CN114685199B

CN114685199B - Composting method based on layered alternate air supply

Info

Publication number: CN114685199B
Application number: CN202011587723.8A
Authority: CN
Inventors: 王选; 唐子贵; 马林; 柏兆海
Original assignee: Jiangsu Cs Niuke Ecological Technology Co ltd
Current assignee: Jiangsu Cs Niuke Ecological Technology Co ltd
Priority date: 2020-12-28
Filing date: 2020-12-28
Publication date: 2023-06-20
Anticipated expiration: 2040-12-28
Also published as: CN114685199A

Abstract

The invention discloses a composting method based on layered alternate air supply, which is characterized in that N air supply points are arranged along the flow direction of air, N is more than or equal to 2, and the N air supply points do not supply air at the same time along the flow direction of the air. The invention can improve the temperature of the compost in the high temperature period and prolong the duration time of the high temperature period through layered interactive air supply. The two-stage continuous gas supply and the bottom single-point gas supply are respectively prolonged by 6d and 11d. The degradation rate of organic matters is improved by 22.2 percent. The harmless process of material composting is accelerated, the harmless index can be met only by 14d, and the time required by bottom air supply is shortened by 50%. Can reduce CH compared with the traditional bottom gas supply ₄ Emission 43.3%, N reduction ₂ The O discharge is 27.0%, and the total ammonia discharge amount is not significantly different from the bottom air supply.

Description

Composting method based on layered alternate air supply

Technical Field

The invention relates to the technical field of biological composting, in particular to a composting method based on layered alternate air supply.

Background

China is a large-population country, and in order to meet the increasing demands of animal products such as meat, eggs, milk and the like, the breeding industry rapidly develops into intensification and large scale, and the production amount of livestock and poultry manure is rapidly increased. According to statistics, the livestock and poultry manure pollution amount in 2020 exceeds 42 hundred million tons. The large-scale and intensive cultivation forms and the traditional crude treatment technology lead to the difficulty in quick and effective conversion and utilization of livestock manure, so that the livestock manure is piled up, and the problems of malodorous gas and greenhouse gas emission and water pollution are caused. Therefore, the utilization of biotechnology, particularly composting technology, is one of the important ways to realize the reduction, harmlessness and recycling of organic wastes. Composting is an important and widely used method to convert manure into stable organic fertilizers and soil amendments, thereby giving the opportunity to intensify the circulation between livestock and farming systems and to reduce the risk of environmental pollution caused by intensive farm manure management.

Problems are faced during composting, mainly due to poor ventilation control during composting, resulting in insufficient oxygen supply and formation of a large number of anaerobic micro-domains in the composting material. The anaerobic environment inhibits the activity of aerobic microorganisms, thereby producing methane (CH) ₄ ) Dinitrogen monoxide (N) ₂ O), ammonia (NH) ₃ ) And other gas discharge, prevent the degradation of compost materials, and prolong the fermentation time of the compost.

The disclosed composting patent CN105523804A which takes fresh pig manure and corn straw as raw materials adopts calcium superphosphate as a conditioner, and the amount of substances of phosphorus element in the added calcium superphosphate is 5-10% of the amount of substances of total nitrogen in the composting raw materials, so as to carry out mixed composting. The aim of promoting and controlling the emission of greenhouse gases in the composting process and simultaneously reducing the volatilization loss of ammonia in the composting process of pig manure composting is achieved.

The method utilizes the acidity of the superphosphate, and achieves the purpose of reducing the volatilization of ammonia by reducing the pH value of the material, and is greatly influenced by the property of the additive. In addition, the optimal pH value in the composting process is 7.5-8.5, the addition amount is too small to play a role in reducing ammonia emission, the addition amount is too large to cause too low pH value of materials, the microbial reaction is inhibited, and meanwhile, the lower pH value can promote greenhouse gas N ₂ O generation. While at the same time. Superphosphate usually contains higher sulfides, which increase the odor H ₂ S is discharged. Therefore, the adoption of the additive to reduce the ammonia gas emission in the composting process is easily affected by the property of the additive, is unstable and has high cost.

The published patent CN106748524A discloses a preparation method of a biological organic fertilizer. After the raw materials are uniformly mixed, respectively carrying out primary fermentation and secondary fermentation, introducing an air duct of an oxygenation device to the bottom of the compost, covering the compost with a film, starting the oxygenation device, introducing oxygen, and carrying out aerobic fermentation for 5-8 days to obtain a primary fermentation material. And (3) conveying the primary fermentation material to a second fermentation field, stirring uniformly, adding potassium fulvate and biological bacteria according to the proportion, mixing uniformly, and carrying out secondary composting fermentation for 2-5 days to obtain a secondary fermentation material. The use of thin film compost covers limits the size of compost that can be used in this method to that of the thin film. In the method, although the biological microbial inoculum is added, the oxygen supply mode in the secondary fermentation process is still open type pile turning treatment, and the generated greenhouse gas cannot be controlled.

Therefore, how to improve the air supply strategy of livestock manure compost, promote the degradation rate of organic substances in the composting process, and reduce the emission of greenhouse gases becomes an urgent task for treating livestock manure.

