Efficiency of a subsurface constructed wetland system using native southwestern US plants

A small-scale three-cell (in series) subsurface (SSF) constructed wetland t hat used 16 previously untested native Arizona plants was found to be effec tive in the treatment of secondary waste at high elevation (2350 m) in nort hern Arizona. Fifteen of the 16 plant species survived in at least one of t he cells in the system. Plant survival depended on their position in the ce lls, with increased survival rates downstream from the effluent input to ce ll 1, on water depth, and on individual species selection. The wetland was effective in removing both chemical pollutants (total Kjeldahl nitrogen [TK N], ammonia, nitrate, total kjeldahl phosphorus [TP], and phosphate) and ba cteriological indicator organisms of human pathogens (total coliforms and f ecal coliforms). The fecal coliform counts of the effluent exiting the thir d cell were below the recreational full-body contact (swimming) standard (2 00 cfu/100 mt) in 14 out of the 15 mo of operation. The TKN and TP concentr ations were reduced by 84 and 73%, respectively compared to nutrients enter ing the system. The loss of N suggests that a combined nitrification/deniti frication process is active in the wetland. However, after 9 mo of operatio n, nitrate levels began to increase beyond the target of 1 mg/L indicating that nitrification rates are exceeding denitrification rates and that the w etland cells are aerobic The constructed wetland system effectively conserv es water. Be cause it is used to irrigate plantings near the constructed we tland, the nutrient concentrations in the effluent aid plant growth.