title: Microbial activity in soils following steam treatment.
abstract: Steam enhanced extraction (SEE) is an aquifer remediation technique that can be effective at removing the bulk of non-aqueous phase liquid (NAPL) contamination from the subsurface, particularly highly volatile contaminants. However, low volatility compounds such as polynuclear aromatic hydrocarbons (PAHs) are less efficiently removed by this process. This research evaluated the effects of steam injection on soil microbial activity, community structure, and the potential for biodegradation of contaminants following steam treatment. Three different soils were evaluated: a laboratory-prepared microbially-enriched soil, soil from a creosote contaminated field site, and soil from a chlorinated solvent and waste oil contaminated field site. Results from field-scale steaming are also presented. Microbial activity before and after steam treatment was evaluated using direct epifluorescent microscopy (DEM) using the respiratory activity dye 5-cyano-2,3, ditolyl tetrazolium chloride (CTC) in conjunction with the fluorochrome 5-(4,6-dichlorotriazinyl) aminofluorescein (DTAF) to yield a quantitative assessment of active and total microbial numbers. DEM results indicate that steamed soils that were analyzed while still hot exhibited microbial activity levels that were below detection. However, soil samples that were slowly cooled, more closely reflecting the conditions of applied SEE, exhibited microbial activity levels that were comparable to presteamed soils. Samples from a field-site where steam was applied continuously for 6 weeks also showed high levels of microbial activity following cooling. The metabolic capabilities of the steamed communities were investigated by measuring cell growth in enrichment cultures on various substrates. These studies provided evidence that organisms capable of biodegradation were among the mesophilic populations that survived steam treatment. Fluorescent in situ hybridization (FISH) analysis of the soils with domain-level rRNA probes suggest that both Archaea and Bacteria survived steam exposure.
authors.affiliation: Department of Civil and Environmental Engineering, University of California, Berkeley 94720-1710, USA. rer26@cornell.edu
authors.forename: Ruth E
authors.initials: RE
authors.lastname: Richardson
authors.forename: C Andrew
authors.initials: CA
authors.lastname: James
authors.forename: Vishvesh K
authors.initials: VK
authors.lastname: Bhupathiraju
authors.forename: Lisa
authors.initials: L
authors.lastname: Alvarez-Cohen
mesh_terms: D001105:Archaea / Q000378:metabolism; D001419:Bacteria / Q000378:metabolism; D001673:Biodegradation, Environmental; D015169:Colony Count, Microbial; D006813:Humidity; D017403:In Situ Hybridization; D008856:Microscopy, Fluorescence; D011084:Polycyclic Aromatic Hydrocarbons / Q000378:metabolism; D012987:Soil / Q000032:analysis; D012988:Soil Microbiology; D013227:Steam; D013696:Temperature
chemical_list: D011084:Polycyclic Aromatic Hydrocarbons; D012987:Soil; D013227:Steam