Use of zeolite and bauxite as filter media treating the effluent of Vertical Flow Constructed Wetlands

Various gravity filters containing zeolite, bauxite and carbonate material were constructed and operated for 3 years, to provide further treatment of the effluent of a pilot-scale Vertical Flow Constructed Wetland (VFCW). Results showed a significant improvement of the VFCW effluent quality at a residence time of 1 day. Zeolite was more effective in nitrogen and organic matter removal, while bauxite in phosphorus retention. The carbonate material had the lowest efficiency among all filter materials used. The filter containing a 50–50% mixture of zeolite and bauxite showed the highest efficiency in pollutant removals. The increase of the residence time from 1 to 2 days did not show a respective statistically significant increase in removal rates. Temperature did not significantly affect the performance of the filters, with the exception of phosphorus removal.