Organic Solid Waste Composting: At a Dead End?
01. Evolution of Composting Technology Over a Century: From Traditional Experience to Large-scale Exploration
The treatment and disposal of organic waste has become a major, unavoidable issue in the field of ecological and environmental protection. Multiple departments including the General Office of the State Council, the Ministry of Agriculture and Rural Affairs, and the National Development and Reform Commission have issued specialized documents on numerous occasions, providing clear deployment requirements for the treatment and disposal of organic waste.
Zheng Guodi explained that from the perspective of technical pathways for solid waste disposal, its ultimate destination is none other than three categories: "up to the sky, into the ground, down to the sea." With the strict implementation of regulations related to marine environmental protection, "down to the sea" disposal has been completely banned. The existing technical pathways now focus on the two major directions of "up to the sky" and "into the ground"—"up to the sky" refers to converting solid waste into gaseous substances through incineration processes, while "into the ground" encompasses various forms such as land utilization, landfilling of incineration ash and slag, and landfilling of raw solid waste.
Zheng Guodi pointed out that although solid waste disposal technologies are diverse and processes evolve rapidly, they always adhere to the fundamental laws of "conservation of mass and energy conservation." On this basis, the core of solid waste resource utilization lies in achieving the dual recovery of mass and energy. The essential principle of whole-process solid waste management, meanwhile, focuses on the precise prevention and control of environmental risks.
Composting, as an important technical means for treating organic solid waste, has a long history of development and deep cultural origins. It is documented in many ancient Chinese agricultural texts. Works such as Qimin Yaoshu, Chen Fu Nong Shu, and Fan Sheng Zhi Shu all record in detail the traditional techniques of mixing and piling straw, fallen leaves, wild grass, and animal manure for fermentation to produce fertilizer, representing the most primitive form of composting.
Modern composting technology differs fundamentally from traditional composting processes. Its development history can be divided into several key stages:
1. Primitive Composting Stage (Before 1920)
Composting in this stage centered on traditional farming experience. Rural areas commonly used natural piling and fermentation to mix and decompose organic materials like straw and livestock manure to make agricultural fertilizer. The process was simple and did not form a systematic technical framework.
2. Technological Germination Stage (1920-1940)
Composting began transitioning from traditional experience to scientific technology. The industry gradually recognized the microbial nature of the composting process and attempted to translate this core principle into quantifiable operational factors and process design parameters, laying a theoretical foundation for the scientific development of composting technology.
3. Rapid Development Stage (1950-1960)
Breakthrough progress was made in the mechanistic research of composting by academia and industry. Related theoretical achievements accelerated their translation into practical applications. The standardization of process design and operational procedures significantly improved, propelling composting technology from the laboratory towards large-scale application.
In China, modern composting technology research oriented towards environmental protection began in the 1970s. Subsequently, driven by continuous national policies, composting technology R&D and project applications entered a period of accelerated development.
During the "Sixth Five-Year Plan" (1981-1985): The former State Economic and Trade Commission established the key research project "Research on the Harmless Treatment and Comprehensive Utilization of Municipal Garbage and Fecal Matter," initiating systematic exploration into the composting treatment of urban organic solid waste.
During the "Seventh Five-Year Plan" (1986-1990): The former Ministry of Construction launched the project "Development Research on New Technologies for the Harmless Treatment of Municipal Waste in Wuxi City," further promoting the process optimization and equipment upgrading of composting technology. The research outcomes provided important support for subsequent technology promotion.
In 1990: The Department of Social Development of the former State Science and Technology Commission and the Department of Science and Technology of the former Ministry of Construction jointly conducted a nationwide evaluation of municipal solid waste treatment projects. Among them, 11 composting technologies were rated as "promotion technologies" and "pilot promotion technologies" respectively, marking the official entry of composting technology into the large-scale promotion stage.
Driven by strong national policies, composting technology achieved leapfrog development, with various process routes and equipment technologies emerging one after another. From the late 1980s to the early 21st century, China's composting industry experienced a vigorous period of development. However, during this period, although the number of composting projects grew rapidly, some projects ultimately stalled due to reasons such as insufficient technological adaptability, extensive operational management, and poor market demand alignment.
02. Core Industry Dilemma: Positioning Deviation and Prominent Odor Problem
A special investigation was conducted into the operational status of domestic large-scale garbage composting plants. Among the dozens of large-scale composting projects examined, the vast majority were in a state of shutdown.
The causes of this industry dilemma can be glimpsed from a comparison of typical cases. While participating in research projects related to the Asian Development Bank, to analyze the key factors for the success or failure of municipal solid waste composting projects, the research team selected two representative projects—composting plants in Guilin and Beijing. Both projects were German aid projects to China, fully importing German process technology and equipment configuration.
