A highly efficient system for treating and recycling anaerobic digestion liquid from kitchen waste

Abstract

The present invention proposes a highly efficient system for the treatment and resource utilization of anaerobic digestion liquid from food waste. The system comprises a desalination system, a denitrification system, a sludge dewatering system, and a reclaimed water system. The food waste to be treated first enters the desalination system. The output of the desalination system at different process stages is connected to the inputs of the denitrification system and the sludge dewatering system, respectively. The output of the denitrification system is then connected to the inputs of the reclaimed water system and the sludge dewatering system. This system is easy to control, reduces operating costs, ensures efficient and stable operation, and enables the reuse of reclaimed water and salt recovery.

Description

Technical Field

[0001] The present invention belongs to the technical field of wastewater treatment and resource utilization, and specifically relates to a system for efficiently treating and resource-utilizing anaerobic digestion liquid of kitchen waste. Background Art

[0002] Food waste is a significant component of municipal solid waste, accounting for approximately 60.2% of the total. Anaerobic digestion, a green, low-carbon process for treating organic solid waste that can generate renewable energy, is widely used in the treatment of food waste. With the nationwide implementation of waste sorting, the organic content of food waste continues to increase, promoting the further application of anaerobic digestion technology in the field of food waste treatment. Accordingly, the amount of anaerobic digestate (slurry), a byproduct of anaerobic digestion of food waste, will also gradually increase. Anaerobic digestate from food waste has high organic matter content, high salt content, high ammonia nitrogen concentration, and high oil content. Improper handling can cause significant secondary pollution and environmental damage.

[0003] Anaerobic digestate from food waste contains high levels of oil (600-1000 mg / L), salt (5-20 g / L), suspended solids (500-3000 mg / L), ammonia nitrogen (1800-3000 mg / L), and organic matter (2500-5000 mg / L), and has a low carbon-nitrogen ratio. It is urgent to find a suitable treatment method. The high salt content and carbon-nitrogen ratio characteristics of anaerobic digestate from food waste lead to traditional water treatment processes facing problems such as high drug consumption, high energy consumption, and microbial susceptibility to salt inhibition, making actual treatment difficult. There are currently some studies that attempt to solve this problem. For example:

[0004] The Chinese invention patent (CN201410822363.3) "A system and method for treating anaerobic fermentation sludge from kitchen waste" still uses the traditional nitrification and denitrification process. Although the system stability can be improved, the overall drug consumption and energy consumption of the system are still at a high level.

[0005] The Chinese invention patent (CN201910338159.7) "A combined treatment process for anaerobic digestion of food waste" proposes the idea of using "anaerobic ammonia oxidation + traditional biological denitrification" technology to reduce investment and operating costs. Among them, anaerobic ammonia oxidation denitrification technology has been proven to be able to treat high-ammonia nitrogen wastewater with low energy consumption (saving 62.5% oxygen, 50% alkalinity, and 100% carbon source). However, the invention does not take into account the serious inhibitory effect of salinity on anaerobic ammonia-oxidizing bacteria.

[0006] Furthermore, the anaerobic digestion liquid treatment process involves the generation of sludge and the need for dewatering. Traditional sludge dewatering methods require significant amounts of dehydrating chemicals (such as polyaluminum chloride and polyacrylamide) and energy consumption. Common sludge dewatering methods, such as centrifugal dewatering and plate and frame filter press dewatering, consume significant amounts of chemicals and result in high treatment costs.

[0007] In summary, the high salt content (5-20 g / L) of anaerobic digestate from food waste severely inhibits microbial denitrification activity. The low carbon-nitrogen ratio of the water results in high chemical and energy consumption for traditional denitrification methods, and the resulting sludge dewatering and disposal also presents challenges. Treatment of anaerobic digestate with high salt content and high ammonia nitrogen content is challenging. Targeted desalination and denitrification technologies are relatively scarce, costly, and involve incomplete treatment processes, with a lack of consideration for resource utilization. Therefore, a systematic and efficient method for desalination, denitrification, and sludge dewatering of anaerobic digestate from food waste is needed. Summary of the Invention

[0008] Based on current technical limitations and needs, the present invention provides a system for the efficient treatment and resource utilization of anaerobic digestion liquid from food waste, which can reduce system operating costs, ensure efficient and stable operation of the system, and realize recycled water reuse and salt recovery.

