Accumulation and Distribution of Lead and Chromium in Laboratory-Scale Constructed Wetlands Inoculated with Metal-Tolerant Bacteria

Abstract

The accumulation and distribution of lead and chromium was tested in a laboratory-scale constructed wetland (CW) inoculated with metal-tolerant bacteria. Two non-inoculated systems also were evaluated, one planted and the other unplanted. Mass balances indicated that 57% of chromium input was accumulated into inoculated CW after 151 days of operation. The distribution was similar in support media and vegetation, in which 78% was transferred to aerial part. Similarly Pb was accumulated 29% in the support media and 39% in vegetation, which was distributed 52% in rhizome and 48% in aerial part. Significantly lower amounts of heavy metals were accumulated in non-inoculated systems than in the inoculated wetlands (p < 0.005). In addition, a markedly higher proportion of chromium in aerial vegetation and of lead in the suspended fraction of the effluent was exhibited, which raises a subsequent recovery of the metal by harvest and settling, respectively. Results indicate that CW inoculated with metal-tolerant bacteria might be a suitable option for treating wastewater with content of lead and chromium.

Keywords::

• biofilm
• heavy metals
• mass balance
• Phragmites australis
• support media

Acknowledgments

The first author acknowledges the doctoral scholarship from Consejo Nacional de Ciencia y Tecnología México. Authors acknowledge the valuable advice of Mrs. Prof. Dr. Irina Salgado-Bernal from the Universidad de La Habana, Cuba. Financial support from UNAM, Facultad de Química PAIP (Programme for Support to Research and Graduate Students Formation, in Spanish) is greatly acknowledged.