Abstract
Constructed wetlands (CWs) have emerged as robust alternatives to traditional wastewater treatment technologies. The efficacy of CWs centers on the intricate interplay of factors, including plant species, substrate attributes, soil conditions, microbial consortia, and operational variables. Microorganisms, the cornerstone of CWs, have a significant influence on mineralization and pollutant mitigation processes. Microbial assemblies within CWs exhibit dynamic responses by adapting novel mechanisms. Here, Proteobacteria possess the ability to efficiently fix nitrogen through innovative pathways, including denitrifying anaerobic methane oxidation (DAMO) and sulfur autotrophic denitrification (SAD). Furthermore, Actinobacteria, Firmicutes, and Gemmatimonadetes have been thoroughly investigated to emphasize their significance in phosphate metabolism. These microorganisms may adapt to various metabolic pathways due to seasonal changes, plant diversity, wastewater composition, and system configuration. On the other hand, microorganisms have been proven to be effective in removing heavy metals in constructed wetlands. Various techniques such as biosorption, transformation, and biomineralization are widely used for this purpose. Therefore, it is essential to conduct a comprehensive investigation of the structure and diversity of microbial communities within constructed wetlands to gain a complete understanding of the system's performance and optimization strategies. This review provides a detailed analysis of microbial studies conducted in constructed wetlands and aimed to understand the mechanisms involved in pollutant removal and the influence of various factors on microbial community prevalence. The outcomes of this review not only deepen our comprehension of CWs and ecosystems, but also provide a basis for knowledgeable choices in their planning and execution, ultimately leading to the responsible stewardship of water resources.