Analysis of Solid Waste Treatment and Management in Typical Chinese Industrial Parks with the Goal of Sustainable Development and Future Suggestions

Abstract

Solid waste disposal and management have become a global problem, which is particularly tricky in China with its large population and rapid urbanization. This study focused on the disposal status of multi-source solid waste as well as the park management of some typical cities of China. Firstly, the main technical methods for solid waste disposal were summarized as follows: landfill, incineration, anaerobic digestion and aerobic compost. Secondly, the network analysis method was applied to seek an optimized method for solid waste disposal and management. Thirdly, typical demonstration parks for solid waste disposal and management were analyzed to study their respective operating modes and strategies for synergistic development in terms of resources, environment and economy and to explore the sustainable development potential of the Guangdong–Hong Kong–Macao operating mode. The results showed that the collaborative disposal and recycling of solid waste are important for cities (especially megacities) to achieve resource conservation and environmental protection. The NIMBY effect and environmental pollution risks caused by decentralized construction could be reduced through the construction of circular industrial parks. Advanced technologies and the national policy for solid waste disposal and recycling in industrial parks of small–medium cities, large–medium cities and megacities were systematically analyzed so as to explore a self-operating management mode of industrial parks. Finally, reasonable suggestions, such as sharing, saving and cycling and propaganda education, as well as green and low-carbon solutions were put forward for solid waste disposal and management in typical industrial parks, effectively resolving the contradiction between economic development and environmental protection so as to help urban sustainable development.

1. Introduction

With the acceleration of urbanization at the beginning of the 21st century, the urban population and resource consumption increased rapidly in China. Subsequently, the problems of human activity and the random stacking of waste have increased and caused more and more serious water and air pollution, endangering the urban environment and affecting the lives and health of residents. If this continues, it will undoubtedly limit the sustainable development of cities.

Municipal solid waste mainly includes general industrial solid waste (non-hazardous industrial solid waste), hazardous industrial solid waste, medical solid waste and urban solid waste. General industrial solid waste refers to any industrial solid waste other than hazardous waste produced by industrial production activities [1]. Industrial hazardous waste refers to toxic, flammable, corrosive, infectious, highly chemically reactive, or other hazardous waste produced from industrial production [2]. Medical waste, produced by medical and health institutions in medical treatment, prevention, health care and other related activities, is directly or indirectly infectious or toxic and includes other types of hazardous waste. It also includes other waste managed and disposed of in accordance with the Management Regulations on Medical Waste [3]. Urban solid waste includes solid waste discharged from urban daily life or from services provided to urban daily life, as well as solid waste that is regarded as urban house refuse under laws and administrative rules and regulations [4]. The annual output of all kinds of solid waste increased by 6.34%, with general industrial waste accounting for 77.07% of municipal solid waste (Figure 1 and Table S1), which could be ascribed to the sharp rise in the urban population with the continuous development of China’s urbanization level.

In recent years, the production of solid waste has increased year by year around the world. In 2020 alone, 2.24 billion tons of solid waste was generated by human beings, amounting to 0.79 kg per person per day. The annual waste generation level is expected to increase by 73% from 2020 to 2050, finally reaching 3.88 billion tons [7]. If so, it will have a serious impact on the urban environment and the daily lives of residents. Therefore, reasonable treatment and effective management of solid waste are particularly important, and their practice will contribute to the sustainable development of the environment, economy and society.

The development of solid waste treatment and disposal has experienced more than half a century of exploration and has made certain achievements in China. Although China has made great strides in establishing a comprehensive regulatory framework for the green development of industrial parks covering different legislative levels, less than 5% of industrial parks are green-certified nationwide. There are still some problems that need to be solved, not only at the technical level but also involving the management of solid waste industrial parks. An industrial park is designed and established according to the requirements of cleaner production, the concept of a circular economy and the principles of industrial ecology, which is the concrete embodiment of a circular economy at a certain regional level in the industrial field. It connects different factories or enterprises through logistics or energy flow transmission to form an industrial symbiotic combination of sharing resources and exchanging by-products, making the waste or by-products of one factory become the raw materials or energy of another factory, simulating the natural system and establishing a “producer–consumer–decomposer” chain in the industrial system. However, the present problem of solid waste industrial parks is that the real effect of a single treatment technology is limited, while the combination of multiple composite technologies could be too complex. In addition, a lack of proper disposal or management modes has damaged the environment and caused a waste of resources.

