Investigation of ethinylestradiol removal from water using chemically and thermally activated garden-waste biochar

• Biochar from mild pyrolysis removed EE2 from aqueous solutions. • KOH activation increased mesopores, surface area, and oxygen groups. • EE2 adsorption followed pseudo-second order kinetics, indicating chemisorption. 17α-Ethinylestradiol (EE2), a synthetic estrogen and endocrine disruptor pharmaceuticals, is frequently detected in aquatic environments, posing ecological and human health risks. Conventional wastewater treatment methods often fail to remove EE2, leading to contamination of surface and ground water. Sustainable and cost-effective strategies are needed, with biochar emerging as a promising solution due to its renewability and suitability for lower-income regions. This study evaluated the efficiency of biochar (BC) in removing EE2 from water and compared it to biochar activated with potassium hydroxide followed by thermal treatment [KBC]. Biochar was produced via mild pyrolysis of garden tree leaves and twigs at 270 °C for 2 h, characterised using Brunauer-Emmett-Teller (BET), Fourier transform infrared spectroscopy (FTIR) and Scanning electron microscopy (SEM). Adsorption experiments were conducted with a 10 mg/L EE2 solution over 180 min, with samples analysed using HPLC. Activated KBC showed a higher removal efficiency during the first hour, however later BC achieved a higher adsorption capacity (15.07 mg/g), and removal efficiency (73.01 %) compared to KBC (13.08 mg/g and 61.55 %, respectively) with a statistically significant difference in removal efficiency (P = 0.034). KBC adsorption followed the pseudo-second-order model suggesting chemisorption while non-activated BC best fit the Elovich model, suggesting heterogeneous chemisorption with intraparticle diffusion as the rate-limiting step. Overall, biochar produced under mild pyrolysis effectively removed EE2, with KOH activation enhancing surface properties. Therefore, this biochar could provide a cost-effective and accessible approach for mitigating EE2 contamination in aquatic environments, with significant potential to support lower-income countries with limited resources.