Evaluation of continuous flow‐through phytoreactors for the treatment of TNT‐contaminated water

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AbstractThe proof of concept for created wetlands to treat groundwater or industrial water contaminated with trinitrotoluene (TNT) was established using bench‐scale, continuous flow reactors with aquatic plants. Contaminant loadings from 0.0132 to 2.488 g/m3/day were tested on phytoreactors using parrotfeather (Myriophyllum aquaticum) as the plant. Reactor removal efficiency and elimination capacity were linearly related to the load of TNT. An algal reactor was also tested at a loading of 0.9671 g/m3/day and removed 93% of the TNT. Some removal was also found in control reactors that contained no plants and minimized algal growth by shielding them from light. However, the removal efficiencies in the controls were much lower. Transformation products, aminodinitrotoluenes (ADNT) and diaminonitrotoluenes (DANT), were detected in the algae and phytoreactors, but not in the controls, indicating that the TNT was being transformed. However, ADNT persisted in the effluent, representing a reactor‐design issue that must be further investigated. ADNT concentrations in the plant material increased with contaminant loading. TNT was only found in plant tissue at the highest loading of 2.488 g/m3/day. Higher concentrations of ADNT were found in the root of the plant, with approximately equal concentrations in the stem and leaf portions. Ratios of 4‐aminodinitrotoluene (4ADNT) versus 2‐aminodinitrotoluene (2ADNT) were higher in the water phase versus what was found in plant material. Because microbial processes tend to favor the formation of 4ADNT, the higher ratio suggests that the removal of TNT is actually a combination of microbial and phyto processes.