Kitchen waste treatment system and treatment method

Abstract

The invention relates to the technical field of kitchen waste treatment, in particular to a kitchen waste treatment system and method. The kitchen waste treatment system comprises an anaerobic fermentation unit, a dehydration unit, a desulfurization unit, a decarbonization unit, a methanol synthesis unit and a wastewater treatment unit; the anaerobic fermentation unit is respectively connected with the desulfurization unit and the dehydration unit, the desulfurization unit is used for treating biogas, and the dehydration unit is used for treating anaerobic digestion liquid; the dehydration unit is further connected with the wastewater treatment unit, the desulfurization unit is further connected with the decarburization unit, the decarburization unit is further connected with the methanol synthesis unit, and the methanol synthesis unit is further connected with the wastewater treatment unit. Through the treatment process, the direct emission amount of carbon dioxide is reduced, meanwhile, the purchase cost of a carbon source and the preparation cost of a process for preparing methanol from carbon dioxide are reduced, and the purposes of reducing emission and reducing the treatment cost are achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of kitchen waste treatment, and particularly relates to a kitchen waste treatment system and a treatment method. Background Art

[0002] Kitchen waste is anaerobically digested to produce biogas and digestate. The methane content in the produced biogas is about 50% - 80%, the carbon dioxide content is about 30% - 40%, the hydrogen sulfide is about 0.1% - 3%, and there are also a small amount of water vapor and other gases. The proportion of the above gas components is related to process parameter design, material types, anaerobic reactor types, and seasonal temperatures. At present, biogas is generally divided into two utilization methods of power generation and natural gas production after desulfurization treatment: one is to enter the power generation unit, and the electricity generated is incorporated into the power grid or directly used in the factory, and the tail gases such as carbon dioxide generated during the power generation process are directly discharged; the other is to carry out decarbonization treatment, and then methane and carbon dioxide are separated, the methane is incorporated into the natural gas pipeline network, and the carbon dioxide is directly discharged into the atmosphere.

[0003] At present, the above biogas utilization methods all result in direct carbon dioxide emissions to a certain extent, causing certain environmental pollution. Taking a certain kitchen waste treatment plant as an example, with a treatment capacity of 600 tons / day, about 54,000 m 3 / day of biogas is produced. After decarbonization, about 33,000 m 3 / d of natural gas is produced, generating good economic benefits. However, at the same time, about 19,000 m 3 / d of carbon dioxide is separated. The density of carbon dioxide is 1.96 g / L, which is equivalent to a weight of about 37.24 tons / day. Calculated annually, the annual carbon dioxide emissions are about 13,592.6 tons, which is a very astonishing quantity. On the other hand, the biogas slurry produced by the anaerobic digestion of kitchen waste has the characteristics of high COD, high ammonia nitrogen, high total nitrogen, and poor biodegradability. A large amount of carbon source needs to be added during the treatment process to complete the denitrification reaction to achieve the purpose of removing total nitrogen. Taking the above kitchen waste treatment plant as an example, the treatment scale of the sewage treatment station is 800 m 3 / d, and the average influent COD, ammonia nitrogen, and total nitrogen concentrations are 8000 mg / L, 2560 mg / L, and 3120 mg / L respectively, and the discharge standards are 500 mg / L, 45 mg / L, and 70 mg / L respectively. The treatment is difficult. Sodium acetate with a concentration of 30% is added as a carbon source, and the daily dosage is about 5 tons. Calculated at the current market price of 2000 yuan / ton, the cost is about 10,000 yuan / d, and the treatment cost per ton of garbage is about 16.7 yuan / ton. For a small-scale kitchen waste treatment plant, this accounts for a relatively large proportion, and the cost pressure is extremely huge. On the other hand, whether sodium acetate or methanol is added to the biochemical reaction tank, there are problems such as explosive growth of microorganisms in a short time, high management costs, low utilization rates, and easy secondary pollution.

[0004] In view of this, the present invention is hereby proposed. Summary of the Invention

[0005] The present invention provides a kitchen waste treatment system and a treatment method, aiming to solve the problems in traditional biogas utilization methods, such as the environmental impact caused by direct carbon dioxide emissions and the high cost of carbon source procurement in the treatment process of biogas slurry wastewater in kitchen waste treatment plants. At the same time, it also solves the problems in traditional carbon dioxide to methanol processes, such as the high cost under high temperature, high pressure and the action of catalysts, as well as the problems of explosive growth of microorganisms in a short time when methanol is directly used as a carbon source, high management cost, low utilization rate and easy secondary pollution.

