The economic feasibility of RDF gasification is influenced by multiple factors, including total capital investment, fixed and variable operating costs, and economic parameters such as net present value and return on investment (Kargbo et al., 2022). Commercial-scale deployment requires substantial capital and a reliable supply of feedstock, which presents a significant barrier to market entry (Sajid et al., 2022). Arena et al. (2015) studied a techno-economic assessment of a small-scale fluidized bed gasifier utilizing SRF for energy production. They concluded that the financial viability of such a system is contingent upon the availability of supportive incentive tariffs. Extending this line of inquiry, Alves et al. (2021) analyzed a small-scale gasification plant (883 kg/h) co-processing sewage sludge and SRF under two sale scenarios: electricity generation and hydrogen production. Both pathways were found economically viable over a 25-year lifetime. Electricity was favored in the short term due to a lower payback period (9 years) and higher IRR (7.5%), while hydrogen offered superior long-term profitability with an NPV of €1.8 million. Sensitivity analysis revealed that capital expenditure was the most influential parameter, and that a 20% increase in hydrogen price (to €4.74/kg) would make hydrogen production profitable even in the short term. Li et al. (2018) emphasized that economic challenges in the design and operation of gasification units continue to hinder commercialization. Despite its importance, economic analysis of RDF gasification remains underexplored. Existing studies highlight that plant size and feedstock cost including RDF disposal and transportation are critical to the viability of the technology. Wang et al. (2017) reported a reduction in hydrogen production cost from €4.40 to €3.85 per kg when plant capacity increased from 1,500 to 2,500 dry metric tons per day. Násner et al. (2017) conducted an economic assessment of an RDF gasification pilot plant at the Federal University of Itajubá (UNIFEI), Brazil. With an initial investment of US$300,000, the project was deemed economically viable for power outputs exceeding 120 kW el . These findings collectively highlight the importance of scale, integration, feedstock logistics, and product market dynamics in determining the economic success of RDF gasification systems.

An LCA is a critical tool for evaluating the environmental sustainability of different technologies including RDF gasification. It quantifies emissions, resource depletion, and energy consumption across all stages of the process using mass and energy balances. An LCA supports informed decision-making and contributes to achieving Sustainable Development Goals (SDGs) (Pandey et al., 2019; Castagnoli et al., 2024). For instance, Al-Moftah et al. (2021) studied an LCA of SRF air gasification for electricity generation in Qatar. Their results demonstrated that SRF gasification substantially reduced environmental impacts compared to MSW landfilling. Notably, climate change emissions decreased by over 40%, while water and fossil resource depletion were reduced by two orders of magnitude. Incorporating solar PV into the gasification system further lowered climate impacts to near-zero. Although terrestrial acidification showed minimal variation across scenarios, the overall results confirmed that SRF gasification can mitigate greenhouse gas emissions, lessen reliance on natural gas, and support Qatar’s National Vision 2030 by reducing landfill dependence and enabling sustainable energy production. Evangelisti et al. (2015) conducted LCA of a combined two-stage gasification and plasma plant processing seven different waste types. Their findings indicated that RDF treatment resulted in the lowest environmental impact regarding global warming and acidification, primarily attributed to its elevated heating value. In contrast, the plant exhibited net environmental benefits across other impact categories, largely due to the offset emissions from electricity generation within the system. López-Sabirón et al. (2015) conducted a comparative environmental assessment of emissions resulting from syngas generated via plasma torch gasification of RDF and coal combustion in cement production. Their analysis demonstrated that RDF-derived syngas offered superior environmental performance across all evaluated impact categories. However, they noted that the overall results were significantly affected by the high electricity demand associated with the plasma torch gasification process. Longo et al. (2020) performed an LCA of electricity generation from RDF in Italy, comparing its eco-profile with electricity from the national grid and multi-Si photovoltaic systems. While RDF-based electricity performed worse in categories such as climate change, human toxicity, and photochemical oxidant formation, it showed superior performance in resource depletion–an increasingly relevant metric in circular economy frameworks. Using a gate-to-gate LCA approach, Dubsok et al. (2024) assessed RDF production in Thailand. Electricity consumption emerged as the dominant environmental burden, contributing 1.66 mPt and 6.81 kgCO_2e in climate change impacts, which is significantly more than diesel or natural gas. These findings align with those of Longo et al. (2020), reinforcing the need to address electricity-related emissions in RDF systems. Marques et al. (2021) identified fossil fuel combustion during transportation and electricity use in MSW pretreatment as major contributors to environmental pollution in RDF gasification. These insights highlight the importance of system-wide LCA to guide sustainable RDF deployment. In conclusion, both economic and environmental assessments are essential for evaluating RDF gasification viability. Future research should focus on integrated techno-economic and life cycle modeling to support policy development and investment decisions.

