Many soils contaminated with high molecular weight hydrocarbons (HMW PAHs) contain PAHdegrading microorganisms. These microbes are often limited in their degradation capability because of some limiting environmental factors (i.e., low aqueous solubility of PAHs, low bioavailability of PAHs, nitrogen or other nutrient limitation, high co-contamination levels such as pentachlorophenol [PCP] that can inhibit PAH biodegradation, etc.). Microcosm studies were done using biostimulation (addition of ground rice hulls as a bulking agent and dried blood as a slow-release nitrogen source) and/or bioaugmentation (addition of Pseudomonas aeruginosa strain 64, a biosurfactant-producer on a vermiculite carrier). Soil from the POPILE, Inc. Superfund site (PAHs at 13,000 mg/kg, average and PCP at 1,500 mg/kg, average) was used. After 11 months, control microcosms (no treatment) showed a 23% decrease in total PAHs and a 48% decrease in total BaP toxic equivalents. The biostimulated microcosms showed a 34% decrease in total PAHs and a 57% decrease in total BaP toxic equivalents, while the biostimulated and bioaugmented microcosms revealed an 87% decrease in total PAHs and a 67% decrease in total BaP toxic equivalents. Pseudomonas aeruginosa strain 64 is not a PAHdeg rader, t herefore, this redu ction in PAHs was due to stimulated deg rada tion by the autochthonou s mic robial community. Pan studies were designed t o tes t the imp roved bioremediation of HMW PAHs Acta Biotechnol. 23 (2003) 2 -3, 179 -196 using biostimulation and/or bioaugmentation on a larger scale. Drywells were used to monitor soil microbial respiration, soil moisture was maintained at 50-80% of the soil field moisture capacity (FMC), cultivation was carried out weekly with rototillers, and microbial biomass and community composition (indigenous microbiota and augmented soil) were determined by PLFA profiles. An initial rapid decrease in PAH concentration was observed in the pan receiving both bioaugmentation and biostimulation (50% degradation at six months). The pan that was biostimulated only achieved the 50% level at seven months. After 16 months, the control pan showed a 12% decrease in PAHs, while biostimulated only and both biostimulated and bioaugmented pans showed an 86 and 87% removal, respectively. These two pans developed similar microbial communities, and these communities were different from that in the control pan 1. Supplementing autochthonous bacterial communities, using slow-release nitrogen fertiliser and bulking agent has great potential for improving landfarming of PAH-contaminated soils.
Dry and wet physical separation processes were tested at Yuma Proving Ground to remove depleted uranium (DU) from soil. Four sample locations were tested that had varied uranium concentration, weathering, and aging of fired, DU residues. Reduction of soil DU concentration was achieved using simple vibratory or agitated screening techniques. For soils into which the DU had been recently fired, these techniques were successful at removing a large fraction (>70 percent) of the total uranium present (by mass). A heavy liquid separation process based on a water/sodium polytungstate solution was tested. This produced a sinking fraction that contained nearly 100-percent uranium and uranium oxide by mass for the less weathered soils. However, this type of wet separation is not currently practical for field use. A water-based separation process using an angled vibrating table to facilitate gravity transport of separated DU was also tested. This method produced a fraction of concentrated uranium along with fractions of soil particles with reduced densities. However, this process required extensive particle size separation prior to use and produced a contaminated waste stream that required secondary treatment. The extent to which DU and DU residues could be removed from the Yuma soils depended on the extent of soil weathering and corrosion of the DU alloy.
Rhizobium tropici, a catalogued symbiotic nodulator of leguminous plants, is also known for its production of a gel-like extracellular polymeric substance (EPS). The natural functions of the biopolymer in the rhizosphere include surface adhesion, self-adhesion of cells into biofilms, formation of protective barriers, water retention around roots, and nutrient accumulation. We performed three treatability studies to evaluate the effectiveness of the biopolymer as a soil amendment to increase slope stability and reduce transport of solids in runoff water, reduce the transport of heavy metals associated with suspended sediment from small arms firing ranges, and reduce the generation of dust. Four soil types were used: Silty Sand (SM), Sandy Silt (ML), Silt (S), and Silty Clay (CL). These soil types were selected because they are prone to wind and water erosion thus presenting possible worst case scenarios. The study of sediment transport demonstrated that the biopolymer soil amendment was able to significantly reduce surface water erosion and particulate and heavy metal transport in leachate. The biopolymer soil amendment effectively maintained the slope stability of a simulated berm. In addition, biopolymer added to the Silty Sand soil at 0.5% (w:w) loading rate reduced dust production compared to the control at all relative humidities, indicating it should perform well in both arid and tropical environments. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents. DESTROY THIS REPORT WHEN NO LONGER NEEDED. DO NOT RETURN IT TO THE ORIGINATOR. DISCLAIMER: The contents of this report are not to be used for advertising, publication, or promotional purposes. Citation of trade names does not constitute an official endorsement or approval of the use of such commercial products. All product names and trademarks cited are the property of their respective owners. The findings of this report are not to be construed as an official Department of the Army position unless so designated by other authorized documents.
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