System and method for resourceful collaborative treatment of domestic sewage and kitchen waste

Abstract

The application discloses a system and method for resourceful and collaborative treatment of domestic sewage and kitchen waste, which is provided with an organically connected enhanced pretreatment unit, a carbon and phosphorus recovery unit, an enhanced biological treatment unit, a deep treatment unit and an energy recovery unit, is based on nitrification and denitrification denitrification treatment, is supplemented by deep treatment of pollutants, efficiently recovers carbon and phosphorus at the front end, adopts a water source heat pump and cogeneration at the tail end to realize energy recycling, deeply treats pollutants of the domestic sewage, outputs high-quality recycled water, collaboratively treats part of the kitchen waste, maximally recycles and utilizes energy and resources in the domestic sewage and the kitchen waste, reduces operation cost of a sewage plant, and contributes to carbon emission reduction and phosphorus crisis solving.

Description

Technical Field

[0001] This invention relates to the field of wastewater treatment technology, specifically to a system and method for the resource-based co-treatment of domestic sewage and kitchen waste. Background Technology

[0002] In recent years, eutrophication of water bodies has become increasingly severe, directly impacting people's daily lives and the normal production activities of industrial enterprises, causing huge direct and indirect economic losses, and adversely affecting the harmonious and stable development of the entire society. Nitrogen and phosphorus are the main causes of eutrophication, and phosphorus is also one of the most important and non-renewable non-metallic mineral resources. It is estimated that the world's currently economically exploitable phosphate rock will be exhausted by the end of this century, and a phosphorus crisis is imminent. Studies show that about 15% of global phosphorus demand is lost annually in wastewater. Therefore, recovering phosphorus from wastewater is a very effective way to alleviate the phosphorus crisis.

[0003] Most existing wastewater treatment plants rely primarily on chemical phosphorus removal for phosphorus removal, and most processes use biological methods like nitrification and denitrification to remove nitrogen. However, wastewater often lacks sufficient carbon sources, necessitating additional carbon supplementation to ensure effluent quality. This addition of carbon sources and phosphorus removal agents significantly increases the operating costs of wastewater treatment plants. Furthermore, wastewater treatment typically consumes substantial amounts of energy to achieve effluent quality standards, making it a high-energy-consuming and high-cost industry.

[0004] Meanwhile, wastewater treatment plants generate large amounts of sludge during operation. Currently in my country, sludge is mainly treated by dewatering and drying to reduce its volume before being sent to landfills or incinerated. However, sludge contains a large amount of organic matter, which can serve as a substrate for anaerobic fermentation. The reason why anaerobic digestion of sludge has not been widely applied is mainly because sludge has a low carbon-to-nitrogen ratio and low content of easily degradable organic matter, making direct anaerobic fermentation alone inefficient. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention provides a system and method for the resource-based co-treatment of domestic sewage and kitchen waste.

[0006] The technical solution adopted in this invention is:

[0007] A system for the resource-based co-treatment of domestic sewage and kitchen waste includes: an enhanced pretreatment unit, a carbon and phosphorus recovery unit, an enhanced biological treatment unit, an advanced treatment unit, and an energy recovery unit;

[0008] The enhanced pretreatment unit is used to remove suspended solids and gravel from domestic sewage;

[0009] The carbon and phosphorus recovery unit includes a flocculation sedimentation tank, a hydrothermal reactor, a MAP recovery device, a first-stage anaerobic reactor, a second-stage anaerobic reactor, a sedimentation tank, a ferrous phosphate sedimentation tank, and a sludge dewatering device.

[0010] The domestic sewage treated by the enhanced pretreatment unit enters the flocculation sedimentation tank for flocculation and sedimentation to obtain PFC sludge; the supernatant produced by the flocculation sedimentation tank enters the enhanced biological treatment unit, the effluent from the enhanced biological treatment unit enters the deep treatment unit, and the effluent from the deep treatment unit is discharged after meeting the standards.

[0011] The enhanced biological treatment unit includes an anoxic tank, an aerobic tank, a post-anoxic tank, a post-aerobic tank, and a secondary sedimentation tank connected in sequence.

[0012] The concentrated sludge produced by the flocculation sedimentation tank and the excess sludge produced by the secondary sedimentation tank are fed into the hydrothermal reactor together.

