These products are designed to encourage or speed up the biodegradation of oil, and are used onshore to help restore polluted sites or to treat polluted waste.
Biodegradation of oil refers to the transformation of carbonated chains by the action of micro-organisms. Over time, the hydrocarbons can be broken down into lighter compounds to the point of complete conversion, i.e. into carbonic gas and water. This is known as mineralisation, which is the ideal purification process, as all the organic carbon is transformed into mineral carbon. However part of the carbon is used by the micro-organisms to mulitply and form biomass, which also requires nitrogen and phosphorus. To give an indication, complete biodegradation of 1 kg of oil consumes 2.6 kg of oxygen and 70 g of nitrogen to produce 1.6 kg of carbonic gas, 1 kg of water and 1 kg of biomass.
The purifying capacity of micro-organisms is limited by a number of factors, as outlined below.
The nature of the hydrocarbons:
Linear paraffins and light aromatics are easily broken down, however branched hydrocarbons, heavy poly aromatics, resins and asphaltenes are much more difficult to break down.
The availability of nutrients:
Complete degradation of 1 kg of hydrocarbon consumes the oxygen dissolved in 300 m³ of water and the nitrogen from nitrates contained in 1000 m³ of water, with reference to the average concentration of seawater.
Biodegradation of oil is therefore a slow process, taking several weeks to several months or even years in the least favourable conditions (little oxygenated sediments), and often remains incomplete, in particular with heavy oil.
Treatment implemented to promote, accelerate or provoke the biodegradation of oil is also known as biorestoration.
are two main types of bioremediation techniques: