Investigation of the Composting Process of Mongolian Horse Manure Utilizing Intelligent Composting Equipment

Abstract

The Inner Mongolia Autonomous Region, known for its famous Mongolian horses, faces significant environmental challenges due to the large-scale rearing of these animals, which produces a substantial amount of manure. If not managed effectively, this manure can lead to severe environmental pollution. The aim of this study was to investigate whether a small-scale intelligent aeration and heating composting system is effective in treating Mongolian horse manure, with the objective of enhancing composting efficiency and resource utilization to support sustainable agricultural development in the region. The equipment was utilized to treat a compost mixture of Mongolian horse manure and corn stover, allowing for an analysis of the changes in key indicators throughout the composting process. The results demonstrated that the equipment maintained high temperatures for up to eight days during the composting process, effectively inactivating pathogens and promoting the efficient decomposition of organic matter. The system also successfully controlled humidity to 12.7% and maintained oxygen concentration within the optimal range. Post-composting analysis revealed that the final compost contained 2.3% nitrogen, 1.3% phosphorus, and 1.2% potassium, with a pH of 6.4 and conductivity of approximately 5.2 mS/cm. Additionally, the carbon-to-nitrogen ratio decreased significantly from 27.3 to 15.9, indicating substantial organic matter degradation. Seed germination tests showed germination rates of 80%, 86%, and 75% for corn, mung bean, and wheat, respectively, with a final seed germination index of 104%. This study concluded that the small aeration and heating composting equipment is highly effective in treating Mongolian horse manure, producing high-quality organic fertilizers that significantly enhance soil fertility and demonstrate considerable potential for supporting sustainable agricultural practices and improving environmental management in the Inner Mongolia Autonomous Region.

1. Introduction

China, a country with a long tradition of horse breeding, has one of the largest horse populations in the world [1,2]. Among its regions, the Inner Mongolia Autonomous Region is particularly notable as the homeland of Mongolian horses, thanks to its rich cultural heritage and favorable geographical and climatic conditions [3,4,5]. This region has a well-established history of horse breeding and husbandry [6]. The Mongolian horse, the most widely distributed indigenous horse breed in China, has developed strong cold resistance and durability through a long process of natural and artificial selection [7,8,9]. Recognizing its unique qualities, the Ministry of Agriculture of the People’s Republic of China has included the Mongolian horse in the national list of protected livestock and poultry genetic resources [10,11].

However, the large-scale breeding of Mongolian horses in Inner Mongolia produces a significant amount of manure, which, if not properly managed, can result in extreme contamination of the surroundings [12,13,14]. Moreover, the region’s over usage of synthetic fertilizers may cause soil degradation, reduced fertility, and lower agricultural product quality, with broader long-term environmental consequences [15,16,17,18,19,20].

Despite its potential as a pollutant, Mongolian horse manure is also a valuable biological resource [21,22,23,24]. It is rich in essential nutrients such as nitrogen, phosphorus, potassium, and organic matter [25]. The continuous use of Mongolian horse manure as an organic fertilizer can substantially increase the soil’s organic matter and active humic acid content, while promoting soil microorganism activity and population growth [26,27,28,29]. This, in turn, enhances soil fertility and overall soil quality [30]. Therefore, converting Mongolian horse manure into organic fertilizer through composting and fermentation offers an effective solution to address manure accumulation [31,32,33]. Additionally, this approach can reduce the negative impact of excessive chemical fertilizer use on soil health [34,35,36,37].

Although traditional pile composting of horse manure is commonly practiced on a large scale, the method proposed in this study offers several advantages. The intelligent aeration-heating composting equipment developed by our research team allows for more precise control of composting conditions, such as oxygen supply and temperature regulation, thereby accelerating the composting process. Moreover, it reduces labor demands and space usage compared to traditional methods. These features make it more efficient and particularly suitable for regions with limited resources or space constraints. Building on the successful development of this small-scale intelligent aeration-heating composting equipment, this study aims to further evaluate its effectiveness in composting Mongolian horse manure [38,39]. The results are expected to contribute to sustainable solutions for ecological agriculture in Inner Mongolia [40].

