Mixed Waste Research Articles

Effect of Extrusion Temperature on Microstructure and Mechanical Properties of Mg–Al–Zn Alloy Prepared by Solid‐State Recycling of Mixed Waste Chips

The recycled Mg–Al–Zn alloys are successfully fabricated through solid‐state recycling of mixed waste chips, including cold pressing and hot extrusion. The effects of extrusion temperature on the microstructure evolution, slip mode, tensile properties, and hardness are studied. The homogeneous fine dynamic recrystallization (DRXed) grains with an average grain size of less than 13.1 μm can be obtained at four different extrusion temperatures (250, 300, 350, and 400 °C). The average grain size of the DRXed grains continuously increases with the rising extrusion temperature. However, the yield strength (YS), ultimate tensile strength (UTS), and elongation to failure (EL) of the recycled alloys increase first and then decrease. The recycled Mg–Al–Zn alloys at 350 °C demonstrate excellent mechanical properties with the YS of 134.6 MPa, UTS of 286.2 MPa, EL of 7.4%, and Vickers hardness of 75.2 HV, respectively. In addition, the slip mode is transformed from the previous basal slip to the coactivation of multiple slips composed of the basal slip, prismatic slip, and pyramidal slip with the rising extrusion temperature.

Waste management systems in the context of sustainability

The present paper deals with waste management systems in the context of sustainability in selected municipalities. The author's team aimed to find the key waste groups according to the classification groups that have a major impact on the volume of waste and the cost of the system, thus facilitating management decision-making. In order to optimise the management of the entire waste management system from the perspective of the statutory municipality, it was first necessary to reduce the original list of 53 waste items to a significantly smaller number. With the help of waste management experts, criteria for reducing the number of waste input items were defined, resulting in a reduced statistical sample of 27 items. Each item is quantified by the amount of waste per year and the cost of the system per year. The mathematical apparatus consisted primarily of calculating average values as well as marginal slopes of waste quantity and cost. The interrelationships between waste groups were graphically recorded in perceptual maps. The individual analyses were carried out primarily for a statutory city, with secondary comparisons of the results with smaller towns and small villages. The analytical procedures verified that the catalogue of basic components of mixed municipal waste can be significantly reduced for decision-making in secondary resource management. The amount of waste selected in each group significantly impacts the cost of the whole waste management system. Of the original 15 waste groups, only three groups appear to be the main ones. The municipal waste group even has a decisive influence on both the quantity of waste and the cost of the whole system. Thanks to these findings, from the point of view of both the manager and the management of the statutory city, it is possible to focus on this core group, which contains the 13 original catalogue items.

Thermochemical Valorization of Plastic Waste Containing Low Density Polyethylene, Polyvinyl Chloride and Polyvinyl Butyral into Thermal and Fuel Energy

Pyrolysis is a promising technology for transforming waste plastics (WPs) into high-value products. In the near future it will play a key role in the circular economy, as a sustainable and environmentally friendly method of managing this waste. Although the literature reports on the pyrolysis of plastics, it is focused on pure polymers. On the other hand, the state-of-the-art knowledge about the pyrolysis of mixed and contaminated WPs is still scarce. Industrial waste processing usually uses polymer mixtures containing various impurities that influence the pyrolysis process during chemical WPs recycling. In the paper the pyrolysis of three types of WPs: low density polyethylene (LDPE), polyvinyl chloride (PVC) and polyvinyl butyral (PVB) from repeated mechanical recycling of plastics, as well as their binary and ternary mixtures, is considered. The influence of particular components on the pyrolysis process is analyzed. The aim is to determine synergistic behavior of the mixtures during the pyrolysis process, which is important for increasing the efficiency and quality of the obtained bioproducts. Methods such as thermogravimetric (TG/DTG) analysis coupled with Fourier transform infrared spectroscopy (FTIR) and mass spectroscopy (MS) are used. The variations in the initial and final temperature of pyrolysis, mass loss and mass loss rate are determined. The content of PVC significantly lowers the initial temperature and mass loss and increases the final temperature. The pyrolysis of the considered mixtures shows a noticeable synergism—in the initial stage of pyrolysis up to a temperature around 450 °C, the mass loss is accelerated compared to what is predicted by simple superposition. The inhomogeneity of the mixtures as well as the waste origin causes a significant variation in the activation energy. Three main conclusions are obtained: (i) if the waste does not contain PVC, the pyrolysis is nearly complete at a temperature around 500 °C at a heating rate of 10 °C/min, whereas PVC is not fully processed even at 995 °C; (ii) the synergistic effects affect significantly the pyrolysis process by accelerating some steps and lowering the activation energy; and (iii) the presence of PVC noticeably lowers the temperature of the first stage of PVB pyrolysis. The investigation results prove that chemical recycling of mixed LDPE, PVC and PVB waste can be an effective method of plastic waste management.

