092] The water inlet pipe 8.5 comprises a horizontal section, an arcuate transition section, and a vertical section arranged in series. The horizontal section passes through the upper portions of the outer shell 8.1 and the middle shell 8.2. The arcuate transition section bends downward 90 degrees and extends to the upper portion of the inner shell 8.3. The outlet of the vertical section is located 0.4 meters above the third stirring blade 8.8.3 of the plug-flow mixing assembly 8.8. A pipeline mixer H is installed on the horizontal section of the water inlet pipe 8.5, which is connected to the magnesium salt dosing pipe H1, the ammonium salt dosing pipe H2, and the alkali dosing pipe H3.

[0093] In this embodiment, the sludge dewatering unit 3 adopts an existing horizontal spiral centrifugal dewatering equipment set.

[0094] In addition, this embodiment is also provided with a control system, which includes online detection instruments, cables and an electrical control cabinet containing a programmable logic controller (PLC). The online detection instruments include a first flow meter K1 arranged on the residual sludge conveying pipeline 12, a second flow meter K2 arranged on the first pipeline 4, a third flow meter K3 arranged on the second pipeline 5, a fourth flow meter K4 arranged on the fifth pipeline 9, an orthophosphate online detector P1 arranged near the supernatant discharge pipe, a pH value online detector P2 arranged in the phosphorus recovery unit 8, and a first pH controller A6 and a second pH controller B6 arranged in the sludge decomposition component; the cables and the electrical control cabinet containing the programmable logic controller (PLC) all adopt existing mature equipment, which can power the online detection instruments and communicate with the online detection instruments. The PLC controls the operation of external dosing equipment and other equipment according to the data detected by the online monitoring instruments and the preset control logic.

[0095] The technical solution of this embodiment is specifically:

[0096] The phosphorus-rich excess sludge (Q1 excess, with a water content of 99.2%) discharged from the sewage treatment biochemical system is mixed with the cracked sludge (Q6 cracked) discharged from the sludge cracking unit 2.1 through the excess sludge conveying pipeline 12 and then enters the sludge concentration unit 1. The phosphorus-rich excess sludge is concentrated in the sludge concentration unit 1 under the action of the carbon source provided by the cracked sludge, and an anaerobic biological phosphorus release effect occurs at the same time, releasing phosphorus in the solid phase into the liquid phase. The low-phosphorus sludge after concentration and biological phosphorus release is discharged from the bottom of the gravity concentration tank. A portion of the concentrated sludge (Q4 cracked) enters the sludge cracking unit 2.1 in the sludge cracking component 2 through the first pipeline 4 for sludge cracking. After the cracking is completed, the sludge enters the pH adjustment unit 2.2 for pH adjustment and then returns to the sludge concentration unit 1. The other portion of the concentrated sludge (Q5 dehydrated) is discharged into the sludge dehydration unit 3 through the second pipeline 5 for dehydration treatment. In this embodiment, the flow rate or mass ratio Q4 breaking of the sludge entering the sludge breaking unit and the total amount of sludge after concentration is: (Q4 breaking + Q5 dehydration) = 0.2; the high-concentration phosphorus-containing supernatant produced by the sludge concentration unit 1 is discharged into the phosphorus recovery unit 8 through the fifth pipeline 9 to recover phosphorus; the sludge dehydrated liquid produced by the sludge dehydration unit is mixed with the supernatant of the sludge concentration unit through the sixth pipeline 11 and discharged together into the phosphorus recovery unit 8 for phosphorus recovery, and the dry sludge is transported for disposal through the dry sludge conveying part 10; the low-phosphorus water discharged from the phosphorus recovery unit is returned to the biochemical pool at the front end of the sewage treatment system through the seventh pipeline 13.

