Sustainable mechanical biological treatment of solid waste in urbanized areas with low recycling rates

Characteristics and management of municipal solid waste in Uyo, Akwa Ibom state, Nigeria

Increased urbanization and population lead to increased consumption of manufactured goods. This ultimately results in increased production of waste. Identifying its composition is crucial for planning an effective solid waste management strategy. This study assesses the characteristics and composition of the waste generated within the Uyo Capital City Development Area of Akwa Ibom State, Nigeria. This is to aid in developing a scientifically supported waste management pilot system for the state. Direct waste sorting and characterization were conducted on the municipal solid waste arriving at the landfill during the study period. Over 50% of the generated wastes are recyclables and composed of plastics, metals, and paper, while the fraction of organic waste is over 30%. Similarly, the waste generation per capita is 1.34 kg/person/day, while the generation forecast over the next ten years is estimated to increase by approximately 40%. Furthermore, over 9,000 surveys were completed by residents to establish a problem statement about the existing waste collection and disposal system, and possible solutions. Importantly, a majority of survey respondents were willing to source-separate their wastes and supported paying a fee for adequate waste collection. This strongly indicates that an integrated waste management system could be established to generate value from the collected waste. Supplementary revenue can be generated through composting, recycling, and land reclamation.

Municipal solid waste management instruments that influence the use of the refuse as fuel in developing countries: A critical review

Landfills are the destination of most of the refuse generated whereas composting, material recycling, and Waste-to-Energy (WtE) technologies are not commonly employed in developing countries. However, the destination for energy purposes could be supplied with this refuse, improving the viability of energy use. Thus, this article raises some questions to identify aspects that could encourage its use as refuse-derived fuel (RDF) in these countries. Among them, does environmental education affect the municipal solid waste (MSW) source separation with emphasis on a destination? Can selective collection and extended producer responsibility (EPR) affect the MSW for energy recovery? Is there competition between the recycling market and the energy market for RDF? A systematic review of the literature was conducted to gather data and provide answers to such questions. This enabled to observe that EPR, selective collect expansion and source separation influence the quantity and quality of waste sent for energy use. Both internal and external factors impact on source separation. Additionally, there is evidence to support that despite several studies showing their technical, economic, environmental and social viability, the methods of energy usage of the refuse still need to improve their deployment in developing countries. In addition to identifying the main research gaps to be filled in future studies, the article also identified the instruments of MSW management that are to be applied in developing countries to divert recyclable and organic waste from landfill.

Conversion of solid wastes and natural biomass for deciphering the valorization of biochar in pollution abatement: A review on the thermo-chemical processes

This overview addresses the formation of solid trash and the various forms of waste from a variety of industries, which environmentalists have embraced. The paper investigates the negative effects on the environment caused by unsustainable management of municipal solid trash as well as the opportunities presented by the formal system. This examination looks at the origins of solid waste as well as the typical treatment methods. Pyrolysis methods, feedstock pyrolysis, and lignocellulosic biomass pyrolysis were highlighted. Explain in detail the various thermochemical processes that take place during the pyrolysis of biomass. Due to its carbon content, low cost, accessibility, ubiquitousness, renewable nature, and environmental friendliness, biomass waste is a unique biochar precursor. This study looks at the different types of biomass waste that are available for treating wastewater. This study discussed a wide variety of reactors. Adsorption is the standard method that is used the most frequently to remove hazardous organic, dye, and inorganic pollutants from wastewater. These pollutants cause damage to the environment and water supplies, thus it is important to remove them. Adsorption is both simple and inexpensive to utilize. Temperature-dependent conversions explain the kinetic theories of biomaterial biochemical degradation. This article presents a review that explains how pyrolytic breakdown char materials can be used to reduce pollution and improve environmental management.