According to the invention, no additional conditioner is added, and only the composting gas supply strategy is regulated, so that the degradation of the livestock manure is promoted, and the emission of greenhouse gases is reduced.

Disclosure of Invention

The invention aims to provide a composting method based on layered alternate air supply, aiming at the problems of low composting efficiency and high greenhouse gas emission in the prior art.

The technical scheme adopted for realizing the purpose of the invention is as follows:

a composting method based on layered alternate air supply is characterized in that N air supply points are arranged along the flow direction of air, N is more than or equal to 2, and the N air supply points supply air alternately (not simultaneously) along the flow direction of the air.

In the above technical scheme, a pile body is arranged during composting, an air outlet is arranged at the top of the pile body, air flows along the height direction of the pile body, one air supply point is positioned at the bottom of the pile body, and other air supply points are positioned at different heights of the pile body.

In the above technical scheme, m pile bodies are arranged during composting, m is more than or equal to 2, and the first pile body to the mth pile body are sequentially connected in series along the flowing direction of gas to form a gas supply system, wherein one gas supply point is positioned at the bottom of the first pile body, and other gas supply points are positioned at different positions of the gas supply system.

A composting method based on layered alternate air supply is characterized in that fermentation raw materials are placed in a fermentation reactor for aeration aerobic fermentation, N air supply points are arranged along the height direction of the fermentation reactor, N is more than or equal to 2, one air supply point is positioned at the bottom of the fermentation reactor, and N air supply points alternately (not simultaneously) supply air along the height direction of the fermentation reactor.

In the above technical scheme, when N is equal to 2, the two air supply points alternately supply air, and when N is greater than 2, the N air supply points alternately supply air in sequence or alternately supply air in sequence.

The top of the fermentation reactor or the pile body is provided with an air outlet, when N is 3, and the air is alternately supplied from bottom to top, the first air supply point firstly supplies air for a period of time, the second air supply point and the third air supply point do not supply air, then the second air supply point supplies air, and in the period of time, the first air supply point and the third air supply point do not supply air, then the third air supply point supplies air, and similarly, the first air supply point and the second air supply point do not supply air. The gas is circulated in this way. When the air is alternately supplied in different orders, the three air supply points respectively supply air according to the needs.

In the technical scheme, N air supply points are uniformly distributed along the height direction of the pile body or the fermentation reactor, and the intervals of every two air supply points in the height direction of the pile body or the fermentation reactor are the same.

In the technical scheme, the height of the pile body is 1.4-6m, and an air supply point is arranged at intervals of 0.7-1.2 m.

In the above technical solution, n=2, and air supply points are set at the bottom and middle sections of the pile or the fermentation reactor, and the air supply points at the bottom and middle sections alternately (not simultaneously) supply air.

In the above technical scheme, when the N air supply points supply air alternately, the air supply time ratio of any two air supply points is (0.8-1.2): (0.8-1.2), the air supply amount ratio of any two air supply points is (0.8-1.2): (0.8-1.2).

In the above technical scheme, each air supply point comprises one or more air supply ports, preferably, each air supply point is provided with a plurality of air supply ports, the air supply ports are circumferentially and uniformly distributed on the inner wall of the reactor body or the fermentation reactor, and each air supply point adopts an air compressor to perform forced ventilation on the fermentation reactor.

In the technical scheme, the material or fermentation raw material of the pile body is kitchen waste, sludge or livestock manure.

In the technical scheme, when the material or the fermentation raw material of the pile body is livestock manure, the C/N of the livestock manure is regulated to be (20-35): 1 and the water content of the livestock manure is regulated to be 45-65% before composting. Creating optimal reaction conditions for the microorganisms participating in the composting reaction.

In the technical scheme, the bottom and the middle section of the fermentation reactor are provided with air supply points, and the air supply points of the bottom and the middle section alternately supply air (not simultaneously). In the same time, when the air supply point at the bottom supplies air, the air supply point at the middle section does not supply air; and in the same time, when the air supply point at the middle section supplies air, the air supply point at the bottom does not supply air.

In the technical scheme, the height of the pile body or the fermentation reactor is h, and the gas supply point of the middle section is positioned at the position of 0.3-0.6 h.

In the technical scheme, when the air is alternately supplied, the air supply time of the air supply points at the bottom is a, the air supply time of the air supply points at the middle section is b, and a: b is (0.8-1.2): (0.8-1.2), when alternately supplying air, the air supply amount of the air supply points at the bottom is L1, the air supply amount of the air supply points at the middle section is L2, and L1:L2 is (0.8-1.2): (0.8-1.2).

In the above technical scheme, a=b, l1=l2, preferably, L1 and L2 are both 0.43-0.45 l·min ^-1 ·kg ^-1 。

The composting method based on layered alternate air supply is characterized in that along the air flowing direction, the first fermentation reactor and the second fermentation reactor … are connected through a communicating pipeline, the bottom of the first fermentation reactor is provided with air supply points, the bottoms of the other fermentation reactors or the communicating pipeline at the bottom of the other fermentation reactors are provided with air supply points, the top of the nth fermentation reactor is provided with an air outlet, fermentation raw materials are respectively placed in each fermentation reactor, and a plurality of air supply points alternately supply air (alternately supply air or alternately supply air in sequence) along the air flowing direction.

