## 3 Results
### Experimental Results
#### 3.1.2 Biodegradation  
A batch culture demonstrating biodegradation of WTCO under four test conditions is presented in Figure 9. In this series of experiments, the first three conditions included WTCO and the confidential dispersant as the oil/dispersant phase, along with the Oppenheimer formula as the petroleum-degrading microbial culture. The fourth condition included WTCO and the Oppenheimer formula, but no dispersant was included with the oil phase. Conditions 1 and 2 included mixing with the paddle impeller at 300 and 600 rpm during the up-front oil dispersion step, prior to commencement of the biodegradation culturing, while conditions 3 and 4 had no oil dispersing step at the beginning. The test condition that resulted in the greatest extent of biodegradation was the fourth condition, which did not include any dispersant formulation. This result suggests that perhaps this particular dispersant has a moderate negative effect upon hydrocarbon biodegradation activity. Nearly complete biodegradation of the dispersed oil was observed in this condition, while for the other three conditions, roughly 50 to 80% removal of the dispersed oil by biodegradation was accomplished.  
Figure 8: Dispersant effectiveness results plotted on a graph of energy dissipation of mixing versus power at the laboratory and pilot scales.  
The next two series of biodegradation experiments provided results very similar in nature to those shown in Figure 8. Thus, the results are shown only in table format in Tables 2 and 3 below. In Table 2, the test conditions that were varied were the dispersant and the oil to dispersant ratio, as indicated in the first two columns of the table. All four conditions gave similar results for the extent of biodegradation (76% to 85% hydrocarbon removal) after culturing for a 21-day duration, with those using the Petroclean as dispersant indicating slightly greater biodegradation extent. These results are quite similar to the 21-day results for conditions 3 and 4 depicted in Figure 8. In this set of experiments, two controls with no bacterial culture added resulted in constant dispersed hydrocarbon levels throughout the entire 21-day period (data not shown).  
In Table 3, the only test condition that was varied was the orbital shaking speed (55 to 200 rpm) used to disperse the oil for 20 min at the beginning of this biodegradation test. The orbital shaking speed used during the culturing step was 150 rpm for all conditions, while the other constants were the use of Petroclean as the dispersant, and the use of the Oppenheimer formula as the added bacterial culture. The results presented indicate a steady rise in the extent of WTCO biodegraded in step with the shaking rpm, with a large difference between the first two conditions of 50 and 100 rpm. In this set of experiments, two controls with no bacterial culture added resulted in constant dispersed hydrocarbon levels throughout the entire 21-day period.  
\begin{table}
\begin{tabular}{c c c} \hline
**Dispersant** & **Oil/Dispersant Ratio** & **\% Oil Biodegraded at 21 Days** \\ \hline Petroclean & 10:1 & 85.4 \\ Petroclean & 10:2 & 82.8 \\ FFT 7\% & 10:1 & 78.6 \\ FFT 7\% & 10:2 & 76.3 \\ \hline \end{tabular}
\end{table}
Table 2: Biodegradation extent for 250 mL shake flask cultures.  
Figure 9: Dispersant effectiveness in the 250-mL Erlenmeyer flask at four different orbital shaking speeds. Condition 1: WTCO, confidential dispersant, and Oppenheimer formula, mixing at 300 rpm during oil dispersion; Condition 2: WTCO, confidential dispersant, and Oppenheimer formula, mixing at 600 rpm during oil dispersion; Condition 3: WTCO, confidential dispersant, and Oppenheimer formula, no mixing in oil dispersion step; Condition 4: WTCO and confidential dispersant only, no mixing in oil dispersion step. All biodegradation tests were conducted at room temperature (nominally 25 \({}^{\circ}\)C).