Quantifying the effect of socio-economic-geo drivers on the change of municipal waste disposal in China by an integrated TWFE-PRF-SDM methodology

Municipal solid waste management and disposal in China have significantly evolved since 2000. Due to China's vast land area and significant socioeconomic and geographic disparities, nationwide waste management strategies need to be further evaluated. This study quantified the effect of social, economic, and geographic drivers on municipal waste disposal activities in 31 provincial-level administrative regions from 2003 to 2020, by establishing a methodology integrated by two-way fixed effects regression model, panel random forest, and spatial Durbin model. The results showed, in the past two decades, socio-economic-geo indicators significantly co-decided the landfill and incineration activities. In particular, the explanatory ability of GDP per capita was above 45%, while land resources and city size also showed great significance. Spatial autocorrelation analysis showed that the relationship between landfill/incineration rates and socio-economic-geo drivers changed notably from unobvious to significant with economic growth. Furthermore, the local economy and land resources displayed more impact than those of the neighboring regions, while sci-tech and education showed clear spatial spillover effects. Chinese government would carefully assess the full-scale promotion policy of incineration plants, landfill is still hold as a reasonable option for regions with specific socio-economic-geo conditions.

A mini review on the main challenges of implementing mechanical biological treatment plants for municipal solid waste in the Latin America region: Learning from the experiences of developed countries

Most of the municipal solid waste (MSW) generated in the Latin America (LATAM) region is currently disposed of in landfills and dumpsites, which results in many negative environmental impacts. Mechanical biological treatment (MBT) is a strategy that combines the mechanical separation of recoverable materials with the biological stabilization of organic matter. MBT plants have proven to be a good alternative for the management of MSW and have been successfully implemented in developed countries for more than 30 years. However, the efficient introduction of these facilities in developing countries, such as those in the LATAM region, requires further feasibility studies. Therefore, this mini review seeks to offer significant insights into the main challenges that must be overcome to facilitate the implementation and operation of MBT plants, considering the unique technological, sociocultural, economic and political context of the LATAM region, through a comparison of the reported experiences of MBT plants in more developed countries with those in the LATAM region. The analysis herein indicates that key actions for the successful operation of MBT plants in the LATAM region include both the implementation of source separation as well as selective collection practices. Moreover, this work shows that other factors, like the establishment of valorization markets with safe working conditions for informal collectors, the development of intermunicipal cooperation schemes and the enforcement of strong regulatory frameworks for waste disposal specifications, are important contextual factors that have allowed the efficient operation of MBT plants in developed countries. Although the implementation of many of these practices will be challenging, such measures are necessary to increase the sustainability of MSW treatment practices in the LATAM region.

Effects of cellulose-based bio-plastics on the aerobic biological stabilization treatment of mixed municipal solid waste: A lab-scale assessment

The aim of this work is to assess how the presence of cellulose-based bio-plastics influence the biological stabilization of mixed Municipal Solid Waste (MSW). For the scope, two cellulose acetate bio-plastics have been mixed with a synthetic mixed waste to create samples with and without bio-plastics. A self-induced biostabilization has been carried out for 7 and 14 days where temperature and off-gas have been monitored continuously. Results about temperature evolution, O₂ consumption, CO₂ production and respiratory quotient did not show a substantial difference regarding both the duration of the process and the presence of cellulose-based bio-plastics on the mixture. On the average, the temperature peak and the maximum daily O₂ consumption and CO₂ production were 52.2 °C, 35.81 g O₂/kg DM *d and 48.95 g CO₂/kg DM *d respectively. Disintegration of bio-plastics samples after 7 and 14 days were comparable (on the average 23.13%). The self-induced biostabilization gave its main contribution after 4 days and resulted almost finished at the end of the day 7 of the process. Results showed that cellulose-based bio-plastics did not give a negative effect on mixed MSW biological stabilization and suggest a possible management, aiming at energy recovery of the outputs.

Environmental Comparison of Different Mechanical–Biological Treatment Plants by Combining Life Cycle Assessment and Material Flow Analysis

The role of Mechanical–Biological Treatment (MBT) is still of the utmost importance in the management of residual Municipal Solid Waste (MSW). These plants can cover a wide range of objectives, combining several types of processes and elements. The aim of this work is to assess and compare, from an environmental point of view, the performance of seven selected MBT plants currently operating in different countries, which represent the main MBT layout and processes. For the scope, a combined Life Cycle Assessment (LCA) and Material Flow Analysis (MFA) approach has been adopted to assess plant-specific efficiencies in materials and energy recovery. Metals recovery was a common and high-efficiency practice in MBT; further recovery of other types of waste was often performed. Each assessed MBT plant achieved environmental benefits: among them, the highest environmental benefit was achieved when the highest amount of waste was recovered (not only with material recycling). Environmental results were strongly affected by the recycling processes and the energy production, with a little contribution from the energy requirement. The impacts achieved by the MBT process were, on average, 14% of the total one. The main condition for a suitable MBT process is a combination of materials recovery for the production of new raw materials, avoiding disposal in landfill, and refuse-derived fuel production for energy recovery. This work can be of help to operators and planners when they are asked to define MBT schemes.

