Socio-economic development drives solid waste management performance in cities: A global analysis using machine learning.

Mismanaged municipal solid waste (MSW), the major source of plastics pollution and a key contributor to climate forcing, in Global South cities poses public health and environmental problems. This study analyses the first consistent and quality assured dataset available for cities distributed worldwide, featuring a comprehensive set of solid waste management performance indicators (Wasteaware Cities Benchmark Indicators - WABI). Machine learning (multivariate random forest) and univariate non-linear regression are applied, identifying best-fit converging models for a broad range of explanatory socioeconomic variables. These proxies describe in a variety of ways generic levels of progress, such as Gross Domestic Product - Purchasing Power per capita, Social Progress Index (SPI) and Corruption Perceptions Index. Specifically, the research tests and quantitatively confirms a long-standing, yet unverified, hypothesis: that variability in cities' performance on MSW can be accounted for by socioeconomic development indices. The results provide a baseline for measuring progress as cities report MSW performance for the sustainable development goal SDG11.6.1 indicator: median rates of controlled recovery and disposal are approximately at 45 % for cities in low-income countries, 75 % in lower-middle, and 100 % for both upper-middle and high-income. Casting light on aspects beyond the SDG metric, on the quality of MSW-related services, show that improvements in service quality often lag improvements in service coverage. Overall, the findings suggest that progress in collection coverage, and controlled recovery and disposal has already taken place in low- and middle-income cities. However, if cities aspire to perform better on MSW management than would have been anticipated by the average socioeconomic development in their country, they should identify ways to overcome systemic underlying failures associated with that socioeconomic level. Most alarmingly, 'business as usual' development would substantially increase their waste generation per capita unless new policies are found to promote decoupling.

Plastic waste reprocessing for circular economy: A systematic scoping review of risks to occupational and public health from legacy substances and extrusion.

The global plastics reprocessing sector is likely expand as the circular economy becomes more established and efforts to curb plastic pollution increase. Via a critical systematic scoping review (PRISMA-ScR), we focused on two critical challenges for occupational and public health that will require consideration along with this expansion: (1) Legacy contamination in secondary plastics, addressing the risk of materials and substances being inherited from the previous use and carried (circulated or transferred) through into new products when reprocessed material enters its subsequent use phase (recycled, secondary plastic); and, (2) Extrusion of secondary plastics during the final stage of conventional mechanical reprocessing. Based on selected literature, we semi-quantitatively assessed nine risk scenarios and ranked them according to the comparative magnitude of risk to human health. Our analysis highlights that despite stringent regulation, industrial diligence and enforcement, occasionally small amounts of potentially hazardous substances contained in waste plastics are able to pass through established safeguards and re-enter (cascade into) the next use phase (product cycle) after being recycled. Although many of these 'inherited' chemical substances are present at concentrations unlikely to pose a serious and imminent threat, their existence may indicate a wider or possible increase in pollution dispersion. Our assessment indicates that the highest risk results from exposure to these substances during extrusion by mechanical reprocessors in contexts where only passive ventilation, dilution and dispersion are used as control measures. Our work sets the basis to inform improved future risk management protocols for a non-polluting circular economy for plastics.

Scaling up resource recovery of plastics in the emergent circular economy to prevent plastic pollution: Assessment of risks to health and safety in the Global South.

Over the coming decades, a large additional mass of plastic waste will become available for recycling, as efforts increase to reduce plastic pollution and facilitate a circular economy. New infrastructure will need to be developed, yet the processes and systems chosen should not result in adverse effects on human health and the environment. Here, we present a rapid review and critical semi-quantitative assessment of the potential risks posed by eight approaches to recovering value during the resource recovery phase from post-consumer plastic packaging waste collected and separated with the purported intention of recycling. The focus is on the Global South, where there are more chances that high risk processes could be run below standards of safe operation. Results indicate that under non-idealised operational conditions, mechanical reprocessing is the least impactful on the environment and therefore most appropriate for implementation in developing countries. Processes known as 'chemical recycling' are hard to assess due to lack of real-world process data. Given their lack of maturity and potential for risk to human health and the environment (handling of potentially hazardous substances under pressure and heat), it is unlikely they will make a useful addition to the circular economy in the Global South in the near future. Inevitably, increasing circular economy activity will require expansion towards targeting flexible, multi-material and multilayer products, for which mechanical recycling has well-established limitations. Our comparative risk overview indicates major barriers to changing resource recovery mode from the already dominant mechanical recycling mode towards other nascent or energetic recovery approaches.

Fully integrated modelling for sustainability assessment of resource recovery from waste.

This paper presents an integrated modelling approach for value assessments, focusing on resource recovery from waste. The method tracks and forecasts a range of values across environmental, social, economic and technical domains by attaching these to material-flows, thus building upon and integrating unidimensional models such as material flow analysis (MFA) and lifecycle assessment (LCA). We argue that the usual classification of metrics into these separate domains is useful for interpreting the outputs of multidimensional assessments, but unnecessary for modelling. We thus suggest that multidimensional assessments can be better performed by integrating the calculation methods of unidimensional models rather than their outputs. To achieve this, we propose a new metric typology that forms the foundation of a multidimensional model. This enables dynamic simulations to be performed with material-flows (or values in any domain) driven by changes in value in other domains. We then apply the model in an illustrative case highlighting links between the UK coal-based electricity-production and concrete/cement industries, investigating potential impacts that may follow the increased use of low-carbon fuels (biomass and solid recovered fuels; SRF) in the former. We explore synergies and trade-offs in value across domains and regions, e.g. how changes in carbon emissions in one part of the system may affect mortality elsewhere. This highlights the advantages of recognising complex system dynamics and making high-level inferences of their effects, even when rigorous analysis is not possible. We also indicate how changes in social, environmental and economic 'values' can be understood as being driven by changes in the technical value of resources. Our work thus emphasises the advantages of building fully integrated models to inform conventional sustainability assessments, rather than applying hybrid approaches that integrate outputs from parallel models. The approach we present demonstrates that this is feasible and lays the foundations for such an integrated model.

