Mechanical-biological Treatment Plants Research Articles

Industrial optical sorting for marine plastic litter management

The aim of this study is to evaluate the possibility of incorporating marine litter from the coast into the management system of the non-selectively collected fraction of Municipal Solid Waste (MSW). With this purpose, the technical feasibility of automatic separation of marine plastic litter is evaluated, which would allow for subsequent recycling. This solution requires mechanical–biological-treatment plants (MBT) to be able to sort marine plastic litter. Poly (ethylene terephthalate) (PET) bottles constitute one of the most commonly reported types of marine plastics. Considering the sorting methods employed in MBT plants, optical sorting tests were performed with marine PET litter and compared with those for post-consumer municipal PET waste, in order to assess whether the current technology implemented in these plants would allow their automatic sorting. Results show that the separation efficiency of PET degraded under marine conditions and outdoors is very high, and close to that of post-consumer municipal PET waste. The separation efficiency by transparent colour for different types of PET materials evaluated is also very effective and similar to that obtained for separation by chemical composition. Therefore, the chemical differences observed would not affect the efficiency of automatic sorting of marine origin PET in a waste treatment plant.

LANDFILL MINING IN THE FRAMEWORK OF INTEGRATED WASTE MANAGEMENT: CASE STUDY OF AN ITALIAN LANDFILL

A remediation project involving landfill mining (LFM) was designed and is ongoing at the 40-year-old Villadose landfill in Rovigo, Italy. The original natural clay lining the bottom of the old landfill is being recovered and used as technical material. Meanwhile newly constructed landfill sectors, designed to contained more than four times more waste than previously are being filled with both excavated waste and fresh municipal solid waste. A laboratory scale experiment was conducted to simulate the expected landfill conditions and analyse the effects of different waste fractions on emissions. The fresh municipal waste although pretreated at a mechanical biological treatment plant shows a significant residual emission potential, in terms of TOC, and NH4. A landfill housing such quality of waste would not be expected to have achieved final storage quality by the end of its aftercare life. The joint disposal of this waste fraction and the substantially degraded excavated waste may contribute to shortening this timeline. This paper reports the landfill mining operation, an assessment of the emissions from the landfill simulation reactors and the implications for the expected landfill behaviour.

Analysis of the Prices of Recycling Byproducts Obtained from Mechanical–Biological Treatment Plants in the Valencian Community (Spain)

Municipal solid waste (MSW) management in Spain, particularly in the Valencian Community, heavily relies on mechanical–biological treatment (MBT) plants followed by landfill disposal. These MBT facilities utilize mechanical processes like shredding, screening, and sorting to segregate recyclables (metals, plastics, paper) from organic material and other nonrecyclables. While public funding supports these plants, private entities manage them through complex, long-term concession contracts. This structure restricts access to crucial data on the sale prices of the byproducts generated during MBT. Publicly available information on relevant company and administration websites is typically absent, hindering transparency surrounding byproduct revenue. This study addresses this gap by analyzing 2012’s available data on revenues obtained from byproduct sales following mechanical treatment at MBT plants within the Valencian Community and comparing them with Spanish national data. This research revealed a significant finding—the statistical distribution of average prices obtained from Ecoembes auctions in the Valencian Community mirrored the corresponding distribution for prices calculated from auctions conducted in other Spanish regions. This suggests a potential uniformity in byproduct pricing across the country. It has also been found that none of the analyzed price distributions exhibited a normal (Gaussian) distribution. The findings also highlight the need for alternative pricing models that move beyond simple averages and account for regional variations and outliers. As actual prices are not available after 2012, this lack of transparency poses a challenge in comprehensively evaluating the economic viability of MBT plants. Furthermore, it raises concerns regarding whether the revenue generated from byproduct sales reflects fair market value. Limited public access to this information can potentially indicate conflicts of interest or inefficiencies within the waste management system.