Perspectives in solid recovered fuel production in Bolivia: Analysis of characteristics and potential benefits

Solid recovered fuels (SRF) can provide another treatment option to the solid waste management (SWM) sector. However, in developing countries, to date, this system approach has not found considerable application. In Bolivia, SRF is not deemed within the national regulation and the final disposal in open dumping areas is still a reality. This research article provides the first attempt in evaluating the SRF characteristics and its potentialities in Bolivia, taking La Paz as a case study. Laboratory analysis of the rejects produced after selective collection and sorting has been conducted, focusing on non-hazardous and non-recyclable waste fractions. The international standards related to EN 15359:2011 for the classification of the SRF were employed, assessing the most feasible mix of materials to provide the highest classification of SRF in terms of low calorific value (LCV), chlorine, and mercury concentration. Results reported that the SRF made of 80% plastics (85% PE and 15% PP) and 20% cellulosic (blend 2), as well as 30% plastics (50% PP and 50% PE) and 70% cellulosic (blend 1), can be considered an alternative fuel in Bolivia. On balance, it has been estimated that the use of non-recyclable plastics and cardboard from municipal solid waste can provide, on average, about 0.9-2.7 billion MJ of energy for cement kilns, solving about 1.4-5.3% of the SWM issues and covering about 8-23.4% of the energy demand for cement production in Bolivia. These results are novel for the scientific literature for estimating the potentialities of SRF in Latin America.

Anaerobic co-digestion of paper sludge: Feasibility of additional methane generation in mechanical-biological treatment plants

In this work, the feasibility of the anaerobic digestion of paper sludge as a co-substrate in anaerobic digestion mechanical-biological treatment (MBT) plants is investigated. In the first phase, the biochemical properties, biomethane potential (BMP), and pollutant contents of 20 different industrial paper sludges are determined. Following the general evaluation in the BMP tests, the second phase of the project involves the semi-continuous co-digestion of six paper sludges in continuous stirred reactors (CSTR). Paper sludges are categorized according to their origin within the pulp and paper mills: Deinking Sludge (DS), Primary Sludge (PS) and Biological Sludge (BS). The analysis of potentially inhibiting elements shows that the concentrations of chlororganic compounds, mineral oil and some heavy metals are highest in DS, while the mean heavy metal loads in all paper sludges are relatively low compared to other industrial sludges. Large differences in total solids (TS) and volatile solids (VS) contents are observed among the different paper sludges investigated, with DS having the highest TS due to the high inorganic contents. The BMP of the investigated sludges ranges from 90 to 355 NL CH₄ kg^-1 VS. In subsequent semi-continuous co-digestion experiments simulating MBT conditions, three DS and two fiber sludges (a mixture of PS and BS) show good methane generation rates, while one fiber sludge causes inhibition and indicates an increase in viscosity. In general, co-digestion of paper sludge in anaerobic digestion MBT plants can be a viable option for energy production and also facilitates a safe disposal of the paper sludge digestates.

Circular economy and frugal innovation: a conceptual nexus

Frugal innovation (FI) and circular economy (CE) are two concepts that are recently being deliberated among researchers, policymakers, businesses, governments, and international organizations. Being a nascent development, both still lack an extant body of theories and data. Undisputedly they both share commonalities in gathering tractions among scholars. But the conceptual relationship between them has been unclear and hence makes it difficult to understand how one can promote the other. The current work constructs a conceptual framework through literature, explicating nexus, characteristics, and indicators of the two concepts and then exploring this framework through case analysis and focus group discussion (FGD). The results of our findings show that the two concepts are outcome of considerations on resource constraints and/or resource optimization; promote redesigning of product and services to minimize resources while achieving core functionality; involve the participation of stakeholders; and are implemented in stages. Most importantly, they foster the three pillars of sustainable development-social equity, economic prosperity, and environmental quality. However, supportive policies and institutions are largely associated with the development of CE which is not the same for FI in most countries. We conclude that FI being mainly operational in the emerging economies could serve as a veritable enabling tool for promoting the CE concept in the developing regions of the globe but will require the support of formal institutions and policies.

