Method for directly utilizing land by preparing green organic fertilizer from kitchen waste anaerobic fermentation biogas residues through thermal hydrolysis and precise oxidation

Abstract

The invention discloses a method for directly utilizing land by preparing a green organic fertilizer from kitchen waste anaerobic fermentation biogas residues through pyrohydrolysis and precise oxidation. A pyrohydrolysis reactor is adopted as a container; high-pressure steam and high-pressure air are used as stirring power to carry out pyrohydrolysis-precise oxidation cooperative treatment on the kitchen waste anaerobic fermentation biogas residues, so that heating and oxidation are synchronously carried out, after the reaction is finished, the biogas residues subjected to heat treatment are dried, and the obtained solid phase is the green organic fertilizer. According to the method, in a high-temperature and high-pressure reaction system, free oxygen widely existing in air serves as an oxidizing agent to excite free radical chain reaction, synergistic degradation of organic matter and oxidative decomposition of toxic and harmful substances are achieved, and finally the organic fertilizer meeting the green standard is generated. According to the method, in-situ harmlessness of the biogas residues is realized by adopting a pyrohydrolysis and precise oxidation synergistic technology, the content of toxic and harmful substances is reduced from the source, and soil pollution caused by application of biogas residue fertilizer is avoided.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of solid waste treatment, and particularly relates to a method for preparing green organic fertilizer directly used in land by means of thermal hydrolysis and precise oxidation of anaerobic fermentation of kitchen waste residue. BACKGROUND

[0002] A large amount of kitchen waste is generated in China every year. According to the National Bureau of Statistics, it is expected to exceed 170 million tons in 2025. The huge amount of kitchen waste and the characteristics of kitchen waste such as easy rotting, stench, breeding of mosquitoes and the like have caused people's concern about the disposal of kitchen waste. Anaerobic digestion is a common technical method for resource utilization of kitchen waste. For large-scale kitchen waste anaerobic digestion plants, after pretreatment of kitchen waste to recover grease and remove mechanical impurities, the prepared slurry is directly fed into the anaerobic digestion tank for fermentation. The derivative of the anaerobic digestion tank is not only biogas which can be resourcefully reused, but also biogas slurry and biogas residue. Among them, the biogas residue is rich in humus and inorganic salt nutrients required for plant growth, and the main nutrient content includes 30% to 50% of organic matter, 10% to 20% of humic acid, 0.8% to 2.0% of total nitrogen, 0.4% to 1.20% of total phosphorus, and 0.6% to 2.0% of total potassium. Therefore, the biogas residue has great agricultural value in improving soil structure and enhancing soil fertility.

[0003] However, due to the short residence time (usually <30 days) of the anaerobic fermentation of the kitchen waste treated on a large scale, the produced biogas residue has low maturity, great biological safety hazards (fecal coliform content >10 4 MPN / g, survival rate of parasitic ova >30%), and high ammonia nitrogen concentration (5000 mg / kg to 15000 mg / kg). If directly applied to the soil, it may cause secondary fermentation and cause root burn of plants or increase the occurrence rate of fly larvae due to the high ammonia nitrogen concentration. In addition, since the biogas residue comes from kitchen waste with different components and properties, the kitchen waste itself or in the transportation process carries a certain amount of toxic and harmful substances such as heavy metals, antibiotics, pharmaceutical hormones, and microplastics. The anaerobic fermentation process has limited effect on the removal of such toxic and harmful substances, and part of the substances may exist in the fermentation system in a dissolved or adsorbed state, finally remaining in the biogas residue. Direct application of the biogas residue without treatment not only causes secondary fermentation to cause soil anoxia, root burn, and emission of foul-smelling gases (NH3, H2S) to pollute the air, but also causes accumulation of toxic and harmful substances in the soil, which endangers the soil environment and ultimately endangers human health through the food chain. SUMMARY

[0004] The technical problem to be solved by the present application is to provide a method for preparing green organic fertilizer directly used in land by means of thermal hydrolysis and precise oxidation of anaerobic fermentation of kitchen waste residue, which is mild in conditions, simple in process, energy-saving and efficient, and easy to control. The obtained green organic fertilizer can be used as a safe soil conditioner.

