Biochar Derived from Sewage Sludge: The Impact of Pyrolysis Temperature on Chemical Properties and Agronomic Potential

The rising volume of sewage sludge from urbanization poses substantial environmental and public health concerns, underscoring the urgency for the implementation of effective waste management strategies. The objective of this study was to evaluate the influence of pyrolysis temperature on the chemical composition and agronomic potential of biochar derived from sewage sludge. The pyrolysis process was conducted at temperatures ranging from 400 °C to 800 °C, and the resulting biochar was analyzed for pH, electrical conductivity, metal content, and carbon fractions. Additionally, phytotoxicity tests were conducted to assess the impact of the biochar on plant germination. The findings indicated that elevated pyrolysis temperatures resulted in an elevated alkalinity, electrical conductivity, and concentration of alkali metals in the biochar. Conversely, these processes resulted in a reduction in total organic carbon content and an increase in heavy metal content, which may limit the potential for biochar to be used in agricultural applications. The phytotoxicity tests indicated that the biochar produced at lower temperatures (400 °C) exhibited positive effects on plant growth when administered at doses of 5 and 10 t·ha−1. Conversely, the biochar produced at higher temperatures (800 °C) demonstrated significant toxicity. The findings indicate that the pyrolysis temperature is a critical factor in determining the suitability of biochar for agricultural applications. The production of biochar at lower temperatures may offer agronomic benefits, whereas the use of higher temperatures increases stability but is associated with the risk of higher heavy metal concentrations.