Field-spent granular activated carbon regeneration via hydrothermal treatment: performance analysis and influencing factors

ABSTRACT Hydrothermal treatment has been proposed as a cost-effective alternative to the conventional high-temperature thermal regeneration of activated carbon. However, previous studies have used laboratory-spiked adsorbents, limiting field relevance. In this study, we evaluated the regeneration of field-spent granular activated carbon (GAC) recovered from two drinking water treatment plants (G1: 10 years; G2: five years) and one wastewater treatment plant (G3: three months). We examined the effects of temperature (160–240 °C), reaction time (3–40 hours), carbon-to-water mass ratio (1:1.6–1:40), and initial fouling level on performance. Overall, a higher temperature, longer duration, and the lowest water fraction condition (GAC-to-water ratio = 1:1.6) yielded a greater recovery of the Brunauer–Emmett–Teller surface area and total pore volume. In particular, surface area of the lightly used sample G3 increased from 981.06 to 1,208.73 m2 g−1, approaching that typical of virgin GAC (1,050–1,200 m2 g−1), whereas that of the heavily used G1 increased from 192.12 to 433.37 m2 g−1. Scanning electron microscopy coupled with energy-dispersive X-ray spectroscopy indicated high levels of inorganic foulants (Al, Si) in long-used carbons before and after hydrothermal treatment. These findings demonstrate that hydrothermal treatment can effectively restore pore properties of lightly fouled field-spent GAC, whereas inorganic accumulation under long-term operation limits regeneration.