Remodeling of Abandoned Land: A Review of Landscape Regeneration and the Reconstruction of Urban Landfill Sites

Abstract

The relationship between people and land is becoming increasingly strained, and the optimal allocation of land resources and the redevelopment of stock has become the main path for urban construction and development. In this context, how to stimulate the potential value of urban landfills through landscape regeneration has attracted much attention. Based on the CNKI (China National Knowledge Infrastructure) database and the Web of Science core collection database, the bibliometric method was used to analyze a total of 1436 Chinese and English studies on urban landfill landscape regeneration using the scientometric literature analysis software CiteSpace 6.2.R3. From this, metrological and visual mapping analyses were undertaken, and literature co-citations were taken to reveal current trends in the research for urban landfill landscape regeneration. The results show that most of the existing studies focus on landfill pollution control (779 articles) and landscape regeneration design (517 articles). Further analysis of the trends shown in publications and research disciplines shows that the future development direction of landfill landscape regeneration will be led by the ecological restoration of the site and the organic combination of site pollution control and landscape planning and design to achieve sustainable landscape reshaping of landfills. This informs recommendations for the regeneration of landfill landscapes.

1. Introduction

Urban landfills are plots of land where industrial waste and domestic waste generated during the urbanization process in various countries accumulate in large quantities, causing the land to lose its original use [1]. Its harm is mainly to occupy land resources and pose a threat to the natural ecological environment and the living environment of residents [2]. After the industrial revolution, rapid global urbanization led to the emergence of a large number of urban landfills. By the end of 2022, the urbanization rate in developed countries in North America and Northern Europe will be as high as 80%, resulting in a huge accumulation of urban waste and the growing phenomenon of “rubbish encircling cities” [3]. In 2022, the United Nations designated the period from 2021 to 2030 as the Decade of Ecosystem Restoration, advocating that governments, companies, and individuals should take concrete action to heal nature and reduce carbon emissions and that urban landfills, as abandoned land that causes significant pollution to the natural ecosystem, should be included in the initiative and strengthened [4].

In contrast to the urbanization process in the Americas and Nordic countries, developing countries are in a period of rapid urbanization, exacerbating the problems in landfills and causing a major ecological hazard in the subsequent development and renewal of cities. China, currently the world’s largest developing country, has reached an urbanization rate of 64.72% [5]. According to China Statistical Yearbook 2021, by the end of 2020, there will be 1287 municipal waste disposal sites in China, 104 more than in 2019, which is an increase of 8.8%. In order to effectively reduce the burden of waste management, the “14th Five-Year Plan” for the development of urban domestic waste classification and treatment facilities in 2021 proposed that by the end of 2025, the domestic waste classification and treatment capacity of 46 key cities, such as municipalities directly under the Central Government, provincial capitals, and municipalities with separate plans, should be further improved, and prefecture-level cities should be basically built according to local conditions [6].

In the face of the current dilemma, developed countries in Europe, America, and Asia need to take concrete actions in terms of urban landfill landscape regeneration and site ecological restoration [7,8,9,10]. China should provide a feasible way to regenerate urban landfill landscapes and serve as a model for the regeneration of similar sites. Therefore, the study analyzes the annual publication trends of China and other countries, including other research, to predict future development trends in this field and create regeneration strategies in line with the national conditions.

2. Research Methodology and Data Collection

2.1. Research Methodology

Bibliometrics is a discipline that uses mathematical and statistical methods to quantitatively analyze the structure, patterns of change, and quantitative relationships in literature and thus explore the direction of scientific and technological development [11]. As the main research method in the context of its discipline, bibliometrics has become an important way for scholars to analyze the literature and obtain information on research hotspots and developments in the field at present. This study uses the scientometric literature analysis software CiteSpace 6.2.R3 to conduct a visual mapping analysis of the literature data related to the field of urban landfill landscape regeneration and renovation, with the data sources of the English literature taken from the Web of Science core collection database and the Chinese literature from the research topic in the CNKI database.

2.2. Data Collection

On 31 December 2022, “landfill renovation” and “landfill landscape regeneration” were used as search terms in the CNKI database. The results of the two searches were combined, and a total of 284 valid Chinese sample documents were obtained by selecting journal papers and dissertations and excluding duplicate documents, which were exported in plain text format. In the Web of Science core collection database, “Landfill” and “Construction” and “Landfill” and “Regeneration” were used. “The year of publication was not limited, the time slice interval was 1 year, and the type of literature was limited to “Article” and “Review”. A total of 1152 articles were obtained from each country and exported in plain text format. The valid samples of Chinese literature and English literature of each country were removed from duplicates using the “Remove Duplicates” function and visualized for knowledge mapping.

