Preparation method of livestock and poultry manure piled water-logged compost with carbon and nitrogen emission reduction and decay promotion functions

Abstract

The invention discloses a preparation method of a livestock and poultry manure piled water-logged compost capable of reducing carbon and nitrogen emission and promoting decay, and belongs to the technical field of organic fertilizers. The method comprises the following steps: mixing livestock and poultry manure and straw according to a fresh weight ratio of (2-3): 1, adjusting the initial moisture content to 65-75%, controlling C / N to be (20-25): 1, and taking the mixture as a basic material; adding 8-15% of biochar, uniformly mixing, putting into a foam box body with the length of 70-80cm, the width of 50-60m and the height of 40-50m, and piling for 30-45 days without turning in the composting period. By adding the straw and the biochar and optimizing the process parameters, the purposes of emission reduction and decay promotion in the static stack retting process are achieved, so that the problems of low decomposition degree and carbon and nitrogen loss of the simple stack retting fertilizer are solved.

Description

Technical Field

[0001] The invention belongs to the technical field of organic fertilizers, and in particular relates to a method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition. Background Art

[0002] With the rapid growth of the breeding, planting and processing industries, a large amount of agricultural solid organic waste has been generated, especially livestock and poultry manure and crop straw. According to statistics, the total amount of manure generated annually in the livestock and poultry breeding process in my country is about 3.8 billion tons, and pig and cattle breeding are the main sources of manure emissions. However, a large amount of livestock and poultry breeding waste cannot be effectively treated and utilized, resulting in livestock and poultry manure becoming one of the sources of environmental pollution. The accumulation of manure will release harmful odors and greenhouse gases, pollute the air; it will also pollute the soil, increase the number of heavy metals and drug-resistant genes; at the same time, it will also increase the nutrients in the water, leading to eutrophication.

[0003] In my country, manure is mainly used as fertilizer by directly returning it to the fields, returning it to the fields after composting, or producing organic fertilizer. Among them, the production of organic fertilizer is mainly achieved through aerobic composting technology, while returning it to the fields after composting mostly uses a simple composting method. Zhu Zhiping et al. found that in the process of utilizing solid manure, more than half of the manure was treated by simple composting and then applied to farmland (Zhu Zhiping et al. The impact of changes in China's livestock and poultry manure management on greenhouse gas emissions. Journal of Agricultural Environment Science, 2020, 39: 743-748). This simple composting treatment method occupies a dominant position in the actual utilization of solid manure, accounting for more than 90%. The reason is that compared with simple composting treatment, aerobic composting has a huge workload. Therefore, simple composting is a low-cost, simple and easy way to utilize manure resources that is currently widely used in China.

[0004] Livestock and poultry manure contains rich organic matter and nutrients such as nitrogen and phosphorus. The composting process is a biochemical process that transforms organic matter in livestock and poultry manure in a local anaerobic environment by decomposing hydrocarbons through microorganisms. This process produces gases such as CH4, CO2 and N2O. Similarly, the nitrogen in the composting process mainly includes organic nitrogen and inorganic nitrogen. Organic nitrogen releases ammonia and nitrogen oxides, while the transformation of inorganic nitrogen produces gases such as nitrous oxide. The greenhouse effect of CH4 is 25 times that of CO2, while N2O is 298 times that of CO2. The quality of compost products will be seriously affected by gas emissions. Similarly, gas emissions will also aggravate climate change. Nitrogen loss during composting is a major problem currently faced. It will reduce the production efficiency of fertilizers and cause air pollution, mainly the release of NH3 and N2O. About 40% of nitrogen will be lost during the composting process, of which about 80% to 95% of nitrogen will be lost in the form of NH3.

[0005] In view of the low temperature of static composting, the difficulty in ensuring the maturity, the insufficient oxygen supply of composting, and the local anaerobic conditions that may cause methane, nitrous oxide and other gases leading to carbon and nitrogen loss, most of the current research is based on aerobic composting, and there is no systematic study on the emission reduction and decomposition promotion effect of composting. However, simple composting has the advantages of low cost and simplicity, which is convenient for large-scale promotion and implementation in rural areas. Therefore, improving the composting process and thus improving the maturity of composting and carbon and nitrogen retention has important economic and social significance. Summary of the invention

[0006] In view of the shortcomings of the prior art, the purpose of the present invention is to provide a method for preparing livestock and poultry manure composting that reduces carbon and nitrogen emissions and promotes decomposition, so as to achieve the purpose of "reducing emissions and promoting decomposition" in the static composting process, thereby solving the problems of low maturity and carbon and nitrogen loss in simple composting.

[0007] In order to achieve the above technical purpose, the inventors took livestock and poultry manure as the main research object, improved the process of simple composting, and finally promoted the maturity of composting by adding auxiliary material straw through a large number of experimental studies and unremitting exploration. At the same time, the carbon and nitrogen losses of composting were reduced by adding biochar additives, and the following technical scheme was obtained: a method for preparing livestock and poultry manure composting with carbon and nitrogen emission reduction and decomposition promotion, the method comprising the following steps:

[0008] (1) livestock and poultry manure and straw are mixed in a ratio of (2-3) to 1 by fresh weight, the initial moisture content is adjusted to 65%-75%, and the C / N is controlled to (20-25):1 as the basic material;

[0009] (2) adding 8 to 15% of biochar based on the mass of the basic material and mixing to obtain a mixed material;

[0010] (3) The mixed material is placed in a foam box with a length of 70 to 80 cm, a width of 50 to 60 m, and a height of 40 to 50 m and piled for 30 to 45 days without turning the pile during the composting period.

[0011] It should be noted that currently more than 90% of farms use simple composting to treat solid feces. Composting can be a simple and low-cost way to treat livestock and poultry feces on the spot. However, the composting process often has low harmlessness, insufficient maturity, resulting in reduced compost quality, and the generation of greenhouse gases, which causes environmental problems such as carbon and nitrogen loss and greenhouse effect. The present invention gradually optimizes the composting process to reduce nutrient loss during the composting process, promote the maturity of the compost, and reduce carbon emissions. It also uses qPCR, high-throughput sequencing, and metagenomics to study emission reduction and promotion mechanisms, providing technical support for the low-carbon and high-efficiency fertilizer utilization of livestock and poultry feces.

[0012] Further preferably, in the method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition as described above, the livestock and poultry manure used is selected from one or a mixture of two or more of the following: pig manure, cow manure, chicken manure, and sheep manure.

[0013] Further preferably, in the method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition as described above, the straw used is selected from one or a mixture of two or more of the following: rape straw, wheat straw, corn straw, and rice straw.

[0014] Preferably, the biochar used in the above-mentioned livestock and poultry manure composting method for reducing carbon and nitrogen emissions and promoting decomposition is prepared by the following method: the rice straw is naturally air-dried or dried, and then large particles of impurities are removed and cleaned, cut into segments, crushed, placed in a ceramic container, sealed, and heated in a muffle furnace at 23-26°C·min -1 The temperature is raised to 680-620°C at a rate of 1.8-2.2 hours, maintained for 1.8-2.2 hours, and then crushed and sieved after cooling. Further preferably, the technical parameters for drying the rice straw are: continuous drying at 55-65°C for 40-60 hours.

[0015] Still further preferably, in the above-mentioned method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition, the amount of biochar added is 10% of the mass of the basic material.

[0016] It is worth noting that the method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition described in the present invention relies on its own microorganisms for degradation and fermentation before and after composting, and does not require the addition of any decomposing agent or microbial agent.

[0017] Compared with the prior art, the method for preparing livestock and poultry manure compost provided by the present invention has the following advantages and significant improvements:

[0018] (1) Adding straw can significantly promote nitrogen retention in the compost, but has no significant effect on reducing carbon loss. It can improve species diversity and richness at the end of composting. It can also promote the abundance of Actinobacteriota. The dominant genera are significantly related to nitrogen retention and gas emission reduction. The degree of maturity and carbon and nitrogen loss of composting with straw addition are better than those of pure pig manure composting. The cumulative emissions of N2O and CH4 are reduced by 84.6% and 62.9% respectively compared with pure pig manure composting. It can also reduce NH3 emissions.

[0019] (2) Adding biochar can slow down the rapid loss of water, increase the pH value of the compost, significantly reduce the carbon loss during the composting process, and the C / N ratio is above 21 at the end of composting, which significantly promotes the maturity of the compost, provides suitable physical and chemical conditions for microorganisms with different characteristics, and increases the diversity of bacterial communities. Adding biochar to straw composting can significantly reduce the emissions of NH3, N2O and CO2 in an aerobic environment, with a decrease of 57.6%, 54.1% and 20.7% respectively.

[0020] (3) Compared with the traditional composting of livestock and poultry manure, the present invention adopts an optimized process of adding straw and biochar to livestock and poultry manure and composting in a foam box, with a composting cycle of 30-45 days. The workload in the whole composting process is small, simple and easy, and can reduce labor. Therefore, under the premise of low investment, it can not only improve the maturity of the compost, but also be beneficial to the preservation of carbon and nitrogen and reduce carbon emissions, and can be made into organic fertilizer for field use. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 : The technical route of the method for preparing livestock and poultry manure composting of the present invention.