In this study, the current situation of solid waste disposal and management in typical industrial parks in China is discussed by analyzing real cases of solid waste disposal and management in typical industrial parks. Network analysis is applied to research the multi-source solid waste disposal of the demonstration park, as well as solid waste management in typical industrial parks of China, following different sizes of cities. We aim to provide possible suggestions for multi-solid waste disposal and management, with a final goal of a green and low-carbon solid waste disposal model to contribute to sustainable urban development.

2. Materials and Methods

Due to its characteristics of bioavailability and mobility, solid waste is difficult to decompose and usually exists for a long time in the environment [8]. It not only occupies land space [9] but also damages the water–soil environment and endangers the lives and health of human beings [10]. What is worse, volatile pollutants formed from the chemical degradation of waste could cause air pollution [11]. At present, solid waste treatment technologies [12,13] mainly include landfill, incineration and biological treatment technologies (aerobic composting and anaerobic digestion).

2.1. Solid Waste Disposal Technology of Landfill

Generally, the most common method of solid waste treatment is landfill [14,15], especially for unsorted waste treatment [16], which has economic advantages [17]. However, landfills take up a large amount of land resources and cause secondary pollution [18]. Moreover, biochemical degradation produces a large amount of toxic leachates in the process of landfill, which can further be aggravated by precipitation [19], surface runoff [20], and groundwater runoff [21,22]. Therefore, landfill technology for solid waste disposal needs improvement for solving the problems of leachates and secondary pollution.

2.2. Solid Waste Disposal Technology of Incineration

Incineration is a common method for solid waste disposal around the world [23,24,25] because of its dual ability to reduce the volume of solid waste [26] and recover energy [27]. However, solid waste incineration produces three types of residues, i.e., bottom ash, fly ash and air pollutants [28]. Among the air pollutants, flue gas is produced in the process of incineration in the form of a secondary pollutant [29]. Furthermore, heavy metal compounds in solid waste whose volatilization point is lower than the combustion temperature could also enter the flue gas and contribute to air pollution [30]. What is worse, incomplete incineration can produce flue gas that contains highly toxic dioxins [31,32]. At present, only a few enterprises in China can achieve clean production and zero waste emission during the incineration process. Thus, incineration treatment is not the best choice for China’s solid waste disposal industry.

2.3. Solid Waste Biological Disposal Technology

Biological disposal methods, including aerobic composting and anaerobic digestion, are technologies that promote resource utilization in the process of solid waste disposal. Compared with traditional landfill, incineration and other physicochemical treatment methods, biological treatment technologies can not only reduce organic solid waste but also turn waste into wealth (organic fertilizers, biogas and others). Biological treatments have the advantages of low cost, green environmental protection and realizing the reuse of resources [33]. However, current biological disposal technologies still have some limitations. For instance, volatile compounds are derivatives of biological treatment that could cause air pollution when entering the environment [34].

Aerobic composting is a method of chemical decomposition of solid waste for extracting useful components through fermentation, degradation and other ways [35,36]. Anaerobic digestion is also a green and environmentally friendly solid waste disposal method with low energy consumption in the absence of oxygen [37]. However, the process of biological disposal can be affected by multiple environmental factors, e.g., temperature, pH, moisture, substrate, carbon source, nitrogen source, C/N ratio, etc. [38,39]. In addition, there is a lack of systematic evaluation for its effectiveness and technical economics [40]. Furthermore, the industrialization promotion of biological disposal technology is another issue worthy of attention.

