Effect of Pyrolysis Conditions on the Surface Morphology and Composition of Sewage Sludge-Derived Biochar

Fathin Ayuni Azizan; Munira Mohamed Nazari; Muhamad Qauyum Zawawi Ahamad Suffin

doi:10.58915/aset.v4i2.2702

Authors

Fathin Ayuni Azizan Universiti Malaysia Perlis
Munira Mohamed Nazari Universiti Malaysia Perlis
Muhamad Qauyum Zawawi Ahamad Suffin Universiti Malaysia Perlis

DOI:

https://doi.org/10.58915/aset.v4i2.2702

Keywords:

Biochar, Proximate Analysis, Pyrolysis Temperature, Retention Time, Scanning Electron Microscopy (SEM)

Abstract

Sewage sludge-derived biochar offers potential for sustainable waste management and agricultural applications. This study investigates the influence of pyrolysis temperature and retention time on the physicochemical and microstructural properties of biochar derived from sewage sludge. Four biochar samples were produced at 300 °C and 600 °C with residence times of 2 and 4 hours. Proximate analysis was conducted to evaluate moisture content, volatile matter, ash content, and fixed carbon, while surface morphology was assessed using Scanning Electron Microscopy (SEM). Moisture content declined slightly with increased severity (12.43% to ~10.34%), indicating most free water was removed at lower temperatures. Results showed that volatile matter decreased from 18.08% to 8.19% with increasing temperature, while ash content increased from 68.62% to 85.60%. Fixed carbon unexpectedly decreased from 13.30% to 4.22% under higher severity. SEM analysis revealed that even at 600 °C, the biochar surfaces remained smooth and compact with minimal pore development. This behavior is attributed to ash accumulation and the thermally stable mineral content of sewage sludge, which suppresses crack formation during pyrolysis. These findings demonstrate that feedstock composition strongly affects biochar structure and may limit its performance in applications requiring high porosity. However, sludge-derived biochar could still be useful for improving soil bulk density or nutrient retention, provided that harmful components such as heavy metals are adequately treated.

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