[0009] In order to solve the above technical problems, the present invention provides a technical solution:

[0010] A system for efficiently treating and recycling anaerobic digestion liquid from kitchen waste, characterized in that: Figure 1 As shown, it includes a desalination system, a denitrification system, a sludge dewatering system and a recycled water system. First, the food waste to be processed enters the desalination system. The output of the desalination system in different process links is connected to the input of the denitrification system and the sludge dewatering system respectively. The output of the denitrification system is connected to the input of the recycled water system and the sludge dewatering system.

[0011] Specifically, the desalination system is an electric adsorption desalination system, the denitrification system is an anaerobic ammonia oxidation denitrification system, the sludge dewatering system is a forward osmosis sludge dewatering system, and the reclaimed water system is a water reuse reclaimed water system.

[0012] The desalination system includes a grid, an oil separation sedimentation tank, a coagulation flotation tank, an electric adsorption tank and a refined salt purification device, which are connected in sequence, wherein: the grid is used to intercept scum, massive floating oil and particulate pollutants; the oil separation sedimentation tank is used to isolate floating oil, scum and grease in the water, and precipitate and remove precipitable matter in the wastewater; the coagulation flotation tank is used to remove finer suspended matter; the electric adsorption tank is used to selectively adsorb and remove monovalent ions in the water and realize salt purification and recovery through the refined salt purification device.

[0013] The coagulation flotation tank includes a front-end reaction tank and a rear-end reaction tank connected in sequence. An appropriate amount of polyaluminum chloride (PAC) and polyacrylamide (PAM) are added to the front-end reaction tank, and a large number of tiny bubbles are released through the vortex flotation aerator to remove most of the suspended matter in the wastewater. A demulsifier is added to the rear-end reaction tank to separate the emulsified oil from the liquid phase, remove the remaining suspended matter and colloid, and the effluent enters the electric adsorption tank for desalination treatment.

[0014] The electrosorption cell includes a flowing electrode liquid, a collecting plate, an ion exchange membrane and an adsorption chamber. The flowing electrode is used to adsorb Na + and Cl - ions, where:

[0015] The adsorption chamber is formed by the collecting plate, the adsorption chamber is attached with an ion exchange membrane, and the adsorption chamber has a flowing electrode liquid; when the incoming wastewater flows through the adsorption chamber, the ion exchange membrane includes a cation exchange membrane and an anion exchange membrane, which can selectively pass through the Na + and Cl - , Na + and Cl - It passes through the ion exchange membrane and is absorbed by the flowing electrode liquid. Finally, the desalination system discharges water through the electric adsorption cell, and the desalinated low-salt wastewater enters the denitrification system.

[0016] At the same time, Na + and Cl - The flowing electrode liquid enters the refined salt purification device to purify the subsequent concentrated brine, and solid NaCl can be recovered through evaporation and crystallization; the brine output by the refined salt purification device enters the sludge dehydration system.

[0017] Among them, the denitrification system includes a nitrite tank, an anaerobic ammonium oxidation tank, a two-stage AO and an MBR (membrane bioreactor), which are connected in sequence; the two-stage AO carries out traditional nitrification and denitrification reactions on the remaining total nitrogen that has not reacted completely at the front end, and the MBR realizes mud and water separation through membrane filtration. The separated sludge to be dehydrated is used to form a sludge dewatering system, and the separated water enters the reclaimed water system.

