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Chromium (Cr) is a critical metal due to its non-substitutable application in the metallurgy industry and highly uneven distribution of global reserve. However, there is a lack of in-depth analysis of global Cr flow patterns and its trade networks among individual cycles, which leaves the potential barriers and opportunities unexplored for improving chromium resource efficiency. Here, we employ a trade-linked multilevel material flow analysis (MFA) to map the global anthropogenic Cr cycle for year 2019. Social network analysis is also used to identify the key countries involved in the global Cr trade network. The results highlight that the global Cr cycle depends substantially on international trade in different forms, of which stainless steel is the leading application. Although South Africa, Kazakhstan, and Turkey are the major Cr primary resource suppliers, China and India play substantial roles in manufacturing Cr-containing products. Regional disparities exist in the scrap contents of individual country cycles, varying from 7% (uncertainty ranges from 4 to 11%) in China to 88% (uncertainty ranges from 87 to 89%) in India. Additionally, several countries are essential in the global Cr redistribution and in the connectivity of the Cr trade network, which may lead to their strong import dependence and even supply disruption.

Food consumption is necessary for human survival. On a global scale, the greenhouse gas (GHG) emission related to food consumption accounts for 19%–29% of the total GHG emission. China has the largest population in the world, which is experiencing a rapid development. Under the background of urbanization and the adjustment of the diet structure of Chinese residents, it is critical to mitigate the overall GHG emission caused by food consumption. This study aims to employ a singleregion input-output (SRIO) model and a multi-regional input-output (MRIO) model to measure GHG emission generated from food consumption in China and compare the contributions of different industrial sectors, uncovering the differences between urban and rural residents and among different provinces (autonomous regions/municipalities), as well as identifying the driving forces of GHG emission from food consumption at a national level. The results indicate that the total GHG emission generated from food consumption in China tripled from 157 Mt CO2e in 2002 to 452 Mt CO2e in 2017. The fastest growing GHG emission is from the consumption of other processed food and meat products. Although GHG emissions from both urban and rural residents increased, the gap between them is increasing. Agriculture, processing and manufacture of food, manufacture of chemical and transportation, storage and post services sectors are key sectors inducing food consumption related GHG emissions. From a regional perspective, the top five emission provinces (autonomous regions/municipalities) include Shandong, Hubei, Guangdong, Zhejiang, and Jiangsu. Based on such results, policy recommendations are proposed to mitigate the overall GHG emission from food consumption.

Fast urbanization and economic prosperity generate huge amount of municipal solid waste (MSW). It is therefore critical to identify the determinants of greenhouse gas (GHG) emissions from MSW treatment and prepare potential GHG mitigation measures. A combined System Dynamics - Logarithmic Mean Divisia Index model is developed to identify the driving forces of GHG emission generated from MSW treatment and explore the mitigation potentials. Shanghai, a typical megacity in China is selected as a case study. Results showed that economic development, population scale and emission intensity were driving forces to induce GHG emissions from MSW treatment, while generation intensity and treatment structure were the factors to mitigate GHG emissions from MSW during 2000-2017. Scenario analysis further revealed that landfill gas utilization and MSW separation improvement were the most effective measures in reducing GHG emissions from MSW treatment, leading to about 88.07% and 85.48% of reduction compared with the business-as-usual scenario in 2050. Scenarios of improving incineration rate, reducing per capita MSW generation and restricting population growth will reduce GHG emissions by 72.29%, 30.06% and 0.30%, respectively. Utilizing landfill gas, improving MSW separation and promoting green behaviors are suggested to mitigate GHG emissions from MSW treatment.

Municipal solid waste (MSW) management and recycling has become an emerging issue in developing countries. Shanghai, the largest megacity in China, is well-known nationwide due to leading China's MSW separation and recycling. Therefore, this paper introduces the Shanghai mode for MSW management and its current situation to enrich existing MSW management studies. Results show that the total generation volume of MSW and amount of MSW generation per capita were 9.00 million tons and 372.16 kg in 2017, increased approximately eight-fold and four-fold compared with the data in 1978, respectively. The MSW treatment rate reached 100% since 2014, with incineration rate increased to 48.56% in 2017. The cost of MSW management after implementing MSW sorting regulation is increased to 985 CNY/ton, including 390 CNY/ton of MSW sorting cost. Then three key features and innovative MSW management modes, namely, mandatory MSW sorting legislation, Green Account program, and the Combined Network program are introduced. Meanwhile, two main challenges are urgent to be responded, including inadequate collecting vehicles and limited wet waste treatment capacity. Finally, policy recommendations on strengthening MSW recycling process, constructing complete terminal treatment industry, and making systematic policies were provided to respond existing challenges.