[0006] Based on this, the present invention has the following technical solutions: In a first aspect, the present invention provides a kitchen waste treatment system, including an anaerobic fermentation unit, a dehydration unit, a desulfurization unit, a decarbonization unit, a methanol synthesis unit and a wastewater treatment unit; The anaerobic fermentation unit is used to generate biogas and anaerobic digestate; The desulfurization unit is used to remove hydrogen sulfide, moisture and impurities in the biogas to obtain a mixed gas; The decarbonization unit is used to separate methane, carbon dioxide and tail gas in the mixed gas; The methanol synthesis unit is used to synthesize and prepare methanol from the carbon dioxide separated by the decarbonization unit; The wastewater treatment unit is used to carry out denitrification reaction with methanol as a carbon source to remove total nitrogen; The anaerobic fermentation unit is respectively connected to the desulfurization unit and the dehydration unit. The desulfurization unit is used to treat biogas, and the dehydration unit is used to treat anaerobic digestate; the dehydration unit is further connected to the wastewater treatment unit, the desulfurization unit is further connected to the decarbonization unit, the decarbonization unit is further connected to the methanol synthesis unit, and the methanol synthesis unit is further connected to the wastewater treatment unit.

[0007] The present invention uses the above-mentioned treatment system to treat kitchen waste. After being treated by the anaerobic digestion unit, biogas and digestate are produced. After the biogas is treated by the desulfurization unit to remove hydrogen sulfide, moisture and impurities in the raw biogas, decarbonization treatment is carried out. Through the treatment of the decarbonization unit, methane, carbon dioxide and tail gas are separated. The separated tail gas is discharged up to standard, the separated methane is directly incorporated into the natural gas pipeline, and the separated carbon dioxide is input into the methanol synthesis unit. The methanol synthesis unit synthesizes methanol from carbon dioxide from the decarbonization unit and other raw materials under the joint action of catalysts, and then transports the methanol to the wastewater treatment unit. On the other hand, the digestate produced by the anaerobic fermentation unit is separated into biogas residue and biogas liquid by the dehydration unit. The biogas residue is transported out for treatment, and the biogas liquid enters the wastewater treatment unit for treatment. The process of the wastewater treatment unit is pretreatment + two-stage AO + MBR + NF. A large amount of carbon source needs to be supplemented in the A section of the two-stage AO to meet the requirement of total nitrogen removal. The methanol generated by the methanol synthesis unit is used to reduce the cost of purchasing methanol externally.

[0008] According to the kitchen waste treatment system provided by the present invention, the anaerobic fermentation unit includes an anaerobic reactor.

[0009] And / or, the desulfurization unit includes a wet desulfurization tower and / or a dry desulfurization tower.

[0010] And / or, the decarbonization unit includes a PSA reaction tower.

[0011] And / or, the methanol synthesis unit includes a reaction tower and a purification tower; preferably, the methanol synthesis unit further includes degradable microcapsule balls; more preferably, the degradable microcapsule balls are polylactic acid degradable microcapsule balls.

[0012] Further preferably, the surface of the degradable microcapsule balls is loaded with magnetic Fe3O4 nanoparticles to make them magnetically responsive, and then the position of the microcapsule balls can be accurately controlled by an external magnetic field, so as to achieve directional enrichment.

[0013] In the present invention, using methanol microcapsule balls as a carbon source for sewage treatment has the following advantages: ① Encapsulate methanol in polylactic acid (PLA) degradable microcapsule balls, and realize the slow release of the carbon source by controlling the thickness of polylactic acid (PLA). The duration can be adjusted from 0 to 10 days, which solves the problem of explosive growth of microorganisms caused by traditional dosing; at the same time, it solves the problems of methanol being flammable, explosive and difficult to manage.

[0014] ② The surface of the microcapsules is loaded with magnetic Fe3O4 nanoparticles, which can be directionally enriched in the denitrification reaction zone by a magnetic field, and the nitrogen removal efficiency is increased by more than 30%.

[0015] ③ Methanol drives the sulfur cycle to cooperate with nitrogen and phosphorus removal. Add microcapsules in the anaerobic section. Methanol is used as an electron acceptor to promote sulfur-oxidizing bacteria (SOB) to convert S 2- into S0 Meanwhile, alkalinity is synchronously released to adjust the pH. In the aerobic section, sulfate-reducing bacteria (SRB) utilize S 0 to reduce nitrate, achieving the co-removal of "sulfur-nitrogen-phosphorus", with a total nitrogen removal rate > 90% and a phosphorus recovery rate > 80%.