Municipal solid waste management: Dynamics, risk assessment, ecological influence, advancements, constraints and perspectives

Global energy consumption has been increasing in tandem with economic growth, putting pressure on the world's supply of renewable energy sources. Municipal Solid waste (MSW) has been reported contributing immensely to the improvement of a secure environment and renewable sources. Energy scarcity and conventional MSW disposal methods in developing countries lead towards many environmental and economic issues. Scientists have been able to experiment with various waste-to-energy conversion technologies in light of this situation. This communication highlights and reviews WtE technologies to convert MSW and other feedstocks into electricity, hydrogen gas, bioethanol along with other value added products like fertilizer(s), platform chemicals as an environmentally friendly products. This review comprehensively summarized the dynamics, risk assessment, ecological influence, advancements, constraints and perspectives altogether in field of municipal solid waste management and treatment. Stare-of-the-art information on ecological influence and risk assessment in handling and transportation of municipal solid waste has been provided. Advanced trends involved in remediation of emerging pollutants and resources obtained from municipal solid wastes have been uncovered. Lastly, this paper comprises constraints and perspectives for uncovering MSW based circular bioeconomy aspects.

Eco-Efficiency Analysis of Integrated Waste Management Strategies Based on Gasification and Mechanical Biological Treatment

Integrated solid waste management (ISWM) strategies are developed towards promoting sustainable approaches for handling waste. Recently, gasification and mechanical biological treatment (MBT) technologies were recognized as effective processes for treating municipal solid waste. This study investigates the feasibility of integrating gasification and MBT technologies in multiple ISWM strategies, compared to incineration- and anaerobic digestion (AD)-based strategies. A comprehensive techno-economic and environmental assessment was carried out to evaluate the performance of the examined ISWM strategies. The evaluation was based on the energy generation potential, carbon footprint, and life cycle costing (LCC). An eco-efficiency analysis was conducted to quantify the environmental costs by incorporating the carbon footprint and LCC results. The proposed strategies were applied for the city of Abu Dhabi, United Arab Emirates, based on local bylaws and guidelines. The analysis revealed that the gasification-based strategy had the highest energy production of 47.0 million MWh, followed by the incineration- (34.2 million MWh), AD- (17.2 million MWh), and MBT-based (14.9 million MWh) strategies. Results of the environmental analysis indicated that the MBT- and AD-based strategies contributed the least to global warming with greenhouse gas emissions of 4442 and 4539 GgCO2-eq, respectively, compared to the gasification- (9922 GgCO2-eq) and incineration-based (15,700 GgCO2-eq) strategies. Furthermore, over a 25-year assessment period, the LCC findings demonstrated that the gasification- and MBT-based strategies were the most financially feasible with a positive net present value (NPV) of USD 364 and USD 284 million, respectively. The eco-efficiency analysis indicated that the MBT and gasification strategies are the most sustainable among the examined strategies. The sustainability of the assessed systems was improved by implementing policy and legal reforms, including incentive programs, less stringent bylaws on digestate, and encouraging source separation of wastes. Overall, this research emphasized the potential environmental and financial benefits of incorporating MBT and gasification technologies into ISWM strategies.

Comparative life cycle analysis of municipal waste management systems: Kırklareli/Turkey case study

Waste-to-energy approaches are becoming increasingly important around the world, and municipal solid waste (MSW) as a renewable and sustainable energy source is of great importance to be considered in preventing climate change. On the other hand, since uncontrolled MSW is a threat to the environment and human health, sustainable municipal solid waste management should be evaluated to reduce negative environmental impacts. In this study, various municipal solid waste management options having energy production were selected and analysed by using SimaPro 9.0.0.49 to determine the most environmentally friendly waste management system. One-ton MSW in Kırklareli/Turkey was chosen as the functional unit. Environmental impacts were calculated via the CLM-IA method; impact groups were abiotic depletion, abiotic depletion (fossil fuels), global warming, ozone layer depletion, human toxicity, freshwater, marine and terrestrial ecotoxicities, photochemical oxidation, acidification and eutrophication. The first results indicated that energy recovery reduces the environmental impacts and future waste management plant of Kırklareli (material separation for recycling, biomethanisation and landfilling) is the best option within the scope of the environment at present.