Correction: Production of hydrogen and methanol from mixed plastic waste: Potential for the European Union

Correction: Production of hydrogen and methanol from mixed plastic waste: Potential for the European Union

Persepsi dan Partisipasi Masyarakat Terhadap Pengelolaan Sampah Rumah Tangga melalui TPS 3R Sulur Berkah dan Makmur Jaya di Kota Jambi

One of the waste reduction efforts carried out by the Jambi City Government is the provision of 3R TPS. The reduction target set by the government until 2030 is 30%. Community participation is really needed to reduce and/or handle waste in an environmentally sound manner, including efforts to sort waste from the source. Waste sorting that is not carried out at the source can result in mixed waste and reduce the economic value of recycled waste. Apart from that, sufficient human resources and a long time are needed to sort the waste at TPS 3R, while the residue must be immediately transported to the TPA so as not to cause a bad smell and discomfort for local residents. Internal conflicts at TPS 3R regarding financial management and several other things resulted in TPS 3R not functioning according to its function. The aim of this research is to examine community perceptions and participation in household waste management through TPS 3R Sulur Berkah and Makmur Jaya in Jambi City. The research method used is descriptive analysis and the main data collection tool is a questionnaire. The research instrument uses a Likert scale with 4 (four) response options. The research results show that 100% of respondents have a positive perception of household waste management through TPS 3R. However, only 62% have high participation in household waste management, the remaining 38% of respondents have low participation.

Production of thermostable recombinant cutinase using mixed food waste: A sustainable approach toward environmental remediation

Recently, there has been a significant surge in the utilization of single-use plastics. Cost-effective degradation of plastics is imperative to reduce the ecological burden. This study explores the overproduction and characterization of a PET (Polyethylene terephthalate) a degrading enzyme, cutinase, in the E. coli BL21 (DE3) expression system. Furthermore, this research delves into the utilization of mixed food waste (MFW) as a sustainable substrate for the production of Cutinase, replacing commercial glucose. The newly isolated strain, Aspergillus terreus, showed the highest glucoamylase activity of 76.10 ± 3.10 U/g. The enzymatic hydrolysis of mixed food waste resulted in 50 ± 0.4 g/L of glucose, used as feedstock for cutinase production. The crude enzyme activity was evaluated to be 11.64 U/mg, and a further 14.11-fold purification was achieved through IMAC. The purified recombinant enzyme showed its maximum activity at 70℃ and pH 7. The metal ion Na+ increased the enzyme activity by 26 % while Zn+2 significantly inhibited the same (47 % inhibition); other ions had little or no effect. Taguchi’s optimization of five variables showed that the concentration of food waste hydrolysate has the maximum impact on enzyme production. The treatment of commercially available PET bottles using the purified enzyme showed characterizable surface degradation effects. This is the first time food waste hydrolysate was used as a sole carbon source to produce recombinant cutinase. This approach can potentially pave the way for sustainable biorefinery and waste management.

Chemical recycling of mixed textile waste.

Globally, less than 0.5% of postconsumer textile waste is recycled, with the majority incinerated or ending up in landfills. Most postconsumer textiles are mixed fibers, complicating mechanical recycling due to material blends and contaminants. Here, we demonstrate the chemical conversion of postconsumer mixed textile waste using microwave-assisted glycolysis over a ZnO catalyst followed by solvent dissolution. This approach electrifies the process heat while allowing rapid depolymerization of polyester and spandex to their monomers in 15 minutes. A simple solvent dissolution enables the separation of cotton and nylon. We assess the quality of all components through extensive material characterization, discuss their potential for sustainable recycling, and provide a techno-economic analysis of the economic feasibility of the process.