[0018] The desalination system uses a forward osmosis sludge dewatering system, which includes a low osmotic pressure side and a high osmotic pressure side, which form an osmotic pressure field. The low osmotic pressure side is a sludge dewatering device, which inputs the sludge to be dehydrated obtained by separation in the denitrification system. The high osmotic pressure side is connected to the brine output end of the desalination system, thereby utilizing the osmotic pressure potential energy of the concentrated brine (brine) generated by the desalination system to dehydrate the excess sludge in the sludge dewatering device. This forward osmosis sludge dewatering system utilizes the osmotic pressure difference and a spontaneous osmotic process to achieve the migration of water from the sludge to the brine. Because this process is spontaneous, no reagents need to be added, and the unit energy consumption is extremely low.

[0019] The regeneration system is connected to the output of the denitrification system to remove refractory organic matter from the water after the sludge and water separation in the denitrification system, and the effluent can be reused as regeneration water. The regeneration system includes a Fenton advanced oxidation tank and a BAF (biological aerated filter).

[0020] The present invention transforms the traditional functional system and, through overall planning and design, makes the technical solution extremely energy-efficient. Compared with the existing technology, the present invention has the following advantages:

[0021] (1) In the desalination system, grease will adhere to the surface of the sludge, blocking the contact between wastewater and sludge, and reducing the biochemical removal efficiency. The demulsification operation of the grease trap and coagulation sedimentation tank can reduce the oil content of the biogas slurry by more than 90%, which is convenient for subsequent treatment;

[0022] (2) In the desalination system, electrosorption technology can significantly reduce the salt content in food biogas, avoid the inhibition of subsequent microbial activity by excessive salt, and realize salt recovery;

[0023] (3) In the denitrification system, the two-stage anaerobic ammonium oxidation process controls the appropriate substrate ratio in the nitrite section, and then performs the anaerobic ammonium oxidation reaction to achieve autotrophic denitrification. Compared with traditional heterotrophic denitrification, it has low energy and drug consumption, is easy to control, has stable operation, and has a high nitrogen removal rate;

[0024] (4) In the sludge dewatering system, forward osmosis sludge dewatering technology utilizes the osmotic pressure difference between the brine generated during the desalination process and the residual sludge to achieve sludge dewatering at low cost. It also utilizes the by-products of the desalination system and greatly reduces the dehydration drug consumption and energy consumption compared to traditional dehydration methods.

[0025] (5) In the recycled water system, the deep treatment of Fenton oxidation and BAF can meet more stringent emission standards without producing concentrated liquid that is difficult to treat later. The effluent can be reused as recycled water. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the system and process flow of the present invention.

[0027] Figure 2 for Figure 1 Schematic diagram of the electrosorption desalination system of the medium-sized electrosorption cell.

[0028] Figure 3 for Figure 1 Schematic diagram of the denitrification system process.

[0029] Figure 4 for Figure 1 Schematic diagram of the recycled water system. DETAILED DESCRIPTION

[0030] The liquid product produced by anaerobic digestion of food waste alone or together with other organic waste is anaerobic digestion liquid of food waste.

[0031] The anaerobic digestate of food waste is characterized by high salt content (5-20g / L), high suspended solids concentration (500-3000mg / L), high ammonia nitrogen (1800-3000mg / L), high organic matter (2500-5000mg / L), and a low carbon-nitrogen ratio. As a result, traditional water treatment processes face difficulties such as high drug consumption, high energy consumption, and microorganisms being easily inhibited by salt, making actual treatment difficult.

[0032] In order to deal with the special treatment target of anaerobic digestion liquid of restaurant kitchen waste, the system of the present invention is further explained below with reference to specific embodiments.

[0033] Example 1

[0034] A system for efficiently treating and recycling anaerobic digestion liquid from kitchen waste, characterized in that: Figure 1 As shown, it includes a desalination system, a denitrification system, a sludge dewatering system and a recycled water system. First, the food waste to be processed enters the desalination system. The output of the desalination system in different process links is connected to the input of the denitrification system and the sludge dewatering system respectively. The output of the denitrification system is connected to the input of the recycled water system and the sludge dewatering system.

