Efficiency of a Subsurface Constructed Wetland System Using Native Southwestern U.S. Plants

Abstract

AbstractA small‐scale three‐cell (in series) subsurface (SSF) constructed wetland that used 16 previously untested native Arizona plants was found to be effective in the treatment of secondary waste at high elevation (2350 m) in northern Arizona. Fifteen of the 16 plant species survived in at least one of the cells in the system. Plant survival depended on their position in the cells, with increased survival rates downstream from the effluent input to cell 1, on water depth, and on individual species selection. The wetland was effective in removing both chemical pollutants (total Kjeldahl nitrogen [TKN], ammonia, nitrate, total kjeldahl phosphorus [TP], and phosphate) and bacteriological indicator organisms of human pathogens (total coliforms and fecal coliforms). The fecal coliform counts of the effluent exiting the third cell were below the recreational full‐body contact (swimming) standard (200 cfu/100 mL) in 14 out of the 15 mo of operation. The TKN and TP concentrations were reduced by 84 and 73%, respectively compared to nutrients entering the system. The loss of N suggests that a combined nitrification/denitrification process is active in the wetland. However, after 9 mo of operation, nitrate levels began to increase beyond the target of 1 mg/L indicating that nitrification rates are exceeding denitrification rates and that the wetland cells are aerobic. The constructed wetland system effectively conserves water. Because it is used to irrigate plantings near the constructed wetland, the nutrient concentrations in the effluent aid plant growth.