Key Takeaways & Executive Findings
- •• • Combustion temperature and blending ratio significantly affect burnout; temperature dominates, with optimal SS mass fraction at 20% for combustion performance. • • N2O and C2H4 emissions are highly sensitive to temperature, blending ratio, and their interaction; N2O formation is markedly suppressed by increasing temperature (e.g., from 850 to 1050 °C). • • Co-combustion with 20% SS reduces SO2 emissions and achieves synergistic NO reduction at 950 °C, while CO, C2H4, C6H6, and C7H8 show antagonistic effects. • • ANN models accurately predict pollutant emissions; combustion temperature, volatile matter, and fixed carbon are key factors. Higher temperatures lower GWP and POCP, but lower MSW proportion increases GWP and AP.
Abstract
Co-combustion of municipal solid waste (MSW) and sewage sludge (SS) offers a promising route for synergistic waste management, yet pollutant release dynamics and environmental trade-offs remain inadequately characterized. This study systematically investigated the combustion behavior, pollutant emissions, and environmental impacts of MSW-SS blends at 850, 950, and 1050 °C with varying SS mass fractions (0–100%). Machine learning models, particularly artificial neural networks (ANN), were optimized to predict pollutant generation, and SHAP analysis identified key influencing factors. Results demonstrated that combustion temperature and blending ratio significantly affected burnout efficiency, with temperature exerting a more pronounced effect. An SS proportion of 20% yielded favorable combustion performance. Among pollutants, N2O and C2H4 emissions were significantly influenced by temperature, blending ratio, and their interaction, indicating high sensitivity to operating conditions. CO and C6H6 were primarily affected by blending ratio, while C7H8 responded to both temperature and blending ratio. N2O and CH4 were predominantly released during the initial combustion stage; elevated temperatures markedly suppressed N2O formation, and co-combustion generally reduced CH4 emissions. A 20% SS blend effectively reduced SO2 emissions, and NO synergistic reduction was optimal at 950 °C. Emissions of CO, C2H4, C6H6, and C7H8 exhibited antagonistic behavior under co-combustion. The ANN model accurately predicted pollutant concentrations, with combustion temperature, volatile matter, and fixed carbon content identified as critical factors. Environmental impact assessment revealed that higher temperatures reduced global warming potential (GWP) and photochemical ozone creation potential (POCP), while lower MSW proportions decreased POCP but increased GWP and acidification potential (AP). Integrating combustion performance, pollutant release, and environmental impacts, an SS proportion of 20% is recommended for optimized co-combustion.
1. Introduction
Municipal solid waste (MSW) and sewage sludge (SS) are two major urban solid waste streams, with annual outputs exceeding 260 million tonnes and 57 million tonnes in China, respectively. The implementation of MSW classification and increased recycling rates have led to fluctuations in waste composition and calorific value, causing operational challenges in incineration plants, such as insufficient feed and low thermal load. Co-combustion of MSW with SS presents a viable strategy to stabilize feed and enhance energy recovery, but the complex interactions between these feedstocks under varying conditions necessitate a thorough understanding of pollutant formation and environmental trade-offs.
Previous studies have individually examined MSW or SS combustion, yet systematic investigations of co-combustion pollutant release and environmental impacts remain limited. This study addresses this gap by analyzing the combustion characteristics and emissions of MSW-SS blends across a range of temperatures and blending ratios. By integrating experimental data with machine learning and SHAP interpretability, we identify key operational parameters and propose optimal conditions to balance combustion efficiency and environmental performance, thereby providing a scientific basis for cleaner co-disposal strategies.
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ZHANG Wei, SUN Yunan, CHEN Guandong, CUI Zhuo, WU Shuang, MA Jiaomei, CHEN Guanyi (2026). Pollutant Generation Characteristics and Environmental Impact Analysis during Co-combustion of Municipal Solid Waste and Sewage Sludge. Journal of Environmental Engineering Technology. https://doi.org/10.13205/j.hjgc.202607001
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Frequently Asked Questions
What is the optimal blending ratio of sewage sludge (SS) with municipal solid waste (MSW) for co-combustion to achieve both good combustion performance and low pollutant emissions?
Based on the study, an SS mass fraction of 20% is recommended. This ratio provides favorable burnout performance and significant reductions in SO2 emissions, while maintaining acceptable levels of other pollutants. At this ratio, combustion temperature can be optimized to further reduce NO emissions, particularly at 950 °C.
How does combustion temperature affect the formation of nitrogenous pollutants like N2O and NO during co-combustion?
Elevated temperatures markedly suppress N2O formation, as N2O is primarily released during the initial combustion stage and decomposes at higher temperatures. For NO, a synergistic reduction is observed at 950 °C, suggesting an optimal temperature window for minimizing nitrogen oxide emissions.
Can machine learning models accurately predict pollutant emissions from MSW-SS co-combustion, and which input variables are most influential?
Yes, artificial neural networks (ANN) demonstrated excellent predictive performance for multiple gaseous pollutants. SHAP analysis identified combustion temperature, volatile matter, and fixed carbon content as the most influential factors affecting pollutant generation. This allows for targeted optimization of operating conditions.
What are the environmental trade-offs when varying the MSW-to-SS ratio?
Lowering the MSW proportion (i.e., increasing SS fraction) reduces photochemical ozone creation potential (POCP) but increases global warming potential (GWP) and acidification potential (AP). Conversely, higher MSW fractions increase POCP but lower GWP and AP. Therefore, a balance must be struck, with 20% SS offering a compromise.
How does co-combustion influence the emissions of organic pollutants like benzene, toluene, and ethylene compared to individual combustion?
Co-combustion generally exhibits antagonistic effects on CO, C2H4, C6H6, and C7H8 emissions, meaning that the emissions from the blend are lower than the weighted sum of individual fuels. This suggests that interactions between MSW and SS during co-combustion inhibit the formation of these organic pollutants.
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