(4) OIL AND GREASE ANALYSIS. Follow the
approved methods listed in ch. NR 219.
(4)
OIL AND GREASE
ANALYSIS. The following analytical method, based on Methods 503A and 503E,
Standard Methods, 15th Edition, shall be used to determine the oil and grease
concentration in wastewater samples from all subcategories in this chapter. The
following hydrocarbon oil and grease method screens out fatty material and the
more polar hydrocarbon interferences peculiar to wastewaters in this category.
The method measures total oil and grease based on the concentration of
hydrocarbons of petroleum origin.
(a)
Outline of method. This method uses a
partition-gravimetric procedure to determine petroleum-based hydrocarbon oil
and grease (O & G-E). Samples of the regulated wastewater discharge,
preserved according to ch. NR 219, are mixed with trichlorotrifluoroethane, a
solvent which extracts dissolved or emulsified oil and grease. Silica gel
absorbs the fatty acids and polar hydrocarbons from the extract, distillation
removes the solvent, and the resulting hydrocarbon residue is weighed to
determine the petroleum-based hydrocarbon oil and grease concentration of the
sample.
(b)
Apparatus. The following apparatus is required for the
oil and grease analysis:
1.
Separatory funnel, 1 liter, with TFE (Teflon or equivalent)
stopcock.
2.
Glass
stoppered flask, 125 ml.
3.
Distilling flask, 125 ml.
4.
Water bath.
5.
Filter paper, 11 cm. diameter,
Whatman No. 40 or equivalent.
6.
Glass funnel.
7.
Magnetic stirrer and Teflon coated
stir bar.
(c)
Reagents. The oil and grease analysis requires the
following reagents:1.
Hydrochloric acid, HCl, 1+1.
2.
Trichlorotrifluoroethane.
(1,1,2-trichloro-1,2,2-trifluoroethane), Freon or equivalent, boiling point
47"'C. The solvent should leave no measurable residue on evaporation; distill
if necessary. Do not use plastic tubing to transfer solvent between
containers.
3.
Sodium
sulfate, Na2SO4, anhydrous crystal.
4.
Silica gel, 60 to 200 mesh, Davidson
Grade 950 or equivalent. Dry at 110'C for 24 hours and store in a tightly
sealed container.
(d)
Procedure. To
determine petroleum-based hydrocarbon oil and grease, collect about one liter
of sample and mark sample level on bottle for later determination of sample
volume. Acidify to pH 2 or lower; generally, adding 5 ml HCl is sufficient.
Transfer to a separatory funnel. Carefully rinse sample bottle with 30 ml
trichlorotrifluoroethane and add solvent washings to separatory funnel. Shake
vigorously for 2 minutes; however, if formation of a stable emulsion is
suspected, shake gently for 5 to 10 minutes. Let layers separate. Drain solvent
layer through funnel containing solvent-moistened filter paper into a clean
glass stoppered flask. If a clear solvent layer cannot be obtained, add 1.0 g
Na2SO4 to the filter paper cone
and slowly drain emulsified solvent onto the crystals; add more Na2SO4 if
necessary. Extract sample in separatory funnel twice more with 30 ml solvent
each, but first rinse sample container with each solvent portion. Combine
filtered extracts in the glass stoppered flask and wash filter paper with an
additional 10 to 20 ml solvent. Add 3.0 g silica gel to solvent extract, add
stir bar, stopper flask, and stir on a magnetic stirrer for 5 minutes. Filter
solution through clean filter paper into tared distilling flask. Wash silica
gel and filter paper with 10 ml solvent and combine with filtrate in distilling
flask. Distill solvent from distilling flask in a water bath at 70° C.
Place flask on a water bath at 70"'C for 15 minutes and draw air through it
with an applied vacuum for the final one minute. Cool flask in desiccator for
30 minutes and weigh.
(e)
Calculation of O & G-E. If the organic solvent is
free of residue, the total gain in weight, E, of the tared distilling flask is
due to the amount (mg) of petroleum-based hydrocarbon oil and grease (O &
G-E) in the sample:
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image
(f)
Use of O & G-E. The O & G-E value shall be used
as the measure of compliance with the oil and grease limitations and standards
set forth in this chapter.