In the field of livestock manure composting into organic fertilizer, numerous studies have been conducted by various scholars. For instance, Cai et al. investigated the effect of the carbon-to-nitrogen ratio (C/N ratio) on the composting process of wheat straw mixed with chicken manure, finding that parameters such as the temperature and pH played key roles in the composting process [41]. Su et al. explored the appropriate ratio of cattle manure to sheep manure in mixed fermentation [42]. Ren et al. developed decomposing implements and researched the technique of composting sheep and cow dung [43,44]. Zhao et al. focused on bacterial diversity and its dynamic changes, examining functional and physicochemical properties at different stages of the swine manure composting process [45]. These studies collectively highlight the wealth of research on livestock manure composting; however, there remains a relative lack of research on the composting and fermentation processes of Mongolian horse manure.

The aim of this study was to evaluate the effectiveness of a small-scale smart aeration and heating composting system in treating Mongolian horse manure. Given the abundance of Mongolian horse manure and the extensive maize cultivation areas in Inner Mongolia, this study explored the feasibility of efficient resource utilization through the use of this specialized composting system. Specifically, Mongolian horse manure was mixed with maize stover to enhance composting efficiency and improve resource utilization. This research not only addresses a gap in the study of composting and fermentation of Mongolian horse manure but also offers valuable insights for the sustainable development of agriculture in China. By improving composting efficiency with specialized equipment, this study introduces a novel technological approach for integrating and optimizing agricultural practices.

2. Materials and Methods

2.1. Structure of Intelligent Composting Equipment

Figure 1 illustrates a physical arrangement and a 3D representation of a compact composting facility that utilizes aeration and heating technology. This plant is especially built to manage horse dung from Mongolia. The range of values is between 42 and 44, inclusive. The equipment consists of five basic components: the control system, aeration heating system, compost fermentation system, and discharge system. The design places a high emphasis on efficient blending and includes advanced real-time monitoring and control capabilities to optimize the decomposition and fermentation of animal excrement. The fermenter has a maximum loading capacity of 64 kg and a volume of 120 L.

The mechanism of this composting equipment is as follows: Mongolian horse manure is introduced into the fermenter in batches, where the stirring device begins operation. As the mixture of Mongolian horse manure and corn stalks enters the fermenter at room temperature, the sensor detects that the internal temperature is below the set threshold. In response, the heating pipe is activated, and after a pre-determined delay based on prior testing, the air pump initiates ventilation. During the composting process, microorganisms decompose the organic matter, consuming oxygen and causing a reduction in the oxygen concentration within the tank. When the sensor detects that the oxygen concentration has fallen below the specified range, the air pump is triggered to maintain the oxygen concentration within the optimal range.

2.2. Instruments Used in Composting Experiments

The composting test equipment is illustrated in Figure 2. To mitigate environmental pollution, the equipment incorporates activated carbon to adsorb odorous gases released during the composting process. Various tools were employed during the test to measure and evaluate the composting efficacy and its impact on seed germination. This study focused on evaluating the quality and effectiveness of the compost by testing the germination rate of seeds using Dokka brand 12-hole seedling pots, universal brand Petri dishes, centrifuge cylinders, and subjective paper filters. Electronic scales were used to accurately weigh the compost materials to ensure accurate compositional ratios, which is critical to the reproducibility and scientific validity of the composting process. In addition, soil multi-element testers (EVANLEY brand, temperature accuracy ± 0.5 °C, moisture accuracy ± 2%, output signal RS485 type, response time < 1 s) were used throughout the composting process to monitor the pH, temperature, moisture, and the levels of key nutrients such as nitrogen, phosphorus, and potassium were monitored throughout the composting process. Centrifuges and filter papers were employed to separate solids from liquids in suspension, thereby preparing filtrates for evaluating the seed germination index. To further analyze the compost’s composition, an elemental analyzer (GLD brand, linearity error: ≤ 0.2%) was utilized to measure the total carbon and nitrogen content. Additionally, an electric blast drying oven was employed to determine the moisture content of the raw materials, which facilitated the optimization of moisture adjustment throughout the composting process. Finally, a horizontal shaker (GLD brand) was used to ensure uniform mixing of samples with water, which is crucial for maintaining accuracy and consistency in the tests.