3. Research Results and Analysis

3.1. Article Volume Analysis

3.1.1. Overview of Literature Publications

Urban landfill landscape regeneration research has been dominated by developed countries that have experienced more rapid urbanization, such as North America and Europe [12]. Landfill landscape transformation practices began in Europe in the 1860s, when the Bit Saumont Park in Paris, France, was transformed from a landfill into a natural landscape garden, providing an important reference [13]. Theoretical research began slightly later, in North America in the 1950s, when American scholars, led by environmental engineering, conducted research on the environmental impacts of landfill gas and leachate on the site, leading to proposed improvements to the landfill process [14]. In the 1970s, botany and ecology began to be considered, with research focusing on the planting of suitable plants on the site [15]. In the 1980s, along with the establishment of the International Society for Restoration Ecology, restoration ecology was introduced into the study of landfill landscape regeneration, focusing on the combination of site ecological restoration with landscape regeneration design and urban economic and cultural development [16]. The research direction in this field tends to be diversified, and the volume of publications is gradually growing.

As shown in Figure 1, relevant studies have appeared internationally since 1991, and the annual number of publications has generally shown an upward trend, which can be divided into three stages.

The first phase is the initial development period (1991–2001). During this period, the annual number of articles published was less than 10, with landfill pollution control and landscape regeneration design approaches as the main research content. The research results of this period mainly came from various developed countries in North America and Europe (such as the United States, the United Kingdom, France, and Canada). In 1991, Hargreaves, an American designer, completed the renovation of Bixby Park, which applied earth art to the site design, and from then onwards the application of aesthetic elements in landfill landscape regeneration and renovation gradually gained more attention. In 1997, American scholar Charles Waldheim [17] put forward “landscape urbanism” and advocated exploring the development and reuse of landfill from the perspective of landscape infrastructure regeneration. In 1998, American scholar Neil Heywood [18] emphasized the use of landscape architecture in landfill landscape regeneration design from the perspective of multidisciplinary collaboration. In England, Germany, and France, in addition to the simple environmental pollution treatment, phytoremediation and the landscape reconstruction of landfills were studied, but the overall volume of literature in this field was relatively low, with only three articles accounting for 6% of the total literature at this stage. In addition to the developed countries in Europe and the United States, Japan, Korea, Singapore, and Israel are the mainstays of Asian countries’ ongoing practical exploration of landfill landscape regeneration. For example, the landscape regeneration of Lanji Island “Sky Park” in South Korea, Kansai Airport in Japan, Simakau Island Nature Reserve in Singapore, and Hiriya Park in Israel have all provided feasible ways to regenerate landfill landscapes in the future.

The second phase is the period of steady growth (2002–2012). In 2004, Russia ratified the Kyoto Protocol and the European Union’s “polluter pays” law came into force, which led to global attention to the environmental and ecological problems caused by landfills. In 2008, Mohsen Mostafavi integrated ecology into landscape urbanism and developed it into “ecological urbanism” [19]. This advocates an interdisciplinary approach to consider landfill landscape regeneration design from ecological, humanistic, and economic perspectives, which provides new theoretical methods for the exploration of landfill landscape regeneration design, and the number of publications has increased slightly since then. The main research efforts of this period were still based on European, North American, and some Nordic countries, such as Denmark [20], and some developed Asian countries, such as Japan and Korea [21,22]. However, a number of developing countries have gradually entered a phase of vigorous development and have also contributed to research in this field, such as China and Thailand [23,24].

The third phase is a period of fluctuating growth (2013–2022). In addition to the developed countries in Europe and the US, which have been the dominant research force, other developed countries in Asia and Oceania, such as Korea, Israel, and Japan [25,26,27], have also launched in-depth studies in this field, providing a variety of research approaches. In addition to research on site pollution control, landscape regeneration design, and post-renovation benefit assessments, research on social aspects such as site selection and the participation of multiple actors in site renovation and post-renovation operations has also been further developed at this stage [28,29,30]. The amount of literature on the theme of the participation of multiple subjects reached 88, which is four times that for the previous theme and accounts for 6% of the literature at this stage; the number of literature on the theme of site selection reached 45, which is twice as many as the previous theme and accounts for 5% of the literature at this stage.

3.1.2. Overview of Chinese Literature

In China, research on landfill transformation began at the end of the 20th century, and the first park transformed by a landfill in China, Fuzhou Aofeng Park, was opened to the public in 1997, with Tianziling Landfill in Hangzhou entering the stage of closure and transformation in 1998. Along with the gradual implementation of a series of site landscape regeneration projects, Chinese scholars have gradually improved their research on the concept of landfills, the significance of site development and reuse, and the restoration of site vegetation [31]. Based on this, some scholars started to research the vegetation restoration and pollution treatment process in landfills; for example, Huang Linan [32] analyzed the factors affecting plant growth in landfills and summarized the ecological problems brought about by site pollution.

According to Figure 2, Chinese research can be divided into two phases based on the number of publications from 1991 to the end of 2022.

The first stage is the initial development period (2000–2012), with an overall increasing trend of annual publications. The total number of publications is 44 in 12 years, with the average annual number of publications being 3–4. The research content mainly explores pollutant treatment technology and site vegetation restoration strategies in landfills from the perspective of environmental engineering disciplines. On the basis of previous studies on landfill restoration, scholars have further investigated the environmental factors affecting the restoration of site vegetation by using field research as the main research tool; for example, Lin Xuerui [33] and Ji Chongche [34] conducted field investigations on Zhongshan City landfill and Shenyang City landfill, respectively, and the results showed that the environmental factors affecting the restoration of site vegetation were mainly landfill gas, waste leachate, and nutrients in the site soil. Li Sheng [35] proposed a “phased planting” model of site revegetation based on further analysis of the factors influencing landfill recovery.

