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preparation of the inoculum. The inoculum is prepared from micro-organisms coming from at least 10 sites mainly in areas were a variety of chemicals are used and discharged. Aerated inoculum is maintained using glucose, peptone and potassium orthophosphate. The inoculum can not be used before one month from its preparation and latest 4 months after its preparation so a new inoculum has to be prepared every 3 months.
This test method do not authorize the use of solvents or emulsifiers for poorly water-soluble test substance. A dead gas space must be kept at a minimum.
The appropriate Theoritical oxygen demand has to be calculated with or without nitrification.
The result using the Chemical oxygen demand instead of ThOD is optional.
The OECD 301D guideline which is the close bottle test is based on dissolved oxygen depletion. The main restriction in this test is the limited amount of test substance which has to be used; indeed, the dissolved oxygen must be in excess and taken into account a concentration of 8-9 mg of dissolved oxygen per liter of test medium at test temperature and the volume of the flask (about 300ml), only 2 to 5 mg of test substance per liter can be used.
Precautions have also to be taken for volatile substance.
Preferably the Theoritical oxygen demand should be known. If not and if the the Chemical oxygen demand is used, you must be sure that the oxidation of the test substance is complete otherwise, it will lead to false biodegradability test results.
The test OECD 301F based on oxygen consumption must be carried out in a real respirometer in which the oxygen is produced electronitically ; this test is carried out at a concentration around 100 mg of test substance per liter preventing the use of BOD flasks. Precautions has to be taken for volatile substance.
As for tests OECD 301 C and OECD 301D, the theoritical oxygen demand should be known for biodegradation calculation but chemical oxygen demand can be used if it has been proven that the oxidation is complete ; if not, the result can be false.
3. Biodegradability on a poorly water-soluble organic compounds
Poorly water-soluble organic compounds are classified as difficult test substances and require appropriate preparation and introduction methods to achieve satisfactory and reliable test results. The ISO 10634 is a guidance for the preparation and treatment of poorly water-soluble organic compounds for the subsequent evaluation of their ultimate biodegradability in an aqueous medium.
Moreover the restrictions on the applicability and selection of the test methods dedicated to biolubricants. some precautions have to be taken.
It is a real competence and experience to conduct this test on water poorly soluble substances.
Various introduction methods exist: •
• • • •
LINK
www.bfblab.com
Direct addition after homogeneization Ultrasonic dispersion
The use of emulsifier or solvents Adsorption on inert support Dispersions
Rue Phocas Lejeune, 10 B-5032 Les Isnes BELGIUM
For more information contact: Mr. Vincent Bouillon Sales Manager
vincent.bouillon@
bfblab.com
Advantages and disadvantages from these various techniques depend on the physical and chemical properties of the substances to be tested. However, there remains many traps which must be avoided:
• Avoid reducing the Bio-availability of the organic compound.
• Avoid the organic compound has a harmful physical effect on micro-organisms.
• Avoid the adsorption of the test substance on the walls of the test vessel.
• Avoid an inoculum from an industrial sewage treatment plant or a pre-adapted inoculum.
• Avoid abiotic degradation such as hydrolysis, photolysis and abiotic oxidation.
• Avoid changing the chemical structure of the test substance.
•
Maintain the test substance homogeneously in the test medium.
• Avoid interferences and contamination with any product (emulsifier, solvent) or material (support) used for the introduction of the poorly water-soluble organic compound.
One of the best way for the implementation of ultimate biodegradability tests on poorly water-soluble organic compounds, is an introduction technique which increase the bio-availability of the test substance and which avoids the mentioned above traps; the poorly water soluble test substance is introduced through the adsorption on a inert support.
4. Conclusion
Based on the applicability of the ultimate biodegradability test methods, the description of some techniques for introducing the poorly-soluble organic test compounds included direct addition, ultrasonic dispersion, adsorption on an inert support and dispersions or emulsions, the use of the theoritical oxygen demand (ThOC) which suppose to know the formula of the test substance and its purity, or relative proportions of major components, the restrictions for using the chemical oxygen demand in the biodegradation calculation, the difficulties to use a inoculum derived from a mixture of sources will result that the most appropriate test fo the ultimate biodegradability evaluation on poorly water soluble organic compounds is the OECD 301B based on CO2 production using the adsorption on inert support as introduction technique.
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LUBE MAGAZINE NO.126 APRIL 2015
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