[0005] To solve the above technical problems, the present application adopts the following technical solutions:

[0006] The method for preparing green organic fertilizer by directly land using of hot hydrolysis and precise oxidation of anaerobic fermentation of kitchen waste residue, adopts a hot hydrolysis reactor as a container, high-pressure steam and high-pressure air as stirring power to perform hot hydrolysis-precise oxidation cooperative treatment on the anaerobic fermentation of kitchen waste residue, so that heating and oxidation are performed synchronously, and after the reaction is completed, the heat-treated residue is dried to obtain the solid phase, which is the green organic fertilizer.

[0007] The above method comprises the following steps:

[0008] (a) pumping the anaerobic fermentation of kitchen waste residue into the hot hydrolysis reactor, stopping feeding when the designed volume is reached, starting the temperature rising program, and heating the residue with high-pressure steam as the heating source;

[0009] (b) when the temperature in the reactor reaches 100 ℃, start to input high-temperature and high-pressure air to cooperate with high-pressure steam as the stirring power to stir the residue;

[0010] (c) after the reaction is completed, the heat-treated residue is dried to obtain the green organic fertilizer.

[0011] The anaerobic fermentation of kitchen waste residue has a water content of 80-85%.

[0012] The high-pressure air is uniformly input into the hot hydrolysis reactor according to the oxygen amount converted into air volume within the reaction period; the oxygen amount is added according to 1-2 times the BOD content.

[0013] The hot hydrolysis reactor has a set pressure of 1.4-2.6 MPa and a set temperature of 140-220 ℃, a linear temperature rising rate of 3-6 ℃ / min, and a temperature and pressure holding time of 0.1-1 h.

[0014] The high-pressure air is input into the reactor after being heated by a pressurizing device under a pressure of 1.6-3 MPa.

[0015] The green organic fertilizer prepared by the above method.

[0016] The above green organic fertilizer meets the evaluation standard of Organic Fertilizer (NY525-2021).

[0017] The above green organic fertilizer is applied in agricultural soil improvement.

[0018] In view of the problems existing in the treatment of anaerobic fermentation of kitchen waste, the inventors establish a method for preparing green organic fertilizer directly land use by precise oxidation of kitchen waste anaerobic fermentation of biogas residue (i.e. precise oxidation of kitchen waste anaerobic fermentation of biogas residue) by precise oxidation of kitchen waste anaerobic fermentation of biogas residue. The heat hydrolysis reactor is used as a container, high pressure steam and high pressure air are used as stirring power to carry out heat hydrolysis-precise oxidation synergistic treatment on kitchen waste anaerobic fermentation of biogas residue, so that heating and oxidation are carried out synchronously. After the reaction is completed, the heat treated biogas residue is dried to obtain the green organic fertilizer. In the high temperature and high pressure reaction system, the oxygen widely existing in the air is used as the oxidant to excite the free radical chain reaction, realize the synergistic degradation of organic matter and the oxidation decomposition of toxic and harmful substances, and finally generate the organic fertilizer meeting the green standard.

[0019] Among them, the introduction of oxygen creates the reaction condition of forming partial oxidation under hydrothermal environment, which can effectively degrade macromolecular organic matter, and part of the high polymer material is dehydrated and carbonized into porous biochar. The optimized mineralization conditions ensure that the biogas residue produces high-quality organic fertilizer under the most economical reaction conditions. The biogas residue may undergo the following reactions in the reactor with high temperature, high pressure and oxidant: (a) macromolecular organic matter (such as protein, polysaccharide, lipid, etc.) is degraded into water-soluble small molecular organic matter (such as short-chain fatty acid, monosaccharide, amino acid, etc.), and the small molecular organic matter is oxidized into carbon dioxide, part of the organic matter is completely mineralized into CO2 and H2O in the environment of oxygen molecule and high temperature and high pressure, and the biogas residue is improved in maturity; (b) bacteria, viruses and insect eggs are inactivated by high temperature; (c) antibiotic, medicinal hormone and other toxic organic substances are oxidized and decomposed into non-toxic substances; (d) a large amount of NH4-N in the biogas residue is oxidized into N2 and a small amount of NO2-N, reducing the NH4-N / NO3-N ratio, avoiding the occurrence of intense nitrification reaction in the soil, and competing for oxygen in the soil to cause root burning, so as to achieve the condition of green organic fertilizer maturity; (e) heavy metal elements are oxidized from low valence ion state to high valence state to form stable compounds, reducing the migration and bioavailability in the environment. After the biogas residue is subjected to the strengthened heat hydrolysis mineralization, the evaluation indexes all meet the evaluation standard of "Organic Fertilizer" (NY525-2021), and the biogas residue can be safely used as green fertilizer for agricultural soil improvement.

