Elaboration of cost-effective adsorbents derived from sewage sludge through hydrothermal carbonization: Influence of process parameters and feedstock components on the adsorption performance

Abstract

Sewage sludge (SS)-derived hydrochar by hydrothermal carbonization (HTC) have demonstrated its potential as an adsorbent. This study investigated the effect of HTC parameters and feedstock components on the adsorption performance of hydrochar, with the aim of enhancing its adsorption performance without modification, thereby expanding applications of waste-derived adsorbent under cost constraints. Water, ash and five model compounds were used to adjust the typical components of SS, then hydrochar was prepared under various HTC parameters. The adsorption quantity of the model pollutants (tetracycline and methylene blue) on hydrochar decreased with an increase in HTC temperature, and there was a minor decrease with prolonged reaction times. Changes in the HTC parameters did not affect the adsorption mechanism of the hydrochar. Notably, humus and lignin emerged as key components affecting the adsorption performance of hydrochars. Compared with the blank control, the adsorption capacities of tetracycline and methylene blue by hydrochar after the addition of 30 wt% humic acid increased by 16.1% and 101.0%, respectively. Moreover, the adsorption capacity of methylene blue increased by 58.5% after adding 30 wt% alkali lignin. The underlying mechanism was elucidated based on hydrochar characterization. Changes in HTC parameters affected the properties of hydrochar and its adsorption performance. The effect of component adjustment on the adsorption performance of hydrochar was attributed to abundance of oxygen-containing functional groups formed by the model compounds during hydrolysis. Component adjustment facilitated the binding of groups to the hydrochar, thereby offering more adsorption sites. This study provides a valuable reference for utilizing SS in the preparation of efficient and low-cost adsorbents.