What formed a contrast was the Nangong Waste Composting Project. The project's designed treatment capacity gradually expanded from an initial 400 tons/day, to 800 tons/day, then 1000 tons/day, ultimately reaching 2000 tons/day. However, it is also currently shut down. It is noteworthy that differences in project positioning directly influenced their phased development trajectories: the Guilin project set the core goal of municipal solid waste composting as fertilizer production, whereas the Nangong project took solid waste volume reduction as its core objective. This divergence in positioning allowed the Nangong project to achieve continuous capacity expansion in its early development, while the Guilin project fell into stagnation earlier.
The comparison of this set of cases reveals a core insight: the core orientation of municipal solid waste composting projects should be environmental protection, not fertilizer production.
Using this as a starting point to examine the development status of China's composting industry, it is not difficult to find that both in the field of municipal solid waste composting and in areas such as straw, municipal sludge, and livestock manure composting, there is a trend of shrinking technology application and sluggish industry development.
Straw Composting: There are very few domestic cases directly using composting processes to treat straw. Straw is more often used as an ingredient in fertilizer production. Even during historical periods of insufficient chemical fertilizer production capacity, only some farmers conducted small-scale composting in fields. A large-scale, industrialized straw composting model has never truly taken shape.
Municipal Sludge Composting: After the 2008 Beijing Olympics, a sludge composting project in Qinhuangdao once became an industry benchmark, attracting visits and study from many parties,堪称 (virtually) a "pilgrimage site" in the sludge treatment field. However, from an overall industry perspective, the proportion of projects using medium-to-large-scale engineered composting processes to treat municipal sludge is extremely low.
Livestock Manure Composting: Compared to the previous two types of organic waste, composting applications for livestock manure are relatively wider. However, such composting mostly belongs to the category of simple piling in agriculture, which is fundamentally different from standardized composting in the environmental protection field. Most small and medium-sized livestock farmers' treatment methods only involve slight improvements on traditional farm composting, such as hardening and anti-seepage treatment of the composting site, adding rain shelter facilities, etc. Truly large-scale projects employing modern processes and equipment are rare. Additionally, anaerobic digestion is also one of the mainstream technical pathways for livestock manure treatment.
The development predicament of China's composting industry has long been attributed to poor product outlets. In the past, municipal solid waste was not effectively sorted, and composting raw materials were mixed with a large amount of impurities, directly affecting compost product quality. Even after the comprehensive implementation of waste sorting and the nationwide rollout of food waste treatment pilot projects, the adoption rate of composting processes remains relatively low, with anaerobic digestion still being the preferred technology for most projects.
Furthermore, compost products face multiple doubts: products may contain pathogens, heavy metals, and other toxic and harmful substances, easily leading to soil pollution; when compost maturity is insufficient, "seedling burning" phenomena can occur; weed seeds in raw materials not thoroughly inactivated may cause farmland weed infestation. Simultaneously, the odor pollution generated during the composting process has also become an important factor restricting project implementation.
However, deeper analysis reveals that most of the above issues can be resolved through technical means: pathogens and weed seeds can be effectively inactivated through high-temperature aerobic fermentation; the content of toxic and harmful substances in food waste itself is limited, and its pollution risk is entirely controllable—in the past, Beijing used to feed pigs with food waste, which shows its limited pollution level. With the enhancement of environmental and food safety standards, the control of food waste has become stricter, further reducing pollution risk.
The real constraint on industry development is the odor problem during composting. As residents' living standards and environmental awareness improve, odor pollution has replaced noise as the primary issue in current environmental complaints and is the core trigger for NIMBY (Not In My Backyard) effects related to solid waste treatment projects. Previously, public opposition triggered by some waste incineration plants in Beijing superficially stemmed from concerns about dioxin pollution, but actually originated from the direct perception of odor during construction and operation. This shows that odor control is a key factor determining a project's social acceptance.
03. Four Core Research Directions for Industrialized Promotion of Composting
Composting is a biochemical process using organic waste as raw material, under certain conditions of moisture, oxygen, temperature, nutrients, etc., where organic matter in the waste is decomposed and transformed into fertilizer through microbial fermentation. Its essence is the fermentation process of organic matter. During fermentation, biodegradable organic matter is converted into relatively stable humus substances.
The industrialized promotion of composting treatment needs to focus on tackling three core issues: conditioner selection, intelligent process control, and odor pollution management. Simultaneously, it must open up product application channels to achieve technology implementation and sustainable industry development.
1. Conditioner
The reasonable selection of conditioners directly affects the control effectiveness of temperature, oxygen, and moisture during composting, thereby determining the level of secondary pollution prevention and control, operational costs, and treatment efficiency. Traditional composting processes mostly use straw as a conditioner, especially in sludge and livestock manure composting, where straw is a key auxiliary material for adjusting the carbon-to-nitrogen ratio and improving material permeability.
However, the supply of straw has significant pain points: On one hand, straw burning was once a persistent problem in agricultural production, causing regional air pollution; On the other hand, when industries like composting and biomass power generation generate large-scale demand, the supply-demand relationship for straw becomes imbalanced, prices rise year by year, and coupled with transportation radius limitations, many straw power plants are forced to shut down due to high raw material costs. The composting industry faces the same raw material supply challenge. Additionally, straw also has derivative problems such as seasonal supply fluctuations, storage land occupation, and fire safety.
