Municipal sewage sludge was pyrolyzed, under various pyrolysis temperatures and holding times, to investigate the pore structure characteristics of the sludge-based biochars obtained. The pore structure of the obtained sludge biochars was measured by the N2 adsorption/desorption at 77 K. The concept of fractal dimension was introduced to determine the pore surface roughness. Experimental results showed that the BET surface area of the sludge biochars increased with pyrolysis temperature increasing, achieving the maximum (i.e. 92.3 m2/g) at 600ºC; the further increase of pyrolysis temperature decreased it. When pyrolysis temperature was less than 500ºC, mesopores were dominant on the obtained biochars and micropores were not observed; over 500ºC, the main pore species were micropores and mesopores. The shape of pores on the sludge biochars differed as pyrolysis temperature increased, varying from silt-shaped pattern to thorough and plate-like patterns. The increase of holding time little altered the pores’ shape but did the pore volume. The pore surface fractal dimensions of the obtained biochars intended to increase with pyrolysis temperature, whereas the prolonging of holding time decreased it at 600-700ºC and augmented it over 700ºC.