[0035] Specifically,

[0036] The desalination system is an electric adsorption desalination system, which outputs NaCl solid after purification;

[0037] The denitrification system is an anaerobic ammonium oxidation denitrification system, and the sludge dewatering system is a forward osmosis sludge dewatering system. The diluted brine is discharged and the dewatered sludge is transported out at the same time.

[0038] The reclaimed water system is a water reuse reclaimed water system.

[0039] The desalination system is used to remove SS (suspended solids) and reduce the oil content and salt content of the digestate (NaCl removal rate 85%-95%).

[0040] To this end, the desalination system ( Figure 1 The invention discloses a method for preparing a wastewater treatment plant, comprising: a screen, an oil separation sedimentation tank, a coagulation flotation tank, an electric adsorption tank and a refined salt purification device, which are connected in sequence, wherein: the screen is used to intercept scum, massive floating oil and particulate pollutants; the oil separation sedimentation tank is used to isolate floating oil, scum and grease in the water, and to precipitate and remove precipitable matter in the wastewater; the coagulation flotation tank is used to remove finer suspended matter; the electric adsorption tank is used to selectively adsorb and remove monovalent ions in the water and realize salt purification and recovery through the refined salt purification device.

[0041] Further:

[0042] The screen is a common existing equipment in this field. As an example, the design includes an artificial coarse screen, a rotary screen machine, a mesh plate type sewage remover and a sewage pool connected in sequence. The grid bar spacing is 50mm, 10mm and 5mm respectively. Aeration devices can be installed at the front and rear ends of the screen machine and in the sewage pool to prevent floating oil and sediment from compacting; intercepting food waste larger than 5mm (small pieces of floating scum and lumps of floating oil), so that the SS removal rate is more than 90%.

[0043] The oil separation sedimentation tank removes scum (pepper shells, Sichuan pepper shells, etc.) in the wastewater that is not intercepted by the front grille, and at the same time removes settleable pollutants (pepper seeds, pepper seeds, mud, sand, sludge, etc.) in the wastewater by sedimentation.

[0044] The coagulation flotation tank includes a front-end reaction tank and a rear-end reaction tank connected in sequence. An appropriate amount of polyaluminum chloride PAC (500-1500 mg / L) and polyacrylamide PAM (10-30 mg / L) are added to the front-end reaction tank. A large number of tiny bubbles are released through a vortex flotation aerator to remove most of the suspended matter in the wastewater. A demulsifier (50-500 mg / L) is added to the rear-end reaction tank to separate the emulsified oil from the liquid phase and remove the remaining suspended matter, colloids, etc. The effluent enters the electric adsorption tank for desalination treatment.

[0045] The electrosorption cell (such as Figure 2 As shown) includes a flowing electrode liquid, a collecting plate, an ion exchange membrane and an adsorption chamber, and uses the flowing electrode to adsorb Na in the wastewater. + and Cl - ions, where:

[0046] The flowing electrode liquid can achieve continuous ion adsorption and is a common existing technology in the field. As an example, it can be prepared by mixing active materials, conductive additives and electrolytes in appropriate proportions.

[0047] The adsorption chamber is formed by the collecting plate, the adsorption chamber is attached with an ion exchange membrane, and the adsorption chamber has a flowing electrode liquid; when the incoming wastewater flows through the adsorption chamber, the ion exchange membrane includes a cation and anion exchange membrane, which has selective permeability. In this embodiment, it is set to selectively pass through Na + and Cl - , but for Ca 2+ Mg 2+ Other ions have a relatively high retention rate, such as Na + and Cl -It passes through the ion exchange membrane and is absorbed by the flowing electrode liquid. Finally, the desalination system discharges the water through the electric adsorption cell, achieving a NaCl removal rate of 80%-95%. The low-salt wastewater after desalination enters the denitrification system.

