Plastic waste circularity is a priority at a global level. Sustainable development goals (SDGs) set the ways to go, and the circular economy principles underlined the ‘green’ strategies to be employed. However, in practice, there is still much to do, especially in developing countries, where open burning and open dumping still represent the common way of plastic waste disposal. This review aims to analyse current plastic waste circular approaches in low-middle income settings. Seven countries were selected based on the economic level and data availability from the authors, and analysed to collect and critically discuss the actions implemented at a city level. Examples of waste minimization and recycling strategies, selective collection systems and public campaigns are reported from Africa, Asia and Latin America. First, a background analysis related to physical and governance aspects of municipal solid waste management systems of the chosen settings was conducted. The assessment was focused on the treatment processes or minimization actions. Then, the applicability of the projects to achieve the SDGs was commented on. The outcomes of the research underline the need to: (1) scale up small-scale and pilot projects, (2) disseminate good practices in more low- to middle-income settings, (3) create synergies among international partners for further replications in cities. Urgent solutions to plastic waste pollution are needed. The review presented practical actions to be implemented now to boost plastic waste circularity in developing cities.

Hydrothermal carbonization (HTC) has developed considerably over the last 15 years and offers a viable alternative for the utilization of municipal and industrial organic waste such as sewage sludge. However, the technology has yet to establish itself as a valorization process for waste biomasses (2024) and is not yet a recognized state of the art. Nevertheless, the HTC technology could gain greater relevance in the future, especially as an alternative valorization pathway for sewage sludge. During HTC, significant amounts of HTC process water (PW) are produced as a byproduct. The process water is inorganically and organically polluted and has to be treated, as it would be a burden on water bodies and thus on the environment if left untreated. In the EU and specifically Germany, industrial wastewater producers like HTC-plant operators are obliged to treat their industrial wastewater before discharging it into the environment. In addition to a large amount of PW and its treatment to the required limits, the organic load and possible persistent and toxic substances pose major challenges for plant operators. Many proven processes from industrial wastewater treatment were transferred for the treatment of PW. Treatment of the PW in a manner that is industrially viable, economically viable, and efficient is crucial for the effective commercialization of HTC technology. In this, the challenges and opportunities of PW composition, management, and treatment, including legal aspects, are mainly discussed. Therefore, the legal framework in the European Union and specifically for Germany will be elaborated. Furthermore, different treatment pathways are also highlighted.

Developing countries face serious environmental, social and economic challenges in managing different types of organic waste. Proper treatment strategies should be adopted by solid waste management systems in order to address these concerns. Among all of the treatment options for organic waste, composting is the most approved method as an effective strategy to divert solid waste from landfills. This experimental research aimed to examine the potential of producing compost from source-separated municipal organic waste in Shiraz, Iran. Market waste (fruits and vegetables) and garden waste (plant residues) were used as the raw input materials. They were subjected to the windrow pile composting method in an open site area. The process was monitored against several physical, chemical and biological parameters. In-situ measurements (temperature and moisture content) were carried out on a daily basis. Sampling and lab analyses were conducted over the period of the biological treatment. The final product was of acceptable moisture and nutrient levels, pH, Electrical Conductivity (EC), and Carbon/Nitrogen ratio. All of the analyzed compost samples had lower concentrations of heavy metals than the Iranian and German standards. Overall, the results obtained revealed that composting is a promising method for municipal organic waste treatment. The findings also imply the effectiveness of the source-separation collection method in the production of high-quality compost.

Organic waste management is challenging in low-middle income countries. Environmental impacts and high management costs affect the sustainable development of cities, an issue that is exacerbated by the lack of social involvement. The research conducted in Iran aims to assess the benefits of organic waste home composting in Shiraz to improve solid waste management (SWM) sustainability. The introduction of a pilot project to assess home composting systems was described, together with an economic, social and environmental analysis. The current SWM system (S0) has been compared with the new strategy proposed (S1), where home composting is considered to be introduced to collect about 10% of the municipal solid waste generated in a 10-year horizon. An economic balance related to the capital costs and operational costs of both systems was introduced, in parallel with a life cycle assessment (LCA) of the SWM system, and a questionnaire survey of the local population. Results showed that S1 leads to around 5% economic savings for the municipality due to the avoidance of organic waste transportation and disposal. Environmental benefits include a lowering of CO ₂ -Eq emissions of about 19,076 tonnes year ⁻¹ . In addition, about 28% of the interviewed ( n = 319) agreed to employ the home composting system at home (CI 5.5%, 95% of confidence level) supporting the theory that about 10% of the organic waste can be segregated and home-composted. The research underlines that home composting can contribute to improve the sustainability of SWM systems in developing countries.

Developing countries face serious environmental, social and economic challenges when it comes to managing different kinds of solid waste. Iran, as one such country, is forced to deal with many difficulties including the absence of a comprehensive policy framework, a lack of technical know-how, insufficient financial resources and lack of proper disposal facilities. This study attempts to suggest ways to overcome those problems by providing applicable waste management solutions to the local conditions. The research was performed in four structured phases: diagnosis of the existing solid waste management system practised, identification of areas of weakness in the waste management frameworks, bridging the gaps to ensure the sustainability of the concepts offered, and finally the provision of affordable solutions. A source-separated collection system for wet and dry fractions was drawn up. Establishment of a mechanical biological treatment facility and the introduction of biological treatment technology were considered as the main treatment options. From the economic point of view, the extended producer responsibility concept was provided as a resource management tool. The involvement of the stakeholders, as well as the public–private partnership model, was identified as the cornerstone in the planning and implementing of the new approaches. A roadmap was consequently designed aimed at gradually introducing a waste management system in a sustainable and environmentally sound manner.

A powerful legal tool in evolving solid waste management (SWM) systems is extended producer responsibility (EPR). It is a mechanism that shifts the responsibility of a product to manufacturers/importers at the ‘end-of-life’ stage. Yet, implementation of the EPR concept has faced difficulties in developing countries. In Iran, as one such country, the principle of EPR system was issued in executive regulation of SWM in 2005, however, so far, it has been limited to a voluntary scheme. The problem merits further investigation. Therefore, this study aims to shed light on the obstacles in the path of developing EPR system for product packaging. The research examines the current SWM systems in four functional classified frameworks: legal, institutional, financial and technical. The strengths, weaknesses, opportunities and threats of the system are elaborated through semi-structured interviews with a senior executive in the Ministry of Interior (MoI). Then, viable methods to increase resource efficiency and sustainable waste treatment are suggested. The change in the financing mechanism in the Budget Law 2020 forces the manufacturers/importers of products containing recyclable components to pay the revenue from one in 1000 products to MoI for developing recycling facilities and incinerators through partnerships with the private sector. This new strategy would promote proper management of product packaging, create more jobs and a market for international cooperation. However, poor source-separation of wet/dry waste, informal sector activities, exclusive focus on the economic aspect of waste management, lack of expertise and public awareness campaigns are the barriers in this regard.