Low-carbon co-disposal of municipal sludge with sintered brick materials: kinetics and emission control

Abstract

Municipal sludge (MS) threatens ecological security and human health, requiring efficient, low-carbon treatment technologies for environmental protection. The sustainable use of MS in brick and tile kilns to manufacture building materials with lower environmental impacts is a promising approach for sludge disposal and resource/energy recovery. This study investigated the kinetics, gas emissions, and synergistic effects of the co-disposal of MS, coal gangue (CG), and shale (SH). Results showed that MS significantly enhanced the combustibility of CG-SH blends, with 5% MS increasing the comprehensive combustion index S by 502%. Kinetic analysis revealed that the combustion of MS-blended systems was best described by a first-order model. At the conversion rate of 0.5, MS combustion processed transition from Power law P6 to Avrami–Erofeev A2.7, reflecting a shift from surface-diffusion-controlled volatilization to nucleation-controlled char oxidation. Gas emissions, especially emissions of reducing species, varied with atmospheric conditions. This affected the release of NO_x through in-situ denitrification, which was critical for air pollution control. The 5% MS blend showed synergistic combustion enhancement, while 20% MS induced the strongest inhibition near 560 °C due to ash-mediated solid-solid reactions. Under inert conditions, the highest suppression was found at 880–1000 °C in the 10% MS blend. This work provides insights and theoretical guidance for optimizing MS co-disposal in brick and tile kilns, facilitating efficient waste treatment, emission control and energy recovery.

Graphical abstract

Keywords

Municipal sludge treatment / Sustainable use / Kinetic mechanism / Gas emission / Interaction

Highlight

	● Sustainable use of sludge in brick and tile kilns reduced waste and energy.
	● Sludge addition significantly enhanced combustibility of coal gangue-shale blends.
	● Gas emission especially reductive species varied with atmospheres and affected NO x .
	● 5% sludge ratio in blends exhibited synergistic combustion enhancement.
	● Most obvious suppressing effect was observed at 10% sludge ratio in pyrolysis.

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