Waste-to-energy Plants Research Articles

Unlocking Value from Municipal Solid Waste Incineration Ash: Electrochemical and Chemical Approaches for Materials Recovery

Nowadays, in the U.S. more than 6.6 million tons of hazardous solid residue, called municipal solid waste incineration (MSWI) ash is annually generated in waste-to-energy (WTE) plants for producing electricity and reducing landfill volume. This ash cannot be further utilized for beneficial applications, so it is mostly buried and has a negative value with the cost of a disposal fee. Moreover, the economics of MSWI is challenged by the decreasing cost of renewableelectricity. However, WSWI ash represents a unique opportunity for valuable element recovery, with the embodied value ranging from $100-400/tonne. We propose an electrochemical and chemical process for mining MSWI ash that utilizes electricity from the WTE plant toelectrolytically produce acid and base streams for materials recovery and refining. We establish a sequential process of electrochemical extraction and chemical precipitation, and successfully recover Cu, Pb, Zn, Mg, Ca, Fe, Al, with a purified silica co-product. Recovery of >90% of the targeted elements at purities >90% is demonstrated. The industry-scale technoeconomic analysis shows our proposed technology will realize the possibility of extracting the embodied mineral value with net positive returns that significantly exceed the combined value of WTE electricity sales and landfilling cost.

Novel approach to CO2 capture: Improving the hybridization between membranes and calcium-looping

A 70 MWe Waste-to-Energy (WtE) plant is modelled to design and evaluate the performance of two CO2 capture strategies: a standalone Calcium-Looping (CaL) process (Case 1) and an innovative hybrid system combining CO2-selective polymeric membranes with CaL (Case 2). The latter involves a CO2 pre-enrichment process facilitated by a pressure gradient within the membrane module, which enhances the CaL performance. The heat released in the CaL process is recovered within a Combined Cycle configuration, taking advantage of the pressurized stream exiting the membrane modules. Comparative analysis reveals that the hybrid system (Case 2) significantly outperforms the standalone CaL process (Case 1) in efficiency and economic viability. With a baseline LCOE for a standard WtE plant without CO2 capture at 150 €/MWh, the LCOE for Cases 1 and 2 are 294 €/MWh and 243.21 €/MWh, respectively. The hybrid system achieves a thermoelectric efficiency of 25.25 %, reducing the energy penalty to 3.32 %points compared to Case 1, which results in 9.49 %points. Furthermore, the cost of avoided carbon emissions is significantly lower in Case 2 (83.82 €/ton CO2) than in Case 1 (155.12 €/ton CO2), underscoring the hybrid system’s superior potential for efficient CO2 capture in WtE applications.

Incineration-source fingerprints and emission spectrums of dioxins with diagnostic application

Despite increasing waste-to-energy (WtE) capacities, there remain deficiencies in comprehension of 136 kinds of tetra- through octa-chlorinated dibenzo-p-dioxin and dibenzofurans (136 PCDD/Fs) originating from incineration sources. Samples from twenty typical WtE plants, encompassing coal-fired power plants (CPP), grate incinerators (GI), fluidized bed incinerators (FBI), and rotary kilns (RK), yielded extensive PCDD/F datasets. Research was conducted on fingerprint mapping, formation pathways, emission profiles, and diagnostic analysis of PCDD/Fs in WtE plants. Fingerprints revealed a prevalence of TCDF, followed by PeCDF, while CPP and RK respectively generated more PCDD and HxCDD. De novo synthesis was the predominant formation pathway except one plant, where CP-route dominated. DD/DF chlorination also facilitated PCDD/F formation, showing general trends of FBI > GI > CPP > RK. The PCDD/F emission intensities emitted in air pollution control system inlet (APCSI) and outlet (APCSO) followed the statistical sequence of RK > FBI > GI > CPP, with the average I-TEQ concentrations in APCSO reaching 0.18, 0.08, 0.11, and 0.04 ng I-TEQ·Nm−3. Emission spectrum were accordingly formed. Four clusters were segmented for diagnosis analysis, where PCDD/Fs in GI and FBI were similar, grouped as a single cluster. PCDD/Fs in CPP and RK demonstrated distinctive features in TCDD, HxCDD, and HxCDF. The WtE plants exceeding the limit value tended to generate and retain fewer TCDD and TCDF yet had higher fractions of HxCDD and HxCDF. The failure of APCS coupled with the intrinsic source strength of PCDD/Fs directly led to exceedance, highlighting safe operational practices. This study motivated source tracing and precise evaluation of 136 PCDD/Fs based on the revealed fingerprint profiles for WtE processes.

