Effect of sewage sludge properties on the biochar characteristic

• Different sewage sludges (SS) were pyrolyzed at varied temperatures.
• The sewage sludge-derived biochars were completely characterized.
• The chemical composition of the SS determines the final properties of the biochar.

The present study evaluated how the initial sewage sludge properties affect the characteristics and composition of sewage sludge-based biochars. Sewage sludges of varying organic matter content were pyrolyzed at temperatures of 500, 600 and 700 °C. The obtained materials were characterized in terms of their composition and physico-chemical as well as their surface and thermal properties. With increasing treatment temperature, the pH, ash content and macro- and micronutrient content increased. The biochar aromaticity also increased. On the other hand, the pyrolysis yield, percentages of H, N and O, molar ratios, polarity of biochars, and crystallite size decreased. The direction of the changes in the content of elemental carbon (C) and in surface area was dependent on the type of sewage sludge. It was found that for some properties of biochars produced could be determined on the basis of an analysis of the properties of the initial sewage sludge.