Anaerobic fermentation technology utilizes aerobic conditions to degrade organic solid waste primarily, through the process of a large number of microorganisms, achieving stabilization and detoxification, and converting it into material suitable for soil improvement and quality enhancement. It significantly recovers nutrients and organic components from organic solid waste, making it a typical resource recovery disposal method. The sources of organic solid waste are complex and variable, including specific particle size, material moisture, type of nutrients, molecular size, complexity, and overall C/N ratio, moisture content, and pore distribution, which determine the feasibility of the aerobic fermentation process. Therefore, the optimization of aerobic fermentation material blending is fundamental to enhancing system operation efficiency and stability. On the other hand, during the microbial oxidation and degradation of mixed organic matter, only 40-50% of the chemical energy can be utilized by microorganisms, with the remainder converted into heat energy, further affecting the microbial activity of the material, system operation efficiency, and product hygiene quality. Hence, aerobic fermentation temperature control is a key process parameter. Generally, it is believed that around 15-20°C and approximately 1.0 m³ are the critical starting temperature and volume for aerobic fermentation of the material, based on different substrate types and local climates.
The vertical fermentation tank principle and technology originated in Germany and were later sold to Japan. Some domestic manufacturers introduced them from Japan in 2013. In Japan, fermentation tanks are used for the fermentation of animal and poultry waste, as well as kitchen waste. Some manufacturers have copied them one-to-one, using them for sludge fermentation. During the sludge fermentation process, a series of issues have arisen, such as the main shaft of the agitation mechanism breaking, paddle blades breaking, drive mechanism ratchet teeth breaking, main shaft key breaking, uneven discharge causing internal collapse, inability to discharge normally, and unstable yield. Frequent culturing of the bacterial bed leads to irregular operation of the sludge fermentation tank. In some areas, large amounts of auxiliary materials are used to reduce the resistance of the drive mechanism and increase the aeration of the sludge. However, the fermentation yield is more than 70% lower than that of animal and poultry waste and kitchen waste, and it is also unstable. This is because the principle, design parameters, and mechanical design of the fermentation tank are based on the material of animal and poultry waste and kitchen waste, their density, porosity, aeration rate, composition, required oxygen content, and municipal sludge are completely different. Therefore, they cannot be used universally. It is necessary to research a targeted high-temperature aerobic fermentation equipment for sludge to solve the existing problems of low sludge fermentation treatment efficiency, high failure rate, large land occupation, severe environmental pollution, and high costs.

With the development of China's economy and urbanization, the volume of urban sewage discharge continues to increase, and the treatment rate of sewage is rising year by year. Sludge is the main solid waste in the urban sewage treatment process, and the organic matter, nutrients, and other pollutants in the sludge are basically transferred into it through microbial, physical, or chemical actions. It is estimated that the sludge production in China in 2011 (with a moisture content of 80%) exceeded 30 million tons. The composition of sludge is complex, consisting of a polymer formed by various microorganisms and the organic and inorganic substances they adsorb. Apart from a large amount of water, it also contains hard-to-degrade organic matter, heavy metals, salts, and pathogens and eggs. The sludge has a high content of organic matter and nutrients such as nitrogen and phosphorus, which, if entering the aquatic environment, could cause significant environmental pollution and is also a great waste of resources. The pathogenic bacteria, organic pollutants, and the odor issues during sludge treatment and disposal have also drawn increasing public attention.
As the issue of sludge treatment and disposal becomes increasingly prominent, China is paying more and more attention to controlling and resolving sludge problems. Since 2007, 9 industry standards for sludge quality in wastewater treatment plants have been formulated, with 6 of them further revised and compiled into national standards. In addition to establishing sludge quality standards, technical documents such as the "Technical Guidelines for the Feasibility of Sludge Treatment and Disposal in Wastewater Treatment Plants" (Draft for Comments), the "Technical Policy for Sludge Treatment and Disposal, and Pollution Prevention in Urban Wastewater Treatment Plants (Pilot)", and the "Technical Guidelines for Sludge Treatment and Disposal in Urban Wastewater Treatment Plants (Pilot)" have also been successively released. These documents provide some guiding regulations on the technical options for sludge disposal, technological trends, specific implementation plans, and investment and financing methods, thereby clarifying the development direction for sludge treatment and disposal in China's urban wastewater treatment plants.
Wastewater sludge treatment technologies include methods such as sanitary landfilling, incineration, aerobic fermentation, and resource utilization. Among these, aerobic sludge composting is recommended in the "Technical Guidelines for the Treatment and Disposal of Sludge from Urban Wastewater Treatment Plants (Trial)" due to its moderate investment and operational costs, while also utilizing the organic matter and nutrients in the sludge. Currently, common aerobic fermentation systems worldwide primarily use concrete structures like troughs, silos, or pile systems. These systems maintain aerobic conditions within the compost mass through manual or mechanical turning combined with natural or forced ventilation to ensure compost temperature and the normal growth of microorganisms. This is an open system, which presents issues such as extended composting time, large land area requirements, and difficulty controlling odors, water vapor, and leachate, significantly affecting the surrounding environment and public health, leading to public complaints. Moreover, existing aerobic fermentation systems struggle to precisely and automatically control the various parameters during the composting process. Therefore, developing a new type of aerobic sludge fermentation system that improves efficiency and addresses issues like prolonged composting time, large land usage, and strong odors is crucial for solving the increasingly prominent sludge problem in wastewater treatment plants in our country.