[0022] Figure 2 : Changes of ammonium nitrogen (a) and nitrate nitrogen (b) during composting.

[0023] Figure 3 : Changes in NH3 emission rate (a) and cumulative emission (b) during composting.

[0024] Figure 4 : Changes in N2O emission rate (a) and cumulative emissions (b) during composting.

[0025] Figure 5 : Changes in CH4 emission rate (a) and cumulative emission (a) during composting.

[0026] Figure 6 : Changes in CO2 emission rate (a) and cumulative emissions (b) during composting.

[0027] Figure 7 : Changes of Shanon index (a) and Simpson index (b) in different composting treatments.

[0028] Figure 8 : Changes of Chao index (a) and Ace index (b) in different composting treatments.

[0029] Fig. 9 : Changes in microbial communities at the phylum level (a) and genus level (b) under different composting treatments.

[0030] Fig.10 : RDA analysis of microbial communities at the phylum level (a) and genus level (b) under different composting treatments.

[0031] Fig.11 : RDA analysis (a) and correlation analysis (b) of physicochemical properties and gas emissions of different composting treatments.

[0032] Fig.12 :Temperature changes during composting process.

[0033] Fig.13 :Moisture changes during composting process.

[0034] Fig.14 :pH changes during composting process.

[0035] Fig.15 : Changes in total carbon (a), total nitrogen (b) and C / N (c) during composting.

[0036] Fig.16 : Changes of total phosphorus (a) and total potassium (b) during composting.

[0037] Fig.17 : Changes in NH3 emission rate (a) and cumulative emission (b) during composting.

[0038] Fig.18 : Changes in N2O emission rate (a) and cumulative emissions (b) during composting.

[0039] Fig.19 : Changes in CH4 emission rate (a) and cumulative emission (b) during composting.

[0040] Fig. 20 : Changes in CO2 emission rate (a) and cumulative emissions (b) during composting.

[0041] Fig.21 : Changes of Shanon index (a) and Simpson index (b) in different composting treatments.

[0042] Fig. 22 : Changes of Chao index (a) and Ace index (b) in different composting treatments.

[0043] Fig.23 : Changes in microbial communities at the phylum level (a) and genus level (b) under different composting treatments.

[0044] Fig.24: RDA analysis of microbial communities at the phylum level (a) and genus level (b) under different composting treatments.

[0045] Fig.25 : RDA analysis (a) and correlation analysis (b) of physicochemical properties and gas emissions of different composting treatments. DETAILED DESCRIPTION

[0046] The technical solution of the present invention is described clearly and completely below through specific embodiments. Based on this embodiment, all other embodiments obtained by ordinary technicians in this field without creative work are within the protection scope of the present invention.

[0047] Example 1 Effect of adding straw on composting process

[0048] 1 Introduction

[0049] At present, there are many studies on the control of composting conditions, but there are few studies on how straw regulation affects the maturity and greenhouse gas emissions of two different composting methods: aerobic composting and simple composting. Therefore, this study selected pig manure as the material, added straw as an auxiliary material, compared traditional composting and aerobic composting, paid attention to the parameters during and after the composting process, measured the physical and chemical indicators of each treatment and its gas emissions, and explored the effect of adding straw in composting and aerobic composting, the speed of maturity, and its effect on gas emissions and carbon and nitrogen retention.

[0050] 2 Materials and methods

[0051] 2.1 Test materials

[0052] The pig manure was collected from a pig farm in Wuxue City, Hubei Province, and the rape straw was taken from a nearby grain processing plant. The basic physical and chemical properties of the composting materials are shown in Table 1.

[0053] Table 1 Basic physical and chemical properties of composting materials

[0054]

[0055] Note: a is dry basis, b is wet basis.

[0056] 2.2 Experimental design

[0057] The experiment set up three treatments, namely: T1, pure pig manure composting treatment; T2, pig manure + straw composting treatment; T3, pig manure + straw composting treatment (turning required); pig manure and rape straw were mixed in a fresh weight ratio of 3:1 in each treatment, the initial moisture content was adjusted to about 65%, and the C / N was controlled at 20-25. The fresh weight of T1 treatment was about 50kg, and the fresh weight was about 30kg due to the addition of rape straw in T2 and T3 treatments. After mixing evenly, they were piled in a box with a size of 52.0cm×38.5cm×37.0cm, and each treatment was set up for 3 repetitions. T3 treatment turned the compost on the 7th and 15th days after the start of composting, and the entire composting cycle was 30d.

[0058] 2.3 Sample collection and determination

[0059] During the composting process, compost samples were collected by five-point sampling method on the 1st, 7th, 15th and 30th days. The weight of each sample was about 200 grams. The sample was divided into three parts, one of which was air-dried and ground, passed through a 100-mesh sieve, and the physical and chemical properties of the compost were measured. The other fresh sample was stored in a refrigerator at 4°C and the moisture content and NH4 + -N、NO3 - -N. The last portion was stored in a -80℃ freezer for determination of microbial indicators.

[0060] Gas samples were collected continuously from 1 to 11 days after the start of composting, and were collected from 9:00 to 11:00 am on the 15th, 16th, 17th, 18th, 23rd, and 30th days. NH3 was determined by boric acid absorption-standard acid titration: a small beaker (100 mL) filled with 50 mL of boric acid absorption solution was placed on the surface of the material, and a large beaker (2 L) with a known cross-sectional area was used to cover the small beaker. The beaker mouth was sealed with material to collect NH3 volatilized within the coverage of the beaker. N2O, CH4, and CO2 were determined by static box-gas chromatography: the static box was a plexiglass barrel with a diameter of 40 cm and a height of 50 cm. When collecting gas, the gas collection barrel was turned upside down on the surface of the material, inserted 5 cm deep, and the barrel mouth was sealed with material. A gas sample was collected with a syringe at 0 and 30 minutes, and stored in an aluminum foil air bag. The temperature in the box was recorded at the same time.

[0061] 3 Results and analysis

[0062] 3.1 Changes of ammonium nitrogen and nitrate nitrogen during composting

[0063] During the composting process, NH4 + -N is one of the main forms of nitrogen. It mainly comes from the decomposition of organic nitrogen compounds, providing a nitrogen source for microorganisms to synthesize amino acids and proteins. The changes in the ammonium nitrogen content of each treatment are similar to the changes in the water content of the pile ( Figure 2a), at the beginning of composting, the initial ammonium nitrogen content of treatments T1, T2 and T3 were 4261, 4171 and 5015 mg / kg, respectively. With the increase of composting time, the ammonium nitrogen content of the pile showed a trend of gradual decrease; at the end of the 30th day of composting, the ammonium nitrogen content of each treatment dropped to 164, 270 and 223 mg / kg, respectively. From the changes in the ammonium nitrogen content of the compost within 1-15 days, it can be seen that the T1 treatment reduced the initial ammonium nitrogen content by 66.2%, while the T2 and T3 treatments reduced it by 90.1% and 95.4%, respectively; compared with the initial ammonium nitrogen content, the three treatments decreased by 96.1%, 93.5% and 95.6%, respectively, and the ammonium nitrogen content of the T2 treatment decreased the least, which was significantly lower than that of the T1 and T3 treatments. During the composting process, the pure pig manure composting treatment lost the most ammonium nitrogen content, while the pig manure straw composting treatment retained ammonium nitrogen significantly better than other treatments.

[0064] As organic matter is continuously decomposed in the compost, nitrogen-containing organic matter is also degraded by microorganisms and releases ammonium nitrogen. In an aerobic environment, nitrite bacteria first convert ammonium nitrogen into nitrite nitrogen, which is then further oxidized into nitrate nitrogen by nitrifying bacteria. Figure 2 As shown in (b), the trends of each treatment were different. With the increase of composting time, the T1 treatment showed a trend of first rising and then falling, while the T2 and T3 treatments showed a trend of gradual increase. At the beginning of composting, the initial nitrate nitrogen content of the T1, T2 and T3 treatments was 24, 39 and 18 mg / kg, respectively; and at the end of composting, the nitrate nitrogen content of the T1, T2 and T3 treatments was 219, 1060 and 3777 mg / kg, respectively, an increase of 89.2, 96.3 and 99.5% compared with the initial nitrate nitrogen content. Compared with pure pig manure composting, mixed straw composting can increase the nitrate nitrogen content, but the increase is not as large as that of aerobic composting.

