Environmental Engineering Reference
In-Depth Information
the laboratory at room temperature on the biocarrier for 2 months without
significant loss in viability and metabolic activity.
Bioaugmentation of microcosms (POPILE soil with PAHs at 13,000 mg/
kg, average, and PCP at 1500 mg/kg, average) was successful for
P. aerugi-
nosa
strain 64. After 11 months of treatment, the control (no treatment)
showed a 23% decrease in total PAH and a 48% decrease in total BaP toxic
equivalents. The biostimulation microcosm (bulking agent and dried blood)
showed a 34% decrease in total PAH and a 57% decrease in total BaP toxic
equivalents. The bioaugmentation microcosm (bulking agent, dried blood,
and
P. aeruginosa
strain 64 on vermiculite) showed an 87% decrease in total
PAH and a 67% decrease in total BaP toxic equivalents.
The addition of microorganisms to improve metabolic capability was
more problematic due to their sensitivity to soil conditions (i.e., toxic creosote
components, competition with indigenous microbial communities, etc.). No
improved decrease in PAHs was observed in soil microcosms after microor-
ganism addition. We were not able to detect these bacteria in the POPILE
soil after a couple of days. Clearly, more research is required to make it a
useful and practical tool to increase cometabolic degradation of HMW PAHs.
7.5.2 Conclusions from LTUs
Respiration analysis, coupled with reduction in heavy PAHs (four, five, and
six rings), demonstrated significant biological activity in the pilot-scale units
even at the very high contaminant concentrations found in the POPILE soil.
Microbiological characterization, using PLFA analysis, showed an increase
in biomass and a divergence of community composition between the LTUs
corresponding to the different treatments. LTU 2, specifically, showed an
increase in the relative percentage of Gram-negative bacteria. However, the
microbial communities of both LTUs were able to degrade PAHs into the
four-ring homologues, including BaP toxic equivalent compounds. There-
fore, although it appears that limited cultivation had a positive impact on
the microbial biomass, in the final analysis, cultivation had minimal impact
on PAH removal, with both pilot units achieving 69% reduction in total PAH.
One of the parameters under study at the pilot scale before field evalu-
ation was the addition of water and nutrients to the soil. The high concen-
tration of hydrophobic contaminants in the soil inhibited aqueous phase
nutrient additions, and results indicated that use of slow-release nutrients
applied in a solid form would be a more effective method of maintaining
an appropriate C:N:P ratio.
7.5.3 Conclusions from trough study
Weekly tilling actually decreased the capacity of the indigenous, unsupple-
mented microbial community to degrade PAHs, even when accompanied
by soil moisture control. The control trough showed a 12% decrease in PAH
contamination compared to the control LTU, which showed >50% decrease