[0013] The supernatant produced by the hydrothermal reactor enters the MAP recovery unit, where magnesium ammonium phosphate crystals are generated. The carbon-containing supernatant produced by the MAP recovery unit enters the anoxic tank, the post-anoxic tank, and the second-stage anaerobic reactor. The phosphorus-rich sludge produced by the hydrothermal reactor enters the first-stage anaerobic reactor along with the kitchen waste. The hydrolysis and acidification products from the first-stage anaerobic reactor enter the sedimentation tank.

[0014] The supernatant from the sedimentation tank enters the ferrous phosphate sedimentation tank, where ferrous phosphate crystals are formed. The supernatant from the ferrous phosphate sedimentation tank then enters the second-stage anaerobic reactor. The hydrolyzed sludge from the sedimentation tank enters the second-stage anaerobic reactor. The biogas produced in the second-stage anaerobic reactor enters the energy recovery unit for power generation. The sludge produced in the second-stage anaerobic reactor enters the sludge dewatering device to form sludge cake.

[0015] Furthermore, the enhanced pretreatment unit includes a coarse screen, a fine screen, and a vortex grit chamber connected in sequence, with the effluent from the vortex grit chamber entering the flocculation sedimentation tank.

[0016] Furthermore, the advanced treatment unit includes a high-density sedimentation tank, a V-type filter, and an ozone contact oxidation tank connected in sequence. The effluent from the secondary sedimentation tank enters the high-density sedimentation tank, and the effluent from the ozone contact oxidation tank is discharged after meeting the standards.

[0017] Furthermore, the effluent from the ozone contact oxidation tank enters the energy recovery unit to recover heat energy.

[0018] Furthermore, the energy recovery unit includes a water source heat pump and a cogeneration system. The effluent from the ozone contact oxidation tank is fed into the water source heat pump to produce hot water, and the biogas produced in the second-stage anaerobic reactor is fed into the cogeneration system to generate electricity.

[0019] A method for the resource-based co-treatment of domestic sewage and kitchen waste in the above system includes the following steps:

[0020] (1) Domestic sewage enters the enhanced pretreatment unit, where suspended solids are removed by screen filtration and sand and gravel are removed by sedimentation.

[0021] (2) The domestic sewage that has been pretreated by the enhanced pretreatment unit enters the carbon and phosphorus recovery unit. First, in the flocculation sedimentation tank, most of the SS, COD and TP in the raw water are flocculated and precipitated by adding polyferric chloride to obtain PFC sludge and supernatant.

[0022] (3) The supernatant obtained in step (2) enters the enhanced biological treatment unit, where nitrification and denitrification reactions are carried out in the anoxic tank and the aerobic tank. Nitrate nitrogen is directly reduced to nitrogen gas and discharged from the system. The effluent from the aerobic tank enters the secondary sedimentation tank for sedimentation and separation.

[0023] (4) The supernatant separated in the secondary sedimentation tank enters the advanced treatment unit, and undergoes coagulation sedimentation, filtration and advanced oxidation in sequence to obtain compliant discharge water;

[0024] (5) The remaining sludge produced in the secondary sedimentation tank and the PFC sludge obtained in step (2) are fed into a hydrothermal reactor for hot hydrolysis to obtain supernatant and phosphorus-rich sludge.

[0025] (6) The supernatant obtained in step (5) enters the MAP recovery device. By adding magnesium chloride in the MAP recovery device, the phosphate ions and some ammonium ions in the supernatant are converted into magnesium ammonium phosphate crystals. The carbon-containing supernatant produced by the MAP recovery device is used as a supplementary carbon source to supply the carbon and phosphorus recovery unit and the enhanced biological treatment unit.

[0026] (7) The phosphorus-rich sludge obtained in step (5) is fed together with kitchen waste into the first-stage anaerobic reactor for hydrolysis and acidification reaction;

[0027] (8) The hydrolysis acidification products of the first-stage anaerobic reactor enter the sedimentation tank for sedimentation and separation to obtain hydrolysis supernatant and hydrolysis sludge;

[0028] (9) The hydrolysis supernatant obtained in step (8) enters the ferrous phosphate precipitation tank and the pH is adjusted by adding alkali to generate ferrous phosphate crystal precipitate and supernatant containing organic acid;

[0029] (10) The hydrolyzed sludge obtained in step (8) and the supernatant obtained in step (9) are fed into the second-stage anaerobic reactor for anaerobic digestion to produce methane. The sludge produced during the anaerobic digestion process is fed into the sludge dewatering device to generate sludge cake.

[0030] Furthermore, in step (5), the temperature of the hydrothermal reactor for hot water hydrolysis is 160-180℃, the pressure is 1.4-2.6MPa, and the time is 0.5-2 hours.

