Advancing plastic pollution hotspotting at the subnational level: Brazil as a case study in the Global South

Identifying sources is crucial for proposing effective actions to combat marine litter pollution. Here, we used an innovative approach to identify hotspots of mismanaged plastic waste (MPW) within Brazil and subsequent leakage to the ocean, based on population density, socio-economic conditions, municipal solid waste management and environmental parameters. We estimated plastic waste generation and MPW for each of the 5570 Brazilian municipalities, which totaled 3.44 million metric tons per year. Then, we estimated the probability of litter mobilization and transport (P) and the relative risk of leakage to the ocean (MPW × P). The Guanabara Bay and La Plata River comprised the main oceanic entry hotspots of litter produced in Brazil. The use of national databases allowed us to increase spatial and temporal granularity, offering a detailed baseline for the application of prevention and mitigation actions. However, overcoming data limitations is still a challenge in Brazil as in other Global South countries.

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.

Mismanagement of Plastic Waste through Open Burning with Emphasis on the Global South: A Systematic Review of Risks to Occupational and Public Health

Large quantities of mismanaged plastic waste threaten the health and wellbeing of billions worldwide, particularly in low- and middle-income countries where waste management capacity is being outstripped by increasing levels of consumption and plastic waste generation. One of the main self-management strategies adopted by 2 billion people who have no waste collection service, is to burn their discarded plastic in open, uncontrolled fires. While this strategy provides many benefits, including mass and volume reduction, it is a form of plastic pollution that results in the release of chemical substances and particles that may pose serious risks to public health and the environment. We followed adapted PRISMA guidelines to select and review 20 publications that provide evidence on potential harm to human health from open burning plastic waste, arranging evidence into eight groups of substance emissions: brominated flame retardants; phthalates; potentially toxic elements; dioxins and related compounds; bisphenol A; particulate matter; and polycyclic aromatic hydrocarbons. We semiquantitatively assessed 18 hazard-pathway-receptor combination scenarios to provide an indication of the relative harm of these emissions so that they could be ranked, compared and considered in future research agenda. This assessment overwhelmingly indicated a high risk of harm to waste pickers, a large group of 11 million informal entrepreneurs who work closely with waste, delivering a circular economy but often without protective equipment or a structured, safe system of work. Though the risk to human health from open burning emissions is high, this remains a substantially under-researched topic.

Characterisation and composition identification of waste-derived fuels obtained from municipal solid waste using thermogravimetry: A review

Thermogravimetric analysis (TGA) is the most widespread thermal analytical technique applied to waste materials. By way of critical review, we establish a theoretical framework for the use of TGA under non-isothermal conditions for compositional analysis of waste-derived fuels from municipal solid waste (MSW) (solid recovered fuel (SRF), or refuse-derived fuel (RDF)). Thermal behaviour of SRF/RDF is described as a complex mixture of several components at multiple levels (including an assembly of prevalent waste items, materials, and chemical compounds); and, operating conditions applied to TGA experiments of SRF/RDF are summarised. SRF/RDF mainly contains cellulose, hemicellulose, lignin, polyethylene, polypropylene, and polyethylene terephthalate. Polyvinyl chloride is also used in simulated samples, for its high chlorine content. We discuss the main limitations for TGA-based compositional analysis of SRF/RDF, due to inherently heterogeneous composition of MSW at multiple levels, overlapping degradation areas, and potential interaction effects among waste components and cross-contamination. Optimal generic TGA settings are highlighted (inert atmosphere and low heating rate (⩽10°C), sufficient temperature range for material degradation (⩾750°C), and representative amount of test portion). There is high potential to develop TGA-based composition identification and wider quality assurance and control methods using advanced thermo-analytical techniques (e.g. TGA with evolved gas analysis), coupled with statistical data analytics.

Evaluating scenarios toward zero plastic pollution

Plastic pollution is a pervasive and growing problem. To estimate the effectiveness of interventions to reduce plastic pollution, we modeled stocks and flows of municipal solid waste and four sources of microplastics through the global plastic system for five scenarios between 2016 and 2040. Implementing all feasible interventions reduced plastic pollution by 40% from 2016 rates and 78% relative to “business as usual” in 2040. Even with immediate and concerted action, 710 million metric tons of plastic waste cumulatively entered aquatic and terrestrial ecosystems. To avoid a massive build-up of plastic in the environment, coordinated global action is urgently needed to reduce plastic consumption; increase rates of reuse, waste collection, and recycling; expand safe disposal systems; and accelerate innovation in the plastic value chain.