[0048] At the same time, 80%-95% of Na + and Cl - The flowing electrode liquid enters the refined salt purification unit, where the concentrated brine is refined. After evaporation and crystallization, solid NaCl is recovered. The recovered solid salt has a purity exceeding 99% and can be used in industrial production processes. Meanwhile, the brine output from the refined salt purification unit enters the sludge dewatering system. The salt concentration of this brine is 50-300g / L NaCl.

[0049] Wherein, the denitrification system ( Figure 3 As shown) includes a nitrite tank, an anaerobic ammonium oxidation tank, a two-stage AO and an MBR (membrane bioreactor), which are connected in sequence, wherein:

[0050] The nitrification tank converts part of the ammonia nitrogen into nitrite nitrogen under aerobic conditions (controlling the ratio of ammonia nitrogen to nitrite in the effluent to be approximately 1:1.32), providing a suitable substrate reaction concentration for the anaerobic ammonium oxidation tank;

[0051] The anaerobic ammonium oxidation tank converts ammonia nitrogen and nitrite nitrogen into nitrogen gas under anaerobic and carbon source-free conditions, with a small amount of nitrate nitrogen produced;

[0052] The two-stage AO carries out traditional nitrification and denitrification reaction on the residual total nitrogen that has not been completely reacted at the front end. The MBR realizes mud and water separation through membrane filtration. The separated sludge to be dehydrated is used to form a sludge dewatering system, and the separated water enters the recycled water system.

[0053] As an example, Figure 3 As shown:

[0054] The nitrite water tank, anaerobic ammonia oxygen tank, and two-stage AO reaction tank all include stirring and temperature detectors. The nitrite water tank and two-stage AO reaction tank include an aeration device and a dissolved oxygen detector, and the two-stage AO reactor is equipped with a dosing pipeline. Furthermore, the nitrite water tank, anaerobic ammonia oxygen tank, and two-stage AO reaction tank are all equipped with a submersible mixer for stirring.

[0055] Preferably, the nitrification pool is equipped with a cooling tower, a temperature of 33-35° C., a dissolved oxygen of 1-3 mg / L, and a pH of 7.5-8.5.

[0056] Furthermore, when the alkalinity of the nitrite pool is insufficient, carbonate or bicarbonate is added, which may be but not limited to solid sodium carbonate. The nitrite pool contains a precipitation area, and the supernatant flows into the anaerobic ammonia oxidation reaction pool.

[0057] Preferably, the temperature of the anaerobic ammonium oxidation tank is 33-35° C., the dissolved oxygen is less than 0.01 mg / L, the pH is 7.5-8.2, and the nitrogen removal rate is 80%-90%.

[0058] Preferably, the temperature of the two-stage AO reaction tank is 33-35°C, the pH is 7.5-8.5, the dissolved oxygen in section A is less than 0.01 mg / L, and the O section adopts disc jet aeration with a dissolved oxygen of 1-3 mg / L;

[0059] The AO reaction tank is supplemented with a carbon source in section A. The carbon source may be, but is not limited to, methanol, sodium acetate, or landfill leachate. The total nitrogen removal rate is 80%-90%, and the organic matter removal rate is 20%-30%.

[0060] Preferably, the MBR is a tubular ultrafiltration membrane module with a pore size of 30 nm, made of polyvinylidene fluoride (PVDF), and a cross-flow velocity of 3-4 m / s. Membrane bioreactors offer high pollutant removal efficiency, good effluent quality, resistance to shock loads, and a small footprint.

[0061] Under the above process conditions, the denitrification system can achieve high-efficiency and low-consumption autotrophic denitrification (nitrogen removal rate 80%-90%) and remove part of the organic matter (organic matter removal rate 20%-30%).