In China, rapid development of electric vehicles resulted in large consumption of lead and lead products such as lead acid batteries (LABs). Recycling LABs is one option to mitigate natural resource depletion and corresponding environmental issues. However, few studies have been conducted to measure the operation of LABs recycling industry. Consequently, it is necessary to initiate such a study so that key barriers on promoting this industry can be identified. Under such a circumstance, this study proposes an emergy-based evaluation framework to evaluate one LABs recycling firm in Yunnan so that the emissions’ impact on human health and ecosystem from this firm can be quantified. A set of emergy-based indicators are established to evaluate the sustainability of this recycling firm. The results show that the investigated system had a higher emergy efficiency compared with that primary ore exploitation system. However, the extremely low values of emergy indicators indicate that this recycling system could not achieve sustainable development goals due to its heavy dependence on nonrenewable resources. Based upon such results and local realities, policy suggestions are raised in order to improve the overall sustainability of such a recycling system.

Urban environmental governance is critical for responding climate change. Existing policies have been inefficient for addressing complicated socio-ecological issues. In order to further promote related studies, it is critical to have a comprehensive review so that recent research progresses can be summarized and future research directions can be identified. Under such a circumstance, this paper aims to conduct a bibliometric review on urban environmental governance, with a focus on addressing climate change. Based on 1697 articles published from 1997 to 2017 and searched from Web of Science, a systematic method combining bibliometric analysis and network analysis is applied to uncover the dynamic trends, academic collaboration and research hotspots. Results show that the overall publication quantity had been gradually improved. The key journals include Journal of Cleaner Production, Sustainability and Energy Policy. Authors from USA have the most publications and international co-authorships, followed by China and UK, while the most influential institution is the Chinese Academy of Science. Moreover, research keywords have been identified, including GHG emission, energy, water, health and transport. In terms of research methods, life cycle assessment and ecological footprint are the dominating methods. In order to further improve research in this field, it is crucial to combine different methods so that more innovative perspectives can be presented. Research findings from this study can also provide valuable policy insights to policy-makers so that appropriate urban environmental governance policies can be raised to mitigate the overall greenhouse gas emission.

Titanium has become a strategic metal due both to its current use in coatings industry and increasing applications in aerospace and renewable energy. China is the largest titanium producer and consumer. In order to move toward carbon neutrality ambition, it is critical to uncover China's overall titanium utilization. Under such a circumstance, this study employs a dynamic material flow analysis method to reveal the evolution trend of China's titanium cycle from 2005 to 2020. The main results show that: (1) China's titanium ore is large in volume but low in grade, ore reserves are closely related with the primary origins, while the secondary origins are scattered; (2) The import dependence of high-grade titanium concentrate exceeded 86%, which indicates that the domestic resource endowment cannot meet with the soaring demand; (3) China's cumulative titanium stock had increased by 70 times during the study period, of which the potential dissipative stock increased from 93.37 kilotons (Kt) in 2005 to 1069.75 Kt in 2020; (4) The regenerative path of titanium scraps is remelting before ingot casting and cascade recovery during manufacturing, and the utilization of reclaimed titanium resource increased from 1.31 Kt in 2005 to 89.57 Kt in 2020 due to technological innovation. These findings reflect that China should not only pay attention on domestic titanium resources and substantial environmental burden associated with titanium mining, processing and utilization, but also seeking new high-grade titanium ores, encourage titanium recycling and diversify titanium resource import countries.

Environmental damage cost can measure the impact of pollution caused by human activity on final safeguard subjects from endpoint perspective. Application of environmental damage cost to municipal solid waste (MSW) management is still rare. To fill such a research gap, this study established a MSW environmental damage cost assessment method using Life Cycle Impact Assessment Method based on Endpoint (LIME) model. Four types of environmental damage cost, namely, primary productivity, social assets, biodiversity and human health for waste treatment were investigated in the city of Shanghai. Results show that the environmental damage cost was 113.7, 116.9, 140.0, 144.0 and 170.8 million dollars in Shanghai from 2014 to 2018, respectively. Damage cost of social assets was the dominant component, accounting for about 55%. Landfill mainly caused social assets damage cost, while incineration mainly caused human health damage cost. Scenarios analysis further revealed that after implementing MSW separation, the total environmental damage cost could be reduced by about 1/3. The best MSW treatment method is fermentation, followed by compost, incineration and landfill, with unit environmental damage cost being 0.22, 4.51, 16.04 and 23.47 USD/ton, respectively.