RDF gasification offers promising economic and environmental advantages, yet it must be situated within the broader waste-to-energy landscape where alternative pathways present distinct trade-offs. Incineration remains the most technologically mature and widely deployed option, providing reliable electricity generation but requiring high capital investment and advanced flue-gas treatment to mitigate emissions of particulates and dioxins; its environmental profile is generally less favorable than gasification, particularly in climate change and human toxicity categories (Evangelisti et al., 2015). Pyrolysis produces syngas, bio-oil, and char with lower emissions than incineration, but its economic viability is constrained by high operating costs and limited commercial deployment; integration with catalysts or renewable inputs such as biomass co-processing can improve eco-performance though further optimization is needed (Alfè et al., 2022). Anaerobic digestion is environmentally favorable for biodegradable fractions of MSW (Miezah et al., 2015), generating biogas with relatively low emissions and benefiting from lower capital costs, but challenges remain in ensuring consistent feedstock supply and managing digestate. Direct combustion of RDF is simpler and cheaper than gasification but less efficient in energy recovery and associated with higher emissions (Salman et al., 2017a). In comparison, RDF gasification balances environmental benefits with economic potential, particularly when integrated with or combined heat and power systems (Ajorloo et al., 2022). While incineration continues to dominate in practice, gasification and pyrolysis demonstrate superior eco-profiles, though both require supportive policies and scale-up to achieve cost competitiveness. This comparative perspective reinforces the importance of evaluating RDF gasification not in isolation but alongside alternative pathways, highlighting opportunities for hybrid systems and integrated techno-economic and environmental modeling to guide sustainable waste-to-energy transitions.

This analysis corresponds to Cluster 1 of the bibliometric map, which focuses on environmental performance and energy efficiency of waste treatment. This section contributes to this cluster by critically evaluating the economic viability and life cycle impacts of RDF gasification systems, emphasizing their role in sustainable energy transitions.

Gasifying agents such as steam, air, oxygen, and CO₂, whether used individually or in combination (e.g., steam–air, oxygen–steam, CO₂–oxygen), significantly affect syngas composition and heating value (Recari et al., 2017a; Pandey et al., 2019). Im-Orb et al. (2016) demonstrated that the choice of gasifying agent alters syngas calorific value. Khan and Al-attab (2022) reported that steam and oxygen gasification yield higher heating values (10–20 MJ/Nm³) compared to air gasification (4–6 MJ/Nm³). Table 6 presents the advantages and disadvantages of the different gasifying agents (Pandey et al., 2019; Mishra and Upadhyay, 2021; Khan and Al-attab, 2022; Salem and Elsherbiny, 2022). Steam gasification is generally preferred due to its superior hydrogen/CO ratio and hydrogen conversion efficiency (Sharma and Sheth, 2016). Haydary (2016) found that air gasification achieved complete RDF conversion with a heating value of 4.4 MJ/m³ at an air-to-RDF ratio of 3.2, while oxygen gasification yielded 10 MJ/m³ at a ratio of 0.65. Increasing S/R ratio enhanced hydrogen and CO₂ concentrations but reduced heating value. Agon et al. (2016) observed consistent medium calorific values (∼10 MJ/m³) across various gasifying agents (CO₂ + oxygen, steam, CO₂ + steam, oxygen + steam).

