Estrone removal from water through adsorption: A critical review of a decade of research

Endocrine-disrupting compounds (EDCs) such as Estrone (E1) pose significant environmental and health risks associated with reproductive disorders in humans and animals. This study highlights the considerable advancements in Estrone removal via adsorption over the past decade, identifies key challenges, and highlights the need for further research in key areas to effectively evaluate adsorbents' practical applications in water and wastewater treatment. In most reported studies, hydrophobic interactions, π-π interactions, and hydrogen bonding appear to be key mechanisms influencing E1 adsorption. The E1 adsorption with most adsorbents is characterized as an exothermic reaction that could take a simple single layer or a complex multilayer form as evidenced by its best fit with Langmuir and Freundlich isotherms and first and second-order kinetics. The optimal conditions for E1 removal were identified as a pH of 7 and 25 °C, closely resembling the natural conditions of most water and wastewater streams. Among all the reviewed materials, two adsorbents stood out: Mesoporous Molecularly Imprinted Polymers (MMIP), which demonstrated the highest maximum adsorption capacity, and modified bricks ferrihydrite, notable for its superior reusability. Considering factors such as cost, environmental impact, and the disposal of exhausted adsorbents, agro-industrial wastes (AIWs) and biochar (BC) appear to have a competitive advantage over the previously mentioned materials and are, therefore, recommended for E1 removal. Several research gaps have been identified in the E1 adsorption area and recommendations were made for future investigation pathways. These include more systematic environmental impact analysis, exploring the use of various waste streams as sources of raw materials for adsorbent synthesis and modification, evaluating the recovery potential of elution solutions used for adsorbent regeneration, and investigating the potential synergy of combining adsorption with advanced oxidation process for simultaneous removal and degradation of E1.