Dr. Dmitri Kopeliovich
Biodegradation is a process of chemical breakdown or transformation of a substance caused by micro-organisms (bacteria, fungi) or their enzymes.
There are two extents of biodegradation of a substance:
Biodegradability is the ability of a substance (oil) to biodegradation measured in a standard test procedure.
In the test a sample of the oil is incubated at 77°F (25°C) for 28 days. The biodegradation of the oil is induced by an inoculum of a mixed population of micro-organisms.
As an inoculum the test may use bacteria from sewage-sludge from a domestic sewage-treatment plant, from natural water, soil bacteria or their combination.
Common oil biodegradability tests are performed in the presence of Oxygen and water (aerobic aquatic biodegradation).
Primary biodegradation is measured by using infrared spectrometer.
Ultimate biodegradation is determined according to the evolution of carbon dioxide (CO2) from the tested sample over that produced in a blank, which contains inoculum only.
Standard bidegradability tests:
The method is used for testing non-volatile oils, which are not inhibitory to the inoculum micro-organisms.
The method is applicable for determination of primary biodegradability. It is widely used for testing Engine oils.
The method determines only ultimate biodegradability by measuring evolving carbon dioxide.
The method is used when the oxygen concentration in the test oil is not the limiting factor for degradation.
The tests determine the rate of the biodegradation:
|White oil (highly refined mineral oil)||25-45|
|Phthalate & Trimellitate Esters||5-80|
|Polyol esters & Diesters||55-100|