Distribution of Per- and Polyfluoroalkyl Substances (PFASs) in a Waste-to-Energy Plant─Tracking PFASs in Internal Residual Streams.

Per- and polyfluoroalkyl substances (PFASs) constitute a diverse group of man-made chemicals characterized by their water- and oil-repellent properties and persistency. Given their widespread use in consumer products, PFASs will inevitably be present in waste streams sent to Waste-to-Energy (WtE) plants. We have previously observed a subset of PFASs in residual streams (ashes, treated process water, and flue gas) from a WtE plant. However, the transport and distribution of PFASs inside the WtE plant have remained unaddressed. This study is part of a comprehensive investigation to create a synoptic overview of the distribution of PFASs in WtE residues. PFASs were found in all sample types except for boiler ash. The total levels of 18 individual PFASs (Σ18PFASs) in untreated flue gas ranged from 5.2 to 9.5 ng m-3, decreasing with 35% ± 10% after wet flue gas treatment. Σ18PFASs in the condensate ranged from 46 to 50 ng L-1, of which perfluorohexanoic acid (PFHxA) made up 90% on a ng L-1 basis. PFHxA was also dominant in filter ash, where Σ18PFASs ranged from 0.28 to 0.79 ng g-1. This study shows that flue gas treatment can capture some PFASs and transfer them into WtE residues.

Techno-environmental analysis to valorize the secondary energy resources from refuse-derived fuel-based waste to energy plant.

The present study quantifies the environmental and sustainability impacts associated with municipal solid waste management (MSWM) in India which plays a vital environmental issue in recent times. The upsurge in population has resulted in massive waste generation, leading to a concerning rise in the level of greenhouse gas (GHG) emissions. Therefore, the sustainable management of MSW has been discussed and highlights the conversion of MSW into refuse-derived fuel (RDF) to identify its potential for generating electricity in waste-to-energy (WtE) plants. The life cycle assessment (LCA) study has been done to identify and compare the environmental impacts associated with different scenarios (SC) as SC1: landfilling without energy recovery, SC2: open burning and SC3: processing of RDF in WtE plant by considering the nine impact categories from the inventory data obtained over a period of 12 consecutive months (Jan 2021-Jan 2022). The results exhibited that the global warming potential caused by emissions of GHG are in the order of SC1 (1188kg CO2 eq) > SC2 (752kg CO2 eq) > SC3 (332kg CO2 eq), respectively from 1 t of MSW. It is concluded that the WtE plant can help in the reduction of environmental issues, strengthening the capacity of electricity generation and improving the aesthetic view of the city which is socially acceptable as well. Thus, WtE technology can help in achieving sustainable development goal 12 to regenerate the sustainable secondary resources for the twenty-first century and minimize global climate change.

Health risk assessment of municipal solid waste incineration emissions based on regression analysis