For example, when n=3, the air supply points at the bottom of the first fermentation reactor are advanced, the air supply points of the rest fermentation reactors are not fed, then the air supply points at the bottom of the second fermentation reactor or the air supply points on the communication pipeline at the bottom of the second fermentation reactor are fed, the air supply points of the rest fermentation reactors are not fed, and finally the air supply points at the bottom of the third fermentation reactor or the air supply points on the communication pipeline at the bottom of the third fermentation reactor are fed, and the air supply points of the rest fermentation reactors are not fed and circulate in sequence.

In the above technical solution, each air supply point includes one or more air supply ports, preferably, each air supply point is provided with a plurality of air supply ports, and the air supply ports are uniformly distributed in the circumferential direction of the pile body or the fermentation reactor. Each air supply point adopts an air compressor to carry out forced ventilation on the fermentation reactor.

In the technical scheme, when the air is alternately supplied, the air supply time ratio of any two air supply points is (0.8-1.2): (0.8-1.2) the air supply amount ratio of any two air supply points is (0.8-1.2): (0.8-1.2).

In the above technical scheme, n=2, the fermentation raw materials are respectively placed in the first fermentation reactor and the second fermentation reactor, the top of the first fermentation reactor is connected to the bottom of the second fermentation reactor through a connecting pipeline, a first air supply point is arranged at the bottom of the first fermentation reactor, a second air supply point is arranged at the bottom of the connecting pipeline or the second fermentation reactor, an air outlet is arranged at the top of the second fermentation reactor, and air is alternately (not simultaneously) supplied to the first air supply point and the second air supply point.

In the same time, when the first air supply point supplies air, the second air supply point does not supply air; and in the same time, when the second air supply point supplies air, the first air supply point does not supply air.

In the technical scheme, the fermentation raw material is kitchen waste, sludge or livestock manure. Preferably, when the fermentation raw material is livestock manure, the C/N of the livestock manure is regulated to be (20-35): 1 before composting, and the water content of the livestock manure is regulated to be 45-65%.

In the technical scheme, when the air is alternately supplied, the air supply time of the first air supply point is a, the air supply time of the second air supply point is b, and a: b is (0.8-1.2): (0.8-1.2), the air supply amount of the first air supply point is L1, the air supply amount of the second air supply point is L2, and L1:L2 is (0.8-1.2): (0.8-1.2).

In the above technical scheme, a=b, l1=l2, preferably, L1 and L2 are both 0.43-0.45 l·min ^-1 ·kg ^-1 . The total aeration of the two fermentation reactors was: 0.87 to 0.91 L.min ^-1 ·kg ^-1 。

Compared with the prior art, the invention has the beneficial effects that:

1. the invention can improve the temperature of the compost in the high temperature period and prolong the duration time of the high temperature period through layered interactive air supply. The two-stage continuous gas supply and the single-point continuous gas supply at the bottom are respectively prolonged by 6d and 11d.

2. Compared with the bottom air supply, the organic matter degradation rate in the composting process is improved by 22.2 percent. The harmless process of material composting is accelerated, the harmless index can be met only by 14d, and the time required by bottom air supply is shortened by 50%.

3. The invention can reduce CH compared with the traditional bottom gas supply ₄ Emission 43.3%, N reduction ₂ The O discharge is 27.0%, and the total ammonia discharge amount is not significantly different from the bottom air supply.

Drawings

FIG. 1 is a schematic diagram of the three composting experiment systems of example 1.

FIG. 2 is a schematic diagram of the three composting experiment systems of example 2.

Fig. 3 is a graph of temperature variation between different air supply systems: (a) is the inter-system temperature, (b) is the lower layer temperature, and (c) is the upper layer temperature.

Fig. 4 is a graph showing oxygen concentration variation between different gas supply systems: (a) is the inter-system oxygen concentration, (b) is the lower oxygen concentration, and (c) is the upper oxygen concentration.

FIG. 5 is a graph showing the variation of water content of materials between different air supply systems: (a) is the water content of the materials between the systems, (b) is the water content of the lower-layer materials, and (c) is the water content of the upper-layer materials.

Fig. 6 variation of germination index of materials from air supply system to air supply system: (a) is the germination index of the materials between the systems, (b) is the germination index of the materials at the lower layer, and (c) is the germination index of the materials at the upper layer.

Fig. 7 changes in organic matter content of materials between different gas supply systems: (a) is the organic matter content of the materials between the systems, (b) is the organic matter content of the lower-layer materials, and (c) is the organic matter content of the upper-layer materials.

Material nitrogen loss variation between different gas supply systems of fig. 8: (a) is the intersystem material nitrogen loss, (b) is the lower layer material nitrogen loss, and (c) is the upper layer material nitrogen loss.

Fig. 9 different ammonia emission conditions of the gas supply system: (a) Is intersystem NH ₃ Discharging (b) the lower layer NH ₃ Discharging (c) the upper NH layer ₃ The exhaust is (d) NH between systems ₃ Cumulative emissions.

