This study focused on the diversity of bacterial communities from two series of two-stage constructedwetlands (CWs) treating tannery wastewater, under different hydraulic conditions. Series were separatelyplanted with Typha latifolia and Phragmites australis in expanded clay aggregates and operatedfor 31 months. The effect of plant species, hydraulic loading and unit stage on bacterial communitieswas addressed through bacterial enumeration and denaturating gradient gel electrophoresis (DGGE).Diverse and distinct bacterial communities were found in each system unit, which was related in partto the type of plant and stage position (first or second unit in the series). Numerical analysis of DGGE profilesshowed high diversity in each unit with an even distribution of species. No clear relation was establishedbetween the sample collection time, hydraulic loading applied and the bacterial diversity.Isolates retrieved from plant roots and substrates of CWs were affiliated with c-Proteobacteria, Firmicutes,a-Proteobacteria, Sphingobacteria, Actinobacteria and Bacteroidetes.Both series were effective in removing organic matter from the inlet wastewater, however, based onbatch degradation experiments it seems that biodegradation was limited by the recalcitrant propertiesof the wastewater
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