[0097] In this embodiment, the sludge cracking unit uses alkali (NaOH or KOH) to stir at room temperature to crack the concentrated sludge. The mass ratio of the sludge discharged into the sludge cracking unit to the total amount of concentrated sludge is: 10%-20%. The amount of alkali added to the sludge cracking unit is controlled by pH, and the cracking pH is: 10.8-11.5. The reaction time of sludge cracking is 20-100min, preferably 40-120min. After alkali cracking, the sludge releases COD (carbon source), ammonia nitrogen, organic nitrogen, orthophosphate, organic phosphorus and other substances into the aqueous phase. The concentration of soluble COD in the cracked sludge is not less than 2000mg / L. After acidification to adjust the pH to 9-10 (preferably 9-9.5), it is converted into cracked sludge; the mass of the cracked sludge is equal to the sum of the mass of the concentrated sludge plus the reagent added during the cracking process, and is mixed with the phosphorus-rich residual sludge discharged from the sewage treatment biochemical system and discharged into the gravity thickening tank. The sludge cracking step in this embodiment simultaneously achieves five technical effects:

[0098] ① The residual phosphorus in the sludge is broken down and released, releasing orthophosphate from the solid phase to the liquid phase, further increasing the amount of phosphorus released from the sludge and further improving the phosphorus recovery rate;

[0099] ② The high-concentration COD (carbon source) released by sludge cracking is returned to the sludge thickening tank as a carbon source for anaerobic biological phosphorus release of the remaining sludge. No external carbon source is required, achieving "waste treatment with waste" and saving the cost of sludge phosphorus release;

[0100] ③ Sludge cracking releases ammonia nitrogen, reducing the amount of ammonium salts (such as ammonium chloride) added to the subsequent phosphorus recovery unit to recover struvite, further saving the cost of phosphorus recovery;

[0101] ④ After the sludge is cracked, the dewatering performance can be improved, and the amount of sludge dewatering chemicals added in the subsequent sludge dewatering unit can be reduced, which is beneficial to improving the treatment efficiency of the subsequent sludge dewatering unit and reducing the cost of sludge dewatering;

[0102] ⑤ The pH of the cracked sludge is adjusted to 9-10 (preferably 9-9.5) by adding acid, and after mixing with the remaining sludge, in this embodiment, the pH of the mixed sludge entering the sludge thickening tank can be between 8-9, forming the most suitable pH for anaerobic biological phosphorus release in the sludge thickening tank.

[0103] Table 1 Main components of sludge before and after sludge concentration

[0104]

[0105] Note: The sludge concentration before concentration (Q1 residue, referring to the excess sludge entering the sludge concentration unit via the excess sludge conveying pipeline 12) in the table is 8 g / L (MLSS). The sludge concentration after sludge concentration and disruption (Q6 disruption) is 20 g / L (MLSS). In this example, the volume of the sludge after concentration and disruption (Q6 disruption) is only approximately 8% of the volume of the excess sludge Q1 residue entering the sludge concentration tank via the excess sludge conveying pipeline. The sludge composition data are all measured by centrifuging the sludge and collecting the supernatant.

[0106] The excess sludge before concentration (Q1 excess) and the sludge after cracking (Q6 cracking) are mixed before entering the sludge concentration unit 1 and then enter the sludge concentration unit 1. Compared with the conventional gravity concentration process, this embodiment not only realizes the physical concentration of sludge in the sludge concentration unit 1, but also achieves the following technical effects:

[0107] ① The excess sludge (Q1 excess) and the cracked sludge (Q6 cracked) are mixed before entering the sludge thickening unit. The mixing process and pipeline transportation process can enable the microorganisms in the excess sludge (Q1 excess) to quickly adsorb the organic components in the cracked sludge (Q6 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 organic matter and microbial cells due to small fluid disturbance in the sludge thickening tank, and allowing more organic components in the cracked sludge to enter the microbial cells in the excess sludge to achieve anaerobic phosphorus release;

[0108] ② Phosphorus-rich microorganisms (such as polyphosphate bacteria) in the residual sludge release the phosphorus in the cells into the water (in the form of orthophosphate, PO4) under the action of breaking down the organic components provided by the sludge under the anaerobic conditions in the sludge concentration unit 1. 3- The anaerobic biological phosphorus release of the entire amount of excess sludge was achieved, creating conditions for subsequent phosphorus recovery;

[0109] ③ The organic nitrogen and organic phosphorus contained in the cracked sludge are converted into ammonia nitrogen and orthophosphate (PO4 3- ), the conversion of organic nitrogen into ammonia nitrogen can save the dosage of ammonia nitrogen reagents 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 through struvite crystallization).

[0110] The test data of the main components of the supernatant before sludge concentration, at the water inlet of the sludge concentration unit, and at the effluent of the sludge concentration unit are shown in Table 2. This embodiment has a significant effect on phosphorus release from sludge, and most of the phosphorus exists in the form of orthophosphate, which can be recovered by the subsequent phosphorus recovery unit 8.

