A comparison of municipal solid waste management in Berlin and Singapore

Solid waste management in the context of the waste hierarchy and circular economy frameworks: An international critical review

Growing populations and consumption drive the challenges of solid waste management (SWM); globalization of transport, food production, and trade, including waste trading, distributes risks worldwide. Using waste hierarchy (WH; reduce, reuse, and recycle) and circular economy (CE) concepts, we updated a conceptual waste framework used by international organizations to evaluate SWM practices. We identified the key steps and the important factors, as well as stakeholders, which are essential features for effective SWM. Within this updated conceptual framework, we qualitatively evaluated global SWM strategies and practices, identifying opportunities, barriers, and best practices. We find that, although a few exceptional countries exhibit zero-waste compliance, most fare poorly, as exhibited by the high waste generation, incineration, and disposal (open dumping, landfilling) volumes. In the Global North, SWM strategies and practices rely heavily on technologies, economic tools, regulatory frameworks, education, and social engagement to raise stakeholder awareness and enhance inclusion and participation; in the Global South, however, many governments take sole legal responsibility for SWM, seeking to eliminate waste as a public "nuisance." Separation and recycling in the Global South are implemented mainly by "informal" economies in which subsistence needs drive recyclable material retrieval. Imported, regionally inappropriate tools, economic constraints, weak policies and governance, waste trading, noninclusive stakeholder participation, data limitations, and limited public awareness continue to pose major waste and environmental management challenges across nations. In the context of the framework, we conclude that best practices from around the world can be used to guide decision-making, globally. Despite variations in drivers and needs across regions, nations in both the Global North and South need to improve WH and CE compliance, and enhance stakeholder partnership, awareness, and participation throughout the SWM process. Partnerships between the Global North and South could better manage traded wastes, reduce adverse impacts, and enhance global environmental sustainability and equity, supporting UN Sustainable Development Goals. Integr Environ Assess Manag 2024;20:9-35. © 2023 The Authors. Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Distribution characteristics and potential risks of bacterial aerosol in waste transfer station

The waste transfer station (WTS) is an important link in the transfer of municipal solid waste (MSW) between the community and disposal terminals. While WTSs facilitate waste collection in communities, odorous gases and bioaerosols can escape from them, thereby negatively affecting their surroundings. In this study, the concentration, particle size distribution, pathogen population, and health risks of bioaerosols were analyzed at different locations in a transfer station. The results showed that the highest viable bacterial aerosol concentration was 10,353 ± 3701 CFU/m³, which was at 5 m from the disposal site. Fifty-three bacterial species, including pathogens, were detected. Of these, 39 were human pathogenic bacteria directly originating from the WTS. Furthermore, health risk assessments indicated unacceptable levels of non-carcinogenic risk for operational workers caused by bacterial aerosols of the WTS work area. In addition, bacterial aerosols may pose a severe health risk to children within a 15 m area of the WTS. The results of this study provide a scientific basis to control and reduce the risk associated with bioaerosol exposure in solid WTSs.

Immobilization of lead (Pb) using ladle furnace slag and carbon dioxide

Global sustainable development faces challenges in greenhouse gas emissions, consumption of energy and non-renewable resources, environmental pollution, and waste landfilling. Current technologies for immobilization of heavy metals face similar challenges; for example, the use of cement, magnesia, lime, and other binders for immobilization of heavy metals is associated with carbon dioxide emission and consumption of limestone/magnesite and energy. In these contexts, this study introduced a novel and sustainable method for immobilization of lead (Pb) by using an industrial solid waste (ladle furnace slag, LFS) and a greenhouse gas (carbon dioxide). In this laboratory investigation, LFS was first mixed with the lead nitrate and then treated by conventional curing (without carbon dioxide) and carbonation curing (with carbon dioxide) for different periods. The treated LFS were then analyzed by various chemical analyses and microanalysis. The results showed that LFS with conventional curing is not effective in immobilization of lead, while LFS with carbonation curing can effectively immobilize lead. The leaching concentrations of Pb from carbonated LFS were four orders of magnitude lower than those with conventional curing. LFS can achieve carbon dioxide uptake of up to 8% of LFS mass. During the carbonation process, carbonates were produced and wrapped LFS particles to prevent the release of lead, lead nitrate was also carbonated into lead carbonate, and the pH of LFS was reduced to 9.36-9.58, close to the minimum solubility of lead carbonate; these are the main reasons for lead immobilization. In summary, the use of LFS with carbon dioxide for immobilization of lead can not only sequester carbon dioxide, but also reduce the cost of binders, non-renewable resource consumption, energy use, and LFS landfilling.