2.3. Materials Used in Composting Experiments

The materials used in the horse manure composting experiment are depicted in Figure 3. In this study, Mongolian horse manure and corn stalks were selected as the composting mixture. The Mongolian horse manure was sourced from Bedoumele Equestrian Club in Hohhot, the Inner Mongolia Autonomous Region, while the corn stover was obtained from our college’s laboratory. The Inner Mongolia Autonomous Region is abundant in organic matter and nutrients. The corn stover, procured from the Agricultural Machinery Laboratory at the College of Electrical and Mechanical Engineering, Inner Mongolia Agricultural University. The detailed composition of these materials is provided in

Table 1. Test material.

Material	Characterization
Mongolian horse dung	Mongolian horse manure is rich in organic matter and fiber, with a moderate moisture content, making it well-suited for composting and conversion into organic fertilizer.
Corn stalks	Cut into 2 to 3 mm to facilitate subsequent mixing of tests
Farmland	Farmland soils are usually rich in nutrients and organic matter, with a loose structure, good permeability and water retention, suitable for plant growth and crop cultivation
Seed	The germination rates of maize, mung bean, and wheat seeds are influenced by the soil environment, making them suitable for experimental measurement of seed germination. Cabbage seeds are specifically used to assess the seed germination index.

.

2.4. Experimental Methods for Composting Mongolian Horse Manure

For composting Mongolian horse manure, the optimal initial moisture content should range between 55% and 60% [43]. Based on previous studies, a compost-to-water mass ratio of 1:2 is recommended. This mixture allows for achieving an optimal carbon-to-nitrogen ratio of 20–25:1 [42,43,44]. In this experiment, the initial feedstock consisted of a mixture of corn stover and Mongolian horse manure in a mass ratio of 1:20. To ensure the precision of these ratios and the reproducibility of the experimental outcomes, the composting process was conducted in stages using plastic buckets to contain the feedstock. The process of ingestion was stratified into a sextet of sequential phases, during which the constituent raw materials were subjected to precise quantification via an electronic weighing mechanism prior (capacity: 30 kg, accuracy: 0.001 kg) to the commencement of each phase. The resultant data from these measurements were meticulously documented for subsequent analysis. Post-incorporation of all composting elements, the MCGS data reimport utility, in conjunction with the empirical test data, was employed to delineate graphical representations that depicted the fluctuations in the parameters of fermentation temperatures, seed germination efficacy, oxygen saturation within the containment vessel, moisture levels, and the seed germination index.

During the composting trial, data acquisition was systematically executed at tri-hourly intervals via a touch screen interface, persisting until the culmination of the composting period. Drawing from extant scholarly research, it has been established that compost can achieve decomposition within a brief time span, typically postulating the completion of three cycles of aeration and thermal processing. In accordance with these precedents, the Mongolian horse manure compost, which was the subject of this investigation, was subjected to a regimen of three sequential aeration and thermal treatments [5]. Upon the introduction of the compost material into the fermentation apparatus, samples were procured on a daily basis to ascertain the precision and comprehensiveness of the collected data. The procedural operations and the granular details of the experimental protocol are graphically represented in Figure 4.

Four sections were created from the fermented horse manure samples that were obtained. To make sure that the experimental findings were unaffected by outside influences, the first component was combined with a predetermined quantity of nutrient-free field soil. After that, the combined soil was equally divided among the seedling pots. After that, seeds of mung beans, wheat, and maize were planted in these pots with the organic compost-soil combination. The effectiveness of the organic compost was evaluated by monitoring and measuring the germination rates of the three types of seeds. Detailed experimental steps and technical descriptions are provided in Figure 5.

An implanted soil sensor was used to assess the compost after the addition of the second portion of fermented Mongolian horse dung sample to a pre-prepared bucket. This sensor monitored the physical and chemical parameters of the compost in real time, generating and recording the corresponding index data. The experimental procedure is illustrated in Figure 6. The sensor output signal is RS485 with a resolution of 0.1 percent and accuracy within 2 percent.

