The role of SRF in achieving the EU landfill targets in the Umbria Region, Italy

In December 2015, the European Commission published the circular economy package “Closing the loop - An European action plan for the Circular Economy” with four quantitative objectives: long-term recycling targets for municipal waste (55% in 2025, 60% in 2030 and 65% in 2035) and landfill target of 10% by 2030. In Umbria (Italy) 43% of waste are landfilled in 2020, so the region is far from the European target. Hence, it is significant to analyse different strategies to improve the waste management in the region. In particular, the main issue is how to reduce waste landfill in the most efficient way. The SRF and waste-to-energy approaches are the most interesting to study as a substitute for landfilling. In the communication “The role of waste-to-energy in the circular economy”, the European Commission clarifies the position covered by the different energy processes in the waste hierarchy and identifying the technologies with the highest potential in terms of efficient management of resources and environmental impact. Among the most efficient waste-to-energy technologies, the document mentions the gasification of recovered solid fuel (SRF) and co-incineration of the resulting synthesis gases in the combustion plant to replace fossil fuels in the production of electricity and heat and co-incineration in the cement production. The European Commission recognizes the important role of energy recovery in the transition to the circular economy, if this does not stop the improvement in recycling rates. In this paper, MSW management policy in Umbria (Italy) and possible solutions are discussed. The paper considers three scenarios in the management of MSW: i) direct combustion of residual waste in waste-to-energy plants; ii) combustion of SRF in waste-to-energy plants; iii) combustion of F-SRF in dedicated plants (cement plant). All three scenarios may be able to match the 10% landfill EU target.


Introduction
The Directive 2008/98/EC [1] establishes a hierarchy for waste management, with prevention as a priority and landfill disposal as the last choice.The European Commission's communication "The role of waste-to-energy in the circular economy" [2] recognizes the importance of these technologies in the transition to a circular economy, as long as they do not hinder recycling efforts.The most efficient wasteto-energy technologies include gasification of solid recovered fuel (SRF) and co-incineration in cement production.
The circular economy package "Closing the loop" [3] includes long-term recycling targets for municipal waste and a landfill target of 10% by 2030.In Umbria region (Italy), 43% of waste was landfilled in 2020 [4], so it is far from the European target and solutions are needed to lower this percentage.The study focuses on waste management in the Umbria Region and presents three alternative scenarios: i) direct combustion of residual waste in waste-to-energy plants; ii) combustion of SRF in waste-to-energy plants; iii) combustion of F-SRF in dedicated plants (cement plant).Finally, the paper compares the three scenarios in terms of their impact on landfill depletion, taking into account traditional fossil fuel and CO2 savings.

Classification
Legislative Decree 205/2010 introduced, in Article 183, paragraph 1, letter cc) of Legislative Decree 152/2006, the definition of Solid Recovered Fuel (SRF): "the solid fuel produced from waste that meets the classification and specification characteristics identified of the UNI CEN/TS 15359 technical standards and subsequent amendments and additions; subject to the application of Article 184-ter, secondary solid fuel, is classified as special waste." SRF is regulated at the European and national scales from two standards, UNI EN 15359:2011 [5] and BS EN ISO 21640:2021 [6] "Secondary Solid Fuels -Classification and Specifications," which sets out a classification system and scheme for defining the properties of SRF.
Fuel SRF (F-SRF) is a category of the various possible types of SRF, which has a classification and specification characteristics so that a declaration of conformity can be issued in compliance with the provisions of Article 8, Paragraph 2 of Ministerial Decree 22/2013 [7].In this way, it is possible to distinguish SRF waste from SRF fuel.SRF fuel ends its waste status and becomes a product [1].
Hence, SRF produced from unsorted solid waste, depending on its characteristics, can be destined for waste-to-energy in dedicated plants or for co-firing in industrial plants, thus reducing the amount of material to be landfilled.
The classification of different types of SRF is based on the requirements of the technical standard UNI EN 15359 "Solid recovered fuels" (SRF), which considers 3 parameters: x lower heating value (LHV).It is an index of energy value, expressed by the statistical measure of the average value, in MJ/kg; x chlorine content (Cl).It is an index of the degree of aggressiveness on plants, expressed with the average value, in percentage units; x mercury content (Hg) It is an index of the significance of environmental impact, expressed as the median or 80th percentile value, in mg/MJ.For each of them, limit values are given to identify 5 classes, so this classification provides 125 different types of SRF depending on the combination of the three parameters and provides the user with immediate and clear information about the fuel.For the purposes of Ministerial Decree 22/2013, F-SRF must respect limits for LHV and Cl as defined by classes 1, 2, 3 and their combinations and, for the parameter Hg, as defined by classes 1 and 2 (table 1).Waste-to-energy plants can be considered as the proper destination of SRF, while F-SRF can be used in cement plants with a production capacity of more than 500 tons per day of clinker and/or thermal power plants with a thermal combustion capacity of more than 50 MW [7].

Production
The F-SRF production process comprises several stages that are operated in a mechanical biological treatment plant (MBT).Firstly, residual waste (unsorted waste from MSW) is sieved to divide fine fraction (organic waste) and coarse fraction (inorganic waste).The fine fraction undergoes a biological treatment (aerobic, anaerobic, or both) and then it is sent to landfill.Coarse fraction has the highest calorific value.
The material goes through an electromagnetic separator to remove any light ferrous fractions that can be recovered.Then, a parasitic current separator is used to extract any non-ferrous metallic fractions.An optical separator is then employed to reduce the presence of plastic fractions containing chlorine.Finally, the material is passed through a shredder-refiner to reduce its size before it is pressed obtaining F-SRF [8], [9].SRF undergoes only sieving, electromagnetic separator, and parasitic current separator.

Data about Umbria Region, Italy
The total municipal solid waste (MSW) production in Umbria is ≈ 439 million kg in 2020, 66.2% of MSW was recycled.The residual waste represented 32.2% of MSW [4].
In 2020 in Umbria the residual waste was 141.5 million kg [10].The management of residual waste involves MBT to reduce its organic content and weight, followed by landfill disposal.The first phase occurs at selection plants, which yield three fractions: metals, coarse fraction (inorganic dry material) sent to landfills, and fine fraction (organic wet material) biostabilized and then sent to landfills.In 2020, 99% (≈ 140 million kg) of the residual waste collected in Umbria underwent selection, resulting in 0.6% (≈ 849 miles kg) of metals sent for recovery, almost 61% (≈ 86 million kg) of coarse fraction disposed of in Umbrian landfills, almost 38% (≈53 million kg) of fine fraction biostabilized in Umbrian plants (with only 0.5% disposed of in biostabilization plants outside the region).Biostabilization produces biostabilized waste equal to the 24% (≈ 34 million kg) of starting residual waste.It is disposed in landfill.An amount of waste equal to the 37 % of the total production was disposed in landfill in 2020 (a total of 162.5 million kg) [4].Considering this regional scenario, it is significant to study other pathways to treat residual waste in order to lower the amount of waste landfilled and reach European target of maximum 10% waste landfilled.

Data
Data are collected in the biggest waste management company of the Region Umbria: when not available, literature data are used.Total amount of residual waste, coarse fraction and fine fraction waste, and LHV values are collected.Moreover LHV, chlorine, and mercury levels are shown in table 3 and taken from sample analyses to identify F-SRF code according to Ministerial Decree 22/2013.

Scenarios description
Three scenarios about residual waste management are described: i) direct combustion of residual waste in waste-to-energy plants; ii) combustion of SRF in waste-to-energy plants; iii) combustion of F-SRF in dedicated plants (cement plant).For these three pathways, energy production and CO2 reduction are evaluated.A residual waste mass balance is analyzed.This study does not consider pollutants analysis, transportation and plant consumption cost.

