Influence of vegetation and substrate type on removal of emerging organic contaminants and microbial dynamics in horizontal subsurface constructed wetlands
Constructed wetlands (CWs) offer an efficient alternative technology for removing emerging organic contaminants (EOCs) from wastewater. Understanding the impact of CW configuration on EOC removal and the dynamics of microbial communities is essential for optimizing CW performance. This study investigated EOC removal and microbial communities in horizontal subsurface flow (HSSF) CWs over a 26-month operational period. Comparison between tuff-filled CWs and gravel-filled CWs revealed that the tuff-filled CWs' superior EOC removal, particularly at longer operation, due to the tuff larger micropores and surface area, which promote microbial growth, sorption, and biodegradation. Partially positively charged EOCs like atenolol and sitagliptin were efficiently removed via sorption processes. In contrast, polar non-sorbing EOCs, such as diclofenac and acyclovir, as well as artificial sweeteners like acesulfame and saccharin, exhibited enhanced removal over time due to enhanced biodegradation resulting from microbial growth and adaptation. The presence of vegetation and different planting methods (plant type, monoculture, and serial planting) had a limited impact, underscoring the dominance of substrate type in CW performance. Microbial community analysis identified two stages: a startup phase (1-7 months) and a maturation phase (19-26 months). During this transition, highly diverse communities dominated by specific species in the early stages gave way to more evenly distributed and relatively stable communities. Proteobacteria and Bacteroidetes remained dominant throughout. Notably, Alphaproteobacteria, Acidobacteria, Planctomycetes, Salinimicrobium, and Sphingomonas were enriched during the maturation phase, potentially serving as bioindicators for EOC removal. In conclusion, this study emphasizes the pivotal role of substrate type and maturation in the removal of EOCs in HSSF CW, considering the complex interplay with EOC physicochemical properties. Insights into microbial community dynamics underscore the importance of taxonomic and functional diversity in assessing CW effectiveness. This knowledge aids in optimizing CWs for sustainable wastewater treatment, EOC removal, and ecological risk assessment, ultimately contributing to environmental protection.