An analytical framework and tool ('InteRa') for integrating the informal recycling sector in waste and resource management systems in developing countries.

In low- and middle-income developing countries, the informal (collection and) recycling sector (here abbreviated IRS) is an important, but often unrecognised, part of a city's solid waste and resources management system. Recent evidence shows recycling rates of 20-30% achieved by IRS systems, reducing collection and disposal costs. They play a vital role in the value chain by reprocessing waste into secondary raw materials, providing a livelihood to around 0.5% of urban populations. However, persisting factual and perceived problems are associated with IRS (waste-picking): occupational and public health and safety (H&S), child labour, uncontrolled pollution, untaxed activities, crime and political collusion. Increasingly, incorporating IRS as a legitimate stakeholder and functional part of solid waste management (SWM) is attempted, further building recycling rates in an affordable way while also addressing the negatives. Based on a literature review and a practitioner's workshop, here we develop a systematic framework--or typology--for classifying and analysing possible interventions to promote the integration of IRS in a city's SWM system. Three primary interfaces are identified: between the IRS and the SWM system, the materials and value chain, and society as a whole; underlain by a fourth, which is focused on organisation and empowerment. To maximise the potential for success, IRS integration/inclusion/formalisation initiatives should consider all four categories in a balanced way and pay increased attention to their interdependencies, which are central to success, including specific actions, such as the IRS having access to source separated waste. A novel rapid evaluation and visualisation tool is presented--integration radar (diagram) or InterRa--aimed at illustrating the degree to which a planned or existing intervention considers each of the four categories. The tool is further demonstrated by application to 10 cases around the world, including a step-by-step guide.

Resource management performance in Bahrain: a systematic analysis of municipal waste management, secondary material flows and organizational aspects.

This paper presents a detailed review of municipal solid waste (MSW) and resource management in Bahrain, using the recently developed UN-Habitat city profile methodology. Performance indicators involve quantitative assessment of waste collection and sweeping, controlled disposal, materials recovery and financial sustainability together with qualitative assessment of user and provider inclusivity and institutional coherence. MSW management performance in Bahrain is compared with data for 20 other cities. The system in Bahrain is at an intermediate stage of development. A waste/material flow diagram allows visualization of the MSW system and quantifies all inputs and outputs, with the vast majority of MSW deposited in a controlled, but not engineered landfill. International comparative analysis shows that recycling and material recovery rates in Bahrain (8% wt. for domestic waste, of which 3% wt. due to informal sector) are generally lower than other cities, whereas waste quantities and generation rates at 1.1 kg capita(-1) day(-1)) are relatively high. The organic fraction (60% wt.) is comparable to that in middle- and low-income cities (50-80% wt.), although on the basis of gross domestic product Bahrain is classified as a high-income city, for which the average is generally less than 30% wt. Inclusivity in waste governance is at a medium stage as not all waste system stakeholders are considered in decision-making. While the system now appears to be financially stable, key pending issues are cost-effectiveness, improving the standards of disposal and deployment of extensive materials recovery/recycling services.

Comparative analysis of solid waste management in 20 cities.

This paper uses the 'lens' of integrated and sustainable waste management (ISWM) to analyse the new data set compiled on 20 cities in six continents for the UN-Habitat flagship publication Solid Waste Management in the World's Cities. The comparative analysis looks first at waste generation rates and waste composition data. A process flow diagram is prepared for each city, as a powerful tool for representing the solid waste system as a whole in a comprehensive but concise way. Benchmark indicators are presented and compared for the three key physical components/drivers: public health and collection; environment and disposal; and resource recovery--and for three governance strategies required to deliver a well-functioning ISWM system: inclusivity; financial sustainability; and sound institutions and pro-active policies. Key insights include the variety and diversity of successful models - there is no 'one size fits all'; the necessity of good, reliable data; the importance of focusing on governance as well as technology; and the need to build on the existing strengths of the city. An example of the latter is the critical role of the informal sector in the cities in many developing countries: it not only delivers recycling rates that are comparable with modern Western systems, but also saves the city authorities millions of dollars in avoided waste collection and disposal costs. This provides the opportunity for win-win solutions, so long as the related wider challenges can be addressed.

19th century London dust-yards: a case study in closed-loop resource efficiency.

The material recovery methods used by dust-yards in early 19th century London, England and the conditions that led to their development, success and decline are reported. The overall system developed in response to the market value of constituents of municipal waste, and particularly the high coal ash content of household 'dust'. The emergence of lucrative markets for 'soil' and 'breeze' products encouraged dust-contractors to recover effectively 100% of the residual wastes remaining after readily saleable items and materials had been removed by the thriving informal sector. Contracting dust collection to the private sector allowed parishes to keep the streets relatively clean, without the need to develop institutional capacity, and for a period this also generated useful income. The dust-yard system is, therefore, an early example of organised, municipal-wide solid waste management, and also of public-private sector participation. The dust-yard system had been working successfully for more than 50 years before the Public Health Acts of 1848 and 1875, and was thus important in facilitating a relatively smooth transition to an institutionalised, municipally-run solid waste management system in England. The dust-yards can be seen as early precursors of modern materials recycling facilities (MRFs) and mechanical-biological treatment (MBT) plants; however, it must be emphasised that dust-yards operated without any of the environmental and occupational health considerations that are indispensable today. In addition, there are analogies between dust-yards and informal sector recycling systems currently operating in many developing countries.