[0065] 2.3.3 Changes in carbon and nitrogen gas emissions during composting

[0066] During the composting process, NH3, as one of the main volatile components, is not only an important way for nitrogen to be lost, but also causes odor pollution to the environment. Nitrogen release is positively correlated with temperature. The higher the temperature, the faster the nitrogen loss. Figure 3 a) It was mainly concentrated in the temperature rise period and high temperature period of composting. The NH3 emission peaks of T1, T2 and T3 treatments all appeared in the early stage of composting, at the 1st, 1st and 7th day, with values ​​of 4.51, 4.02 and 5.29 mg.m 2 .h -1 Among them, the emission peak of T3 treatment is the largest. Figure 3 As shown in b, at the end of composting, the cumulative NH3 emissions of the three treatments were 0.69, 0.63, and 0.62 gm 2Compared with T1 treatment, T2 and T3 treatments both reduced NH3 emissions by 8.13% and 10.6%, respectively. Compared with pure pig manure composting, pig manure mixed with straw composting can reduce NH3 emissions, but the reduction is less than that of aerobic composting.

[0067] During the first 10 days of the composting process, nitrogen was transformed and released into N2O through nitrification and denitrification, which was the main peak period of N2O emission in each treatment group. Both T1 and T2 treatments reached the peak of N2O emission on the third day, while T3 treatment reached the peak of N2O emission on the fourth day, which were 57.88, 9.07 and 59.86 mg.m 2 .h -1 ( Figure 4 a) The emission peak of treatment T2 was the lowest. At the end of composting, the cumulative N2O emissions of the three treatments were 5.70, 1.14 and 5.43 gm 2 ( Figure 4 b), T2 was significantly different from T1 and T3 (p≤0.1); the cumulative N2O emission of T2 was significantly lower than that of T1 and T3, with a reduction of 79.9% and 79.00%, respectively. Compared with pure pig manure composting and aerobic composting, pig manure mixed with straw composting can significantly reduce N2O emissions.

[0068] CH4 is mainly produced by methanogens under anaerobic conditions. CH4 emissions from each treatment were concentrated in the first 10 days of composting, and the trend of CH4 emissions was similar to that of N2O emissions ( Figure 5 a) The CH4 emission peaks of T1, T2 and T3 treatments all appeared in the early stage of composting, at the 1st, 3rd and 3rd day, with values ​​of 458.3, 394.7 and 534.2 mg.m 2 .h -1 At the end of composting, the cumulative CH4 emissions of the three treatments were 41.12, 18.69 and 49.79 gm 2 ( Figure 5 b); Compared with T1 and T3 treatments, T2 treatment reduced CH4 emissions by 54.5% and 62.5% respectively; the cumulative CH4 emissions of T3 treatment increased by 17.4% compared with T1 treatment. Compared with pure pig manure composting and aerobic composting, pig manure mixed with straw composting can significantly reduce CH4 emissions, and aerobic treatment can also increase CH4 emissions.

[0069] Organic matter is rapidly decomposed by microorganisms, resulting in the release of a large amount of CO2 gas, so CO2 emission is the main channel for carbon loss. CO2 emissions from each treatment are mainly concentrated in the first 15 days of composting, and the trend fluctuates greatly between treatments. However, as the composting time increases, CO2 emissions show a trend of gradually decreasing ( Figure 6a) Both T1 and T2 treatments reached their CO2 emission peaks on the third day, while T3 treatment reached its CO2 emission peak on the first day, which were 16.67, 28.46 and 43.36 gm respectively. 2 .h -1 At the end of composting, the cumulative CO2 emissions of the three treatments were 6639, 7417 and 9066 g.m 2 There were significant differences among the treatments ( Figure 6 b); Compared with T1, T2 and T3 treatments increased CO2 emissions by 10.5% and 18.2%, respectively. Compared with pure pig manure composting, pig manure mixed with straw composting increased CO2 emissions during the composting process, but the increase was less than that of aerobic composting.

[0070] 2.3.4 Changes in microbial community structure during composting

[0071] 2.3.4.1 Changes in Shannon, Simpson, Chao and Ace indices of community diversity

[0072] Shanon index and Simpson index are usually used to measure species diversity. Among them, Shanon index is one of the important indicators for evaluating sample microbial diversity. It is similar to Simpson diversity index and is often used to reflect the alpha diversity level of a community. The higher the Shanon index value, the richer the diversity of the community. Figure 7 It can be seen that the initial Shanon index of each treatment was between 1.6 and 1.8, and the Shanon indexes of T1, T2 and T3 treatments were 1.77, 1.61 and 1.68, respectively. Among them, the initial Shanon index of T1 pure pig manure compost was significantly higher than that of other treatments. At the end of 30 days of composting, the Shanon index of each treatment was 2.10, 2.04 and 2.09, respectively, which increased compared with the initial level, with an increase of 15.8%, 21.0% and 19.6%, respectively. Among them, the increase in T1 treatment was the smallest, while the increase in T2 treatment was the most significant. It can be seen that adding straw auxiliary materials will reduce the initial Shanon index and reduce the initial community diversity, but will significantly increase the Shanon index during the composting process, thereby promoting the community diversity of the compost product.

[0073] The Simpson index is a crucial quantitative indicator for assessing the diversity of microbial communities. This index is often used by ecologists to quantitatively describe the richness of biodiversity in a particular habitat. The index is negatively correlated with the diversity level of the community, that is, the larger the index value, the lower the diversity of the community. Figure 7It can be seen that the initial Simpson indices of treatments T1, T2, and T3 are 0.26, 0.30, and 0.28 respectively, and there is no significant difference among the treatments. Among them, the Simpson index of treatment T1 is the smallest, and the community diversity is higher. At the end of 30-day composting, the Simpson indices of treatments T1, T2, and T3 are 0.21, 0.22, and 0.20 respectively, showing a decrease compared with the initial values, with the reduction rates being 20.3%, 26.7%, and 28.4% respectively. The performance of each treatment is T1 < T2 < T3. Different from the Shannon index, the Simpson index shows that adding straw cannot well promote the diversity of the compost bacterial community. On the contrary, it will reduce the diversity of its community.

[0074] The Chao index and Ace index are usually used to characterize the richness of microbial communities. As Figure 8 shown in Fig. a, with the increase of composting time, the Chao index of each treatment shows an upward trend. The initial Chao indices of treatments T1, T2, and T3 are 219, 212, and 215 respectively. Among them, the initial Chao index of treatment T1 is the highest, and adding straw will reduce the initial Chao index of composting. At the end of 30-day composting, the Chao indices of each treatment increase to 234, 237, and 229 respectively, with the increase rates being 6.27%, 10.5%, and 6.10% respectively. Among them, the increase of treatment T1 is the most significant. It can be seen that adding straw composting treatment reduces the initial Chao index, but will significantly increase the Chao index of the compost end product, improve the richness of compost microorganisms, but the increase amplitude of the Chao index of adding straw composting is less than that of the composting treatment, and the effect is not significant.

[0075] The Ace index is another index for evaluating the number of OTUs in a community. In ecological research, the Ace index is one of the commonly used indices for estimating the total number of species. As Figure 8 shown in Fig. b, the change trend of the Ace index is the same as that of the Chao index.

[0076] 2.3.4.2 Bacterial communities at the phylum and genus levels

[0077] From Fig. 9aIt can be seen that at the phylum level, the dominant phylum of the bacterial community in each treatment belongs to the Proteobacteria. According to the ranking of bacterial community abundance at the phylum level, the top five are Proteobacteria, Bacteroidota, Actinobacteriota, Firmicutes and Chloroflexi. The Proteobacteria of each treatment did not change significantly during the composting process. It was 41% to 46% initially. By the end of composting, the proportion decreased, but it was still the largest proportion (37% to 41%). The initial proportions of Bacteroidetes in T1, T2 and T3 treatments were 22.6%, 20.9% and 21.5%, respectively; the initial proportions of Firmicutes were 12.1%, 11.6% and 13.9%, respectively. By the end of 30 days of composting, the proportions of Bacteroidota were 7.14%, 8.47% and 13.9%, respectively. % and 8.40%; Firmicutes accounted for 1.62%, 1.38% and 1.58% respectively, which were all decreased compared with the initial level. The decreases of Bacteroidota were 68.4%, 59.5% and 60.9% respectively, and the decreases of Firmicutes were 86.6%, 88.1% and 88.6% respectively. Adding straw can reduce the decrease in the abundance of Bacteroidota, but increase the decrease in the abundance of Firmicutes, while there is no significant difference in the decrease between composting and composting treatments. The initial proportions of Actinobacteriota in T1, T2 and T3 treatments were 10.4%, 9.96% and 10.4%, respectively; while the initial proportions of Chloroflexi were 1.64%, 1.18% and 1.20%, respectively. At the end of 30 days of composting, the proportions of Actinobacteriota in each treatment were 10.6%, 19.3% and 19.3%, respectively, with an increase of 1.89%, 48.4% and 46.15%; The proportions of Chloroflexi were 15.9%, 8.14% and 10.6% respectively, with an increase of 89.7%, 85.5% and 88.7%. Adding straw can significantly increase the abundance of Actinobacteriota in compost products. Judging from the abundance proportion after composting, compared with T1 pure pig manure treatment, adding straw as an auxiliary material will increase the abundance of Actinobacteriota, but reduce the abundance of Chloroflexi.