The second stage is a period of fluctuating growth (2012–2022), in which the research introduces landscape architecture and attempts to break down the disciplinary barriers between landscape architecture and environmental engineering to conduct interdisciplinary research [36]. In addition to site contamination management, the research topic also involves the development of policies and regulations in this field [37,38,39,40] and the development of suggestions for site landscape regeneration designs [41,42,43,44]. In 2011, the State Council approved the Opinions on Further Strengthening the Work of Urban Domestic Waste Disposal, which proposed that the whole process of urban waste disposal control and management needs to be effectively strengthened. The use of legal, administrative, economic, and technical means to continuously improve the level of urban domestic waste treatment provides policy support. By the end of 2022, the total number of papers on landfill policy analysis had reached 31, with the research content mainly drawing on the governance experience of the United States, and the policies and regulations of the United Kingdom, Canada, Germany, and other countries were also covered. At the level of landscape regeneration design, domestic research mainly summarizes and analyzes excellent foreign cases and draws on foreign design concepts. In 2014, Yu Kongjian and other designers introduced and translated Ecological Urbanism to provide a new theoretical approach to landfill landscape regeneration design.

After 2016, influenced by the policies related to waste classification and management and the series of academic conferences on waste-land regeneration design, the topics of landfill research in China have been enriched, resulting in large fluctuations and changes in the number of articles published on landfill landscape regeneration design research. The “Implementation Plan of Domestic Waste Classification System” introduced in 2017 proposed that, by the end of 2020, there needed to be an establishment of laws, regulations, and standard systems related to waste classification, so the themes of landfill-related research during this period are mainly site pollution control measures and related policy and regulation improvement, with a decrease in attention to site landscape regeneration design. There was close cooperation between the Second Brownfield Regeneration and Ecological Restoration Conference, the Second International Conference on Brownfield Regeneration and Ecological Restoration, and the Second China Sustainable Environmental Restoration Conference, with the research theme focusing on promoting effective collaboration between urban environmental restoration and landscape construction. The 14th Five-Year Plan for the Development of Urban Domestic Waste Separation and Disposal Facilities (2021) was proposed, which promoted research into landfill landscape renovation, with the number of articles issued in this field reaching a record high this year.

3.2. Time Zone Analysis of Literature Keywords

In the Keyword Time Zone Knowledge Map, the larger the node, the more frequently the keyword appears, and the higher the research intensity. In order to screen out the low-frequency words with less relevance, the threshold value was set to 10 in CiteSpace (i.e., the minimum frequency of keywords was 10 occurrences), and a time zone knowledge graph of landfill renovation keywords at home and abroad was generated (Figure 3 and Figure 4). The top 10 keywords in each graph were selected, and their occurrence frequency, centrality, and year of first occurrence were summarized and presented (

Table 1. List of keyword relevance in international literature.

Serial Number	Frequency	Betweenness Centrality	Year of First Occurrence	Keyword
1	45	0.08	1995	Adsorption
2	33	0.01	2008	Recycling
3	32	0.01	2007	Land use
4	28	0.01	2006	Heavy metal
5	26	0.05	2008	Landfill
6	25	0.02	2000	Landfill leachate
7	24	0.01	2004	Activated carbon
8	24	0.02	2007	Sustainability
19	22	0.03	2008	Circular economy
10	20	0.02	2002	Waste management

and

Table 2. List of keyword relevance in Chinese literature.

Serial Number	Frequency	Betweenness Centrality	Year of First Occurrence	Keyword
1	99	1.27	1998	Landfill site
2	32	0.24	2009	Eco-restoration
3	19	0.12	2008	Ecological restoration
4	19	0.10	2007	Landfill leachate
5	17	0.17	2006	Landscape architecture
6	11	0.03	2009	Landscape design
7	11	0.21	2012	Domestic waste landfill
8	10	0.07	2000	Leachate
9	10	0.03	2007	Antiosmosis
10	10	0.06	2004	Landfill site

).

Comprehensive chart analysis shows that the initial development period (1991–2001) of international landfill landscape regeneration and transformation research was mainly focused on the analysis of pollutant management and pollution treatment process optimization in landfills, and the research direction was relatively singular. The keywords were “Adsorption”, “Regeneration”, “Landfill”, “Urban ecology”, “Silica”, “Urban ecology” and “Siloxane”. In the period of steady growth (2002–2012), in addition to the traditional research on landfill pollutant management, the research diversified, with the appearance of keywords such as “recycling”, “land use”, and “climate change”. This indicates that the research in this field is influenced by the deterioration of global environmental problems and the increase in social awareness of environmental protection. Further analysis of the literature shows that the research during this period also involved the design of landfill landscape regeneration [45,46,47], government management [48,49,50,51,52], and policy support [53,54,55] in the process of landfill landscape regeneration.

