Adsorption of aqueous phase contaminants of emerging concern by activated carbon: Comparative fixed-bed column study and in situ regeneration methods

This work investigated the adsorption of five model contaminants of emerging concern (CECs) that are released daily in domestic effluents (caffeine, hydrochlorothiazide, saccharin, sulfamethoxazole and sucralose) onto two activated carbons (ACs), in fixed-bed column experiments with different aqueous matrices (ultrapure water, wastewater treatment plant (WWTP) effluent and WWTP effluent pretreated by reverse osmosis and photoperoxidation (reuse water)). The ACs were chemically similar, but AC1 had smaller particles (0.7-1.7 mm) and lower surface area (551 m2 g-1) than AC2 (1.2-2.4 mm and 716 m2 g-1). AC1 had a higher adsorption capacity (qads) for the CECs in the downflow mode. Overall, the qads values of the CECs followed the order: caffeine > sulfamethoxazole > hydrochlorothiazide = saccharin > sucralose. In the downflow mode, preferential pathways reduced the hydraulic retention time (HRT) of the fixed-bed column loaded with AC, which reduced the useful lifetime of column and the adsorption capacity. Nevertheless, the adsorption capacity and useful lifetime of the fixed-bed columns remained similar in the upflow mode (no preferential pathways were observed) regardless of the AC used. Since the HRTs were also found to be similar, it was evident that the crucial factor influencing the adsorption of the CECs was the HRT, which played a pivotal role in the overall process becoming evident. Compared to ultrapure water, use of the WWTP effluent reduced qads for all the CECs by up to 4.1 times, while reuse water reduced qads by up to 1.2 times. The AC1 could be in-situ regenerated using ethanol, with a global efficiency of 97.2 %. The results showed the importance of pretreatment techniques and optimization of the operational parameters, such as HRT, for enhancing the useful lifetime and qads of fixed-bed columns.

Automated summary

This study investigates the adsorption capacity of two activated carbons on five model contaminants in different aqueous matrices. The results show that the AC1 has a higher adsorption capacity in the downflow mode, but preferential pathways reduce its useful lifetime. Additionally, the wastewater treatment effluent and pretreated water have a significant impact on the adsorption capacity of the contaminants.