[0111] Table 2 Main components of sludge before thickening, sludge thickening tank inlet, and sludge thickening tank effluent

[0112]

[0113] Note: The sludge concentration (MLSS) before sludge concentration (Q1 residual, referring to the excess sludge entering the sludge concentration unit via excess sludge conveying pipeline 12) in the table is 8 g / L. The data before sludge concentration are measured by centrifuging the sludge and taking the supernatant. The sludge concentration of the mixed liquor at the sludge concentration tank inlet is approximately 8.8 g / L. In this example, the volume of the concentrated sludge is 40% of the volume of the pre-concentration sludge (Q1 residual). The concentrated sludge entering the decomposition unit (Q4 decomposition) accounts for 20% of the total volume of the concentrated sludge (Q4 decomposition + Q5 dewatering). The NaOH reagent added to the sludge decomposition unit is in solid form. The density of the post-decomposition sludge is similar to that of the pre-decomposition sludge (Q4 decomposition). The volume of the post-decomposition sludge (Q6 decomposition) accounts for 8% of the volume of the pre-concentration sludge (Q1 residual). The composition of the mixed liquor at the sludge concentration tank inlet is measured by taking the supernatant obtained by centrifuging the mixed liquor.

[0114] The phosphorus recovery unit 8 described in this embodiment uses magnesium ammonium phosphate crystals (struvite) to recover phosphorus in the liquid phase. The wastewater containing orthophosphate from the sludge concentration unit 1 and the sludge dehydration unit 3 is mixed with reagents (magnesium chloride, ammonium chloride, and sodium hydroxide) in the pipeline mixer H and then enters the phosphorus recovery unit 8. The dosage of magnesium chloride and ammonium chloride reagents is based on the ratio of Mg:NH4 + : P = 1.3:1.3:1 (molar ratio), the pH of the crystallization reaction is controlled at 9.5-10, the third stirring blade rotates to generate an upward thrust, stirring and mixing the liquid and suspended particles, so that the liquid mixture circulates.

[0115] The orthophosphate in the influent and the crystal-forming ions (magnesium ions and ammonium ions) in the reagent are contacted and mixed under the mechanical stirring conditions of the third stirring blade to form tiny magnesium ammonium phosphate crystals (crystal nuclei). The tiny crystals circulate in the first water flow ascending channel A and the water flow descending channel B along with the water flow. When passing through the folded plate vortex assembly 8.9 and the modular vortex assembly 8.10, the crystal-forming ions in the wastewater are further contacted and mixed under the action of the large number of micro-vortices generated by the vortex assembly, and the tiny crystal particles are fluidized. Under the action of the micro-vortices, the tiny crystals and the crystal nuclei and the crystal-forming ions fully collide and contact with each other. Secondary nucleation occurs, achieving self-induced crystallization without the need for external seed crystals. The crystal particle size gradually increases. When the crystal particle size and mass increase to a certain level, large crystals gradually and automatically separate from the circulating water flow under the action of gravity and flow into the crystal aggregation area D. After crystallization is completed, the water flow enters the annular solid-liquid separation area. Fine crystal particles entrained in the water flow are further separated from the solid by gravity and the action of the inclined plate assembly. After the crystal particles settle, they slide to the crystal aggregation area D under the action of gravity. The supernatant after precipitation is collected upward and collected in the water collection tank 8.4, and discharged from the phosphorus recovery unit 8 through the drain pipe 8.6. The struvite crystals accumulated in the crystal aggregation area D are regularly discharged through the discharge port 8.7 to a separate dehydration and separation device. In this embodiment, the phosphorus recovery unit has an orthophosphate recovery rate of greater than 80%, and the recovered product is struvite.

[0116] The low-phosphorus liquid discharged from the phosphorus recovery unit is returned to the biochemical pool at the front end of the sewage treatment system through the seventh pipeline 13.

[0117] In this embodiment, the sludge dewatering unit adopts existing conventional sludge dewatering technology and equipment (such as a horizontal screw centrifugal dewatering machine) to dewater the concentrated sludge. During the dehydration process, no aluminum salt, iron salt or other reagents that can form precipitates with phosphate ions are added. Only a small amount of polyacrylamide is added. The sludge dewatering liquid is returned to the phosphorus recovery unit to recover phosphorus, and the dewatered dry sludge is transported out for separate disposal.