The tertiary phase of the experimental protocol was dedicated to the ascertainment of the germination index. In order to preserve the viability of the compost samples, they were initially conserved at a temperature of 4 °C. The methodology for processing the samples is delineated as follows: the compost specimens were combined with ultrapure water in a mass-to-volume ratio of 1:10 and agitated in a horizontal shaker for the duration of 2 h to facilitate the extraction of organic constituents. Subsequently, the resultant mixture was subjected to centrifugation under standardized conditions, specified as a 10-min duration at a preset rotational velocity. Upon completion of the centrifugation process, the supernatant liquid was subjected to filtration through a filter paper to eliminate any fine particulate matter suspended within it. Subsequently, a precise volume of 5 milliliters of the filtrate was measured and transferred to a sterile Petri dish, which had been pre-equipped with a layer of filter paper. To maintain uniformity across the experimental conditions, twenty robust chard seeds were uniformly distributed within each Petri dish. The dishes were then placed in an incubator, where they were maintained at a consistent temperature in the absence of light for a period ranging from 4 to 7 days, allowing for the germination of the seeds. To evaluate the impact of the compost extract on the germination process, ultrapure water served as a control group in the experimental design. The detailed steps of the experiment and the presentation of results are illustrated in Figure 7. GI (%) = (the average germination rate of seeds in the treatment group × the average root length of seedlings in the treatment group)/(the average germination rate of seeds in the control group × the average root length of seedlings in the control group) × 100%. Higher germination index (GI) readings often indicate reduced toxicity levels in compost, making it more favorable for plant growth and indicating a higher level of compost maturity.

The culminating segment of the experimental series was oriented towards the quantification of the total carbon and nitrogen content within the compost samples. For the compost samples, a pre-treatment procedure was used to ensure measurement accuracy. In order to reduce the impact of moisture on the ensuing measurements, this technique started with the samples being air-dried to a consistent weight. Once the samples achieved a stable weight, they were processed through mechanical milling to achieve a fine powder consistency. This powder was then sieved through a 60-mesh sieve to ensure a homogenous particle size distribution across the sample, which is critical for the accuracy of the analytical techniques employed in the determination of elemental content. Prior to the elemental analysis, a meticulous weighing of each sample was conducted, with the initial weight post-air-drying meticulously documented. Subsequently, the samples were deposited into designated crucibles, which were specifically designed for such analytical procedures. The determination of the total carbon and nitrogen content within the samples was then executed using an elemental analyzer, a sophisticated instrument capable of providing precise measurements of these elements. Following the quantification of carbon and nitrogen, the ratio of carbon to nitrogen was computed for each sample. The specific procedures and results of the experiment are illustrated in Figure 8.

In the preliminary examination of the ongoing test data, it was discerned that the quantified parameters demonstrated minimal variability across brief temporal spans. Leveraging this insight, and with the objective of augmenting the efficacy of subsequent data processing and analytical endeavors, a triad of discrete temporal junctures was elected for the aggregation and graphical elucidation of the data: 7 a.m., 3 p.m., and 11 p.m. on a daily basis. In the ensuing graphical representations, the principal horizontal axis delineates the data procured at 11 p.m. each day, with the two ancillary scales aligning with the data amassed at 7 a.m. and 3 p.m. of the identical day. As an example, the number ‘1’ on the main axis represents the data collected at 11 p.m. on the first day, and the secondary scales next to it represent the data collected at 7 a.m. and 3 p.m. on the same day. The rationale behind this judicious selection and portrayal of temporal benchmarks is to streamline the data presentation, render the trends at each designated time point more perspicuous and, by extension, amplify the efficacy of data interpretation.

3. Results and Discussion

3.1. Variations in Temperature throughout the Procedure of Composting

One of the most important factors influencing the overall quality of compost is its temperature. Maintaining an appropriate range of raised temperatures is essential to efficiently remove pathogenic bacteria and ensure the quality and safety of the final compost product [42,43,44]. The temperature fluctuations that are seen when Mongolian horse dung composts are illustrated in Figure 9.