[0016] In summary, using degradable microcapsule balls to release methanol in the wastewater treatment unit can further improve the removal efficiency of total nitrogen and total phosphorus; meanwhile, it can solve the problems of explosive growth of microorganisms caused by traditional dosing and the high management difficulty caused by the flammability and explosiveness of methanol.

[0017] And / or, the dehydration unit includes a centrifuge.

[0018] And / or, the wastewater treatment unit includes a pretreatment device, a two-stage AO treatment device, an MBR treatment device, and an NF treatment device.

[0019] Preferably, the pretreatment device includes a grille and a flotation tank; the two-stage AO treatment device includes two-stage AO sewage treatment tanks and supporting aeration equipment and reflux equipment; the MBR treatment device includes an MBR membrane system and supporting water pump and blower equipment; the NF includes an NF membrane system and supporting water pump equipment, chemical dosing equipment, and cleaning equipment.

[0020] In a second aspect, the present invention provides a method for treating kitchen waste implemented by using the above-mentioned kitchen waste treatment system, including: S1: Input kitchen waste into the anaerobic fermentation unit to generate biogas and digestate; S2: Input the biogas into the desulfurization unit to remove hydrogen sulfide and particulate impurities in the biogas to obtain a mixed gas; input the digestate into the dehydration unit for solid-liquid separation to separate out biogas slurry and biogas residue; S3: Input the mixed gas into the decarbonization unit to separate out methane, carbon dioxide, and tail gas; transport the biogas residue separated by the dehydration unit for external treatment, and input the separated biogas slurry into the wastewater treatment unit; S4: Incorporate the methane separated by the decarbonization unit into the natural gas pipeline network, input the separated carbon dioxide into the methane synthesis unit for methanol preparation, and discharge the separated tail gas after treatment to meet the standards; S5: Encapsulate the methanol generated by the methanol synthesis unit in polylactic acid degradable microcapsule balls and transport it to the wastewater treatment unit for use, and the wastewater is discharged after meeting the standards.

[0021] According to the method for treating kitchen waste provided by the present invention, in S1, the anaerobic fermentation conditions include: temperature: 35 - 37 °C, residence time: 30 - 40 d.

[0022] According to the food waste treatment method provided by the present invention, in S2, a wet desulfurization and / or dry desulfurization process is adopted; wherein, in the wet desulfurization process, the inlet hydrogen sulfide concentration ≤ 2000 ppm, and the outlet concentration ≤ 150 ppm; in the dry desulfurization process, the inlet hydrogen sulfide concentration ≤ 150 ppm, and the outlet concentration ≤ 10 ppm.

[0023] According to the food waste treatment method provided by the present invention, in S3, a centrifugal dehydrator is used for dehydration, the medium temperature is 35 - 37 °C, the solid load is 800 - 900 kg / h, and the solid content of the discharged material ≥ 25%.

[0024] According to the food waste treatment method provided by the present invention, in S3, a pressure swing adsorption decarbonization technology is adopted, the methane content in the inlet gas ≥ 60%, the methane content after purification ≥ 97%, and the pressure after purification is 0.35 - 0.45 MPa.

[0025] According to the food waste treatment method provided by the present invention, in S4, the carbon dioxide generated by the decarbonization unit is synthesized into methanol by an electrochemical - enzyme catalysis coupling process, and the generated methanol is encapsulated in polylactic acid degradable microcapsule balls, and then the degradable microcapsule balls are transported to the wastewater treatment unit for use as wastewater treatment raw materials; Preferably, S4 includes the following steps: Step 1: Electrochemically reduce CO2 to formic acid; using a non - noble metal as a catalyst, electrolyze CO2 into formic acid at normal temperature and pressure; Step 2: Biologically enzyme - catalyze the synthesis of methanol from formic acid; use formate dehydrogenase in methylotrophic bacteria to efficiently convert formic acid into methanol at normal pressure and 30 - 40 °C; Step 3: Adopt an in - situ separation technology, use an ionic liquid - membrane separation coupling system to continuously separate the methanol product; Step 4: Generate slow - release methanol microcapsules; encapsulate methanol in polylactic acid (PLA) degradable microcapsule balls.

[0026] Traditional carbon dioxide - to - methanol relies on high temperature and high pressure (200 - 300 °C, 5 - 10 MPa) and noble metal catalysts (such as Cu / ZnO / Al2O3, etc.), with high energy consumption and the catalyst is prone to failure. Methanol is an inflammable, explosive and chemical, and is mostly used as a directly added liquid carbon source in sewage treatment, with strict management requirements, high management costs, low utilization rate and easy to cause secondary pollution.