FIG. 10 illustrates different greenhouse gas emissions from the gas supply system: (a) Is inter-system CH ₄ Discharging (b) the lower CH ₄ Discharging (c) the upper CH ₄ And (d) is CH ₄ Cumulative emissions; (e) For intersystem N ₂ O is discharged, (f) is the lower layer N ₂ O is discharged, (g) is N of the upper layer ₂ O is discharged, (h) is N ₂ O cumulative emissions.

In fig. 3-10, a# system: a traditional bottom air supply; b# system: layering and continuously supplying air; c# system: and (5) layering and intermittently supplying air.

Detailed Description

The present invention will be described in further detail with reference to specific examples. It should be understood that the specific embodiments described herein are for purposes of illustration only and are not intended to limit the scope of the invention.

Example 1

1.1 composting Process

The top of the fermentation reactor is provided with an air outlet, when N is 3, the first air supply point firstly supplies air for a period of time from bottom to top, the second air supply point and the third air supply point do not supply air in the period of time, then the second air supply point supplies air, the first air supply point and the third air supply point do not supply air in the period of time, then the third air supply point supplies air, and the first air supply point and the second air supply point do not supply air in the same way. The gas is circulated in this way.

In this example, n=2, gas supply points are set at the bottom and middle of the reactor or the fermentation reactor, and the gas supply points at the bottom and middle alternately (not simultaneously) supply gas.

When the air is alternately supplied, the first air supply point supplies air for 10min, the air supply amount is 3L/min, and the second air supply point supplies air for 10min, and the air supply amount is 3L/min.

In the above technical scheme, the air supply point of bottom includes an air supply mouth, and the air supply point of middle section sets up a plurality of air supply mouths, and the air supply mouth equipartition is in fermentation reactor's circumference, and every air supply point all adopts air compressor to carry out forced draft to fermentation reactor.

1.2 composting materials

The materials used in the test were chicken manure and wood dust. Chicken manure is from a layer farm in the south Liu Cun area of Shijia, and wood chips are from a wood processing plant in the south Liu Cun area of Shijia. The basic properties of the raw materials are shown in Table 1.1.

1.3 composting apparatus

Experiments were performed in a computer controlled 100L bench top cylindrical intelligent composting reactor. Vacuum pumps were connected to aeration tubes at the bottom of the reactor and in the middle of the reactor to provide positive pressure aeration, clean (fresh) air passing through the compost material from bottom to top. The ventilation is controlled by a computer-controlled program through a flowmeter. Gas sampling points are arranged at the middle layer and the top of the reactor, tail gas passes through a conical flask, and boric acid is used for absorbing NH ₃ . A schematic of the composting reactor is shown in figure 1.

1.4 protocol

Chicken manure is mixed with sawdust to provide porosity to the compost mixture and to adjust the initial moisture content. The C/N ratio of the mixture was 25:1 and the moisture was 70%. After thorough mixing, 90kg of the mixed material was placed on average in a composting system. As in fig. 2, the experiment had three treatments: a) Conventional bottom feed (a system): adopting continuous air supply at the bottom, wherein the air supply amount is 6L/min, and no external air supply is arranged in the middle; b) Layered continuous air feed (b system): adopting bottom continuous air supply, wherein the air supply amount is 3L/min, the middle part is externally added with continuous air supply, and the air supply amount is 3L/min; c) Layered intermittent air supply (c system): the bottom and the middle are alternately supplied with air, the alternating frequency is 10 min/time, and the air supply amount is 6L/min.

1.5 sample collection and determination

System emissions NH were measured by boric acid absorption from the middle and top of the system during composting ₃ GHGs were sampled with an air bag and measured by gas chromatography. Gas extraction frequency: once daily. Solid sampling is carried out on the materials:

day

0, 3, 7, 10, 14, 21, 28, 35; 300g of solid sample is taken each time (100 g is taken as one sample by adopting a five-point sampling method, 3 repeated samples are taken from each reactor, the total is 300g, the sample represents the property of the lower layer or the upper layer of materials), the sample number, the sampling date and the like are recorded, and the solid sample is placed in a freezer at the temperature of minus 20 ℃ for freezing, and is to be tested. Each treatment was repeated three times.

Samples of the collected starting materials and compost mixtures were analyzed for Germination Index (GI), total KN and total organic carbon according to the compost Material test Standard method (TMECC, 2002). Degradation of organics was calculated using equation (1):

wherein X1 is the initial organic content and X2 is the final organic content (Bernal et al 2009).

The nitrogen loss calculation method adopts the following equation:

wherein: n (N) _loss (%) represents the nitrogen loss rate,%; n represents the nitrogen content of the initial material, g/kg; n' represents the nitrogen content of the treated material, g/kg; w is an organic matterDegradation rate,%.

To assess the maturity of the compost, a compost sample was extracted with deionized water at a ratio of 1:10 (on a dry weight basis). Extractant (10 ml) was added to the petri dish with filter paper at the bottom. Ten cress seeds were then added and incubated at a constant 25 ℃ for 48 hours. The germination index of the compost sample extractant was compared using deionized water as a control. The Germination Index (GI) was calculated following the following formula described by HKORC (2005):

wherein:

a1 represents the germination index of seeds of the compost leaching solution,%;

a2 represents the average root length of the compost leaching solution cultured seeds, and mm;

b1 represents the seed germination index,%;

b2 represents the average root length of the deionized water cultured seeds, mm.

