# Microbial Bioremediation and Biodegradation of Petroleum Products--A Mini Review
## 4 Emerging Biodegradation Technologies
### Factors Influencing the Degradation of Petroleum Hydrocarbons  
Climatic factors can also have a substantial impact on the pace and extent of biodegradation (Figure 6). At spill sites, variables such as oxygen and nutrient accessibility can also be exploited to improve innate biodegradation (i.e., using bioremediation). Other variables, such as salinity, are usually uncontrollable. The large extent to which biodegradation can affect a given environment causes some difficulties in accurately predicting the success of bioremediation efforts [57; 64]. Another source of uncertainty is the lack of awareness of the impact of various environmental factors on the rate and degree of biodegradation. Bioremediation is viewed as a tool to speed up the process of natural biodegradation in a cost-effective and environmentally friendly manner. However, bioremediation takes time, and the concentration and composition of pollutants, temperature, soil pH, oxygen status, and salinity are strongly influenced by the bioremediation of petroleum-contaminated soils [81]. Plants and microbes cannot thrive in oil-rich soils. In this case, it was inoperable or had poor efficiency for bioremediation.  
\begin{table}
\begin{tabular}{c c c c} \hline \hline
**Bioremediation Technology** & \multicolumn{2}{c}{**Recent Applications**} & \multicolumn{2}{c}{**Results**} \\ \hline Biopiling & \(\bullet\) & Treatment of petroleum & \(\bullet\) & 69\% maximum degradation was observed for one of the tests. \\  & & contaminated soil via biopile system & \(\bullet\) & Overall reduction of 86\% TPH \\  & & for 80 days [72] & \(\bullet\) & removal was achieved, biopile system was used for 4 days for 21\% \\  & & Treatment of Kuwait petroleum & & removal of residual TPH after \\  & & contaminated soil via biowashing & & biowashing. \\  & & and biopiling system for 20 days & \(\bullet\) & 98\% removal efficiency of TPH was achieved using co-composing \\  & & & within 90–120 days [74] & \(\bullet\) & Between 50–79\% removal of TPH was observed. \\  & & & contaminated soils for 98 days [75] & \(\bullet\) & 99\% removal efficiency achieved after 2 months \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\  & & & & \\ \end{tabular}
\end{table}
Table 4: Recent application of some of the bioremediation techniques and the results achieved.  
Furthermore, some highly soluble petroleum derivatives have more significant cytotoxicity for bacterial biodegradation, while other compounds do not have significant inhibitory effects on bacterial growth [60]. Temperature plays a crucial role in bioremediation and influences biodegradation reactions. Temperature can indirectly affect biodegradation performance by affecting bacterial growth and metabolism, changing soil matrix, and the mode of appearance of pollutants. Petroleum and its derivatives can fill soil voids, reducing the amount of soil oxygen [14; 82]. The metabolism of aerobic microorganisms was partially disturbed under reduced or absent oxygen conditions, and the bioavailability and degradation efficiency of pollutants was reduced. Various essential enzymes are the main components of the biodegradation of petroleum hydrocarbons. To reduce the efficiency of biodegradation, changes in pH can affect the activities of the enzymes. On the other hand, changes in pH and high salinity inhibit microbial growth and metabolism. In addition, the lack of a technique to track the survival and activity of microorganisms in an acceptable environment can also limit the use of bioremediation.