Remediation of RDX- and HMX-contaminated groundwater using organic mulch permeable reactive barriers

Abstract

Organic mulch is a complex organic material that is typically populated with its own consortium of microorganisms. The organisms in mulch breakdown complex organics to soluble carbon, which can then be used by these and other microorganisms as an electron donor for treating RDX and HMX via reductive pathways. A bench-scale treatability study with organic mulch was conducted for the treatment of RDX-and HMX-contaminated groundwater obtained from a plume at the Pueblo Chemical Depot (PCD) in Pueblo, Colorado. The site-specific cleanup criteria of 0.55 ppb RDX and 602 ppb HMX were used as the logical goals of the study. Column flow-through tests were run to steady-state at the average site seepage velocity, using a 70%:30% (vol.:vol.) mulch:pea gravel packing to approach the formation's permeability. Significant results included: (1) Complete removal of 90 ppb influent RDX and 8 ppb influent HMX in steady-state mulch column effluent; (2) pseudo-first-order steady-state kinetic rate constant, k, of 0.20 to 0.27 h − 1 based on RDX data, using triplicate parallel column runs;(3) accumulation of reduced RDX intermediates in the steady-state column effluent at less than 2% of the influent RDX mass; (4) no binding of RDX to the column fill material; and (5) This article is a U.S. government work, and is not subject to copyright in the United States.be used to design and implement a pilot-scale organic mulch/pea gravel permeable reactive barrier (PRB) at the site.

Dynamic and equilibrium studies of the RDX removal from soil using CMC-coated zerovalent iron nanoparticles

“…The concentration of RDX degraded during the experiments conducted in the present paper reached 10 mg kg À1 (of soil) by layer at PV ¼ 4.5 and v ¼ 1.6 cm min À1 . This compares quite favorably with similar results that removed only 90 mgkg À1 of RDX from RDX-contaminated soil mixed with mulch packed into a flow-through column (Ahmad et al, 2007). The presently observed overall RDX removal is an order of magnitude higher than that seen in the presence of organic mulch.…”

Considerations for the design of organic mulch permeable reactive barriers

“…Since mulch PRBs are packed under controlled conditions with specific well-mixed materials, these PRBs tend to display a dispersivity that is relatively smaller and more consistent than dispersivities observed in heterogeneous groundwater-bearing units (GWBUs) surrounding the PRB. Tracer tests conducted as part of a bench-scale column study yielded an average longitudinal dispersivity value of 3.6 percent of bed-length, with a range of 2.3 to 5.8 percent of bed-length (Ahmad et al, 2006). The 3.6 percent longitudinal dispersivity is significantly smaller than the typical 10 percent default value utilized in groundwater transport models.…”

“…The difference between the two model curves is simply the seepage velocity, a parameter dependent on porosity. Experimental details are reported elsewhere (Ahmad et al, 2006). association with highly lignified vascular cells (e.g., xylem tracheids in gymnosperms) prevalent in trees.…”

“…Mulch biowalls have a proven performance record for treating nitrate (Robertson & Anderson, 1999;Robertson & Cherry, 1995;Robertson et al, 2000), acid mine drainage (Benner et al, 1997(Benner et al, , 1999, chlorinated solvent (Aziz et al, 2001;Haas et al, 2000;Henry et al, 2003), explosives (Ahmad et al, 2006), and perchlorate (Xu et al, 2003) contamination. Several mulch biowall projects are currently under way at multiple U.S. Department of Defense (DOD) facilities.…”

Efeitos secundários resultantes da aplicação de métodos oxidativos para degradação de contaminantes orgânicos em solos

“…Estes possuem como característica principal a presença de anel benzênico. São substâncias voláteis, menos densas que a água (LNAPL -Light nonaqueous phase liquids), utilizadas principalmente para aumentar o índice de octanagem da gasolina (AHMAD; SCHNITKER; NEWELLET, 2007;HORNIG et al, 2008;LOURENÇO, 2006).…”