Consequential life cycle assessment of demolition waste management in Germany

ContextBulk mineral waste materials such as construction and demolition waste are Germany’s largest waste stream. Despite the availability of high-quality recycling pathways such as road base layers, waste concrete is predominantly recycled into lower-quality recycling pathways like earthworks or unbound road construction. This is due to low demand for recycled aggregates in road base layers and frost protection layers, especially in public procurement.PurposeThis study assesses the environmental consequences of increasing high-quality recycling of waste concrete in the near future to provide decision support for public procurement in Germany. The focus lies on climate change due to its importance for decision-makers. However, 17 other impact categories were assessed to avoid problem shifting.MethodsLife cycle assessment (LCA) is applied with background data from ecoinvent 3.9.1. Impact assessment was conducted at midpoint level using IPCC 2021 and ReCiPe Midpoint (H). Foreground data were taken from literature and expert interviews. In line with the goal of this LCA, a consequential modeling approach was followed to account for changes in the material flow system. Substitution creates a cascade effect previously omitted in consequential LCA studies, in which lower quality recycling materials replace higher quality recycling materials in their respective utilization pathways.Results and discussionIncreasing the high-quality recycling of waste concrete into road base layers causes a reduction in environmental impacts for all 18 impact categories, as it replaces natural aggregate and avoids backfilling of mixed mineral waste and excavated earth through substitution effects. Transport distances and ferrous metal recovery were identified as hot spots. Sensitivity analyses show that only transport is a significant issue.ConclusionIncreasing the high-quality recycling of waste concrete in Germany is recommended in terms of environmental impacts. Lower-quality recycling is environmentally feasible only in cases where the avoided transport distances for natural aggregates and backfilling are significantly lower than the additional transport distances for high-quality recycling.

Supercritical Water Liquefaction of Mixed Waste Polystyrene, Polypropylene, and Polyethylene for Production of High Yield Oils.

Supercritical water liquefaction of different plastic wastes has been investigated under high-temperature and high-pressure conditions. The supercritical water liquefaction of commonly used plastic types, comprising polystyrene (PS), polypropylene (PP), and low-density polyethylene (LDPE) as well as their mixtures, is reported. The experiments were carried out at varying feedstock-to-water ratios with a residence time of 60 min under supercritical water reaction conditions. The process produced high oil yields of over 97 wt %, with the highest yields obtained at a plastic:water ratio of 1:3; at higher levels of input water, the yield of oil decreased slightly. The gas phase mainly consisted of light hydrocarbons such as methane, ethane, propane, and butane, with propane found to be the most abundant gas component. Aromatic hydrocarbons and alicyclic hydrocarbons were the major products in the product oil from the supercritical water liquefaction of polystyrene and polypropylene, whereas alkanes were predominant in the oil obtained from LDPE. Analysis of the oil obtained from binary (1:1) and ternary (1:1:1) plastic mixtures showed it exhibited aromatic hydrocarbons as the major constituent, indicating synergistic interaction. It was found that the incorporation of PP in the mixture facilitated the production of cyclic compounds and suppressed the production of alkanes. Supercritical water liquefaction offers an effective solution to plastic pollution, producing valuable products without the need for catalysts.

Analysis of Waste Utilization of Refuse Derived Fuel (RDF) Into Briquettes for Steam Power Electric Generation

Waste in Indonesia reaches 65.2 million tons/year, dominated by organic and inorganic waste. Around 36% of the total waste has not been managed properly, including 4K1P waste (paper, wood, cloth, rubber, and plastic), which is flammable and can be made into RDF briquettes using the pyrolysis method and paraffin adhesive which will used three variations of raw materials, namely from organic, inorganic and mixed waste. The quality of the three briquettes was compared based on calorific value, ash content, water content, and PLTU fuel requirements if used as fuel for a 7.5 MW capacity PLTU. The weight of the initial raw material for briquettes is 2 kg which produces 875 grams of paper carbon charcoal, 648 grams of wood, 1.09 kg of plastic, 856 grams of cloth, and 1.16 kg of rubber, resulting in 10 pieces of organic, inorganic and mixed briquettes each. The test results show that inorganic briquettes have the best quality with a calorific value of 8,075.92 cal/g, water content of 1.75%, and ash content of 10.84%, where the calorific value and water content meet SNI-01-6235-2000. The minimum fuel requirement for a PLTU using RDF briquettes is inorganic briquettes, namely 3.05 tonnes/hour with an annual requirement of 26,205.6 tonnes/year. It can be concluded that inorganic briquettes have the best quality and require the least amount of fuel to be used in PLTU.

