In Situ Bioremediation of Perchlorate in Vadose Zone Soil Using Gaseous Electron Donors: Microcosm Treatability Study

Abstract

A series of microcosm experiments were performed to determine the effectiveness of various gaseous electron donors (including hydrogen, 1‐hexene, ethyl acetate, and liquefied petroleum gas [LPG]) for supporting biological perchlorate reduction under different electron donor concentrations and soil moistures. Under high soil moisture (16% w/w) conditions, complete or partial perchlorate degradation was achieved with all of the tested electron donors, except for ethyl acetate. Hydrogen was the most promising of the tested electron donors, achieving complete perchlorate degradation with first‐order rate constants ranging from 0.13 to 0.20 day−1 and reducing concentrations to non‐detectable levels within 35 to 42 days. The LPG and 1‐hexene each promoted partial perchlorate reduction, with average first‐order rate constants of 0.05 and 0.11 day−1, respectively. Although significant perchlorate reduction was observed with as little as 13% moisture, the moisture content for complete perchlorate degradation in this particular soil was determined to be 17%.

In Situ Destruction of Perchlorate and Nitrate Using Gaseous Electron Donor Injection Technology

“…The more significant change in hydrogen concentration relative to oxygen concentration suggests that hydrogen was the primary factor affecting perchlorate reduction. Treatability study data conclusively demonstrated perchlorate reduction in the presence of hydrogen, whereas perchlorate reduction in the presence of LPG was not significantly different from the control (Cai et al 2010).…”

“…If soil moisture is too low then biological activity can be inhibited. Treatability tests of site soil demonstrated that perchlorate reduction was possible with 16% moisture but not with 7% moisture (Cai et al 2010). In addition, if soil moisture is very high, for example in clay, then gas transport may be hindered and insufficient electron donors will be delivered to promote perchlorate biodegradation.…”

“…Some inhibition may have occurred at low moisture contents compared to high‐moisture contents, but 95% perchlorate destruction was observed at a moisture content of 6.8%. Laboratory treatability data demonstrated perchlorate biodegradation at 16% moisture but not at 7% moisture (Cai et al 2010). Thus perchlorate destruction performance in the field appeared to be greater than predicted by the laboratory treatability study.…”

“…The objective of this study was to demonstrate that GEDIT was capable of promoting perchlorate and nitrate destruction in the vadose zone at the Inactive Rancho Cordova Test Site (IRCTS) in Rancho Cordova, California. Previous laboratory studies using soil collected from the IRCTS propellant burn area (PBA) were conducted to determine which, if any, electron donors could promote perchlorate biodegradation (Cai et al 2010). The electron donor candidates tested were hydrogen, 1‐hexene, ethyl acetate, and liquefied petroleum gas (LPG), also known as commercial propane.…”

Transport and degradation of perchlorate in deep vadose zone: implications from direct observations during bioremediation treatment

“…In the vadose zone, natural attenuation and biodegradation of perchlorate are considered very limited (Gal et al, 2009). Nevertheless, studies have shown that perchlorate can be metabolized in unsaturated soil whenever reducing conditions (< 110 mV) (Attaway and Smith, 1993;Shrout and Parkin, 2006) are achieved and an available electron donor is introduced (Tipton et al, 2003;Frankel and Owsianiak, 2005;Nozawa-Inoue et al, 2005;Evans and Trute, 2006;Cai et al, 2010).…”