[0078] Fig. 9b shows the dominant bacteria at the genus level in the T1, T2 and T3 treatments. More than 75% to 80% of the bacterial genera are other genera that have not yet been identified. At the genus level, it can be seen that the genera with the highest abundance include Luteimonas, Halopseudomonas and Cellvibrio. The abundance of Luteimonas in each treatment was about 2% to 3% in the early stage of composting. At the end of composting, only the T2 treatment accounted for 3.40%, and the abundance of Luteimonas in other treatments was very small. The genera of Halopseudomonas and Cellvibrio only existed in the early stage of composting, and the Cellvibrio genus was only found in the T2 and T3 treatments with added straw, accounting for 7.92% and 4.15%. At the end of composting, the abundance of the above two genera disappeared.

[0079] 2.3.4.3 RDA analysis

[0080] Redundancy analysis revealed a direct relationship between compost physicochemical parameters and bacterial community succession. Fig.10 a shows the correlation of fungi with physicochemical parameters and gas emissions at the genus level under T1, T2 and T3 treatments. These include temperature, moisture, pH, NH4, NO3, TC, TN, C / N ratio, TP and TK as physicochemical parameters, and NH3, N2O, CH4, CO2 as gas emissions. RDA1 and RDA2 accounted for 61.15% and 16.00% of the total variation associated with the microbial community, respectively, and together explained 77.15% ( Fig.10 b). These unclassified genera under Planctomycetes, Bacteroidetes and Chloroflexi were significantly positively correlated with NH3, N2O, CH4, CO2 gas emissions and physicochemical properties of NO3, TN, TK, and negatively correlated with temperature and pH. Luteimonas was positively correlated with other physicochemical properties (moisture, C / N ratio, NH4, TN and TK). It can be seen that these dominant but unclassified genera have a significant effect on gas emissions. Moisture, C / N ratio, NH4, TN and TK are more significantly affected by the physicochemical indicators of Luteimonas.

[0081] according to Fig.10As shown in the figure, at the phylum classification level, 93.23% of the variation in microbial community composition can be characterized by the two sorting axes RDA1 and RDA2. Chloroflexi and Actinobacteriota are significantly positively correlated with NH3, N2O, CH4, and CO2 gas emissions, among which Chloroflexi has the most significant effect; and are significantly positively correlated with physical and chemical indicators such as temperature, NO3, TN, and TK. These three phyla are related to gas emissions and nitrogen retention as well as nutrient accumulation of compost products. Firmicutes, Proteobacteria, and Bacteroidota are significantly positively correlated with pH, ​​moisture, TC, TP, and C / N, and are more correlated with maturity.

[0082] 2.3.5 Factors affecting compost maturity and carbon emissions

[0083] During the composting process, correlation analysis was conducted on various factors affecting composting, including physical and chemical properties and gas emissions. The correlation analysis showed that NH3 emissions were significantly negatively correlated with CH4, and the correlation with other indicators was not high ( Fig.11 b). CH4 is significantly positively correlated with pH, ​​and significantly negatively correlated with TC and TP. It can be seen that pH has a significant impact on NH3 and CH4 gas emissions. Temperature, pH, TN, TK and NO3 are positively correlated with CO2 emissions, among which temperature, TK and NO3 are significantly positively correlated. N2O emissions are negatively correlated with temperature and TN, which corresponds to the change pattern of temperature and TN.

[0084] The relationship between compost maturity and gas emissions can also be more intuitively understood through the redundancy analysis (RDA) of compost physicochemical properties and gas emissions. During the composting process, Axis-1 and Axis-2 can explain 52.02% and 7.01% of the total variance related to the microbial community, respectively. Fig.11 a). It can be seen that the effects of temperature, moisture, TC, C / N ratio and NH4 on the composting process are mostly concentrated in the early stage of composting. Gas emissions are more closely related to the physical and chemical properties in the later stage. pH, TN, TK and other indicators are significantly correlated with gas emissions. Gas emissions will cause the loss of carbon and nitrogen elements in the compost, but have a significant impact on some nutrients in the compost, so it is very necessary to reduce carbon and nitrogen losses.

[0085] Example 2 Effect of adding biochar on the composting process

[0086] 1 Introduction

[0087] This example is used to explore the effects of straw and biochar addition on the maturity and gas emission reduction of livestock and poultry manure during aerobic composting, as well as the mechanism of bacterial community succession during aerobic composting of livestock and poultry manure.

[0088] 2 Materials and methods

[0089] 2.1 Test materials

[0090] The dairy cow dung was collected from Tianshenjia Company in Wuxue City, Hubei Province, and the rape straw was taken from a nearby grain processing plant. The biochar was prepared according to the following method: the harvested rice straw was naturally air-dried (or dried continuously at 60°C for 48 hours), and then large particles of impurities were removed and cleaned; the air-dried rice straw was cut into segments and crushed in a multifunctional crusher (speed: 30000r / min), and the crushed rice straw was weighed in a ceramic container, sealed and heated in a muffle furnace at 25°C·min －1 The temperature was raised to 600 °C at a rate of 1.5 °C and maintained for 2 h. After cooling, the obtained biochar was crushed through a 100-mesh sieve.

[0091] The basic physical and chemical properties of compost raw materials are shown in Table 2.

[0092] Table 2 Basic physical and chemical properties of composting materials

[0093]

[0094] Note: a is dry basis, b is wet basis.

[0095] 2.2 Experimental design

[0096] Four treatments were set up in the experiment. A foam box with a length, width and height of 75*56*47cm was used, with a total mass of 55kg. The moisture content of each pile was controlled at 65-75%, the weight ratio of cow dung to rape straw was about 2-3:1, and the C / N ratio of the pile was adjusted to about 25-30;1. Aerobic composting and composting treatments were carried out for 45 days. Aerobic composting treatment was turned on the 7th, 15th, 24th and 33rd days. The experimental treatments are as follows:

[0097] Table 3 Different composting (fermentation) treatments with biochar added

[0098]

[0099] 3.2.3 Sample collection and determination

[0100] The collection and determination of samples are the same as in Example 1.

[0101] 3.3 Results and Analysis

[0102] 3.3.1 Changes in basic physical and chemical properties during composting

[0103] The heat released during microbial activities and the decomposition of organic matter is an important factor causing temperature changes during the composting process. Each treatment experienced a heating period (0 - 2 days), a high-temperature period (3 - 16 days), a cooling period (16 - 35 days), and a maturity period (35 - 45 days), and finally tended to be stable( Fig.12 ). During the composting process, the temperature of each treatment showed a trend of rising rapidly first and then falling, and finally stabilizing close to the ambient temperature; the temperature of each treatment rose rapidly in the early stage. C2 reached the highest temperature of 73.3℃ on the 3rd day, while the treatments of C1, BC1, and BC2 reached the highest temperature on the 4th day, which were 76.5℃, 71.3℃, and 69.0℃ respectively; except for the C1 treatment where the high-temperature period lasted for 11 days (>50℃), the high-temperature periods of the C2, BC1, and BC2 treatments lasted for 14 days. On the 35th day, the temperatures of the C1, C2, and BC2 treatments all dropped to about 30.0℃. Different from this, the BC1 treatment dropped to 30℃ on the 37th day. Thus, it can be seen that compared with the composting of pure cow dung and straw, the composting of cow dung and straw with biochar added can extend the duration of the high-temperature period and the cooling period, and can achieve the same temperature trend as aerobic composting.

[0104] The rate of compost maturity depends on the temperature of the compost pile. During the composting process, the average temperature of each treatment was between 43 - 46℃ (Table 4). The differences in the average temperature and cumulative temperature of the compost pile between the composting treatment and the composting treatment reached a significant level. The cumulative temperatures of the C1 and BC1 treatments were 2017℃ and 2012℃, respectively, which were significantly lower than those of the C2 and BC2 treatments (p≤0.1). On the 1st - 2nd day of composting, the average temperatures of the aerobic treatments of C2 and BC2 were 51.8℃ and 52.5℃, respectively, which were significantly higher than those of the C1 and BC1 treatments (48.8℃ and 49.8℃); on the 3rd - 16th day of composting, the C2 treatment (56.0℃) was significantly lower than other treatments; on the 16th - 35th day of composting, the average temperatures of the composting treatments C1 and BC1 (38.6℃ and 38.4℃) were significantly lower than those of the C2 and BC2 aerobic treatments (42.4℃ and 43.3℃). On the 35th - 45th day of composting, the differences in the temperatures of the 4 treatment compost piles reached a significant level, specifically showing that C2 (32.4℃) < BC2 (32.6℃) < C1 (34.4℃) < BC1 (35.0℃); overall, except for the compost maturity period, the overall temperature in other periods of the aerobic treatment was higher than that of the composting treatment. Among them, adding biochar in the aerobic composting treatment can increase the temperature of the compost pile, but the effect is not obvious in the composting treatment.

[0105] Table 4 Temperature differences of different compost (composting) treatments (℃)

[0106] Note: Different letters in the same column indicate significant differences P≤0.1, the same below.

