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| Biological treatment of spent MRF is one method of
disposal. It is often used after membrane separation
of the fluid. You may want to find out about membrane separation before you read about
biological treatment. Click to read about other disposal
options. |
How does biological treatment work?
| Bacteria like those that contaminate metal removal fluids in the manufacturing
environment can also be used to treat metalworking fluids for disposal. |
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| Spent metal removal fluids are first stored in a reactor tank, and then air is added
via diffusers near the bottom of the tank in quantities great enough to create a
positive dissolved oxygen level, typically about 2.0 mg/L. The solution is kept warm,
about 90oF to 100oF, and bacteria are allowed to digest the various
chemical compounds. The bacteria are first selected by trials, and then added and re-bred
as necessary. Substantial digestion of the spent metal removal fluid can take weeks, but
treating just the permeate from an ultrafilter,
for example, can be accomplished in 72 hours. |
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| Also, after biological treatment, a membrane system, such as an ultrafilter, can be
used to filter the wastewater. The bacteria are rejected by the ultrafilter and then
returned back to the digestion tank for re-use. |
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| Several large, heated tanks are required to hold several days’, or possibly
weeks’, worth of storage. An air blower capable of maintaining 2.0 mg/L dissolved
oxygen is necessary. Access to a company that supplies bacteria engineered to various
industrial waste streams is also desirable. A spare quantity of bacteria is necessary to
keep on hand in order to rapidly recover from an accidental bacterial kill. |
What are the advantages
and disadvantages of biological treatment?
Advantages:
 | Some materials that are difficult to treat by ultrafiltration, such as fatty acids , can
be biologically treated. |
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| Some materials, such as amines, can be biologically treated, whereas they cannot be
treated by either chemical or ultrafiltration methods. |
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Disadvantages:
| Some chemical compounds do not readily degrade by biological treatment. |
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| Biocides used in the manufacturing environment greatly inhibit biological reactions. |
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| Digestion rates are slow, in general days or weeks, requiring large storage tanks. |
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| Changing from one metal removal fluid to another can greatly reduce or eliminate
effective treatment. |
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| Bacteria must be fed constantly, or they will die off. If they die off, re-acclimating
the bacteria to the waste stream may take several days. |
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Contact Chris Roman, 