(2) Monitoring temperature and gas indexes:

reactor temperature and oxygen content (O) were monitored automatically (every 15 minutes) in three zones (upper, middle and lower) of composting material ₂ ) And recorded by a computer, followed by calculation of the daily average. To evaluate NH ₃ To discharge NH in the outlet gas ₃ Absorbed in boric acid and its concentration was determined by titration (Komilis and Ham, 2000). The greenhouse gases were collected by sampling the gas flow at each sampling point with an inert sealed gas bag. Determination of N by gas chromatography ₂ O and CH ₄ Agilent 7890B equipped with ECD and FID detector). The accumulated greenhouse gas emissions were calculated according to equation (3) as follows:

Q＝p×∑CV/Δt×273/T (3)

wherein Q = cumulative greenhouse gas emissions; p = gas density; c = gas concentration; Δt=sampling time; t=ambient temperature for sampling time Δt.

1.6 composting Process assessment

1.6.1 composting temperature

Three temperature probes (upper, middle and lower) are respectively arranged on an upper layer and a lower layer in the reactor for real-time temperature recording, the average value of the six temperature probes is taken as the system temperature, the average value of the three temperature probes on the upper layer is taken as the upper layer temperature, and the average value of the three temperature probes on the lower layer is taken as the lower layer temperature.

As shown in fig. 3, the temperature of each composting system showed a distinct warm-up period, cool-down period, and rotten period over the experimental time. The different air supply systems have obvious influence and difference on the change of the temperature of the pile body. In addition to the substantial leveling of the systems during the warming period, the temperature of the c-system during the high temperature period (material temperature higher than 50 ℃) averages 56.3 ℃ and is higher than 52.4 ℃ of the b-system and 50.7 ℃ of the a-system during other composting processes. And the duration of the lower high-temperature period of the system c is 14d, which is 5d longer than that of the system b and 12d longer than that of the system a respectively; indicating that intermittent air supply has good temperature maintenance capability. The lower layer temperature of each system has little difference along with the change trend of the composting time, the upper layer temperature of each system has larger difference, and the b system and the c system reach high-temperature fermentation level, but the a system is always kept below 50 ℃ after the first turning (the 4 th day of the experiment). Overall, the c-system high temperature phase is higher in temperature and lasts about 5 days longer than the b-system. The contribution of the temperature difference between the systems is mainly from the upper layers of the composting system.

1.6.2 oxygen concentration variation

Three oxygen concentration probes (upper, middle and lower) are respectively arranged on an upper layer and a lower layer in the reactor for real-time temperature recording, the average value of the six oxygen concentration probes is taken as the system oxygen concentration, the average value of the three oxygen concentration probes on the upper layer is taken as the upper layer oxygen concentration, and the average value of the three oxygen concentration probes on the lower layer is taken as the lower layer oxygen concentration.

The oxygen content of the reactor is a direct index for reflecting whether the reactor is in an aerobic state or not, and also reflects the intensity of the material fermentation reaction; on the premise that the material composition and other conditions such as process control are the same, the oxygen consumption speed is high, which indicates that the material fermentation reaction is faster. As shown in fig. 4, the oxygen concentration of each composting system shows a change trend of descending and then ascending, and shows periodic fluctuation along with turning of materials. And c, the oxygen concentration of the system is the lowest before the experimental process for 20d, and the lowest value reaches 14.9%, so that the respiration of microorganisms in the system is obvious, and the metabolism of the microorganisms is vigorous. The lower layer oxygen concentration of each system has a larger difference (figure 4 b), and the lower layer oxygen concentration of the c system is the lowest, the fluctuation is more severe, probably due to intermittent air supply and intermittent oxygen supply, the continuous consumption of oxygen in the materials by microorganisms can be realized, but the activity of microorganism metabolism can be also illustrated to a certain extent. The lowest concentration of oxygen in the upper layer of each system was the system a, and the lowest value was 14.3% (FIG. 4 c). Mainly because the upper layer of the system a only receives the air flow with lower oxygen concentration supplied from the lower layer, and the upper layers of the system b and the system c can be supplied with fresh air in the middle layer of the system. Overall, the overall oxygen concentration of the system was greater than 14% at each aeration rate, and did not inhibit the composting process (Jiang et al, 2015). The lower layer of the system is more severely consumed, and the oxygen concentration variation of each system mainly contributes to the lower layer of the composting system.

