Studies
In Water Phase Batch Studies, the results showed a potential for indigenous bacteria to be capable of degrading all 13 PAHs (Figure 12-24). Compared to natural attenuation, biostimulation showed an increase in performance by indigenous community.
Benz(a)anthracene was the only PAH that showed the same results and activity in both natural attenuation and biostimulation (Figure 16). It was hypothesized that biostimulation would increase microbial activity, thus, increasing the digestion of PAHs. All PAH concentrations plotted were a result of finding the median concentration between the triplicate batches studied.
Figure 12: Water Phase Batch Studies degradation of 3-ring aromatic acenaphthylene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in acenaphthylene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that
biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 13: Water Phase Batch Studies degradation of 3-ring aromatic anthracene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares
represent amended contaminated soil samples. The rapid decrease in anthracene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 14: Water Phase Batch Studies degradation of 3-ring aromatic fluorene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in fluorene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 15: Water Phase Batch Studies degradation of 3-ring aromatic phenanthrene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in phenanthrene may have been due to a number of factors including biodegradation, volatilization and
readsorption back on to the soils. There is an indication that biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples. Phenanthrene trends are different than the other 13 PAH trends found in the Water Phase Batch Study experiments. This may been due to many reasons, including a lag phase in the batches where the bacteria were still immobile from being kept at such cold conditions or a lack in vapourization when the lid was opened causing contaminated biostimulated samples to degrade very slowly in the first couple of days.
Figure 16: Water Phase Batch Studies degradation of 4-ring aromatic benz(a)anthracene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in
benz(a)anthracene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that
biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 17: Water Phase Batch Studies degradation of 4-ring aromatic chrysene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in chrysene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 18: Water Phase Batch Studies degradation of 4-ring aromatic pyrene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in pyrene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 19: Water Phase Batch Studies degradation of 5-ring aromatic benzo(b)fluoranthene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in
benzo(b)fluoranthene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that
biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 20: Water Phase Batch Studies degradation of 5-ring aromatic benzo(k)fluoranthene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in
benzo(k)fluoranthene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that
biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 21: Water Phase Batch Studies degradation of 5-ring aromatic benzo(a)pyrene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in benzo(a)pyrene may have been due to a number of factors including biodegradation, volatilization and
readsorption back on to the soils. There is an indication that biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 22: Water Phase Batch Studies degradation of 6-ring aromatic indeno(123-cd)pyrene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in ideno(123- cd)pyrene may have been due to a number of factors including biodegradation,
volatilization and readsorption back on to the soils. There is an indication that
biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 23: Water Phase Batch Studies degradation of 5-ring aromatic dibenz(a,h)anthracene where: (a) blue triangle represent unamended contaminated soil samples and (b) red
squares represent amended contaminated soil samples. The rapid decrease in
dibenz(a,h)anthracene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. There is an indication that
biostimulation is effective in the first couple of days due to the lower concentrations of the biostimulated samples versus naturally attenuated samples.
Figure 24: Water Phase Batch Studies degradation of 5-ring aromatic benzo(g,h,i)perylene where: (a) blue triangle represent unamended contaminated soil samples and (b) red squares represent amended contaminated soil samples. The rapid decrease in
benzo(g,h,i)perylene may have been due to a number of factors including biodegradation, volatilization and readsorption back on to the soils. Both biostimulated samples and naturally attenuated samples appear to degrade at similar rates in this observation.
In general, PAH degradation in this study showed biostimulated studies reached below detectable levels before naturally attenuated studies, with a difference of approximately 2 mg/kg by the third day. Mair et al. (2013) had also recorded a 10% increase in biostimulation degradation as opposed to natural attenuation. Farahanai and Mirbagheri (2011) found after 4 weeks, biostimulation yielded better degradation than natural attenuation at 45.7% PAH removed versus 37.2% PAH removed. After three weeks, biostimulated and naturally attenuated batches in this study decreased to undetectable for all PAHs. Both biostimulated and natural attenuated batches showed rapid degradation in the first 3 days. It is well known that with bacterial degradation, sequentially, there is a lag phase, an exponential growth phase and a stationary phase followed by a death phase, where food reserves are depleted and conditions become unfavourable to bacteria, resulting in autolysis (Ghaly et al. 2013,
Ekundayo and Osunla 2013, Narasimhulu and Nanganuru 2010). An explanation as to why a lag phase was not shown in these samples is that these samples came to Western University already contaminated and the amount of time it was contaminated could have been the time when the lag phase occurred in these samples. Another explanation was that during the two months of being kept in the refrigerator, a lag phase could have also been occurring at this period of time as well, and once analysis began, the bacteria may have already been in the exponential growth phase. The rapid decrease within the initial few days may have been a combination of many factors such as volatilization, biostimulation, and re-adsorption of PAHs back on to soils.