Forecasting the waste production hierarchical time series with correlation structure

AbstractContinuous increase in society’s prosperity causes overwhelming growth of the produced municipal solid waste. Circular economy initiatives help to solve this problem by creating closed production cycles, where the produced waste is recycled, or its energy is recovered. An embedment of such principles requires implementation of new waste management strategies. However, these novel strategies must be based on the accurate forecasts of future waste flows. Municipal solid waste production data demonstrate behavior of hierarchical time series. Among all possible approaches to hierarchical times series forecasting, this article is focused on the reconciliation of the base waste generation forecasts. The novel method, that is based on the game-theoretically optimal reconciliation of hierarchical time series, is presented. The modified approach enables to incorporate interdependencies between time series using correlation matrix and to obtain the forecasts corresponding to the unique solution of the optimization problem. The potential of the proposed abstract approach is demonstrated on the waste production data of paper, plastics (both primarily sorted by households), and mixed municipal solid waste from the Czech Republic.

Stapler Strategies for Upcycling Mixed Plastics.

Mechanical recycling is one of the simplest and most economical strategies to address ever-increasing plastic pollution, but it cannot be applied to immiscible mixed plastics and suffers from property deterioration after each cycle. By combining the amphiphilic block copolymer strategy and reactive compatibilization strategy, we designed a series of stapler strategies for compatibilizing/upcycling mixed plastics. First, various functionalized graft copolymers were accessed via different synthetic routes. Subsequently, the addition of a very small amount of stapler molecules induced a synergistic effect with the graft copolymers that improved the compatibility and mechanical properties of mixed plastics. These strategies were highly effective for various binary/ternary plastic systems and can be directly applied to postconsumer waste plastics, which can increase the toughness of mixed postconsumer waste plastics by 162 times. Most importantly, it also effectively improved the impact resistance, adhesion performance, and three-dimensional (3D) printing performance of mixed plastics, and permitted the recycling of plastic blends 20 times with minimal degradation in their mechanical properties.

Characterization, recyclability, and significance of plastic packaging in mixed municipal solid waste for achieving recycling targets in a Swedish city

About 60% of plastic packaging in Sweden ends up in mixed municipal solid waste (MSW), which is incinerated with energy recovery. This status quo presents a missed opportunity to meet ambitious recycling targets. This study aims to provide a detailed characterization of plastic packaging in mixed MSW to assess its potential for recycling and its significance in improving the overall recycling rate. A case study involving a Swedish city was conducted wherein a sample of 5500 kg of mixed MSW from 920 households was characterized. From the 31% recycling rate, improvement of up to 59% can be achieved by diverting this misplaced plastic packaging into the existing recycling system. An additional 9% increase remains challenging to achieve due to the occurrence of non-recyclable attributes like black and multilayer packaging. The highlighted key enabler is the combination of correct household waste separation behavior and the establishment of mechanical sorting facilities to recover plastic waste from mixed MSW. These recycling potentials and associated challenges are discussed in the context of Sweden's ongoing efforts across the plastic packaging value chain. Furthermore, the importance of extended waste characterization is emphasized as a tool for identifying recycling potentials and monitoring the effectiveness of measures in enhancing circularity and resource-efficiency.

Driving selective upcycling of mixed polyethylene waste with table salt

Advanced recycling offers a unique opportunity for the circular economy, especially for mixed and contaminated plastics that are difficult to recycle mechanically. However, advanced recycling has barriers such as poor selectivity, contaminant sensitivity, and the need for expensive catalysts. Reported herein is a simple yet scalable methodology for converting mixed polyethylene (high-density and low-density polyethylene recycled polyethylene) into upcycled waxes with up to 94% yield. This high yield was possible by performing the reaction at a mild temperature and was enabled by using inexpensive and reusable table salt. Without table salt, in otherwise identical conditions, the plastic remained essentially undegraded. These upcycled waxes were used as prototypes for applications such as water- and oil-resistant paper, as well as rheology modifiers for plastics. Their performance is similar to that of commercial wax as well as rheology modifiers. A preliminary economic analysis shows that the upcycled waxes obtained by this table salt-catalyzed approach offer three times more revenue than those reported in the literature. This pioneering discovery opens the door for a circular economy of plastics in general and polyolefins in particular.

