Production and characterization of pellets with sewage sludge for use as an energy and environmental alternative

Abstract

This study investigates the production and characterization of pellets incorporating sewage sludge as a partial substitute for lignocellulosic biomass, aiming at its valorization as an alternative energy source and environmentally sustainable solution. Pellets were produced using different proportions of sewage sludge and Pinus wood powder (0%, 25%, 50%, 75%, and 100%) in a pilot-scale pellet mill (1,500 kg·h⁻ 1 ). The samples were characterized in terms of moisture content, ash content, volatile matter, fixed carbon, higher calorific value (HHV), elemental composition (TXRF), thermal behavior (TGA), and gaseous emissions during pyrolysis (EGA-FTIR). Moisture content ranged from 1.89 to 6.76%, complying with ISO 18134–2 standards. Ash content increased proportionally with sludge incorporation (0.85 to 29.96%), reflecting the inorganic fraction of the residue. The HHV varied between 14.45 and 19.01 MJ·kg⁻ 1 , with formulations containing up to 50% sludge meeting the ISO 18125 requirement (≥ 16.56 MJ·kg⁻ 1 ). Thermogravimetric analysis indicated increased thermal stability with higher sludge content, attributed to elevated mineral matter. Gas analysis revealed the predominance of CO₂, CH₄, and oxygenated compounds, with no detection of toxic gases at critical levels under the evaluated conditions. The results demonstrate that the incorporation of sewage sludge up to 50% in pellet formulations is technically feasible for energy applications, contributing to waste management strategies and circular economy practices while maintaining acceptable fuel properties.

Bibliographic Information