[0031] Furthermore, in step (6), the amount of MgCl2 added is: magnesium to phosphorus molar ratio 1:1.

[0032] Furthermore, the hydrolysis and acidification reaction in step (7) takes more than 48 hours, the temperature is 35-37°C, the initial pH range is 6-7, and the pH range after the hydrolysis and acidification is 4-5.

[0033] Furthermore, in step (10), the temperature of the anaerobic digestion reaction is 35–37°C, the hydraulic retention time is 25–30 days, and the pH range is 7–7.5.

[0034] The beneficial effects of this invention are:

[0035] (1) This invention sets up an organically connected enhanced pretreatment unit, carbon and phosphorus recovery unit, enhanced biological treatment unit, advanced treatment unit and energy recovery unit. Based on nitrification and denitrification denitrification treatment, supplemented by advanced pollutant treatment, the front end performs efficient recovery of carbon and phosphorus, and the end end uses water source heat pump and cogeneration to realize energy recovery and utilization. While deeply treating pollutants in domestic sewage and producing high-quality reclaimed water, it also co-treats some kitchen waste, maximizing the recovery and utilization of energy and resources in domestic sewage and kitchen waste, greatly reducing the operating cost of sewage treatment plants, and contributing to reducing carbon emissions and solving the phosphorus crisis.

[0036] (2) The present invention performs hot water hydrolysis reaction on the concentrated sludge produced by the flocculation sedimentation tank and the excess sludge produced by the secondary sedimentation tank under high temperature and high pressure. This not only decomposes the recalcitrant macromolecular organic matter in the concentrated sludge and excess sludge to produce easily degradable soluble organic matter, thereby increasing the subsequent methane production; but also causes the microorganisms contained in the sludge to disintegrate, releasing a large amount of nitrogen and phosphorus, with the total phosphorus released being mainly phosphate ions.

[0037] (3) This invention combines chemical and biological methods. It not only recovers phosphate and ammonium ions from the supernatant of the hydrothermal reactor through MAP chemical precipitation, but also utilizes the dissimilatory iron reduction of microorganisms during the anaerobic process to convert ferric phosphate into ferrous phosphate. Furthermore, anaerobic hydrolysis and acidification provide an acidic environment to increase the solubility of ferrous phosphate, allowing phosphorus to be separated from the sludge. Compared to chemical methods for phosphorus recovery, this invention is safer and more environmentally friendly, while also reducing the use of acid and alkali reagents.

[0038] (4) This invention enables phosphorus-rich sludge and kitchen waste to be rapidly hydrolyzed and acidified in the first-stage anaerobic reactor through a two-stage anaerobic reaction, thereby accelerating the hydrolysis efficiency of recalcitrant organic matter in the phosphorus-rich sludge and providing an acidic environment for the dissolution of ferrous phosphate. Furthermore, it can simultaneously control the reaction conditions of the first and second-stage anaerobic reactors, ensuring that both are in optimal working condition. The organic acids produced in the first-stage reactor can also undergo rapid acetylation and methanation reactions in the second-stage reactor, greatly accelerating the second-stage anaerobic reaction rate and increasing the content of methanogenic bacteria in the system, thereby increasing the treatment efficiency and methane production of the entire anaerobic system.

[0039] (5) This invention utilizes sludge hot hydrolysis technology and synergistic anaerobic digestion technology of sludge and kitchen waste to make the resource utilization of sludge possible. Hot hydrolysis technology can greatly increase the hydrolysis rate of sludge and increase the content of easily biodegradable organic matter; synergistic anaerobic digestion of sludge and kitchen waste can balance the carbon-nitrogen ratio of the system, improve the stability of the anaerobic fermentation process and the overall biogas production. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the wastewater resource recovery and energy recovery treatment system of the present invention;

[0041] In the diagram: 1-Enhanced pretreatment unit; 6-Coarse screen; 7-Fine screen; 8-Swirl grit chamber; 2-Carbon and phosphorus recovery unit; 9-Flocculation sedimentation tank; 10-Hydrothermal reactor; 11-MAP recovery device; 12-First-stage anaerobic reactor; 13-Sedimentation tank; 14-Ferrous phosphate sedimentation tank; 15-Second-stage anaerobic reactor; 16-Biogas storage tank; 17-Sludge dewatering device; 3-Enhanced biological treatment unit; 18-Anoxic tank; 19-Aerobic tank; 20-Post-anoxic tank; 21-Post-aerobic tank; 22-Secondary sedimentation tank; 4-Deep treatment unit; 23-High-density clarifier; 24-V-type filter; 25-Ozone contact oxidation tank; 5-Energy recovery unit; 26-Water source heat pump; 27-Plant heating / cooling; 28-Cogeneration system. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of the present invention clearer, the technical solutions of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and a preferred embodiment.

