Bacterial communities involved in the nitrogen cycle in constructed wetlands

Abstract

The high wastewater production rate and its lack of treatment is forcing the search for treatment systems that are efficient, economic, easy to operate and maintain. Additionally, the effluent reuse or reclamation must be considered in any modern wastewater treatment system. Constructed wetlands represent a promising technology in this respect, however, the knowledge and research on the microbial processes involved in the biodegradation of contaminants is still under development. This work reports on the evaluation of heterotrophic, nitrifying and nitrogen fixing bacterial groups present in the support media (gravel) and water column of three constructed wetlands (Cws). These latter are working under different hydraulic loading rates and with different plant species: Phragmites australis, Heliconia psittacorum or without vegetation. The highest densities of nitrifying and N-fixing 21bacteria (5.35 and 7.18 log units gr-, respectively) were found with P. australis, while the CWloaded with H. psittacorum exhibited the lowest densities regardless of the tested bacterial groups. Finally, the unplanted CWshowed the highest density of 1heterotrophic bacteria (7.22 log units gr-). In conclusion, the high bacterial counts found in this study suggest that an important metabolic activity and an interesting bacterial dynamics take place within CWs units operated in the tropics.