[0062] Wherein, the desalination system adopts a forward osmosis sludge dewatering system (such as Figure 4 As shown), it includes a low osmotic pressure side and a high osmotic pressure side, which form an osmotic pressure field; the low osmotic pressure side is a sludge dewatering device, which inputs the sludge to be dehydrated obtained by separation of the denitrification system; the high osmotic pressure side is connected to the brine (concentrated brine, 50-300g / LNaCl) output end of the desalination system, so that the osmotic pressure potential energy of the concentrated brine (brine) generated by the desalination system is used to dehydrate the residual sludge in the sludge dewatering device. This forward osmosis sludge dewatering system uses the osmotic pressure difference and realizes the migration of water in the sludge to the brine based on the spontaneous osmotic process. Since the process is spontaneous, no chemicals need to be added, and the unit energy consumption is at an extremely low level. After dehydration, the sludge moisture content is reduced from 96%-99.5% to 80-85%.

[0063] The sludge dewatering device is fed with the sludge to be dewatered separated by the denitrification system in real time. The sludge remains in the sludge dewatering device and contacts the high osmotic pressure side. The dewatered sludge cake is then immediately removed from the sludge dewatering device and transported for disposal.

[0064] The regeneration water system is connected to the output of the denitrification system to remove refractory organic matter from the water after the sludge and water separation in the denitrification system, and the effluent can be reused as regeneration water. This is a conventional technology in the industry.

[0065] To this end, the reclaimed water system includes a Fenton advanced oxidation tank and a BAF (biological aerated filter). The Fenton system includes reaction, flocculation, and precipitation units. The BAF contains biological fillers, which include but are not limited to ceramsite, pine bark, volcanic rock, etc.

[0066] Preferably, as an example, the Fenton reaction is performed by adding ferrous ions (1000-3000 mg / L) and hydrogen peroxide (500-1500 mg / L) to oxidize the refractory organic matter. After treatment, the COD and chroma of the wastewater are significantly reduced, while the biodegradability of the biogas slurry wastewater is improved, creating favorable conditions for deep denitrification. BAF further reduces organic matter and total nitrogen.

[0067] Example 2

[0068] Based on the efficient treatment and resource utilization system of anaerobic digestion liquid of restaurant kitchen waste disclosed in the present invention, the treatment and working process of the present invention are further introduced:

[0069] (1) The wastewater from the anaerobic digestion of food waste is intercepted by three screens (the spacing between the bars is 50 mm, 10 mm, and 5 mm respectively) to intercept a large amount of floating scum, bulk oil, and particulate pollutants and enter the sewage pool. The hydraulic retention time of the sewage pool is 4 hours, and aeration and stirring devices are installed inside to prevent the floating oil and sediment from clumping.

[0070] (2) Wastewater flows from the sewage pool into the oil separation sedimentation tank with a hydraulic retention time of 4 hours. It can not only isolate the floating oil, scum and grease in the water, but also precipitate and remove the precipitable matter in the wastewater. The bottom sediment sludge and upper floating oil are discharged into the sludge tank through the gantry type scraper and suction machine;

[0071] (3) The effluent from the oil separation tank is treated by coagulation and flotation. Coagulation and flotation can remove some of the finer suspended solids still contained in the effluent from the oil separation tank. 1000 mg / L of PAC and 25 mg / L of PAM are added to the reaction tank before the coagulation and flotation tank. A large number of tiny bubbles are released by the vortex flotation aerator to remove most of the suspended solids in the wastewater. 300 mg / L of demulsifier is added to the reaction tank at the rear end of the coagulation and flotation tank to separate the emulsified oil from the liquid phase. The removal rate of SS and animal and vegetable oils is above 80%;

[0072] (4) Desalination treatment of the condensed gas floatation water. When the water flows through the adsorption chamber, Na + and Cl - Ions pass through the ion exchange membrane and are absorbed by the flowing electrode liquid, and the NaCl content in the effluent water is reduced by about 90%;

[0073] (5) The concentrated brine produced by electrosorption is evaporated, concentrated and crystallized to produce a solid with a NaCl purity greater than 99%, which can be used in industrial production;

[0074] (6) The desalination wastewater is subsequently denitrified and pumped into the nitrification tank. The hydraulic retention time is 48 h, the sludge concentration is 3-5 g / L, and partial nitrification occurs at a temperature of 35 ° C, dissolved oxygen 2 mg / L, sodium carbonate provides alkalinity, and pH 7.5-8.5. Ammonia nitrogen is oxidized to nitrite nitrogen, and the ratio of nitrite nitrogen to ammonia nitrogen in the effluent is 1.1 ± 0.1.

