Hydrothermal carbonization of activated sewage sludge over ammonia-treated Fenton sludge to produce hydrochar for clean fuel use

Fenton sludge was hydrothermally treated with ammonia (ATFS) and used as a catalyst for the hydrothermal carbonization (HTC) of activated sewage sludge (ASS) to produce a hydrochar for fuel use. HTC reactions were performed at temperatures varying from 200 to 260 C for 1 h with or without the addition of 7.6 wt.% ATFS. The ASS concentration was kept constant at 10 wt.%. Lowe hydrochar yield was always observed at higher temperatures as more organic matter stayed in the aqueous phase post reaction. With the addition of ATFS, the hydrochar yield was increased by 7-18% compared with that without catalyst at different temperatures. All the hydrochar had lower N content than that of ASS, particularly the hydrochar produced with the addition of ATFS. More than half of the energy in the ASS was recovered in the hydrochar. ATFS, which stayed with the hydrochar after ASS HTC of, favored the combustion of hydrochar by reducing the combustion activation energy of the hydrochar. ATFS was a promising catalyst for the production of clean hydrochar via the HTC of ASS.