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Article

Study on the Emission Characteristics of Pollutants During the Waste-to-Energy Process of Landfill Waste and Municipal Solid Waste

by
Zongao Zhen
,
Xianchao Xiang
and
Xiaodong Li
*
State Key Laboratory of Clean Energy Utilization, Institute for Thermal Power Engineering, Zhejiang University, Hangzhou 310027, China
*
Author to whom correspondence should be addressed.
Energies 2025, 18(17), 4515; https://doi.org/10.3390/en18174515
Submission received: 17 July 2025 / Revised: 10 August 2025 / Accepted: 21 August 2025 / Published: 25 August 2025
(This article belongs to the Special Issue Studies on Clean and Sustainable Energy Utilization)
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Abstract

As landfill mining becomes more widely applied, growing attention is being paid to the waste-to-energy conversion of landfill waste. Co-disposal of landfill waste with municipal solid waste represents one of the primary strategies for achieving energy recovery of landfill waste. In this paper, the emission characteristics of pollutants were systematically analyzed during the co-disposal of landfill waste and municipal solid waste in a full-scale municipal solid waste incineration. The study investigated the formation patterns of toxic PCDD/Fs and gaseous pollutants under different co-disposal ratios of landfill waste (0%, 15%, 25%, 35%, and 45%). In total, 136 PCDD/Fs were analyzed to investigate the influence of co-disposal ratios on PCDD/F formation in both flue gas and fly ash. The influence of varying co-disposal ratios on the phase and elemental composition of fly ash was also investigated. Co-disposal led to a significant reduction in the toxic PCDD/F concentration at the boiler outlet, mainly attributed to the higher sulfur content of LW compared to MSW. With increasing co-disposal ratios, the annual emission amounts of toxic PCDD/Fs in fly ash significantly increased. The ∑PCDD/∑PCDF ratio in both flue gas of boiler outlet and fly ash also increased, indicating an enhancement of the precursor formation pathway, while the de novo synthesis pathway was relatively suppressed. The fly ash exhibited a high proportion of highly chlorinated dioxins (degree of chlorination: 7.19–7.23), likely due to their low saturated vapor pressure. According to the Hagenmaier congener distribution, high co-disposal ratios (25–45%) suppressed the chlorination of DD/DF in fly ash but promoted the formation of gas-phase PCDFs. Different co-disposal ratios significantly influenced both the emission concentrations and removal efficiencies of air pollutants, including NOx, SO2, and HCl. Although co-disposal did not alter the crystalline phase composition of fly ash, it led to an increased content of heavy metals such as Cu, Hg, and Pb.

1. Introduction

The remediation of aging municipal solid waste (MSW) landfills in China has attracted increasing attention from both the academic community and the public [1]. Nationwide, over 8 billion tonnes of MSW have been landfilled, occupying approximately 550 million m3. More than 75% of landfills commissioned before 2005 have been closed, with an estimated 7900 hectares requiring urgent remediation and over 200 million tonnes of landfill waste (LW) needing treatment [2]. Driven by rapid urbanization, numerous aging landfills originally situated on the outskirts are now integrated into urban areas [3]. These facilities commonly face dual challenges of capacity exhaustion and environmental degradation, including persistent leachate leakage [4] and uncontrolled landfill gas emissions [5], imposing significant ecological and public health pressures. Landfill mining (LFM) has emerged as a key strategy for landfill remediation, offering the advantages of resource recovery, land reuse, and comprehensive pollution control. Over the past decade, hundreds of landfill sites in China have implemented LFM technologies [6,7,8].
LW from LFM typically contains 30–50% combustible materials, mainly comprising plastic, paper, wood, and textile [9,10]. Due to the high contamination level of these materials, waste-to-energy conversion is considered the most appropriate stabilization pathway, as material recycling remains technically and economically limited [11,12]. In Europe, approximately 500,000 landfills have been identified; LFM of all landfills could lead to an annual reduction of 75 million tonnes of CO2 emissions over the next 20–30 years [13]. In China, the energy content of landfilled plastics is estimated to be equivalent to 1.37 billion tonnes of standard coal [14]. Meanwhile, the MSW incineration (MSWI) plants of China have expanded rapidly, with the number of incineration facilities rising from 130 in 2011 to approximately 927 in 2023, and the total design capacity exceeding 1 million tonnes per day [15]. Co-incineration of LW with MSW has emerged as a promising strategy to achieve energy recovery of landfill waste while addressing feedstock shortages in certain incineration plants. Studies have shown that co-incineration improves overall combustion performance [16,17]. The refuse-derived fuel (RDF) from LW can stabilize the heating value of the feedstock and maintain temperature uniformity within the combustion chamber [18]. However, due to prolonged biochemical degradation, LW typically exhibits high ash content and elevated chlorine, sulfur, and heavy metal levels—properties that significantly differ from those of MSW [11,19,20]. These differences may lead to changes in pollutant formation and distribution, including PCDD/Fs, air pollutants (HCl, SO2, NOx), and fly ash [16,21,22]. The formation pathways of PCDD/Fs are highly dependent on the synergistic interaction between chlorine sources and transition metals, particularly Cu and Fe [23], and are closely linked to the distribution of chlorine in the combustion zone and the catalytic effects of these metals. The volatilization behavior of heavy metals, in turn, is jointly governed by combustion temperature and residence time. In aged landfill waste, chlorine-containing plastics and chlorides continuously release chlorine through thermal degradation, while CuO/CuCl2 in the ash fraction can catalyze PCDD/F formation within the 250–450 °C temperature window [24]. Shibamoto et al. [25] reported that increasing the mass fraction of an external chlorine source from 0.3% to 0.9% raised the PCDD/F toxic equivalent by a factor of 2.4, highlighting that controlling the Cl-to-metal ratio is critical in co-incineration. Heavy metal volatilization is simultaneously influenced by temperature and residence time, with chlorine promoting the formation of metal chlorides and enhancing their volatility [26]. In mixed feeds of aged landfill waste and MSW (35/65%), Pb and Cd volatilization rates peaked at 47% and 38%, respectively, within the 850–950 °C range, whereas Ni and Cr—due to the rapid solid-phase formation of high-melting-point oxides—exhibited residual fractions above 80% [27]. Moreover, each 0.1 wt% increase in chlorine concentration can further elevate Pb volatilization by 3–5% [28], underscoring the importance of feedstock conditioning and dechlorination pretreatment in co-incineration systems. Current research on pollutant emissions from MSW co-incinerating LW remains limited and primarily focused on laboratory-scale experiments. Knowledge regarding the formation mechanisms of co-incinerated pollutants, particularly PCDD/Fs, in full-scale systems, remains inadequate.
In this study, five co-disposal conditions (0%, 15%, 25%, 35%, 45% of LW with MSW) were tested to evaluate their effects on emissions of toxic PCDD/Fs (2,3,7,8-substituted PCDD/Fs), air pollutants (HCl, SO2, NOx), and fly ash in a full-scale MSW incinerator. Furthermore, the emission characteristics of 136 kinds of tetra- to octa-chlorinated dibenzop-dioxin and dibenzofurans (136 PCDD/Fs) were analyzed to investigate the influence of co-disposal ratios on PCDD/F formation in both flue gas and fly ash. The paper provides critical technical insights for the practical implementation of LW energy recovery.

2. Materials and Methods

2.1. Profile of the Studied MSWI Plant and Landfill

The research was conducted at a full-scale MSWI plant in Wenzhou, Zhejiang Province, China. The plant has a designed waste treatment capacity of 1450 tons per day, but currently only processes 850 tons. Approximately 600 tons of capacity is available to handle landfill waste. A schematic diagram of the incinerator system is provided in Figure 1, with sample points marked in red. The incinerator system includes a waste pool, grate incinerator, selective non-catalytic reduction (SNCR), semi-dry spray neutralizer, activated carbon injection, fabric filter, and chimney. For the fuel of this study, the MSW was sourced from residential areas, while the landfill waste came from the Baotian Landfill in Wenzhou. A total of 1200,000 m3 of MSW was landfilled in the Baotian Landfill, where an LFM project is currently underway. As of 2023, 400,000 tons of waste had been excavated and handled, with the combustibles sent to the MSWI plant for disposal.