Life Cycle Assessment of Advanced Circulating Fluidized Bed Municipal Solid Waste Incineration System from an Environmental and Exergetic Perspective

The production of clean and efficient energy from municipal solid waste (MSW) is extremely urgent matter due to an increasing energy demand and environmental concerns. In this study, a high steam parameter (520 °C, 7.9 MPa) circulating fluidized bed (CFB) MSW incineration system, equipped with a mechanical, biological treatment and external heat exchanger systems, was introduced and a comparative study with a typical mechanical grate (450 °C, 5.3 MPa) incineration system and conventional CFB (485 °C, 5.3 MPa) incineration system was carried out from a life-cycle, environmental and exergetic perspective which could assess different energy and material outputs based on real operating data. Moreover, the potential system optimization of this advanced CFB system was proposed. The results showed that the advanced CFB system was more environmentally friendly and resource-efficient than conventional MSW incineration systems. The recovery of material should be given priority over energy recovery. According to the assessment of the environment, and energy and material recovery, a process improvement with an incinerated refuse-derived fuel and a semi-compost produced by MBT as a soil conditioner was highly recommended.

Evaluation of Inoculated Waste Biological Stabilization Degree by Olfactometric Methods

As a result of compounds’ transformation in the waste biostabilization phases, there is an increase in odor nuisance and health problems among people exposed to odorants. Linking the odor concentration to the degree of waste biostabilization may be an important tool for the assessment of individual technological variants of biostabilization. The study aimed to link the odor emissions to the biostabilization degree in individual process variants that differed in the inoculum. The tests were carried out on inoculated windrows on the waste mechanical-bological treatment open site. Odor concentrations were measured during the entire seven-week process of biostabilization (weeks 1–7) and compared with kinetics parameters of organic compounds’ decomposition. The olfactometric tests showed the necessity of using the preparation to reduce the value of odor concentration. Research proved that the decrease of odor concentration values could be useful to indicate the particular phases of biostabilization. Also, the proposed method provides an opportunity to optimize the process concerning the function related to the low degree of odor nuisance of the technologies, including selection of environmentally safe inoculum. This issue has application values that may result in the implementation of new control systems for waste stabilization bioreactors and the evaluation of applied technological solutions.

Giving credit to residual bioresources: From municipal solid waste hydrolysate and waste plum juice to poly (3-hydroxybutyrate)

Municipal solid waste (MSW) is massively generated all over the world. Its organic fraction (OFMSW), which represents a high percentage of MSW, mainly contains biodegradable materials, namely food waste, paper and garden waste. The social cost of OFMSW treatment and/or disposal is a serious and widespread problem, particularly in highly populated areas. Thus, effective and innovative solutions, which include the upgrading of OFMSW, are being currently sought. In fact, the OFMSW abundance, availability and average composition suggest its considerable potential within the circular economy desideratum, paving the way to valorisation approaches. In this context, an OFMSW sugar-rich hydrolysate and its validation as a substrate for the production of the polyester poly(3-hydroxybutyrate) (P(3HB)), to date the only bioplastic easily biodegradable in marine environment, were successfully obtained in a previous study. Based on those results, this work addresses the upscaling of the fermentative production, in fed-batch mode, of P(3HB) by Burkholderia sacchari. The OFMSW hydrolysate was used as cultivation medium due to its balanced nutrient composition, while a plum waste juice, also rich in sugars, was applied as feed to the bioreactor. By implementing this strategy, a maximum P(3HB) production of 30 g·L^-1 with an accumulation of 43% g (P(3HB))/g cell dry weight (CDW) after 51 h, was achieved. The use of the hydrolysate as initial medium resulted in higher CDW (71 g·L^-1) than that of the simulated hydrolysate (62 g·L^-1 in average), probably because the OFMSW hydrolysate favours biomass growth in detriment of P(3HB) production.