[0118] Applying the technical solution of this embodiment has the following beneficial effects:

[0119] 1. Existing sludge decomposition and phosphorus release technologies all use the method of decomposing the entire amount of excess sludge. This embodiment only requires the addition of alkali to decompose 10%-20% of the concentrated sludge, and then uses the COD (organic component) released by the decomposition as a carbon source for the polyphosphate microorganisms (polyphosphate bacteria) in the entire amount of excess sludge entering the thickening tank. Anaerobic phosphorus release occurs in the anaerobic environment of the sludge thickening tank without the need for an external carbon source. The new scheme of alkaline phosphorus decomposition of a small amount of concentrated sludge + anaerobic biological phosphorus release of the entire amount of excess sludge achieves low-cost and efficient phosphorus release from the entire amount of excess sludge. In this embodiment, the equipment investment and operating costs (drug consumption, electricity consumption) of the sludge breakdown unit are only equivalent to 10%-20% of the existing full-volume sludge alkaline phosphorus decomposition process, and the equipment footprint can also be saved; the addition of the broken sludge shortens the anaerobic biological phosphorus release time of the remaining sludge in the gravity thickening tank to 6 hours, which is only 1 / 80 of the time required for the traditional sludge anaerobic digestion process (anaerobic digestion time 20-30 days), greatly reducing the equipment investment and operating costs of sludge phosphorus release and phosphorus recovery.

[0120] 2. Some of the phosphorus and nitrogen elements released into the liquid phase by existing physical phosphorus decomposition (ultrasound, thermal hydrolysis, mechanical ball milling) and chemical phosphorus decomposition (acid, alkali) technologies exist in the form of organic phosphorus and organic nitrogen, which are difficult to recycle. In this embodiment, the sludge after alkaline decomposition is returned to the thickening tank. The organic phosphorus and organic nitrogen released during the sludge decomposition process are converted into orthophosphate and ammonia nitrogen by the anaerobic environment of the thickening tank and the action of anaerobic microorganisms in the residual sludge. They can be recovered by the subsequent phosphorus recovery unit, which can further improve the phosphorus recovery rate and reduce the cost of adding ammonia nitrogen reagents to the phosphorus recovery unit.

[0121] 3. At present, most urban sewage treatment plants in China adopt the technical route of sludge gravity concentration + sludge dewatering for the treatment of residual sludge, and have built sludge concentration tanks and sludge dewatering facilities. In this embodiment, the gravity concentration tank adopts the existing conventional gravity concentration tank. When it is necessary to recover phosphorus from the residual sludge of the existing sewage treatment plant, it is only necessary to add a sludge cracking component (only 10%-20% of the total concentrated sludge needs to be cracked, and there is no need to crack the entire amount of concentrated sludge), a sludge phosphorus recovery device, and a control system. By making corresponding modifications to the pipeline, the sludge phosphorus resource recovery of the existing sewage treatment plant can be economically and conveniently realized.

[0122] 4. In this embodiment, the phosphorus recovery unit adopts an outer shell, a middle shell, and an inner shell to form a three-layer shell arrangement, forming a circulating flow channel formed by the first water flow rising channel, the water flow descending channel, and the second water flow rising channel. The plug flow stirring component and the folded plate vortex component are arranged from top to bottom in the first water flow rising channel, and the modular vortex component is arranged in the water flow descending channel, forming a mechanical stirring mixed crystallization + hydraulic vortex crystallization composite system. Due to its special structure, hydraulic classification is achieved during operation, so that the solution is fully mixed with materials and the crystal particles are fluidized, and self-induction is achieved without the need for external crystal seeds. The crystal particles are larger in size and purity than those in traditional stirred crystallization. The first water flow rising channel and the water flow descending channel form a water flow circulation channel to automatically sort the crystal particles. Particles with large size and mass will automatically separate from the circulating water flow under the action of gravity and be discharged into the crystal gathering area. Crystal particles with small size and mass continue to crystallize in the water flow circulation channel. The crystal particles collected in the crystal gathering area have larger size and higher purity than those in traditional stirred crystallization. The inclined plate component is arranged in the second water flow rising channel, which can perform secondary separation on the fine crystal particles entrained in the water flow, thereby further improving the recovery efficiency of the phosphorus crystal particles.

[0123] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that various modifications and variations of the present invention are possible. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention are intended to be within the scope of protection of the present invention.

