2530 FLOATABLES*
2530 A. Introduction
One important criterion for evaluating the possible effect of
waste disposal into surface waters is the amount of floatable
material in the waste. Two general types of floating matter are
found: particulate matter that includes “grease balls,” and liquid
components capable of spreading as a thin, highly visible film
over large areas. Floatable material in wastewaters is important
because it accumulates on the surface, is often highly visible, is
subject to wind-induced transport, may contain pathogenic bac-
teria and/or viruses associated with individual particles, and can
significantly concentrate metals and chlorinated hydrocarbons
such as pesticides and PCBs. Colloidally dispersed oil and grease
behave like other dispersed organic matter and are included in
the material measured by the COD, BOD, and TOC tests. The
floatable oil test indicates the readily separable fraction. The
results are useful in designing oil and grease separators, in
ascertaining the efficiency of operating separators, and in mon-
itoring raw and treated wastewater streams. Many cities and
districts have specified floatable oil and grease limits for waste-
water discharged to sewers.
2530 B. Particulate Floatables
1.
Discussion
a. Principle: This method depends on the gravity separation of
particles having densities less than that of the surrounding water.
Particles that collect on the surface and can be filtered out and dried
at 103 to 105°C are defined by this test as floatable particles.
b. Application: This method is applicable to raw wastewater,
treated primary and secondary effluent, and industrial wastewater.
Because of the limited sensitivity, it is not applicable to tertiary
effluents or receiving waters, whether freshwater or seawater.
c. Precautions: Even slight differences in sampling and han-
dling during and after collection can give large differences in the
measured amount of floatable material. Additionally, uniformity
of the TFE* coating of the separation funnel is critical to ob-
taining reliable results. For a reproducible analysis treat all
samples uniformly, preferably by mixing them in a standard
manner, before flotation and use consistently prepared separation
funnels as much as possible. Because the procedure relies on the
difference in specific gravity between the liquid and the floating
particles, temperature variations may affect the results. Conduct
the test at a constant temperature the same as that of the receiv-
ing water body, and report temperature with results.
d. Minimum detectable concentration: The minimum repro-
ducible detectable concentration is approximately 1 mg/L. Al-
though the minimum levels that can be measured are below 1
mg/L, the results are not meaningful within the current estab-
lished accuracy of the test.
2.
Apparatus
a. Floatables sampler with mixer: Use a metal container of at
least 5 L capacity equipped with a propeller mixer on a separate
stand (Figure 2530:1), and with a 20-mm-ID bottom outlet cocked
* Approved by Standard Methods Committee, 2010. Editorial revisions, 2011.
* Teflon or equivalent.
Figure 2530:1. Floatables sampler with mixer.
1
at an angle of 45° to the container wall in the direction of fluid
movement. The 45° angle assures that even large particles will flow
from the container into the flotation funnels where the sample is
withdrawn. Fit exterior of bottom outlet with a short piece of tubing
and a pinch clamp to allow unrestricted flow through the outlet.
Coat inside of container with TFE as uniformly as possible, using a
TFE spray to prevent oil and grease from sticking to the surface.
b. Flotation funnel: Use an Imhoff cone provided with a TFE
stopcock at the bottom and extended at the top to a total volume
of 3.5 L (Figure 2530:2). Coat inside of flotation funnel with
TFE as uniformly as possible to prevent floatable grease particles
sticking to the sides. Mount flotation funnels as shown in Figure
2530:3 with a light behind the bottom of the funnels to aid in
reading levels.
c. Filter holder: Coat inside of top of a standard 500-mL
membrane filter holder with TFE, again taking all possible
precautions to obtain a uniform TFE coating.
d. Filters, glass fiber, fine porosity.†
e. Vacuum flask, 500 mL.
f. TFE coating: Follow instructions that accompany commer-
cially available coating kits. Alternatively, have necessary glass-
ware coated commercially. Uniform coatings are key to the
reliability of the test results, but in practice are difficult to obtain.
3.
Procedure
a. Preparation of glass fiber filters: See Section 2540D.3a.
b. Sample collection and treatment: Collect sample in the
floatables sampler at a point of complete mixing, transport to the
laboratory, and place 3.0 L in the flotation funnel within 2 h after
sample collection to minimize changes in the floatable material.
† Whatman GF/C or equivalent.
T
ABLE
2530:I. C
OEFFICIENT OF
V
ARIATION AND
R
ECOVERY FOR
P
ARTICULATE
F
LOATABLES
T
EST
Type of
Wastewater
Average
Floatables
Concentration
mg/L
No. of
Samples
Coefficient
of Variation
%
Recovery
%
Raw* 49 5 5.7 96
Raw 1.0 5 20 92
Primary effluent 2.7 5 15 91
* Additional floatable material added from skimmings of a primary sedimentation
basin.