RDF from Compost-Like-Output’s Produced in the MBT Installation in the Case of Marszów, Poland

At most of the installations for the mechanical and biological treatment of waste operated in Poland, the 0–80 mm fraction, separated from the municipal waste stream, are completely stored after biostabilization. Such an action does not fit into the EU strategy focused on circular waste management. The purpose of this study was to assess the technical feasibility of recovering the mineral fractions contained in the compost-like-output (CLO) on a technological line designed for glass recovery. The research started in January 2019, lasted for the next 12 months, and covered 29 measurement series. The following two high-energy fractions were separated from the CLO: 10–35 mm light fraction after separation in the air separator (M-1) and 35–80 mm light fraction after separation in the air separator (M-2). The stabilization processing on the glass recovery line allowed for the recovery of two high energy fractions in the total amount of 24.5% of the processed, and it stabilized the product’s mass. In terms of materials, the M-1 and M-2 wastes were a mixture of organic, paper, and plastic materials. Under the Refuse Derived Fuel (RDF) classification, according to the European Committee for Standardization, the tested waste fell within the following classes: waste M-1: 4NCV2Cl4Hg and M-2: 4NCV1Cl4Hg.

Evaluation of the biochemical methane potential of residual organic fraction and mechanically-biologically treated organic outputs intended for landfilling

Mechanical biological treatment (MBT) approaches are being adopted to manage residual municipal waste (RMW) to promote the prevention or reduction of potential environmental impacts of landfilling. From this perspective, the present study aimed to increase the knowledge of the biological (anaerobic) stability of different MBT organic outputs and, conversely, initial methane generation from residual organic waste. Biochemical methane potential (BMP) tests, along with initial and final characterisations of substrates and digestates, were conducted on: a mechanically separated organic fraction from RMW (ms-OFRMW); a first MBT organic output represented by a biostabilised organic fraction from RMW (bios-OFRMW); and a different MBT organic output represented by a biodried fine fraction from RMW (biod-FFRMW). The ms-OFRMW had a BMP of 445.6 Nml CH₄ g VS^-1, which was comparable or even higher than those from separately collected and source-sorted organic fractions. The fibre and liquor fractions of the digestate from ms-OFRMW with inoculum showed potential profiles of P-rich amendment and N-rich fluid phase, respectively, even satisfying environmental limits (with the exclusion only of Cu and Zn contents in fibre fraction that, however, remained within typical ranges for agricultural digestates). The BMPs for bios-OFRMW and biod-FFRMW were 143.4 and 261.0 Nml CH₄ g VS^-1, respectively, indicating that these streams may still contribute to landfill methane generation. The BMPs for bios-OFRMW, biod-FFRMW, and ms-OFRMW were positively associated with the degrees of conversion of the substrates (17, 32, and 55%, respectively) and the potential dynamic respiration indexes (955, 3126, and 6062 mg O₂ kg VS^-1 h^-1, respectively).

Composting versus mechanical-biological treatment: Does it really make a difference in the final product parameters and maturity

One of crucial waste management problems is the management of organic waste. This activity employs the composting. In case of green waste, its application seems reasonable, whereas the use of selected mixed waste raises problems related to the compost quality. Across countries, the non-sterile organic fraction of municipal solid waste is being separated through the mechanical-biological treatment. The technology is a solution of waste treatment and meets objectives set out in the Landfill Directive. There are many problems associated with the use of output products. The use of compost as a fertilizer requires determination of its impact on the environment. Compost quality can be assessed using analytical methods and phytotoxicity tests. Therefore, the aim of this study was to describe changes in physico-chemical, enzymatic, phytotoxicity and vegetation parameters occurring in composts from two systems - a prismatic installation for green waste, and a mechanical-biological treatment installation. The compost from green waste exhibited greater stability. Values of dehydrogenase activity were lower if compared with the mechanically and biologically treated compost, which indicates lower compost maturity. The biomass production of Brassica napus L. and Fetuca rubra L. was higher in the variant with the application of green compost. The influence on Hordeum vulgare L., Cannabis sativa L., and Sinapis alba L. depended on the plant type and the compost used. Nevertheless, the compost from green waste was less toxic. The evidence from this study suggests that the mechanical-biological treatment had problems associated with the maturation and quality of the final product.