[0020] Compared with the prior art, the present application has the following outstanding advantages:

[0021] (1) The heat hydrolysis and precise oxidation technology of the present application is applied to the mineralization of kitchen waste anaerobic fermentation of biogas residue, which can effectively promote the degradation of easily decomposed organic matter in the biogas residue and avoid secondary fermentation.

[0022] (2) The treated biogas residue can be used as a safe green organic fertilizer, which can be applied to agricultural production without secondary treatment, and has good economic and environmental benefits.

[0023] (3) The present application adopts the enhanced thermal hydrolysis technology, which can efficiently degrade the toxic organic substances such as antibiotics, medicinal hormones and microplastics remaining in the biogas residue through precise oxidation dominated by oxygen in the air, and oxidize heavy metal elements to form stable compounds.

[0024] (4) The present application uses O2 in the air as an oxidant, which is widely available and unlimited in resources, and will not cause secondary pollution to the organic fertilizer product.

[0025] (5) After the biogas residue is treated by the enhanced thermal hydrolysis mineralization method of the present application, the plant nutrient elements and the proportion of difficult-to-degrade humus in the dry basis of the biogas residue are improved, the seed germination rate (GI) is >80%, the fecal coliform bacteria count and the death rate of parasite eggs meet the GB8172 standard, the ammonia nitrogen concentration is reduced, and the soil will not be burned by the rapid nitrification reaction caused by the application of the biogas residue. The sample product is brown or grayish brown and powdery, which meets the standard of "Organic Fertilizer" (NY 525-2021) and can be used as a safe soil conditioner.

[0026] In summary, the present application adopts the thermal hydrolysis and precise oxidation technology, combines the methods of two different fields to produce a "1+1>2" degradation and mineralization effect, realizes the in-situ harmless treatment of the biogas residue, reduces the content of toxic and harmful substances from the source, and avoids the pollution of the soil caused by the application of the biogas residue fertilizer. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 is the flow chart of the precise oxidation enhanced thermal hydrolysis mineralization method of the present application. DETAILED DESCRIPTION

[0028] I. Basic steps and operation instructions

[0029] (a) The centrifugal dewatering in the dehydration plant produces kitchen waste anaerobic fermentation residues with a moisture content of 80-85%. Screw pumps are used to pump the centrifugal residues in the silo into the high-pressure thermal hydrolysis reactor. The feed quantity is monitored by a liquid level meter or a weight sensor. When the design volume (i.e. the filling volume is 70-85%, with space reserved for steam and air) is reached, the feeding is stopped and the reactor is sealed. The high-pressure steam generator is started, and the steam inlet valve at the bottom of the reactor is opened to heat the residues with high-pressure steam as the heating source. The temperature rising program can be set by DCS (Distributed Control System) or PLC (Programmable Logic Controller), and the steam valve opening is automatically adjusted. The set pressure of the thermal hydrolysis reactor is 1.4-2.6 MPa, and the set temperature is 140-220°C, with a linear temperature rising rate of 3-6°C / min. When the reactor temperature and pressure reach the set values (e.g. 180°C, 2.0 MPa), the temperature rising phase is over. The system switches to the "heat preservation" mode, and the DCS / PLC will automatically adjust the steam supply according to the real-time monitored temperature to maintain the temperature at the set value within the range of 140-220°C, and the pressure is stabilized at 1.4-2.6 MPa. The set value of the safety relief valve at the top of the reactor should be higher than the upper limit of the operating pressure (e.g. 2.8 MPa) to ensure automatic relief when the pressure is too high. In this phase, high-pressure air continues to be supplied at the set flow rate. The heat preservation and pressure retention time is controlled at 0.1-1 hour according to the oxidation degree.