This study examined the potential health risks posed by the operation of 96 waste-to-energy (WtE) plants in 30 cities in the Bohai Rim of China. Utilizing a sophisticated simulation approach, the Weather Research and Forecasting (WRF) model coupled with the California Puff (CALPUFF) model, we obtained the spatial distribution of pollutants emitted by WtE plants in the atmosphere. Hazard indices (HI) and cancer risks (CR) were calculated for each plant using the United States Environmental Protection Agency's recommended methodologies. The results indicated that both HIs and CRs were generally low, with values below the accepted threshold of 1.0 and 1.0 × 10−6, respectively. Specifically, the average HI and CR values for the entire study area were 2.95 × 10−3 and 3.43 × 10−7, respectively. However, some variability in these values was observed depending on the location and type of WtE plant. A thorough analysis of various parameters, such as waste composition, moisture content, and operating conditions, was conducted to identify the factors that influence the health risks associated with incineration. The findings suggest that proper waste sorting and categorization, increased cost of construction, and elevated height of chimneys are effective strategies for reducing the health risks associated with incineration. Overall, this study provides valuable insights into the potential health risks associated with WtE plants in the Bohai Rim region of China. The findings can serve as useful guidelines for law enforcement wings and industry professionals seeking to minimize the risks associated with municipal solid waste (MSW) management and promote sustainable development.

Energy Recovery from Residual Municipal Solid Waste: State of the Art and Perspectives within the Challenge to Climate Change

Among the technologies for the recovery of energy from waste, in particular residual municipal solid waste (rMSW), combustion is the most widely used thermo-chemical treatment process associated with thermal and electric power production by a steam cycle, named, shortly, Waste to Energy (WtE). Today, more than 500 WtE plants in the EU, about 400 in China and 76 in the USA are in operation, based on efficient technologies and advanced air pollution control systems. Energy recovery can be accomplished also by means of gasification; however, the presence of impurities together with the atmospheric pressure, at which syngas is normally produced, impose the feeding of syngas to a conventional steam cycle, leading to generally lower performances than WtE. The energy recovered by WtE offsets traditional energy sources such as fossil fuels and related emissions, providing savings in term of climate change. However, the savings obtainable by replacing electricity and/or heat will diminish as the energy systems will hopefully become increasingly renewable. Over this medium–long-term horizon, one possibility is to capture the CO2 from WtE flue gases and to store/use it. From the life cycle assessment perspective, it has been calculated that the introduction of CO2 capture and storage in WtE, despite energy penalties, is able to reduce the impact on climate change. The alternative approach, proposed to contain the emissions of greenhouse gases in the thermal treatment of waste, is using the carbon contained in it to produce commonly used chemical compounds (waste to chemicals). The benefits, in terms of reductions of greenhouse gases, are expected from the possibility of obtaining chemicals that can replace their analogue normally produced from fossil sources. To date, only one WtC demonstration plant is operating by being fed by rMSW-derived waste, and some similar initiatives are planned, but still adequate assurances in terms of robust knowledge of the involved complex processes, above all, if applied to highly inhomogeneous feed streams such as those obtained from rMSW, are not available. Once the several initiatives come to completion, it will enable waste management professionals to assess performance and to begin to consider such a facility in their planning.

Techno-economic assessment of the CO2 value chain with CCUS applied to a waste-to-energy Italian plant