[0107] By Fig.13 As shown in the figure, the moisture content of cow dung compost is usually between 60% and 80%. Too high or too low moisture content may affect the quality of composting and the progress of the composting process. The initial moisture content of C1 and C2 treatments was 68.2% and 68.5%, respectively, and the initial moisture content of BC1 and BC2 treatments was 62.8% and 63.0%, respectively. The initial moisture content of the biochar treatment was slightly lower. With the increase of composting time, the moisture content of the pile showed a trend of gradual decrease. At the end of the 45th day of composting, the moisture content of C1, C2 and BC1 treatments was 48.6%, 48.1% and 47.7%, respectively, while the moisture content of BC2 treatment was 54.3%. Compared with the initial moisture content, the decreases of C1 and C2 treatments were 28.8% and 23.5%, respectively, and the decreases of BC1 and BC2 treatments were 20.7% and 24.3%, respectively. Among them, the moisture loss of C1 treatment was the largest, and the loss of C2 treatment was the smallest. From the changes in compost moisture content within 1-17 days, it can be seen that the C1 and BC1 treatments decreased by 14.8% and 22.3% respectively compared with the initial moisture, while the C2 and BC2 treatments decreased by 2.9% and 5.8%. It can be seen that the moisture of the natural composting treatment was lost rapidly during the composting temperature rise period and high temperature period, while the moisture of the aerobic composting treatment mainly decreased rapidly during the temperature drop period and the maturity period. Compared with cow dung straw composting, adding biochar can slow down the loss of moisture.

[0108] The pH value of cow dung itself is slightly alkaline or alkaline, and the pH value will change during the composting process. Maintaining an appropriate pH value helps promote the decomposition of organic matter. Fig.14 As shown, the pH values ​​of each treatment were between 8.7 and 9.3. At the beginning of composting, the pH values ​​of C1 and BC1 treatments were 8.75 and 8.78, respectively, and the pH values ​​of C2 and BC2 treatments were 8.81 and 8.87, respectively. With the increase of composting time, the pH values ​​of each treatment showed a trend of first rising rapidly, then decreasing, and then rising again; during the composting warming period and high temperature period, the pH values ​​of C1, BC1, C2 and BC2 treatments all rose rapidly and then decreased. On the 9th day, the pH values ​​of each treatment increased to 9.19, 9.23, 9.42 and 9.31, respectively, and then decreased rapidly. In the late stage of composting, the pH of each treatment showed a slow rising trend. At the end of composting, the pH values ​​of C1, BC1, C2 and BC2 treatments were 9.02, 9.24, 9.32 and 9.23, respectively, which were all increased by 0.27, 0.46, 0.42 and 0.44 units compared to the initial values, with the BC2 treatment increasing the most and the C1 treatment increasing the least. The pH change trend during composting was consistent with the temperature change trend and was positively correlated with the temperature change. Adding biochar could significantly increase the pH value of compost.

[0109] Total carbon content is one of the important indicators for evaluating compost quality and fertilizer efficiency, which reflects the decomposition and transformation of organic matter in the raw materials. Fig.15As shown in a, the initial total carbon contents of the C1 and C2 treatments were 36.2% and 36.5%, respectively, and the initial total carbon contents of the BC1 and BC2 treatments were 40.7% and 40.3%, respectively, among which the initial total carbon content of the added biochar treatment was slightly higher than that of the other treatments. The trend of total carbon content in C1, BC1 and BC2 treatments was a trend of first decreasing and then increasing, while C2 treatment gradually decreased with time. At the end of the 45th day of composting, the total carbon content of C1 and C2 treatments was 32.7% and 32.3%, respectively, and the total carbon content of BC1 and BC2 treatments was 38.6% and 38.5%, respectively. Compared with the initial total carbon, the decreases in C1 and C2 treatments were 9.85% and 11.5%, respectively, and the increases in BC1 and BC2 treatments were 5.00% and 4.30%, respectively. From the changes in total carbon in composting within 1-30 days, it can be seen that C1 and C2 treatments decreased by 3.10% and 10.3% respectively compared with the initial total carbon, while BC1 and BC2 treatments decreased by 1.59% and 1.78%. It can be seen that the total carbon loss of each treatment is mainly in the mature stage of composting, and the addition of biochar can slow down the loss of carbon.

[0110] A key indicator for evaluating the fertilizer efficiency of compost is the total nitrogen content in the compost. Generally speaking, the total nitrogen content in the compost can provide the nitrogen elements required by plants, and a high nitrogen content can improve the quality of the compost. Fig.15 As shown in Figure b, at the beginning of composting, the total nitrogen content of C1 and C2 treatments was 2.59% and 2.42%, respectively, and the total nitrogen content of BC1 and BC2 treatments was 1.52% and 1.47%, respectively. The initial total nitrogen content of the added biochar treatment was slightly lower than that of the other treatments. The total nitrogen content of each treatment showed a gradual increase with the composting time. At the end of the 45th day of composting, the total nitrogen content of C1 and C2 treatments was 2.67% and 2.65%, respectively, and the total nitrogen content of BC1 and BC2 treatments was 1.79% and 1.73%, respectively. Compared with the initial total nitrogen, the increases in C1 and C2 treatments were 29.9%, and the increases in BC1 and BC2 treatments were 17.6%, respectively. From the changes in total nitrogen in the compost within the 1st to 17th day, it can be seen that the C1 and C2 treatments increased by 31.6% and 21.5% respectively compared with the initial total nitrogen, while the BC1 and BC2 treatments increased by 21.6% and 17.0%; among them, the increase was significant during the composting warming and high temperature period. The composting and aerobic composting treatments showed the same change trend, but the addition of biochar did not significantly promote the accumulation of nitrogen.

[0111] The C / N ratio of compost refers to the ratio of carbon to nitrogen in compost, which is important for evaluating the maturity and quality of compost. Fig.15As shown in Figure c, the C / N ratio of each treatment gradually decreased with the composting time. The initial C / N ratios of C1, C2, BC1 and BC2 were 17.1, 17.6, 26.7 and 27.5, respectively. At the end of composting, the C / N ratios of C1, C2, BC1 and BC2 were 12.3, 12.2, 21.9 and 22.3, respectively. The C1 and C2 treatments decreased by 27.8% and 30.7%, respectively, while the BC1 and BC2 treatments decreased by 18.0% and 16.4%. From the changes in the C / N ratio of the composting within 1-17 days, it can be seen that the C / N ratio of C1 and C2 treatments decreased by 24.6% and 24.1%, respectively, compared with the initial C / N ratio, while the BC1 and BC2 treatments decreased by 20.0% and 13.2%. In the entire composting period, the decrease in C / N ratio was mainly concentrated in the warming period and high temperature period of the composting, among which the C / N ratio of the treatment without biochar addition decreased significantly.

[0112] Depend on Fig.16 As shown in Figure a, the total phosphorus and potassium contents of aerobic composting treatments (C2 and BC2) increased rapidly with composting time during the composting process, while the natural composting treatments (C1 and BC1) decreased on the 9th day (during the high temperature period), and then increased rapidly with time. The initial total phosphorus contents of C1, BC1, C2 and BC2 treatments were 1.0%, 1.0%, 0.9% and 0.8%, respectively. At the end of the 45th day of composting, the total phosphorus contents of each treatment were 1.3%, 1.1%, 1.6% and 1.4%, respectively. Compared with the initial total phosphorus, the increases of C1 and BC1 treatments were 24.4% and 6.17%, respectively, and the increases of C2 and BC2 treatments were 79.4% and 75.2%, respectively. Among them, the increase of C2 treatment was the highest, while the increase of BC1 treatment was the smallest. It can be clearly seen that aerobic composting treatments (C2 and BC2) are conducive to the accumulation of total phosphorus content in compost, and the effect of adding biochar is not obvious.

[0113] Total potassium content of each treatment ( Fig.16b) It gradually increases with the increase of composting time. The initial total potassium content of C1, BC1, C2 and BC2 treatments were 2.7%, 2.4%, 2.6% and 2.5%, respectively. At the end of the 45th day of composting, the total potassium content of each treatment was 3.9%, 3.5%, 4.6% and 3.9%, respectively. Compared with the initial total potassium, the increase of C1 and BC1 treatments was 42.1% and 42.9%, respectively, and the increase of C2 and BC2 treatments was 77.7% and 60.8%, respectively. Among them, the increase of C2 treatment was the highest, which was also significant as the total phosphorus treatment. From the changes in total potassium in composting within 1-30 days, it can be seen that the total carbon in C1 and BC1 treatments increased by 31.0% and 32.0%, respectively, compared with the initial total carbon, while that in C2 and BC2 treatments increased by 62.9% and 40.0%. It can be seen that the increase in total potassium content in each treatment was mainly concentrated in the early stage of composting, and the increase was slow in the subsequent maturity period. At the end of composting, the total phosphorus and total potassium contents of each treatment showed the order of C2>BC2>C1>BC1.