[0027] In the present invention, those skilled in the art can select a specific non - noble metal as a catalyst in Step 1, such as NiFe - LDH layered double metal hydroxide, etc.

[0028] In the present invention, the electric energy for the electrochemical reaction in Step 1 comes from the photovoltaic system of the sewage treatment plant.

[0029] In the present invention, those skilled in the art can select specific methylotrophic bacteria in step 2 as needed, such as Methylobacterium extorquens etc.

[0030] According to the food waste treatment method provided by the present invention, in S5, a two-stage AO process is included; wherein, the hydraulic retention time of the first-stage anoxic tank is 2 - 3 d, the hydraulic retention time of the first-stage aerobic tank is 4 - 5 d, the hydraulic retention time of the second-stage anoxic tank is 4 - 5 d, the hydraulic retention time of the second-stage aerobic tank is 4 - 5 d, the aerobic sludge age is 20 - 30 d, the MLSS is 8500 - 9500 mg / L, the MLVSS is 5000 - 6000 mg / L, the nitrification rate is 0.025 - 0.035 kgNH4 + -N / (kgMLSS·d), the denitrification rate is 0.035 - 0.045 kgNO3-N / (kgMLSS·d), the sludge production coefficient is 0.24 kgVSS / kgCOD, the air-water ratio is (45 - 55):1, the reflux ratio of the first-stage AO is (45 - 55):1, and the reflux ratio of the second-stage AO is (25 - 35):1.

[0031] According to the food waste treatment method provided by the present invention, in S5, after the two-stage AO process, an MBR process and an NF process are further included; wherein, the MBR uses PVDF hollow fiber membranes, and the designed membrane flux is 25 - 30L / (m 2 ·h); the NF uses polyamide materials, and the designed membrane flux is 10 - 20L / (m 2 ·h).

[0032] The food waste treatment system and treatment method provided by the present invention reduce the direct emissions of carbon dioxide during the conventional biogas utilization process and reduce the cost of carbon source procurement during the biogas slurry treatment process through the above treatment process, achieving the purpose of reducing emissions and lowering the treatment cost. At the same time, the present invention solves the problems of high cost in the traditional carbon dioxide to methanol process under high temperature, high pressure and the action of catalysts, as well as the explosive growth of microorganisms in a short time when methanol is directly used as a carbon source, high management cost, low utilization rate and easy secondary pollution. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] In order to more clearly illustrate the technical solutions in the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the following drawings are some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can also be obtained based on these drawings.

[0034] Figure 1It is a process flow diagram for the treatment of kitchen waste provided by the present invention. Detailed implementation manners

[0035] To make the objectives, technical solutions and advantages of the present invention clearer, the technical solutions in the present invention will be clearly and completely described below with reference to the accompanying drawings in the present invention. Apparently, the described embodiments are some but not all of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present invention without making creative efforts belong to the scope of protection of the present invention.

[0036] Unless otherwise specified, all kinds of raw materials used in the examples and comparative examples are commercially available conventional raw materials, and the technical means used are conventional means well known to those skilled in the art.

[0037] The following combines Figure 1 to describe a kitchen waste treatment system and method provided by the present invention.

[0038] As Figure 1 shown, a method for comprehensive utilization of biogas from anaerobic treatment of kitchen waste provided in this embodiment includes the following steps: S1. Input the kitchen waste into the anaerobic fermentation unit to generate biogas and digestate; S2. Input the biogas into the desulfurization unit to remove hydrogen sulfide and particulate impurities in the biogas, and input the digestate into the dehydration unit for solid-liquid separation to separate out biogas slurry and biogas residue; S3. Input the desulfurized biogas into the decarbonization unit to separate out methane, carbon dioxide and tail gas; transport the biogas residue separated by the dehydration unit for external treatment, and input the biogas slurry separated into the wastewater treatment unit; S4. Incorporate the methane separated by the decarbonization unit into the nearby natural gas pipeline, input the separated carbon dioxide into the methane synthesis unit, and discharge the separated tail gas after treatment to meet the standards; S5. Encapsulate the methanol generated by the methanol synthesis unit in polylactic acid degradable microcapsule balls and transport it to the wastewater treatment unit for use, and discharge the wastewater after reaching the standards.

