Mining Energy from Wastewater: Coupling Hydrothermal Liquefaction and Anaerobic Digestion for Municipal Sludge Treatment
Résumé
Hydrothermal liquefaction (HTL) is an emerging process that converts organic waste into a liquid biofuel, named biocrude, by means of water at elevated temperature and pressure. Recently, it became attractive for potentially replacing anaerobic digestion (AD) for municipal sludge treatment. This study assessed carbon and energy recovery from sludge by HTL at a wide range of reaction temperatures (290–360°C) and retention times (0–30 min). Considering much carbon is partitioned with the HTL aqueous phase during sludge treatment, AD was used for further energy recovery. Results suggested that mesophilic AD was more suitable for HTL aqueous treatment compared to thermophilic AD. Considering biocrude, hydrochar, and biogas from HTL aqueous, coupling HTL with AD can recover up to 87% of energy from municipal sludge. The results demonstrate that integrating the hybrid HTL–AD process could boost energy recovery from wastewater treatment plants with near-zero solids for final disposal.