The experimental timeline spanned an approximate duration of 12 to 13 days, encompassing a composting regimen executed within an artificially regulated milieu, replete with ventilation and thermal conditioning. The thermophilic phase of the composting procedure, which is pivotal for pathogen reduction and material breakdown, endured for approximately 7 days. Subsequent to this interval, the compost pile’s temperature descended beneath 40 °C within a 24 h period, signifying the cessation of the thermophilic fermentation stage [42]. The findings of this study’s composting trials using Mongolian horse dung meet recognized criteria, demonstrating the well-designed and efficacious small-scale ventilated and heated composting system that can safely handle animal and poultry waste. These results further affirm the practicality and efficiency of the equipment and methodologies employed in this research for achieving optimal composting outcomes.

3.2. Moisture Changes during Composting

Regulating moisture is crucial for the process of compost fermentation and is a key indicator for assessing the excellence of organic fertilizers. Maintaining optimal humidity levels is essential for the continued activity of the microbial community. The microbial population is in charge of breaking down and converting organic materials, and it is this population that determines how palatable and nutritious the finished product will be. The composting process may be negatively impacted by very high or low humidity levels. Low humidity may slow down the decomposition of organic materials, which might have an impact on the compost’s maturity and general quality. However, high humidity may provide conditions that hinder the development of microorganisms, which might hinder the composting process [42,43,44]. Figure 10 illustrates the variations in humidity throughout the composting process, highlighting the crucial importance of humidity in ensuring the effectiveness of composting.

The moisture content of the compost exhibited a steady and gradual decrease as it underwent decomposition. The elevated temperature during the high-temperature stage resulted in a significant increase in the rate of water evaporation. The acceleration was a result of the thermal energy generated by microbes during the decomposition of organic matter, in addition to the elevated temperature. The humidity of the compost steadily decreased and reached a stable level due to the slower evaporation of water caused by the decreasing outside temperature, which also resulted in a steady fall in the compost’s temperature. Based on the testing results, the moisture content of the compost reached a stable average of around 12.7% at the completion of the fermentation phase. According to the industry standard for organic fertilizer, Organic Fertilizer (NY 525-2012), the moisture content of the fertilizer must not exceed 30% [43]. The moisture content produced from the fermentation of Mongolian horse dung compost in this experiment was significantly below the maximum limit, meeting all industrial norms. This indicates that the strategy of regulating moisture levels throughout the composting process was effective in preserving the quality of the final product.

3.3. Oxygen Concentration Changes during Composting

An essential element of the composting process is the level of oxygen content. An elevated oxygen content creates an optimal metabolic environment for aerobic bacteria, enhancing the decomposition of organic materials and preserving the quality of the compost. Conversely, anaerobic conditions may occur in certain parts of the compost when there is insufficient oxygen, inhibiting the growth of aerobic microbes. In addition, this may result in the release of malodorous gases such as methane (CH₄) and hydrogen sulfide (H₂S) [42,43,44]. Figure 11 illustrates the fluctuations in oxygen concentration throughout the composting of Mongolian horse dung. These visual data emphasize the crucial role that oxygen concentration plays in the composting process.

As fermentation continues, the oxygen content in the tank progressively drops throughout the composting process. On the other hand, with every regular aeration, the concentration of oxygen increases regularly. The impact is most noticeable in the cooling phase as the compost gets closer to maturity and microbial activity decreases, which lowers the requirement for oxygen. In addition, the fermenter’s semi-closed design retains gases in the tank throughout the development phase, which aids in maintaining a slightly higher oxygen content. This design enhances the compost’s efficient maturation by guaranteeing a steady oxygen supply throughout the composting process.

3.4. Changes in Seed Germination during Composting

This study aimed to verify the influence of compost quality on seed germination by selecting three representative crops typically cultivated in the Inner Mongolia Autonomous Region: wheat, mung beans, and maize. Compost samples were combined in the appropriate proportions with locally sourced agricultural soil to conduct seed germination experiments. In order to assess the impact of compost on the potential for seed germination, the number of plants that successfully germinated for each crop was tallied, and the germination percentage was calculated in a controlled environment. The germination potential of seeds demonstrates that compost positively influences the soil ecosystem. Additionally, the rate at which seeds germinate not only reveals the viability of the seeds but also reflects this impact [42,43,44]. The impact of blending agricultural soil with fermented organic compost derived from Mongolian horse dung on seed germination rates is illustrated in Figure 12.