Recently, post-combustion CO2 removal has been considered also for the CO2 separation from the flue gases of Waste-to-Energy (WtE) plants, that manage high amounts of Municipal Solid Waste (MSW) by combusting it and generating power and heat. Moreover, because of the presence in MSW of an organic waste fraction, net negative CO2 emissions are feasible when integrating CCUS systems into WtE plants. Currently, to the best of the authors’ knowledge, there are only few incineration plants around the world that are successfully coupled with a carbon capture system, resulting in near-zero (or even negative) CO2 emission power generation.This work focuses on the evaluation of the whole value chain of the non-biogenic CO2 that is emitted in a power plant located in Northern Italy and on its possible utilization, from the CO2 source in the flue gas to the market-ready product.The design of the process for the CO2 removal from the flue gas has been carried out specifically for the considered flue gas to be treated with an aqueous solution of MonoEthanolAmine 30% wt., the benchmark solvent used in other types of power plants (fuelled by coal and natural gas). The main process parameters (e.g., lean loading, absorber packing height, regenerator packing height, regenerator pressure, gas inlet temperature, solvent inlet temperature) have been selected in order to optimize the reboiler duty and the water requirement, the latter being usually not considered in literature works dealing with this type of analysis. Then, the CO2 utilization has been evaluated, considering the options of both sequestration in the Adriatic Sea and utilization of CO2 for production of sodium bicarbonate, on the basis of the information available in the literature.In compliance with Directive 2003/87/EC and with the Italian legislation, Waste-to-Energy plants that treat municipal solid waste are currently exempt from the application of the CO2 Emissions Trading System (ETS). This article speculates about the application of the ETS to an urban WtE plant, located in Northern Italy, and evaluates its economic implications by comparing the purchase of emission quotas with the construction of a CCS or CCU plant.A business plan, detailing the obtained revenues from the utilization and from the avoided cost of purchasing emission allowances and the expenses related to the operation of the carbon capture plant, taking into account the taxes and the inflation, has been created and used for comparing the two considered CO2 value chains. For the option of CO2 sequestration, sensitivity analyses on the variation of investment costs (+10 %), operating costs (+10 %) and revenues (−10 %) have been performed and the breakeven value of the ETS certificate that can make the Net Present Value (NPV) non-negative has been determined. For the option of CO2 utilization, the revenue from sodium bicarbonate that can make its production profitable has been evaluated.

PROSPECTS OF WASTE TO ENERGY FROM CONTROLLED LANDFILL SYSTEM IN CIREBON, WEST JAVA

This research aimed to examine the potential of waste from controlled landfills a raw material for a Waste-to-Energy (WtE) plant. The research employed the qualitative method with direct observation. Data were analyzed descriptively. The results showed that the composition of waste in Cirebon was mostly dominated by household food waste (52.41%), followed by plastic (15.58%) and paper (8.05%). Based on the amount of existing waste and the projected amount in Cirebon City and Cirebon Regency, the waste can potentially be used as raw material for WtE plant. The energy generated from this waste can be sold to PLN, creating a positive utilization of the waste. It is projected that Cirebon City will produce 1319 m3/day of waste, and Cirebon Regency will produce 4767.65 m3/day (1161.26 tons/day) in 2023. Therefore, further research is needed to develop appropriate, efficient, and environmentally friendly technology for the municipal solid waste management system in Cirebon.

Examining waste-to-energy technology potential through the pilot project of Bantargebang Waste-to-Energy Power Plant

Municipal waste management in Indonesia, particularly Jakarta, poses a significant environmental challenge. Jakarta has been relying on the Bantargebang landfill to address its waste disposal needs for many years. Due to the persistent accumulation of waste, the Bantargebang landfill nears its maximum capacity. In response, a Waste-to-Energy (WtE) power plant was introduced in Bantargebang, serving as a pioneering initiative for WtE technology implementation in Indonesia. The Bantargebang WtE Plant employs incineration technology to convert municipal waste into electricity. Despite its usefulness, there are general environmental concerns about WtE plants, specifically focusing on their emissions and the potential presence of hazardous substances This research assesses the Bantargebang WtE Plant’s performance based on 2022 operational data, specifically examining waste reduction efforts and comparing incineration byproducts, including FABA (Fly Ash, Bottom Ash), and flue gas emissions, against government standards. The study indicates the plant can reduce waste mass by 96.5%. Furthermore, the WtE plant’s byproducts align with government standards for flue gas emissions and FABA residue. These results emphasize the potential of large-scale WtE power plants to achieve sustainable waste management goals in Indonesia. Nonetheless, there are opportunities for maximising waste accumulation reduction performance and enhancing operational value of WtE plant.

