# Bioaugmentation Treatment of a PAH-Polluted Soil in a Slurry Bioreactor
## 3 Results and Discussion
### Chemical Analysis
Our bioslurry approach, together with bioaugmentation processes using well-known PAH-degraders capable of producing biosurfactants such as _P. stutzeri_[50; 51] and _R. erythropolis_[52; 53], overcame these difficulties. On the whole, the three experiments showed similar results after 15 days, although Treatment A (only autochthonous microorganisms) showed a slightly inferior performance. Nevertheless, Treatment C (addition of _Pseudomonas_ strain) achieved a greater degradation of all fractions of the PAHs at three days, thereby suggesting a much better adaptation and/or synergies with the autochthonous microbial populations. Given this result, we propose that the _Pseudomonas_ strain would be useful to accelerate the degradation process in a real-scale treatment in larger bioreactors. Regarding the qualitative evolution of the contaminants, there was a remarkable reduction in the abundance and variety of the initial pool of contaminants after 15 days of treatment (Figures 4 and 5; for more details about the variety of contaminants present on this site, see [40]). This reduction affected mainly lighter PAHs and specially alkyl-PAHs (see peaks 6, 8, 17, and 21 in Figure 4). However, there was also an evident decrease in the unresolved complex mixture (UCM), heavy PAHs, and heterocyclic compounds. Conversely, a recalcitrant compound different to PAHs (Bis(2-ethylhexyl)phthalate (DEHP), peak 24 in Figure 4 and labelled in Figure 5) was not affected. In addition, although present at much lower contents than PAHs, n-alkanes were notably degraded (Figure 4). This finding indicates the wide metabolic abilities of the soil microorganisms, which attacked both aromatic and aliphatic compounds. Of note, although the lighter n-alkanes were relatively much more degraded than the heavier ones, the latter were also clearly biodegraded, as occurred with the aromatic fraction (Figure 4). The relative depletion of n-C\({}_{17}\) and n-C\({}_{18}\), when compared with isoprenoids such as phytane and prismate, indicates a preferential degradation of linear alkanes, as observed in other studies [41; 54]. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c c c} \hline \hline  & \multirow{2}{*}{**Initial**} & \multicolumn{4}{c}{**1 day**} & \multicolumn{4}{c}{**3 days**} & \multicolumn{4}{c}{**7 days**} & \multicolumn{4}{c}{**15 days**} & \multicolumn{4}{c}{**\% Reduction after 15 days**} \\ \cline{2-13}  & & \(A\) & \(B\) & \(C\) & \(A\) & \(B\) & \(C\) & \(A\) & \(B\) & \(C\) & \(A\) & \(B\) & \(C\) & \(A\) & \(B\) & \(C\) \\ \hline
**two-ring PAHs** & 145.7 & 104.1 & 72.2 & 80.2 & 76.1 & 67.9 & 23.0 & 26.7 & 37.5 & 12.6 & 25.1 & 15.6 & 20.7 & 82.8 & 89.3 & 85.8 \\ \hline
**three-ring PAHs** & 108.3 & 70.0 & 71.5 & 70.0 & 53.9 & 49.0 & 17.1 & 25.5 & 37.3 & 12.0 & 26.8 & 22.0 & 15.7 & 75.3 & 79.7 & 85.5 \\ \hline
**four- to** & & & & & & & & & & & & & & & & & \\
**six-ring PAHs** & 78.0 & 57.6 & 58.8 & 61.9 & 51.0 & 51.2 & 24.8 & 22.2 & 31.8 & 16.3 & 21.9 & 21.8 & 19.0 & 72.0 & 72.0 & 75.6 \\ \hline
**Total PAHs** & 332.2 & 231.7 & 202.5 & 212.2 & 180.9 & 168.1 & 64.9 & 74.4 & 106.5 & 40.9 & 73.7 & 59.4 & 55.5 & 77.8 & 82.1 & 83.3 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Evolution of PAH content (mg/kg) in the six pilot-scale parcels. The relative standard deviations (RSD) for PAHs were in a range, from a minimum of 1% for Benzo[a]anthracene to a maximum of 9% for Naphthalene.