Odor control technologies for municipal solid waste mechanical biological treatment plant: a review

Odor control technologies for municipal solid waste mechanical biological treatment plant: a review

Syngas Purpose Pyrolysis-Gasification of Organic Fractions of MSW over Metal-Loaded Y-Zeolite Catalysts

The increasing environmental consideration and the growth of instability of the energy market call for methods that can process the organic fraction of municipal solid waste (OFMSW) into fuel instead of disposal. Due to the pyrolysis and gasification that are efficient procedures to achieve valuable products, gasification of OFMSW with different particle sizes and compositions was carried out in the presence of Ni and Ni-Ce-loaded Y-zeolite in a multizone tubular kiln reactor. During the experiments, 500°C was applied in the first reactor zone, while the 2nd zone was at an elevated temperature of 600°C or 900°C in the presence of steam. The combined pyrolysis and gasification experiments were also carried out without a catalyst with the same operating conditions. The feedstock was collected from the organic fraction of a Hungarian mechanical-biological treatment (MBT) plant and was separated into four different fractions based on particle size: <1 cm dry biomass and fine particles, 1-2 cm paper-rich, 2-6 cm paper and plastic-rich feedstocks, and <6 cm mixture of these fractions. During the experimental work, product yields; gaseous product composition; the ratio of H2/CO, CO2/CO, and CH4/CO; and lower heating value were determined in the function of feedstock composition, the applied temperature, and catalysts. It was found that the hydrogen content and H2/CO ratio of gaseous products were increased due to catalyst application and temperature elevation in the 2nd reactor zone. The addition of Ce to the Ni/Y-zeolite catalyst was advantageous in the case of hydrogen formation at a lower temperature (600°C). The hydrogen and methane content of products obtained from the catalytic pyrolysis-gasification of paper and plastic-rich OFMSWs on elevated temperatures were higher, which increased the lower heating value of those products. Based on the elemental analysis of the obtained solid residues, it was found that paper/plastic-rich feedstock released hydrogen and carbon with a higher extent. 1-2 cm feedstock-related solid residues had the highest H/C ratio which caused a 12.5-12.8 MJ/kg gross heating value. As a result, combined pyrolysis and gasification appear to be an efficient method to attain valuable outputs from OFMSW not only in gas but also in solid products.

Performance evaluation of trommel screens: A case study of a municipal solid waste treatment plant

The efficient and effective operation of trommel screens is essential for the economic and environmental sustainability of mechanical biological treatment (MBT) based solid waste treatment plants. The present study evaluated the performance of four trommel screens (aperture sizes of 80, 32, 16, and 4 mm) being used at the MBT plant of the Municipal Corporation Karnal, India. The performance of trommel screens was evaluated at a fixed speed of rotation and inclination angle. For optimum performance, trommel screens must be operated at a particular range of feed rates with regular cleaning every four hours of operation. The organic recovery achieved by 80 mm and 32 mm aperture size trommel screen was 26.95 % and 95.82 %. The organic quality improvement achieved by 80 mm and 32 mm trommel screens was 122.50 % and 108.89 %. The trommel screen's heating value improvement and energy recovery ranged from 70.68 % to 135.16 % and 28.27 % to 98.74 %, respectively. The oversized fractions of trommel screens of opening sizes 80 mm and 32 mm meet the fuel specification prescribed by the Indian Solid Waste Management Rules 2016. The trommel screen's Specific Energy Consumption (SEC) ranged from 0.63 kWh/tonne to 5.66 kWh/tonne. The learnings and outcomes of this study are helpful for designers, policymakers, operators of solid waste treatment plants, and researchers.

Acidogenic fermentation of biowaste coupled with nitrogen recovery using selective membranes to produce a VFA-rich liquid with a high C/N ratio