[0075] (7) The supernatant of the nitrite effluent enters the anaerobic ammonium oxidation tank with a hydraulic retention time of 36 hours and a sludge concentration of 3-5 g / L. The anaerobic ammonium oxidation reaction is carried out at a temperature of 35°C. Ammonia nitrogen and nitrite nitrogen react to produce nitrogen gas, accompanied by a small amount of nitrate nitrogen. The nitrogen removal rate is 75%-85%. The pH of the reaction process is controlled at 7.5-8.5 by dilute hydrochloric acid, and the nitrogen removal rate is 80%-90%.

[0076] (8) Since the anaerobic ammonium oxidation effluent still contains a small amount of nitrate nitrogen and unreacted ammonia nitrogen and nitrite nitrogen, traditional nitrification and denitrification reactions occur in the two-stage AO. The reaction temperature is 35°C. There is no aeration in the A section, and denitrification occurs. Nitrite nitrogen and nitric nitrogen are reduced to nitrogen gas. The O section is aerated, and the dissolved oxygen is 3 mg / L. Ammonia nitrogen is oxidized to nitrite nitrogen, and nitrite nitrogen is further oxidized to nitric nitrogen. The reflux ratio is 300%, the nitrogen removal rate is 80%-90%, and the organic matter removal rate is 20%-30%. The hydraulic retention time of the two-stage AO is 24h, and the sludge concentration is 5-8g / L. This process does not require the consumption of carbon source. The water after the reaction enters the tubular ultrafiltration membrane with a pore size of 30mm. The membrane effluent is deeply treated, and the concentrated liquid is returned to the two-stage AO.

[0077] (9) The membrane effluent is subjected to a "Fenton oxidation + aerated biological filter combined process". The pH is adjusted to 3 by acid solution, and 1400 mg / L ferrous ions and 700 mg / L H2O2 are added. The ferrous ions catalyze the decomposition of hydrogen peroxide to produce hydroxyl radicals with strong oxidizing ability. The strong oxidizing effect of hydroxyl radicals oxidizes and decomposes the molecular structure of difficult-to-biodegrade organic matter in the sewage. At the same time, the ferrous ions are oxidized to trivalent iron ions. By adding alkali solution, the pH is adjusted to 8 to form iron hydroxide precipitation. The auxiliary coagulant PAM acts as a flocculation reaction, thereby removing some organic matter through precipitation. The aerated biological filter is added to remove inorganic nitrogen through the aeration process and the addition of a small amount of carbon source. This process can effectively remove difficult-to-biodegrade organic matter and total nitrogen in sewage to meet the emission standards (COD 100 mg / L, total nitrogen 40 mg / L). It can also be used as recycled water for dust prevention, irrigation, car washing, etc.

[0078] (10) The sludge retention time of the two-stage AO is 30 days, and the moisture content of the residual sludge is 96%-99.5%. The two sides of the selective permeable membrane are residual sludge and brine (about 300g / L NaCl), respectively. Due to the pressure difference between the two ends of the membrane, water flows from the residual sludge side to the brine side, and the moisture content of the residual sludge is reduced to 80%, meeting the requirements for dewatered sludge transportation and disposal.