Establishing a sub-sampling plan for waste-derived solid recovered fuels (SRF): Effects of shredding on representative sample preparation based on theory of sampling (ToS)

The uncertainty arising from laboratory sampling (sub-sampling) can compromise the accuracy of analytical results in highly inherent heterogeneous materials, such as solid waste. Here, we aim at advancing our fundamental understanding on the possibility for relatively unbiased, yet affordable and practicable sub-sampling, benefiting from state of the art equipment, theoretical calculations by the theory of sampling (ToS) and implementation of best sub-sampling practices. Solid recovered fuel (SRF) was selected as a case of a solid waste sample with intermediate heterogeneity and chlorine (Cl) as an analyte with intermediate variability amongst waste properties. ToS nomographs were constructed for different sample preparation scenarios presenting the trend of uncertainty during sub-sampling. Nomographs showed that primary shredding (final d₉₀ ≤ 0.4 cm) can reduce the uncertainty 11 times compared to an unshredded final sub-sample (d ≈ 3 cm), whereas cryogenic shredding in the final sub-sample can decrease the uncertainty more than three times compared to primary shredding (final d₉₀ ≤ 0.015 cm). Practices that can introduce bias during sub-sampling, such as mass loss, moisture loss and insufficient Cl recovery were negligible. Experimental results indicated a substantial possibility to obtain a representative final sub-sample (uncertainty ≤ 15%) with the established sub-sampling plan (57-93%, with 95% confidence), although this possibility can be considerably improved by drawing two final sub-samples instead (91-98%, with 95% confidence). The applicability of ToS formula in waste-derived materials has to be investigated: theoretical ToS calculations assume a poorer performance of the sub-sampling plan than evidenced by the experimental results.

Statistical quantification of sub-sampling representativeness and uncertainty for waste-derived solid recovered fuel (SRF): Comparison with theory of sampling (ToS)

The level of uncertainty during quantification of hazardous elements/properties of waste-derived products is affected by sub-sampling. Understanding sources of variability in sub-sampling can lead to more accurate risk quantification and effective compliance statistics. Here, we investigate a sub-sampling scheme for the characterisation of solid recovered fuel (SRF) - an example of an inherently heterogeneous mixture containing hazardous properties. We used statistically designed experiments (DoE) (nested balanced ANOVA) to quantify uncertainty arising from material properties, sub-sampling plan and analysis. This was compared with the theoretically estimated uncertainty via theory of sampling (ToS). The sub-sampling scheme derives representative analytical results for relatively uniformly dispersed properties (moisture, ash, and calorific content: RSD ≤ 6.1 %). Much higher uncertainty was recorded for the less uniformly dispersed chlorine (Cl) (RSD: 18.2 %), but not considerably affecting SRF classification. The ToS formula overestimates the uncertainty from sub-sampling stages without shredding, possibly due to considering uncertainty being proportional to the cube of particle size (FE ∝ d³), which may not always apply e.g. for flat waste fragments. The relative contribution of sub-sampling stages to the overall uncertainty differs by property, contrary to what ToS stipulates. Therefore, the ToS approach needs adaptation for quantitative application in sub-sampling of waste-derived materials.

Post-consumer plastic packaging waste in England: Assessing the yield of multiple collection-recycling schemes

The European Commission (EC) recently introduced a 'Circular Economy Package', setting ambitious recycling targets and identifying waste plastics as a priority sector where major improvements are necessary. Here, the authors explain how different collection modalities affect the quantity and quality of recycling, using recent empirical data on household (HH) post-consumer plastic packaging waste (PCPP) collected for recycling in the devolved administration of England over the quarterly period July-September 2014. Three main collection schemes, as currently implemented in England, were taken into account: (i) kerbside collection (KS), (ii) household waste recycling centres (HWRCs) (also known as 'civic amenity sites'), and (iii) bring sites/banks (BSs). The results indicated that: (a) the contribution of KS collection scheme in recovering packaging plastics is higher than HWRCs and BBs, with respective percentages by weight (wt%) 90%, 9% and 1%; (b) alternate weekly collection (AWC) of plastic recyclables in wheeled bins, when collected commingled, demonstrated higher yield in KS collection; (c) only a small percentage (16%) of the total amount of post-consumer plastics collected in the examined period (141 kt) was finally sent to reprocessors (22 kt); (c) nearly a third of Local Authorities (LAs) reported insufficient or poor data; and (d) the most abundant fractions of plastics that finally reached the reprocessors were mixed plastic bottles and mixed plastics.