Claims

1. A method for treating excess sludge, characterized in that: including a phosphorus release step; The phosphorus releasing step comprises the steps: Step S1, sending the phosphorus-rich excess sludge (Q1) to the sludge concentration unit (1) for concentration treatment to obtain concentrated sludge (Q3) and supernatant (Q2); Step S2: sending the concentrated sludge with a mass or flow ratio of 10% to 20% to the sludge decomposition unit (2.1) for decomposition treatment to obtain decomposition-treated sludge; sending the remaining concentrated sludge to the sludge dehydration unit (3) for sludge dehydration treatment to obtain dry sludge and sludge dehydrated liquid; Step S3, circulating the cracked sludge obtained in step S2 to the sludge concentration unit (1) in step S1; It also includes a phosphorus recovery step, specifically including: The supernatant obtained in step S1 is input into a phosphorus recovery unit (8) for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water; Alternatively, the supernatant obtained in step S1 and the sludge dewatering liquid obtained in step S2 are input into a phosphorus recovery unit (8) for phosphorus recovery treatment to obtain phosphorus crystals and low-phosphorus water.

2. The method for treating excess sludge according to claim 1, wherein: The step S3 also includes a pH adjustment step, specifically: the sludge after the cracking treatment in step S2 is sent to the pH adjustment unit (2.2) for pH adjustment to obtain pH-adjusted sludge, and then the pH-adjusted sludge (Q6) is circulated to the sludge concentration unit in step S1; the pH value in the pH adjustment unit (2.2) is controlled within a range of 9-10; the pH value in the sludge cracking unit is controlled within a range of 10.8-11.5; the sludge after the cracking treatment in step S3 is mixed with the phosphorus-rich residual sludge and then transported to the sludge concentration unit through a pipeline for a flow time of not less than 3 seconds.

3. The method for treating excess sludge according to claim 2, wherein: The concentration time of the phosphorus-rich excess sludge in the sludge concentration unit is 6-24 hours; the reaction time of the sludge decomposition treatment in the sludge decomposition unit is 20-100 minutes; the control range of the pH value in the pH adjustment unit is 9-9.5; the pH value of the sludge after the decomposition treatment and the phosphorus-rich excess sludge after mixing in step S3 is 8-9.

4. The method for treating excess sludge according to any one of claims 1 to 3, characterized in that: The sludge concentration unit (1) is a gravity concentration tank; the sludge concentration unit (1) is provided with a residual sludge feed port (1.1), a concentrated sludge discharge port (1.2), and a supernatant discharge port (1.3); the residual sludge feed port (1.1) is connected to a residual sludge conveying pipeline (12); The sludge breaking unit (2.1) 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 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 connected to the first accommodating cavity (A1.1); the first mud inlet pipe (A3) is connected to the concentrated sludge outlet (1.2) of the sludge concentration unit through a first pipe (4); the first mud outlet pipe (A4) is connected to the pH value adjustment unit (2.2) through a fourth pipe (7); 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).

5. The method for treating excess sludge according to claim 4, wherein: 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 through 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 measuring electrode.

6. The method for treating excess sludge according to claim 4, characterized in that: 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 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 detachable cover (A1.4).

7. The method for treating excess sludge according to claim 4, characterized in that: The pH value adjustment unit (2.2) comprises a second shell (B1), a second stirring assembly (B2), a second mud inlet pipe (B3) and a second mud 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 connected to the second accommodating cavity (B1.1); the second mud inlet pipe (B3) is connected to the first mud outlet pipe (A4) via a fourth pipe (7), and the second mud outlet pipe (B4) is connected to the residual sludge inlet (1.1) via a third pipe (6); 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), and 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).