2.4. Network Analysis Method

In order to improve the efficiency of multi-source solid waste disposal and management [41], VOS viewer 1.6.18, a software tool for constructing and visualizing bibliometric networks, was applied to understand which factors were more important in the field of solid waste disposal and management (Table S2). Co-authorship networks, citation-based networks, and co-occurrence networks were created based on data download from Web of Science (WoS), Scopus, Dimensions, and Lens. Co-authorship networks and co-occurrence networks were created based on PubMed data [42]. Data collection was mainly based on published data (see Section 3.1 for details), as well as field research of the Guangdong–Hong Kong–Macao Greater Bay Area (GBA) solid waste disposal demonstration park. Generally, WoS is the most widely used database worldwide [43]. The keywords for screening and research were as follows: TS = (“solid waste”) and/or (“solid waste treatment” or “solid waste disposal” or “solid waste management”). All the works retrieved from 2000 to 2023 included papers and journals but excluded minutes, abstracts, editorial materials, data files and letters [44,45]. Finally, 54,765 works were retrieved from the WoS database (Table S3) and visualized according to the keywords (Table S2) in the studies. Moreover, keywords that appeared at least 800 times were selected for clustering. Among them, 36 general keywords without valuable information were deleted from the selected dataset. The occurrence frequency of keywords in the literature was obtained in the most representative years (Figure S1). Then, 185 refined keywords were imported into the VOS viewer software to obtain 4 data clusters (Table S2).

3. Results and Discussion

3.1. The Demonstration Park of Multi-Source Solid Waste Disposal and Management

The network analysis map for solid waste disposal/management (Figure 2) comprises around 63% occurring keywords [46,47]. The first cluster (green) includes keywords such as management, impact, assessment, waste management, methodology, etc., focusing on the impact assessment of solid waste disposal/management methodology. The second cluster (red) mainly introduces cases involved in the centralized disposal of solid waste, with keywords including concentration, removal, mechanism and sample. The third category (blue) is dedicated to disposal technologies and by-products, containing keywords of anaerobic digestion, biogas, temperature, pyrolysis and others. The fourth cluster (yellow) mainly includes substances produced in the solid waste disposal process, such as heavy metal, fly ash, copper, sludge and others. The nodes of management, impact and concentration are significantly larger, which indicates that the centralized disposal and management of solid waste have been a hot topic in the field of solid waste disposal since then, which is reflected in solid waste management and disposal parks.

The construction of solid waste management demonstration parks is a key measure to solve the “Not in My Back Yard (NIMBY) effect” of solid waste disposal [48]. Constructing a venous industrial park (waste-free cities) with “solid waste park coordinated disposal management” at the core is an effective and fundamental method to solve the problem of solid waste surplus and resource shortage while practicing the concept of sustainable development. It is an innovative way to realize the harmonious coexistence of urban development and the ecological environment [49]. Based on the seventh census data and city size criteria (Figure 3), cities with a permanent population of less than 500,000 are small cities. Cities with a permanent urban population of more than 500,000 and less than 1 million are medium-sized cities, and those with an urban permanent population of more than 1 million and less than 5 million cities are big cities. Meanwhile, cities with a permanent urban population of more than 5 million are megacities. Based on data from the Statistical Yearbook, we determined the production volume of general industrial waste and hazardous waste in Chinese provinces from 2016 to 2022 (Figure 3 and Figure S2). The construction characteristics of demonstration parks of different sizes in small- and medium-sized cities, large- and medium-sized cities and megacities were analyzed in order to promote the experience of solid waste demonstration park construction.