This study investigated the impact of organic compost derived from Mongolian horse dung on the germination of mung bean, wheat, and maize seeds. By monitoring the rate of seed germination and related indicators at the conclusion of the artificial external temperature increase phase on day five, this research examined the impact of compost on a variety of crops. The germination rates of the different crops showed substantial variation, as shown by the statistics. Mung bean seeds had the highest germination rate at 86%, whilst wheat seeds showed the lowest rate at 75%. The findings suggest that the effectiveness of compost derived from Mongolian horse dung in promoting seed germination varies depending on the kind of crop.

3.5. Changes in pH during Composting

The acid-base balance is a crucial factor influencing the quality of the final compost product during the composting process [42,43,44]. The dynamic trend of pH values throughout the composting process for various amounts of Mongolian horse dung is illustrated in Figure 13.

The pH of the compost varied throughout the composting process, transitioning from moderately alkaline to slightly acidic. It fluctuated until it reached a stable value of 6.4 at the end of the composting time. The pH level momentarily increased during the intermediate stage due to a significant ammonia release from the heat breakdown process. The pH of the compost mixture rose as a consequence of the breakdown of proteins and other nitrogenous materials at high temperatures, which released free ammonia. Anoxic conditions arose due to a decrease in the rate of decomposition induced by alterations in the microbial habitat and a drop in temperature inside the compost. During this maturation stage, microorganisms initiated the conversion of ammonia, which was generated by breakdown into nitrites and nitrates. These molecules consumed the alkaline components of the compost and gradually reduced the pH. During the final phases of the process, more intricate organic molecules undergo decomposition and transform into stable substances such as fulvic and humic acids. In addition to minerals, these complexes of stable organic materials also contributed to the further stability of pH. The humic acid complexes ultimately kept the pH of the compost at a slightly acidic level, which was ideal for plant development. According to the Organic Fertilizer Industry Standard (NY 525-2012) [44], composted and decomposing organic fertilizer should have a pH level between 5.5 and 8.5. This requirement is fulfilled by the organic fertilizer that was assessed in this study.

3.6. Variations in EC Values throughout the Composting Process

Electrical conductivity (EC) is a measure of the ability of a compost medium to conduct an electric current, which is indicative of the presence of dissolved ions within the matrix. This parameter is a surrogate for the assessment of solute concentration, particularly that of soluble salts, and it provides insight into the nutrient availability as well as the potential for osmotic stress on plant life. The ionic composition of the compost leachate is directly responsible for modulating the EC value. An enhancement in the concentration of ions, such as those resulting from the dissolution of salts, minerals, and other soluble components, leads to an increase in the medium’s conductivity. Conversely, a reduction in ionic concentration results in decreased conductivity [46].

Figure 14 illustrates the changes in electrical conductivity (EC) during the composting of Mongolian horse manure, with the final organic manure exhibiting an EC of 5.2 ms/cm. Due to the early decomposition of organic materials and little microbial activity, the EC was initially low. As composting progressed, microbial decomposition of organic matter produced more small molecules, causing an increase in the EC value. The EC values saw a notable rise throughout the fermentation stage as a result of heightened microbial activity and accelerated degradation of organic materials. In the later stages, weakened microbial activities and decreased compost temperature caused the EC value to stabilize or decrease slightly, reflecting the transformation and balance of substances in the compost maturation process.

3.7. Fluctuations in the Levels of Nitrogen, Phosphorous, and Potassium during the Process of Composting

The three essential elements that fluctuate throughout the composting process are potassium (K), phosphorous (P), and nitrogen (N). These variations are crucial for determining the compost result’s quality, maturity, and nutritional value. Furthermore, the form and quantity of nitrogen (N), phosphorus (P), and potassium (K) in compost not only serve as important indicators of its age but also directly impact its ability to sustain soil health and enhance crop growth [42,43,44]. Figure 15 illustrates the fluctuations in the levels of phosphorus, potassium, and nitrogen concentrations that arise throughout the fermentation process of compost derived from Mongolian horse dung.