Figure 2530:2. Floatables flotation funnel and filter holder.
Figure 2530:3. Flotation funnels and mixing unit.
FLOATABLES (2530)/Particulate Floatables
2
FLOATABLES (2530)/Particulate Floatables
While the flotation funnel is being filled, mix sampler contents with
a small propeller mixer. Adjust mixing speed to provide uniform
distribution of floating particles throughout the liquid but avoid
extensive air entrapment through formation of a large vortex.
c. Correction for density and for concentration effects: When
a receiving water has a density and ion concentration different
from that of the waste, adjust sample density and ion concentra-
tion to that of the receiving water. For example, if the receiving
water is ocean water, place 1.5 L sample in flotation funnel and
add 1.5 L filtered seawater from the receiving area together with
mixture of 39.8 g NaCl, 8.0 g MgCl
2
䡠6H
2
O, and 2.3 g
CaCl
2
䡠2H
2
O. The final mixture contains the amount of
floatables in a 1.5-L sample in a medium of approximately the
same density and ion concentration as seawater.
d. Flotation: Mix flotation funnel contents at 40 rpm for 15
min using a paddle mixer (Figure 2530:3). Let settle for 5 min,
mix at 100 rpm for 1 min, and let settle for 30 min. Discharge 2.8
L through bottom stopcock at a rate of 500 mL/min. Do not
disturb the sample surface in the flotation funnel during dis-
charge. With distilled water from a wash bottle, wash down any
floatable material sticking to sides of stirring paddle and funnel.
Let remaining 200 mL settle for 15 min and discharge settled
solids and liquid down to the 40-mL mark on the Imhoff cone.
Let settle again for 10 min and discharge until only 10 mL liquid
and the floating particles remain in funnel. Add 500 mL distilled
water and stir by hand to separate entrapped settleable particles
from the floatable particles. Let settle for 15 min, then discharge
to the 40-mL mark. Let settle for 10 min, then discharge drop-
wise to the 10-mL mark. Filter remaining 10 mL and floating
particles through a preweighed glass fiber filter. Wash sides of
flotation funnel with distilled water to transfer all floatable
material to filter.
e. Weighing: Dry and weigh glass fiber filter at 103 to 105° C
for exactly 2 h (see Section 2540D.3c).
4.
Calculation
mg particulate floatables/L ⫽(A⫺B)
C
where:
A⫽weight of filter ⫹floatables, mg,
B⫽weight of filter, mg, and
C⫽sample volume, L. (Do not include volume used for density
or concentration correction, if used.)
5.
Precision and Bias
Precision varies with the concentration of suspended matter in
the sample. There is no completely satisfactory procedure for
determining the bias of the method for wastewater samples but
approximate recovery can be determined by running a second
test for floatables on all water discharged throughout the proce-
dure, with the exception of the last 10 mL. Precision and bias are
summarized in Table 2530:I. Experience with the method at one
municipal treatment plant indicates that the practical lower limit
of detection is approximately 1 mg/L.
6. Bibliography
H
EUKELEKIAN
,H.&J.B
ALMAT
. 1956. Chemical composition of the
particulate fractions of domestic sewage. Sewage Ind. Wastes 31:
413.
ENGINEERING-SCIENCE,INC. 1965. Determination and Removal of Float-
able Material from Waste Water. Rep. for U.S. Public Health Serv.
contracts WPD 12-01 (R1)-63 and WPD 12-02-64, Engineering-
Science, Inc., Arcadia & Oakland, Calif.
H
UNTER
,J.V.&H.H
EUKELEKIAN
. 1965. Composition of domestic sewage
fractions. J. Water Pollut. Control Fed. 37:1142.
N
USBAUM
I.&L.B
URTMAN
. 1965. Determination of floatable matter in
waste discharges. J. Water Pollut. Control Fed. 37:577.
S
CHERFIG
,J.&H.F.L
UDWIG
. 1967. Determination of floatables and
hexane extractables in sewage. In Advances in Water Pollution
Research, Vol. 3, p. 217, Water Pollution Control Federation,
Washington, D.C.
S
ELLECK
, R.E., L. W. B
RACEWELL
&R.C
ARTER
. 1974. The Significance
and Control of Wastewater Floatables in Coastal Waters. Rep. for
U.S. Environmental Protection Agency contract R-800373, SERL
Rep. No. 74-1, Sanitary Engineering Research Lab., Univ. Califor-
nia, Berkeley.
B
RACEWELL
, L.W. 1976. Contribution of Wastewater Discharges to Sur-
face Films and Other Floatables on the Ocean Surface. Thesis,
Univ. California, Berkeley.