In the fluctuating phase of research (2013 to present), the research entry point has been refined. In addition to the analysis of pollutant management in landfills and the analysis of site landscape regeneration design, it also focuses on the analysis of comprehensive benefit assessment and public behavior management in the middle and later stages of landfill landscape regeneration and transformation, with the keyword “Environmental” appearing. The research also focuses on the evaluation of the benefits and public behavior management in the middle and later stages of landfill landscape regeneration, with the keywords “Environmental”, “Space use”, “Sustainability,” and “Waste management”.

In the initial development period of landfill landscape regeneration and renovation research in China (2000–2012), the research focused on landfill pollution treatment and process optimization and landfill landscape regeneration design concepts and approaches, shown in the keywords “leachate”, “reverse osmosis”, “landscape reclamation”, “landscape gardening”, and “urban park”. In the period of fluctuating growth (2012–present), the research content has been enriched and the perspective has been innovated in order to optimize the technology, improve the standard of waste pollution treatment, and combine artistry and ecology in landscape regeneration design. This includes keywords such as “membrane biochemical reactor”, “rainwater sewage diversion”, “standard improvement”, “landscape park”, “upgrading”, “ecological design”, and “land art”.

3.3. Research Institute Analysis

The size of the nodes in the Collaborative Network Mapping of Research Institutions indicates the number of articles published by the institution, the connectivity between the nodes indicates the co-occurrence between the institutions, and the network density indicates the closeness of the individual nodes. From Figure 5, there are 251 nodes and 111 connecting lines in the field of international landfill landscape regeneration and renovation, with a network density of 0.0035, indicating that the cooperation network of relevant research institutions in this research field is not evident and is relatively fragmented, and the cooperation among relevant research institutions is weak, with each research independently or limited to cooperation within a limited area. The top three research institutions in terms of the number of publications are Chinese Acad Sci—Chinese Academy of Sciences, US Geol Survey—United States Geological Survey, and Chinese Res Inst Environm Sci—Chinese Research Academy of Environmental Sciences, among which US Geol Survey mainly published in the 1990s, while Chinese Acad Sci and Chinese Res Inst Environm Sci published in the 1990s. This shows that the United States has been guiding the direction of research in this field and providing guidance for other developed and developing countries. The number of articles published in Chinese Acad Sci and Chinese Res Inst Environm Sci increased only in the early 21st century, indicating that compared to developed countries in Europe and the US, research in this field started late in China and is now in a period of development with more abundant results.

As shown in Figure 6, there are a total of 137 existing nodes and 83 connecting lines of relevant research institutions in the field of landfill landscape regeneration and transformation research in China, with a network density of 0.0089, also meaning that the cooperation network of relevant research institutions in this field is relatively scattered, and most of them are not active and seldom cooperate with other research institutions. The trend of publications and the analysis of keywords in the literature show that landfill landscape regeneration involves multiple levels, such as waste pollution control, landscape regeneration design, and the participation of multiple subjects. It is necessary to further strengthen cross-border collaboration and communication at all levels, and the current loose cooperation among institutions will affect the depth and breadth of research as well as the breakthrough of key technologies and problems in this field.

3.4. Literature Co-Citation Analysis

Due to the early start of research on landfill landscape regeneration and transformation, relevant design theories and landscape design methods have been improved in their theoretical and practical exploration. As shown in Figure 7, the paper “Enhancing the use of waste activated sludge as bio-fuel through selectively reducing its heavy metal content”, published by Schweigkofler in HAZARD MATER—Journal of Hazardous Materials in 2001, has been widely used, and the second-most cited article was “Enhancing the use of waste activated sludge as bio-fuel through selectively reducing its heavy metal content” by Dewil in ENERG CONVERS MANAGE—Energy Conversion and Management, 2006. The literature is published in a relatively diverse range of journals, with a focus on biology, scientific resources, energy, and landscape design, reflecting the diversity of disciplines involved in the field of urban landfill landscape regeneration research.

In recent years, research into pollutant management and treatments has been expanding, with the research content no longer limited to site waste pollution management and basic landfill transformation but focusing on the benefits of landfill landscape regeneration and transformation on the social and ecological environment. For example, Geyer R [56,57] focused on the development of a circular economy and advocated shifting the current waste management model to a more beneficial recycling and reuse model for ecology and resource utilization. This is echoed by some designers in Italy, the Netherlands, and Belgium, such as Marin and B. De Meulder, who have both proposed the idea of connecting urban landscape design with urban waste recycling [58,59]. Scarlat N [60,61] also took the use of biogas energy in landfills as the starting point, focusing on the reuse of various waste materials and reducing the burden of waste treatment and management in landfills. However, Wang HS [62] and Gandy M [63] proposed a landscape regeneration pathway that combines site landscape design and site ecological restoration, which is generally accepted by researchers [64,65,66,67,68,69]. By the end of 2022, the number of publications on this topic was 315, indicating that attention to this topic is increasing and will likely become a potential direction for future research.

