K2O Consulting is here to answer any of your industrial
wastewater treatment related questions. The follow is a
list of commonly asked questions and answers. If you
question is not listed below, feel free to
contact us with your question for a prompt answer!
Oil/Water Separation FAQ's
Q) What is the difference between
"free oil" and "dissolved oil"?
A) Free oil is oil that will settle to the top of
water given a reasonable amount of time. Free oil is in
droplet form and coalesces with other oil droplets upon
contact with each other. This coalescing enhances the
oil separation process based on Stokes Law. Dissolved
oil is not in droplet form and will not rise to the top
of water regardless of the amount of time that it is
immersed with the water. Dissolved oil stays in solution
with the water indefinitely.
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Q) What factors are important in sizing an oil/water separator?
A) Temperature of the
water, viscosity of the water, specific gravity of the
oil in the water, knowledge of the oil droplet size
amount of suspended solids present. All of these
parameters must be considered when selecting the size
and type of oil/water separation equipment to be used.
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Q) Why is it important to know the difference between free oil and dissolved oil present in a waste stream?
A) It is very important to
know if there is dissolved oil in a waste stream. That
is because dissolved oil will pass through a media type
filter or oil/water separator such as dissolved air
flotation, dissolved gas flotation, API separator or
lamella type oil/water separator. Dissolved oil must be
chemically treated to break any emulsion prior to being
treated with the equipment described above. Otherwise, a
different technology must be used.
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Reverse Osmosis FAQ's
Q) How do I know if pretreatment will be required in front of a reverse osmosis (RO) system being used for boiler feed water?
A) A common oversight in
designing reverse osmosis systems is the Silt Density
Index of the water to be fed to the RO system. RO
membranes have a fine porosity and are susceptible to
fine particles called silt which may not be apparently
visible. This is a relatively simple and short test that
can prevent frequent RO membrane cleanings and even
membrane fouling. It is especially important to test
river water and is also recommended to test city water
intended to be used for boiler feed water. Once the silt
density index is known, an experienced water treatment
company or consultant can recommend the type of
pretreatment that will be required.
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Q) Why is it important to have a complete and balanced water analysis prior to sizing a reverse osmosis (RO) system?
A) A complete and balanced
water analysis should always be done prior to sizing an
RO system. The anions and cations should add up to zero.
With this balanced water analysis, a computer model can
be run which will determine the number and array of RO
membranes required. It will also determine the rejection
rate of the RO membranes which is important in
determining if the RO system will provide the desired
water quality.
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Q) What are two proven methods of removing nitrates from water?
A) Ion exchange and reverse
osmosis (RO) have been proven to effectively remove
nitrates from water down to safe drinking levels. Ion
exchange is selective so, only the nitrates are removed
while other ions pass through the system. Removal
efficiencies of 95-99% are possible with ion exchange.
Reverse osmosis will also provide similar removal
efficiencies but will remove other ions in the water
along with the nitrates.
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Media Filtration FAQ's
Q) For media filtration, why is it important to have a particle size distribution of the suspended solids?
A) Different types of media
filters produce different porosity or interstices sizes.
Media filters work best when the particle size
distribution is “normal”. That means there are particles
of various sizes in various concentrations. In this way,
the particles themselves can enhance removal and
increase the efficiency of the media filter. If the
particle size distribution shows that many of the
particles are fine and make up most of the
concentration, a media filter may not effectively remove
those particles.
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Q) Why is walnut shell filtration effective for free oil removal?
A) Black walnut shells have
been known to have an affinity for oil for a long time.
Pulverized walnut shells are used in the cosmetic
industry to take oil off skin. Walnut shell media is
adsorbent to oil, meaning that the free oil will adhere
to the surface of the media but not be absorbed into the
media. This allows for cleaning and regeneration of the
media. Walnut shell media has the proper hardness and
modulus of elasticity which enable it to have an
attrition rate of only 7% per year.
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Biological FAQ's
Q) How do I know if simple flotation type separators will reduce Biochemical Oxygen Demand (BOD) and Chemical Oxygen Demand (COD) down to acceptable discharge limits?
A) Biochemical Oxygen
Demand (BOD) and Chemical Oxygen Demand (COD) can be in
two states in water. They can be dissolved in the water
or they can be residual with organics. Obtaining an
analysis for total BOD and COD will not be enough to
determine if a flotation separator will remove enough of
the BOD and COD to meet discharge limits. An analysis
for free and dissolved BOD and COD must be done in order
to determine if flotation separation is sufficient or,
if further biological treatment will be required.
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River Water Filtration FAQ's
Q) Can a micro filter be used in place of a clarifier for river water filtration?
A) Yes, a micro filter can
be used in place of a conventional clarifier. This is a
growing trend because of the space savings and lower
operational costs. Note that turbidity of the river
water should be measured in NTU’s (Nephelometric
Turbidity Units) prior to sizing the micro filters.
Measuring the turbidity will help in determining the
rejection rate of the micro filter and hence, provide an
accurate permeate flow rate.
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