HR: 0830h
AN: H11D-0892    [PDF]
TI: BIOVENTING - Groundwater Aeration by Discontinuous Oxygen Gas Pulse Injections
AU: * Schirmer, M
EM: mario.schirmer@ufz.de
AF: UFZ Centre for Environmental Research Leipzig-Halle in the Helmholtz Association, Department of Hydrogeology, Theodor-Lieser-Str. 4, Halle/Saale, 06120 Germany
AB: Groundwater aeration by discontinuous oxygen gas pulse injections appears to be a promising concept for enhanced natural attenuation of dissolved contaminants that are susceptible for oxygenase enzyme attacks. Oxygen amendments facilitate indigenous microbiota to catabolize groundwater pollutants, such as aromatics, that are considered to be recalcitrant in absence of dissolved oxygen. As a rule, natural attenuation of many pollutants under aerobic conditions is considerably faster than under anaerobic conditions. Thus, enhancing the dissolved oxygen level appears to be worthwhile. In situ aeration of groundwater has been accomplished by air sparging, H2O2-supply, or by utilization of oxygen release compounds. However, continuous aeration of previously anaerobic groundwater is not desirable for several reasons: (a) economic efforts too high, (b) pollutant dislocation towards surface (desired only in air sparging), (c) risk of aquifer clogging (gas clogging, oxidation of ferrous iron, formation of bioslimes). In contrast, discontinuous oxygen gas sparging provides only for periodical groundwater aeration which is followed by microaerobic and suboxic conditions. Microaerobic conditions can prevail spatially (e.g., at plume fringes or within biofilms) or temporarily (e.g., at discontinuous bioventing). They still allow adapted bacteria to transform environmental pollutants to less toxic compounds, e.g., aromatic ring cleavage after dioxygenasis attack. Ring cleavage products, on the other hand, may be degraded more easily by anaerobic consortia than the initial aromatic compounds, making oxygen depletion periods highly intriguing in regard to an initiation of natural attenuation processes at plume fringes. In our work we outline the effect of oxygen depletion conditions on biodegradation of monchlorobenzene (MCB) as they occur subsequently to temporary aeration periods. For microaerobic conditions, relative to the oxygen supply, a stoichiometric transformation of MCB to cis,cis-2-chloromuconate is demonstrated. In order to examine effects of enhanced natural attenuation, initiated by aeration, on geohydraulics, discontinuous oxygen gas injections were simulated in two flow-through systems. Design, processing, and first results of our ongoing research are presented for the automatized lab column system CAMERA and a pilot field reactor at a MCB polluted site at Bitterfeld, Germany. Bubble mediated oxygen gas transfer is briefly discussed in light of the model presented recently by Holocher (Environ. Sci. Technol., 2003. 37: p. 1337-1343).
DE: 1615 Biogeochemical processes (4805)
DE: 1831 Groundwater quality
SC: Hydrology [H]
MN: 2003 Fall Meeting