[0043] Implementation Method 1

[0044] like Figure 1 As shown, this embodiment of the invention provides a system for the resource-based co-treatment of domestic sewage and kitchen waste, comprising: an enhanced pretreatment unit 1, a carbon and phosphorus recovery unit 2, an enhanced biological treatment unit 3, a deep treatment unit 4, and an energy recovery unit 5.

[0045] The enhanced pretreatment unit 1 includes a coarse screen 6, a fine screen 7, and a vortex grit chamber 8 connected in sequence; the front end of the coarse screen 6 is equipped with a domestic sewage inlet, and the rear end of the vortex grit chamber 8 is equipped with a clean water outlet. The enhanced pretreatment unit 1 can remove large sand and suspended solids from the water, while reducing the amount of residual sludge generated subsequently.

[0046] The carbon and phosphorus recovery unit 2 includes a flocculation sedimentation tank 9, a hydrothermal reactor 10, a MAP recovery device 11, a first-stage anaerobic reactor 12, a sedimentation tank 13, a ferrous phosphate sedimentation tank 14, a second-stage anaerobic reactor 15, a biogas storage tank 16, and a sludge dewatering device 17. The enhanced biological treatment unit 3 includes an anoxic tank 18, an aerobic tank 19, a post-anoxic tank 20, a post-aerobic tank 21, and a secondary sedimentation tank 22 connected in sequence.

[0047] Domestic sewage treated by the enhanced pretreatment unit 1 enters the flocculation sedimentation tank 9 for flocculation and sedimentation to obtain PFC sludge; the supernatant produced by the flocculation sedimentation tank 9 enters the enhanced biological treatment unit 3. The concentrated sludge produced by the flocculation sedimentation tank 9, together with the residual sludge from the secondary sedimentation tank 22, enters the hydrothermal reactor 10; the supernatant from the hydrothermal reactor 10 enters the MAP recovery device 11 to generate magnesium ammonium phosphate crystals; the carbon-containing supernatant produced by the MAP recovery device 11 enters the anoxic tank 18, the post-anoxic tank 20, and the second-stage anaerobic reactor 15; the phosphorus-rich sludge produced by the hydrothermal reactor 10, together with kitchen waste, enters the first-stage anaerobic reactor 12; the first-stage anaerobic reactor 12 undergoes hydrolysis. Acidification products enter sedimentation tank 13; the hydrolyzed supernatant from sedimentation tank 13 enters ferrous phosphate sedimentation tank 14, where ferrous phosphate crystals are generated; the supernatant containing organic acids separated from ferrous phosphate sedimentation tank 14 enters the second-stage anaerobic reactor 15; the hydrolyzed sludge from sedimentation tank 13 enters the second-stage anaerobic reactor 15; the biogas generated from the second-stage anaerobic reactor 15 enters biogas storage tank 16; and the sludge generated from the second-stage anaerobic reactor 15 enters sludge dewatering device 14 to generate sludge cake.

[0048] The flocculation sedimentation tank 9 is equipped with a chemical inlet and a ferrous phosphate (PFC) feeding device. The ferrous phosphate (PFC) feeding device adds flocculant to the flocculation sedimentation tank 9 through the chemical inlet. The flocculant can be an inorganic flocculant or an organic flocculant. Inorganic flocculants include polyferric chloride (PFC), polyaluminum chloride (PAC), etc. PFC is selected in this system to provide conditions for subsequent ferrous phosphate recovery.

[0049] The hydrothermal reactor 10 is equipped with a domestic sludge inlet and a waste sludge inlet. Domestic sludge produced in the flocculation sedimentation tank 9 enters the hydrothermal reactor 10. In existing wastewater treatment processes, domestic sludge from the flocculation sedimentation tank is typically dewatered and then landfilled or incinerated, failing to efficiently utilize the organic matter in the sludge. Furthermore, incineration plants have high requirements for the moisture content of dewatered sludge. This invention enables effective resource utilization of domestic sludge by subjecting it and the waste sludge from the enhanced biological treatment unit 3 to a high-temperature, high-pressure hydrothermal reaction in the hydrothermal reactor using superheated steam. This not only allows for rapid and efficient hydrolysis of both the domestic sludge and waste sludge, increasing the content of readily degradable organic matter and enhancing anaerobic fermentation, but also releases phosphorus from the waste sludge, particularly organic phosphorus from biological sources, primarily in the form of phosphate, facilitating subsequent phosphorus recovery. The supernatant produced in the hydrothermal reactor 10 enters the MAP recovery tank 11.