2.2. Design of Co-Disposal Tests

To investigate the effects of LW co-disposal on PCDD/F emissions and formation, co-disposal tests were conducted under four operating conditions with co-disposal ratios of 0%, 15%, 25%, and 45%, respectively, over a five-day period. As shown in Figure A1, MSW and LW were stored and composted in the waste pool five days prior to the tests. These wastes were mixed in the designated proportions and fed into the incinerator the night before each test to stabilize combustion conditions. Throughout the co-disposal test period, the incineration system operated stably, ensuring the boiler load exceeded 70%. To prevent fouling in the flue, the incineration system conducts soot-blowing operations three times per day.

2.3. Waste Characteristics

MSW and LW were collected in accordance with CJ/T 313-2009 [29], vacuum-sealed, and transported to the laboratory for detailed analysis. The samples were dried at 105 °C, and moisture content was determined following the CJ/T 313–2009. Subsequently, a liquid nitrogen mill was used to grind the dry samples into particles (<1 mm). The volatile matter and ash content were determined according to ASTM E 897-88 [30] and ASTM E 830-87 [31], respectively. Fixed carbon content was calculated using the chemical balance method. Elemental analysis (C/H/N/S/O) was performed using the elemental analyzer (Vario Macro Cube, Elementar, Hesse, Germany). Table 1 and Figure A2 show the characteristic of MSW and LW. The net calorific value (Qner, ar) of the samples was measured using the bomb calorimeter (XRY-1c, Laboao, Zhengzhou, China). LW primarily consists of textiles and plastics, which contribute to a higher calorific value compared to MSW. However, due to a significant amount of soil adhering to its surface, LW has a higher ash content, potentially affecting combustion stability and leading to increased production of FA and slag.

2.4. Sampling and Analysis

Dioxin sampling in flue gas was carried out following HJ 77.2-2008 [32]. Sampling points were installed at the inlet and outlet of the flue gas purification system. For each operating condition, two parallel samples were collected, with each sampling run lasting for 3 h. The gas sampler (ZR-3720, Junray, Qingdao, China) was employed for dioxin sampling in flue gas. Before sampling, a recovery standard was added to the XAD-2 resin to evaluate the efficiency and reliability of the sampling process. All collected samples, including the filter, XAD-2 resin, and impinger solution, were stored at low temperature for preservation. An online FTIR monitoring system (DX-4000, Gasmet, Vantaa, Finland) was used to continuously monitor air pollutants (NO, NO2, SO2, and HCl). All calculated concentrations of PCDD/Fs and major air pollutants were standardized to 11% O2, 273.15 K, and 100 kPa, following GB 18485–2014 [33]. The FA without chelation or solidification treatment was collected from the fabric filter. The samples were also stored at low temperature in amber glass bottles and delivered to the laboratory for analysis.
The phase composition of FA was analyzed using X-ray diffraction (XRD; D/max 2550PC, Tokyo, Japan), while the elemental distribution on the outer surface of FA was measured using X-ray fluorescence (XRF; PANalytical Axios, Almelo, The Netherlands). Heavy metal analysis of FA was performed following the USEPA 3050 standard [34], using a combined digestion method with HNO3, HF, and HClO4. The concentrations of heavy metals were quantitatively determined by ICP-MS (Agilent 7900, Agilent Technologies, Santa Clara, CA, USA). Moreover, detailed procedures for the analysis of PCDD/Fs in flue gas and fly ash are provided in the Supplementary Materials.

3. Results

3.1. Impact of Co-Disposal on Toxic PCDD/Fs

3.1.1. Toxic PCDD/F Concentrations

Table 2 presents the concentrations, emission factor (EF) and emission amounts (EA) of toxic PCDD/Fs in flue gas and FA under different co-disposal conditions at corresponding sampling points. At the BO, the total and I-TEQ concentration of PCDD/Fs in the primary flue gas of MSWI were 3.18 ng/Nm3 and 0.32 ng I-TEQ/Nm3, respectively. These values were notably higher than those observed under co-disposal conditions. The suppression of dioxin formation may be due to the elevated sulfur content of LW relative to fresh MSW [35]. Cai et al. reported that co-disposal of LW and RDF resulted in reduced dioxin emissions [22]. The concentrations of toxic PCDD/Fs in flue gas at the chimney (CH) for MSWI and 15%, 25%, 35%, 45% co-disposal decreased from 0.07 ng/Nm3 to 0.09, 0.08, 0.06, 0.06 ng/Nm3, respectively, demonstrating a significant reduction in gas-phase PCDD/Fs due to the APCS. The removal efficiencies of the APCS for toxic PCDD/Fs were 98.4% (MSWI) and 94.7%, 92.9%, 98.0%, 98.4% (15%, 25%, 35%, 45% co-disposal). This APCS meets the emission limit value for toxic PCDD/Fs in flue gas (0.1 ng I-TEQ/Nm3, GB 18485-2014 [33]) for LW co-disposal. For the FA, the concentrations of toxic PCDD/Fs for 15%, 25%, 35%, and 45% co-disposal are similar to MSWI. This suggests that LW co-disposal has minimal impact on the solid-phase PCDD/Fs in the FA. However, these results exceed the limit value (50 ng I-TEQ/kg, HJ 1134-2020 [36]), indicating that detoxification treatment is required for the FA [37].
Additionally, the ratios of PCDDs to PCDFs (∑PCDD/∑PCDF) in the flue gas of BO for MSWI and 15%, 25%, 35%, and 45% co-disposal were 0.66 and 0.77, 0.80, 0.67, and 0.66, respectively. For the FA, the ratios were 2.76 and 2.90, 3.10, 3.15, and 3.17, respectively. The higher ∑PCDD/∑PCDF ratios in both flue gas and FA from LW co-disposal, compared to MSWI, suggest an increased generation of precursors during LW co-disposal, thereby promoting the precursor synthesis of PCDD/Fs [38]. Furthermore, the higher ∑PCDD/∑PCDF ratios in FA compared to flue gas may be attributed to the lower vapor pressure of PCDDs relative to PCDFs [39].
In addition, Table 2 includes data on the emission factors and emission amounts of toxic dioxins. These values fall within the emission range reported for PCDD/Fs in flue gas from MSW incineration plants (27–225 ng I-TEQ/ton of fuel), indicating that LW co-disposal did not significantly impact the toxic PCDD/F emissions in flue gas [40]. LW co-disposal substantially increased toxic PCDD/F emissions in the FA, with EF and EA values of 3.56, 5.06, 5.00, and 4.83 µg I-TEQ/ton and 962.17, 1365.97, 1349.5, and 1355.38 mg I-TEQ/year, respectively, for 15%, 25%, 35%, and 45% co-disposal. These values were significantly higher than those for MSWI (3.30 µg I-TEQ/ton and 891.87 mg I-TEQ/year), which can be attributed to the higher ash content in LW, leading to increased FA production. FA was identified as the primary source of toxic PCDD/Fs, accounting for over 99% of total emissions. This is because the surfaces of FA particles serve as key sites for the formation of toxic PCDD/Fs [41,42]. In conclusion, while LW co-disposal reduces the concentrations of toxic PCDD/Fs in primary flue gas at the boiler outlet, it significantly increases PCDD/F emissions in the FA, thus exacerbating the challenges associated with FA disposal.

3.1.2. The Distribution of Toxic PCDD/Fs

To further assess the impact of LW co-disposal on the distribution of toxic PCDD/F congeners, Table 2 presents the chlorination degrees of toxic PCDD/Fs (dCl-PCDD/Fs). The results indicate that LW co-disposal had no significant effect on the chlorination degree of PCDD/Fs. Additionally, the chlorination degree of PCDD/Fs in the FA (7.19–7.23) was higher than that in the flue gas of BO (6.36–6.64), likely due to the lower vapor pressure of highly chlorinated PCDD/Fs.
Figure 2 illustrates the congener profiles of toxic PCDD/Fs for MSWI and 15%, 25%, 35%, and 45% co-disposal. The concentration of toxic PCDDs was primarily dominated by OCDD and 1,2,3,4,6,7,8-HpCDD. In the flue gas of BO, LW co-disposal increased the proportion of OCDD in the congener profile from 56% to 60%. Different toxic PCDD/F congeners contributed variably to the I-TEQ, with 2,3,7,8-TCDD, 1,2,3,7,8-PeCDD, and 2,3,4,7,8-PeCDF being the primary contributors to the I-TEQ concentration of toxic PCDD/Fs. In the FA, 2,3,4,7,8-PeCDF was the predominant contributor to the I-TEQ concentration of toxic PCDD/Fs, with minimal variation among the other congeners. Overall, LW co-disposal did not significantly alter the congener profiles of toxic PCDD/Fs.

3.2. Impact of Co-Disposal on Formation Pathways of PCDD/Fs

3.2.1. The Distribution of PCDD/F Congeners

Table 3 presents the total concentrations of individual homologues from 136 PCDD/F congeners. As expected, the total concentrations of PCDD/Fs in the flue gas of BO decreased, consistent with the observed trends in toxic PCDD/F emissions. In the FA, the PCDD/F concentrations for the MSWI (7.86 ± 1.61 µg/kg) were similar to those for the 10% co-disposal condition (7.22 ± 1.32 µg/kg), while significantly higher concentrations were observed for the 25%, 35% and 45% co-disposal conditions, at 9.83 ± 0.23 µg/kg, 9.36 ± 0.046 µg/kg, and 8.80 ± 0.017, respectively. In terms of total PCDD/F emissions, the EF of PCDD/Fs increased with the co-disposal ratio, rising from 235.83 µg/ton of fuel (MSWI) to 259.85, 413.06, 421.16, and 437.58 µg/ton of fuel (15%, 25%, 35%, 45%).
Figure 3 illustrates the fingerprints and distribution of 136 PCDD/F congeners. Co-disposal of LW had a minimal impact on the congener fingerprint, with only slight variations in detail. Similarly, the dCl-PCDD/Fs in the flue gas of BO and in the FA showed little difference between the MSWI and the 15%, 25%, 35%, and 45% co-disposal (Table 3), likely due to the fact that LW primarily consists of textiles and plastics, which have similar physicochemical properties to those in MSW. Moreover, in the flue gas of BO, PCDD/Fs were predominantly composed of low-chlorinated PCDFs, with TCDF, PeCDF, and HxCDF accounting for 68% to 75% of the total. In the FA, PCDD/Fs were mainly composed of high-chlorinated PCDDs (HxCDD, HpCDD, and OCDD constituting approximately 49%) and low-chlorinated PCDFs (TCDF, PeCDF, and HxCDF comprising approximately 34%). Correlation analysis between homolog concentrations and the co-disposal ratio (Figure 4) revealed that the concentration of all PCDD congeners in flue gas decreased as the co-disposal ratio increased. Among PCDFs, only 1,2,8,9-TCDF and OCDF were positively correlated with the co-disposal ratio, while the concentrations of other TCDF congeners and all PeCDF/HxCDF congeners decreased with increasing co-disposal ratio. The concentration of HpCDF showed no correlation with the co-disposal ratio. In contrast, most PCDD and TCDF/PeCDF congeners in the FA increased in concentration as the co-disposal ratio increased, while OCDF exhibited a negative correlation with the co-disposal ratio. The concentrations of HxCDF and HpCDF in the FA showed no correlation with the co-disposal ratio. In summary, LW co-disposal reduces the formation and emission of PCDD/Fs in primary flue gas, while increasing PCDD/F content in the FA, likely due to the higher chlorine content and calorific value of LW, which influence the co-incineration process.

3.2.2. Formation Pathways of PCDD/Fs

PCDD/Fs are formed through two primary pathways: precursor synthesis and de novo synthesis. Precursor synthesis generates PCDD/Fs, primarily PCDDs, via condensation or catalytic chlorination reactions of precursors. The main precursors include (1) chlorophenols (CP); (2) dibenzodioxins (DD) and dibenzofurans (DF); and (3) short-chain aliphatic hydrocarbons [43]. De novo synthesis, on the other hand, involves the catalytic oxidation and chlorination of residues from chlorine-containing compounds and hydrocarbons, with PCDFs being produced in much greater quantities than PCDDs. To identify the PCDD/F formation pathway under different conditions, the total ∑PCDD/∑PCDF is calculated in Table 3. As the co-disposal ratio increases, the ∑PCDD/∑PCDF in the flue gas of BO rises from 0.24 (MSWI) to 0.27, 0.32, 0.26, 0.28 (15%, 25%, 35%, 45%), respectively. Similarly, in the FA, the ratio increases from 1.42 (MSWI) to 1.47, 1.59, 1.59, 1.55 (15%, 25%, 35%, 45%). These results indicate an increase in the PCDD content relative to total PCDD/Fs, suggesting that LW co-disposal promotes the precursor synthesis pathway. The higher proportion of PCDDs relative to PCDFs in the flue gas of BO suggests that de novo synthesis plays a more prominent role in PCDD/F formation during co-combustion than precursor synthesis. Conversely, the opposite trend in the FA suggests that precursor synthesis is the dominant pathway, possibly due to the memory effect of residuals in bag filters, which leads to the accumulation of PCDDs, as PCDDs tend to accumulate more readily in the FA [44,45].

3.2.3. Effect on CP-Route Synthesis

CP-route synthesis refers to a significant and representative precursor pathway that directly generates PCDD/Fs through the condensation or rearrangement of CP [46,47]. The representative congeners formed via the CP route primarily include 1,3,6,8- and 1,3,7,9-TCDD, 1,2,4,6,8-/1,2,4,7,9-, 1,2,3,6,8-, and 1,2,3,7,9-PeCDD, as well as 1,2,3,4,6,8-HxCDD, and 2,4,6,8-/1,2,3,8-/1,2,3,6-/1,4,6,9-/1,6,7,8-/1,2,3,4-/2,3,6,8-TCDF [48]. Figure 5 calculates the correlation coefficients (R) between CP-route congener contents and the total PCDD/F congener contents in the flue gas and FA, respectively. Most CP-route congeners exhibit positive correlations with each other, indicating that LW co-disposal has no effect on the formation mechanism of the CP route. Additionally, CP-route congeners and certain PCDD congeners display strong correlations, suggesting that chlorination and dechlorination interactions occur between CP-route congeners and other PCDD congeners due to the adjacent substitution positions of chlorine [49].
The relative importance of CP-route congeners is summarized in Table 4, based on their percentage within their respective homolog groups. Under different operational conditions, TCDD (34.6–43.9% in BO, 61.8–74.2% in FA), PeCDD (61.7–66.8% in BO, 78.9–84.0% in FA), and HxCDD (48.3–50.2% in BO, 67.4–75.9% in FA) consistently show high relative importance in the CP pathway, likely due to the uniformity of the CP formation mechanism. In contrast, the relative importance of 1,2,3,8-/1,2,3,6-/1,4,6,9-/1,6,7,8-/1,2,3,4-/2,3,6,8-TCDF is low, likely because TCDF is primarily generated through de novo synthesis. As the co-disposal ratio increases, the relative importance of PCDD congeners formed via the CP pathway slightly increases in the flue gas. In the FA, the relative importance of PCDD congeners in the CP pathway (25%, 35%, 45%) is significantly higher compared to the MSWI and 10% co-disposal conditions. The proportion of TCDF congeners in the CP pathway in the FA shows a negative correlation with some PCDF congeners, further indicating that LW co-disposal strengthens the CP pathway. This may be due to the higher ash content of LW, which likely worsens combustion conditions and increases the generation of precursors. The relative importance of TCDD congeners in the CP pathway is notably higher in the FA than these in the flue gas of BO, and most non-CP pathway PCDD congeners in the FA exhibit a negative correlation with the co-disposal ratio (Figure 4). This suggests that precursor synthesis in the FA is more inclined toward the CP pathway than flue gas, and increasing the co-disposal ratio significantly enhances the contribution of the CP pathway to PCDD/F formation in the FA.