4. Review of Chinese and International Research Themes

From the above analysis, it can be seen that the breadth and depth of landfill landscape regeneration research in both China and internationally are expanding, and the research themes focus on landfill pollution control and landfill landscape regeneration design. Landfill site assessment methods and site landscape regeneration policies and regulations are new areas and directions of research in recent years, and relevant research needs to be further developed.

4.1. Landfill Pollution Management Research

Landfill ecological restoration is the basis of landscape regeneration and needs to be based on the premise of site pollution control. According to the analysis of the annual number of publications, 779 papers were published in this field in China and internationally, accounting for 54% of the total. On this basis, combined with the analysis of the literature cited together, it is clear that landfill site pollution treatment-related research has been the cornerstone of regeneration and renovation research. Combined with the keyword analysis, it can be seen that the landfill management project is mainly divided into the shaping and treatment of the waste pile and the collection and discharge of pollutants. In the treatment of waste piles, various European and American countries (USA, Germany, UK, Canada, etc.) and various developed countries in Asia (Japan, Korea) focus on the reuse of waste materials and industrial development, such as waste composting, incineration, power generation, and the use of recycled materials [70,71,72]. The treatment of pollutants mainly involves the collection and conductive drainage of waste leachate and methane gas. At present, the mainstream way of treating landfill waste leachate internationally is a combination process, with the more novel waste leachate treatment technologies being short-range nitrification anaerobic ammonia oxidation, short-range denitrification anaerobic ammonia oxidation, and electro-oxidation, and the more widely used and mature process in China is the combination process route of “anaerobic + biochemical + membrane depth treatment” [73,74,75].

From the co-occurrence map of Chinese and international research institutions, it can be seen that universities and design institutes are important in the field of landscape regeneration and the reconstruction of landfill sites at home and abroad, and the participation of relevant government departments and other social environmental protection organizations is not high. Moreover, the cooperation network among research institutions is loose, lacking close cooperation across disciplines, which affects the breakthrough of key issues in landscape regeneration and the reconstruction of landfill sites.

4.2. Landfill Landscape Regeneration Design Study

In addition to the necessary site waste pollution control, landfill landscape regeneration transformation should focus on the combination of site ecological restoration and site landscape artistry, aiming to achieve an integration of ecology, artistry, and culture after site transformation. According to the annual analysis of Chinese and international publications, there are 517 papers on landfill landscape regeneration design, accounting for 36% of the total number of publications. Combining the annual publication trends in China and internationally and comparing another research topic, which is site pollution control, we can see that although the research on landfill landscape regeneration design started late, it has gradually occupied a dominant position in recent years and will become one of the hot spots in future research on landfill landscape regeneration and transformation.

Analyzed from the perspective of literature keywords (see Figure 3 and Figure 4), it can be seen that the research on urban landfill landscape regeneration design is mainly focused on two major fields: site landscape regeneration design concept and the landscape transformation path [76,77].

(1) Based on the analysis of the development history of landfill landscape regeneration design and related research disciplines (

Table 3. Landfill landscape regeneration main research disciplines (Top 5).

	Serial Number	Major Disciplines	Number of Published Articles	Proportion of Published Documents
China	1	Environmental science and resource utilization	189	66%
	2	Architectural science and engineering	57	20%
	3	Macroeconomic management and sustainable development	7	2.4%
	4	Forestry	6	2.1%
	5	Artistic aesthetics	4	1.4%
International	1	Major disciplines	452	39%
	2	Environmental Sciences Ecology	289	25%
	3	Engineering	123	10%
	4	Agriculture	106	9.0%
	5	Biodiversity Conservation	97	8.1%

), it can be seen that this field involves a wide range of theoretical systems, including ecology, modern aesthetics, ecological ethics, landscape ecology, landscape urbanism, and other multidisciplinary design ideas, as well as environmental science and resource utilization, economics, forestry, agronomy, art, and other disciplines, among which ecology has the most profound influence on its development. The “ecological urbanism” proposed by Mohsen Mostafavi emphasizes the continuation of the spiritual culture of the place, and this theory has guided many practical transformation projects, such as the preservation of the gabions containing recycled waste and soil in La Viejo Park, which was transformed into the landscape wall of the site, and the preservation of the discarded industrial glass in Glass Beach Park, which also became the landscape wall of the site. This theory has guided many practical transformation projects, such as the preservation of the gabions containing recycled waste and soil in La Vergne Park and their transformation into a landscape wall; the preservation of discarded industrial glass in Glass Beach Park, which has become a major feature of the site; and the transformation of the original garbage pile into an industrial and artistic site using discarded garbage as material in Sharon Park, all of which reflect the continuation of the culture of the place [78,79]. The practical exploration of a series of site landscape regeneration and transformation is combined in Candlestick State Park, Clear Spring Park in New York, Graves Nature Park in Barcelona, and Chambers Gully Park in Australia. It is known that the currently developed countries in Europe, North America, Oceania, and Asia, using urban landfill landscape regeneration design transformation as the main model for urban park construction, with ecological restoration theory as its main design theory, focus on site ecological design, the comprehensive use of landscape restoration, ecological restoration, and other means to build the landfill into an environmentally friendly park.