This research focuses on the production of a liquid stream rich in volatile fatty acids (VFAs) and low ammoniacal nitrogen content (<0.1 g N/L) from biowaste. The liquid stream was obtained by combining (i) mixed culture acidogenic fermentation to maximise VFA production and (ii) gas-permeable membrane (GPM) contactor to recover ammoniacal nitrogen. Three batch fermentation tests of biowaste collected in a full-scale mechanical-biological treatment plant provided high and stable VFA concentrations (37–39 g CODVFA/L). VFAs represented 73–81 % of the soluble chemical oxygen demand (sCOD) concentration, with a predominance of acetic, propionic and butyric acids. A highly specialized microbial community was observed in all batch tests, with Bacteroidota and Firmicutes as predominant phyla (>90 % of relative abundance). The GPM contactor recovered more than 99 % of the ammoniacal nitrogen in the fermentation liquid without VFA losses. The suitability of the produced fermentation liquid with a high C/N ratio for downstream applications was evaluated using biomethane potential tests (BMP) at different total ammonium nitrogen (TAN) concentrations (0.76–3.15 g N/L) and circumneutral pH. Despite achieving similar ultimate methane yields (279–314 NmL CH4/g CODfeed), lower TAN concentrations in the biowaste fermentation liquid improved anaerobic biodegradation kinetics, enhancing its potential applicability for methane production.

Composting and Mechanical Biological Treatment for Reducing Greenhouse Gas Emissions in Bizerte, Tunisia

This study seeks to develop effective solutions and strategies for waste management in the Tunisian municipality of Bizerte by addressing the urgent need for sustainable waste management practices in light of the global imperative to mitigate climate change. With a specific focus on reducing greenhouse gas emissions, this investigation aligns with Tunisia’s commitment to international agreements, including the Paris Agreement and the Global Methane Pledge. This study begins with an exploration of background information, followed by data collection and waste characterization to determine the current situation and to detect gaps that exist in terms of waste management in Bizerte municipality. Two scenarios are proposed as potential solutions for the municipality. The first examines a green waste composting facility with a 1000-ton yearly capacity, which has been operational since 2020. This study describes the compost production process and evaluates the quality of compost derived from green waste. This approach demonstrates its potential for delivering significant environmental and economic benefits. The second scenario delves into the implementation of a mechanical biological treatment (MBT) plant for sustainable handling of residual waste while contributing to a reduction in the municipality’s overall environmental footprint. Using the Sweet software, version 4.0.2, July 2022. this study quantifies the potential reduction in greenhouse gas emissions resulting from composting to be 3%, while the MBT achieves a reduction of 28%.

Experimental investigation of sorted municipal solid wastes producer gas composition in an updraft fixed bed gasifier

Three kinds of municipal solid waste (MSW) from mechanical biological treatment plants, i.e., Fraction after Drum Separator (FDS), Solid Recovered Fuel (SRF) and Plastic Packaging Mixture (PPM), were investigated. These samples were gasified in fixed-bed updraft gasifier under allothermal (800 °C) air supply conditions. Two different air equivalence ratios (ER), i.e., 0.15 ± 0.02 and 0.21 ± 0.04 were created to determine the influence on MSW producer gas properties. Derivative thermogravimetry analysis shows the same volatile release temperatures (330 °C, 500 °C) for all tested MSW kinds. Chromatography analysis of MSW producer gas revealed that the reduction of ER from 0.21 to 0.15 increase the heating value of combustible gases. PPM producer gas contains the highest H2 content – 11.39 %. The highest tar content (47.44 g/m3) was measured in SRF producer gas and primarily consisted of benzene, toluene, naphthalene, and acenaphthylene. The results of the sorted MSW gasification experiments show that the allothermal updraft fixed-bed gasifier is suitable for the production of producer gas that can be used in gas engines.

Refuse-derived fuel (RDF) production and analysis in mechanical-biological treatment (MBT) plant from the municipal solid waste

This study reports on the potential of refuse-derived fuels (RDF), which are produced from Sulaimani Municipal solid waste (MSW) using a biodrying process. Plastic, organic wastes, iron materials, and textiles were used in the formulation of RDF samples. A sample of raw MSW material was collected comprising of 40.6% organic, 29.3% plastic, 6.3% Textiles, 5.1% paper, 3.1% wood, 4.6% glass and stone, 5.2% iron containing materials, and 1.3% others. Physical and chemical properties of the RDF were investigated, including its moisture, ash, total chlorine, and heavy metal content with, calorific value. Based on the experimental results, RDF produced from MSW can be classified into net calorific and total chlorine content values NCV 2 and Cl 4 respectively. In accordance with the European Committee for Standardization (CEN standard), the results of this preliminary investigation of RDF samples made from non-biodegradable and non-recyclable MSW fractions, is necessary to analyze a larger pool of samples in order to project appropriate RDF energy-recovery-enhancing composition.