[0050] The MAP recovery tank 11 is equipped with a magnesium chloride inlet and a magnesium chloride feeding device. The magnesium chloride feeding device adds magnesium chloride to the MAP recovery tank 11 through the magnesium chloride inlet. The amount of magnesium chloride added should make the magnesium-phosphorus molar ratio in the reaction system of the MAP recovery tank 11 1:1. The carbon-containing supernatant produced by the MAP recovery tank 11 can not only supplement the carbon source required by the subsequent anoxic tank and post-anoxic tank, but the remaining carbon-containing supernatant can also be used as raw material to input into the second-stage anaerobic reactor.

[0051] The first-stage anaerobic reactor 12 is equipped with a food waste inlet. Food waste is a substrate that is easily hydrolyzed and acidified, which can not only co-ferment with sludge in anaerobic fermentation, but also rapidly lower the pH of the entire anaerobic system to 4-5, creating optimal conditions for sludge hydrolysis and acidification and subsequent dissolution of ferrous phosphate. The first-stage anaerobic reactor 12 has a constant-temperature water bath heating jacket to provide a mesophilic reaction environment, and also has a stirring function to ensure that the food waste, phosphorus-rich sludge, and microorganisms in the reactor are fully mixed under the action of the stirring equipment.

[0052] The second-stage anaerobic reactor 15 is equipped with a biogas outlet. The second-stage anaerobic reactor has a constant temperature water bath heating jacket to provide a medium temperature reaction environment, and has stirring, bottom slag discharge and top scum removal functions to ensure the normal operation of the methanogenic reaction.

[0053] The sludge dewatering device 17 is equipped with a sludge cake outlet and a biogas slurry outlet; specifically, the sludge dewatering system can be a filter press, centrifuge or other devices, and preferably the solid content of the dewatered sludge cake is in the range of 15wt% to 25wt%.

[0054] By setting up carbon and phosphorus recovery unit 2, carbon and phosphorus resources can be recovered at the front end of the system, and biogas can be generated for power generation in subsequent units. Part of the generated carbon source can supply the subsequent enhanced biological treatment unit. While achieving carbon and phosphorus recovery, this not only reduces the processing load of subsequent processes but also effectively recovers energy and resources. Furthermore, this carbon and phosphorus recovery unit combines chemical and biological methods for phosphorus recovery. Through MAP precipitation, microbial dissimilatory iron reduction, and anaerobic hydrolysis acidification to provide an acidic environment for the dissolution of ferrous phosphate, phosphorus recovery is safer, more environmentally friendly, and more efficient, reducing the use of acid and alkali reagents. At the same time, the two-stage anaerobic reactor also significantly increases the anaerobic digestion efficiency and biogas production of phosphorus-rich sludge and kitchen waste.

[0055] The secondary sedimentation tank 22 returns sludge to the anoxic tank 18 via a sludge return pipe. In actual use, operating parameters can be adjusted according to different conditions such as influent concentration and temperature. The aerobic tank 19 returns nitrified liquid to the anoxic tank 18 via a nitrification liquid return pipe; different operating parameters are adjusted according to different conditions such as influent concentration and temperature. Preferably, the sludge return ratio is 100-200%, and the digestate return ratio is 300-400%. Preferably, the dissolved oxygen (DO) in the aerobic tank is controlled at 2-4 mg / L.

[0056] The anoxic pool 18 is equipped with a flow promoter to achieve mud-water mixing and mixed liquid flow.

[0057] The aerobic tank 19 is uniformly equipped with an aeration system and aeration pipes at the bottom, providing a good aerobic environment for microorganisms, and achieving uniform mixing of mud and water through aeration.

[0058] The post-anoxic tank 20 is equipped with a dosing device, and preferably the dissolved oxygen (DO) in the post-aerobic tank is controlled at 2-4 mg / L.

[0059] The enhanced biological treatment unit 3 can effectively remove organic pollutants and total nitrogen from wastewater through multi-stage biological reactions, improve the quality of effluent, and ensure that the effluent meets discharge standards.

[0060] The advanced treatment unit 5 includes a high-density clarifier 23, a V-type filter 24, and an ozone contact oxidation tank 25 connected in sequence.