Temperature is a pivotal factor in RDF gasification, influencing the balance between endothermic and exothermic reactions. Higher temperatures favor endothermic reactions, enhancing syngas yield, heating value, CCE, and reducing tar formation (Násner et al., 2017; Mishra and Upadhyay, 2021). However, elevated temperatures also increase operational costs. Recari et al. (2016) investigated the thermal behavior of two distinct SRFs under identical operating conditions and observed that elevating the temperature within the range of 750 °C–850 °C led to higher gas production, lower tar formation, and variable calorific values that did not follow a linear trend. Asaad et al. (2023) found that calorific value was higher at 675 °C than at 775 °C, suggesting non-linear temperature effects. Ren et al. (2022) investigated steam gasification of RDF with CaO modification. Optimal hydrogen yield (69%), gas yield (1.372 m³/kg-RDF), and hydrogen yield (0.935 m³/kg-RDF) were achieved at 960 °C and S/R ratio = 2, with CaO modification at 650 °C. Higher CaO adsorption temperatures reduced hydrogen yield due to diminished adsorption capacity. Liu et al. (2023) studied RDF gasification in a fluidized bed, finding optimal efficiency (44.83%) and LHV (6.77 MJ/m³) at 850 °C and ER = 0.23. Oxygen enrichment (OP = 40%) increased LHV by 112% and hydrogen by 76.4%. Steam addition under enriched oxygen conditions further boosted hydrogen yield to 21.3% at S/R ratio = 0.73. Catalytic reforming using Ni–Ce–La catalysts increased hydrogen by 3.27%, syngas yield by 13%, and tar removal by 91.5%. These findings suggest that temperature must be carefully optimized and integrated with gasifying agents and catalysts for best results.

Particle size affects heat and mass transfer, reaction kinetics, and syngas quality. Optimal particle sizes vary by reactor type: ≤51 mm for fixed bed, ≤6 mm for fluidized bed, and ≤0.15 mm for entrained flow reactors (Sikarwar et al., 2016; Mishra and Upadhyay, 2021; Asaad et al., 2023). While the effect of particle size in biomass gasification has been extensively studied (Yahaya et al., 2019; Zhou et al., 2020), RDF-specific data are scarce.

Different RDF formulations exhibit distinct physical and chemical characteristics; however, only a limited number of studies have examined how RDF composition influences gasification performance. Hervy et al. (2019) investigated air-blown SRF gasification in a lab-scale bubbling fluidized bed and demonstrated that feedstock composition strongly affects syngas quality and conversion efficiency. Their comparative analysis of two industrial SRFs showed that biomass-rich SRF (SRF1, dominated by paper/carton) produced syngas with higher hydrogen content and greater carbon conversion, while plastic-rich SRF (SRF2) generated more stable light hydrocarbons (CH₄, C₂H₄, C₆H₆) but yielded lower hydrogen due to polymer chain decomposition. Inorganic species present in ash-rich SRF1 catalyzed gasification reactions, enhancing conversion, whereas synergistic plastic–biomass interactions in SRF2 promoted secondary reactions that led to char formation. Šuhaj et al. (2020) further highlighted the role of RDF composition by gasifying individual RDF fractions with tire pyrolysis char as a tar-cracking catalyst. Their results showed that plastics produced the highest tar and hydrocarbon gas yields, accompanied by the lowest CO₂ content in the product gas, while the paper fraction generated hydrogen-rich syngas with comparatively low tar levels. This underscores how plastics and biomass fractions contribute differently to syngas composition and tar formation, reinforcing the importance of compositional balance in RDF feedstocks. Other studies have reported that minor variations in RDF composition do not significantly alter its heating value, which typically ranges from 19.1 to 20.0 MJ/kg (Zeeshan et al., 2024b). Alfè et al. (2022) emphasized that RDF composition and reactor type govern the quantity and characteristics of tars formed during gasification. Similarly, Recari et al. (2016) and Recari et al. (2017a) noted that RDFs with higher carbon and hydrogen fractions yield greater amounts of CO and hydrogen under comparable operating conditions.

S/R is defined as the ratio of steam to RDF in mass ( m steam m RDF ) that is introduced into the gasifier. According to Cai et al. (2024), the S/R ratio is a critical parameter in gasification, as it governs hydrocarbon steam reforming, water–gas shift reactions, and the system’s overall energy equilibrium. When properly optimized, the S/R ratio enhances hydrogen generation, which is vital for producing high-quality syngas, while simultaneously minimizing tar and char formation. Ribeiro et al. (2017) performed RDF gasification using different gasifying agents. They reported a syngas yield with the following properties: hydrogen-51%, CO₂-32%, CO-11% and CH4-6% at an optimum S/R of 1.0. A further increase of S/R increased the contents of hydrogen and CO₂ whereas the content of CO, CH₄ and heating value were decreased. This is in broad concordance with the conclusion made by Haydary (2016).

