Biochar-Amended Constructed Wetlands for Simultaneous Removal of Pharmaceutical Residues and Microplastics from Municipal Wastewater: Integrating Circular Economy and Microbial Ecology

Abstract

The occurrence of pharmaceutical residue and microplastic pollution together in municipal wastewater presents a major, underexplored challenge in terms of pollution. This study developed and evaluated a two-stage vertical-flow–horizontal-flow constructed wetland (CW) system amended with three engineered biochars derived from agricultural residues (rice husk, sugarcane bagasse, and walnut shell) pyrolyzed at 600 °C for the simultaneous removal of six pharmaceutical compounds (ciprofloxacin, sulfamethoxazole, diclofenac, carbamazepine, ibuprofen, and atenolol) and polyethylene microplastics (10–100 µm). A 12-month field-scale experimental campaign (n = 144 composite samples) coupled with batch kinetic assays, 16S rRNA microbial community profiling, and life cycle inventory was performed. The walnut-shell biochar amendment (BC-WS) achieved the highest mean removal efficiencies: 96.4% for total pharmaceuticals, 92.1% for microplastics, and 87.3% for chemical oxygen demand, with hydraulic retention time of 48 h and organic loading of 8.5 g COD m⁻² d⁻¹. Kinetic modeling revealed pseudo-second-order sorption (R² = 0.94–0.99) and first-order microbial degradation (k = 0.082–0.146 h⁻¹). Microbial analysis showed enrichment of Nitrospira, Denitratisoma, and Hydrogenophaga by 3.4–5.7× relative to unamended controls, indicating functional redundancy for xenobiotic metabolism. A circular-economy assessment demonstrated a 38% reduction in global warming potential when biochar sourced from local agro-residues replaced conventional sand/gravel substrates. The proposed BC-WS system offers a low-cost, energy-neutral, and ecologically robust solution aligned with Sustainable Development Goals 6, 12, 13, and 14. The integration of biochar amendment with constructed wetlands represents a paradigm shift from end-of-pipe treatment to resource-recovery-based pollution control.