Characterization of gaseous products and activated chars from pyrolysis of sewage sludge in the presence of activating agent

Sewage sludge (SS) and SS impregnated with activating agents (ZnCl₂ and KOH) were pyrolyzed in a fixed-bed reactor to produce gaseous fuel and activated char. The effects of heating rate, pyrolysis temperature and activator type on gas yields, pore structure and adsorption properties of activated char were systematically studied. The results demonstrated that increasing the pyrolysis temperature from 450 °C to 850 °C proportionally enhanced H₂ and CO yields from the rapid pyrolysis of SS, while CH₄ yield showed minimal variation between 650 °C and 850 °C. ZnCl₂ notably increased the CO yield, reaching 71.9 ml·g⁻¹ at 850 °C, but caused a marked reduction in CH₄ yield under the tested conditions. Similarly, KOH promoted CO yield at 750 °C and 850 °C, with minimal impact on CH₄ production. Both activators facilitated higher H₂ yields in the range of 450–550 °C, while the maximum H₂ yield (109.8 ml·g⁻¹) was observed at 850 °C in the absence of activator. The activated char derived from ZnCl₂-assisted pyrolysis exhibited well-developed micro- and mesopore structures, with specific surface areas ranging from 188.2 to 54.1 m²·g⁻¹ across pyrolysis temperatures of 450–850 °C. When evaluated as adsorbents for methylene blue removal, activated char with greater specific surface area and total pore volume exhibited superior adsorption capacity. The adsorption process was well-described by the pseudo-second-order kinetic model.