Remediation of polyaromatic hydrocarbons (PAHs) through landfarming with biostimulation and bioaugmentation

Many soils contaminated with high molecular weight hydrocarbons (HMW PAHs) contain PAH-degrading 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 PAH-degrader, therefore, this reduction in PAHs was due to stimulated degradation by the autochthonous microbial community. Pan studies were designed to test the improved bioremediation of HMW PAHs 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.