High-performance activated rice straw biochar: a sustainable triple-bottom-line adsorbent for removal of water pharmaceutical pollution

Abstract

Remediation of pharmaceuticals in aquatic systems is crucial due to their substantial environmental and health impacts. In this study, a novel adsorbent from agricultural waste, activated rice straw residue biochar (activated RSR-BC), is developed to overcome the limits of existing water treatment technologies in eliminating sulfamethoxazole (SMX) and clindamycin (CLN) pollutants. Characterization of the synthesized activated RSR-BC adsorbent was done by XRD, SEM, BET, and FTIR to assess its physical and chemical properties. The BET-specific surface area increased after activation by 2.37 times, from 278.92 m² g⁻¹ to 662.51 m² g⁻¹, and the total pore volume increased. The Activated rice straw residue biochar (activated RSR-BC) showed excellent performance in removing (SMX) and (CLN). The adsorbent demonstrated a theoretical maximum adsorption capacity of 297.4 mg g⁻¹ at pH 3 and 184.7 mg g⁻¹ at pH 5 for SMX and CLN, respectively. Additionally, a prototype fixed-bed column system demonstrated high efficiency, removing 97.92% of SMX from continuous-flow wastewater effluent within 40 minutes. Beyond targeting specific contaminants, the activated RSR biochar also improved overall wastewater quality by significantly reducing total suspended solids (TSS), chemical oxygen demand (COD), biological oxygen demand (BOD), and total organic carbon (TOC). The main adsorption mechanisms identified include pore-filling, electrostatic attraction, hydrogen bonding, and π–π electron donor–acceptor (EDA) interactions, with chemisorption acting as the rate-limiting step. Moreover, activated RSR-BC material can be reused up to four times with 69.7% removal, highlighting its effectiveness in removing pharmaceuticals from water. Overall, this study demonstrates how agricultural waste, such as rice straw, can be valorized into a high-performance adsorbent for advanced water purification, supporting sustainable development goals (SDGs) and circular economy principles.