title: Multiscale characteristics dynamics of hydrochar from hydrothermal conversion of sewage sludge under sub- and near-critical water.
abstract: Dewatered sewage sludge was upgraded to hydrochar using hydrothermal conversion in sub- and near-critical water. Three characteristic temperature regimes responsible for the upgrading were identified. Drastic hydrolysis of carbohydrates, amide II or secondary amines occurred at 200°C while noticeable decarboxylation initiated above 260°C. Elevated temperature improved porosity but did not induce higher surface area. Aliphatic C was mainly transformed to aromatic hydrocarbon rather than aromatic C-O in subcritical water, whereas COO/N-CO and aromatic C-O were decomposed to carbohydrate C at 380°C. Below 300°C, carbon functionalities in hydrochars were thermally stable and faster decomposition of N than C-(C,H) resulted in dramatic decline of N/C. Above 300°C, C-H was gradually polymerized to aromatic C-(C,H) which was considerably transformed to C-(O,N) and C-H at 380°C. CaO favored intense destruction of aromatic C-C/C-H, anomeric O-C-O, C-H and C-(O,N) functionalities but introduced more aromatic C-O and OC-O.
authors.affiliation: Cambridge Centre for Advanced Research and Education in Singapore, School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore; Division of Environmental and Water Resources Engineering, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: Chao
authors.initials: C
authors.lastname: He
authors.affiliation: Cambridge Centre for Advanced Research and Education in Singapore, School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore.
authors.forename: Jun
authors.initials: J
authors.lastname: Zhao
authors.affiliation: Cambridge Centre for Advanced Research and Education in Singapore, School of Chemical and Biomedical Engineering, Nanyang Technological University, 62 Nanyang Drive, Singapore 637459, Singapore. Electronic address: yhyang@ntu.edu.sg.
authors.forename: Yanhui
authors.initials: Y
authors.lastname: Yang
authors.affiliation: Division of Environmental and Water Resources Engineering, School of Civil and Environmental Engineering, Nanyang Technological University, 50 Nanyang Avenue, Singapore 639798, Singapore.
authors.forename: Jing-Yuan
authors.initials: JY
authors.lastname: Wang
mesh_terms: D002244:Carbon / Q000737:chemistry; D006358:Hot Temperature; D006838:Hydrocarbons / Q000737:chemistry*; D006868:Hydrolysis; D012722:Sewage / Q000032:analysis / Q000737:chemistry*; D013696:Temperature; D018505:Waste Management / Q000379:methods*; D014867:Water / Q000737:chemistry*
chemical_list: D006838:Hydrocarbons; D012722:Sewage; D014867:Water; D002244:Carbon
keywords: Atomic ratio; Carbon functionality; Near-critical water; Subcritical water; Surface morphology