3.2.4. Effect on Chlorination of DD/DF

According to the electrophilic aromatic substitution mechanism, the chlorination of DD/DF follows the sequence 2→8→3→7→1→4→6→9 [50]. If the chlorination of DD or DF is a key pathway in the formation of PCDD/Fs, significant chlorination would be expected at the β-positions of 2, 3, 7, and 8 [51]. The Hagenmaier distribution (Table 5) was introduced to assess the formation tendencies of 2,3,7,8-congeners and to explore their relationships with the co-disposal ratio [52]. The Hagenmaier value (%) represents the percentage of each 2,3,7,8-PCDD/F isomer relative to the total concentration of its corresponding homolog group, and for OCDD and OCDF, it represents their percentage within the total PCDD and PCDF, respectively. A higher Hagenmaier value indicates a stronger formation tendency for that isomer within its homolog group.
In the flue gas of BO, the Hagenmaier value for 2,3,7,8-PCDDs was 34.3 (MSWI) and 32.6, 35.8, 34.8, and 34.4 (15%, 25%, 35%, 45%), respectively, showing no significant variation with the co-disposal ratio. However, in the FA, the Hagenmaier values for 2,3,7,8-PCDDs were 21.4, 21.9, and 24.5 (25%, 35%, 45%), significantly lower than 28.7 (MSWI) and 30.2 (15%). This suggests that co-disposal has minimal impact on DD chlorination in flue gas, but high co-disposal ratios can reduce DD chlorination in the FA. As mentioned earlier, high co-disposal ratios significantly enhance the CP pathway for PCDD formation in the FA, which may weaken the competing DD chlorination pathway.
For 2,3,7,8-PCDFs in flue gas, the Hagenmaier values were 18.6, 17.8, and 17.2 (25%, 35%, 45%), slightly higher than 16.5 (MSWI) and 15.2 (15%). In contrast, the Hagenmaier values for 2,3,7,8-PCDFs in the FA were 23.7, 23.6, and 25.2 (25%, 35%, 45%), significantly lower than 27.9 (MSWI) and 28.4 (15%). This suggests that higher co-disposal ratios slightly enhance DF chlorination in flue gas but reduce DF chlorination in the FA. For the flue gas, this may be attributed to the high co-disposal ratio of LW, which increases ash content, deteriorates combustion conditions, and promotes precursor formation. For the FA, LW co-disposal may slow the desorption of Cl from the solid phase to the gas phase, enhancing the pathway for the oxidation and cleavage of macromolecular carbon structures, leading to the direct generation of PCDFs.

3.2.5. Effect on De Novo Synthesis

Precursor synthesis is the primary pathway for PCDDs, while de novo synthesis predominantly forms PCDFs [53,54]. As shown in Figure 3, the main homologues of PCDFs include 1,2,4,7-/1,2,4,6-/1,3,4,7-/1,3,7,8-TCDF (15.8–20.2% of total TCDF), 1,3,6,7-/1,2,4,8-/1,3,7,9-TCDF (10.0–11.7% of total TCDF), 1,2,3,6,8-/1,3,4,7,8-/1,2,4,7,8-PeCDF (19.3–25.1% of total PeCDF), 1,3,6,7,8-/1,3,4,6,7-/1,2,4,6,7-PeCDF (15.3–16.7% of total PeCDF), 1,3,4,6,7,8-/1,2,4,6,7,8-HxCDF (27.7–28.8% of total HxCDF), and 1,2,3,4,6,7,8-HpCDF (54.8–71.3% of total HpCDF). The mass fractions of PCDF homologues in both the flue gas and FA follow the order TCDF > PeCDF > HxCDF > HpCDF > OCDF, which is consistent with the characteristic fingerprint of de novo synthesis [55]. Furthermore, changes in the co-disposal ratio had minimal impact on the fingerprint distribution of PCDD/Fs in flue gas. However, in the FA, most PeCDF, HxCDF, HpCDF, and OCDF concentrations decreased as the co-disposal ratio increased (Figure 4), suggesting that LW co-disposal suppresses de novo synthesis in the FA.

3.3. Impact of Co-Disposal on Air Pollutants

For air pollutant emission characteristics, co-disposal ratios significantly affect the generation, treatment efficiency, and final emissions of air pollutants (NOx, SO2, and HCl), as illustrated in Table 6. The NOx concentration of BO exhibited a non-monotonic trend with increasing co-disposal ratio. The highest NOx concentration was 266.02 mg/Nm3 (MSWI). This decreased to 243.23 mg/Nm3 (15%), rebounded to 260.39 mg/Nm3 (25%), dropped further to 227.72 mg/Nm3 (35%), and rose again to 232.23 mg/Nm3 (45%). These fluctuations may result from variations in nitrogen content of LW and dynamic changes in combustion conditions such as temperature and oxygen availability. Correspondingly, NOx concentrations of CH showed a rise–fall–rise trend: increasing from 67.0 mg/Nm3 (MSWI) to a peak of 80.8 mg/Nm3 at 25%, then declining to 76.66 mg/Nm3 at 35%, followed by a slight rise to 78.21 mg/Nm3 at 45%. This indicates that the denitrification efficiency declined progressively from 74.8% (MSWI) to 66.3% (35%, 45%). SO2 concentration of BO increased from 33.94 mg/Nm3 (MSWI) to 46.95 mg/Nm3 (15%), sharply peaked at 92.17 mg/Nm3 (25%), dropped to 39.85 mg/Nm3 (35%), and rose slightly to 45.85 mg/Nm3 (45%). These shape fluctuations reflect inconsistent sulfur content of LW. SO2 concentration of CH remained extremely low (0.09–4.48 mg/Nm3), with a desulfurization efficiency of 95.1–99.8%. However, a notable emission peak occurred at 25% co-disposal (4.48 mg/Nm3), suggesting that high-sulfur waste could challenge end-of-pipe treatment systems. HCl concentrations of BO showed a fluctuating pattern: 127.65 mg/Nm3 (MSWI), decreasing to 110.43 mg/Nm3 (15%), rising to 143.8 mg/Nm3 (25%), and then dropping to 107.72 mg/Nm3 (35%) and further to 101.39 mg/Nm3 (45%). HCl concentrations of CH increased from 17.2 mg/Nm3 (MSWI) to 22.72 mg/Nm3 (25%), then decreased to 16.82 mg/Nm3 (35%). The treatment efficiency remained stable at 82–86%. However, variations in chlorine content due to co-disposal could increase the load on end-of-pipe control.

3.4. Impact of Co-Disposal on Physicochemical Characteristics of FA

Changes in fuel composition typically influence the physicochemical properties and potential toxicity of FA from MSWI plants [22,56,57]. To assess the potential impact of LW co-disposal on FA properties, various analytical methods were employed to characterize the composition and toxicity of FA under different co-disposal conditions.

