Changes

Temperature is an important factor affecting hydrocarbon biodegradation rate. The optimum temperatures for hydrocarbon biodegradation are dependent on the environment of the hydrocarbons. For instance, Figure 1 shows that the highest biodegradation rate for soil environment will occur between 30-40 oC, for freshwater environment between 20-30 oC and for marine environment between 15-20 oC.<ref name="6Das" />

Temperature is an important factor affecting hydrocarbon biodegradation rate. The optimum temperatures for hydrocarbon biodegradation are dependent on the environment of the hydrocarbons. For instance, Figure 1 shows that the highest biodegradation rate for soil environment will occur between 30-40 oC, for freshwater environment between 20-30 oC and for marine environment between 15-20 oC.<ref name="6Das" />

[[File:GeoWikiWriteOff2021-Aljezen-Figure1.jpg|framed|center|Figure 1 summarizes the optimum biodegradation rates depending on the environment  and the needed temperature.<ref name="6Das" />]]

[[File:GeoWikiWriteOff2021-Aljezen-Figure1.jpg|framed|center|{{figure number|1}}summarizes the optimum biodegradation rates depending on the environment  and the needed temperature.<ref name="6Das" />]]

Besides temperature, nutrient supply is a very crucial element controlling hydrocarbon biodegradation process. The concentrations of these nutrients will vary depending on the environment. For example, nitrogen, phosphorus and potassium present in low levels in freshwater wetlands due to the high demand of these elements by the plants. On the other hand, the presence of surplus nutrients can negatively impact the hydrocarbon biodegradation process.

Besides temperature, nutrient supply is a very crucial element controlling hydrocarbon biodegradation process. The concentrations of these nutrients will vary depending on the environment. For example, nitrogen, phosphorus and potassium present in low levels in freshwater wetlands due to the high demand of these elements by the plants. On the other hand, the presence of surplus nutrients can negatively impact the hydrocarbon biodegradation process.

There are two main pathways for hydrocarbon biodegradation. The first occurs in the presence of oxygen (aerobic). The second process can occur in the absence of oxygen (anaerobic) The aerobic mechanism is highlighted in figure 2.

There are two main pathways for hydrocarbon biodegradation. The first occurs in the presence of oxygen (aerobic). The second process can occur in the absence of oxygen (anaerobic) The aerobic mechanism is highlighted in figure 2.

[[File:GeoWikiWriteOff2021-Aljezen-Figure2.jpg|thumbnail|Figure 2 shows the mechanism to biodegrade hydrocarbons with the presence of oxygen. (Nilanjana Das, 2011)]]

[[File:GeoWikiWriteOff2021-Aljezen-Figure2.jpg|framed|center|{{figure number|2}} shows the mechanism to biodegrade hydrocarbons with the presence of oxygen.<ref name="6Das" />]]

The normal alkane (C1-C8 n-alkane) in figure 2 will react with oxygen with the help of monooxygenase enzyme produced by living organisms (e.g. bacteria), and converts the normal alkane to an alcohol and oxidize iron from Fe2+ to Fe3+. Under aerobic conditions, simple aromatics such as benzene, xylene and toluene can be degraded.  Typically, this requires 3mg/L of dissolved oxygen to degrade 1 mg/L of these aromatics (i.e. 3:1 ratio).  If the dissolved oxygen content is lower than 3:1 then the biodegradation rate is slower.

The normal alkane (C₁-C₈ ''n''-alkane) in figure 2 will react with oxygen with the help of monooxygenase enzyme produced by living organisms (e.g. bacteria), and converts the normal alkane to an alcohol and oxidize iron from Fe2+ to Fe3+. Under aerobic conditions, simple aromatics such as benzene, xylene and toluene can be degraded.  Typically, this requires 3mg/L of dissolved oxygen to degrade 1 mg/L of these aromatics (i.e. 3:1 ratio).  If the dissolved oxygen content is lower than 3:1 then the biodegradation rate is slower.

Compared to aerobic degradation, anaerobic degradation is considered to proceed much slower This is because anaerobic pathways require more energy, i.e. they are energetically unfavorable. There are three different pathways that anaerobic microbes can utilize to biodegrade hydrocarbons. All three pathways require inserting an oxidizing group into the molecule, which makes it more active and thus easier to transform to microbial-consumable products such as fatty acids. The first pathway is called fumarate addition and this pathway is used by bacteria to activate C3 to C20 alkanes and alkyl-substituted aromatics such as xylene and toluene. The mechanism proceeds via addition to the double bond by terminal or pre-terminal alkyl group from the alkanes or alkyl-substituted aromatics then followed by the removal of a carbon dioxide molecule (fig.3) [7][8].  

Compared to aerobic degradation, anaerobic degradation is considered to proceed much slower This is because anaerobic pathways require more energy, i.e. they are energetically unfavorable. There are three different pathways that anaerobic microbes can utilize to biodegrade hydrocarbons. All three pathways require inserting an oxidizing group into the molecule, which makes it more active and thus easier to transform to microbial-consumable products such as fatty acids. The first pathway is called fumarate addition and this pathway is used by bacteria to activate C3 to C20 alkanes and alkyl-substituted aromatics such as xylene and toluene. The mechanism proceeds via addition to the double bond by terminal or pre-terminal alkyl group from the alkanes or alkyl-substituted aromatics then followed by the removal of a carbon dioxide molecule (fig.3) [7][8].