APPLICATION OF PALLADIUM (Pd) CATALYSIS WITH FORMIC ACID AS A REDUCTANT FOR THE IN SITU TREATMENT OF GROUNDWATER CONTAMINATED WITH NITROAROMATIC COMPOUNDS (NACS), CHLORINATED ALIPHATIC HYDROCARBONS (CAHS), AND NITRATE D. Landon Phillips 1 , Matthew D. Welling 2 , Mark R. Stevens 3 , Krishna Pallavi 4 , Mark N. Goltz 5 and Abinash Agrawal* Department of Geological Sciences, Wright State University, 3640 Colonel Glenn Hwy., Dayton, OH 45435, USA, Email: abinash.agrawal@wright.edu 1 39 CES/CEX, APO AE 09824, Email: dennis.phillips@incirlik.af.mil 2 305 AMW/PO, McGuire AFB, NJ 08641, USA, Email: mark.stevens2@McGuire.af.mil 3 36 CES/CEV, Andersen AFB, APO AP 96543, USA, Email: matthew.welling@andersen.af.mil 4 Wittman Hydro Planning Associates Inc., Blooming, IN, E-mail: krishna.pallavi@hotmail.com 5 Air Force Institute of Technology, WPAFB, OH, USA, Email: mark.goltz@afit.edu *Author to whom inquiries may be addressed Abstract A bench-scale investigation of reduction of chlorinated aliphatic hydrocarbons (CAHs), nitroaromatic compounds (NACs), and nitrate with commercially available monometallic Pd/γ- alumina catalysts has been carried out in flow-through column reactors. Experimental results for the reduction of CAHs, NACs and nitrate with formic acid (HCOOH) as an electron donor show zero-order to pseudo first-order transition (Michaelis-Menten kinetics) with decreasing substrate concentrations. Reaction kinetics are dependent on factors such as initial substrate loading and reductant (formic acid) concentration. Due to in situ buffering by formic acid, catalyst deactivation over time is minimal. The short residence times needed for the destruction of the substrates demonstrate the potential of using the Pd-formic acid system (Pd-HCOOH) as a component of a technology to remediate NAC-, CAH- or nitrate-contaminated groundwater in situ. Introduction Laboratory investigations at Stanford University (1-3) have shown that groundwater contaminated with chlorinated aliphatic hydrocarbons (CAHs) may be efficiently treated by palladium (Pd)-catalysis with molecular hydrogen as a reductant. During treatment, the CAH is reduced in the following hydrodehalogenation reaction: X-Cl + 2H + + 2e -  X-H + H + + Cl - (1) This approach is currently being evaluated in the field, using in-well catalytic reactors and molecular hydrogen to effect in situ destruction of CAHs in the groundwater (4). The field evaluations involve use of circulating wells to capture and treat CAH-contaminated groundwater without the need to extract water from the subsurface. When molecular hydrogen was used as a reductant to dehalogenate CAHs, reversible catalyst deactivation was observed (3). Further, the use of hydrogen as a reductant to promote in situ dehalogenation poses some practical problems because it is an explosive, low-solubility gas. As an alternative to hydrogen, this study investigates the potential of using formic acid