3.4.1. XRD Analysis

Figure 6 shows the XRD analysis of FA under various LW co-disposal conditions. The results indicate that the primary crystalline phases in the FA include CaO, CaClOH, Ca(OH)2, CaSO4, CaCO3, NaCl, KCl, and SiO2. These crystalline phases are predominantly composed of Ca-rich and Cl-rich compounds and remain largely unchanged across different conditions. This is likely due to LW being primarily composed of plastics, textiles, and other organic solid wastes with physicochemical properties similar to those of the corresponding components in MSW. CaO and Ca(OH)2 mainly originate from the lime injected during the semi-dry spray neutralization process in the APCS [58]. The Cl in the FA primarily originates from Cl-rich waste components, such as food residues and plastics. Alkali metal chlorides, which have relatively low boiling points, easily vaporize into the flue gas and condense at lower temperatures, becoming concentrated on the surface of FA particles and leading to a high chloride salt content in the FA. In conclusion, the XRD patterns of FA reveal only minor distinctions, indicating that LW co-disposal has a limited effect on the crystalline phases of FA.

3.4.2. Elemental Composition

The elemental composition of FA from various LW co-disposal conditions was further analyzed using XRF and ICP-MS. Table 7 and Table 8 list and compare the primary elemental composition and heavy metal content in the FA, respectively. The major elements in the FA from MSWI are Ca (34.9–36.4%), O (15.6–16.7%), and Cl (13.9–15.2%). In addition to alkali metals, Al, Fe, and Mg are the predominant metal elements present in the FA. Combined with the XRD results, it is evident that FA of various LW co-disposal conditions exhibits a consistent metal oxide–SiO2-Al2O3 system.
The concentration of heavy metals in the FA increased significantly with LW co-disposal. Specifically, Cu content increased from 412 mg/kg (MSWI) to 453, 551, 511, and 526 mg/kg (15%, 25%, 35%, 45%), respectively. Similarly, Cd content increased from 135 mg/kg to 146, 281, 235, and 207 mg/kg, Ba content increased from 172 mg/kg to 191, 436, 278, and 357 mg/kg, and Pb content increased from 300 mg/kg to 364, 1320, 683, and 749 mg/kg. Additionally, Hg content increased from 7.5, 7.2 mg/kg (MSWI, 10%) to 12.9, 9.7, and 8.4 (25%, 35%, 45%) mg/kg, respectively.
In conclusion, LW co-disposal has minimal impact on the primary elemental composition of FA but significantly increases the concentrations of certain heavy metals. LW contains complex humic substances and higher concentrations of heavy metals compared to MSW, resulting in a substantial increase in the heavy metal content of FA produced through LW co-disposal.

4. Discussion

This study systematically investigated, in a full-scale mechanical grate incineration system, the effects of co-incinerating LW and MSW at varying blending ratios (0–45%) on the emissions of PCDD/Fs, air pollutants, and fly ash characteristics. The results are consistent with key findings reported in the literature, while also extending current understanding. At the BO, gaseous PCDD/Fs (I-TEQ) generally decreased with increasing LW blending ratio, with the most pronounced reduction observed at 25% (see Table 2 and Figure 3). This observation agrees with previous mechanistic studies [35,48,53], which have demonstrated that sulfur-containing components can inhibit de novo synthesis by passivating catalytically active copper sites, thereby reducing gas-phase PCDD/F formation. Moreover, the relative abundance of PCDF congeners decreased while that of PCDD congeners increased at the BO, in line with changes in Hagenmaier profiles and indicative of a shift toward precursor pathways and a corresponding suppression of the de novo pathway for PCDFs [52,59].
In contrast to the reductions observed at the BO, the TEQ load and heavy metal concentrations in the FA increased significantly (see Table 2 and Table 8), with greater enrichment of highly chlorinated, low-volatility congeners and heavy metals such as Cu, Cd, Pb, and Hg in the particulate phase. The phase-partitioning results—showing that more than 99% of the total TEQ is retained in the solid phase—are consistent with the high capture efficiencies of full-scale APCDs [60,61] and with the particulate-phase affinity of dioxins [24,53,59,62]. Through the multi-blend experimental design, this study further elucidates the relationship between feedstock characteristics, formation mechanisms, and end-of-pipe control loads.
For air pollutants, HCl and SO2 concentrations at the BO peaked around the 25% blending ratio, while NOx levels showed relatively small variations (see Table 6). After APCD treatment, stack emissions remained low, in agreement with performance reported for modern MSWI systems [63]. Nevertheless, the acid gas peaks observed at 25% blending may increase reagent consumption and by-product generation, necessitating careful operational balancing.
Overall, under full-scale and multi-blend conditions, this study confirms laboratory-scale mechanistic trends and provides engineering-relevant data that fill a key knowledge gap regarding LW–MSW co-incineration. From a practical perspective, the acid gas peaks at approximately 25% blending call for proactive planning of reagent dosing, secondary product management, and pressure-drop budgets. Given the increased FA management burden resulting from LW blending, strategies for fly ash classification, stabilization, and compliant disposal or safe utilization should be integral to co-incineration operations. The EF and EA data presented herein can be directly applied for emission inventory development, permit applications, and cost–risk trade-off analyses, supporting operational decision-making.
However, the study has limitations. The results are based on a single full-scale mechanical grate MSWI with a specific APCD configuration, and their applicability to other furnace types and pollution control systems remains to be confirmed. Each operating condition was sampled for only approximately three hours with two replicates; although sufficient for steady-state characterization, this approach does not capture seasonal variations, start-up and shut-down conditions, or abrupt changes in feed composition. Feedstock characterization was not sufficiently detailed to differentiate between organic and inorganic chlorine, sulfur speciation, and metal valence or particle size distributions, constraining mechanistic interpretation.
Future research should involve long-term, multi-season monitoring across diverse furnace types and APCD configurations to capture operational variability and feedstock differences. Detailed feedstock characterization—including chlorine and sulfur speciation, metal valence states, and particle size distributions—combined with reaction kinetics analyses would enable more precise attribution of precursor and de novo pathway contributions. In addition, studies should explore stabilization and resource recovery technologies for co-incineration fly ash to mitigate FA-related risks, while considering the application of artificial intelligence in landfill waste disposal [64]. Furthermore, life cycle assessment should be incorporated to develop integrated environmental–economic optimization frameworks that support efficient and sustainable co-incineration.

5. Conclusions

In the study, a series of waste-to-energy experiments were conducted using a full-scale MSW incineration system, in which LW co-incinerated MSW. The main conclusions are as follows:
(1)
By comparing five co-disposal conditions (0%, 15%, 25%, 35%, and 45%), it was found that the LW co-disposal led to a significant reduction in the toxic PCDD/F concentration at the BO (from 3.18 ng/Nm3 down to 1.69 ng/Nm3). This reduction is mainly attributed to the higher sulfur content of LW compared to MSW. The toxic PCDD/F concentration at the CH of all conditions met the national emission limit (0.1 ng I-TEQ/Nm3, GB 18485–2014), with removal efficiencies exceeding 92.9%. However, co-disposal significantly increased the EF and EA in the FA. While co-disposal improves flue gas pollutant control, it also enhances the environmental risks associated with FA, highlighting the need for enhanced FA management strategies.
(2)
With increasing co-disposal ratio, the ∑PCDD/∑PCDF ratio in flue gas of BO and FA increased, suggesting enhanced precursor pathways. Moreover, highly chlorinated congeners dominated in the FA (average chlorination degree: 7.19–7.23), likely due to their low vapor pressure and high tendency to adsorb on particulate surfaces. Hagenmaier profile analysis further indicated that higher co-disposal ratios (25–45%) inhibited the chlorination of DD/DF congeners in the FA but promoted gas-phase formation of PCDFs. These findings suggest that co-disposal alters combustion conditions and FA physicochemical properties, thereby reshaping dioxin formation pathways.
(3)
The co-disposal ratio has a noticeable impact on the emission concentrations and removal efficiencies of air pollutants, including NOx, SO2, and HCl. With an increasing ratio, NOx concentrations fluctuated but showed an overall declining trend. SO2 and HCl concentrations at the BO first increased and then decreased with increasing ratio. Despite these variations, the overall flue gas concentrations remained at low levels. Nevertheless, the potential load impacts caused by high-sulfur and high-chlorine LW require careful attention to avoid local overload or system instability.
(4)
Although the co-disposal did not alter the crystalline phase composition of fly ash (mainly consisting of CaO, CaClOH, NaCl, and KCl), it led to an increased content of heavy metals such as Cu, Hg, and Pb. Ca, O, and Cl remained the dominant elements in the fly ash, while the addition of LW caused significant enrichment of certain heavy metals.

