Comparative Life Cycle Assessment of Pyrolysis and Hydrothermal Carbonization for Sewage Sludge Treatment in Colombia

The sustainable management of sewage sludge (SS) requires comparative evaluations that capture both environmental impacts and the trade-offs associated with emerging and established treatment routes. This study applies life cycle assessment (LCA) to compare hydrothermal carbonization (HTC), rotary kiln pyrolysis, and incineration using SS from the Salitre WWTP in Bogotá, Colombia, based on a life cycle inventory that integrates experimental characterization, Aspen Plus simulations, and Ecoinvent datasets modeled in EASETECH. Thirteen ILCD midpoint impact categories were assessed, and uncertainty was evaluated through global sensitivity analysis (GSA) and Monte Carlo simulations. The results show that the three technologies distribute their impacts differently across categories, as follows: HTC yields reductions in several categories due to carbon storage and fertilizer substitution but presents toxicity-related impacts linked to heavy metal transfer to soils; pyrolysis produces a pyrochar with metal retention and nutrient recovery potential that influences climate and resource-related categories while remaining sensitive to sludge composition; and incineration influences climate categories without the potential toxic effects of using chars in soils, reduces sludge volume, and facilitates subsequent nutrient recovery processes from ash, with lower uncertainty due to its technological stability. These results support circular economy strategies in low- and middle-income countries by clarifying the environmental conditions under which carbonized materials or ash-derived recovery pathways can be incorporated into sludge treatment systems.