The dynamics of the nitrogen, phosphorous, and potassium content during the composting of Mongolian horse dung is illustrated in Figure 15. The nitrogen content initially increased and then decreased, reaching 2.3% by the end of fermentation. This pattern shows how organic nitrogen is first converted into inorganic nitrogen at the start of the composting process, followed by a decline in the total nitrogen content due to nitrogen volatilization triggered by rising temperatures. However, the increase in inorganic nitrogen improved its bioavailability. The phosphorus content consistently increased throughout the composting process, stabilizing at 1.3% by the end of fermentation. This increase was due to the gradual conversion of organic phosphorus into readily absorbable inorganic phosphorus. The potassium content also steadily rose to 1.2% by the end of fermentation. Potassium remained relatively stable, primarily in ionic form, making it easily absorbable by crops. The evaporation of water during composting contributed to the relative concentration of potassium. The test results indicate that the nitrogen, phosphorus, and potassium concentrations were higher than 1.2%, 0.6%, and 1.2%, respectively, in accordance with the national standard GB 7959-2016 for organic fertilizers, indicating that all compost samples met the relevant requirements for organic fertilizers [43].

3.8. Fluctuations in the Carbon-to-Nitrogen Ratio during the Composting Process

The carbon-to-nitrogen (C/N) ratio plays a crucial role in determining microbial activity, the speed of composting, and the overall quality of the final product throughout the composting process. A balance between the carbon and nitrogen needs of microorganisms is achieved by an optimal carbon-to-nitrogen ratio of 20–25:1, which encourages microbial development and speeds up the breakdown of organic waste to produce high-quality mature compost. A carbon-to-nitrogen (C/N) ratio that is abnormally high might be a sign of low nitrogen availability, which would limit microbial activity, impede compost maturation, and perhaps even cause nitrogen depletion. In contrast, an excessive quantity of nitrogen is detected by an extremely low C/N ratio, leading to an accelerated release of ammonia and loss of organic nitrogen. This has an impact on the environment and may also reduce the amount of nitrogen available in the final product. Therefore, in order to create a composting process that is both efficient and long-lasting, it is necessary to adjust the carbon-to-nitrogen ratio to meet the nutritional requirements of microorganisms [42,43,44].

Figure 16 illustrates the gradual decrease of the carbon-to-nitrogen (C/N) ratio during the composting process. Initially, there is a sudden decrease in the ratio, which is then followed by a more gradual decline that eventually reaches a stable level between 15 and 16. Compost is considered mature when the carbon-to-nitrogen (C/N) ratio reaches around 15. This indicates that it has significant fertilizing properties and is very stable, making it suitable for use in agriculture [42,43,44].

3.9. Germination Index Variations during Composting

The germination index (GI) of seeds is a vital tool for determining if compost contains plant development inhibitors, which may lead to phytotoxicity. As the GI integrates both the seed germination rate and seedling root length, it is widely recognized as an effective method for evaluating compost maturity. Figure 17 illustrates the variation curve of the seed germination rate in the composting process of Mongolian horse manure.

The gradual increase in the seed germination index (GI) during the first phases of composting suggests the existence of substances in the compost that hinder plant growth. The inhibitors gradually decreased or disappeared as the composting process progressed, resulting in a faster development of the intermediate stage of the GI. This indicates a substantial improvement in the maturity of compost and a noticeable reduction in its phytotoxicity. The compost seemed to be approaching its ideal state of maturity as the GI development peaked in the last phases of compost maturation. The GI value of the finished organic compost is 104%. When the GI value of compost is more than 80%, it is deemed to be adequately decomposed and almost devoid of dangerous materials that might impede plant development [42,43,44].