Supplementary Materials

The following supporting information can be downloaded at https://www.mdpi.com/article/10.3390/en18174515/s1: Chapter S1: Procedure of PCDD/F pre-treatment and analysis; Chapter S2: Statistical analysis; Table S1: Information of USEPA1613 recovery standards added during pre-treatment of PCDD/Fs; Table S2: Information of USEPA23 recovery standards added during pre-treatment of PCDD/Fs; Table S3: Instrumental parameters of PCDD/F analysis of gas chromatography/high-resolution mass spectrometry (HRGC/HRMS); Table S4: Full titles of PCDD/F homologues; Table S5: Information of 2,3,7,8-PCDD/Fs and corresponding I-TEF; Table S6: Information of 136 PCDD/Fs; Table S7: Correlation analysis between the concentration of dioxin congeners and the co-incineration ratio; Table S8: Correlation analysis between the percentage distribution of dioxin congeners and the co-incineration ratio; Table S9: Correlation analysis between 1,3,7,9-, 1,3,6,8-TCDD, 1,2,4,6,8/1,2,4,7,9, 1,2,3,6,8-, 1,2,3,7,9-PeCDD, 1,2,3,4,6,8 HxCDD and 1,2,3,8/1,2,3,6/1,4,6,9/1,6,7,8/1,2,3,4/2,3,6,8-TCDF with all other PCDD/F congeners of flue gas; Table S10: Correlation analysis between 1,3,7,9-, 1,3,6,8-TCDD, 1,2,4,6,8/1,2,4,7,9, 1,2,3,6,8-, 1,2,3,7,9-PeCDD, 1,2,3,4,6,8 HxCDD and 1,2,3,8/1,2,3,6/1,4,6,9/1,6,7,8/1,2,3,4/2,3,6,8-TCDF with all other PCDD/F congeners of fly ash.

Author Contributions

Conceptualization, Z.Z. and X.L.; data curation, Z.Z.; formal analysis, X.X. and X.L.; funding acquisition, X.L.; investigation, Z.Z. and X.X.; methodology, X.L.; project administration, X.L.; resources, X.X.; software, Z.Z.; supervision, X.L.; validation, Z.Z., X.X. and X.L.; visualization, Z.Z. and X.X.; writing—original draft, Z.Z.; writing—review and editing, X.X. All authors have read and agreed to the published version of the manuscript.

Funding

This research was funded by the Key Research and Development Program of Zhejiang Province, grant number 2022C03082.

Data Availability Statement

The original contributions presented in this study are included in the article. Further inquiries can be directed to the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

Abbreviations

The following abbreviations are used in this manuscript:
MSWMunicipal Solid Waste
LWLandfill Waste
LFMLandfill Mining
MSWIMunicipal Solid Waste Incineration
RDFRefuse-Derived Fuel
APCSAir Pollution Control System
SNCRSelective Non-Catalytic Reduction
BOBoiler Outlet
CHChimney
FAFly Ash
EAEmission Amount
EFEmission Factor
PCDDsPolychlorinated Dibenzo-p-Dioxins
PCDFsPolychlorinated Dibenzofurans
PCDD/FsPolychlorinated Dibenzo-p-Dioxins and Dibenzofurans
136 PCDD/Fs136 Kinds of Tetra- to Octa-Chlorinated Dibenzop-Dioxin and Dibenzofurans
Nm3Normal Cubic Meters
I-TEQInternational Toxic Equivalency Quantity
I-TEFInternational Toxic Equivalency Factor
MMoisture
AAsh
VVolatile
FcFixed Carbon
Qner,arNet Calorific Value
arReceived Basis
dDry Basis
CPChlorophenol
DDDibenzodioxin
DFDibenzofuran
XRDX-ray diffraction
XRFX-ray fluorescence

Appendix A

Energies 18 04515 g0a1
Figure A1. Flow diagram of co-disposal tests.
Figure A1. Flow diagram of co-disposal tests.
Energies 18 04515 g0a1
Energies 18 04515 g0a2
Figure A2. Composition of combustible materials in MSW and LW.
Figure A2. Composition of combustible materials in MSW and LW.
Energies 18 04515 g0a2