ComLife cycle assessment of municipal solid waste management systems in Ho Chi Minh City

Life cycle assessment (LCA) is a methodology used to evaluate the environmental impacts of municipal solid waste management (MSWM) systems. In this article, the authors apply the LCA method to investigate the best solution for the MSWM system in Ho Chi Minh city, supported by GaBi software. The LCA results from three scenarios of waste-to-energy, composting, and landfilling reveal their effects on global warming potential, acidification potential, eutrophication potential, and photochemical ozone creation potential. Overall, the results indicate that waste-to-energy and composting scenarios are competitive options.Waste-to-energy is environmentally friendly with a total environmental impact of 62%, which is only a quarter of the impact of landfilling. The composting scenario in the mechanical-biological treatment plant shows promising results of 81% reduction in environmental impact, while landfilling is the most polluting scenario with a total environmental impact potential of 257%. In this study, the scenarios are only investigated from an environmental perspective, for the economic and social impacts of waste management, other decision-making tools should be considered.

Regional management options for floating marine litter in coastal waters from a life cycle assessment perspective

PurposeDespite the increasing number of publications focusing on the management of marine plastic debris, most research is carried out using an upstream perspective, focused on sources and pathways of marine litter accumulation, as well as actions to prevent plastics from entering the environment. The aim of this paper is therefore to investigate a combination of waste management technologies for marine litter in order to inform decision-making on environmental impact hotspots at regional level.MethodA study of the North Sea German Bight identified existing technologies suitable for the collection and treatment of floating marine debris including, recycling of plastics, mechanical biological treatment (MBT), and landfilling. Processing data for reported marine litter compositions in the region are used to inform the modelling of a waste management strategic plan (WMSP) aimed at valorising various fractions. Hence, collected floating marine litter is separated into derelict fishing gear (DFG) and mixed marine litter (MML) which are sent respectively to a recycling plant for plastic granulates production and to an MBT plant for recovery of metals and electricity generation. Environmental impacts of the WMSP are evaluated using the Life Cycle Assessment methodology and compared with incineration considered as the prevalent waste scenario.Results and discussionAs partly expected, the LCA results reveal higher environmental performance in all impact categories for the incineration scenario. In particular, the WMSP contributes to Global Warming Potential (GWP) more than 10 orders of magnitude less than the incineration scenario. However, the breakdown of results related to the WMSP indicates the highest contribution to environmental impacts attributed to electricity and heat generation from refused-derived fuel and emissions at the combined heat and power plant, as well as electricity and diesel consumption. Lowest contributions are attributed to the recycling plant. The sensitivity analysis revealed low contributions to GWP if plastic debris such as DFG is diverted to recycling while toxicity-related categories are improved by efficient metal and energy recovery at the MBT plant.ConclusionFindings of this study show that no single treatment method is enough rather a combination of different treatment pathways should be designed considering the composition and properties of accumulated marine litter in a specific area. However, recovering plastic litter and diverting useful materials from waste-to-energy to recycling improve the environmental performance. Reviews suggest inclusion of valorisation treatment options in future WMSPs of marine litter such as plastic-to-fuel technologies.

An assessment of the current situation and recommendation of management scenarios for municipal solid waste management in Ho Chi Minh city

Ho Chi Minh city (HCMC) is currently facing a critical problem of the uncontrollable municipal solid waste (MSW). The most common waste disposal practice in the city is landfilling, but this is not a sustainable solution. From 2010 to 2022, the amount of waste generated has increased annually, from 6,000 tons/day to 9,200 tons/day, with an average growth rate of 6-8% per year. This study calculated the average emission factor of various districts in the city such as districts 1, 3, etc. at 0.83 kg/capita/day and district Binh Chanh, Cu Chi, etc. at 0.73 kg/capita/day and forecasted that the amount of waste will reach approximately 16,100 tons/day by 2050. Currently, 80-90% of collected MSW is landfilled, while only 10% is recycled. Composting and energy recovery practices are rarely used. This paper reviewed the current solid waste practice in HCMC and proposed four management scenarios to develop a sustainable solid waste management system. The first scenario is landfilling, which involves non-segregated waste disposal at the source. The second scenario is recycling, which involves segregating waste at the source for recycling, reuse, and waste reduction. The third scenario is composting, which requires using a mechanical-biological treatment plant for sorting, composting, and producing fuel from waste. The fourth scenario is waste-to-energy, which uses a waste incineration plant to generate energy from waste.