CFD design of a novel device for temperature profile measurement in Waste-to-Energy plants

Monitoring the flue gas temperature is a crucial issue for Waste-to-Energy (WtE) plants companies, since it is essential to preserve the materials in the post-combustion chamber, the energy efficiency of the plants as well as to control the emissions of pollutants. As of today, the temperature of flue gases in such plants is commonly monitored by means of thermocouples, infrared pyrometers or aspirated thermocouples. However, all these instruments show limitations in terms of accuracy and reliability inside post-combustion chambers. In this paper, the authors present the thermo-fluid dynamics design of a novel device aimed at mitigating the issues of existing technologies, realised by using the modern CFD techniques. Numerical analyses, performed with the open-source OpenFOAM code, allowed to find a suitable shape for the device and to give a first estimate of the measuring errors, which are of the order of 2% (∼26 K at the typical working temperature of WtE plants’ post-combustion chambers).

Policy Measures, Practices and Challenges of Waste-to-Energy: Perspectives from Nigeria and Nepal

There are environmental and health concerns associated with some waste-to-energy (WtE) technologies, such as incineration, which emit pollutants that can harm the environment and public health. Furthermore, there is limited research on the sustainability and feasibility of WtE. This study provides a comparative analysis of waste management practices in Nigeria and Nepal and highlights the challenges and potential for implementing WtE plants. A comprehensive literature review was conducted, and data were gathered from online sources for analysis. The findings of this study suggest that both countries face significant challenges in managing solid waste, including inadequate infrastructure, lack of awareness among policymakers, and limited resources for managing waste. However, there is potential for implementing WtE technologies as a sustainable solution for managing solid waste in these regions. The challenges associateed with WtE technology, including the high capital cost of establishing facilities and environmental and health concerns, must be addressed to fully realize the benefits of this technology.

Aligning Stakeholders and Actors: A New Safety and Security-Based Design Approach for Major National Infrastructures

This study introduces a systems-theoretic methodology to meet the requirements of a major national infrastructure for safety and security-based design by enhancing the alignment of stakeholders and actors in the project. Safe-by-Design (SbD) is an engineering concept for risk management that considers safety as much as possible in the design phase. The article presents the results of a case study conducted to investigate the efficacy of recent system safety models and analysis techniques in the major national infrastructure of a Waste-to-Energy (WtE) project under consideration in Iceland. The structures and roles within the system responsible for constructing the WtE plant, given the sustainability and circular economy restrictions, are addressed in the study. Stakeholders’ roles and responsibilities are analyzed, yielding their feedback on potential risks and creating a positive image of the project. Also, suitable ways to enter the project and finance it are devised. In essence, this enables the creation of a safety and security-based design approach. Furthermore, detailed documentation of the system model development is presented. The novelty of the study lies in the application of STAM, STPA, and STECA as an SbD approach for a major infrastructure project. Also, the methods discussed here have not been used in a WtE project as far as we know.

Modeling and assessing the integration of [formula omitted] capture in waste-to-energy plants delivering district heating

The waste-to-energy (WtE) sector is assuming an increasingly important role in net-zero pathways owing to its hard-to-abate emissions and its inherent potential for generating negative emissions. Thus, exploring effective strategies for CO2 capture and storage (CCS) integration with WtE plants that address the challenge posed by their coupling to district heating (DH) networks and the need to deliver both heat and electricity to customers is essential. This study presents a mass and energy balance model of a WtE plant with post-combustion CO2 capture process to assess the integrated system’s energetic feasibility. Results show that despite the extensive DH demand in heat-based WtE plants, enough excess heat is available to capture around 60% of the CO2 generated. As such, negative emissions can be achieved without external heat requirement at an efficiency reduction of 16%. By incorporating heat pumps and utilizing CCS waste heat for district heating, CO2 capture can be maximized at a total efficiency reduction as low as 36%. This is comparable to CCS in power-based WtE plants with no district heating. These findings highlight potential efficiency gains through the synergistic integration of CO2 capture and district heating, providing additional opportunities for WtE plants to contribute to the net-zero transition.