3.2. Solid Waste Management in Typical Industrial Parks of China

3.2.1. Multi-Source Solid Waste Collaborative Disposal Parks in Small–Medium Cities

Small–medium cities refer to cities with a population of less than one million. The number of small–medium cities in China has reached 2160, accounting for 56% of the total number of cities. Small–medium cities gather a huge population, resources, industries, environment and other development factors and have become an important support for China’s economic and social development. Moreover, the improvement of their development quality has had complete and decisive significance for the modernization process of Chinese style. Due to the conflict between the growing demand for economic development and the shortage of land resources, the practice of “collaborative disposal” could optimize the economy of urban solid waste. Taking Zhangjiagang, a new port industrial city in Jiangsu Province, as an example [50,51], the average daily production of household waste was around 1800 tons [52]. In the solid waste collaborative treatment park, multiple solid wastes, such as domestic waste, kitchen waste, municipal sludge, sick and dead animals, local scrapped vehicles, general industrial solid waste and hazardous waste, were waiting to be treated [53]. The construction of a resource recycling chain in the solid waste disposal park mainly aimed to create “internal circulation with waste as the source” and “external circulation with products as the beginning” (Figure 4). Based on the characteristics of land projects and facilities, a water cycle chain (recycled water), gas cycle chain (landfill gas power generation), electric cycle chain (incineration power generation) and heat cycle chain (waste heat cycle) were constructed inside the park to achieve park management.

In this way, household waste is transported to the incineration plant for power generation, while the generated electricity is sent to the charging station of logistics vehicles in the park. The heat generated is reused in the park through underground heating pipes, and the incineration residue is sent to a sanitary landfill for landfilling [54]. The wastewater generated in the processes of kitchen waste disposal, municipal sludge pretreatment and incineration power generation [55] as well as landfill leachate is centrally disposed to produce clean water for water recharge in the park [56]. The unusable residue generated in the disposal processes of the kitchen waste treatment plant, construction waste treatment plant and waste resource treatment enterprises should be sent to a sanitary landfill, while the biogas generated in the landfill process shall be used for power generation [57]. The electricity generated by incineration is sent to the power grid for surrounding residents to use [58]. Kitchen waste could be turned into microbial fertilizer for agriculture and soil condition adjustment [59]. Construction waste could be recycled or repurposed into building materials or other products through effective resource utilization. In general, this solid waste management constitutes the material and energy link between the project facilities in the park.

Due to the small size of Zhangjiagang city and the initial stage of waste classification, the output of solid waste in Zhangjiagang city was relatively small, centralized disposal had no economic benefit, and the environmental pollution of decentralized disposal was relatively large. With the application of the new sharing–saving–cycling mode, the solid waste disposal capacity of this park reached more than 900,000 tons per year, and the comprehensive utilization rate of solid waste was as high as 90%. In general, a collaborative disposal mode could help small–medium cities realize the goal of multi-source full green consumption.

3.2.2. Multi-Source Solid Waste Collaborative Disposal Parks in Large–Medium Cities

For a large–medium city with a permanent population of 500,000 to 5 million, the first thing to be solved in the process of solid waste treatment is the collaborative treatment of environmental pollution generated by cross-border solid waste. Taking the Yangtze River Economic Belt as an example (Figure 5), the basic idea was to promote urban–rural integration to build a cycle model of collaborative solid waste disposal [60]. Urban and rural areas help each other to deal with the surrounding solid waste and can jointly educate urban and rural residents to enhance their environmental awareness.

A comprehensive, integrated industrial park with the dual target of environmental governance and ecological protection was built for the coordinated treatment and disposal of solid waste in the Yangtze River Economic Belt, which includes three main parts (Figure 5): an incineration power generation system, a resource utilization system and a landfill system. The waste incineration power generation system is the energy center of the industrial park, which provides the energy supply for other processes internally [61]. Firstly, waste (especially the combustible portion) is sent to the incineration system for treatment. Secondly, fly ash and construction waste are used together to produce green recycled building materials [62]. Then, the remaining inert solid waste (including some hazardous waste) which cannot be treated by the current technologies is sent to the landfill plant for final disposal.