[0061] The effluent from the secondary sedimentation tank 22 enters the high-density clarifier 23, which is equipped with PAC and PAM dosing devices. Preferably, the dosages of PAC and PAM are 10–40 mg / L and 0.1–5 mg / L, respectively. This is used to address the problem of instantaneous exceedances of total phosphorus in the effluent due to water quality fluctuations under ultra-high discharge standards.

[0062] The V-shaped filter 24 is equipped with uniformly coarse quartz sand filter media to solve the problem of instantaneous exceedance of suspended solids (SS) in the effluent caused by water quality fluctuations under ultra-high discharge standards.

[0063] The ozone contact oxidation tank 25 is equipped with an ozone dosing device to address the issue of instantaneous COD exceeding the standard in the effluent due to water quality fluctuations under ultra-high emission standards. Simultaneously, the ozone contact oxidation tank also serves as an effluent disinfection and decolorization unit. Preferably, the contact time in the ozone contact oxidation tank is 15–30 minutes, and the ozone dosage is 5–20 mg / L.

[0064] The advanced treatment unit 4 further removes trace pollutants from wastewater through sedimentation, filtration, and advanced anaerobic processes, enabling it to meet discharge standards or be used as recycled water.

[0065] The energy recovery unit includes a water source heat pump 26 and a combined heat and power system 28.

[0066] Part of the effluent from the ozone contact oxidation tank 25 enters the water source heat pump 26 to produce hot water. This hot water can be connected to a heating pipeline for heating the plant area. The water source heat pump 26 can fully recover the heat energy from the water. Preferably, the water source heat pump can adopt an intelligent operation and scheduling mode. The design parameters and operating mode for the combined operation of the water source heat pump and the gas boiler are determined based on a technical and economic comparison.

[0067] The biogas in the biogas storage tank 16 enters the cogeneration system 28 and generates electricity through the generator set. At the same time, the hot flue gas generated during the operation of the generator set can also be recycled for waste heat. The resulting waste heat recovery hot water can provide the required temperature environment for the first and second stage anaerobic reactors.

[0068] Energy recovery unit 5 can recover the energy from the recycled water produced at the back end, and at the same time use the biogas generated by the carbon and phosphorus recovery unit to generate electricity, thus achieving efficient energy recovery and utilization.

[0069] Implementation Method 2

[0070] This embodiment provides a method for the resource-based co-treatment of domestic sewage and kitchen waste using the system described in Embodiment 1, comprising the following steps:

[0071] (1) Domestic sewage enters the enhanced pretreatment unit. After the suspended solids in the water are removed by the screen filter, the sand and gravel in the water are removed by the sedimentation. The sewage first passes through the coarse and fine screens to remove large suspended solids in the sewage; then it enters the vortex grit chamber to remove inorganic sand and gravel with a specific gravity greater than 2.65 and a particle size greater than 0.2mm in the sewage, so as to prevent the pipes from being blocked and mechanical wear caused in the subsequent treatment process.

[0072] (2) The domestic sewage pretreated by the enhanced pretreatment unit enters the carbon and phosphorus recovery unit. First, in the flocculation sedimentation tank, most of the SS, COD and TP in the raw water are flocculated and precipitated by adding polyferric chloride to obtain PFC sludge and supernatant.

[0073] (3) The supernatant obtained in step (2) enters the enhanced biological treatment unit, where denitrification and nitrification reactions are carried out in the anoxic tank and the aerobic tank. Nitrate nitrogen is directly reduced to nitrogen gas and discharged from the system. The effluent from the aerobic tank enters the secondary sedimentation tank for sedimentation and separation.

[0074] (4) The supernatant separated in the secondary sedimentation tank enters the advanced treatment unit, and undergoes coagulation sedimentation, filtration and advanced oxidation in sequence to obtain compliant discharge water;

[0075] (5) The remaining sludge produced in the secondary sedimentation tank and the PFC sludge obtained in step (2) are fed into a hydrothermal reactor for hot hydrolysis to obtain supernatant and phosphorus-rich sludge.

[0076] (6) The supernatant obtained in step (5) enters the MAP recovery device. By adding magnesium chloride in the MAP recovery device, the phosphate ions and some ammonium ions in the supernatant are converted into magnesium ammonium phosphate crystals. The carbon-containing supernatant produced by the MAP recovery device is used as a supplementary carbon source to supply the carbon and phosphorus recovery unit and the enhanced biological treatment unit.