Towards Lightweight Neural Networks for Garbage Object Detection

In recent years, garbage classification has become a hot topic in China, and legislation on garbage classification has been proposed. Proper garbage classification and improving the recycling rate of garbage can protect the environment and save resources. In order to effectively achieve garbage classification, a lightweight garbage object detection model based on deep learning techniques was designed and developed in this study, which can locate and classify garbage objects in real-time using embedded devices. Focusing on the problems of low accuracy and poor real-time performances in garbage classification, we proposed a lightweight garbage object detection model, YOLOG (YOLO for garbage detection), which is based on accurate local receptive field dilation and can run on embedded devices at high speed and with high performance. YOLOG improves on YOLOv4 in three key ways, including the design of DCSPResNet with accurate local receptive field expansion based on dilated-deformable convolution, network structure simplification, and the use of new activation functions. We collected the domestic garbage image dataset, then trained and tested the model on it. Finally, in order to compare the performance difference between YOLOG and existing state-of-the-art algorithms, we conducted comparison experiments using a uniform data set training model. The experimental results showed that YOLOG achieved AP0.5 of 94.58% and computation of 6.05 Gflops, thus outperformed YOLOv3, YOLOv4, YOLOv4-Tiny, and YOLOv5s in terms of comprehensive performance indicators. The network proposed in this paper can detect domestic garbage accurately and rapidly, provide a foundation for future academic research and engineering applications.

Household waste management in Singapore and Shanghai: Experiences, challenges and opportunities from the perspective of emerging megacities

Due to rapid economic development and urbanisation, emerging megacities with dense populations have witnessed a significant increase in waste generation. Megacities face challenges in developing sustainable waste management systems. Considerable heterogeneity exists across megacities in management strategies. The two selected emerging megacities, Singapore (a city-state) and Shanghai, have similar developmental characteristics, but their waste management modes differ strikingly. This study assessed the two modes in terms of management strategies, environmental effects, economic costs, and social outcomes. Environmental footprint analysis and cost quantification were employed for the assessment based on public data. The research results would permit a deeper understanding of the long-term sustainability of each mode while considering the feasibility of implementation across different contexts. It was found that the waste management system in Singapore had a relatively lower environmental impact than Shanghai before Shanghai's new waste segregation and recycling policy in 2019. However, when the effect of fossil fuel substitution is taken into account, the environmental burden in Shanghai can be lowered more substantially than the one in Singapore. Although Shanghai had more economic burden for the waste segregation at source, it tended to implement the circular economy principles (e.g., reduce, reuse, and recycling) better and improve its sense of community significantly. Based on the practical experiences from the two representative megacities, suggestions for better waste management practices were provided for Singapore, Shanghai, and other emerging megacities with similar circumstances. In addition, challenges and opportunities related to household waste segregation and recycling were identified to guide future practices in emerging megacities.

