Enhanced microplastics removal from sewage effluents via CTAB-modified magnetic biochar: Efficacy and environmental impact

Sewage treatment plants (STPs) are identified as a significant pathway of microplastics (MPs) re-entry into the environment through effluent discharge, thereby emphasizing the need for reliable and efficient treatment methods. This study investigated MPs removal from sewage effluents using cetyl trimethyl ammonium bromide (CTAB)-modified magnetic biochar (RH-MBC-CTAB) as an adsorbent. Biochars from different biomass were synthesized, surface modified, characterized, and compared for their MPs removal efficacy from aqueous matrices. Batch adsorption studies were initially conducted on synthetic water with 1 μm sized polystyrene (PS) MPs using different MP concentrations (1–10 mg/L) and varying adsorbent dosages (1–10 mg/50 mL) to assess the effect of different process parameters, viz. pH (2–10), humic acid (6–25 mg/L), and competitive ions (0.01–0.2 M). The maximum MPs removal (98%) was achieved at the favorable conditions: initial MPs concentration: 10 mg/L, RH-MBC-CTAB dose: 7 mg/50 mL, pH 4, mixing speed: 180 rpm, and contact time: 3 min. Electrostatic attraction and hydrogen bonding were likely to remove MPs while the MPs adsorption was best fitted by the pseudo-second-order kinetics model (R² = 0.91) and Langmuir isotherm model (R² = 0.94) with the maximum adsorption capacity of 247.52 mg/g. Further, the application of RH-MBC-CTAB on the real-time sewage effluents from sequencing batch reactor (SBR) and moving bed biofilm reactor (MBBR)-based STPs spiked with MPs showed up to 96% MPs removal. The reusability results revealed that developed RH-MBC-CTAB could maintain good stability for up to three reusability cycles, therefore offering extensive potential for the removal of MPs from sewage effluents.