Laboratory study on the hydraulic characteristics of mechanically and biologically treated waste in China

Mechanical biological treatment (MBT) can greatly reduce the amount of municipal solid waste (MSW) and has become a hot topic in environmental geotechnical engineering. To study the effects of factors such as the pressure, dry density, compression time under pressure, strain, and hydraulic gradient, permeability tests with saturated MBT waste were conducted by using a compression and permeability combined apparatus in an environmental geotechnical laboratory. The results showed that Darcy's law was applicable to the saturated MBT waste. The permeability coefficient was found to be inversely related to the pressure, dry density, compression time under pressure and strain. The logarithmic permeability coefficient and the variables (e.g., pressure) could largely be fitted to a linear function. Additionally, a prediction model for the permeability coefficient was established, and the permeability coefficient at different depths of MBT landfills was predicted. The results were then compared to previous studies on MSW and MBT waste to investigate the permeability mechanism.

Assessment of municipal solid waste selective collection scenarios with geographic information systems in Bolivia

The analysis of municipal solid waste (MSW) selective collection (SC) scenarios is compulsory for planning future policies and actions towards circular economy. The use of geographic information system (GIS) is appropriated for obtaining reliable data about SC yields and management costs. However, in low-middle income countries, advanced assessments are difficult to introduce due to the lack of technical knowledge, financial support and the presence of the informal recycling sector. This research aims to assess the main potentialities of the introduction of SC systems in a Bolivian developing city taking into account the informal SC system in place. The study was conducted with QGIS3.8 software in order to evaluate the main advantages of the implementation of formal and informal recycling chains. Results reported that, comparing the implementation of formal SC of MSW with the scenario that considered the inclusion of the informal recycling, the activity of waste pickers allows reducing the expenses of about 10%, increasing the recycling rate of about 3.5%, and reducing the distances traveled with compactor trucks of about 7%. It means that, the annual path traveled by the collection trucks for gathering about 16,000ty^-1, is reduced by 2734kmy^-1, reducing the waste disposed to landfill of about 543.6ty^-1 and the expenses of about €59,000 per year. The presentation of these results to policy-makers can support decision-making boosting the implementation of recycling activities including waste pickers. The study provided a contribution to the scientific literature assessing the main challenges and opportunities for implementing the circular economy in developing regions.

Introduction of the circular economy within developing regions: A comparative analysis of advantages and opportunities for waste valorization

The introduction of effective solid waste management strategies in developing countries should be considered for improving sustainability at global level. Many barriers should be overcome, concerning the introduction of environmental policies, effective investments, social inclusion and public awareness, which are significant issues in low-middle income countries. The Circular Economy could represent the answer for improving current solid waste management activities worldwide, since denote the principle of waste valorization and recycling for boosting developing economies. This paper is focused on this theme, analyzing main opportunities for improving the current state of solid waste management in developing big cities. The solid waste management of two countries are reviewed: Romania is the emerging country where Circular Economy is becoming a future objective due to economic aids and strength regulations which the European Union (EU) established for the nations forming parts the alliance; as a comparison, Bolivia is reported for evaluating main differences founded for developing recycling systems in a no-EU country. These two case studies could be of interest for highlighting main pros and cons of the participation into a wide organization like the EU for introducing in short terms Circular Economy principles. Moreover, a theoretical Circular Economy model for developing big cities in low-middle income countries is described within the study for effectively comparing which chances can spread for these countries as regard municipal solid waste exploitation. Despite the economic level, Romania and Bolivia are both facing with many solid waste management issues although in different magnitude. For the Romanian case study, it is visible how it cannot achieve the European goals for 2020 due the need of change in public recycling behavior. Bolivia, instead, represents the case where international aids and new investments are required, considering the informal sector into the formal management system as a real opportunity for improving local recycling rate. In conclusion, the comparison suggests how external supports led to implement the principles of the Circular Economy within a developing region. The model of Circular Economy proposed is recommended for developing big cities in order to advance a new form of safe employment, encouraging the activities that are still in action (i.e. informal sector) and boosting the principles of sustainable development.