Depth-Wise Separable Convolution Attention Module for Garbage Image Classification

Currently, how to deal with the massive garbage produced by various human activities is a hot topic all around the world. In this paper, a preliminary and essential step is to classify the garbage into different categories. However, the mainstream waste classification mode relies heavily on manual work, which consumes a lot of labor and is very inefficient. With the rapid development of deep learning, convolutional neural networks (CNN) have been successfully applied to various application fields. Therefore, some researchers have directly adopted CNNs to classify garbage through their images. However, compared with other images, the garbage images have their own characteristics (such as inter-class similarity, intra-class variance and complex background). Thus, neglecting these characteristics would impair the classification accuracy of CNN. To overcome the limitations of existing garbage image classification methods, a Depth-wise Separable Convolution Attention Module (DSCAM) is proposed in this paper. In DSCAM, the inherent relationships of channels and spatial positions in garbage image features are captured by two attention modules with depth-wise separable convolutions, so that our method could only focus on important information and ignore the interference. Moreover, we also adopt a residual network as the backbone of DSCAM to enhance its discriminative ability. We conduct the experiments on five garbage datasets. The experimental results demonstrate that the proposed method could effectively classify the garbage images and that it outperforms some classical methods.

Incineration Fly Ash and Its Treatment to Possible Utilization: A Review

Incineration has gained popularity over landfill as a key solution for the reduction of massively increasing volumes of municipal solid waste (MSW) generation worldwide and in particular China. However, it is not the end solution. The disposal of the incineration residues, which are enriched with a wide range of heavy metals and soluble salts, has become a challenge for the environmental managers. The aim of this study was to review the increasing urbanization and its repercussion on waste generation in China; waste management options were compared for possible environmentally friendly considerations. Treatment techniques of incineration fly ash were discussed to determine the effectiveness of obtaining environmentally stable material, and, finally, possible applications of incineration fly ash for utilization were discussed based on identifying the processing suitability, performance and environmental impact of incineration fly ash for its applications.

Risk of faecal pollution among waste handlers in a resource-deprived coastal peri-urban settlement in Southern Ghana

Resource-deprived coastal peri-urban settlements in Southern Ghana are characterized by indiscriminate solid waste disposal and open defecation practices. Persons engaged in waste handling in such communities perform their activities with little or no personal protective equipment. They are thus confronted with the risk of faecal pollution of the hands and other bodily parts. A mixed method approach was used to investigate 280 waste handlers performing different activities to estimate recent faecal pollution of their hands and to observe the utilization of personal protective equipment and sanitation/hygiene facilities during work. The log concentration of E. coli on hands of waste handlers after work (8.60 ± 4.20 CFU/hand, mean ± standard deviation) was significantly higher compared with the E. coli log concentration before work (2.95 ± 1.89 CFU/hand, mean ± standard deviation) (p<0.001). The odds of faecal pollution was significantly higher (aOR 4.2; 95% CI: 1.9-9.1) for workers aged 35 years and above compared with those less than 35 years; and for workers at public toilet facilities (aOR 3.0; 95% CI: 1.0-8.4) compared with those who worked for private waste handling companies. Female workers were, however, 60% less likely (aOR 0.4; 95% CI: 0.2-0.8) to experience faecal pollution of their hands compared with males. The workers had limited access to water and sanitation and hygiene facilities, and about one-fifth (n = 59; 21.1%) did not use personal protective equipment during work. Waste handlers should be provided and instructed in proper use of personal protective equipment, have access to sanitation facilities and adopt improved hygiene behaviour to avoid the risk of faecal pollution and associated disease risk.

Methodology for Assessment of Alternative Waste Treatment Strategies Using Entropy Weights

Energy recovery from municipal solid waste is one of the means to attain sustainable development. Multiple factors involving several location specific situations, both measurable and intangible, makes decision making for technology selection very difficult. In this paper, a multi criterion evaluation system for municipal solid waste treatment strategies is established on the basis of specific, measurable, attainable, relevant and trackable situations, to prove the effectiveness of this method. From among various alternatives, three prominent strategies, namely, incineration, anaerobic digestion and composting are considered for the evaluation. Exhaustive data collection is done from conducting field studies, as well as from published data. Three types of communities are evaluated by this technique, namely, typical cities in developed countries, ‘A’ grade cities in India and ‘B’ grade cities in India. The purpose of the study is to evaluate the effect of community specific situations on the right choice of waste disposal method using a technique for order of preference by similarity to ideal solution (TOPSIS) approach, where weights of criteria are determined by means of entropy weight method. The case study shows that the proposed evaluation results are reliable, which are more coincident with the reality, since the most relevant factors for selection have been used backed by exhaustive field data collection. Policy makers gain from the outcome of this study by guiding them through technology selection. So, the adopted approach should be promoted widely in the evaluation of waste treatment strategies, to realize sustainable development.

