Micropollutant removal efficiency and microbial community of different hybrid constructed wetland systems

Micropollutants (MPs), including antibiotics, neonicotinoids, and phthalic acid esters (PAEs), are increasingly detected in domestic wastewater, posing substantial environmental and public health risks. This study evaluates the removal performance and underlying microbial mechanisms in six pilot-scale hybrid constructed wetlands (HCWs), each employing different combinations of vertical flow (VF), horizontal flow (HF), and surface flow (SF) systems. A total of 25 MPs were monitored, with influent concentrations ranging from 0.98 to 13,071.67 ng/L. PAEs exhibited the highest concentrations, followed by antibiotics and neonicotinoids. High removal efficiencies were achieved for fluoroquinolones (80.3-98.4 %) and short-chain PAEs (80.1-88.4 %), while neonicotinoids showed lower removal efficiencies (11.4-61.4 %). The removal efficiency of MPs increased with rising log Kow values but declined after surpassing a certain threshold. The initial treatment stage was critical to overall performance, with the VF-HF-SF configuration (HCW1) achieving the highest removal efficiency, followed by VF-SF-HF (HCW2). Microbial community analysis revealed that the initial wetland type influenced microbial composition, with Proteobacteria dominating across all systems. HCWs with VF as the first stage exhibited more complex and modular microbial networks, potentially enhancing pollutant degradation capacity. Co-occurrence network analysis indicated a predominance of microbial cooperation over competition, and key bacterial taxa involved in the treatment process were identified. Dissolved oxygen (DO) was a major environmental factor shaping microbial communities and enhancing MPs removal. This study highlights the importance of initial wetland configuration and DO in optimizing HCW systems for MPs mitigation and offers insights for the development of effective nature-based solutions.