B
RACEWELL
, L.W., R.E. S
ELLECK
&R.C
ARTER
. 1980. Contribution of
wastewater discharges to ocean surface particulates. J. Water Pol-
lut. Control Fed. 52:2230.
2530 C. Trichlorotrifluoroethane-Soluble Floatable Oil and Grease
1.
Discussion
The floatable oil and grease test does not measure a precise
class of substances; rather, the results are determined by the
conditions of the test. The fraction measured includes oil and
grease, both floating and adhering to the sides of the test
vessel. The adhering and the floating portions are of similar
practical significance because it is assumed that most of the
adhering portion would otherwise float under receiving water
conditions. The results have been found to represent well the
amount of oil removed in separators having overflow rates
equivalent to test conditions.
The QC practices considered to be an integral part of each
method are summarized in Table 2020:I.
2.
Apparatus
a. Floatable oil tube (Figure 2530:4): Before use, carefully
clean tube by brushing with a mild scouring powder. Water must
FLOATABLES (2530)/Trichlorotrifluoroethane-Soluble Floatable Oil and Grease
3
FLOATABLES (2530)/Trichlorotrifluoroethane-Soluble Floatable Oil and Grease
form a smooth film on inside of cleaned glass. Do not use
lubricant on stopcock.
b. Conical flask, 300 mL.
3.
Reagents
a. 1,1,2-trichloro-1,2,2-trifluoroethane*:See Section 5520C.3b.
b. Hydrochloric acid, HCl, 6N.
c. Filter paper.†
4.
Procedure
a. Sampling: Collect samples at a place where there is a strong
turbulence in the water and where floating material is not trapped at
the surface. Fill floatable oil tube to mark by dipping into water. Do
not use samples taken to the laboratory in a bottle, because oil and
grease cannot be redispersed to their original condition.
b. Flotation: Support tube in a vertical position. Start flotation
period at sampling site immediately after filling tube. The standard
flotation time is 30 min. If a different time is used, state this
variation in reporting results. At end of flotation period, discharge
the first 900 mL of water carefully through bottom stopcock, stop-
ping before any surface oil or other floating material escapes. Rotate
tube slightly back and forth about its vertical axis to dislodge sludge
from sides, and let settle for 5 min. Completely discharge sludge
that has settled to the bottom or that comes down from the sides
with the liquid. Scum on top of the liquid may mix with the water
as it moves down the tube. If mixing occurs, stop drawing off water
before any floatables have been lost. Let settle for 5 min before
withdrawing remainder of water. After removing water, return tube
to laboratory to complete test.
c. Extraction: Acidify to pH 2 or lower with a few drops of 6NHCl,
add 50 to 100 mL trichlorotrifluoroethane, and shake vigorously. Let
settle and draw off solvent into a clean dry beaker. Filter solvent
through a dry filter paper into a tared 300-mL conical flask, taking care
not to get any water on filter paper. Add a second 50-mL portion of
trichlorotrifluoroethane and repeat extraction, settling, and filtration into
the same 300-mL flask. A third extraction may be needed if the amount
of floatables in sample exceeds 4 mg/L. Wash filter paper carefully with
fresh solvent discharged from a wash bottle with a fine tip. Evaporate
solvent from flask as described in Section 5520B.4. For each solvent
batch, determine weight of residue left after evaporation from the same
volume as used in the analysis.
5.
Calculations
Report results as “soluble floatable oil and grease, 30 min (or
other specified) settling time, mg/L.”
Trichlorotrifluoroethane-soluble floatable oil and grease, 30 min
settling time, mg/L
⫽
共A⫺B)⫻1000
mL sample
where:
A⫽total gain in weight of tared flask, mg, and
B⫽calculated residue from solvent blank of the same volume
as that used in the test, mg.
6.
Precision and Bias
There is no standard against which bias of this test can be
determined. Variability of replicates is influenced by sample heter-
ogeneity. If large grease particles are present, the element of chance
in sampling may be a major factor. One municipal wastewater
discharge and two meat-packing plant discharges, both containing
noticeable particles of grease, were analyzed in triplicate. Averages
for the three wastewaters were 48, 57, and 25 mg/L; standard
deviations averaged 11%. An oil refinery made duplicate determi-
nations of its separator effluent on 15 consecutive days, obtaining
results ranging from 5.1 to 11.2 mg/L. The average difference
between pairs of samples was 0.37 mg/L.
7. Bibliography
P
OMEROY
, R.D. 1953. Floatability of oil and grease in wastewaters.
Sewage Ind. Wastes 25:1304.
* Freon or equivalent.
† Whatman No. 40 or equivalent.
Figure 2530:4. Floatable oil tube, 1-L capacity.
FLOATABLES (2530)/Trichlorotrifluoroethane-Soluble Floatable Oil and Grease
4
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