A novel bulk density-based recognition method for kitchen and dry waste: A case study in Beijing, China

Identification technology of household kitchen and dry solid waste has played a major part in improving the accuracy of residents' separation by intelligent outdoor trashcan, which is an effective integral solid waste management tool for growing household solid waste (HSW). Our study aims to present a novel and simple recognition method for kitchen and dry waste based on bulk density. In three communities in Beijing, 270 bagged waste samples were collected, and their moisture content, separation accuracy, and bulk density, characterized. Then a bulk density index was developed to straightforwardly express residents' waste source separation accuracy by linear regression analysis above physical properties. In the 3 Beijing communities, we demonstrated a clear distinction in the bulk density index, for dry, mixed, and kitchen waste of <115, 115-211, >211 kg/m³, respectively. Our results provide a theoretical basis for the establishment of an intelligent waste supervision system, which is of great significance for waste management in developing countries like China.

Effect of source-classified and mixed collection from residential household waste bins on the emission characteristics of volatile organic compounds

The implementation of domestic waste classification following the principles of reduction, recycling, and harmlessness is an effective method to improve the urban and rural environments and to promote resource recycling. However, in many developing countries, the community residents lack awareness of the benefits of classified collection, which leads to a lack of initiative to classify MSW. To make the people realize the importance of MSW classification and increase the classification dynamics, Suzhou, China was taken as an example in this study, and residential areas were selected as sampling sites for classified and mixed collection of domestic waste. The main components of the odorous volatile organic compounds (VOCs) emitted from the dustbins via different disposal modes were determined by sampling in spring, summer, autumn, and winter. In addition, the ozone formation potential (OFP) and human health risk assessment of the VOCs were analyzed. Halogenated compounds were the major pollutants from the household waste dustbins of the residential areas. However, aromatic compounds contributed the most to the OFP of the VOCs. The OFP of VOCs reached the highest peak in summer, which was 1.02 × 10³ μg/m³. Furthermore, more attention needs to be paid in classifying waste to reduce the concentration of OFP. Although there was a carcinogenic risk in spring and summer, it declined after waste classification. Compared with mixed collection, the source-classified collection of garbage had advantages in terms of controlling the emission of VOCs, ozone formation potential, and human health risk. These results could provide the evidence demonstrating the advantages of waste classification and attract people's attention. Furthermore, the results can also provide impetus to those countries, where separate collection of waste has not yet been implemented, to improve the enthusiasm for classification and the integrity of waste classification system. Residents should be encouraged to classify household waste in residential areas.

Determination of the Least Impactful Municipal Solid Waste Management Option in Harare, Zimbabwe

Six municipal solid waste management (MSWM) options (A1–A6) in Harare were developed and analyzed for their global warming, acidification, eutrophication and human health impact potentials using life cycle assessment methodology to determine the least impactful option in Harare. Study findings will aid the development of future MSWM systems in Harare. A1 and A2 considered the landfilling and incineration, respectively, of indiscriminately collected MSW with energy recovery and byproduct treatment. Source-separated biodegradables were anaerobically treated with the remaining non-biodegradable fraction being incinerated in A3 and landfilled in A4. A5 and A6 had the same processes as in A3 and A4, respectively, except the inclusion of the recovery of 20% of the recoverable materials. The life cycle stages considered were collection and transportation, materials recovery, anaerobic digestion, landfilling and incineration. A5 emerged as the best option. Materials recovery contributed to impact potential reductions across the four impact categories. Sensitivity analysis revealed that doubling materials recovery and increasing it to 28% under A5 resulted in zero eutrophication and acidification, respectively. Increasing material recovery to 24% and 26% under A6 leads to zero acidification and eutrophication, respectively. Zero global warming and human health impacts under A6 are realised at 6% and 9% materials recovery levels, respectively.