[0077] (7) The phosphorus-rich sludge obtained in step (5) is fed together with kitchen waste into the first-stage anaerobic reactor for hydrolysis and acidification reaction;

[0078] (8) The hydrolysis acidification products of the first-stage anaerobic reactor enter the sedimentation tank for sedimentation and separation to obtain hydrolysis supernatant and hydrolysis sludge;

[0079] (9) The hydrolysis supernatant obtained in step (8) enters the ferrous phosphate precipitation tank and the pH is adjusted by adding alkali to generate ferrous phosphate crystal precipitate and supernatant containing organic acid;

[0080] (10) The hydrolyzed sludge obtained in step (8) and the supernatant obtained in step (9) are fed into the second-stage anaerobic reactor for anaerobic digestion to produce methane. The sludge produced during the anaerobic digestion process is fed into the sludge dewatering device to generate sludge cake.

[0081] In the preferred step (5), the hydrothermal reactor is heated at a temperature of 160–180°C, at a pressure of 1.4–2.6 MPa, and for a time of 0.5–2 hours.

[0082] The preferred dosage of MgCl2 in step (6) is: magnesium to phosphorus molar ratio 1:1.

[0083] The preferred step (7) hydrolysis acidification reaction time is more than 48 hours, the temperature is 35-37℃, the initial pH range is 6-7, and the pH range after the hydrolysis acidification is completed is 4-5.

[0084] The preferred step (7) has a carbon-to-nitrogen mass ratio of 20 to 30 for the mixture of kitchen waste and phosphorus-rich sludge.

[0085] In step (9), alkali is added to adjust the pH of the sedimentation tank to 7-8.

[0086] The preferred step (10) has an anaerobic digestion temperature of 35–37°C, a hydraulic retention time of 25–30 days, and a pH range of 7–7.5.

[0087] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications are also within the protection scope of the present invention.

Claims

1. A system for the resource-based co-treatment of domestic sewage and kitchen waste, characterized in that, include: Enhanced pretreatment unit, carbon and phosphorus recovery unit, enhanced biological treatment unit, advanced treatment unit, and energy recovery unit; The enhanced pretreatment unit is used to remove suspended solids and gravel from domestic sewage; The carbon and phosphorus recovery unit includes a flocculation sedimentation tank, a hydrothermal reactor, a MAP recovery device, a first-stage anaerobic reactor, a second-stage anaerobic reactor, a sedimentation tank, a ferrous phosphate sedimentation tank, and a sludge dewatering device. Domestic sewage treated by the enhanced pretreatment unit enters the flocculation sedimentation tank for flocculation and sedimentation to obtain PFC sludge. The supernatant produced by the flocculation sedimentation tank enters the enhanced biological treatment unit, the effluent from the enhanced biological treatment unit enters the deep treatment unit, and the effluent from the deep treatment unit is discharged after meeting the standards. The enhanced biological treatment unit includes an anoxic tank, an aerobic tank, a post-anoxic tank, a post-aerobic tank, and a secondary sedimentation tank connected in sequence. The concentrated sludge produced by the flocculation sedimentation tank and the excess sludge produced by the secondary sedimentation tank are fed into the hydrothermal reactor together. The supernatant produced by the hydrothermal reactor enters the MAP recovery unit, where magnesium ammonium phosphate crystals are generated. The carbon-containing supernatant produced by the MAP recovery unit enters the anoxic tank, the post-anoxic tank, and the second-stage anaerobic reactor. The phosphorus-rich sludge produced by the hydrothermal reactor enters the first-stage anaerobic reactor along with the kitchen waste. The hydrolysis and acidification products from the first-stage anaerobic reactor enter the sedimentation tank. The supernatant from the sedimentation tank enters the ferrous phosphate sedimentation tank, where ferrous phosphate crystals are formed. The supernatant from the ferrous phosphate sedimentation tank then enters the second-stage anaerobic reactor. The hydrolyzed sludge from the sedimentation tank also enters the second-stage anaerobic reactor. The biogas produced by the second-stage anaerobic reactor enters the energy recovery unit for power generation; the sludge produced by the second-stage anaerobic reactor enters the sludge dewatering device to generate sludge cake.

2. The system for the resource-based co-treatment of domestic sewage and kitchen waste according to claim 1, characterized in that, The enhanced pretreatment unit includes a coarse screen, a fine screen, and a vortex grit chamber connected in sequence. The effluent from the vortex grit chamber enters the flocculation sedimentation tank.