Advances in Corrosion Mitigation for Waste-to-Energy Systems: Evaluating Coatings and Application Techniques

Waste-to-Energy (WTE) systems, utilizing post-recycled municipal solid waste (MSW) and other biomass materials, are proven alternatives to landfilling for sustainable waste management. These processes offer benefits such as reduced landfill space, decreased methane emissions, and minimized waste volume. However, operational challenges, specifically high-temperature corrosion (HTC) of superheater tubes, hinder their efficiency due to the presence of chlorine, alkaline salts, and sulfates. To address this issue, a range of coating techniques have been developed, with thermal spray techniques, particularly high velocity oxy-fuel (HVOF) spray, proving the most effective for protecting superheater tubes. A comparative analysis of experimental data from multiple studies indicates that coatings with Alloy 625, Alloy C-276, Colmonoy 88, FeCr, IN625, NiCr, NiCrTi, and A625 offer high corrosion resistance at relatively low material costs, with corrosion rates below 1 mm/year. High chromium, nickel, and molybdenum content coatings perform exceptionally well under high-temperature and high-chlorine conditions. Notably, T92 and P91, due to their low cost and high corrosion resistance, are strong candidates for superheater tubes operating at 550°C. While A625 demonstrates excellent corrosion resistance, its high cost limits its practicality. Ultimately, the selection of suitable coatings depends on the specific WTE plant design and operating experience. The additional cost of applying these coatings is a minor fraction of the overall financial gains, as it extends the superheater tubes' lifetime and reduces plant downtime for tube repair or replacement.

Achieving sustainable emissions in China: Techno-economic analysis of post-combustion carbon capture unit retrofitted to WTE plants

China's aims of achieving CO2 emissions peak by 2030 and carbon neutrality by 2060 are crucial in guiding international efforts to mitigate climate change. Amine-based solvent technologies for capturing CO2 on a large scale have been implemented as retrofits in various industrial facilities, with a particular focus on coal-fired power plants. Nonetheless, its implementation within the waste-to-energy (WTE) industry is considerably limited and non-existent in China. This work presents a technical and economic evaluation of retrofitting a generic WTE facility in China with a carbon capture system. A rate-based process simulation model of the capture plant was developed in Aspen Plus, and the effect of equipment installation factors on capital cost was evaluated via the enhanced detailed factor (EDF) method. A set of key performance indicators were evaluated. The findings indicate that the energy demand linked to the capture system caused a decrease in efficiency by 13.17%, 14.85%, and 16.56% at 85%, 90%, and 95% capture rates, respectively, and the overall exergy efficiency of the system was reduced by 5.5%, 8.27%, and 10.63%, respectively. The estimated CO2 captured costs range from €56.41/tCO2 to €58.95/tCO2, while CO2 avoided costs range from €153.33/tCO2 to €236.47/tCO2. Retrofitting a CO2 capture unit at WTE facilities has the potential to substantially contribute to achieving the country's emission reduction targets. However, the successful implementation requires a comprehensive policy structure. This work offers some insights into the prospective integration of CO2 capture technology in China's WTE industry.

Techno-economic assessment of energy and environmental impact of waste-to-energy electricity generation

This study explored cumulative 127.5MW waste to energy (WtE) potential in five populous cities of Pakistan based on local waste characterization profiles and global standards. The 50MW WtE plant in Lahore using National electricity regulator codes and practices resulted in an attractive Levelized cost of electricity (LCOE) of US¢ 7.86/kWh over 25 years with a $151.5 million investment cost. The net savings to Lahore Waste Management Company can be $103.4 and $137.7 million respectively with and without tipping fees on account of waste disposal cost, bricks revenue using bottom ash, and waste fee. The project developers can get net savings of $16.9 and $51.5 million respectively with and without tipping fees other than LCOE. Furthermore, the greenhouse gas emissions of 216.6 million tons of CO2eq can be saved throughout plant life against 279 GWh/year energy generation, in terms of grid emission factor and current methane release into the atmosphere from the dumping site.

