Page 40 - March 2020 - WT Site

evaporate. The results are the weight of the oil residue remaining solvent. For highest accuracy, UV Fluorescence analyzers should
after evaporation. This method has a minimum reporting limit be calibrated to the target oil in the process. However, when used
of 5 ppm. Because of the evaporation step light hydrocarbons with a generic calibration, the results can indicate the removal
are under reports by this method. This analytical method cannot efficiency of a treatment system by comparing samples before
be used for light hydrocarbon processes or processes that aim and after treatment.
to achieve low concentrations. The figure included shows how
the EPA method does not have any response to changing
concentrations of a process, while an InfraRed technology does.

The procedures for preparing a water sample for analysis can be
manipulated to best demonstrate the performance of a water
treatment system. For instance, if a treatment system is designed
to remove 99% of the oil and solid droplets that are 10 microns
and larger, the sample can be prepared to differentiate particles
larger than 10 microns. The method might first test a sample of
water using a solvent and acid, then test another sample which
is first passed through a 10 micro filter, and then the acid and UV Fluorescence can operate with different light wavelengths.
solvent used to prepare the sample. When the results of the When analysis of light hydrocarbons or low concentrations is
second test are subtracted from the first, the results will be the needed, a deep UV light source, with a short wavelength should
concentration of oil that was in droplets greater than 10 microns. be chosen. Most crude oils and light gas condensates can be
measured below 1 ppm. However, when a heavy oil is to be
InfraRed analytical methods are often used for water analysis. measured and toluene is to be used as the extraction solvent, a
The solvent used must be considered for the extraction efficiency, light source with a longer wavelength should be chosen. Toluene
operating cost and solvent disposal. If the extraction solvent can be measured by short wavelength light sources, but is optically
is a hydrocarbon, it must be evaporated before analysis of the clear to longer wavelengths and therefore not measured.
remaining oil film can be performed. Similar to the EPA 1664A
method, the IR analysis of light hydrocarbons will not have much
resolution at low concentrations. Non-hydrocarbon solvents can
be used without evaporation, allowing for better sensitivity to
light hydrocarbons. For these solvents the analysis is made in the
solvent for a quick result.

Conclusions
UV Fluorescence is also common for water sample analysis. All
common solvents (hydrocarbons and nonhydrocarbons) can be Advances in water treatment technologies are allowing discharge
used with UV Fluorescence. For instance, when analyzing heavy, water quality to improve significantly. With these advances, the
high asphaltenic crude oils, toluene can be used as an extraction water can be re-used or recycled in ways not previously available.

42 Water Today - The Magazine March 2020