[0030] (b) When the temperature in the reactor reaches and stabilizes at 100°C (at this time, the viscosity of the biogas residue is significantly reduced, which can reduce the oxygen mass transfer resistance from the gas phase to the liquid phase, while avoiding premature entry to take away heat, and slow down the temperature rise in the system), start the high-pressure air compressor, slowly open the high-pressure air inlet valve at the bottom of the reactor, and start to pass high-pressure air (1.6-3 MPa) in conjunction with high-pressure steam as stirring power to stir the biogas residue, and use a pressure regulating valve (PIC) to stabilize the air pipeline pressure. In the high-temperature and high-pressure hydrolysis reactor, the heat and oxygen are uniformly applied to the biogas residue due to the sufficient stirring of the biogas residue by the high-pressure gas, realizing the full contact of the gas-solid two phases and the accurate oxidation of the biogas residue. To ensure good stirring effect and heat transfer to the biogas residue in the reactor, the high-pressure steam and high-pressure air inlet diffusion ports can be uniformly arranged at the bottom of the reactor. The source of oxygen is mainly the oxygen molecules in the air. To avoid the slow system temperature rise caused by the high-pressure air taking away a large amount of heat, the air passed into the reactor can be heated to near the reaction temperature by using an electric heating sleeve, a coil type heat exchanger or a steam heat exchanger as a preheating device. To ensure accurate oxidation of part of the organic matter in the biogas residue, the amount of oxygen required during the entire reaction period is calculated according to the oxidation degree, and the air inlet amount is kept uniform from the start of high-pressure air inlet until the end of the reaction. The flow rate of the high-pressure air is determined according to the BOD content and mineralization degree in the mixed liquor, and is added at 1-2 times the BOD content (i.e. 1-2 g O2 per 1 g BOD), to meet the needs of accurate oxidation in this design, and is uniformly passed into the hydrolysis reactor during the reaction period.

[0031] According to the ratio of BOD to COD accumulated in the past, the total amount of oxygen required is calculated by detecting SCOD on site by rapid digestion spectrophotometry and converting it into the amount of BOD. The calculation formula is: required oxygen mass (kg) = total amount of BOD in biogas residue (kg) x (1.0-2.0). The coefficient selection principle is that if stabilization and avoidance of secondary fermentation are the main targets, 1.0-1.5 is taken. If deep mineralization, oxidation of part of the ammonia nitrogen, efficient degradation of trace organic matter such as antibiotics, etc. are required, 1.5-2.0 is taken. Convert the oxygen mass into air volume (at normal temperature and pressure), then the required air volume (m³) = [required oxygen mass (kg) / 0.21] / 1.2 (where 0.21 is the oxygen volume fraction in air, and 1.2 is the air density, unit kg / m³). According to the total reaction time (from the start of air inlet to the end of holding), the constant flow rate of the air flow meter is calculated and set. The calculation of the air flow rate is air flow rate (m³ / h) = required air volume (m³) / total reaction time (h), and the instantaneous flow rate and cumulative flow rate of the air are measured by a suitable flow meter.

[0032] (c) After the reaction is completed, the heat-treated biogas residue is subjected to drying treatment. In order to make full use of the high-temperature steam and high-temperature biogas residue in the reactor, a heat exchanger can be used to conduct the heat to the biogas residue to be dried, so that the water is evaporated, and other drying auxiliary equipment such as a belt dryer and a disc dryer is used to dry the biogas residue to a water content of ≤30%, so as to obtain a solid organic fertilizer product (green and environmentally friendly biogas residue organic fertilizer). Sampling and detection of seed germination index (GI), fecal coliform bacteria count, parasite egg mortality rate and ammonia nitrogen content meet the standards of "Organic Fertilizer" (NY 525-2021), and can be safely used for agricultural production.