Claims

1. A system for efficiently treating and recycling anaerobic digestion liquid from kitchen waste, characterized in that: It includes a desalination system, a denitrification system, a sludge dewatering system and a reclaimed water system. First, the food waste to be processed enters the desalination system. The output of the desalination system in different process links is connected to the input of the denitrification system and the sludge dewatering system respectively. The output of the denitrification system is connected to the input of the reclaimed water system and the sludge dewatering system, wherein: The desalination system is an electric adsorption desalination system, and the desalination system includes a grid with a grid spacing of 50 mm and 10 mm, 5mm, and also includes an oil separation sedimentation tank, a coagulation flotation tank, an electric adsorption tank and a refined salt purification device, which are connected in sequence, wherein: the grid is used to intercept scum, massive floating oil and particulate pollutants; the oil separation sedimentation tank is used to isolate floating oil, scum, and grease in the water, and precipitate to remove precipitable matter in the wastewater; the coagulation flotation tank is used to remove finer suspended matter; the electric adsorption tank is used to selectively adsorb and remove monovalent ions in the water and realize salt purification and recovery through the refined salt purification device; the coagulation flotation tank includes a front-end reaction tank and a rear-end reaction tank connected in sequence, and an appropriate amount of polyaluminum chloride PAC and polyacrylamide PAM are added to the front-end reaction tank, and a large number of tiny bubbles are released through the vortex flotation aerator to remove most of the suspended matter in the wastewater, and a demulsifier is added to the rear-end reaction tank to separate the emulsified oil from the liquid phase, remove the remaining suspended matter and colloid, and the effluent enters the electric adsorption tank for desalination treatment; the electric adsorption tank includes a flowing electrode liquid, a collecting plate, an ion exchange membrane and an adsorption chamber, and uses the flowing electrode to adsorb Na + and Cl - Ions, wherein: the adsorption chamber is formed by a collecting plate, the adsorption chamber is attached with an ion exchange membrane, and the adsorption chamber has a flowing electrode liquid; when the incoming wastewater flows through the adsorption chamber, the ion exchange membrane includes a cation and anion exchange membrane, which can selectively pass through Na + and Cl - , Na + and Cl - It passes through the ion exchange membrane and is absorbed by the flowing electrode liquid. Finally, the desalination system effluents through the electric adsorption cell, and the desalinated low-salt wastewater enters the denitrification system. At the same time, it absorbs Na + and Cl - The flowing electrode liquid enters the refined salt purification device to purify the subsequent concentrated brine. Solid NaCl can be recovered through evaporation and crystallization. The brine output from the refined salt purification device enters the sludge dehydration system. The denitrification system is an anaerobic ammonium oxidation denitrification system, which includes a nitrite tank, an anaerobic ammonium oxidation tank, a two-stage AO and an MBR membrane bioreactor, which are connected in sequence; the two-stage AO performs traditional nitrification and denitrification reactions on the remaining total nitrogen that has not been completely reacted at the front end, and the MBR achieves sludge and water separation through membrane filtration. The separated sludge to be dehydrated is used to form a sludge dewatering system, and the separated water enters the reclaimed water system; The sludge dewatering system is a forward osmosis sludge dewatering system, and the reclaimed water system is a water reuse reclaimed water system. The sludge dewatering system adopts a forward osmosis sludge dewatering system, including a low osmotic pressure side and a high osmotic pressure side, which form an osmotic pressure field. The low osmotic pressure side is a sludge dewatering device, which inputs the sludge to be dewatered obtained by separation in the denitrification system; the high osmotic pressure side is connected to the brine output end of the desalination system, so that the osmotic pressure potential energy of the concentrated brine generated by the desalination system is used to dewater the residual sludge in the sludge dewatering device. The forward osmosis sludge dewatering system utilizes the osmotic pressure difference and realizes the migration of water in the sludge to the brine based on the spontaneous osmotic process. Since the process is spontaneous, no reagents need to be added, and the unit energy consumption is at an extremely low level. The regenerated water system is connected to the output of the denitrification system to remove refractory organic matter in the water after mud and water separation in the denitrification system, and the effluent is reused as regenerated water; the regenerated water system includes a Fenton advanced oxidation tank and a BAF aerated biological filter.

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