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Energies 18 04515 g001
Figure 1. Schematic diagram of the incinerator system co-incinerating LW (SNCR: selective non-catalytic reduction; BO: boiler outlet; FA: fly ash; CH: chimney).
Figure 1. Schematic diagram of the incinerator system co-incinerating LW (SNCR: selective non-catalytic reduction; BO: boiler outlet; FA: fly ash; CH: chimney).
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Energies 18 04515 g002
Figure 2. Total (a,c,e) and I-TEQ (b,d,f) concentration (%) of toxic PCDD/F congeners under MSWI and LW co-disposal conditions.
Figure 2. Total (a,c,e) and I-TEQ (b,d,f) concentration (%) of toxic PCDD/F congeners under MSWI and LW co-disposal conditions.
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Energies 18 04515 g003
Figure 3. The fingerprints and distribution of PCDD/F congeners under MSWI and LW co-disposal conditions (the numbers on the horizontal axis represent the substitution positions of PCDD/F homologues).
Figure 3. The fingerprints and distribution of PCDD/F congeners under MSWI and LW co-disposal conditions (the numbers on the horizontal axis represent the substitution positions of PCDD/F homologues).
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Energies 18 04515 g004
Figure 4. Correlation analysis between dioxin congener concentration/mass distribution and co-incineration ratio (r1: correlation coefficient between the flue gas dioxin concentration and the co-incineration ratio; r2: correlation coefficient between the FA dioxin concentration and the co-incineration ratio; r3: correlation coefficient between the flue gas dioxin mass distribution and the co-incineration ratio; r4: correlation coefficient between the FA dioxin mass distribution and the co-incineration ratio).
Figure 4. Correlation analysis between dioxin congener concentration/mass distribution and co-incineration ratio (r1: correlation coefficient between the flue gas dioxin concentration and the co-incineration ratio; r2: correlation coefficient between the FA dioxin concentration and the co-incineration ratio; r3: correlation coefficient between the flue gas dioxin mass distribution and the co-incineration ratio; r4: correlation coefficient between the FA dioxin mass distribution and the co-incineration ratio).
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Energies 18 04515 g005
Figure 5. Correlation analysis between 1,3,7,9-, 1,3,6,8-TCDD, 1,2,4,6,8/1,2,4,7,9, 1,2,3,6,8-, 1,2,3,7,9-PeCDD, 1,2,3,4,6,8 HxCDD and 1,2,3,8/1,2,3,6/1,4,6,9/1,6,7,8/1,2,3,4/2,3,6,8-TCDF with all other PCDD/F congeners of flue gas (left) and FA (right).
Figure 5. Correlation analysis between 1,3,7,9-, 1,3,6,8-TCDD, 1,2,4,6,8/1,2,4,7,9, 1,2,3,6,8-, 1,2,3,7,9-PeCDD, 1,2,3,4,6,8 HxCDD and 1,2,3,8/1,2,3,6/1,4,6,9/1,6,7,8/1,2,3,4/2,3,6,8-TCDF with all other PCDD/F congeners of flue gas (left) and FA (right).
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Energies 18 04515 g006
Figure 6. XRD results of FA from MSWI and LW co-disposal conditions (1: SiO2; 2: NaCl; 3: KCl; 4: CaSO4; 5:CaCO3; 6: Ca(OH)2; 7: CaO; 8: CaClOH; 9: Al2O3).
Figure 6. XRD results of FA from MSWI and LW co-disposal conditions (1: SiO2; 2: NaCl; 3: KCl; 4: CaSO4; 5:CaCO3; 6: Ca(OH)2; 7: CaO; 8: CaClOH; 9: Al2O3).
Energies 18 04515 g006
Table 1. Physicochemical characteristics (mean value) of MSW and LW.
Table 1. Physicochemical characteristics (mean value) of MSW and LW.
Analysis Index LW MSW
Proximate analysisMar%38.8853.70
Ad28.5713.16
Vd64.6273.46
Fcd6.8110.02
Ultimate analysisCd45.4847.60
Hd4.915.95
Nd1.110.82
Sd0.790.34
Od16.5728.86
Cld1.430.44
Calorific valueQner, arkJ/kg9653.237606.21
ar: received basis; d: dry basis.
Table 2. Mean concentrations, emission factors, and emission amounts of toxic PCDD/Fs under MSWI and LW co-disposal conditions.
Table 2. Mean concentrations, emission factors, and emission amounts of toxic PCDD/Fs under MSWI and LW co-disposal conditions.
BO CH FA
Unit MSWI 15% 25% 35% 45% MSWI 15% 25% 35% 45% Unit MSWI 15% 25% 35% 45%
∑PCDDsng/Nm31.240.860.750.880.930.020.030.030.020.03µg/kg2.202.122.502.392.43
∑PCDFsng/Nm31.951.120.941.311.40.050.060.060.040.05µg/kg0.800.730.810.760.74
∑PCDD/Fsng/Nm33.181.991.692.192.330.070.090.080.060.06µg/kg2.992.863.313.153.21
I-TEQng I-TEQ/Nm30.320.190.140.200.230.0050.010.010.0040.005µg I-TEQ/kg0.110.100.120.110.11
∑PCDD/∑PCDF/0.660.770.800.670.660.430.410.460.480.51/2.762.903.103.153.17
dCl-PCDDs7.337.407.437.417.427.247.317.267.437.527.567.567.547.567.55
dCl-PCDFs5.725.736.005.966.117.046.936.906.916.896.246.276.126.146.19
dCI-PCDD/Fs6.366.456.646.546.657.097.047.017.087.077.217.237.197.227.21
Emission Factorng I-TEQ/ton fuel/////21.4224.1727.8318.3520.48µg I-TEQ/ton fuel3.303.565.065.004.83
Emission Amountsmg I-TEQ/year/////5.786.537.514.965.61mg I-TEQ/year891.87962.171365.971349.501355.38
Table 3. Concentrations and partitions of 136 PCDD/F homologues under MSWI and LW co-disposal conditions.
Table 3. Concentrations and partitions of 136 PCDD/F homologues under MSWI and LW co-disposal conditions.
BO (ng/Nm3) CH (ng/Nm3) FA (µg/kg)
0% 15% 25% 35% 45% 0% 15% 25% 35% 45% 0% 15% 25% 35% 45%
TCDD0.710.60.430.550.53 0.150.10.20.090.13 0.230.220.440.40.35
±0.12 ±0.0093 ±0.02 ±0.12 ±0.03±0.037 ±0.022 ±0.098 ±0.016 ±0.017±0.049 ±0.047 ±0.0071 ±0.0018 ±0.086
PeCDD0.670.530.380.530.48 0.0190.0250.030.0250.03 0.540.490.730.680.63
±0.13±0.040±0.020±0.13±0.04±0.00042±0.0011±0.0082 ±0.011±0.0053±0.093±0.084±0.017 ±0.0038±0.012
HxCDD0.940.670.590.710.66 0.0150.0250.0280.020.02 1.191.011.711.641.45
±0.25±0.081±0.049±0.15±0.18±0.0012±0.0023±0.0057±0.0061±0.0052±0.26±0.21±0.029±0.0073±0.0057
HpCDD0.920.630.580.690.63 0.0130.0160.0190.0130.02 1.311.281.671.561.50
±0.17±0.056±0.030±0.14±0.05±0.00093±0.0028±0.0046±0.0029±0.0037±0.25±0.26±0.037±0.0083±0.028
OCDD0.950.750.670.790.74 0.0170.0210.0220.020.02 1.341.291.481.461.41
±0.076±0.035±0.039±0.16±0.08±0.0016±0.0033±0.0020±0.0036±0.0022±0.29±0.18±0.035±0.0041±0.031
TCDF9.536.694.416.345.81 0.270.210.290.180.23 1.151.031.61.51.38
±2.37±0.23±0.47±1.17±1.08±0.039±0.0063±0.063±0.0220.044±0.27±0.21±0.043±0.0080±0.19
PeCDF4.792.952.093.232.76 0.0640.0760.0790.0530.07 0.830.730.980.940.88
±1.23±0.14±0.19±0.73±0.34±0.0038±0.0066±0.018±0.00870.013±0.15±0.12±0.019±0.0037±0.064
HxCDF2.371.311.091.691.36 0.030.0530.0570.0390.05 0.730.660.730.710.70
±0.77±0.14±0.11±0.32±0.13±0.0066±0.0096±0.019±0.0072±0.0055±0.15±0.12±0.027±0.0058±0.020