[0033] II. Parameter selection explanation

[0034] (a) Moisture content of biogas residue (80-85%): 80-85% moisture content is an ideal balance point that can be stably treated by conveying pumps, heat exchangers and other equipment. If the moisture content is too high, it means that a large amount of water needs to be heated, and the steam consumption is huge, which is not economical. During the process of high-temperature steam being introduced, the biogas residue will be diluted, and the moisture content of the biogas residue will increase.

[0035] (b) Reaction temperature (140-220℃): 140-220℃ covers the temperature at which common organic matter begins to degrade. Large molecular organic matter (protein, polysaccharide, lipid) is hydrolyzed into small molecular soluble matter at high temperature, and the higher the temperature, the more intense the reaction.

[0036] (c) Reaction pressure (1.4-2.6MPa): The saturation vapor pressure corresponding to 140-220℃ is 0.4-2.3MPa. The reaction pressure is set considering the air flow under high temperature and high pressure, and the pressure relief valve is adjusted by the control system to maintain the pressure of the reaction kettle, so as to ensure the stability of the temperature.

[0037] (d) Oxygen supply (O2:BOD=1-2:1): In the present application, according to the degree of precise oxidation, 1-2 g of O2 is added for 1 g of BOD. The more the amount of oxygen added, the higher the degree of oxidation, and the higher the required cost.

[0038] (e) Duration (0.1-1h): The duration is the time for heat preservation and pressure maintenance. According to the requirement of precise oxidation, if the content of easily degradable organic matter is low, the duration can be appropriately shortened; if the content of easily degradable organic matter is high, the duration can be appropriately prolonged.

[0039] III. Application example

[0040] According to the basic steps and operation in I, the biogas residue of anaerobic fermentation of kitchen waste is treated by using the present application, which is as follows:

[0041] (a) The kitchen waste anaerobic fermentation biogas from a kitchen waste high-temperature anaerobic fermentation plant in Nanning, Guangxi, was subjected to 15-25 days of high-temperature anaerobic fermentation. The sludge concentration (TS) in the digester increased from 8-10% at the time of feeding to 12-15%. The methane yield decreased from the normal value of 0.8-1.2 m 3 / kg VS to 0.5-0.6 m 3 / kg VS. The 80% moisture content kitchen waste anaerobic fermentation biogas produced after centrifugal dewatering of the sludge in the high-temperature anaerobic fermentation tank had a VS / TS range of 40-50%, and a methane yield of less than 10-20 mL CH4 / g VS. The kitchen waste biogas stored in the silo after centrifugal dewatering was pumped into the high-pressure thermal hydrolysis reactor using a screw pump. The feed quantity was monitored using a liquid level meter, and feeding was stopped when the reactor reached 80% of its rated working capacity, the feed valve was closed, and the reactor was sealed. The high-pressure steam generator was started, and the steam inlet valve at the bottom of the reactor was opened. The temperature was set to increase at a rate of 6℃ / min using PLC (programmable logic controller), and the steam valve opening was automatically adjusted to allow the temperature to increase linearly.

[0042] (b) When the internal temperature of the reactor reached and stabilized at 100℃, the high-pressure air compressor was started, and the high-pressure air inlet valve at the bottom of the reactor was slowly opened. The pressure of the high-pressure air was stabilized at 1.6 MPa, and was used together with the high-pressure steam as the stirring power to ensure that the gas and solid phases were fully mixed. The air entering the reactor was preheated using an electric heating sleeve to heat the air to near the reaction temperature.

[0043] (c) According to the accumulated BOD / COD ratio of 0.4 for the biogas, the SCOD was detected on site by rapid digestion spectrophotometry to be 8 g / L, and the amount of BOD was converted to be 8 x 2 x 0.4 = 6.4 g / L (the SCOD value was measured for 80% moisture content biogas, diluted to 90% moisture content, and the supernatant was centrifuged to measure SCOD. The SCOD measurement value x 2 was used to approximately reflect the SCOD contained in 1 L of 80% moisture content biogas). The oxygen required for thermal hydrolysis of 2 t of biogas = 2 x 6.4 x 1 = 12.8 (kg). The oxygen mass was converted to the air volume at normal temperature and pressure = [12.8 ÷ 0.21] ÷ 1.2 = 50.79 (m3). In this example, the thermal hydrolysis temperature was 170℃, and the holding time was 1 h, so the air flow rate was 50.79 ÷ 1.19 = 42.68 (m³ / h) (0.69 is the sum of 0.19 h for heating from 100℃ to 170℃ and 1 h for holding time).