8. The method for treating excess sludge according to claim 1, wherein: The phosphorus recovery unit (8) comprises an outer shell (8.1), a middle shell (8.2), an inner shell (8.3), a water inlet pipe (8.5), a drain pipe (8.6), a discharge port (8.7), a plug-flow stirring assembly (8.8), a folded plate vortex assembly (8.9), a modular vortex assembly (8.10), and a slanted plate assembly (8.11); The outer shell (8.1) comprises a first cylindrical barrel ( 8.1.1) and a first conical cylinder (8.1.2) that is wide at the top and narrow at the bottom and closed at the bottom, wherein a receiving chamber (8.1.3) is provided in the first cylindrical cylinder (8.1.1), and a receiving chamber (8.1.4) communicating with the receiving chamber (8.1.3) is provided in the first conical cylinder (8.1.2); a water collecting trough (8.4) is provided on the upper portion of the receiving chamber (8.1.3); The middle shell (8.2) comprises a second cylindrical body (8.2.1) and a second conical body (8.2.2) which is wide at the top and narrow at the bottom and has an opening at the lower end, the second cylindrical body (8.2.1) having a accommodating chamber c (8.2.3) provided therein, and the second conical body (8.2.2) having a accommodating chamber d (8.2.4) in communication with the accommodating chamber c (8.2.3) provided therein; the upper end of the second conical body (8.2.2) is located in the accommodating chamber a (8.1.3) and the lower end thereof is located in the accommodating chamber b (8.1.4); The inner shell (8.3) comprises a third cylindrical body (8.3.1) disposed within the c accommodating cavity (8.2.3); the third cylindrical body (8.3.1) comprises an e accommodating cavity (8.3.2) with openings at both upper and lower ends; The e accommodating chamber (8.3.2) forms a first water flow ascending channel (A); a water flow descending channel (B) is formed between the inner wall of the second cylindrical cylinder (8.2.1) and the outer wall of the third cylindrical cylinder (8.3.1); the annular area between the inner wall of the first cylindrical cylinder (8.1.1) and the first conical cylinder (8.1.2), the outer wall of the second cylindrical cylinder (8.2.1) and the second conical cylinder (8.2.2), and the water collecting trough (8.4) form a second water flow ascending channel (C); the plug-flow stirring assembly (8.8) and the folded plate vortex assembly (8.9) are arranged from top to bottom in the first water flow ascending channel (A); the modular vortex assembly (8.10) is arranged in the water flow descending channel (B); the inclined plate assembly (8.11) is arranged in the second water flow ascending channel (C); the lower part of the accommodating chamber (8.1.4) forms a crystal aggregation area (D); The water inlet pipe (8.5) is connected to the supernatant discharge port (1.3), and the water inlet pipe (8.5) penetrates the side wall of the first columnar barrel (8.1.1) and the side wall of the second columnar barrel (8.2.1) and is inserted into the upper part of the first water flow rising channel (A), and the water outlet end of the water inlet pipe (8.5) is lower than the position of the water collecting tank (8.4); the drainage pipe (8.6) is connected to the water collecting tank (8.4); and the discharge port (8.7) is connected to the crystal aggregation area (D).

9. The method for treating excess sludge according to claim 8, characterized in that: The plug-flow stirring assembly (8.8) includes a third driving power source (8.8.1), a third stirring shaft (8.8.2) and a third stirring blade (8.8.3), and the connection end of the third stirring shaft (8.8.2) is connected to the third driving power source ( 8.8.1), the third stirring blade (8.8.3) is arranged on the free end of the third stirring shaft (8.8.2); the water outlet end of the water inlet pipe (8.5) is located 20-50 cm above the third stirring blade (8.8.3); The folded plate vortex component (8.9) is located directly below the plug-flow stirring component (8.8), and the folded plate vortex component (8.9) comprises a first folded plate (8.9.1) and a second folded plate (8.9.2) arranged in parallel. The first folded plate ( 8.9.1) comprises a plurality of connecting plates connected in sequence, wherein the angle α between two adjacent connecting plates is 80°-100°; the first folding plate (8.9.1) and the second folding plate (8.9.2) are mirror-image structures; The modular vortex assembly (8.10) comprises a plurality of vortex units stacked or spaced apart, each vortex unit being a hollow cylindrical body formed by a first vertical plate (8.10.1), a second vertical plate (8.10.2), an upper arc-shaped outer frame (8.10.3), an upper arc-shaped inner frame (8.10.4), a lower arc-shaped outer frame (8.10.5) and a lower arc-shaped inner frame (8.10.6); a vortex sheet is installed in the vortex unit, and the cross-section of the vortex sheet is at least one of a triangle, a semicircle and a rectangle; The inclined plate assembly (8.11) comprises a plurality of settling inclined plates arranged in parallel, the settling inclined plates being arranged at an angle to the inner wall of the a-accommodation chamber; and the inclined plate assembly (8.11) is located in the middle and lower part of the a-accommodation chamber.

Images