Drinking water treatment residuals, a low-cost and environmentally friendly adsorbent for the removal of hormones - A review

The declining water bodies' pristine characteristics due to the entry of emerging pollutants (EP) have been a growing concern for the past two decades. In the context of the effort that has been made to remove EP from water matrices, adsorption processes are economically attractive and feasible for EP removal. Among the commonly mentioned low-cost adsorbents (natural materials, agriculture and industrial wastes, sewage sludge or water treatment residuals), this review discusses the applicability of drinking water treatment residuals (DWTR) for the removal of hormones. DWTR have been widely reported as being effective in the adsorption of phosphate, heavy metals, and dyes. However, there is still a lack of knowledge on their application as adsorbent of hormones, such as estrone (E1), 17β-estradiol (E2) and 17α-ethinylestradiol (EE2) from water matrices. The sole study conducted on this topic, which involved a comprehensive characterization of the adsorption process for hormones using non-modified DWTR, indicates a maximum adsorption capacity of 8.748 μg/g for E2 and 14.557 μg/g for EE2. Furthermore, some studies refer to powdered activated carbon- DWTR (PAC-DWTR) as a new category of DWTR, with possible adsorption availability from powdered activated carbon (PAC) to be further explored. Finally, the application of DWTR should always be supported not only by standard toxic leaching procedures but also by ecotoxicological assessments. Nonetheless, the upcycling of DWTR into an adsorption material may offer new ways to manage this former residue in the water sector and provide alternatives for EP removal.