With the development of urbanization in our country, the volume of wastewater discharge is increasing, leading to a growing amount of sludge in cities. Sludge is a byproduct of wastewater treatment and consists of a complex non-homogeneous mixture of organic fragments, microorganisms, inorganic particles, colloids, etc. Traditional sludge treatment methods include incineration, burial, and landfilling, which not only pollute the living environment but also waste resources to some extent. One common sludge treatment process is fermentation composting, but during the fermentation process, a large amount of gas far above room temperature, containing a significant amount of water vapor, is produced. Current technology often discharges these gases directly into the atmosphere or collects them for secondary treatment through filter pools. This results in the underutilization of heat in the gases and the ineffective removal and recovery of water vapor, which may prolong the fermentation cycle, affect the fermentation effect, and potentially pollute the environment. Some fermentation and composting processes are conducted outdoors, which not only affects the surrounding environment but also leads to significant temperature fluctuations in the fermentation materials due to environmental or human factors, impacting the fermentation outcome.

With the improvement of urban economic levels and the change in living quality in our country, the production of municipal solid waste has also rapidly increased. At the same time, a large amount of agricultural waste, animal and poultry feces, and ash soil are mixed into the municipal solid waste, resulting in a high organic matter content in the municipal waste. However, in the past, most towns have simply buried, temporarily stacked, or burned rural waste, which has polluted soil, water bodies, and the atmosphere, as well as caused a great waste of usable resources. Even in some areas where organic matter in municipal waste has been composted, issues such as long composting cycles, low product yields, and low product purity still exist. Therefore, how to provide a device that fully utilizes the organic matter in municipal waste is an urgent problem that technical personnel in this field need to solve.
The aerobic fermentation process of sludge compost generally consists of primary composting and secondary composting. The primary composting includes pre-mixing of raw and auxiliary materials, compost aerobic fermentation, turning and aerating, oxygen supply, and deodorization. The primary sludge compost aerobic fermentation process plays a crucial role in the reduction, harmless treatment, and stabilization of sludge, and involves many factors to control, such as moisture, temperature, aeration, and oxygen supply. Among these factors, the temperature change of the sludge heap is a key indicator to measure whether the aerobic fermentation of sludge compost is normal, and also a direct and sensitive indicator reflecting the normality of the heap fermentation. The requirements for the temperature of the sludge compost heap can be summarized as follows: during the primary composting fermentation process, the temperature should rise steadily in the early stage, maintain a moderate temperature change during the high-temperature phase, and decline slowly in the later stage. The temperature change in the early stage of primary composting fermentation must handle the relationship between "fast" and "stable," meaning the compost fermentation should start quickly but the temperature rise should not be too rapid, and it should be as stable as possible; the temperature change during the high-temperature maintenance phase should be moderate, ideally controlled between 55-65 degrees Celsius, not exceeding 70 degrees, as excessive temperature can cause the compost material to 'sinter'. In summary, temperature is a very important and direct control factor in the control of the aerobic fermentation process of sludge compost.