Valorization of Primary Sludge and Biosludge from the Pulp Mill Industry in Uruguay Through Hydrothermal Carbonization

Although nowadays landspreading and incineration are the conventional disposal methods for the primary sludge (PS) and biosludge (BS) generated in the wastewater treatment plants of the pulp mill industry in Uruguay, their direct incineration for energy recovery is the most preferable one. Here, we propose the hydrothermal carbonization (HTC) method as a pre-treatment to improve the fuel characteristic of PS and BS. Proximate and ultimate analysis, scanning electron microscopy, and thermogravimetric analysis show that the HTC affects PS and BS differently regarding carbon fixation, energy densification and energy conversion efficiency. Moreover, ash composition measured by X-ray fluorescence indicates that the HTC effectively diminishes the slagging and fouling indexes for both feedstocks, which can increase the life expectancy of boilers. Alternative PS, BS, and their hydrochars were activated with H₃PO₄ to produce activated carbons, i.g. the BET specific surface area was as high as 800 m²/g for PS-AC, and exhibits CO₂ adsorption capacity of 5 mmol/g at 10 bar at 273 K. These studies provide alternatives to direct incineration and landspreading of PS and BS in Uruguay to reduce their environmental impact, either by enhancing their fuel quality or by converting them into much more valuable products to face air pollution. Graphical Abstract: [Figure not available: see fulltext.]