Removal of TNT using plants in constructed wetlands

The TNT degradation study was conducted using three typical wetlands plant litter types (straw, cattail, and bulrush) in hydroponic solution. TNT (220 mu M) was rapidly and completely removed with all plants (10 g/L) within three to five days at 20 degrees C. The first order rate constant of TNT disappearance using straw litter was 0.59 day(-1) at 20 degrees C, and similar rates were observed with bulrush and cattail ranging from 0.56 to 1.33 day(-1). TNT removal first resulted in an initial increase of 4-aminodinitrotoluene (4-ADNT). The concentration of 4-ADNT also decreased and was below detectable limits after further incubation. Disappearance of 4-ADNT could have been due to further reduction to 2,4-diamino-6-nitrotoluene (2,4-DANT). The same patterns of metabolites formation and degradation were observed with other bulrush, and cattail carbon sources. A significant difference in TNT degradation rates (0.12 day(-1) at 10 degrees C) was observed with 10 degrees C difference. The maximum combined level of metabolites concentration was only 10 to 18 % of the initial TNT. From extraction study, we found the trace amounts of 4-ANDT and 2,4-DANT, but no TNT was detected. The C-14 study and sorption experiment also showed that TNT mineralization did not take place, and the TNT disappearance have been the result of a combination of two processes; initial sorption followed by bacterial degradation. A mesocosm scale constructed wetlands for treating TNT is now underway at the Richmond Field Station (Richmond, CA).