Sixty per cent of the millions of barrels of oil consumed per day world over, reach stipulated destinations through the sea. In the event of an oil spill over water, a floating oil slick of about 1 mm thickness is initially formed on the surface. With time the slick thins out and spreads, aided by the wind, waves, currents and weather conditions. The lack of a fixed boundary and the constant motion of the surface make the task of treating spills over water with bioremediation far more challenging than treating those on land.
Despite great care, precautions and stringent norms, spills continue to occur. The need of the hour is effective ways in which to treat the spills. Methods used on land are different from those used over water. On water – a spill may be left to the sun, waves and weather action, ultimately resulting in the evaporation of the oil; containment and skimming techniques may be used; sorbents may be used to absorb the oil; in situ burning can be done for spills away from coastal settlements and dispersants can be used to chemically break down oils. It is to be understood here that all these methods have their own specific challenges and/or side effects.
An alternative to oil spill clean up is through the use of microbes. Biodegradation is a natural process whereby bacteria or other microorganisms act upon organic molecules to break them into simpler substances. When these microbes are added to contaminated environments, such as oil spill sites, they can accelerate the natural biodegradation process. Use of these naturally occurring microbes to clean up oil contaminated environments is termed as bioremediation.
The Energy and Resources Institute (TERI), after seven years of research has developed the Oilzapper which is a cocktail of five different oil degrading bacterial strains, mixed with a carrier material – powdered corn-cob. Oilzapper feeds on hydrocarbons present in the crude oil and the oil sludge generated by oil refineries, and converts them into harmless carbon dioxide and water. This indigenous product has been successfully used on land by Oil and Natural Gas Corporation (ONGC) at Kalol and Mehsana in Gujarat, India.
Although bioremediation methods have been used successfully in treating oil contaminations on land, they are still being tested for their effectiveness at sea. Potential bioremediation approaches for marine oil spills fall into three major categories.
Fertilization approach: Addition of nutrients like nitrogen, phosphorus, potassium etc., stimulate the growth of indigenous microorganisms. This is also called nutrient enrichment approach.
Seeding with naturally present microbes: The technique involves the introduction of special assemblages of oil degrading microorganisms to a spill site. Such microbes may or may not be accompanied by nutrients.
Seeding with GEMs: Introduction of genetically engineered microorganisms (GEMs) with special oil degrading properties. Although this approach has potential, it is currently not being considered for remediating oil spills.
Of all the above approaches, the fertilization approach has been tested most rigorously. Researchers view it as a promising method to treat oil spills. They have observed that in most marine environments the rate of biodegradation is usually limited by the amount of nutrients, and not the availability of the oil degrading microbes. Therefore, addition of nutrients in these systems can greatly enhance the rate of biodegradation. In areas where native organisms grow slowly or are unable to degrade any particular hydrocarbon compound, seeding approaches can be useful.
Bioremediation methods too have a sizeable number of limitations. Their effectiveness can be tested along the coastal areas, but not at open sea. Conducting and monitoring open sea experiments is extremely difficult as the winds, waves, and currents create a constantly changing environment. These conditions also make it difficult to keep the microbes or nutrients in contact with the spilled oil for a period long enough to stimulate degradation. Moreover, there are possibilities of side effects. As the microorganisms degrade the oil, they may accumulate heavy metals like cadmium and lead, and introduce them into the marine food chain. In this way, the metals may accumulate in larger organisms and can prove harmful and detrimental in the long run.
Application of bioremediation methods and whether they are to be used as a primary or secondary response tool will vary depending on the condition of oil spills. All response
approaches are designed to minimise the damage caused by a spill. Their effectiveness will depend on how efficiently and to what extent they can control the adverse impact of the spill incident. In India successful testing and application of products like Oilzapper on oil sludge of refineries gives hope that we may soon be successful with bioremediation of marine oil spills too.