Hydrothermal carbonization of grapefruit peels in swine manure-derived liquid: Property of resulting hydrochars and activated carbons

Grapefruit peels (GP) and swine manure (SM) are solid wastes that can be transformed into carbonaceous ma-terials via hydrothermal carbonization (HTC). Nevertheless, how to effectively utilize liquid residual from HTC remains an issue. Herein, HTC of grapefruit peels (GP) in the liquid from HTC of SM was conducted at 220 to 260 degrees C, aiming to probe influence of SM liquid on evolution of property of hydrochar and activated carbons (AC) from subsequent activation of hydrochar. The results indicated that organics in SM liquid reacted with hydro -char, enhancing yield of hydrochar by 9.6 % at 260 degrees C via forming additional solid deposits. Such cross -interactions involved transfer of nitrogen-containing organics from SM liquid to the GP-derived hydrochar, consuming aldehydes/ketones and aromatization at especially 260 degrees C. This produced hydrochar of higher aro-matic nature, thermal stability, and C/O ratio. The HTC in SM liquid at 220 degrees C retained abundant aliphatic structures in hydrochar and produced AC with developed pore structures (1056.7 m2/g). The superior porosity of the ACs with micro-mesopores texture rendered the good removal efficiencies (91.4 %) of Cr (VI) in aqueous solution. The ACs electrodes also showed good specific capacitance, reaching 356F g-1 at 1 A g-1 and 178F g-1 at 2 Ag- 1.