Bacterial community dynamics in horizontal flow constructed wetlands with different plants for high salinity industrial wastewater polishing

This study is focused on the diversity of bacterial communities from two series of horizontal subsurface flow constructed wetlands (CW) polishing high salinity tannery wastewater. Each series was planted with Arundo donax or Sarcocornia sp. in a substrate composed by expanded clay and sand. Chemical and biochemical oxygen demand removal efficiencies were similar in each series, varying between 58 and 67% (inlet COD 218 ± 28 mg L⁻¹) and 60 and 77% (inlet BOD₅ 37 ± 6 mg L⁻¹), respectively. High numbers of culturable bacteria were obtained from substrate and root samples - 5.75 × 10⁶-3.95 × 10⁸ CFU g⁻¹ recovered on marine agar and 1.72 × 10⁷-8.46 × 10⁸ CFU g⁻¹ on nutrient agar. Fifty bacterial isolates were retrieved from the CW, related phylogenetically to Firmicutes, Actinobacteria, Bacteroidetes, α-, β-, and γ-Proteobacteria. Changes in the bacterial communities, from roots and substrate of each series, related to the plant species, hydraulic loading rates and along CW operation were examined using denaturating gradient gel electrophoresis (DGGE). The clustering analysis suggested that a diverse and distinct bacterial community inhabits each series, which was related to the type of plant present in each CW.