[0039] This embodiment provides a treatment system for kitchen waste, including: An anaerobic fermentation unit, a dehydration unit, a desulfurization unit, a decarbonization unit, a methanol synthesis unit and a wastewater treatment unit; The anaerobic fermentation unit is used to generate biogas and anaerobic digestate; The desulfurization unit is used to remove hydrogen sulfide, moisture and impurities in the biogas to obtain a mixed gas; The decarbonization unit is used to separate methane, carbon dioxide and tail gas in the mixed gas; The methanol synthesis unit is used to synthesize methanol by synthesizing carbon dioxide separated by the decarbonization unit; The wastewater treatment unit is used to carry out denitrification reaction with methanol as the carbon source to remove total nitrogen; The anaerobic fermentation unit is respectively connected to the desulfurization unit and the dehydration unit. The desulfurization unit is used to treat biogas, and the dehydration unit is used to treat anaerobic digestate; the dehydration unit is further connected to the wastewater treatment unit, the desulfurization unit is further connected to the decarbonization unit, the decarbonization unit is further connected to the methanol synthesis unit, and the methanol synthesis unit is further connected to the wastewater treatment unit.

[0040] The anaerobic fermentation unit is mainly used to carry out anaerobic reaction on food waste. Specifically, the anaerobic fermentation reaction refers to a complex biochemical process in which organic substances (such as food waste, municipal sludge, human and livestock manure, straw, weeds, etc.) under certain moisture, temperature and anaerobic conditions, through the decomposition and metabolism of various microorganisms with a large number and different functions, finally form a mixed gas such as methane and carbon dioxide. The anaerobic fermentation unit is connected to the desulfurization unit and the dehydration unit. After the food waste is treated by the anaerobic fermentation unit, biogas and digestate are produced. The produced biogas is transported to the desulfurization unit for further treatment, and the produced digestate is transported to the dehydration unit for further treatment.

[0041] The desulfurization unit removes hydrogen sulfide in biogas; common biogas desulfurization methods include: dry desulfurization, wet desulfurization, biological desulfurization and other desulfurization methods. After the biogas is treated by the desulfurization unit, a mixed gas of methane and carbon dioxide is produced; the biogas desulfurization unit is connected to the decarbonization unit.

[0042] The decarbonization unit separates carbon dioxide and methane in the mixed gas to produce methane and carbon dioxide. The decarbonization process mainly includes absorption method, pressure swing adsorption method, low temperature condensation method and membrane separation method. The decarbonization unit is connected to the methanol synthesis unit.

[0043] The methanol synthesis unit generates methanol through processes such as compression, synthesis, gas separation, and rectification of carbon dioxide and hydrogen under the action of a catalyst, and at the same time generates part of the tail gas. The methanol synthesis unit is connected to the wastewater treatment unit.

[0044] The dehydration unit separates the mixture in the digestate into solid and liquid, producing biogas residue and biogas slurry. The dehydration unit uses a centrifugal dehydrator for solid-liquid separation. The dehydration unit is connected to the wastewater treatment unit.

[0045] The wastewater treatment unit adopts the process of pretreatment + two-stage AO + MBR + NF. During the treatment process, the degradable microcapsule balls containing methanol produced by the methanol synthesis unit are used as raw materials to carry out denitrification reaction to remove total nitrogen.

[0046] The working principles and working methods of each component of this system will be briefly described below. Specifically, the kitchen waste is treated by the anaerobic fermentation unit to generate biogas and digestate. The digestate enters the desulfurization unit. After being treated by the desulfurization unit, hydrogen sulfide and impurities in the biogas are removed. The treated mixed gas enters the decarbonization unit for utilization: entering the decarbonization unit, the mixed gas is treated by the decarbonization unit to separate methane and carbon dioxide. Methane enters the natural gas pipeline network for users to use, and carbon dioxide enters the methanol synthesis unit for further treatment; in the methanol synthesis unit, the carbon dioxide generated from the decarbonization unit is synthesized into methanol by the electrochemical-enzyme catalytic coupling process, and the methanol is encapsulated in polylactic acid (PLA) degradable microcapsule balls. The degradable microcapsule balls are transported to the wastewater treatment unit for use as raw materials for sewage treatment; on the other hand, the digestate generated by anaerobic fermentation enters the dehydration unit for treatment, the biogas residue is separated and transported out for treatment, and the biogas slurry is separated and enters the wastewater treatment station for treatment. The carbon source used in the denitrification reaction during the treatment process comes from the methanol synthesized in the methanol synthesis unit.

[0047] There are 5 anaerobic reactors, each with a diameter of 25 meters and a height of 22 m. Vertical stirring and external heat exchange of the reactor are adopted; medium-temperature (35 - 37 °C) anaerobic fermentation is designed, with an organic matter load of 2.64 kg VS / m 3 d and a retention time of 36 d.