Proposal for Implementation of Extraction Mechanism of Raw Materials during Landfill Mining and Its Application in Alternative Fuel Production

New approaches to waste management and the demands of the circular economy have changed the management of landfills. Over time, the decomposition of buried waste primarily determines the amount of recyclable and combustible materials. This pilot study attempted to assess the feasibility of extracting and recovering energy-intensive raw materials from landfills by developing a waste extraction mechanism and creating a solid recovered fuel (SRF) production line for use as a replacement fuel in the cement industry. The proposed mechanism consisted of two stages. The first stage was recommended to be carried out on the landfill territory by screening out the fine fraction and extracting inert materials and bulky waste. The second stage should be on the mechanical biological treatment (MBT) plant’s territory by adding additional technological equipment to the MBT line. The productivity of the SRF production line was calculated and was 4.9 t/h. The mechanism proposed in the work was tested at the operating test site in Lithuania. The composition of Landfill Mined Residues (LMRs) was studied, and the energy potential of the studied part of the landfill was calculated, which was 196,700 GJ. It has been found that the SRF produced complies with the European Union (EU) standard and, according to its classification characteristics, belongs to class III and can be used as a replacement fuel in the clinker firing process. An environmental and economic efficiency assessment was conducted using SRF in the cement kiln. The calculation result showed that using 10% SRF as a replacement fuel for coal used in clinker firing at 2.51 t/h would save 1274 USD/h in coal costs. This use of SRF will emit 3.64 t/h CO2 and achieve a net savings of 1355 USD/h. The mechanism proposed in this work aimed at reducing waste in landfills by converting materials into energy resources will help achieve the circular economy’s goals.

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.

Use of a novel water separation process for the recovery of the mineral fraction from the stabilized organic fraction found in municipal waste.

Currently, the Stabilized Organic Fraction (SOF) 0-80 mm separated from the municipal waste stream is sent in its entirety to landfill in the mechanical-biological treatment plants operating in Poland. Such action does not align with the adopted EU strategy focused on waste management in the circular economy. This study aimed to assess the technical feasibility of the process of purification of mineral fractions with a grain size of 10-80 mm separated from SOF on a technological installation designed for glass recovery, built at the Marszów Plant. In terms of material, mineral fractions are a mixture of stones, rubble and glass, contaminated with various components, mainly organic. In 2020, the glass recovery installation was expanded with an innovative process of gravity separation to separate mineral fraction from SOF with the use of a jigging machine. A pulse jig used in the mining industry for coal enrichment processes was used for the first time in municipal waste management. The installation allows for the recovery of between 71.1 and 96.6% of mineral fractions contained in the input (84.8 ± 9.5% on average). The proportion of organics, plastics and other impurities in the waste is 4.1 ± 2.1% of the fraction mass. The process consumed water at an average rate of 0.34 ± 0.10 m3 tonnes-1 of treated waste and generated 0.26 ± 0.09 m3 tonnes-1 of wastewater. Electricity consumption averaged 1.20 kWh tonne-1 input.

Energy recovery options for the management of cellulose-based bio-plastics and mixed municipal solid waste