Neodymium is widely used for magnetic materials in electronic devices, electric vehicles and home appliances. China is facing challenges of increased neodymium demand and a lack of neodymium recycling systems. However, few studies focus on neodymium resource utilization in China—a major consumer of this resource. This study traces and forecasts neodymium flows and stocks in China using dynamic material flow analysis from a life cycle perspective. The results show that China's demand for neodymium at the use stage had increased over 20 times during 2000-2017. By contrast, official neodymium production has only doubled, indicating the existence of illegal mining to meet the increasing neodymium demand. Also, the total net neodymium exports have continuously decreased due to reduced export of primary products and intermediate products. In addition, smuggling of primary products remains an issue and needs to be eliminated. Wind turbines and electric vehicles will become major neodymium consumption sectors greatly increasing future demand requirements. To avoid insufficient recycling and illegal neodymium mining, more appropriate neodymium management policies should be released to balance neodymium supply and demand.

Graphite is considered a critical mineral because of its importance to clean energy transition and global supply concentration. This critical role is evident for electric vehicles that depends on lithium-ion batteries using graphite as anode material. China is the world's largest producer and consumer of natural graphite due to its booming economy and rapid penetration of clean energy driven by carbon neutrality ambition. Given this background, this study conducts a dynamic material flow analysis of natural graphite to reveal the evolution trend of graphite flows in China from 2001 to 2018. Main results include: (1) China's graphite resource experienced extensive utilization to meet demands from domestic consumption (55-83%) and exportation (17-45%); (2) Of the 1643 Gg/yr graphite entering China's anthroposphere, 15% accumulates in in-use stock and 34% enters the waste stage, and secondary graphite only accounts for 0.7-5.7% of the total supply; (3) Releases of graphite (1271 Gg/yr) are mainly divided into tailings, dissipative losses in use, and post-consumer losses; (4) The export-production ratio has increased from 16% in 2001 to 40% in 2018; (5) Graphite demand from electric vehicles is estimated to be 18 times the current level by 2030 (2340 Gg). These results imply that China should not only prepare national policies on managing the overall graphite production activities in response to concerns about domestic resource loss and environmental disruption induced from extractive and processing activities, but also prepare policies encouraging appropriate graphite recycling from safety and economic feasibility perspectives.

Shanghai is the first city to implement Municipal Solid Waste (MSW) sorting regulation in China, and it also has policies on economy, demography, MSW collection and treatment. Therefore, it is crucial to understand the impacts of these polices on MSW management for Shanghai. System dynamics model is a prevailing method to simulate impacts of various policies on MSW management from a dynamic and complex perspective. Besides, different from existing studies that consider only a certain process of MSW management, our system dynamic model simulate the entire process of MSW production, sorting, collection and final treatment. Seven scenarios are set to simulate the impacts of these policies. Results show that economic policy has great impact on future MSW management. MSW generation in 2035 will decline by 3.25 Million tonnes if Gross Domestic Production growth rate decrease by 1%. Demographic policy will reduce MSW generation per capita, but increase the total amount of MSW generation. MSW sorting policy will decrease total demand of MSW landfill, but soar the demand of food waste treatment facility. Treatment method policy will not play a big role in decreasing total demand of MSW landfill. Finally, policy implications including prudent economic and demographic policy, strengthening biochemical treatment capacity and comprehensive utilization of residues are proposed. It is anticipated that this system dynamic model and policy implications can contribute to the MSW management of other 45 Chinese cities that are planning to implement sorting regulation soon, or even other global cities.

Due to rapid economic growth and population increase, problems of environmental pollution, climate change, and resource depletion have become increasingly serious in China. Recyclable waste recycling (RWR) is becoming one of the key approaches to simultaneously respond to the above issues, and the Chinese government has begun to regulate and promote source separation and urban waste recycling in recent years. However, several barriers still exist, and it is therefore crucial to review China’s RWR system in order to identify these barriers, and propose appropriate solutions. This paper firstly summarizes the current situation for China’s RWR: 1. recycling in 2016 reached 246 million tons (515 billion RMB), with 0.3% increase from the previous year; 2.regulations have been greatly strengthened in recent years, although regulations on specific RW, source separation, and interrelated technology are still lacking; 3. a pilot recycling program at the city level was initiated in 2006, covering 90 cities, 51,550 recycling sites, 341 collection centers, 63 terminal markets, and 123 recycling & processing bases. The paper then identifies several key problems and challenges, including ineffective governance and market construction, inefficient source separation, and the lack of a recycling information platform. In responding to these barriers, a number of solutions are proposed: an integrated RWR framework using a Public-Private-Partnership (PPP) investment model; combining the RWR system with municipal solid waste (MSW) collection system; and using internet technology to establish a comprehensive information platform. The use of internet technology is suggested as a unique and effective way of solving China’s RWR problems.