Catalysts play a pivotal role in enhancing the overall performance of RDF gasification, particularly in improving syngas quality and reducing undesirable byproducts. Their presence facilitates key reactions that lower CO₂ content, increase the hydrogen/CO ratio and CH₄ fraction, and significantly reduce tar formation, which is one of the major operational challenges in thermochemical conversion processes (Khan and Al-attab, 2022; Asaad et al., 2023; Sieradzka et al., 2024). From an environmental standpoint, the use of catalysts is highly beneficial. They promote higher conversion rates of waste into energy and contribute to cleaner syngas production. However, their integration into RDF gasification systems introduces economic trade-offs, primarily due to increased operational costs (Sieradzka et al., 2025). This cost–benefit tension underscores the need for careful techno-economic evaluation when selecting catalytic systems. In contrast, Hu et al. (2018) demonstrated that catalytic cracking is both economically and technically feasible for syngas purification. Among various catalyst types, natural catalysts (e.g., dolomite, olivine, clay minerals) have gained attention due to their low cost, availability, and effectiveness in tar cracking. These materials offer a practical alternative to synthetic or metal-based catalysts, especially in large-scale or decentralized RDF gasification setups. Sajid et al. (2022) provided a comprehensive review of catalyst effects on gasification, highlighting their influence on reaction kinetics, product distribution, and system stability. Importantly, the interaction between temperature and catalyst must be critically considered. Both parameters influence similar reaction pathways, and their synergistic or antagonistic effects can significantly alter gasification outcomes. For instance, Li et al. (2016) observed that the performance of metal-based catalysts was noticeable within a temperature range of 800 °C–900 °C. As noted by Šuhaj et al. (2019), indiscriminate catalyst addition without thermal optimization may lead to suboptimal performance or unnecessary cost escalation. Despite promising results, very few comparative studies have been reported in the literature on catalyst types, loading rates, regeneration cycles, and long-term stability under RDF-specific conditions. For instance, Recari et al. (2017a) found that, under comparable experimental conditions in a laboratory-scale fluidized bed reactor, dolomite proved more effective than olivine in reducing tar formation during oxygen/steam gasification of two types of SRFs. Future research should focus on evaluating catalyst performance across diverse RDF compositions, integrating catalyst selection with process modeling and life-cycle assessment, and exploring hybrid catalytic systems and co-catalyst formulations for enhanced hydrogen yield and tar mitigation. In summary, while catalysts offer substantial environmental and technical benefits in RDF gasification, their deployment must be guided by rigorous cost–performance analysis and tailored to the specific feedstock and reactor configuration.

Studies have consistently identified tar formation as one of the major challenges hindering the commercialization and deployment of gasifiers, particularly for rural electrification (Ramadhani et al., 2022; Jothiprakash et al., 2025). Tar refers to condensable organic compounds, primarily aromatic hydrocarbons, present in syngas produced during gasification. These compounds condense at lower temperatures, leading to fouling of equipment, catalyst deactivation, and reduced CGE. In RDF gasification, tar formation is especially problematic due to the heterogeneous nature of the feedstock, which typically includes plastics, paper, biomass, and inorganic fractions (Ramadhani et al., 2022; Šuhaj et al., 2020; Jayanarasimhan et al., 2024; Bashir et al., 2025).

Tar compounds in RDF gasification are commonly classified into primary, secondary, and tertiary groups, reflecting their chemical structures and formation pathways (Ramadhani et al., 2022; Jayanarasimhan et al., 2024). Primary tars are generated during the pyrolysis of biomass fractions, such as lignin-derived phenolics. Secondary tars arise from radical reactions that lead to the formation of olefins and light aromatics, while tertiary tars consist mainly of polycyclic aromatic hydrocarbons (PAHs), produced through polymerization and condensation at moderate temperatures. The relative contribution of these pathways is strongly influenced by operating conditions, including temperature, ER, S/R, and feedstock composition, etc. (Ramadhani et al., 2022; Jayanarasimhan et al., 2024). Operating parameters play a decisive role in tar behavior. For example, raising gasification temperature between 750 °C and 900 °C promotes tar cracking, steam/dry reforming, and Boudouard reactions, thereby reducing tar content. Higher ER oxidizes tars but simultaneously lowers syngas heating value and CGE due to CO₂ formation. Adequate steam promotes reforming and water–gas shift, reducing tar while increasing hydrogen yield (Jayanarasimhan et al., 2024).