The incomplete degradation of bio-plastics waste is undermining the suitability of current anaerobic digestion (AD) and composting, opening up the exploration of new treatment routes, including mixed waste. Bio-plastics are treated with mixed waste in a mechanical-biological treatment (MBT) plant with the production of a dry fraction for incineration and a biologically stable one for landfill. An alternative post-treatment of the bio-stabilised waste based on AD is possible. It follows that the main goal of this study is to verify the feasibility of managing cellulose-based bio-plastics with mixed municipal waste, comparing the AD of the MBT plant outputs with the possible solution of incineration. Experimental lab tests have been carried out to describe the two processes, whose results were the basis for an economic analysis. The values of biochemical methane potential (BMP) and higher heating value (HHV) are used as an index for AD and incineration, respectively. Samples with and without bio-plastics were created; fresh and processed (7 and 14 days of biostabilization) samples were, thus, analysed. For AD, the fresh waste averaged 177 NmL CH4/gVS and a 22% and 33% decrease in BMP value was achieved after 7 and 14 days of biostabilization, respectively. Samples with and without bio-plastics revealed a similar trend. 7 and 14 days of biostabilization increased the HHV of fresh waste (18.01 J/kg) of 16.1% and 19.7%, respectively. Bio-plastics did not significantly change the HHV. The economic analysis revealed the suitability of both AD and incineration, irrespective of the presence of bioplastics.

Can the biological stage of a mechanical–biological treatment plant that is designed for mixed municipal solid waste be successfully utilized for effective composting of selectively collected biowaste?

Although the requirements for overall recycling rates can only be met when organic recycling is not overlooked, information is scarce regarding adaption to biowaste composting of existing mechanical–biological treatment (MBT) plants originally designed for stabilization of organic municipal solid waste (OFMSW). Thus, this study aimed to assess the suitability of the operational conditions in the biological part of a full-scale MBT plant now used for stabilization of OFMSW (working line: closed-module–covered-pile–open-pile) with a view to producing compost from biowaste. Temperatures above 75 °C were maintained in the closed module and reached again in the covered pile, indicating that intensive organic-matter mineralization occurred in both stages. In the covered pile, the temperature sharply decreased, indicating depletion of easily biodegradable organic matter. An aerobic 4-day respiration test (AT4) value below 10 mg O2/g dry matter, the cut-off for assessing compost stability, was obtained after 8 weeks. However, a high content of humic substances (HS), reflecting compost maturity, was obtained only after 120 days. The increase in HS content proceeded in two phases. In the first phase (45–84 day), the rate constant and the rate of HS formation were lower than in the second phase (84–120 day) (0.072 vs. 0.087 day−1, 1.97 vs. 3.06 mg C/(g organic matter·d)). All the above-mentioned indicators and the nutrient content (N, P, K, Mg, Ca) in the compost indicates that the biological stage of an MBT plant can successfully treat biowaste. This is in accordance with a circular economy and will contribute to increasing recycling rates.

Optimization of the Biostabilization Process of an Italian Mechanical–Biological Treatment Plant to Account for Changes in Waste Composition

In this paper, we present a case study on the optimization of the biostabilization process of an Italian mechanical–biological treatment (MBT) plant to account for changes in feed waste composition related to a progressive increase in separate collection of MSW fractions, biowaste in particular. After ten years of operation (2009–2019), a decrease of the stabilization degree of the output material of the plant was detected, with Dynamic Respiration Index (DRI) values above the established limit of 1,000 mgO2/kgVS/h (average values of 4,000 mgO2/kgVS/h determined weekly for eight weeks). The investigations carried out in 2019 on the waste samples feeding the MBT plant showed that paper and plastic materials constitute around 75% of the input waste to the two aerobic bioreactors of the MBT plant, against 55% at the start-up (2009). Furthermore, the airflow rates and the moisture content analyzed weekly for eight weeks in the bioreactors resulted below the optimal values suggested in the literature. To improve the performances of the biostabilization process, a series of modifications were implemented in the plant. The main modification involved the primary mechanical treatment by varying the mesh size of the screens to 50 mm circular holes mesh. Furthermore, the configuration of the aerobic bioreactors was changed by placing the two bioreactors in series (instead of the previous configuration in parallel) and using a screening unit (25 mm) between the two bioreactors instead of at the end of the process. In this way, the residence time of the materials in the aerobic treatment was enhanced from 16 days with the previous configuration to 27 days. Together with an increase of the airflow rates of around 40% and a water supply of approximately 10% in the bioreactors, these modifications allowed to achieve the desired stability of the output waste, with DRI values below 1000 mgO2/kgVS/h.Graphical

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.