Waste bunker size optimization under uncertainty: Application of inventory models with real data simulation

Waste-to-Energy (WtE) technologies play a prominent role in recovering energy from waste. One of the aspects ensuring the operability and economic sustainability of WtE plants is the size optimization of a waste bunker assigned to each WtE plant, whose main target is to ensure waste homogeneity for effective operation. Each WtE plant faces various uncertain challenges, such as planned and unplanned shutdowns during which the plant is inactive and not ideally coordinated with waste collection companies, further importing the collected waste into the waste bunker, mainly due to existing contracts. This work aims to develop a scenario-based model to support strategic capacity planning by capturing various uncertain attributes and optimizing the waste bunker size while minimizing the total costs composing the investment, inventory, and waste shortage costs. The model is tested on a case study from the Czech Republic. The main result can be summarized such that for a specific case of a newly situated WtE facility with a considered capacity of 100kt/y, the model suggests a bunker of size ca. 4,200m3 for a middle scenario. However, this is strongly related to other attributes of a particular WtE project (e.g., waste properties or cost parameters).

Impact of the New Electricity Remuneration Scheme on the Waste-to-Energy Recovery Activity in Portugal

The remuneration scheme for the electricity produced by Waste-to-Energy (WtE) recovery plants has changed recently in Portugal according to 2020 legislation. The new model, linking the electricity remuneration from WtE plants to the spot electricity prices, is expected to bring greater uncertainty in the waste activity, which is a novelty for the sector. In Portugal, Valorsul is the municipal waste treatment entity responsible for the recovery and treatment of municipal solid waste (MSW) produced in 19 municipalities in the Lisbon area. This paper highlights the impact of the new Portuguese electricity remuneration scheme for electricity from waste on Valorsul’s WtE plant. For this purpose, the new remuneration scheme is modeled and simulated based on electricity spot market price scenarios, which are compared with the base case scenario of the former remuneration scheme. Considering different electricity prices for the electricity produced by the WtE plant, the present study anticipates the consequences of the gate-fee of such regulatory changes. Results show that any price changes in the electricity remuneration scheme are offset by equivalent changes in the waste gate-fee. Consequently, the change in the remuneration of the electricity from the WtE plant is, in fact, neutral for the Valorsul accounts and lower revenues from the electricity generation activity of the WtE will negatively impact the gate-fee prices paid by the waste users.

Sequential extraction procedure of municipal solid waste incineration (MSWI) bottom ash targeting grain size and the amorphous fraction

Introduction: Bottom ash (BA) constitutes a significant by-product obtained during the incineration of municipal solid waste in waste-to-energy (WtE) plants. BA is a heterogeneous material made of different fractions, glass, minerals, metals, and unburned residual organic matter. Due to the non-hazardous nature of the unburned material, BA can be effectively recycled, becoming a valuable resource. However, BA displays a high content of potentially toxic elements (PTEs) within its finer grain size. The presence of these elements raises concerns regarding the potential toxicity associated with BA.Materials and methods: The release of PTEs in the smaller fraction (0.063–0.2 mm; 0.3–0.5 mm; 2–4 mm; bulk <4 mm) of BA collected from the Parma WtE plant was investigated using a new five-step sequential extraction procedure (SEP). Through this method, both leached solutions and solid residues were analyzed by inductively coupled plasma-mass spectroscopy (ICP-MS), X-ray powder diffraction (XRPD), and X-ray fluorescence (XRF) analysis. This integrated approach provided valuable insights into the mineralogy, chemical composition, and PTEs leachability of BA.Results and discussion: The novelty of this work is the development of a new SEP protocol specifically designed and planned for an anthropogenic material such as BA. The weight reduction recorded after each step is linked to the progressive disappearance of both crystalline and amorphous phases. Water-soluble phases, such as salts, are the first to react, followed by the carbonate fraction in the second step. At the end of the procedure, only quartz, corundum, and Ti-oxide are identified. Among the PTEs, Pb exhibits the highest release, particularly during the acid attack, followed by Zn. The significant release of Ni during the oxidizing and reducing steps can potentially be linked to hydroxides and metallic alloys, respectively. The integration of XRF and Rietveld refinement results on solid residues enabled the identification of several types of amorphous materials and their chemical evolution during the sequential extraction.