[0114] 3.3.2 Changes in carbon and nitrogen gas emissions during composting

[0115] Usually, livestock and poultry manure contains a large amount of nitrogen compounds, and these organic wastes will be decomposed by microorganisms during the composting process, and the nitrogen compounds in them will release ammonia. Fig.17 As shown in a, the NH3 emissions from composting are all concentrated in the early stage of composting (warming and high temperature period). The C1 and BC2 natural composting treatments reached their emission peaks on the second day, with values ​​of 6.7 and 9.1 mg.m 2 .h -1 ; C2 and BC2 aerobic composting treatments reached their peaks on the 4th and 7th days, respectively, at 116.0 and 60.8 mg.m 2 .h -1 , and the peaks are all near the turning of the compost. At the end of composting, the cumulative NH3 emissions from C1, BC1, C2 and BC2 treatments ( Fig.17 b) 0.88, 0.63, 9.22 and 4.01 gm respectively 2 The cumulative NH3 emission from C2 treatment was the highest, and that from BC1 treatment was the lowest. Compared with C1 and C2 treatments without biochar addition, BC1 and BC2 treatments with biochar addition significantly reduced ammonia emissions by 27.8% and 57.6%, respectively; and compared with different composting methods, the cumulative NH3 emission from natural composting treatment was significantly lower than that from aerobic composting treatment.

[0116] During the composting process of livestock and poultry manure, the generation of N2O is closely related to the transformation of nitrogen forms. Fig.18As shown in a, N2O emissions are mostly concentrated in the early stage of composting. There are two peaks in N2O emissions from C1 and BC1 composting, with 15.24 and 13.47 mg.m on the 3rd and 1st day, respectively. 2 .h -1 On the 29th day, 7.87 and 5.01 mg.m 2 .h -1 The emissions from C2 and BC2 composting treatments were mostly concentrated in the first 16 days, with the peak emission on the third day, emitting 31.85 and 21.55 mg.m 2 .h -1 Compared with the composting treatment, the emission peak of the composting treatment was higher than that of the composting treatment, and the emission peak of the treatment with biochar addition was higher than that of the treatment without compost addition. Fig.18 b shows that the cumulative N2O emissions from treatments C1, BC1, C2, and BC2 are 7.05, 3.24, 3.12, and 4.38 gm, respectively. 2 , among which the C1 treatment had the highest cumulative N2O emission, and the C2 treatment had the lowest cumulative N2O emission. The gas emissions from the composting treatment were concentrated in the first 16 days of composting, while the N2O from the composting treatment was continuously emitted during the composting process. As for the composting treatments (C1 and BC1), compared with the C1 treatment, the addition of biochar to the BC1 treatment could significantly reduce the N2O emission by 54.08%, while the composting treatment showed the opposite trend, and the addition of biochar promoted the emission of N2O. It can be seen that the addition of biochar can significantly reduce the emission of N2O in the composting treatment.

[0117] In anaerobic environments, methanogens produce CH4 by reducing CO2 or hydrocarbons. Fig.19 As can be seen from a, CH4 emissions from C1, BC1, C2, and BC2 treatments were mostly concentrated in the first 7 days, except for the peak emission from C1 treatment (388 mg.m 2 .h -1 ) appeared on the second day, the other treatments all reached their peak on the third day, which were 530, 295 and 1005 mg.m 2 .h -1 , among which BC2 treatment has the highest emission peak, and C2 treatment has the lowest emission peak; the emission peaks of C1 and C2 treatments are lower than those of BC1 and BC2 treatments. Fig.19 b) From the perspective of treatment, the cumulative CH4 emissions from C1 and C2 are 27.3 and 18.9 gm 2 The cumulative CH4 emissions from BC1 and BC2 were 50.1 and 47.1 gm 2The emissions from each treatment were mostly concentrated in the first 7 days of composting, and also occurred during the maturity period of composting. The CH4 emissions from the treatment with biochar addition were higher than those from the treatment without biochar addition, and the C2 treatment had the lowest emissions. The addition of biochar did not significantly reduce CH4 emissions during the composting process, but on the contrary increased CH4 emissions.

[0118] Depend on Fig. 20 It can be seen from a that CO2 was emitted within 45 days of composting, showing a fluctuating trend. The emissions of each treatment were mostly concentrated in the first 20 days. The CO2 emission peaks of C2 and BC2 treatments occurred within 1-2 days after the compost was turned over. The emission peaks of each treatment appeared on the third day of composting, when microbial activities were frequent and more gas was produced. The emission peaks of C1, BC1, C2 and BC2 treatments were 61.2, 81.7, 56.0 and 99.0 mg.m 2 .h -1 Among them, the CO2 emission peak of BC2 treatment was the highest, and that of C2 treatment was the lowest. The emission peaks of biochar-added treatments (BC1 and BC2) were higher than those of treatments without biochar addition (C1 and C2). Fig. 20 b shows that the cumulative CO2 emissions of each treatment are 20251, 16051, 19725 and 17209 g.m 2 Among them, the C1 treatment had the highest cumulative CO2 emission, and the BC1 treatment had the lowest cumulative CO2 emission, which was similar to the N2O emission pattern. As for the composting treatments (C1 and BC1), compared with the C1 treatment, the addition of biochar to the BC1 treatment could significantly reduce CO2 emissions by 20.74%, while the composting treatment showed the opposite trend. The addition of biochar promoted CO2 emissions. It can be seen that the addition of biochar can significantly reduce CO2 emissions in the composting treatment.

[0119] 3.3.3 Changes in microbial community structure during composting

[0120] 3.3.3.1 Changes in Shannon, Simpson, Chao and Ace indices of community diversity

[0121] An important evaluation index of microbial diversity is the Shanon index. It is similar to the Simpson index and is usually used to measure the diversity within a community (alpha). The higher the Shanon index, the higher the diversity level of the community. The index is obtained by weighting the richness and evenness of different species in the sample. Fig.21aIt can be seen that the initial Shanon index of each treatment was different, among which the C1 and BC1 composting treatments were 1.84 and 1.86, respectively, while the C2 and BC2 composting treatments were 1.72 and 1.58, respectively. At the end of 45 days of composting, the C1 and BC1 composting treatments dropped to 1.59 and 1.75, respectively, with a decrease of 13.5% and 5.87%, respectively; while in the aerobic composting treatment, the opposite trend appeared, and the C2 and BC2 composting treatments rose to 1.90 and 1.78, respectively, with an increase of 10.6% and 12.8%, respectively. It can be seen that the addition of biochar in the composting treatment showed a significant reduction in the decline of the Shanon index, while in the aerobic composting treatment it promoted the increase of the Shanon index.

[0122] The Simpson index is one of the important indicators for quantifying the biodiversity of a particular area. It was proposed by Edward Hugh Simpson in 1949. The index is widely used in the field of ecology to quantitatively describe the diversity of biological communities. The higher the Simpson index value, the lower the diversity level of the community. Fig.21 b It can be seen that the initial Simpson index of C1, BC1 and C2 treatments were 0.22, 0.20 and 0.23, respectively, while that of BC2 treatment was 0.32. Compared with the other three treatments, the initial Simpson index of the aerobic treatment with biochar addition was significantly higher than that of the other treatments. At the end of 45 days of composting, the C1 and BC1 composting treatments increased to 0.31 and 0.24, respectively, with increases of 38.2% and 17.1%, respectively; while in the aerobic composting treatment, the opposite trend was shown, and the C2 and BC2 composting treatments decreased to 0.21 and 0.25, respectively, with decreases of 9.65% and 20.4%, respectively. The addition of biochar in the composting treatment significantly promoted the increase of the Simpson index, while in the aerobic composting treatment, it significantly reduced the decrease of the Simpson index. The Simpson index showed the same but opposite trend as the Shanon index. Therefore, the addition of biochar can provide suitable physical and chemical conditions for microorganisms with different characteristics and increase the diversity of bacterial communities.

[0123] The richness indices Chao and Ace are often used to assess the diversity of microbial communities. The Chao index is an algorithm-based indicator for estimating the total number of operational taxonomic units (OTUs) in a sample. It was first proposed by Chao in 1984 and is widely used in the field of ecology to predict the total number of species. Fig. 22a It can be seen that the Chao index of each treatment showed an upward trend with the increase of composting time. The initial Chao index of C1 and BC1 composting treatments was 18.3 and 21.7, respectively, and the initial Chao index of C2 and BC2 composting treatments was 21.3 and 20.8, respectively. Among them, the initial Chao index of C1 treatment was the lowest, and the initial Chao index of BC1 treatment was the highest. Adding biochar can significantly increase the initial Chao index of composting, (a) improving the richness of composting microorganisms. At the end of 45 days of composting, the Chao index of C1 and BC1 composting treatments increased to 21.7 and 22.3, respectively, and the Chao index of C2 and BC2 composting treatments increased to 23.8 and 23.7, respectively. Among them, the most significant increase was 18.2% in C1 treatment, and the least increase was 3.08% in BC1 treatment. It can be seen that adding biochar will increase the initial Chao index and improve the richness of initial microorganisms in composting, but the increase during the composting process is not as large as that of the composting treatment without biochar. Compared with aerobic composting treatment, the Chao index increased significantly when composting without biochar was used.