[0048] The desulfurization unit is divided into wet desulfurization and dry desulfurization processes. For the wet desulfurization process, the designed treatment capacity is 2500 Nm 3 / h, the inlet hydrogen sulfide concentration is ≤ 2000 ppm, and the outlet concentration is ≤ 150 ppm; for the dry desulfurization process, the designed treatment capacity is 2500 Nm 3 / h, the inlet hydrogen sulfide concentration is ≤ 150 ppm, and the outlet concentration is ≤ 10 ppm; there are 4 wet desulfurization towers, each with a single size of diameter 1400 mm and height 15 m; there are 4 dry desulfurization towers, each with a single size of diameter 1500 mm and height 3 m.

[0049] The decarbonization unit adopts pressure swing adsorption decarbonization technology. The designed treatment capacity is 2500 Nm 3 / h, the inlet methane content is ≥ 60%, the purified methane content is ≥ 97%, the purified pressure is 0.4 MPa, and there are 2 sets of PSA reaction towers, with a single set treatment capacity of 1250 Nm 3 / h.

[0050] Specifically, in an embodiment provided by the present invention, the methanol synthesis unit synthesizes methanol by the electrochemical-enzyme catalytic coupling process and encapsulates the methanol in polylactic acid (PLA) degradable microcapsule balls. Specifically as follows: Step 1: Electrochemically reduce CO2 to formic acid. Using a non-noble metal catalyst (NiFe-LDH layered double metal hydroxide), electrolyze CO2 into formic acid at room temperature and atmospheric pressure, and the electrical energy is sourced from the photovoltaic system of the sewage treatment plant.

[0051] Step 2: Biocatalytic synthesis of methanol from formic acid. Utilize methylotrophic bacteria ( Methylobacterium extorquens ), whose highly active formate dehydrogenase efficiently converts formic acid into methanol under mild reaction conditions (30 - 40 °C, atmospheric pressure).

[0052] Step 3: Adopt in-situ separation technology and use an ionic liquid-membrane separation coupling system to continuously separate the methanol product in real-time, avoiding inhibition of microorganisms, and increasing the conversion rate to over 85% (traditional process < 60%).

[0053] Step 4: Generate slow-release methanol microcapsules. Encapsulate methanol in biodegradable microcapsule spheres of polylactic acid (PLA), and control the slow release rate of the carbon source by controlling the thickness of the polylactic acid, with an adjustable duration of 0 - 10 days.

[0054] The dehydration unit uses a centrifuge for dehydration. There are 3 centrifuges, with 2 in use and 1 standby. Each centrifuge has a capacity of 26 m 3 / h, a power of 22 kW, a medium temperature of 35 - 55 °C, a solid load of 850 kg / h, and a solid content in the discharge of ≥ 25%.

[0055] The wastewater treatment unit includes a pretreatment device, a two-stage AO treatment device, an MBR treatment device, and an NF treatment device. The pretreatment device includes a grille and a flotation tank; the two-stage AO treatment device includes two-stage AO sewage treatment tanks and supporting aeration equipment and reflux equipment; the MBR treatment device includes an MBR membrane system and supporting water pump and blower equipment; NF includes an NF membrane system and supporting water pump equipment, dosing equipment, and cleaning equipment.

[0056] The treatment capacity of the wastewater treatment unit is 800 m 3 / d, adopting the pretreatment + two-stage AO + MBR + NF process; main process parameters: HRT in the first-stage A tank is 2.5 d, the first-stage O tank is 4.1 d, the second-stage A is 4.1 d, the second-stage O is 4.1 d, the aerobic sludge age is 25 d, MLSS is 9000 mg / L, MLVSS is 5400 mg / L, and the nitrification rate is 0.03 kgNH4 +-N / (kgMLSS·d), the denitrification rate is 0.04 kgNO3-N / (kgMLSS·d), the sludge production coefficient is 0.24 kgVSS / kgCOD, the sludge production coefficient is 0.24 kgVSS / kgCOD, the air-water ratio is 50:1, and the reflux ratio of the first-stage AO is 50, and the reflux ratio of the first-stage AO is 30. The MBR uses PVDF hollow fiber membranes, and the designed membrane flux is 28 L / (m 2 .h), the NF uses polyamide materials, and the designed membrane flux is 15 L / (m 2 .h).

