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.

Thermochemical treatments such as pyrolysis and hydrothermal carbonization (HTC) are increasingly used to convert municipal sewage sludge into solid products, offering benefits in contaminant reduction, pathogen sanitization, and nutrient recovery. This study assesses the agronomic potential of pyrochars and hydrochars produced under varying temperatures and residence times. Pyrolysis was performed at 250–520 °C for 20 and 60 min, while HTC was conducted at 180–300 °C for 30–120 min. Proximate and ultimate analyses revealed that pyrochars exhibit higher thermal stability and fixed carbon content, whereas hydrochars contain less condensed aromatic structures, indicating greater chemical reactivity but lower long-term stability. Surface area measurements showed meso- and macropore development in both materials, with hydrochars ranging from 14.7 to 86.0 m²·g⁻¹ and pyrochars from 12.7 to 41.7 m²·g⁻¹. Pyrochars tend to have a near-neutral pH, while hydrochars are slightly acidic. Hydrochars also retain higher levels of available nutrients (N, P, and S), particularly at lower temperatures, making them promising for agricultural applications. Agronomic evaluation confirmed greater N-NH₄⁺ and phosphorus availability in hydrochars compared to pyrochars, suggesting their potential as soil amendments or fertilizer additives. However, the mobility of heavy metals requires further assessment to ensure environmental safety.