(2) An analysis of the types of research institutions in this field and the composition of the disciplines involved in each research institution shows that an interdisciplinary and collaborative approach should aim to achieve the landscape regeneration of landfills. Tarakci-Eren [80] combined the management of contaminated water in landfills with the design of site vegetation, focusing on the ecological restoration of landfills in a way that reduces human intervention. Macek Tomas [81] used transgenic plants with environmental benefits as an entry point to discuss the potential role of next-generation transgenic plants in preventing and reducing chemical pollution and converting contaminated sites into safe agricultural or recreational lands. Wischut M [82] focuses on the shaping of the spirit of place in landfill landscape regeneration based on the perspective of the site’s historical context. Fouad [68] et al. proposed a mitigation strategy that combines the water quality management of polluted sites with the design of landscape regeneration foundations based on the environmental ecology and development of the surrounding areas brought about by the degradation of waterways and landfill pollution in the Nile Delta. Zheng Xiaodi [83] integrates environmental health and landscape architecture, systematically exploring the spatial design strategies and landscape transformation approaches of the site of the Hiriya landfill in Israel, providing a theoretical basis and practical reference for interdisciplinary cooperation in landscape regeneration design. Some other scholars emphasize the importance of artistic expression and the continuation of the spirit of place, such as Li Yan [84], who discusses the educational significance of these factors; Feng Xingbao [85], based on the perspective of urban landscape art design, explains the importance of the coordinated development of the site and its urban environment; Zhu Yufan [86] proposes to combine environmental engineering technology, site ecological restoration, and artistic aesthetic effects, and advocated the unified planning and layout of environmental engineering facilities and landscape facilities in the form of geodetic art. However, some scholars have reservations about this, such as Ni Zhen [87], who points out that the ecological restoration and natural development process of landfill sites is uncertain, and that the scientific nature of the unified planning of regeneration sites in the form of art is insufficient.

The above analysis shows that landfill landscape regeneration design is a comprehensive site construction that includes ecological restoration, basic landscape reconstruction, the expression of the spirit of place, and the integration of site history and culture. It is necessary to pay attention to the combination of site ecology and functional art in the design process, so the cross-collaboration among various disciplines should be strengthened, and the expression of the spirit of place and the continuation of regional history should be highlighted while realizing ecological restoration to reflect the local nature of the site.

4.3. Landfill Site Assessment Methodology

Landfill site assessment is the evaluation of all the risks faced by the redevelopment of a site, and, based on the results of the evaluation, a suitable redevelopment plan is developed to achieve the regeneration of the abandoned landscape [77]. An analysis of the annual number of publications and trends between China and the international community shows that there are only 95 publications on landfill site assessment methods, which is less than 8% of the total number of international publications. The discussion of the asset assessment of known or suspected contaminated sites was initiated in 1984 in North American countries such as the USA and Canada [88], but the research in this area was only re-emphasized in 2013 and development has been slow.

Further keyword analysis shows that the main themes of the international literature in this area are site risk assessment (68 articles), value assessment (17 articles), and sustainable development assessment (8 articles), and the main research methods are multivariate and quantitative, with evaluation indicators including human health, natural environment, liability risk, economic benefits, resource allocation, social decision making, and cultural heritage [89]. The research in this field in China mainly focuses on the assessment of land reuse benefits, environmental risk assessment, and site redevelopment value assessment [76,90,91,92]. Based on the research results and the recommendations of Chinese scholars, it can be seen that although the construction of an evaluation index system for the regenerated landscape of landfills and other waste sites has been explored, a universal, complete, and authoritative index system has not yet been formed in China.

4.4. Landfill Landscape Regeneration and Renovation Policy

The important role of landfill landscape regeneration policies and standards is mainly reflected in two aspects: firstly, it defines the power and responsibility relationship in landfill management, so that traceable polluting enterprises can bear certain management costs for site restoration; secondly, it helps to unify site pollution management and post-testing standards, effectively avoiding the covering up of residual pollutants in the site through visual beautification. An analysis of the annual volume and trends of publications in China and internationally shows that since the 1970s, developed countries in North America and Europe have started theoretical research and practical exploration on landfill remediation and redevelopment, but the number of publications related to policy and regulatory research is only 45, less than 4% of the total number of publications.

Based on the analysis of the development process of landfill and other abandoned land regeneration policies and regulations, as well as keywords in the literature, it is clear that all countries focus on the role of public agenda in the decision-making process and encourage public participation in the process of policy and regulation development. For example, after the “New York Love River pollution incident” in 1978, the public’s willingness to legislate on environmental protection and contaminated site management increased, which promoted the legislative process of waste-land management in the United States [93]. Since then, a series of landfill transformation practices, such as Clearspring Park, La Viejo Landfill in Spain, and Bysby Park, have further strengthened global environmental awareness and public recognition of the regeneration value of contaminated sites, prompting countries to accelerate the legislative process [94]. At present, China has not yet issued laws and regulations specifically for the regeneration of waste sites, and its treatment and reuse are mainly combined with or referenced to relevant laws related to environmental protection, lacking the systematization and completeness of targeted laws [95]. Scholars’ research on landfill and other abandoned land regeneration policies and regulations focuses on learning from successful international experiences; for example, Jianjian Zhang [96] compared and analyzed European and American abandoned land regeneration policies from the levels of the legislative system, law enforcement departments, and restoration standards to provide a theoretical basis for the improvement of policies related to abandoned land regeneration design in China; Sidong Luo [97] further pointed out that based on the analysis of American abandoned land governance policies, the regeneration design of each urban landfill should be based on the current situation of urban social, economic, and cultural development and rely on policy support, market mechanism mediation, and the joint participation of multiple subjects in operation to solve the problems of economic and cultural development in the late stage of site transformation.

