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

[Display omitted] • HTC of GP in SM liquid enhances hydrochar production via cross-interactions of intermediates. • Nitrogen from SM transfers to hydrochar via condensation with aldehydes/ketones. • HTC of GP in SM forms hydrochar of higher carbon content. • HTC at 260 °C promotes aromatization, minimizing mesopore in activating hydrochar. • Retained aliphatic structures in hydrochar are keys in creating developed pores. Grapefruit peels (GP) and swine manure (SM) are solid wastes that can be transformed into carbonaceous materials 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 °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 hydrochar, enhancing yield of hydrochar by 9.6 % at 260 °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 °C. This produced hydrochar of higher aromatic nature, thermal stability, and C/O ratio. The HTC in SM liquid at 220 °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 A g−1. [ABSTRACT FROM AUTHOR]