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.

A series of column studies, using site-specific soil and groundwater, were conducted to determine the feasibility of biologically active zone enhancement (BAZE) process for reductive biotransformation of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in groundwater. This treatability study examined the use of four amendments (acetate, ethanol, soluble starch, and acetate plus ammonium), which served as electron donors. Triplicate columns, with groundwater residence time of about 27.5 h, were used for each amendment treatment and the amendment control. In treatment columns amendment dosing was 500 mg/L C for carbon sources and 100 mg/L N for ammonium. Each of the amendment treatments reduced RDX inlet concentrations of 100 g/L to less than 1 g/L. The highest first-order RDX biodegradation rate ranged between 0.140 and 0.447 h −1 for acetate amended columns as compared to 0.037 to 0.083 h −1 in control columns (no amendment). The addition of soluble starch resulted in increased toxicity (based on Microtox ® analysis) that was partially removed by biological activity in the columns. Ethanol addition itself did not result in increased toxicity but biological activity in this system did induce Microtox ® toxicity. Acetate did not have any Microtox ® toxicity associated with it. The addition of ammonium as a nitrogen source did not significantly increase the removal rate of RDX. Based on these observations acetate was selected for the field demonstration. Published by Elsevier B.V.

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