Solid waste pollution treated in a distributed organic ecological park is mainly used to treat organic waste that is not suitable for long-distance transportation in urban and rural areas [63]. For example, people could transform organic solid waste into ecological products and realize the goal of resource recycling and pollution reduction [64]. In detail, agricultural and forestry waste with a low moisture content could be converted into biochar, bio-oil and syngas through the pyrolysis process, while excrements of livestock with a high moisture content and fruit or vegetable residues could be converted into organic fertilizers and biogas through anaerobic digestion or aerobic composting [65,66]. This biogas could be used as vehicle energy for the environmental logistics chain externally and also provide energy for the pyrolysis system internally. Biochar could be further processed into carbon-based compounds or organic fertilizers to improve the soil environment quality. The remaining unusable part should be returned to the solid waste pollution comprehensive treatment industrial park for safe guaranteed treatment through the environmental logistics chain.

Through the systematic coupling of pollution control and ecological construction in the intensive comprehensive industrial park, it was considered highly possible to achieve the goal of setting up a zero-waste city along the Yangtze River Economic Belt [67]. This approach could contribute to the construction of an ecological civilization in large–medium cities in China.

3.2.3. Solid Waste Disposal and Resource Recycling Industrial Parks in Megacities

Cities with a permanent population of more than five million are defined as megacities. The GBA covers only about one-fifth of the country’s land area, but it supports one-third of its population and generates one-third of its economy. Therefore, a reasonable solid waste disposal mode for the GBA is essential to manage resources, energy and environmental factors in the whole process of multi-source solid waste recycling. In fact, Dongguan city has already set up a number of environmental protection projects for the disposal of municipal solid waste and solved the problems of industrial solid waste disposal by establishing a centralized disposal park. As a result, it handles all the tasks of solid waste disposal in the GBA [68,69]. In this industrial park, the coordinated treatment of kitchen waste and household waste, the sewage treatment system and other projects work together to achieve a circular process within the industrial park [70]. This comprehensive utilization treatment sometimes allows for the recycling and reuse of domestic waste for electricity generation. It could be an effective way in the long term to achieve the goal of resource utilization (Figure 6). Furthermore, hazardous waste is harmlessly treated by oxygen-enriched side blowing to eliminate environmental risks. In detail, the discarded materials enter the plasma reactor, where the organic materials react rapidly under the action of high temperature (>1200 °C), while the inorganic materials melt to form a molten slurry at an even higher temperature (>1450–1600 °C) [71]. Physicochemical treatment is quite important in the process of hazardous waste disposal to reduce or even eliminate the harm of liquid hazardous waste after heat treatment. After that, the material is then sent to the next process for final disposal [72]. The sludge with about 60% water content is dried by natural air to remove part of the adsorbed water on the surface of the sludge; then, it is dried by a rotary kiln with natural gas as the heat source [73]. When the temperature in the furnace is as high as 1200–1300 °C, the heat released by coke combustion melts the charge, where heat provided from the combustion of natural gas overheats the melt. Heavy metal salts in the sludge are decomposed into oxides at the high temperature and then reduced into elemental substances and other heavy metals by contacting with coke [74], which allows to achieve an innovative heavy metal removal technology.

The core process for kitchen waste treatment is “pretreatment + anaerobic digestion”, which achieves a certain degree of clean production. For instance, biogas is produced continuously, and biogas residue can be recycled [75]. The sewage treatment center also applies biological filters for deodorization. In addition, an air curtain is set up at each gate of the workshop to prevent the leakage of toxic gases in the workshop, so as to ensure that all odors in the workshop are led to the deodorization equipment through the air duct after treatment.

After the implementation of the corresponding protective measures, the project site selection could meet the requirements of the site selection standards for the temporary storage and disposal of hazardous waste. The solid waste disposal park in Dongguan is a exemplary model in the GBA which can effectively dispose of solid waste to the greatest extent as well as solve the environmental problems caused by the non-standardized disposal of hazardous industrial waste. By accelerating innovative ways to meet human needs, integrating resource issues into the delivery of multilateral environmental agreements and identifying sustainable ways to use resources, the vision of green, low-carbon and sustainable development of the GBA could be realized with this system.

3.3. Suggestions for Industrial Park Sustainable Development

The demand for solid waste disposal in China has been growing rapidly during the past few years. Subsequently, the construction of solid waste treatment industrial parks has become a new trend, and their existence enables waste to be recycled and reused.

