Hydrocarbons: Bioremediation Strategies

Bioremediation strategies for hydrocarbons depend on their locations in the environment: Hydrocarbon vapors in the air can be filtered using biofilters that utilize organisms indigenous to the filter material or provided by a soil or commercial inoculum (vector for introducing specific species of bacterium). See Halogenated Organic Solvents for more on filters.

In the ocean chemical dispersants can be used to stimulate biodegradation by increasing the surface area of the oil available for microbial attachment, and perhaps providing nutrients to stimulate microbial growth.

Oil can penetrate surface gravel on shorelines, creating a situation that is easily remedied by aerobic bacteria (the gravel is highly permeable and therefore conducive to oxygen availability). Because nitrogen and phosphorous are the limiting nutrients in this type of environment, strategies focus on the addition of nutrients for a significant length of time. See Halogenated Organic Solvents and Halogenated Organic Compounds for more on nutrients.

In areas that lack oxygen, aeration is likely to be most effective (ie: marshes and mangroves). See Halogenated Organic Solvents and Nitrogens for more on aeration.

“Pump and treat” refers to a groundwater purification technique that involves bringing contaminated water to the surface, removing free product by flotation, and re-injecting the cleaned water into the aquifer. As in other environments, adding oxygen and nutrients can stimulate the degradation of residual hydrocarbons that are not extracted by pumping. “Bioslurping” involves pumping the liquid contaminant phase out, while drawing in air to stimulate aerobic degradation. Fertilizer nutrients are frequently added at the air injection wells.See Halogenated Organic Solvents and Halogenated Organic Compounds for more on nutrients.

In any contaminated site, biodegradation can be enhanced through the addition of oxidizing molecules such as oxygen, nitrate, ferric iron, sulfate, and CO2.

In contaminated soil, oxygen is a likely limiting nutrient, and soil tilling is widely practiced. “Bioventing” can also be a successful remedy, wherein air is injected through some wells, and extracted through others to both strip volatiles and provide oxygen to indigenous organisms. Plants can also be used to help deliver air to soil microbes. Some other methods include; biopiles, composting, and slurry bioreactors (for more information see Halogenated Organic Solvents).

SOURCES: Prince

Specific Techniques:

Composting - Contaminated soil is mixed with decaying organic material that is rich in nutrients, aiding in the microbial degradation of hydrocarbons.

Surfactants - Substances having both hydrophobic and hydrophillic properties surround hydrocarbons, pulling them away from sediment particles and increasing the bioavailability of the hydrocarbons.

Fungi - Certain species of fungi produce enzymes that are capable of breaking down polycyclic aromatic hydrocarbons (PAHs).

Plants - Certain plants can consume hydrocarbons, converting the carbon into plant material and releasing water and harmless gases. Some of the time, the roots of the plant are in a symbiotic relationship with bacteria in the soil, thereby creating a more efficient bioremediation process. Fertilizers can be added to increase the amount of plant matter and speed up the degradation of the hydrocarbons.

Fertilizers - Often times the biodegradation of hydrocarbons is hindered by a lack of oxygen. In this case, nitrogen, sulfur and ferric oxide can be added as alternate electron acceptors to aid in the oxidation-reduction reaction.

The above methods have been successfully combined for increased efficiency in hydrocarbon degradation.