3.10. Discussion of the Composting Process

In this research, we examined important variables that affected the temperature, humidity, oxygen concentration, pH, conductivity, nutritional content (N, P, and K), carbon-to-nitrogen proportion, and seed germination index during the composting process of Mongolian horse dung. These criteria are critical for evaluating the quality, maturity, and possible agricultural uses of compost. Our findings revealed that temperature variations corresponded with typical composting stages, humidity was effectively controlled, and oxygen levels were consistently maintained under aerobic conditions. Nutrient conversion proceeded efficiently, while pH stabilized within a slightly acidic range. Additionally, conductivity levels indicated effective nutrient concentration, and both the carbon-to-nitrogen ratio and seed germination index confirmed that the compost was mature and suitable for agricultural use.

The results of our study align with previous research on livestock manure composting. For instance, Cai et al. [41] explored the effect of the carbon-to-nitrogen ratio on composting wheat straw mixed with chicken manure, highlighting the crucial roles of the temperature and pH. Similarly, Su et al. [42] examined the best combinations of sheep and cattle dung for the combination, emphasizing the need to maintain suitable composting conditions. Further, Ren et al. [43,44] developed specialized equipment for sheep and cow manure composting, advancing composting technology, while Zhao et al. [45] studied bacterial diversity and physicochemical properties during swine manure composting. Collectively, these studies underscore the importance of critical parameters that influence the compost quality across various types of livestock manure.

Nevertheless, there is a limited number of research specifically addressing the composting and fermentation of Mongolian horse manure. Our study addresses this gap by providing empirical evidence on the effectiveness of a specialized composting system tailored to Mongolian horse manure. Compared to traditional large-scale pile composting methods, the optimized system offers several key advantages. It provides enhanced control over composting conditions, leading to higher quality and more stable compost, and addresses limitations of traditional methods, such as inconsistent oxygen supply and fluctuating temperatures.

The advanced composting process described in this study integrates refined ventilation and heating structures that allow for more precise control of the composting environment, improving overall efficiency. These improvements accelerate compost maturation, enhance the seed germination index, and reduce the moisture content. Consequently, the final compost product meets national organic fertilizer standards, showcasing its potential to enhance soil fertility and support sustainable agriculture, particularly in the Inner Mongolia Autonomous Region.

While the results of this study are promising, several limitations need to be considered. This research was conducted in a controlled environment, and further research is required to assess the compost’s long-term impacts on crop yields and soil health in diverse agricultural settings. Additionally, since this study focuses exclusively on Mongolian horse manure, future research should investigate the applicability of this composting system to other types of livestock manure.

Moreover, while the redesigned composting equipment proved effective, there is still room for further optimization. Future work could aim to enhance the scalability of the system, improve energy efficiency, and incorporate advanced real-time monitoring technologies. These enhancements could shorten the composting cycle and improve the overall quality of the compost product. The deployment of this equipment not only improves the effectiveness of the decomposition procedure but also provides essential technical support for the sustainable utilization of livestock manure resources, thereby contributing to the overall sustainability of agricultural production.

4. Conclusions

(1)

This study demonstrates the effectiveness of small aeration and heating composting equipment in processing Mongolian horse manure. The equipment successfully maintained high temperatures for up to eight days, which ensured efficient organic matter decomposition. It also consistently controlled humidity, maintaining it below 30%, with an optimal level of 12.7%, while sustaining a continuous aerobic environment, which is essential for successful composting.

(2)

The resulting compost met national organic fertilizer standards, with nitrogen, phosphorus, and potassium contents reaching 2.3%, 1.3%, and 1.2%, respectively. The final pH value of 6.4, being within the slightly acidic range, is suitable for most crops. Additionally, the electrical conductivity, measured at approximately 5.2 mS/cm, indicated balanced nutrient concentrations without posing a risk of soil salinization.

(3)

The carbon-to-nitrogen ratio decreased from 27.3 to 15.9, reflecting effective organic matter degradation. The seed germination index reached 104%, surpassing the 80% threshold for compost maturity, thereby confirming both the maturity of the compost and its agricultural safety. These findings underscore the potential of small aeration and heating composting equipment to produce high-quality organic fertilizer, thereby supporting sustainable agricultural practices in the Inner Mongolia Autonomous Region.