HpCDF0.920.560.60.860.67 0.0160.0330.0320.0230.03 0.450.420.410.40.41
±0.23±0.055±0.095±0.12±0.08±0.0035±0.0056±0.0082±0.0052±0.0082 ±0.081±0.066±0.017±0.0024±0.021
OCDF0.180.150.210.250.20 0.0430.0440.0410.0320.04 0.0870.080.080.0790.08
±0.024±0.0040±0.057±0.022±0.043±0.0035±0.00045±0.0043±0.0017±0.004±0.024±0.019±0.0028±0.00053±0.00034
∑PCDDs4.183.182.653.273.03 0.220.190.30.170.22 4.624.36.035.745.36
±0.75±0.22±0.16±0.71±0.32±0.041±0.031±0.12±0.039±0.076±0.94±0.78±0.12±0.025±0.026
∑PCDFs17.7911.668.412.3710.81 0.430.420.50.330.42 3.252.923.83.623.45
±4.62±0.56±0.91±2.36±0.87±0.056±0.029±0.11±0.045±0.038±0.67±0.54±0.11±0.020±0.034
∑PCDD/Fs21.9714.8411.0515.6413.84 0.640.610.80.50.64 7.867.229.839.368.80
±5.37 ±0.79 ±1.07 ±3.07 ±1.78±0.10 ±0.060 ±0.23 ±0.084 ±0.14±1.61 ±1.32 ±0.23 ±0.046 ±0.017
∑PCDD/∑PCDF0.240.270.320.260.28 0.510.460.60.530.53 1.421.471.591.591.55
dCl-PCDDs6.176.126.266.196.29 4.725.084.775.074.97 6.656.686.56.526.57
dCl-PCDFs4.734.674.824.824.77 4.815.14.95.015.00 5.225.245.055.075.12
dCl-PCDD/Fs5.014.985.175.115.13 4.785.094.855.034.99 6.066.15.945.966.00
Emission Factor84.2554.9337.3852.5454.832.962.73.262.012.66 235.83259.85413.06421.16437.58
(ug/ton fuel)
Table 4. Relative importance (%) of CP-route congeners in the BO and FA for MSWI and LW co-disposal conditions.
Table 4. Relative importance (%) of CP-route congeners in the BO and FA for MSWI and LW co-disposal conditions.
CP-Route Congeners BO FA
MSW 10% 20% 25% 45% MSW 10% 20% 25% 45%
1,3,7,9-TCDD10.5711.9913.0012.4112.679.7412.539.469.5810.06
1,3,6,8-TCDD23.9829.4130.9130.0431.1252.0151.3764.7863.5662.78
Sum of TCDD34.5541.3943.9042.4543.7961.7563.9074.2473.1472.84
1,2,4,6,8/1,2,4,7,9-PeCDD27.8330.9330.8830.8230.8834.2434.8936.8336.8335.43
1,2,3,6,8-PeCDD21.7123.7623.7423.3223.6131.1030.1832.6831.5731.83
1,2,3,7,9-PeCDD12.2112.0712.0011.8311.7713.5714.1114.4914.0214.32
Sum of PeCDD61.7466.7666.6265.9766.2578.9179.1984.0082.4281.58
1,2,3,4,6,8-HxCDD48.2550.2348.4448.4048.1268.0067.3575.7075.9275.88
2,4,6,8-TCDF1.902.182.222.202.202.262.262.242.112.17
1,2,3,8/1,2,3,6/1,4,6,9/
1,6,7,8/1,2,3,4/2,3,6,8-TCDF		6.786.887.787.487.587.928.407.167.997.58
Sum of TCDF8.699.069.999.689.7810.1810.669.4110.109.75
Sum of PCDD/Fs8.8310.4310.589.8510.24 19.0318.2824.2624.0324.14
Table 5. Hagenmaier profiles of 2,3,7,8-PCDD/F isomers for MSWI and LW co-disposal conditions (%).
Table 5. Hagenmaier profiles of 2,3,7,8-PCDD/F isomers for MSWI and LW co-disposal conditions (%).
Hagenmaier Profile (%) BO FA
0% 15% 25% 35% 45% 0% 15% 25% 35% 45%
2,3,7,8-TCDD5.94.74.24.44.432.502.001.601.701.77
1,2,3,7,8-PeCDD7.86666.003.203.502.502.402.80
1,2,3,4,7,8-HxCDD4.73.84.34.44.171.601.701.101.001.27
1,2,3,6,7,8-HxCDD1.61.311.21.173.903.506.906.405.60
1,2,3,7,8,9-HxCDD3.73.83.83.83.802.002.101.401.401.63
1,2,3,4,6,7,8-HpCDD51.251.250.851.651.2049.1049.6047.3046.1047.67
OCDD19.519.821.92120.9018.2019.0013.2013.8015.33
Sum of 2,3,7,8-PCDDs34.332.635.834.834.4028.7030.2021.4021.9024.50
2,3,7,8-TCDF43.93.63.53.674.404.104.104.104.10
1,2,3,7,8-PeCDF7.576.36.36.536.906.807.306.907.00
2,3,4,7,8-PeCDF9.69.110.29.79.6710.5010.209.509.509.73
1,2,3,4,7,8-HxCDF14.21415.514.414.6310.8011.7011.0011.0011.23
1,2,3,6,7,8-HxCDF1.810.71.10.930.700.600.800.700.70
2,3,4,6,7,8-HxCDF8.29.19.99.19.3712.8012.5012.2012.1012.27
1,2,3,7,8,9-HxCDF0.60.30.30.40.330.200.200.200.200.20
1,2,3,4,6,7,8-HpCDF63.261.854.956.657.7771.3070.8068.0068.0068.93
1,2,3,4,7,8,9-HpCDF10.911.215.31212.836.807.407.908.007.77
OCDF11.32.521.932.702.702.102.202.33
Sum of 2,3,7,8-PCDFs16.515.218.617.817.2027.9028.4023.7023.6025.23
Sum of 2,3,7,8-PCDD/Fs20.319.423.221.721.4328.5029.7022.0022.4024.70
Table 6. Concentrations of air pollutants for MSWI and LW co-disposal conditions.
Table 6. Concentrations of air pollutants for MSWI and LW co-disposal conditions.
Co-Disposal Ratio Sampling Points NOx SO2 HCl
mg/Nm3
0%BO266.02 ± 19.6533.94 ± 3.17127.65 ± 12.98
CH67.00 ± 8.340.13 ± 0.7317.20 ± 5.11
15%BO243.23 ± 18.6146.95 ± 8.89110.43 ± 11.37
CH64.00 ± 9.441.33 ± 0.5519.18 ± 8.22
25%BO260.39 ± 23.7192.17 ± 15.26143.8 ± 17.70
CH80.80 ± 9.114.475 ± 1.5422.72 ± 8.47
35%BO227.72 ± 28.5139.85 ± 10.86107.72 ± 10.26
CH76.66 ± 11.610.09 ± 0.0616.82 ± 3.87
45%BO232.23 ± 35.6345.85 ± 15.17101.39 ± 17.33
CH78.21 ± 8.670.12 ± 0.0518.66 ± 1.66
Table 7. Compositions (%) of FA for MSWI and LW co-disposal conditions.
Table 7. Compositions (%) of FA for MSWI and LW co-disposal conditions.
Components MSW 15% 25% 35% 45%
Ca35.41 34.87 35.47 36.43 36.68
K3.71 3.44 3.12 3.31 3.26
Na2.10 2.07 2.61 2.55 2.18
Si4.75 4.91 4.27 4.51 4.64
Al1.74 1.77 1.61 1.67 1.71
Fe1.53 1.60 0.76 1.14 0.98
Mg1.42 1.48 1.30 1.29 1.32
O15.56 15.98 16.51 16.72 16.95
S4.05 4.21 4.13 4.26 4.16
Cl15.15 13.94 13.99 13.64 13.82
Others14.58 15.72 16.24 14.49 14.30
Table 8. Metal elements (mg/kg) of FA for MSWI and LW co-disposal conditions.
Table 8. Metal elements (mg/kg) of FA for MSWI and LW co-disposal conditions.
Components MSW 10% 20% 25% 45%
Cu412.0453.0551.0511.0526.0
Ni33.0 37.9 16.7 19.9 24.2
Cr1460.0 1830.0 1230.0 873.0 687
Zn3500.0 3880.0 4650.0 3330.0 3469
As39.6 36.9 37.2 34.0 36.4
Se3.6 3.4 3.4 3.2 3.5
Cd135.0 146.0 281.0 235.0 207.0
Ba172.0 191.0 436.0 278.0 357.0
Hg7.5 7.2 12.9 9.7 8.4
Pb300.0 364.0 1320.0 683.0 749.0
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Zhen, Z.; Xiang, X.; Li, X. Study on the Emission Characteristics of Pollutants During the Waste-to-Energy Process of Landfill Waste and Municipal Solid Waste. Energies 2025, 18, 4515. https://doi.org/10.3390/en18174515

AMA Style

Zhen Z, Xiang X, Li X. Study on the Emission Characteristics of Pollutants During the Waste-to-Energy Process of Landfill Waste and Municipal Solid Waste. Energies. 2025; 18(17):4515. https://doi.org/10.3390/en18174515

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Zhen, Zongao, Xianchao Xiang, and Xiaodong Li. 2025. "Study on the Emission Characteristics of Pollutants During the Waste-to-Energy Process of Landfill Waste and Municipal Solid Waste" Energies 18, no. 17: 4515. https://doi.org/10.3390/en18174515

APA Style

Zhen, Z., Xiang, X., & Li, X. (2025). Study on the Emission Characteristics of Pollutants During the Waste-to-Energy Process of Landfill Waste and Municipal Solid Waste. Energies, 18(17), 4515. https://doi.org/10.3390/en18174515

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