Research on the Driving Mechanism of Waste Separation Behavior: Based on Qualitative Analysis of Chinese Urban Residents

Waste source separation is the fundamental premise to ensure effective waste recycling. Whether the entire waste recycling and reduction process can be effectively carried out depends on the waste source separation. Clarifying the driving mechanism of waste separation behavior plays an important role in effectively guiding the urban residents' waste separation behavior and achieving waste recycling. In this study, qualitative analysis was used to explore the driving mechanism of waste separation behavior. Through the open coding, axial coding and selective coding of the in-depth interview data collected from 323 Chinese urban residents, the study has proposed and verified the four-dimensional structure of waste separation behavior, namely, waste separation behavior of habit, decision, relationship, and citizen. The main driving factors of urban residents' waste separation behavior have been clarified. On this basis, a theoretical model for the driving mechanism of waste separation behavior was constructed in this study. Ten main categories of factors have been presented, namely, value orientation, cognition of separation, regulatory focus, preferences for comfort, perception of separation empowerment, policy and standards, products and facilities, group norms, links trustworthiness, and social demography variables. Moreover, four typical relationship structures were proposed. Finally, the intervention policy suggestions were made to effectively guide the urban residents' waste separation behavior.

Asking Sensitive Questions Using the Randomized Response Approach in Public Health Research: An Empirical Study on the Factors of Illegal Waste Disposal

A survey study is a research method commonly used to quantify population characteristics in biostatistics and public health research, two fields that often involve sensitive questions. However, if answering sensitive questions could cause social undesirability, respondents may not provide honest responses to questions that are asked directly. To mitigate the response distortion arising from dishonest answers to sensitive questions, the randomized response technique (RRT) is a useful and effective statistical method. However, research has seldom addressed how to apply the RRT in public health research using an online survey with multiple sensitive questions. Thus, we help fill this research gap by employing an innovative unrelated question design method. To illustrate how the RRT can be implemented in a multivariate analysis setting, we conducted a survey study to examine the factors affecting the intention of illegal waste disposal. This study demonstrates an application of the RRT to investigate the factors affecting people's intention of illegal waste disposal. The potential factors of the intention were adopted from the theory of planned behavior and the general deterrence theory, and a self-administered online questionnaire was employed to collect data. Using the RRT, a covariance matrix was extracted for examining the hypothesized model via structural equation modeling. The survey results show that people's attitude toward the behavior and their perceived behavioral control significantly positively affect their intention. This paper is useful for showing researchers and policymakers how to conduct surveys in environmental or public health related research that involves multiple sensitive questions.

Influence of the expansion of the selective collection in the sorting infrastructure of waste pickers' organizations: A case study of 16 Brazilian cities

Although recycling is a viable alternative to minimizing the impacts of the Municipal Solid Waste (MSW), identification of the local recycling market is a requirement for its empowerment. This paper aims to assess the recyclable solid waste market in 16 cities of Brazil. Through the application of interviews, field research and secondary data collection this research observed that while relying on poor infrastructure and on Government subsidies, the 12 pickers organizations surveyed can deliver 18.53% of recyclable waste to recycling with an average sorting productivity of 109 kg/picker/day and average earnings of US$ 293.40/picker/month. Based on the validated methods, 17% of these organizations were classified as having average efficiency, whereas 82% of them operated with very low efficiency. The investment required for the adequacy and expansion of the sorting capacity of waste pickers' organizations has been estimated at US$ 2.5 M, which could be counterbalanced by the savings with the current US$ 2 M/year spent with the disposal of recyclable waste into landfills. We also estimate new 189 job openings in the pickers' organizations to meet the requirements of the proposed scenario, contrasting with the current 93 cooperative members currently formalized. Regarding the consumer market, only few recycling companies were identified in the region, which may justify the low price paid for waste. The market for recyclables is mostly composed of micro and small companies that generally carry out the collection, transportation, sorting, and commercialization.