1.6.3 Water content Change of Material

The removal of pile moisture during composting is related not only to pile moisture content but also to pile dry matter loss. The composting by utilizing the reactor composting device has less influence on the change of the water content of the piled body. In the composting process, the overall water content of the compost material is not greatly changed and basically floats within the range of 10 percent. As shown in FIG. 5a, the material reduction trend is strong due to the loss of dry matters in the composting process, and the water content of the pile bodies of the b system and the c system is slightly increased to 73.4% and 72.0% respectively. While the system a is gradually declined to reach 68.3 percent. The variation difference of the lower water content of each composting system is obvious. The a system gradually descends, the b system has a slight upward trend, and the c system remains substantially unchanged (fig. 5 b). The reason for this difference is mainly due to the difference between the water content reduction caused by the entrainment of water vapor by the air flow during composting and the increase in water content caused by the loss of dry matter during composting. The water content change of the upper layer of each composting system is in an ascending trend, the highest of the system a reaches 76.7%, the second of the system c is 76.1%, and the lowest of the system b is 73.4% (figure 5 c). The lower layer steam is liquefied and mixed with the material after being carried into the upper layer by the air flow, and the air flow flowing through the lower layer material carries partial steam, so that the threshold of the lower layer steam taking away the steam from the upper layer is reduced under the same saturation pressure, and the water discharge of the upper layer material is influenced to a certain extent. The change in pile moisture of each composting system primarily contributes to the underlying layers from the system.

1.6.4 germination index variation

Germination Index (GI) is an important index reflecting the innocuous process of compost. As shown in FIG. 6a, the germination index of each system stack gradually increases, wherein the germination index of the system c increases faster, and reaches 76.5% (. Gtoreq.70%) when composting for 14 days, so as to reach the standard of innocuity of compost, and the system a and the system b both need 28 days (three repeated samples are taken for the upper layer and the lower layer respectively, and the average value obtained by uniformly calculating the total of six samples). The germination index of the lower layer of each system showed a gradual increase trend, and the germination index difference between each system was small (fig. 6 b). The germination index of the lower layer of the system c was 72.2% for 10 days in the experiment, and each of the systems a and b was 14 days (three replicates were taken for the lower layer and the average value was calculated). The trend of germination index of upper layer of each system is larger (figure 6 c), the germination index of upper layer of c system is faster to increase, the germination index of 14d is 76.5% (. Gtoreq.70%) when experiment is carried out, and 28d is needed when germination index of a system and b system is above 70% (three repeated samples are taken from upper layer, and calculated average value is obtained). On the whole, under the condition of less influence on germination index of the lower-layer materials, the alternating intermittent air supply treatment of the system c accelerates the harmless process of composting of the upper-layer materials.

1.6.5 organic matter degradation rate

As shown in fig. 7a, the organic matter degradation rates of the three gas supply systems all gradually increase. And c, the degradation rate of the system is always kept the highest, the degradation amplitude is the largest, and the degradation rate reaches 23.3% until the experiment is finished (35 d). The systems a and b were 19.1% and 20.6%, respectively (three replicates were taken for each of the upper and lower layers, and the average value was calculated for the total of six samples). The fastest degradation of The Organic Matter (TOM) in the lower layer of the system is system a (fig. 7 b), the degradation range reaches 25.3%, mainly due to sufficient oxygen supply. And secondly, the system c and the system b are respectively reduced by 3.3 percent and 6.3 percent compared with the system a (three repeated samples are taken at the lower layer, and the average value obtained by calculation is calculated). The gas supply point increased in the middle part enables the upper material to be fully supplied with oxygen, and the intermittent gas supply can better preserve heat in the material, so that the degradation rate of organic matters on the upper layer of the system is highest as a system c, and the degradation rate of the system a is lowest as a system b, wherein the degradation rate of the system a is respectively 24.5%, 22.3% and 12.8% (shown in figure 7 c) (the upper layer takes three repeated samples, and the calculated average value is calculated). Overall, the organic matter degradation amplitude of the c system for alternately supplying air is the largest, and the organic matter degradation of the pile body of each composting system mainly contributes to the upper layer of the system.

1.6.6 total Nitrogen loss Rate

As shown in fig. 8a, the total nitrogen loss rates of the three gas supply systems gradually increase. And when composting is finished, the loss rate of the c system is always kept the highest, and the degradation amplitude is the largest. By the end of the experiment (35 d), the total nitrogen loss reached 18.9%. The systems a and b were 15.6% and 16.6%, respectively (three replicates were taken for each of the upper and lower layers, and the average value was calculated for the total of six samples). The nitrogen loss rate of the system a at the lower layer of the system is always kept highest, the loss rate at the end of the experiment is 20.0%, and the loss rates of the system b and the system c at the lower layer of the system are respectively 16.4% and 19.1% (shown in figure 8 b) (three repeated samples are taken at the lower layer, and the calculated average value is obtained). The highest total nitrogen loss rate of the upper layer of each system is c system, the highest total nitrogen loss rate can reach 18.6%, and the highest total nitrogen loss rate of the upper layer of each system is b system, the lowest degradation rate of a system is 16.8% and 11.2% (figure 8 c) respectively (the upper layer takes three repeated samples, and the calculated average value is obtained). The experiment shows that the temperature of the multi-air supply site composting system is higher, the rapid decomposition of organic nitrogen on the upper layer is promoted, and more nitrogen is lost. And c, the degradation amplitude of organic matters of the system is maximum, and the stack nitrogen loss of each composting system mainly contributes to the upper layer of the system.