3. The system for the resource-based co-treatment of domestic sewage and kitchen waste according to claim 2, characterized in that, The advanced treatment unit includes a high-density sedimentation tank, a V-type filter, and an ozone contact oxidation tank connected in sequence. The effluent from the secondary sedimentation tank enters the high-density sedimentation tank, and the effluent from the ozone contact oxidation tank is discharged after meeting the standards.

4. The system for resource-based co-treatment of domestic sewage and kitchen waste according to claim 3, characterized in that, The effluent from the ozone contact oxidation tank enters the energy recovery unit to recover heat energy.

5. A system for the resource-based co-treatment of domestic sewage and kitchen waste according to claim 4, characterized in that, The energy recovery unit includes a water source heat pump and a cogeneration system. The effluent from the ozone contact oxidation tank is fed into the water source heat pump to produce hot water, and the biogas produced in the second-stage anaerobic reactor is fed into the cogeneration system to generate electricity.

6. A method for the resource-based co-treatment of domestic sewage and kitchen waste using the system of claim 1, characterized in that, Includes the following steps: (1) Domestic sewage enters the enhanced pretreatment unit, where suspended solids are removed by screen filtration and sand and gravel are removed by sedimentation. (2) The domestic sewage that has been pretreated by the enhanced pretreatment unit enters the carbon and phosphorus recovery unit. First, in the flocculation sedimentation tank, most of the SS, COD and TP in the raw water are flocculated and precipitated by adding polyferric chloride to obtain PFC sludge and supernatant. (3) The supernatant obtained in step (2) enters the enhanced biological treatment unit, where nitrification and denitrification reactions are carried out in the anoxic tank and the aerobic tank. Nitrate nitrogen is directly reduced to nitrogen gas and discharged from the system. The effluent from the aerobic tank enters the secondary sedimentation tank for sedimentation and separation. (4) The supernatant separated in the secondary sedimentation tank enters the advanced treatment unit, and undergoes coagulation sedimentation, filtration and advanced oxidation in sequence to obtain compliant discharge water; (5) The remaining sludge produced in the secondary sedimentation tank and the PFC sludge obtained in step (2) are fed into a hydrothermal reactor for hot hydrolysis to obtain supernatant and phosphorus-rich sludge. (6) The supernatant obtained in step (5) enters the MAP recovery device. By adding magnesium chloride in the MAP recovery device, the phosphate ions and some ammonium ions in the supernatant are converted into magnesium ammonium phosphate crystals. The carbon-containing supernatant produced by the MAP recovery device is used as a supplementary carbon source to supply the carbon and phosphorus recovery unit and the enhanced biological treatment unit. (7) The phosphorus-rich sludge obtained in step (5) is fed together with kitchen waste into the first-stage anaerobic reactor for hydrolysis and acidification reaction; (8) The hydrolysis acidification products of the first-stage anaerobic reactor enter the sedimentation tank for sedimentation and separation to obtain hydrolysis supernatant and hydrolysis sludge; (9) The hydrolysis supernatant obtained in step (8) enters the ferrous phosphate precipitation tank and the pH is adjusted by adding alkali to generate ferrous phosphate crystal precipitate and supernatant containing organic acid; (10) The hydrolyzed sludge obtained in step (8) and the supernatant obtained in step (9) are fed into the second-stage anaerobic reactor for anaerobic digestion to produce methane. The sludge produced during the anaerobic digestion process is fed into the sludge dewatering device to generate sludge cake.

7. A method for the resource-based co-treatment of domestic sewage and kitchen waste according to claim 6, characterized in that, In step (5), the temperature of the hydrothermal reactor for hot water hydrolysis is 160-180℃, the pressure is 1.4-2.6MPa, and the time is 0.5-2 hours.

8. A method for the resource-based co-treatment of domestic sewage and kitchen waste according to claim 6, characterized in that, In step (6), the amount of MgCl2 added is: magnesium to phosphorus molar ratio 1:

1.

9. A method for the resource-based co-treatment of domestic sewage and kitchen waste according to claim 6, characterized in that, The hydrolysis and acidification reaction in step (7) takes more than 48 hours, the temperature is 35-37℃, the initial pH range is 6-7, and the pH range after the hydrolysis and acidification is 4-5.

10. A method for the resource-based co-treatment of domestic sewage and kitchen waste according to claim 6, characterized in that, In step (10), the temperature of the anaerobic digestion reaction is 35-37℃, the hydraulic retention time is 25-30 days, and the pH range is 7-7.5.

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