Structure of the microbial communities in vertical-flow constructed wetlands.

Constructed wetlands with vertical water flow (VFCW) are a widespread approach to remove a wide range of pollutants from wastewater. Classical French system is a VFCW technology which is very effective in removing organic matter; however, it may exhibit certain problems with N and P removal. The Azoe-NP process has been developed to improve denitrification and P removal compared to Classical French system due to additional treatment stage on trickling filter. Microorganisms mediate these processes during the wastewater purification in VFCWs, therefore the knowledge on the structure and diversity of microbial communities is an important step to manage and improve the design and performance of the VFCWs. Here, we determined the structure of the microbial communities of the VFCWs with the classical French and Azoe-NP processes in order to identify possible differences in microbial groups that determine the efficiency of pollutants removal.The main difference between these two systems is that Azoe-NP process is highly efficient in nitrogen removal compared to classical French CWs. Such advantage is achieved by partial saturation of filter beds creating an anoxic zone, favourable for denitrification and additional pre-treatment stage - trickling filter, which is inhabited by denitrifiers (Thiothrix, Rhodoferax, Flavobacterium, Rhodobacter) and possibly creates specific conditions facilitating activity of denitrifying bacteria in the following stages of wastewater treatment.