1.6.7 Ammonia emission

NH extracted from top gas sampling point of reactor ₃ As an upper layer NH ₃ Discharge amount of NH extracted from middle layer gas sampling point of reactor ₃ As the lower layer NH ₃ Discharge amount.

The emission of ammonia is a major part of the nitrogen loss (in terms of nitrogen mass) in the compost raw material, which determines the amount of nitrogen remaining in the compost. As shown in FIG. 9a, each systemUnified stack NH ₃ Daily discharge (upper NH) ₃ Discharge amount and lower layer NH ₃ Average value of discharge amount) changes exhibit a tendency to be high-first-low. System NH ₃ The main discharge time is concentrated in the warm-up period and the high-temperature period. a System NH within the previous 7d ₃ The emission is highest, reaching the highest value of 7.2g/d at the 2 nd. While experiments were carried out for 8-16d, NH of c system ₃ Daily emissions were at the highest, and were maintained at 1.2g/d on average. Lower layer NH of each composting system ₃ The discharge amount is in a trend of high and low (figure 9 b), wherein the discharge amount of the system a is 6.6g/d at the highest, and the oxygen supply is sufficient mainly because of the large air supply amount, so that the quick conversion of the easily degradable organic nitrogen into NH is facilitated ₃ And (5) discharging. Upper layer NH of each composting system ₃ The emissions also show a trend of high-first low-last. c upper layer NH of system ₃ The highest emission amount reaches 3.6g/d at peak value, and the duration of high emission amount reaches about 16 days longer, thus becoming the NH of the system ₃ The main source of emissions (fig. 9 c). Overall, each system stack NH ₃ The daily discharge amount change mainly contributes to the lower layer of the system in the first 7 days, so that the cumulative discharge amount of ammonia gas in the system is the highest; after 7 days the main contribution was turned to the upper system layer, causing the cumulative emissions from the c-system to reach a maximum and at 19d to reach a cumulative peak of 215.8g.

1.6.8 greenhouse gas emissions

CH extracted from top gas sampling point of reactor ₄ As the upper layer CH ₄ Discharge amount, CH extracted from middle layer gas sampling point of reactor ₄ As the lower layer CH ₄ Discharge amount.

CH ₄ Is one of the main greenhouse gases released by aerobic composting, mainly comprising the methanogen to CO under anaerobic condition ₂ And H is ⁺ And acetic acid (Awasthi et al, 2017). Thus, CH in composting ₄ The production of (a) indicates that a portion of the compost material is not sufficiently O ₂ And (5) supplying. As shown in FIG. 10a, CH is present throughout the composting process ₄ The trend of the emission rate shows an overall trend of rising and then gradually decreasing, which may be related to the high temperature at the initial stage of composting and the rapid degradation of organic matter.With the rise of temperature, a large amount of organic matters are decomposed, so that the oxygen supply is insufficient, and partial areas are in an anaerobic state, so that a large amount of CH is generated ₄ Generates and thus CH ₄ The discharge rate of (c) increases rapidly at an early stage. The lower layer conditions of each system have similar variation trend, and the lower layer CH of the intermittent air supply c system is used in the composting temperature rising and high temperature period ₄ The highest emission can reach 18.1mg/d. But at the upper layer of each system, the system a has no gas supply site, lacks oxygen supplement and is CH ₄ The discharge relative to the other two sets of systems is significantly higher than the other two sets of systems (P < 0.05). Overall, a system CH ₄ Daily discharge (upper CH) ₄ Emissions and lower CH ₄ Average value of discharge amount) is significantly higher than other two groups of multi-site air supply systems (P < 0.05), c system CH ₄ The daily discharge is lowest, which is reduced by 43.3 percent and 4.1 percent compared with the system a and the system b respectively. Multiple-site air supply can reduce the composting CH ₄ The emissions were significantly promoted (fig. 10 d).

N extracted from top gas sampling point of reactor ₂ O as upper layer N ₂ O discharge amount, N extracted from middle layer gas sampling point of reactor ₂ O as the lower layer N ₂ O emissions.

N ₂ O is another important gaseous product produced by the nitrogen process in the composting process and is considered a powerful greenhouse gas (Zhu-Barker et al, 2017). Mainly by both ammonium nitrate and denitrified nitrate nitrogen (Awasthi et al 2016). As shown in fig. 10e, each system N ₂ The change in the O-day discharge amount shows a tendency to rise after going high. Wherein the daily discharge of the system a is obviously higher than that of other composting systems (P is less than 0.05), the average daily discharge is 5.0mg/d, and 34.2 percent and 18.2 percent of the daily discharge of the system b and the daily discharge of the system c are respectively higher than those of the system b and the system c. Composting high temperature stage, c System N ₂ The O day emissions are highest and the main contribution comes from the upper layers of the system. This may be due to the large amount of NH generated by the c-system at the early stage of composting ₄ ⁺ Accumulation, incomplete nitrification/denitrification processes are performed simultaneously, both of which typically will convert NH ₄ ⁺ Conversion to N ₂ O. After composting for 25 days, a large amount of N is produced in all processes ₂ O, which may be due to a decrease in composting temperature and an increase in nitrate concentration (Wang et al, 2018). Overall, a system N ₂ Cumulative O emission (upper layer N) ₂ O emission and lower layer N ₂ Average value of O emissions) increased to the highest over c-system at experiment 25d (fig. 10 h), with the main contribution from upper layers of the system, b-system and c-system N ₂ The cumulative emission of O is significantly lower than that of the system a (P < 0.05), which is reduced by 16.3% and 27.0% respectively. Description of Multi-site air feed N was reduced ₂ The reduction in O emissions, especially in the upper layers of the system, is more pronounced (FIG. 10 g).

