A Microcosm Study on Remediation of Explosives‐contaminated Groundwater Using Constructed Wetlands^a

Abstract

Anaerobic degradation of TNT and TNB in gravel systems was rapid and similar to removal rates in parrot feather lagoons. Planted and unplanted anaerobic gravel systems were the only treatments that provided significant reduction of RDX and HMX. Planted systems with parrot feather had no effect on removal rates of explosives in anaerobic gravel systems. Reciprocating wetlands were not effective in biodegrading RDX or HMX, but were very efficient at removing COD. A scaled-up concept for bioremediating contaminated groundwater can be envisioned with the data obtained in the current study. The effectiveness of anaerobic gravel systems indicate an anaerobic subsurface-flow constructed wetland can be established as the primary treatment for remediation with C added to the influent or step fed down the length of the wetland. Another option would be to add compost as a more permanent source of C to the gravel substrate. With time, the need for C supplementation may be reduced with the C exudates and redox lowering potential of certain plants like canarygrass (Phalaris arundinacea). As a secondary treatment, a reciprocating wetland would appear to be a logical choice to quickly remove C released in effluent waters of the anaerobic wetland.

Phytoremediation in Wetland Ecosystems: Progress, Problems, and Potential

“…Sikora et al (1997) found both TNT and TNB were rapidly degraded (Figure 3) under anaerobic substrate conditions; however, the presence of M. braziliense made no apparent difference in removal rates. Substrate bacterial action seemed to play the biggest role in explosives degradation (Sikora et al, 1997). Recommendations for larger-scale testing of these degradation pathways is also made by Sikora et al (1997); however, lists of additional wetland plant species (e.g., the screening list of Best et al [1997]) should also be evaluated.…”

“…Microcosm design created anaerobic and aerobic conditions by using added carbon to enhance bacterial uptake of oxygen (causing anaerobic waters) and siphon-driven reciprocating water exchange to produce more aerobic waters (Sikora et al, 1997). Sikora et al (1997) found both TNT and TNB were rapidly degraded (Figure 3) under anaerobic substrate conditions; however, the presence of M. braziliense made no apparent difference in removal rates. Substrate bacterial action seemed to play the biggest role in explosives degradation (Sikora et al, 1997).…”

“…Effects of aerobic vs. anaerobic substrate conditions on wetlands degradation of explosives have also been evaluated (Sikora et al, 1997). Microcosm experiments using parrot feather (Myriophyllum braziliense) tested phytoremediation effectiveness for several explosives: TNT, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,2,5,7-tetrazocine (HMX), and 1,3,5-trinitro-benzene (TNB) from the U.S. Army Milan Ammunition plant near Milan, Tennessee (Sikora et al, 1997).…”

“…Microcosm experiments using parrot feather (Myriophyllum braziliense) tested phytoremediation effectiveness for several explosives: TNT, hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX), octahydro-1,3,5,7-tetranitro-1,2,5,7-tetrazocine (HMX), and 1,3,5-trinitro-benzene (TNB) from the U.S. Army Milan Ammunition plant near Milan, Tennessee (Sikora et al, 1997). Microcosm design created anaerobic and aerobic conditions by using added carbon to enhance bacterial uptake of oxygen (causing anaerobic waters) and siphon-driven reciprocating water exchange to produce more aerobic waters (Sikora et al, 1997). Sikora et al (1997) found both TNT and TNB were rapidly degraded (Figure 3) under anaerobic substrate conditions; however, the presence of M. braziliense made no apparent difference in removal rates.…”

Wetlands

“…Thus, in plant selection for wetland construction, consideration of explosives removal potential and biomass production were considered essential. Sikora et al (1997) reported that the anaerobic degradation of TNT and TNB in anaerobic SSF constructed wetland systems was rapid and similar to removal rates in parrot feather wetlands. Vegetated and unvegetated anaerobic SSF systems were found to be the only systems that provided significant reduction of RDX and HMX.…”