Result and discussion
Three different samples of coarse fraction waste were characterized in order to measure their chlorine and mercury content and LHV value.All analysis were performed by ACCREDIA-accredited test laboratory n. 0181 L according to UNI CEI EN ISO/IEC 17025:2018 [11].Table 3 shows the class code of coarse fraction waste analyzed in the considered mechanical treatment plant.The coarse fraction waste characterization defines a F-SRF with code 311.Residual waste LHV is 10 MJ/kg as received [12], [13].The disposed waste is 10.2 million kg. Figure 1 shows the flowchart of the process, simplified mass balance, energy and CO2 output of the process.

Second scenario
In the second scenario, residual waste undergoes a MBT.Fine fraction waste was biostabilized while coarse fraction is fired in waste-to-energy plant.Ashes and slags are produced as combustion residues.The disposed waste is equal to 40.2 million kg. Figure 2 shows the flowchart of the process, simplified mass balance, and energy and CO2 output of the process.

Third scenario
In the third scenario, residual waste undergoes a MBT.Fine fraction materials were biostabilized while coarse fraction is burned in a cement plant.This process does not produce residues because they concur to produce the clinker structure.The disposed waste is 34 million kg. Figure 3 shows the flowchart of the process, simplified balance, and energy and CO2 output of the process.

Figure 3. F-SRF fired in cement factory
Petcoke and CO2 saving can be evaluated.By dividing the energy output for petcoke LHV (34 million MJ/kg [8]), the weight of petcoke saved in each scenario can be calculated.Considering fossil carbon (Cfossil) % in petcoke and SRF (87% and 28% mass respectively [8]) it is found the CO2 output for each fuel multiplying Cfossil for factor conversion 3.67 [15].Then subtracting CO2 SRF output to CO2 petcoke output, the CO2 saved is found.In the first scenario the same value of SRF Cfossil is taken for residual waste.Figure 4 shows petcoke and CO2 saved.Table 4 shows the calculation.Umbria landfill residual capacity is 808 thousand m 3 at the end of 2020 so it is possible to define landfill depletion in the three different scenarios.Considering 800 kg of waste are about 1 mc [16], table 5 shows Umbria landfill depletion in years, waste disposed (in kg and m 3 ), and % landfill on total waste considering only residual waste.

Conclusion
The present paper proposes three scenarios to manage residual waste consisting in waste-to-energy solutions and petcoke thermal substitution in cement factory.A focus on SRF explains their production, legislation, and application in aforementioned waste managements.The first scenario shows the best result in terms of waste production but is the worst in fossil fuel and CO2 reduction.All three scenarios are below the 10 % landfill EU target.This paper shows the potentiality of these three pathways in residual waste management that can be put into practice to produce energy and so reduce the emitted CO2.Moreover, the diminishing of waste disposed in landfill is a crucial achieved goal.More studies are needed to make a more precise mass, energy and CO2 balances.Finally, a life cycle analysis is needed to estimate environmental, economic, and social impact.

Figure 1 .
Figure 1.Residual waste directly fired in waste to energy plant

Figure 2 .
Figure 2. SRF fired in waste to energy plant

Figure 4 .
Figure 4. Petcoke and CO2 saved in the three scenarios.

Table 1 .
SRF classification: green boxes show the characteristics needed to define F-SRF.Chemical and physical parameters are defined in Annex A, Part 1 of the UNI EN 15359 standard, expressed as the mean/median of the individual parameters.Only for F-SRF the Ministerial Decree 22/2013 defined thresholds (table 2).

Table 2 .
Chemical and physical thresholds.No limit values have been set for ash and moisture.Setting limit values for ash and moisture is left to specific agreements between manufacturer and user.
[14]he first scenario, residual waste is directly fired in a waste-to-energy plant.The outputs are 1415 million MJ, 88.5 million kg CO2eq[12], 7 million kg ashes, 32 million kg of slags that are mostly recovered[14].

Table 5 .
Umbria landfill depletion.is the current model in which biostabilized and coarse fraction were put in landfill.