[0124] As one of the commonly used indicators for evaluating the total number of species in the field of ecology, the Ace richness index and the Chao index have different algorithms. The index aims to estimate the number of operational taxonomic units (OTUs) in a community and was originally proposed and promoted by Chao scholars. Fig. 22 b It can be seen that, except for the BC1 treatment, the Ace index of the other treatments showed an upward trend with the increase of composting time. The initial Ace index of the C1 and BC1 composting treatments was 12.8 and 29.6, respectively, and the initial Ace index of the C2 and BC2 composting treatments was 21.3 and 22.2, respectively, which was similar to the Chao index. Among them, the initial Ace index of the C1 treatment was the lowest, and the initial Ace index of the BC1 treatment was the highest. Adding biochar would also significantly increase the initial Ace index of the composting. At the end of 45 days of composting, the Ace index of the C1, C2 and BC2 treatments increased to 22.2, 23.8 and 23.7, respectively, with an increase of 77.3%, 19.5% and 7.64%, respectively, among which the C1 treatment increased the most significantly; on the contrary, the Ace index of the BC1 composting treatment decreased to 22.3, a decrease of 24.6%. It can be seen that, unlike the Chao index, adding biochar will also increase the initial Ace index and improve the initial microbial richness of the compost, but it will significantly reduce the Ace index of the compost during the composting process, and at the end, the microbial richness in the pile will drop significantly. Similarly, compared with aerobic composting treatment, the Ace index increased significantly when the biochar-free composting treatment was used.

[0125] 3.3.3.2 Bacterial communities at the phylum and genus levels

[0126] Depend on Fig.23It can be seen from a that the dominant bacteria in the bacterial communities of each treatment at the phylum level belong to the Bacteroidota. At the phylum level, the top five species in the microbial communities of each treatment are Bacteroidota, Firmicutes, Proteobacteria, Chloroflexi and Actinobacteriota. In addition to the BC1 treatment, the initial dominant bacteria were Chloroflexi, accounting for 22.6%. The initial dominant bacteria in the C1, C2 and BC2 treatments were all Firmicutes, accounting for 31.8%, 31.1% and 49.5%, respectively. At the end of 45 days of composting, the dominant bacteria in the C1, BC1, C2 and BC2 treatments were all Bacteroidota, accounting for 49.4%, 33.1%, 36.2% and 38.0% respectively, among which the BC2 treatment increased significantly, increasing by 73.5% compared with the initial level; and for the Firmicutes, which had the highest initial proportion, the proportions in each treatment were 19.4%, 21.8%, 20.8% and 19.1% respectively, among which the BC2 treatment also decreased significantly, decreasing by 90.4% compared with the initial level.

[0127] Fig.23 b shows the dominant bacteria at the genus level in the C1, BC1, C2 and BC2 treatments. More than 40% to 60% of the bacterial genera are other unidentified genera. At the genus level, the genera with the highest abundance include Chryseolinea, Flavobacterium, Luteimonas, Anseongella, Sinomcrobium and Planktosalinus. The abundance of Chryseolinea was low in the early stage of composting, but by the end of composting, the abundance of aerobic treatments C2 and BC2 increased to 11.5% and 20.9%, respectively; Flavobacterium was also very low in the early stage of composting, but by the end of composting, the abundance of C1 and BC1 composting treatments increased to 8.16% and 5.07%; and there was also the abundance of Anseongella, which was completely absent in the early stages of the treatments, but by the end of the treatments, it reached 3% to 6% of the abundance in each treatment.

[0128] 3.3.3.3RDA analysis

[0129] Redundancy analysis revealed a direct relationship between compost physicochemical parameters and bacterial community succession. Fig.24a shows the correlation of bacteria with physicochemical parameters and gas emissions at the genus level under C1, BC1, C2 and BC2 treatments. Including temperature, moisture, pH, TC, TN, C / N ratio, TP and TK as physicochemical parameters, and NH3, N2O, CH4, CO2 as gas emissions. 28.33% and 17.05% of the total variance associated with the microbial community was explained by RDA1 and RDA2 in the redundancy analysis, respectively. Flavobacterium and Chryseolinea were significantly positively correlated with pH, ​​TN, TP and TK, and also significantly positively correlated with NH3, N2O, CH4, CO2 as gas emissions. Several other dominant bacteria were significantly positively correlated with temperature, moisture, TC and C / N ratio. It can be seen that these genera have a significant effect on gas emissions. The indicators of temperature, moisture, TC and C / N have a more significant effect on other dominant bacterial groups.

[0130] like Fig.24 As shown in Figure b, at the phylum level, RDA1 and RDA2 explained 66.81% of the microbial changes. Bacteroidetes, Proteobacteria and Actinobacteria were significantly positively correlated with the gas emissions of NH3, N2O, CH4 and CO2, among which Bacteroidetes had the most significant impact; and were significantly positively correlated with the physical and chemical indicators pH, TN, TP and TK. These three phyla were related to gas emissions, nitrogen retention and nutrient accumulation of compost products. Firmicutes and Chloroflexi were significantly positively correlated with indicators such as temperature, moisture, TC and C / N, and were more correlated with maturity.

[0131] 3.3.4 Factors affecting compost maturity and carbon emissions

[0132] The physical and chemical properties and gas emissions during composting were analyzed for correlation with various composting factors. Fig.25 b) Correlation analysis shows that NH3 emission is significantly positively correlated with TP and TK, and significantly negatively correlated with N2O and CO2, which is also consistent with the law of gas emission. It has poor synergistic emission reduction effect with N2O and CH4, but has significant effect on nutrient retention. N2O emission is significantly positively correlated with temperature, and gas emissions are mostly concentrated in the warming period. It is significantly negatively correlated with pH, ​​TP and TK. The increase in pH will also reduce N2O emissions to a certain extent. The correlation between CH4 and CO2 is similar to the correlation between the physical and chemical properties of compost. TC and C / N ratio are significantly positively correlated with it. This also confirms that the gas emission shown above is significantly negatively correlated with the changes in TC and C / N ratio, and with moisture, TN and TK. Similarly, the loss of moisture and TN nutrients is also accompanied by an increase in CH4 and CO2 gas emissions.

[0133] Through RDA analysis of compost physicochemical properties and gas emissions ( Fig.25 a) It is also possible to more intuitively understand the relationship between maturity and gas emissions during the composting process. During the composting process, Axis-1 and Axis-2 can explain 48.61% and 18.26% of the total variance related to the microbial community, respectively. It can be seen that the effects of temperature and moisture on the composting process are mostly concentrated in the early stages of composting, and gas emissions are more closely related to the physical and chemical properties in the later stages. Indicators such as pH, TN, TP, and TK show a significant correlation with gas emissions. Gas emissions will cause the loss of carbon and nitrogen elements in the compost, but have a significant impact on some nutrients in the compost, so it is very necessary to reduce carbon and nitrogen losses.

[0134] 3.4 Discussion

[0135] 3.4.1 Effect of adding biochar on compost maturity

[0136] During the composting process, the maturity of the compost is very important. There are many factors that affect the maturity of the compost. Temperature is an important parameter that affects microbial activity. Livestock and poultry manure is converted into humus through microbial activity to form efficient organic fertilizer. In this experiment, each treatment reached the high temperature period on the 3rd day and lasted for 11 to 14 days. The highest temperature could reach above 70°C. Among them, the BC2 treatment with biochar and cow dung straw composting can extend the duration of the high temperature period and the cooling period, and can achieve the same temperature trend as aerobic composting. This is because biochar has a large specific surface area, so it can better absorb and hold water, which helps to control the evaporation loss of water inside the composting system. In addition, this characteristic also slows down the rate at which the temperature of the composting system drops. Water content that is too high or too low is not suitable for composting maturity, and an appropriate moisture content is very necessary. The moisture of C1 and BC1 natural composting treatments is lost rapidly during the composting heating and high temperature periods, while the moisture of C2 and BC2 aerobic composting treatments mainly decreases rapidly during the cooling and maturity periods. Compared with cow dung and straw composting, adding biochar can slow down the loss of moisture. The pH value of cow dung itself is slightly alkaline or alkaline, and the pH will change during the composting process. Maintaining an appropriate pH value helps promote the decomposition of organic matter. Excessive acidity or alkalinity will affect the composting maturity process. Fig.14As shown in the figure, the change trend of the pH of the pile body is that it first increases, then drops sharply, and finally rises again. In the early stage of composting, the pH value of each treatment group rises rapidly, which may be due to the enhanced microbial activity and the increase in the temperature of the pile body, which promotes the decomposition of organic acids; at the same time, the ammoniation reaction is intensified and the nitrification reaction is inhibited, resulting in the alkalinity of the compost material. The reason for the subsequent decrease in pH value may be the occurrence of nitrification, and the ammonia is converted and utilized by microorganisms. At the end of composting, the pH value of each treatment was between 8.7 and 9.3. Obviously, the addition of biochar increased the pH of the compost. The C / N ratio of each treatment showed a downward trend during the composting process. The C / N ratios of C1 and C2 treatments were 12.3 and 12.2, while the C / N ratios of BC1 and BC2 with biochar added were 21.9 and 22.3. It is generally believed that when the C / N ratio of compost is <20, it is considered to be basically mature. In this experiment, BC1 and BC2 treatments reached maturity. The results show that the addition of biochar helps to accelerate the composting process. At the end of composting, the total phosphorus and total potassium contents of each treatment group increased significantly. This is because phosphorus and potassium will not be volatilized during the composting process, but will be relatively enriched due to the reduction of total dry matter content. However, adding biochar will not increase their content, and the effect is not significant.