[0057] Specifically, in an embodiment provided by the present invention, the nitrogen and phosphorus removal treatment of the wastewater treatment unit includes the following steps: Step 1: Denitrification to remove total nitrogen. In the A section of the two-stage AO, using polylactic acid degradable microcapsule balls as the carbon source, converting nitrate in the wastewater into N2O and N2, so as to achieve the purpose of removing total nitrogen. Among them, the surface of the microcapsules is loaded with magnetic Fe3O4 nanoparticles, which can be directionally enriched in the denitrification reaction zone through a magnetic field, improving the denitrification efficiency by more than 30%.

[0058] Step 2: Methanol-driven sulfur cycle for synergistic nitrogen and phosphorus removal. In the A section of the two-stage AO, add degradable microcapsule balls, and methanol is used as an electron donor to promote sulfur-oxidizing bacteria (SOB) to convert S²⁻ into S 0 , simultaneously releasing alkalinity to adjust the pH; in the O section of the two-stage AO, sulfur-reducing bacteria (SRB) use S 0 to reduce nitrate, realizing the synergistic removal of "sulfur-nitrogen-phosphorus", with a total nitrogen removal rate > 90% and a phosphorus recovery rate > 80%.

[0059] Through the anaerobic treatment and biogas comprehensive utilization method of food waste of the present invention, the carbon dioxide utilization rate can reach more than 98%. In the practical example, about 19,000 cubic meters of carbon dioxide are separated out 3 / d, the density of carbon dioxide is 1.96 g / L, which is equivalent to a weight of about 37.24 tons / day. Calculated on an annual basis, the annual carbon dioxide emissions are reduced by 13,592.6 tons, which is a very considerable amount; on the other hand, 1 mol of CO2 can synthesize 1 mol of CH3OH, the molar mass of methanol is 32.04 g / mol, the molar volume of CO2 is 22.4 L / mol, and the molar mass is 22.4 g / mol. Based on the about 19,000 cubic meters of carbon dioxide separated out in the practical example 3Calculated by / d, 27.18 tons of methanol can be synthesized. The amount of carbon source added to the wastewater treatment unit every day is about 5 tons of sodium acetate as the carbon source. Calculated at the current market price of 2000 yuan / ton, the cost is about 10,000 yuan per day, and about 3.65 million yuan of carbon source cost is required per year. Using the separated carbon dioxide to synthesize methanol as the carbon source can, on the one hand, reduce the annual methanol procurement cost by about 3.65 million yuan, and the surplus can be sold to large nearby sewage treatment plants. The total economic benefit is about 19.71 million yuan.

[0060] Therefore, through the comprehensive utilization method of biogas of the present invention, the environmental damage caused by carbon dioxide emissions is reduced, and at the same time, the procurement of carbon sources in the process of treating biogas slurry wastewater in the food waste treatment plant is reduced, so as to achieve the purpose of reducing the operating cost.

[0061] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. A kitchen waste treatment system, characterized in that: It includes anaerobic fermentation unit, dehydration unit, desulfurization unit, decarbonization unit, methanol synthesis unit and wastewater treatment unit; The anaerobic fermentation unit is used to produce biogas and anaerobic digestate; The desulfurization unit is used to remove hydrogen sulfide, moisture and impurities in the biogas to obtain a mixed gas; The decarbonization unit is used to separate methane, carbon dioxide and tail gas from the mixed gas; The methanol synthesis unit is used to synthesize methanol from the carbon dioxide separated by the decarbonization unit; The wastewater treatment unit is used to carry out denitrification reaction using methanol as a carbon source to remove total nitrogen; The anaerobic fermentation unit is connected to a desulfurization unit and a dehydration unit respectively. The desulfurization unit is used to process biogas and the dehydration unit is used to process anaerobic digestion liquid. The dehydration unit is further connected to a wastewater treatment unit. The desulfurization unit is further connected to a decarbonization unit. The decarbonization unit is further connected to a methanol synthesis unit. The methanol synthesis unit is further connected to a wastewater treatment unit.

2. The kitchen waste treatment system according to claim 1, characterized in that: The anaerobic fermentation unit includes an anaerobic reactor; And / or, the desulfurization unit includes a wet desulfurization tower and / or a dry desulfurization tower; And / or, the decarbonization unit comprises a PSA reaction tower; And / or, the methanol synthesis unit includes a reaction tower and a purification tower; preferably, the methanol synthesis unit also includes a device for generating degradable microcapsule beads; more preferably, the device is a device for generating polylactic acid degradable microcapsule beads; And / or, the dehydration unit comprises a centrifugal dehydrator; And / or, the wastewater treatment unit includes a pretreatment device, a two-stage AO treatment device, an MBR treatment device and a NF treatment device.

