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| Membrane separation is one way of treating metal removal
fluids for disposal. Click to find out about other disposal
options. |
What is membrane separation?
| In membrane separation, spent metal removal fluids are pumped from a process tank at a
moderate pressure (typically 30 to 50 PSIG) and rapid flow to a series of membranes. This
flow is typically between 750 to 1,100 gallons per square foot of membrane per day and is
referred to as the feed rate. Large molecules and virtually all
petroleum products are blocked at the membrane surface. The compounds that do not
pass through the membrane are referred to as the reject. |
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| The water-like solutions that pass through the membrane are referred to as the
"permeate". The rate at which the permeate flows through the membrane is called
the flux rate. Click for more information about the flux rate--how it is measured and when it becomes
unacceptably low. |
What about the membranes?
Membranes come in two basic sizes:
- microfiltration, rated at 0.1 to 1.0 micron
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2. ultrafiltration, rated from 0.001 to 0.1
micron, the most typical membrane size rate at
0.005 micron. |
Membranes can be configured in various ways and have varying life spans:
 | round tubes with approximately 0.5" or 1" internal diameter, which can last
from 3 to 8 years |
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| hollow fibers with an approximate internal diameter of 0.030", which can last from
1 to 2 years |
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| flat sheets wrapped in a spiral configuration, lasting from 3 to 8 years |
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| flat sheets that are vibrated or turbulated with mechanical "wipers," lasting
from 3 to 8 years |
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Operating cost, including membrane depreciation over time, is between 0.5
and 1.0 cents per gallon.
Some companies are now using ultrafilter membranes followed by nanoporous filter (NF)
membranes or reverse osmosis
(RO) membranes. These membranes are more sensitive to fouling than ultrafilter membranes,
even though the NF membranes or the RO membranes only see the permeate from the
ultrafilter. The treated water after two stage UF/NF or UF/RO can be suitable for re-use
in other industrial process water requirements such as non-critical parts washing and
rinsing. |
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| An influent storage tank, a processing tank, and an oil-hauling tank are
necessary. The processing tank should be equal to one-half of the daily average flow.
Truck spill containment may be required for the oil hauling tank pump-outs by a contract
service. |
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| See details of the characteristics of pollutants after
ultrafiltration separation. |
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What are
the advantages and disadvantages of membrane separation?
Advantages:
| Membrane separation consistently separates a wide variety of emulsion, surfactant, and
chelating chemistries and various mixtures. |
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| It requires no specific chemical knowledge. |
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| Complex instrumentation is not required. |
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| The method does not require constant attention. |
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| The basic concept is simple to understand. |
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Disadvantages:
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| Certain solvents can quickly and permanently destroy the membrane. |
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| Certain colloidal solids, especially graphite and residues from vibratory deburring
operations, can permanently foul the membrane surface. |
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| The energy cost is higher than chemical treatment, although less than evaporation. |
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| Oil emulsions are not "chemically separated," so secondary oil recovery can be
difficult. |
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| Synthetics are not effectively treated by this method. |
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Contact Chris Roman, 