[0137] 3.4.2 Effects of biochar addition on carbon and nitrogen losses during composting

[0138] The essence of the composting process is that organic matter is gradually transformed in a cycle of continuous decomposition and resynthesis. Under the combined effects of high carbon-nitrogen ratio and concentration effect, the total nitrogen content of C1, BC1, C2 and BC2 treatments increased compared with the initial value at the end of composting. At the same time, the carbon-nitrogen ratio of each treatment group decreased rapidly in the warming stage, while it decreased more slowly in the high temperature period and cooling period; the possible reason for this phenomenon is that the high C / N ratio in the early stage of composting is conducive to accelerating the degradation of organic matter, and the higher the carbon-nitrogen ratio, the greater the degree of degradation. It is worth noting that the total nitrogen content of the treatment group without biochar addition increased more significantly. In general, the addition of biochar can effectively reduce the carbon loss caused by carbon gas emissions. The composting treatment mainly loses in the form of N2O-N, while the aerobic composting treatment loses mostly in the form of NH3-N. Compared with the treatment without biochar addition, the addition of biochar to composting significantly reduced the proportion of CH4-C, CO2-C and TC losses during composting. And the reduction of CO2-C loss by adding biochar to composting treatment is due to the addition of biochar to aerobic treatment. The BC1 and BC2 treatments with the addition of biochar significantly reduced ammonia emissions, by 27.8% and 57.6% respectively; and compared with different composting methods, the cumulative NH3 emissions of natural composting treatment were significantly lower than those of aerobic composting treatment; in terms of the cumulative emissions of N2O and CO2, compared with other treatments, the BC2 treatment had the lowest emissions. In general, the addition of biochar can effectively reduce gas emissions.

[0139] 3.4.3 Effect of biochar addition on microbial succession in composting

[0140] The composting process is a complex system regulated by multiple factors. In this process, microbial communities play an indispensable role. They not only participate in the degradation of usable waste materials, but their activity is also restricted by relevant environmental conditions. In this experiment, the abundance of BC1 and BC2 treatments with biochar addition was high in the early stage, but at the end, the abundance decreased. This may be due to the long duration of the high temperature period of the pile body, and a large number of harmful bacteria and some beneficial bacteria died due to the high temperature, which led to a decrease in species richness in the later stage.

[0141] In this study, the main microbial communities under the phylum attributes include Bacteroidota, Firmicutes, Proteobacteria, Chloroflexi and Actinobacteriota. The presence of dominant bacterial populations is closely related to the nutrient metabolism and material circulation process in the pile. The dominant phylum in the thermophilic stage is Firmicutes, which plays a key role in the decomposition of cellulose. Bacteroidetes is the dominant bacterial community in the mature stage. Xanthomonas is an aerobic microorganism that can catalyze the reduction of nitrate to nitrite and has an inhibitory effect on the utilization of glucose. These are the main dominant bacteria in the late stage of composting.

[0142] Through RDA analysis, we can more intuitively understand that temperature is not only a key parameter for evaluating the composting process, but also directly affects the activity of bacteria and the degree of degradation of organic matter; total nitrogen (TN) is an important nutrient element, and its content level is closely related to bacterial activity, which in turn affects the conversion and maturity of nitrogen in the composting system. In this experiment, gas emissions are related to nutrient retention and maturity. Whether at the phylum level or underwater, dominant microorganisms are significantly positively correlated with gas emissions. Bacterial flora structure and function play an important role in the composting process and are key factors affecting compost maturity and gas emissions.

[0143] 3.5 Summary

[0144] (1) During the composting process, the addition of biochar can slow down the rapid loss of water, increase the pH value of the compost, and significantly reduce the carbon loss during the composting process. At the end of composting, the C / N ratio was above 21, which significantly promoted the maturity of the compost. The composting treatment showed the same trend as the composting treatment, but the composting treatment was slightly better than the composting treatment.

[0145] (2) As for composting, compared with cow dung and straw composting, composting with biochar can significantly reduce the emissions of NH3, N2O and CO2 by 57.6%, 54.1% and 20.7% respectively under an anaerobic environment, but increase the emission of CH4. For different composting methods, adding biochar can reduce the loss of carbon in the compost.

[0146] (3) The addition of biochar can provide suitable physical and chemical conditions for microorganisms with different characteristics, increasing the diversity of bacterial communities, but not their richness; it also increases the abundance of Bacteroidetes and Chloroflexi, which are dominant genera that are highly correlated with gas emissions.

[0147] IV. Conclusion and Outlook

[0148] 4.1 Conclusion

[0149] (1) Adding straw can significantly promote nitrogen retention in the compost, but has no significant effect on reducing carbon loss. It can also improve species diversity and richness at the end of composting. It can also promote the abundance of Actinobacteriota. The dominant genera are significantly related to nitrogen retention and gas emission reduction. The maturity and carbon and nitrogen losses of the T2 composting treatment with straw addition are better than those of pure pig manure composting. Among them, the cumulative emissions of N2O and CH4 are reduced by 84.6% and 62.9% respectively compared with pure pig manure composting. It can also reduce NH3 emissions, but the reduction is less than that of aerobic composting.

[0150] (2) Adding biochar can slow down the rapid loss of water, increase the pH value of the compost, significantly reduce the carbon loss during the composting process, and the C / N ratio is above 21 at the end of composting, which significantly promotes the maturity of the compost, provides suitable physical and chemical conditions for microorganisms with different characteristics, and increases the diversity of bacterial communities. BC2 straw composting with biochar can significantly reduce the emissions of NH3, N2O and CO2 in an anaerobic environment, with a decrease of 57.6%, 54.1% and 20.7% respectively, but it will increase the emission of CH4.

[0151] In general, the results of Example 1 show that the degree of maturity and emission reduction effect of composting by adding auxiliary material straw reached the same trend as aerobic composting. Even better than aerobic composting, The composting effect is very good, but the carbon loss is relatively serious. On the basis of Example 1, the composting technology is optimized by adding biochar, which also achieves a good effect in reducing carbon loss and has a significant effect in reducing gas emissions; compared with aerobic composting, simple composting can significantly optimize the composting technology by adding auxiliary materials such as straw and biochar additives to compost, while reducing labor and costs. Therefore, it is recommended to add straw and 10% biochar for 45d composting, which can well optimize the traditional composting technology, improve the maturity of the compost, and greatly reduce carbon and nitrogen losses, thereby improving the quality of the compost.

Claims

1. A method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition, characterized in that: The method comprises the following steps: (1) livestock and poultry manure and straw are mixed in a ratio of (2-3) to 1 by fresh weight, the initial moisture content is adjusted to 65%-75%, and the C / N is controlled to (20-25):1 as the basic material; (2) adding 8 to 15% of biochar based on the mass of the basic material and mixing to obtain a mixed material; (3) The mixed material is placed in a foam box with a length of 70 to 80 cm, a width of 50 to 60 m, and a height of 40 to 50 m and piled for 30 to 45 days without turning the pile during the composting period.

2. The method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition according to claim 1, characterized in that: The livestock and poultry excrement is selected from one or a mixture of two or more of the following: pig excrement, cow excrement, chicken excrement, and sheep excrement.

3. The method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition according to claim 1, characterized in that: The straw is selected from one or a mixture of two or more of the following: rape straw, wheat straw, corn straw, and rice straw.

4. The method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition according to claim 1, characterized in that: The biochar is prepared according to the following method: the rice straw is naturally air-dried or dried, and then large particles of impurities are removed and cleaned, cut into segments, crushed, placed in a ceramic container, sealed, and heated in a muffle furnace at 23-26°C·min -1 The temperature is raised to 680-620°C at a rate of 1.8-2.2 hours, and then crushed and sieved after cooling.

5. The method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition according to claim 4, characterized in that: The technical parameters for drying the rice straw are: continuous drying at 55-65°C for 40-60 hours.

6. The method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition according to claim 4, characterized in that: The added amount of the biochar is 10% of the mass of the basic material.

7. The method for preparing livestock and poultry manure compost for reducing carbon and nitrogen emissions and promoting decomposition according to any one of claims 1 to 6, characterized in that: No composting agent is added before or after composting.

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