The stratified intermittent gas supply may effectively increase the oxygen content in the upper gas supply of the reactor, reduce heat loss caused by excessive gas supply in the lower layers, increase temperature and extend the duration of the composting high temperature period. Compared with the traditional bottom gas supply method, the degradation rate of organic matters in the composting process is improved by 22.2 percent, the volatilization of ammonia is equivalent, but CH is obviously reduced ₄ Emission 43.3% and N ₂ O emission 27.0%. Layered intermittent gas supply can accelerate the harmless process of composting the upper layer material. The overall germination index of the 14d composting system can meet the innocuous index and shorten the time required for other treatments by 50%.

Example 2

A composting method based on layered alternate air supply is characterized in that along the air flowing direction, a first fermentation reactor and a second fermentation reactor … are connected through a communicating pipeline, the bottom of the first fermentation reactor is provided with an air supply point, the bottoms of the other fermentation reactors or the communicating pipeline at the bottom of the other fermentation reactors are provided with air supply points, the top of the nth fermentation reactor is provided with an air outlet, fermentation raw materials are respectively placed in each fermentation reactor, and a plurality of air supply points alternately supply air along the air flowing direction.

In this embodiment, n=2, the fermentation raw materials are respectively placed in the first fermentation reactor and the second fermentation reactor, the top of the first fermentation reactor is connected to the bottom of the second fermentation reactor through a connecting pipeline, a first air supply point is arranged at the bottom of the first fermentation reactor, a second air supply point is arranged on the connecting pipeline, an air outlet is arranged at the top of the second fermentation reactor, and air is alternately (not simultaneously) supplied to the first air supply point and the second air supply point. In the same time, when the first air supply point supplies air, the second air supply point does not supply air; and in the same time, when the second air supply point supplies air, the first air supply point does not supply air.

The first air supply point is an air supply port, the second air supply point is an air supply port, and the air supply points all adopt an air compressor to carry out forced ventilation on the fermentation reactor.

The same principle of the test method and the same raw materials as in example 1 were selected, and in order to collect the upper and lower gases respectively, this example used two 50L bench-type cylindrical intelligent composting reactors connected in series. A vacuum pump was connected to the aeration tube at the bottom of each reactor to provide positive pressure aeration.

The performance parameters of example 2 were verified and the effect was similar to example 1.

Optionally, two composting reactors connected in series are provided with a gas distributor after the connecting pipeline enters the second fermentation reactor, so that the gas distribution in the reactors is more uniform.

The foregoing is merely a preferred embodiment of the present invention and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present invention, which are intended to be comprehended within the scope of the present invention.

Claims

1. A composting method based on layered alternate air supply is characterized in that N air supply points are arranged along the flow direction of air, N is equal to 2, and the N air supply points do not supply air at the same time along the flow direction of the air;

the composting device is characterized in that a pile body is arranged during composting, an air outlet is formed in the top of the pile body, air flows along the height direction of the pile body, one air supply point is located at the bottom of the pile body, and the other air supply point is located at the middle section of the pile body.

2. A composting method based on layered alternate air supply is characterized in that fermentation raw materials are placed in a fermentation reactor for aeration aerobic fermentation, N air supply points are arranged along the height direction of the fermentation reactor, N is equal to 2, one air supply point is positioned at the bottom of the fermentation reactor, the other air supply point is positioned at the middle section of the fermentation reactor, and the N air supply points do not supply air simultaneously along the height direction of the fermentation reactor.

3. The layered alternating air supply-based composting method according to claim 1, wherein the height of the pile is 1.4-6 m.

4. The composting method based on layered alternate air supply as claimed in claim 1 wherein air supply points are provided at the bottom and the middle section of the pile, and the air supply points at the bottom and the middle section supply air alternately.

5. The composting method based on layered alternate gas supply as claimed in claim 2, wherein gas supply points are provided at the bottom and the middle section of the fermentation reactor, and the gas supply points at the bottom and the middle section supply gas alternately.

6. The composting method based on layered alternate air supply as claimed in claim 2, wherein when the N air supply points supply air alternately, the air supply time ratio of any two air supply points is (0.8 to 1.2): (0.8-1.2), the air supply amount ratio of any two air supply points is (0.8-1.2): (0.8-1.2).

7. A layered alternating air supply based composting method as claimed in claim 2, characterized in that each air supply point comprises one or more air supply openings.

8. The composting method based on layered alternate air supply as claimed in claim 2 wherein a plurality of air supply ports are provided at each air supply point, the air supply ports are circumferentially and uniformly distributed on the inner wall of the pile body or the fermentation reactor, and each air supply point adopts an air compressor to forcibly ventilate the fermentation reactor.