Analyzing from the perspective of research institutions, it can be seen that the current research takes design institutes and universities as the main body of landfill landscape regeneration and transformation and lacks the participation of the public and relevant government departments.

5. Landfill Landscape Regeneration Development Trend and Suggestions

In view of the current global crisis of waste, in order to further promote urban renewal and upgrading in developed countries and to provide developing countries with a direction and forward-looking recommendations for urban landfill landscape regeneration in line with their national conditions, the current situation of urban landfill landscape regeneration research in China, the largest developing country, and international countries is analyzed, and the development trend of global landfill landscape regeneration is predicted and recommendations are made accordingly.

According to the analysis of the annual publication volume, publication trends, and keywords of landfill landscape regeneration research in China and internationally, the two main independent research themes are landfill waste pollution control and site landscape regeneration design, and only a few studies focus on site transformation assessment and related policy development. According to the analysis of research institutions and main research disciplines, it can be seen that the cooperation of research institutions in each country is relatively sparse and institutions operate mostly as single bodies.

By further analyzing the main research contents of landfill landscape regeneration and transformation, we can see that the current landfill landscape regeneration and transformation is led by ecological restoration, and the main way is to combine site pollution control and site landscape regeneration design. In order to promote the sustainable development of landfill landscape regeneration and realize the value coupling and practical integration of landscape design strategy and ecological restoration, it is proposed that future transformation should be based on landscape design strategy, taking the regeneration and transformation process as a clue and ecological restoration as a means, strengthening the cross-cooperation among various disciplines and institutions, paying attention to the site assessment research after landscape regeneration and transformation, and encouraging the active participation of various social entities. Later treatment and operation can aim to achieve the sustainability of the later operation of the site and the unity of ecological benefits, landscape aesthetic benefits, economic benefits, and social benefits. This can be achieved by the following:

(1) Strengthen the collaboration of various research institutions with each other and conduct comprehensive research on site spatial data and social and humanistic data. On the one hand, this adheres to the priority of ecology and strengthens the expansion and integration of landscape gardening and ecology. The American scholar Mohsen Mostafavi [98] and the Chinese scholar Yu Kongjian [99] both proposed that the basic guidelines are site-specific, sustainable, and require little human intervention. Therefore, in order to maintain the original natural landscape community of the landfill site and reduce the damage to the original ecosystem during the landscape regeneration and transformation of the site, it is necessary to do a good job in the preliminary ecological survey of the landfill site. Norway scholars Erikstad, Lars and Hagen, Dagmar [100], American planner and landscape architect Frederick Law Olmsted [101], and Chinese scholars Zheng Xiaodi [102] and Zhu Yufan [103] all suggest that landfill landscape regeneration should be based on the perspective of urban history, actively explore the core cultural elements of the place, and focus on the excavation and collation of the spirit of the place. On the other hand, Neil Heywood suggests that the integration of landscape architecture, design, and sociology should be strengthened. Pre-spatial data research of landfill sites should adhere to the joint in-depth research of various local environmental regulatory departments and various research institutions, combine geography, apply geographic information system (GIS) technology to survey the current situation of landfill waste sites, and use artificial intelligence, virtual reality, IOT BIM, and other computer digital technologies, with the help of Civil3D 2019, Sketchup 2020, and other software to achieve the quantitative collection, simulation, and analysis of urban landfill landscape design information. A comprehensive database of basic site information will be constructed, and information on the location of the waste site, environmental data such as soil and water quality, and information on actions taken to address the contaminated site will be made available to the public, enabling information sharing between research institutions and academics, assisting designers to comprehensively grasp the site information, developing site-specific landscape regeneration design strategies, and providing data support for post-evaluation.