Comprehensive study on social, compositional and thermal aspects of household solid waste for waste-to-energy potential estimation in Tashkent city

The management of household solid waste (HSW) has emerged as a key issue in developing nations. A critical analysis of the physical and chemical components of MSW management and infrastructure is necessary to address current socioeconomic issues. According to the World Bank projections, the annual global generation of solid waste from municipalities is expected to reach 2.59 billion tons by 2030 and and 3.40 billion tonnes by 2050. Inadequate handling of waste products frequently results in harm to the environment, the spread of diseases, and the generation of greenhouse gases, all of which have contributed to climate change and global warming. The waste-to-energy (WtE) strategy, which drastically reduces waste volume and produces renewable energy, has been adopted by a number of countries to address these issues. In this study, the social, compositional, and thermal aspects of household solid waste in a typical Tashkent District were studied. A Social survey was conducted to investigate residents’ behavior towards waste sorting. The survey was conducted in the Uchtepa district of Tashkent, Uzbekistan. The composition of household solid waste was studied to explore the fractional distribution of the waste in the area. The American Society for Testing and Materials (5231–92) and European PN-EN standards were used for sampling, sorting, and for the rest of the analyses. Subsequently, proximate and ultimate analyses were performed to better understand combustion properties. A high heating value was identified to estimate the energy generation potential of household solid waste. Social survey results showed that the waste generated in the apartments will be discarded either on the day of its generation or the maximum after three days. Overall, 52 % of the respondents chose to sort their waste, compared to 48 % who had no real desire to separate their household solid waste. Food waste, plastics, and paper constituted 70 % of the total waste generated in the district. The mixed waste sample had a high heating value of 23.87 Mj/kg. The analysis revealed an energetic potential of HSW generated from the landfill as thermal energy.

Tailored HZSM-5 catalyst modification via phosphorus impregnation and mesopore introduction for selective catalytic conversion of polypropylene into light olefins

The waste polyolefin composition varies regionally due to different sorting technologies, emphasizing the necessity for a robust catalyst capable of selectively converting pyrolysis vapors into valuable light olefins while maintaining stability. HZSM-5, a microporous catalyst, efficiently cracks polyethylene (PE) pyrolysis vapors rich in linear aliphatics. However, polypropylene (PP) pyrolysis typically yields branched olefins, potentially hindering effectiveness of HZSM-5 due to mass transfer constraints and coke blockage in micropores. This study modifies HZSM-5 through phosphorus impregnation, mesopore introduction, and steam treatment to evaluate the impact of acidity, pore size, and surface modifications on catalyst stability and light olefin selectivity during PP pyrolysis vapor cracking. Subsequent experiments reveal the superior stability of modified catalysts. Phosphorus-modified (P-HZSM-5ss) and mesoporous phosphorus-modified (P-mesoHZSM-5ss) catalysts retain 72 % and 80 % of their initial activity after 150 runs, respectively, while the parent HZSM-5 experiences a rapid 44 % activity loss. P-mesoHZSM-5ss demonstrates the highest light olefin selectivity (63 wt%) after 150 runs, attributed to improved accessibility of branched olefinic products to active sites within catalyst pores. Further optimization achieves exceptional light olefin selectivity of 84 wt% at 117 ms contact time and 550 °C, surpassing maximum selectivity of the parent catalyst. Comparative analyses of PP, PE, and mixed polyolefinic waste pyrolysis vapor cracking revealed the influence of polyolefin type on optimal operational conditions, stressing the need for flexibility in operating conditions to scale up the proposed polyolefin recycling method. This study highlights the potential of tailored catalyst modifications and process optimization to efficiently convert PP into valuable light olefins, advancing sustainable polyolefin recycling technologies.

Lifecycle Assessment of Strategies for Decarbonising Wind Blade Recycling toward Net Zero 2050

The wind energy sector faces a persistent challenge in developing sustainable solutions for decommissioned Wind Turbine Blades (WTB). This study utilises Lifecycle Assessment (LCA) to evaluate the gate-to-gate carbon footprint of high-profile disposal and recycling methods, aiming to determine optimal strategies for WTB waste treatment in the UK. While this article analyses the UK as a case study, the findings are applicable to, and intended to inform, recycling strategies for WTB waste globally. Long-term sustainability depends heavily on factors like evolving energy grids and changing WTB waste compositions and these must be considered for robust analysis and development strategy recommendations. In the short to medium term, mechanical recycling of mixed WTB waste is sufficient to minimise Global Warming Potential (GWP) due to the scarcity of carbon fibre in WTB waste streams. Beyond 2040, carbon fibre recycling becomes crucial to reduce GWP. The study emphasises the importance of matching WTB sub-structure material compositions with preferred waste treatment options for the lowest overall impact. Future development should focus on the extraction of carbon fibre reinforced polymer (CFRP) structures in WTB waste streams, commercialising large-scale CFRP structure recycling technologies, establishing supply chains, and validating market routes for secondary carbon fibre products. In parallel, scaling up low-impact options, like mechanical recycling, is vital to minimise WTB waste landfilling. Developing viable applications and cost-effective market routes for mechanical recyclates is necessary to displace virgin glass fibres, while optimising upstream recycling processes based on product requirements.