[0044] (d) When the reactor temperature and pressure reach the set values of 170°C and 2.0 MPa, respectively, the temperature rising stage ends. The system switches to the "temperature maintaining" mode, and the PLC automatically adjusts the steam supply according to the real-time monitored temperature to maintain the temperature and pressure at 170°C and 2.0 MPa, respectively. The safety relief valve at the top of the reactor should be set higher than the upper limit of the operating pressure (e.g., 2.8 MPa) to ensure automatic relief in case of overpressure. During this stage, high-pressure air continues to be supplied at the set flow rate.

[0045] (e) After the temperature maintaining time ends, the steam valve and air inlet valve are automatically closed, the pressure is released, and after the pressure in the reactor is equal to the atmospheric pressure, the discharge valve is opened to discharge the pyrolysis-end biogas residue from the reactor. The heat of the high-temperature steam during pressure release and the high-temperature biogas residue just discharged is transferred to the to-be-dried biogas residue by a heat exchanger to evaporate the water in the biogas residue, and a belt dryer is used to dry the biogas residue to a moisture content of ≤30% to obtain a solid organic fertilizer product (green organic fertilizer).

[0046] The green organic fertilizer prepared in the application example was tested together with untreated centrifugal biogas residue (detection method: standard detection specified in the national organic fertilizer agricultural industry standard NY525-2021), and the test results are as follows:

[0047]

[0048] (f) A leafy vegetable was planted in an agricultural land in Xixiangtang District, Nanning, and two plots of equal area were allocated, one of which was applied with the aforementioned green organic fertilizer with a moisture content of 30%, and the other was used as a control group. The green organic fertilizer was applied at a rate of 9 kg / m 3 After one growth cycle from planting to harvesting, the biomass (fresh weight) above the roots was taken as the comparison, and it was found that the biomass increased by 23% compared with the control group, and the color was greener.

Claims

1. A method for preparing green organic fertilizer directly land use by thermal hydrolysis precision oxidation of anaerobic fermentation of biogas residue of kitchen waste, characterized in that: The hot hydrolysis reactor is used as a container, high-pressure steam and high-pressure air are used as stirring power to treat the anaerobic fermentation residue of kitchen waste by hot hydrolysis-precise oxidation cooperation, so that heating and oxidation are synchronized, and after the reaction is completed, the treated residue is dried to obtain green organic fertilizer. ​ 2. The method of claim 1, wherein It comprises the following steps: (a) pumping the anaerobic fermentation residue of kitchen waste into the hot hydrolysis reactor, stopping feeding when the designed volume is reached, starting the temperature rising program, and heating the residue with high-pressure steam as the heating source; (b) when the temperature in the reactor reaches 100 ℃, start to input high-pressure air to cooperate with high-pressure steam as the stirring power to stir the residue; (c) after the reaction is completed, the treated residue is dried to obtain green organic fertilizer.

3. The method of claim 1, wherein: The anaerobic fermentation residue of kitchen waste has a water content of 80-85%.

4. The method of claim 1, wherein: The high-pressure air is uniformly input into the hot hydrolysis reactor according to the oxygen content converted into air volume within the reaction period; the oxygen content is 1-2 times the BOD content.

5. The method of claim 1, wherein: The set pressure of the hot hydrolysis reactor is 1.4-2.6 MPa, the set temperature is 140-220 ℃, the linear temperature rising rate is 3-6 ℃ / min, and the temperature and pressure holding time is 0.1-1 h.

6. The method of claim 1, wherein: The high-pressure air is heated to a pressure of 1.6-3 MPa by a pressurizing device and then enters the reactor.

7. Green organic fertilizer prepared by the method of any one of claims 1-6.

8. The green organic fertilizer according to claim 7, characterized in that It meets the evaluation standard of "Organic Fertilizer" (NY525-2021).

9. The green organic fertilizer of any one of claims 7 or 8 for use in agricultural soil improvement.

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