Carbon-source bio-enhanced activated carbon (CBEAC) for efficient ammonia nitrogen removal in water treatment: Performance improvement and microbial mechanisms

Excessive ammonia nitrogen (NH₃-N) in water hinders SDG 6 achievement. Conventional purification processes for NH₃-N removal start slowly and are vulnerable to temperature fluctuations, necessitating more stable and efficient technologies. Bio-enhanced activated carbon (BEAC) with heterotrophic nitrifier Acinetobacter harbinensis HITLi7 T enhances NH₃-N removal but is limited by influent oligotrophy; thus, we developed carbon-source bio-enhanced activated carbon (CBEAC) by adding glucose to BEAC, aiming to improve NH₃-N removal and clarify microbial mechanisms. With influent NH₃-N at 1.72–2.25 mg/L, CBEAC outperformed BAC and BEAC: better start-up removal, reaching China's 0.5 mg/L drinking water limit in 16 days, with stable effluent at 0.13 ± 0.06 mg/L (93.58 ± 3.08% removal). Glucose raised influent permanganate index (PI) to 5.41 ± 0.99 mg/L, yet CBEAC maintained low effluent PI (1.24 ± 0.62 mg/L, no significant leakage) with PI removal of 4.16 ± 0.88 mg/L (77.39 ± 10.39% efficiency), higher than BAC/BEAC. Glucose enhanced the system biological activity and synergized with strain HITLi7 T to improve the NH₃-N removal efficiency of the microbial community. In this process, the compensatory effect triggered by the altered nutrient environment and dynamic changes of HITLi7 T activated the homogeneous selection of ammonia-transforming microbiota. Meanwhile, the physical adhesion of extracellular polymeric substances (EPS) and microenvironmental nutrient gradient restricted species dispersal, which not only improved microbial functional modularity and community network correlation density but also intensified the competitive utilization of NH₃-N by autotrophic-heterotrophic microbiota. These findings enriched the theoretical basis for the NH₃-N removal mechanism of CBEAC and provided strong support for its application in water treatment.