Berrueco et al. (2015) experimentally confirmed that increasing temperature and ER in SRF gasification reduces tar and char yields, with optimal conditions around 800 °C–850 °C and ER values of 0.30–0.35. However, they also noted that higher temperatures increase tar aromaticity, complicating downstream removal. Recari et al. (2016) reinforced these findings by demonstrating that higher temperatures (850 °C) and the use of calcined dolomite as bed material significantly improved syngas quality, increasing the hydrogen/CO ratio and carbon conversion while reducing tar content. Their study of two SRFs showed that dolomite promoted tar cracking reactions, leading to lower tar yields compared to sand, while oxygen/steam as a gasification agent enhanced syngas calorific value but also increased the release of minor contaminants. Importantly, they highlighted that tar levels and contaminant release were strongly dependent on SRF composition and ash fraction, underscoring the role of feedstock heterogeneity in determining tar behavior. Further work by Recari et al. (2017a) examined the effect of different bed materials (i.e., sand, dolomite, and olivine) on oxygen/steam gasification of SRFs at 850 °C. Their results showed that mineral catalysts promoted tar cracking and char conversion, with dolomite proving far more effective than olivine in reducing tar compounds and larger PAHs. Olivine, however, exhibited activity for naphthalene cracking and was more effective in reducing nitrogenous contaminants (HCN and NH₃), likely due to its iron content. They also observed that SRF feedstock composition influenced contaminant release, with fuels containing lower heteroatom and ash levels producing fewer minor contaminants. Overall, dolomite achieved the most significant tar reduction, though at the expense of higher NH₃ levels, highlighting the trade-offs between tar abatement and nitrogen chemistry.

Recent work has explored novel catalysts such as tire pyrolysis char for tar cracking in RDF gasification, showing promising reductions in tar yield (Šuhaj et al., 2020). Despite these advances, conventional tar removal strategies remain problematic. Physical scrubbing requires downstream treatment of contaminated liquor, while thermal cracking consumes part of the produced syngas to sustain the high operating temperature. Catalytic approaches have attracted considerable attention, yet many catalysts suffer from rapid deactivation and issues of cost or toxicity, limiting their practical application (Ramadhani et al., 2022). Koritár and Haydary (2025) further demonstrated the complexity of tar management in RDF gasification. Their study on RDF pellets in a two-stage batch reactor showed raw syngas tar concentrations of 14.97 g/Nm³, which were reduced by catalytic treatment with Ni/activated carbon to 2.11 g/Nm³, achieving a maximum removal efficiency of 85.89%. However, repeated use and regeneration of the catalyst decreased its cracking ability, highlighting the challenge of catalyst stability. Moreover, they observed that increasing catalyst loading and operating temperature in the catalytic stage enhanced tar removal, but coke deposition reduced pore volume and surface area, limiting long-term performance.

Chen et al. (2022) added another dimension to the tar challenge by focusing on measurement and monitoring. In their 20 kW pilot-scale steam-oxygen gasification of SRF, they developed a flexible tar sampling system (FTSS) and an on-line gas chromatography (GC) method to improve accuracy and efficiency in tar quantification. Their results showed strong correspondence between off-line and on-line measurements, with real-time monitoring of benzene, toluene, and xylene (BTX) loads around 18–19 g/m³ at 850 °C. They also demonstrated that tar carbon fractions decreased significantly with higher temperatures (from 68 g/m³ at 650 °C to 25 g/m³ at 850 °C). These advances highlight that reliable tar monitoring is essential not only for understanding tar behavior but also for optimizing operating conditions and validating mitigation strategies in pilot-scale systems.

Section 3.3.6 directly reflects the thematic priorities of Cluster 5 in the bibliometric map, which emphasizes pyrolysis, syngas, and tar as critical byproducts and pollutants in RDF conversion. By synthesizing studies from 2015 onward, the discussion captures the cluster’s high-citation focus on tar management and its role in shaping syngas quality. More recent contributions (Ramadhani et al., 2022; Šuhaj et al., 2020; Chen et al., 2022; Koritár and Haydary, 2025) extend this trajectory, highlighting advances in catalytic cracking, operating condition optimization, and novel tar monitoring methods.