## 3 Results
### Diesel Oil Removal Efficiency  
All microcosms were set up with an initial diesel oil concentration equal to 70 g\(\cdot\)kg\({}^{-1}\) of soil, and the pollutant concentration was monitored along the test.  
In Figure 5, the percentage of removed contaminant is reported for microcosms with C/N = 60 and 300 after 35 days. Each value is the average derived from twice-replicated analyses on two extracts.  
The findings showed that a limited amount of pollutant was removed, in both C/N ratios, independently of the water content.  
Figures 6 and 7 report the monitoring of removed diesel oil by microcosms with C/N = 120 and C/N = 180, respectively. For these results, each value is the average derived from twice-replicated analyses of two extracts.  
As previously mentioned, the pollutant removal efficiency was calculated considering (a) C\({}_{0}\) = 70 g\(\cdot\)kg\({}^{-1}\) of soil and (b) C\({}_{0}\) measured by analysis.  
In these tests, the diesel oil removal was evident from the start, even if appreciable results could be found after about two months.  
The data showed that in the first month, the removal was influenced by the water content. Moreover, in the first 7 days for both C/N ratios, the water content that gave the highest removal result maintained this position for the entire test duration:  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Microcosm No.** & **u\% (By Weight)** & **C/N Ratio** &
\begin{tabular}{c} **Cumulative Fluorescein Production** \\ **(mg\(\cdot\)kg\({}^{-1}\) of Soil)** \\ \end{tabular} \\ \hline
1 & 8 & 60 & 3 \\ \hline
2 & 8 & 120 & 3 \\ \hline
3 & 8 & 180 & 10 \\ \hline
4 & 8 & 300 & 6 \\ \hline
5 & 12 & 60 & 1 \\ \hline
6 & 12 & 120 & 7 \\ \hline
7 & 12 & 180 & 12 \\ \hline
8 & 12 & 300 & 3 \\ \hline
9 & 15 & 60 & 1 \\ \hline
10 & 15 & 120 & 11 \\ \hline
11 & 15 & 180 & 5 \\ \hline
12 & 15 & 300 & 5 \\ \hline \hline \end{tabular}
\end{table}
Table 4: Cumulative fluorescein production in 30 days.  
* after 7 days, the microcosm with u% = 8% b.w. and C/N = 120 had the highest percentage of removed diesel oil and this trend continued throughout the test;
* for microcosms with C/N = 180, the highest removal was always achieved with u% = 12% b.w.  
These data proved that the biostimulation process is efficient when right conditions are adopted.  
Figure 5: Diesel oil removal efficiency (C/N = 60 and C/N = 300, t = 35 days).  
Figure 6: Diesel oil removal efficiency with C/N = 120: (a) C\({}_{0}\) = 70 g\(\cdot\)kg\({}^{-1}\) of soil; (b) C\({}_{0}\) was measured.  
Figure 7: Diesel oil removal efficiency with C/N = 180: (a) C\({}_{0}\) = 70 g\(\cdot\)kg\({}^{-1}\) of soil; (b) C\({}_{0}\) was measured.  
The effect of water content was evident in the first days, whereas in the last run period, the percentage of removed diesel oil was similar for all microcosms with the same C/N ratio.  
In general, the data trends showed that:  
* for both C/N ratios, after t = 70-75 days, the removal efficiency grew slowly: this is a feature to be considered for real-scale applications, in order to reach a compromise between long remediation times and achieved removal;
* for C/N = 180, the removal efficiency was always lower than for C/N = 120.