In order to promote efficient solid waste disposal and material recycling, different disposal options for solid wastes have been drawn up according to different city sizes (Figure 7). Small–medium cities should adopt collaborative disposal and intensive circulation for the rational use of land resources [76]. As for large–medium cities, urban–rural integration should be promoted to jointly educate urban and rural residents to enhance their environmental awareness [77]. Megacities should adopt the recycling mode to achieve green and low-carbon sustainable development [78].

Despite the differences based on city size, three common points of solid waste disposal and management should be considered [79]. Firstly, people should adhere to the construction concept of sharing–saving–recycling (Figure 7). The centralized construction mode in the park should be rationally selected and scientifically planned according to the characteristics of the wastes being processed and the technological characteristics of the project, with the aim of complementarily matching the technological and resource advantages [80]. Regardless of the city size, people should fully cooperate to share disposal technologies, as well as human resources and material resources, to improve the degree of waste resource reuse efficiency.

Secondly, government sectors and educational institutions at all levels should strengthen publicity and education on garbage classification and waste recycling (Figure 7) so as to promote public awareness of environmental protection [81]. In detail, relevant departments should take advantage of media resources to carry out science popularization activities on solid waste disposal technology, publicize information on solid waste classification [82] and help the public to understand the environmental protection effect of rational disposal of solid wastes.

Finally, green and low-carbon concepts should be implemented throughout the solid waste disposal process. This is precisely the key work that must be conducted in the field of solid waste disposal under the background of the “dual carbon target” [83]. It is necessary to develop new energy, strengthen water circulation and establish a material circulation system. A low-carbon and environmental protection demonstration park should be built in most cities according to the different urban scales. Further, the waste recycling park should incorporate and continuously innovate technologies related to solid waste treatment and environmental management [84]. In addition, research and development platforms should be provided for pollution control and environmental risk warning in the field of solid waste disposal and management.

3.4. Advancement of China’s Solid Waste Industry Development

Developed countries such as the United States, Germany and Japan have established refined management models for the whole process of solid waste disposal. In the United States, data analysis was conducted on solid waste handling in order to understand the behavior and consumptive pattern of consumers and provide data support for the development of source reduction and recycling strategies. Germany’s recycling of waste focuses on the research and development of waste treatment technology and the recycling of packaging plastics. Japan has made great efforts to develop a circular economy, formulated waste recycling rate indicators and paid attention to recycling and resource regeneration when sorting and disposing of garbage. In general, the utilization of solid waste resources is an important entry point and provides support for sustainable development. Based on foreign experience and China’s national conditions, we put forward suggestions for the development of China’s solid waste industry parks, namely to promote the industrialization process and the integration of an ‘industrial chain, innovation chain, talent chain and capital chain’. Moreover, a scientific and creative resource highland should be created that strengthens the demonstrations and guidance, gathers talent advantages, builds a high-level cooperation platform and comprehensively promotes the high-quality development of the solid waste resource utilization industry.

4. Conclusions and Prospect

Generally, municipal solid wastes include industrial waste, hazardous waste, household waste, etc. The landfill, incineration and biological disposal technologies for different types of solid waste have become quite mature in China, although the combined techniques for multi-solid waste require more practice and improvement. In cities of different sizes, solid wastes could have distinct different disposal and management modes, as well as requiring different industrial demonstration parks. In this study, three typical industrial parks for multi-solid waste disposal and resource utilization were investigated in depth and systematically analyzed through statistical network analyses. After analyzing the characteristics of multi-source solid waste disposal and reuse models of small, medium and large cities in different dimensions, innovation points could be popularized and referenced for resource–environment synergy. Possible suggestions for solid waste disposal as well as industrial park management in China were provided, following three principles: sharing–saving–cycling, publicity and education and green and low-carbon. The above measures could not only promote solid waste disposal efficiency but also give opportunities for material recycling, energy saving and environmental protection, which would undoubtedly be beneficial for the sustainable development of urban resources and the environment.