The core idea to solve this predicament lies in developing inorganic conditioners to replace traditional straw, freeing the process from dependence on organic conditioners through technological innovation, and reducing the uncertainty and cost pressure of raw material supply from the source.
2. Process Control
The stability of composting process control directly determines fermentation effectiveness and product quality. Past composting projects often suffered from extensive process management, leading to insufficient fermentation and fluctuating product quality. The iteration of process control technology has always been closely related to equipment upgrades driven by industry demands.
Twenty years ago, composting automatic control technology was widely questioned. Today, automation and even intelligent control have become industry consensus. The core support for this transformation is technological breakthroughs in monitoring and control equipment. Early composting monitoring relied on manual timed sampling, requiring staff to work night shifts to check parameters like ventilation volume. With the application of timed control boards and temperature sensors, composting processes initially achieved temperature feedback control.
However, relying solely on temperature feedback is far from enough. To achieve rapid degradation of organic matter, precise regulation of oxygen is crucial. This necessitates supporting oxygen detection equipment to establish a dual-parameter monitoring system of "temperature + oxygen." By deploying multi-dimensional sensors for temperature, oxygen, moisture, etc., and feeding monitoring data back to the control system in real-time, intelligent start-stop of fans can be achieved: ensuring sufficient oxygen supply during the heating phase, maintaining stable parameters during the high-temperature maturation phase, and regulating moisture content during the later cooling phase.
The integration of the entire monitoring hardware and control software forms an intelligent composting control system. This not only enables remote operation, significantly reducing the intensity of manual on-site work but can also optimize the entire process flow in conjunction with supporting production equipment, promoting the transformation of composting from "experiential operation" to "precision management."
3. Odor Management
Odor pollution has replaced noise as the primary issue in current environmental complaints and is the core obstacle restricting the implementation of composting projects. The mechanism of odor generation from organic solid waste is clear: Under anaerobic conditions, organic matter decomposed by microorganisms produces strong-smelling substances like hydrogen sulfide and volatile organic compounds. Under aerobic conditions, the decomposition products of organic matter are mainly water and carbon dioxide, with only a small amount of ammonia escaping, significantly reducing odor production and pollution levels.
Based on this principle, odor management should follow the full-process prevention and control concept of "source reduction—process control—end treatment":
(1) Source Reduction: Optimize raw material pretreatment, improve material permeability through crushing and homogenizing mixing to reduce the formation of anaerobic microenvironments at the root.
(2) Process Control: Reasonably design pile structure and ventilation systems to ensure the pile remains in an aerobic state throughout; simultaneously minimize the frequency of material turning—just as garbage bins in residential areas have minimal odor when stationary but emit intensified odor when turned during collection and loading, reducing pile disturbance can effectively lower odor escape. Additionally, setting up cover layers can further block odor diffusion.
(3) End Treatment: Abandon single biological deodorization technology pathways. Adopt combined processes like "biological deodorization + physical adsorption + chemical scrubbing" to achieve precise treatment for different odor components and improve deodorization efficiency.
Effectively solving the odor problem can fundamentally resolve the NIMBY effect of composting projects.
4. Process Integration and Product Outlets
The development of the composting industry also needs to rely on the standardization of process equipment to lower project implementation barriers. The construction process of traditional composting plants was cumbersome and procedurally complex. The introduction of standardized equipment has achieved "modular configuration"—for example, a single unit's processing capacity is fixed at 30 tons, and projects can flexibly increase or decrease the number of units according to demand, greatly simplifying approval procedures and reducing civil construction area and operational costs. Simultaneously, enclosed equipment design further enhances odor control levels, and operation becomes simpler, allowing workers to start and stop with a single button.
Compost products are not lacking a market; rather, the technology has failed to match application needs. Beyond the traditional agricultural field, compost products can expand into broader application scenarios: In Changshu, Jiangsu, compost products were used to repair low-lying land for turf production, enabling continuous production; precious flower and tree cultivation can use it as high-quality substrate; pasture land damaged by oil and gas extraction in northwestern China, and metal mine restoration in karst areas of Guangxi and Guizhou, can all consume large amounts of compost products.
04. Conclusion
Looking ahead to the future development of the solid waste composting industry, three core principles are proposed: First, follow scientific laws and reject false technologies that violate "conservation of mass and energy conservation." Second, rely on technological innovation, using industry demands as the guide to drive industry progress through equipment upgrades and process optimization. Third, adhere to the original intention of environmental protection, avoiding exaggeration of resource value and one-sided pursuit of resource utilization benefits, and frankly acknowledge the industry's need for government investment and cost guarantees.
Source：https://mp.weixin.qq.com/s/fWIyoKndLdm3xf0hh1PFDw