Alternatives for solid waste management in Isfahan, Iran: a case study

This articles presents the status of municipal solid waste (MSW) management practices in the city of Isfahan, Iran. It provides an overview of the generation, collection, separation, recycling and disposal of MSW. Field studies were carried out from 2009 to 2010. According to this study, the city generates about 399,000 metric tons of MSW per year, of which 72.5% is organic matter. In Isfahan more than 90% of the MSW is collected by official municipal forces and the other 10% is collected by informal collectors. About 70% of the MSW in Isfahan is composted to produce a humus material, 5% is rejected and 25% is stockpiled for future use as fuel in a waste-to-energy incineration plant. Non-compostable waste and other residues are landfilled. This investigation also includes an analysis of economic benefits that could be realized by implementing incineration and a discussion of the challenges confronted in Isfahan for implementing changes to the city's existing MSW management system. This article concludes with recommendations for improving the city's MSW management system.

Projecting the environmental profile of Singapore's landfill activities: Comparisons of present and future scenarios based on LCA

This article aims to generate the environmental profile of Singapore's Semakau landfill by comparing three different operational options associated with the life cycle stages of landfilling activities, against a 'business as usual' scenario. Before life cycle assessment or LCA is used to quantify the potential impacts from landfilling activities, an attempt to incorporate localized and empirical information into the amounts of ash and MSW sent to the landfill was made. A linear regression representation of the relationship between the mass of waste disposed and the mass of incineration ash generated was modeled from waste statistics between years 2004 and 2009. Next, the mass of individual MSW components was projected from 2010 to 2030. The LCA results highlighted that in a 'business as usual' scenario the normalized total impacts of global warming, acidification and human toxicity increased by about 2% annually from 2011 to 2030. By replacing the 8000-tonne barge with a 10000-tonne coastal bulk carrier or freighter (in scenario 2) a grand total reduction of 48% of both global warming potential and acidification can be realized by year 2030. Scenario 3 explored the importance of having a Waste Water Treatment Plant in place to reduce human toxicity levels - however, the overall long-term benefits were not as significant as scenario 2. It is shown in scenario 4 that the option of increased recycling championed over all other three scenarios in the long run, resulting in a total 58% reduction in year 2030 for the total normalized results. A separate comparison of scenarios 1-4 is also carried out for energy utilization and land use in terms of volume of waste occupied. Along with the predicted reductions in environmental burdens, an additional bonus is found in the expanded lifespan of Semakau landfill from year 2032 (base case) to year 2039. Model limitations and suggestions for improvements were also discussed.

Home and community composting for on-site treatment of urban organic waste: perspective for Europe and Canada

As a result of urbanization and economic prosperity, which has accelerated the generation of municipal solid waste (MSW) along with its organic fraction, the management of MSW is a challenge faced by urban centres worldwide, including the European Union (EU) and Canada. Within a concept of waste recovery, the source separation and on-site treatment of urban organic waste (UOW) can resolve some of the major economic issues faced by urban centres along with the environmental and social issues associated with landfilling. In this context and in a comparison with the traditional landfilling practice, this paper examines on-site UOW composting strategies using a combination of centralized composting facilities, community composting centres and home composting. This study consisted of a feasibility and economic study based on available data and waste management costs. The results indicate that on-site treatment of UOW using practices such as home and community composting can lower management costs by 50, 37 and 34% for the rich European countries (annual GDP over US$25,000), the poorer European countries (annual GDP under US$25 000), and Canada, respectively. Furthermore, on-site composting can reduce greenhouse gas emissions by 40% for Europe and Canada, despite gas capture practices on landfill sites. However, the performance of home composters and the quality of the compost products are issues to be further addressed for the successful implementation of UOW on-site composting.