In Indonesia, plastic constitutes the second largest component of municipal solid waste; however, 58% remains uncollected. Most plastic recycling depends on informal sectors, accounting for only 10% of the total, leaving the remainder to potentially harm the environment. This paper analyzes how cities in Indonesia have tackled their plastic waste problems from the perspective of the integrated sustainable waste management framework. This study focuses on plastic waste management (PWM) in three cities: Bandung, Yogyakarta, and Magelang. Data were collected from 41 semi-structured interviews, a plastic waste composition data analysis, and site visits. The research outcomes include a comprehensive analysis of stakeholder roles, plastic waste flow, plastic waste composition data, and various challenges in PWM. This study identifies three main stakeholders in collecting plastic wastes: the Department of Environment as the main local government body, community-based waste banks, and private waste management companies. Most recyclable plastic waste is recovered through waste banks and private collection services. In 2022, the predominant types of plastic waste in Bandung, Yogyakarta, and Magelang City were soft plastics, thick plastics, and hard plastics, respectively. The challenges for the PWM stem from various aspects in political, legal, and institutional; environmental; financial and technical; and socio-cultural spheres. Positive trends towards an integrated system are observed, although full integration has not yet been achieved. The research recommends a multi-stakeholder cooperative approach involving municipal authorities, waste banks, and private collectors, responsive to local conditions and emphasizing sustainability aspects throughout waste management stages for a sustainable resource recycling in developing countries.

Plastic product consumption and disposal are widespread. Given that these products are derived from crude oil, it is critical to reduce their consumption and effectively recycle plastic waste as recycled resources to achieve a low-carbon society. Japan enacted the “Containers and Packaging Recycling Law” in 2000, encouraging the recycling of plastic packaging and containers. However, material recycling of plastic waste has stalled due to recycling costs and technical challenges. This paper examines and evaluates the transition process and operational status of Japan’s recycling policy for plastic containers and packaging, as well as clarifies the limits of resources recycling. The limits and issues of current identification technology are discussed by analyzing the characteristics of plastic marks and detecting the material compositions of waste samples. The paper also discusses a new sorting technology that uses terahertz waves to improve plastic recycling. This analysis revealed that plastic containers are typically made of two or more plastic materials, which makes resources recycling more difficult. Terahertz waves are safer than other high-accuracy sorting technologies currently in use. Thus, material recycling can be expanded by accurately analyzing the composition of plastic waste and introducing sorting devices appropriate for achieving the circular economy with sustainable resource recycling.

Accurate identification of plastic materials from post-consumer food container and packaging waste is crucial for enhancing the purity and added value of recycled materials, thereby promoting recycling and addressing the issue of plastic pollution. However, the diverse characteristics of post-consumer plastics-such as variations in shape and additives-cause variations in spectral features like transmittance, even within the same material type. In this study, we combined near-infrared (NIR) and terahertz (THz) spectroscopies with machine learning (ML) techniques, specifically XGBoost and Bayesian optimization, to accurately identify transparent polyethylene terephthalate (PET), transparent polystyrene (PS), and black PS. We achieved a precision score exceeding 90%. Furthermore, using explainable AI (XAI) techniques, we evaluated the roles of NIR and THz waves in distinguishing between these plastics. We found that transmittance measured at a frequency of 0.140 THz was effective for identifying transparent PS, while the transmittance at 0.075 THz was crucial for identifying transparent PET. Additionally, NIR spectroscopy proved to be highly effective in distinguishing black PS from transparent plastics. Our findings indicate that the significance of THz frequencies varies depending on the material, highlighting that the identification technology developed in this study not only complements widely used NIR spectroscopy but also offers valuable insights into selecting effective frequencies for high-precision identification systems. Additionally, we discuss potential directions for further research to advance identification systems utilizing THz spectroscopy and ML techniques based on these findings.

In recent years, with the rapid spread of next-generation vehicles (NGVs), China, Japan, and South Korea (CJK) have been leading the development of vehicle batteries. As development strategies and policy trends of NGVs battery are changing in CJK, the competition among battery manufacturers is expected to become more intense in the future. However, there are few international comparative studies on the development policy, production, and sales of NGV batteries in CJK. Based on the review and investigation of the technical development, policy trends, and the world market share of vehicle batteries in CJK, this study spots trends in the features of development strategies and policies of NGV batteries in CJK, and further inspects the interrelationships in these three countries comprehensively. The result shows that CJK have different focuses on the development of NGVs battery technology and policymaking. It is predicted that in the future competition of the vehicle battery market, Japan is likely to be far surpassed by China and South Korea. Based on grasping the development strategies and policy trends of vehicle batteries in CJK, this study plays an important role in the academic research and policymaking of the production, sales, regeneration, and resource recycling of the NGVs and vehicle batteries.

Each year, more than 5 million Waste Mobile Phones (WMP) is generated in Japan. Since WMPs contain many rare metals and precious metals, it is essential to collect and recycle high-value metal resources from them effectively. Although multiple stakeholders have already developed WMP collection routes, these WMP collection routes’ current status is unclear. Furthermore, some WMP collection routes can only collect a small number of WMP, and so, their resource efficiency is low. This research aims to clarify each WMP collection route’s characteristics and evaluate their resource efficiency by conducting interview research on related stakeholders and the WMP dismantle experiment. The result shows that local government, authorized recyclers, and telecom carriers are the major stakeholders in collecting WMPs in Japan. To improve the WMP collection rate in cities with high population densities, using the local government’s collection route and installing an authorized recycler’s collection station is considered to be more effective. In cities with low population densities, the collection stations built by authorized recyclers are sufficient. The collection stations can also improve recycling behavior by offering points. Furthermore, the telecom carriers are encouraged to participate in the WMP collection business, but they should figure out a way to monitor the flow route of secondhand phones they exported and prompt the proper recycling of exported phones.

Each year, a large amount of waste paper (WP) is generated in Japan, and due to the change in lifestyle with the COVID-19 pandemic, the WP collection and recycling system in Japan faces new challenges. Although the government of Japan has installed WP collection systems, the efficiency of these traditional WP collection systems is too low, and this causes inconvenience to the governments, residents, and other stakeholders. On the other hand, some recycling companies in Japan are trying to establish a nontraditional WP collection system by setting their own WP collection stations in cooperative supermarkets. Yet, the efficiency of this new system has not been clarified. This research aims to investigate the current status, operational characteristics, and the role of recycling companies’ WP collection stations in the Japanese WP collection system. By performing trade area analysis and stepwise OLS regression, this research will evaluate WP collection stations’ efficiency. Moreover, this research will also discuss how the new WP collection system improves WP collection efficiency and residents’ convenience. The results show that WP collection stations efficiency is particularly high in large supermarkets with many parking spaces and long business hours, as well as in areas with many families with children. Recycling companies’ WP collection system could create a system, which can satisfy resident, government, and recycling company interests at the same time.