Efficient and Robust Dynamic Crosslinking for Compatibilizing Immiscible Mixed Plastics through In Situ Generated Singlet Nitrenes.

Creating a sustainable economy for plastics demands the exploration of new strategies for efficient management of mixed plastic waste. The inherent incompatibility of different plastics poses a major challenge in plastic mechanical recycling, resulting in phase-separated materials with inferior mechanical properties. Here, this study presents a robust and efficient dynamic crosslinking chemistry that effectively compatibilizes mixed plastics. Composed of aromatic sulfonyl azides, the dynamic crosslinker shows high thermal stability and generates singlet nitrene species in situ during solvent-free melt-extrusion, effectively promoting C─H insertion across diverse plastics. This new method demonstrates successful compatibilization of binary polymer blends and model mixed plastics, enhancing mechanical performance and improving phase morphology. It holds promise for managing mixed plastic waste, supporting a more sustainable lifecycle for plastics.

Characterization and impact of oxygenates in post-consumer plastic waste-derived pyrolysis oils on steam cracking process efficiency

Mechanical recycling of mixed packaging waste has limitations due to challenging separation into pure polyolefin streams which often leads to low quality recyclates. A solution to improve overall recycling rates of polyolefins is chemical recycling. One promising approach is conversion into a liquid product via pyrolysis and subsequent steam cracking of the pyrolysis oil towards light olefins. In this study, distilled fractions of pyrolysis oils from PE and PP-rich waste were characterized via GC × GC including normal and reversed-phase column configurations with a special focus on oxygenated components. Distilled pyrolysis oils were subsequently steam cracked in 20/80 weight‐based blends with conventional naphtha. All pyrolysis oil samples contained substantial amounts of oxygenates (1–10 wt%) which poses a huge challenge for steam cracker feedstocks and it was found that ketones are the most prevailing oxygenate group. Steam cracking experiments showed slightly increased ethylene yields of the blends compared to pure fossil naphtha, with the PE-derived samples outperforming the PP-derived samples. Furthermore, diesel-range distillation cuts led to higher formation of heavy products compared to the naphtha-range cuts. Increased formation of CO was observed as a consequence of the substantial oxygen contamination which can be a deal-breaker in industrial steam crackers. This work shows that distilled pyrolysis oils with conventional naphtha are promising steam cracking feedstocks if intermediate processing steps are performed to remove the oxygenates and other impurities using, for instance, hydrotreatment. With the findings of this work, such upgrading processes can be designed in a more effective way.

Strontium leaching from municipal waste subjected to incineration

The aim of the study was to determine the content and leachability of Sr in ashes obtained through combusting municipal waste in household furnaces. The waste had been collected as a mixed stream and as separate fractions (i.e. furniture, sponges, waste paper, PCV packaging, plastic-coated paper cartons, imitation leather, rubber, textiles and polystyrene). Using single-step chemical extractions, (HCl + HNO3, H2O, 0.01 M CaCl2, 0.1 M CH3COOH), we determined the total content of Sr (TC) and proportions of the following fractions: water-leachable, phytoavailable and easily soluble and bound to carbonates. We also analyzed the effect of reducing pH in the extraction solutions on St leachability from the study material. The study showed that Sr concentration in ash generated from the combustion of conventional fuels, alternative fuels and municipal waste ranged from 114 to 1006 mg/kg. The largest amounts of Sr were found in ash generated from the combustion of alternative fuels (coal pellets 488–1006 mg/kg), conventional fuels (hard coal 430–670 mg/kg) and mixed waste (237–825 mg/kg). The most mobile fraction of Sr (water-leachable) comprised from 1.3% to nearly 91% TC; the phytoavailable fraction and the ion-exchange and carbonate-bound fraction comprised 3–92% TC and 9–72% TC, respectively. We also found that the greatest pH reductions do not always entail the greatest amounts of extracted Sr. A much more significant factor in this respect is the mineral and chemical composition of primary materials, which can buffer changes in pH. The Risk Assessment Code (RAC) values pointed to a varied environmental risk and the highest RAC values (> 70) were found for coal pellets, wood pellets, straw, rubber and plastic containers for mixed oils.