An overview of chemical additives present in plastics: Migration, release, fate and environmental impact during their use, disposal and recycling

Over the last 60 years plastics production has increased manifold, owing to their inexpensive, multipurpose, durable and lightweight nature. These characteristics have raised the demand for plastic materials that will continue to grow over the coming years. However, with increased plastic materials production, comes increased plastic material wastage creating a number of challenges, as well as opportunities to the waste management industry. The present overview highlights the waste management and pollution challenges, emphasising on the various chemical substances (known as "additives") contained in all plastic products for enhancing polymer properties and prolonging their life. Despite how useful these additives are in the functionality of polymer products, their potential to contaminate soil, air, water and food is widely documented in literature and described herein. These additives can potentially migrate and undesirably lead to human exposure via e.g. food contact materials, such as packaging. They can, also, be released from plastics during the various recycling and recovery processes and from the products produced from recyclates. Thus, sound recycling has to be performed in such a way as to ensure that emission of substances of high concern and contamination of recycled products is avoided, ensuring environmental and human health protection, at all times.

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.

'Wasteaware' benchmark indicators for integrated sustainable waste management in cities

This paper addresses a major problem in international solid waste management, which is twofold: a lack of data, and a lack of consistent data to allow comparison between cities. The paper presents an indicator set for integrated sustainable waste management (ISWM) in cities both North and South, to allow benchmarking of a city's performance, comparing cities and monitoring developments over time. It builds on pioneering work for UN-Habitat's solid waste management in the World's cities. The comprehensive analytical framework of a city's solid waste management system is divided into two overlapping 'triangles' - one comprising the three physical components, i.e. collection, recycling, and disposal, and the other comprising three governance aspects, i.e. inclusivity; financial sustainability; and sound institutions and proactive policies. The indicator set includes essential quantitative indicators as well as qualitative composite indicators. This updated and revised 'Wasteaware' set of ISWM benchmark indicators is the cumulative result of testing various prototypes in more than 50 cities around the world. This experience confirms the utility of indicators in allowing comprehensive performance measurement and comparison of both 'hard' physical components and 'soft' governance aspects; and in prioritising 'next steps' in developing a city's solid waste management system, by identifying both local strengths that can be built on and weak points to be addressed. The Wasteaware ISWM indicators are applicable to a broad range of cities with very different levels of income and solid waste management practices. Their wide application as a standard methodology will help to fill the historical data gap.

Up-cycling waste glass to minimal water adsorption/absorption lightweight aggregate by rapid low temperature sintering: optimization by dual process-mixture response surface methodology

Mixed color waste glass extracted from municipal solid waste is either not recycled, in which case it is an environmental and financial liability, or it is used in relatively low value applications such as normal weight aggregate. Here, we report on converting it into a novel glass-ceramic lightweight aggregate (LWA), potentially suitable for high added value applications in structural concrete (upcycling). The artificial LWA particles were formed by rapidly sintering (<10 min) waste glass powder with clay mixes using sodium silicate as binder and borate salt as flux. Composition and processing were optimized using response surface methodology (RSM) modeling, and specifically (i) a combined process-mixture dual RSM, and (ii) multiobjective optimization functions. The optimization considered raw materials and energy costs. Mineralogical and physical transformations occur during sintering and a cellular vesicular glass-ceramic composite microstructure is formed, with strong correlations existing between bloating/shrinkage during sintering, density and water adsorption/absorption. The diametrical expansion could be effectively modeled via the RSM and controlled to meet a wide range of specifications; here we optimized for LWA structural concrete. The optimally designed LWA is sintered in comparatively low temperatures (825-835 °C), thus potentially saving costs and lowering emissions; it had exceptionally low water adsorption/absorption (6.1-7.2% w/wd; optimization target: 1.5-7.5% w/wd); while remaining substantially lightweight (density: 1.24-1.28 g.cm(-3); target: 0.9-1.3 g.cm(-3)). This is a considerable advancement for designing effective environmentally friendly lightweight concrete constructions, and boosting resource efficiency of waste glass flows.