(2) Strengthen the cross-fertilization of landscape architecture with ecology, environmental engineering, art, aesthetics, folk culture, and other disciplines in order to realize the unity of ecology and art in the transformation of sites on the basis of enhancing the ecological sustainability of landfills combined with landscape design strategies. Using ecological restoration means that waste piles can be treated to promote site pollution control, such as the Trashmore Peak design in the United States, Germany’s Duisburg Landscape Park, Malaysia’s Bukit Tagsr landfill, and Hong Kong, China’s West Cao Wan landfill and Hangzhou Tianziling Landfill. Based on the preliminary ecological research of the site, the landscape garden design method was applied to build a rich plant community in order to ensure the natural succession of the site’s landscape community. For example, the site vegetation restoration can be based on the renovation of Bangkok Urban Forest Park. This focused on the rate of vegetation succession and irrigation and the use of landscape gardening design methods to build a variety of plant communities. Site stormwater runoff can be based on Sharon and Ravichon Park, whose rivers are used to store rainwater for plant irrigation and to alleviate flooding. In the process of regenerating the site, the emphasis is on design, urban planning, and folk culture, respecting the social and economic basis of the site and actively using the core elements of regional culture. The space is structurally organized, highlighting the site’s history, culture, and social customs. The artistic approach used by American landscape designer Hargreaves in the renovation of Byblos Park showcases how regional culture can be incorporated into a landscape and then combined with the creative approach of earth art. The topography of the site can also be shaped by the texture of the farmland and woods by changing the colors of the site structures, highlighting the local character and unique cultural elements.

(3) Actively construct a systematic and scientific landfill landscape regeneration evaluation index system to provide a scientific basis for the design results and the evaluation of the project after completion. On the one hand, this can be combined with sociology to construct a systematic scientific landfill landscape regeneration evaluation index system, such as that of the Indonesian scholars Amelia R and Basyuni M [104] in the context of Indonesia’s climate change mitigation strategy, the assessment of plant growth and carbon storage potential in the restoration of mangroves in abandoned ponds in North Sumatra, and its data set and results as a national urban. The data set and results serve as an important reference for landscape design. However, the site regeneration design transformation can be combined with geography and the application of geo-information mapping to more accurately portray changes in the spatial and temporal dynamic patterns of the ecological landscape before and after the site transformation. To clarify the components and influencing factors of landfill landscape regeneration evaluation, based on a unified conceptual framework and the principles of comprehensiveness and operability, various research institutions coordinate and cooperate to further improve it, adjust the focus of each index of the landscape evaluation system, establish a systematic landscape evaluation index system, and comprehensively evaluate the reuse potential and availability of each landfill site. We will continue to strengthen the scientific, systematic, practical, and standardized nature of the study of abandoned urban landfill sites and further establish a systematic and scientific landscape regeneration evaluation index system to provide guidance for design assessment and subsequent management.

(4) In order to ensure the development of the renovated site is sustainable, in-depth cooperation with various groups such as the community, universities, enterprises, and the government should be strengthened. This encourages multi-scale public involvement in the early planning, planning, implementation, and operation stages, and extends the public’s multi-scale participation to the entire project construction process, protecting the public’s right to know, deepening public awareness of contaminated land management, and facilitating the expression of the public’s wishes to enhance the satisfaction of residents after the site transformation. Secondly, in order to actively attract investment from multiple parties, we can draw on the successful experience of Qingquan Park to encourage enterprises and the public to become involved in the management and later operation of the site and actively promote cooperation with relevant corporate investors. In addition, by applying the circular economy principles in urban landscape design proposed by Italian scholar Amenta, L [105] and Marin and De Meulder, B [106], we can regenerate and transform the landfill landscape, recycling the original materials of the site and reducing the economic cost of site reconstruction while retaining the original characteristics of the site. Finally, at the policy-making level, the National Environmental Policy Act, the Clean Air Act, and the Resource Conservation and Recovery Act promulgated by the US federal and state governments can be used to control the pollutants in landfills at the source, as well as the “polluter pays” principle in the Superfund Act to strictly control the pollution of local landfills. The Superfund Act defines the relationship between power and responsibility in landfill management. At the level of land use and soil pollution control, the Soil Protection Act of the Netherlands and the Federal Soil Protection Act of Germany, as well as China’s 2016 Soil Pollution Prevention and Control Action Plan, the Soil Environment Management Measures for Contaminated Land (for trial implementation), and the 2019 Soil Pollution Prevention and Control Law can be used to establish a framework of soil quality assessment standards and can therefore improve the contaminated soil management system.

6. Conclusions

In 2022, the European Union (a political and economic union established by several European countries) stated at the 27th United Nations Climate Change Conference (COP27) that it plans to increase its emission reduction targets under the Paris Climate Agreement and reduce the emissions of polluting gases from waste sites. In 2020, China also announced its vision of achieving carbon peaking and carbon neutrality based on its inherent need to promote sustainable development, and as a result, global interest in the regeneration of landfills and other abandoned landscapes has been increasing. In the future, research should further strengthen cooperation between research institutions in different countries and actively explore design ideas and technical means suitable for national conditions and local culture, including helping to promote waste separation and solve the dilemma.

In this paper, the perspective of urban landfill landscape regeneration is mainly focused on the level of “landfill landscape regeneration design”, with the main analysis content being the landscape regeneration design of the site and a brief analysis of the policy formulation, economic and social development strategies, and engineering and construction-related issues involved in the design process. However, in the actual construction of urban landfill landscape regeneration, social, political, and economic aspects are involved, so the recommendations made in this study based on the landscape regeneration design perspective need to be further demonstrated and adjusted in practice by countries and regions, taking into account their national conditions, economy, culture and the development of pollution control-related technologies.