3. A method for treating kitchen waste implemented by the kitchen waste treatment system according to claim 1 or 2, characterized in that: include: S1: Input the food waste into the anaerobic fermentation unit to produce biogas and digestate; S2: The biogas is input into the desulfurization unit to remove hydrogen sulfide and particulate impurities in the biogas to obtain a mixed gas; the digestate is input into the dehydration unit for solid-liquid separation to separate the biogas slurry and biogas residue; S3: The mixed gas is input into the decarbonization unit to separate methane, carbon dioxide and tail gas; the biogas residue separated by the dehydration unit is transported out for treatment, and the separated biogas liquid is input into the wastewater treatment unit; S4: The methane separated from the decarbonization unit is integrated into the natural gas pipeline network, the separated carbon dioxide is input into the methane synthesis unit for the production of methanol, and the separated tail gas is treated to meet the emission standards; S5: The methanol generated by the methanol synthesis unit is encapsulated in polylactic acid biodegradable microcapsule balls and transported to the wastewater treatment unit for use. The wastewater is discharged after meeting the standards.

4. The method for treating kitchen waste according to claim 3, characterized in that: In S1, the anaerobic fermentation conditions included: temperature: 35~37℃, residence time of 30~40 days.

5. The method for treating kitchen waste according to claim 3 or 4, characterized in that: In S2, wet desulfurization and / or dry desulfurization processes are adopted; wherein, in the wet desulfurization process, the inlet concentration of hydrogen sulfide is ≤2000ppm, and the outlet concentration is ≤150ppm; in the dry desulfurization process, the inlet concentration of hydrogen sulfide is ≤150ppm, and the outlet concentration is ≤10ppm.

6. The method for treating kitchen waste according to any one of claims 3 to 5, characterized in that: In S2, a centrifugal dehydrator is used for dehydration, the medium temperature is 35~37℃, the solid load is 800~900 kg / h, and the solid content of the discharge is ≥25%.

7. The method for treating kitchen waste according to any one of claims 3 to 6, characterized in that: In S3, pressure swing adsorption decarbonization technology is used, the methane content of the inlet gas is ≥60%, the methane content after purification is ≥97%, and the pressure after purification is 0.35~0.45MPa.

8. The method for treating kitchen waste according to any one of claims 3 to 7, characterized in that: In S4, the carbon dioxide generated by the decarbonization unit is synthesized into methanol by an electrochemical-enzymatic catalytic coupling process, and the generated methanol is encapsulated in polylactic acid degradable microcapsule balls, and then the degradable microcapsule balls are transported to the wastewater treatment unit for use as a wastewater treatment raw material; Preferably, S4 comprises the following steps: Step 1: Electrochemical reduction of CO2 to generate formic acid: Using non-precious metals as catalysts, CO2 is electrolyzed into formic acid at room temperature and pressure; Step 2: Bio-enzyme catalyzes formic acid to synthesize methanol; formic acid is efficiently converted into methanol using formate dehydrogenase in methylotrophic bacteria at normal pressure and 30-40°C; Step 3: Using in-situ separation technology and an ionic liquid-membrane separation coupling system, the methanol product is separated in real time; Step 4: Produce sustained-release methanol microcapsules; encapsulate methanol in degradable microcapsule balls.

9. The method for treating kitchen waste according to any one of claims 3 to 8, characterized in that: S5 includes a two-stage AO process; the hydraulic retention time of the first anoxic tank is 2~3 days, the hydraulic retention time of the first aerobic tank is 4~5 days, the hydraulic retention time of the second anoxic tank is 4~5 days, the hydraulic retention time of the second aerobic tank is 4~5 days, the aerobic sludge age is 20~30 days, the MLSS is 8500~9500 mg / L, the MLVSS is 5000~6000 mg / L, and the nitrification rate is 0.025~0.035kgNH4 + -N / (kgMLSS.d), the denitrification rate is 0.035~0.045 kgNO3-N / (kgMLSS.d), the sludge production coefficient is 0.24 kgVSS / kgCOD, the gas-water ratio is (45~55):1, the first-stage AO reflux ratio is (45~55):1, and the second-stage AO reflux ratio is (25~35):

1.

10. The method for treating kitchen waste according to claim 9, characterized in that: In S5, after the two-stage AO process, the MBR process and the NF process are also included; among them, the MBR adopts PVDF hollow fiber membrane, and the designed membrane volume is 25~30L / (m 2 ·h); NF is made of polyamide material, and the designed membrane volume is 10~20L / (m 2 h).

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