Waste management and recycling in the former Soviet Union: the City of Bishkek, Kyrgyz Republic (Kyrgyzstan)

The UN-Habitat Integrated Sustainable Waste Management (ISWM) benchmarking methodology was applied to profile the physical and governance features of municipal solid waste (MSW) management in the former Soviet Union city of Bishkek, capital of the Kyrgyz Republic. Most of the ISWM indicators were in the expected range for a low-income city when compared with 20 reference cities. Approximately 240,000 t yr(-1) of MSW is generated in Bishkek (equivalent to 200 kg capita(-1) yr(-1)); collection coverage is over 80% and 90% of waste disposed goes to semi-controlled sites operating with minimal environmental standards. The waste composition was a distinctive feature, with relatively high paper content (20-27% wt.) and intermediate organic content (30-40% wt.). The study provides the first quantitative estimates of informal sector recycling, which is currently unrecognised by the city authorities. Approximately 18% wt. of generated MSW is recycled, representing an estimated annual saving to the city authorities of US$0.7-1.1 million in avoided collection/disposal costs. The waste management system is controlled by a centralised municipal waste enterprise (Tazalyk); therefore, institutional coherence is high relative to lower-middle and low-income cities. However, performance on other governance factors, such as inclusivity and financial sustainability, is variable. Future priorities in Bishkek include extending collection to unserved communities; improving landfill standards; increasing recycling rates through informal sector cooperation; improving data availability; and engaging all stakeholders in waste management strategy decisions. Extending the scope and flexibility of the ISWM protocol is recommended to better represent the variation in conditions that occur in waste management systems in practice.

Solid recovered fuel: materials flow analysis and fuel property development during the mechanical processing of biodried waste

Material flows and their contributions to fuel properties are balanced for the mechanical section of a mechanical-biological treatment (MBT) plant producing solid recovered fuel (SRF) for the UK market. Insights for this and similar plants were secured through a program of sampling, manual sorting, statistics, analytical property determination, and material flow analysis (MFA) with error propagation and data reconciliation. Approximately three-quarters of the net calorific value (Q(net,p,ar)) present in the combustible fraction of the biodried flow is incorporated into the SRF (73.2 ± 8.6%), with the important contributors being plastic film (30.7 MJ kg(ar)(-1)), other packaging plastic (26.1 MJ kg(ar)(-1)), and paper/card (13.0 MJ kg(ar)(-1)). Nearly 80% w/w of the chlorine load in the biodried flow is incorporated into SRF (78.9 ± 26.2%), determined by the operation of the trommel and air classifier. Through the use of a novel mass balancing procedure, SRF quality is understood, thus improving on the understanding of quality assurance in SRF. Quantification of flows, transfer coefficients, and fuel properties allows recommendations to be made for process optimization and the production of a reliable and therefore marketable SRF product.

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.

The biogenic content of process streams from mechanical-biological treatment plants producing solid recovered fuel. Do the manual sorting and selective dissolution determination methods correlate?

The carbon emissions trading market has created a need for standard methods for the determination of biogenic content (chi(B)) in solid recovered fuels (SRF). We compare the manual sorting (MSM) and selective dissolution methods (SDM), as amended by recent research, for a range of process streams from a mechanical-biological treatment (MBT) plant. The two methods provide statistically different biogenic content values, as expressed on a dry mass basis, uncorrected for ash content. However, they correlate well (r(2)>0.9) and the relative difference between them was <5% for chi(B) between 21% (w)/w(d) and 72% (w)/w(d) (uncorrected for ash content). This range includes the average SRF biogenic content of ca. 68% (w)/w(d). Methodological improvements are discussed in light of recent studies. The repeatability of the SDM is characterised by relative standard deviations on triplicates of <2.5% for the studied population.

Biodrying for mechanical-biological treatment of wastes: a review of process science and engineering

Biodrying is a variation of aerobic decomposition, used within mechanical-biological treatment (MBT) plants to dry and partially stabilise residual municipal waste. Biodrying MBT plants can produce a high quality solid recovered fuel (SRF), high in biomass content. Here, process objectives, operating principles, reactor designs, parameters for process monitoring and control, and their effect on biodried output quality are critically examined. Within the biodrying reactors, waste is dried by air convection, the necessary heat provided by exothermic decomposition of the readily decomposable waste fraction. Biodrying is distinct from composting in attempting to dry and preserve most of biomass content of the waste matrix, rather than fully stabilise it. Commercial process cycles are completed within 7-15 days, with mostly H(2)O((g)) and CO(2) loses of ca. 25-30% w/w, leading to moisture contents of <20% w/w. High airflow rate and dehumidifying of re-circulated process air provides for effective drying. We anticipate this review will be of value to MBT process operators, regulators and end-users of SRF.

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.