Alternating pure oxygen and air cycles for the biostabilization of unsorted fraction of municipal solid waste

Biostabilisation is a process of treating the unsorted fraction of municipal solid waste (UFMSW) mechanically pre-treated. Although concepts such as circular economy would seem to limit biostabilization, several authors have recently described the advantages of biostabilization in regions where recycling systems are inadequate. In this perspective, the development of new MBT technologies is of considerable importance. The objective of the study was to evaluate the effects of the use of alternating air and oxygen cycles on the treated waste stability as well as on the quality of leachate and process gaseous emissions. Two Herhof biocells were prepared for this purpose. One implemented the conventional process and the other the "Air + O₂" process. The biostabilization of the inlet UFMSW (3965 ± 1965 mgO₂/kgVS/h) resulted in a final product with a dynamic respirometric index almost equal in both processes. The mass balance indicated that of the 400 tons representing the input waste, 37.57% were biostabilized waste, 0.29% leachate and 62.14% CO₂ and odours. However, the biostabilized waste was lower than that of the conventional process (equal to 40.18%). The Air + O₂ system resulted in a shorter duration, increased production of leachate (although characterized by higher quality) and process gaseous emissions quality. The energy balance (20.3 kJ/kg per input waste) and cost analysis (80.0 €/ton per input waste) showed values equal or better to those of the conventional system. By contrast, weakness was in the O₂ diffusion system. Although a life cycle analysis is necessary, the results highlighted the feasibility of the proposal especially for emergency situations.

Environmental assessment of existing and alternative options for management of municipal solid waste in Brazil

Life cycle assessment (LCA) was used to evaluate and compare three different categories of management systems for municipal solid waste (MSW) in Brazil: (1) mixed waste direct disposal systems, (2) separate collection systems, based on wet-dry streams, and (3) mixed waste mechanical-biological systems, including materials recovery. System scenarios were built around main treatment techniques available and applicable in developing countries, and considered barriers as well as potential synergies between waste management and other industrial production. In the first category systems, we measured the impact magnitude of improper disposal sites (semi-controlled and controlled dumps) still used for approximately 40% of collected MSW, and found that sanitary landfills could decrease it 3-5 fold (e.g. GWP, from 1100-1200 to 250-450 kg CO2 eq. t^-1 waste). As an alternative, waste incineration did not show significant benefits over sanitary landfilling, due to limitations in energy utilization and the low-carbon background electricity system. Category two of systems, revealed recycling benefits and the necessity as well as potential risks of biological treatment for wet streams. Simple wet-dry collection could result in relatively high levels of contamination in compost outputs, which should be mitigated by intensive pre- and post-treatment. Potential impact of air emissions from biological degradation processes was important even after anaerobic digestion processes. Biogas upgrading and use as vehicle fuel resulted in bigger savings compared to direct electricity production. Lastly, category three, mechanical-biological systems, displayed savings in most environmental impact categories, associated with materials recovery for recycling and refuse-derived fuel (RDF) production and utilization in cement manufacturing.

Efficiency of landfill leachate treatment in a MBR/UF system combined with NF, with a special focus on phthalates and bisphenol A removal

In this study, a pilot-scale membrane bioreactor (MBR) was operated at a municipal solid waste plant (MSWP) to treat a mixture of landfill leachates (LLs) obtained from modern (MP-LLs) and previous (PP-LLs) waste cells. The MBR unit combined anoxic and aerobic zones with external ultra- and nanofiltration (MBR/UF and MBR/UF/NF, respectively). In addition to the removal of macropollutants, special attention was given to phthalates (PAEs) and bisphenol A (BPA). According to the obtained results, the MBR/UF system with acclimated biomass was effective for treating LLs, and the obtained effluent was generally similar in quality to raw municipal wastewater. The MBR biomass showed high potential for BPA and PAEs biodegradation/biotransformation as confirmed by a metagenomic approach. Only a high chloride concentration (1960 mg Cl^-/L), which was twice the value acceptable by Polish regulations for industrial wastewater entering the municipal wastewater system, justifies the additional usage of the NF unit. Notably, a decreasing amount of biodegradable organic matter in MBR influent is expected with time because of changes in the biochemistry of modern waste cells; therefore, an external carbon source would probably be needed to support denitrification. However, the cooccurrence of an aerobic and anaerobic ammonia-oxidizing community with denitrifying bacteria provides the opportunity for advanced removal of nitrogen and organic carbon.