Enhanced pharmaceutical wastewater treatment using a zeolite-modified dual-circulation anaerobic reactor

Pharmaceutical wastewater poses significant treatment challenges due to its high concentrations of organic pollutants, toxic compounds, and ammonia nitrogen. Conventional anaerobic reactors such as internal circulation (IC) and expanded granular sludge bed (EGSB) have limited capabilities in handling microbial inhibition and achieving efficient ammonium adsorption efficiency. To address these limitations, this study proposes a double-circulation anaerobic reactor integrated with NaCl-high-temperature modified zeolite to enhance treatment performance. The reactor was commissioned through three sequential phases: sludge acclimation, loading rate escalation, and stable operation. Key operational parameters, including hydraulic retention time (HRT), temperature, and reflux ratio, were systematically evaluated, leading to the identification of optimal conditions: HRT of 24 h, temperature of 35 °C, and an external reflux ratio of 3. Results indicate that the modified zeolite effectively improves pore structure and liquid-phase ammonium concentration shifted from increasing to decreasing trends. During the stable operation phase, chemical oxygen demand (COD) and total organic carbon (TOC) removal rates reached 86% and 87%, respectively, while liquid-phase ammonium concentration shifted from increasing to decreasing trends, and biogas production rose to 20.4  L/d. Microbial community analysis reveals that the modified zeolite promotes biofilm formation, enriches beneficial microbial populations, and enhances the structural stability of the microbial ecosystem. This study presents a promising technical solution for the efficient anaerobic treatment of high-strength pharmaceutical wastewater.