United States
Environmental Protection
Agency
Risk Reduction Engineering
Laboratory
Cincinnati OH 45268
Research and Development
EPA/600/S2-89/052 Dec. 1989
&EPA Project Summary
Assessing Chemical Releases
and Worker Exposures from a
Filter Press
James Scott, Keith Sherban, and Mary Marshall
Chemical releases and worker
exposures associated with the
filtration of an industrial wastewater
sludge were characterized. The filter
was a recessed chamber filter press
with an open filtrate discharge
system. Chemical releases and
worker exposures for a selected
chemical were measured over four
operational cycles and various
aspects of the filtration operation
believed to influence the
measurement values were
documented. The filter press and
ancillary systems are described as a
reference for the measured releases
and exposures. Bulk samples of the
feed stream, filter cake, and filtrate
effluent were taken together with the
mass quantities for the batch
filtration cycles to further define the
operational conditions. The three
sequential stage activities
comprising each filtration operation
are described along with worker
exposures and durations for each
stage. Ventilation patterns around the
filter press were monitored.
The worker's time-weighted aver-
age exposures to total copper (low
vapor pressure, highly insoluble
form) during the 113-minute opera-
tional cycle ranged from 3.1 to 25
u.g/m3. The sludge feed and filter
cake copper concentrations were
approximately 0.1 and 1.0 weight per-
cent. A noticeable difference in
worker techniques was observed
which may account for the large
range of inhalation exposures during
the cake removal stage. During this
stage, the inhalation exposures
ranged from 11 jig/mS to 130 jig/m3.
The manual removal of filter cake
comprised only 15% of the time in an
average filtration cycle, but produced
72% of the worker's inhalation
exposure.
This Project Summary was
developed by EPA's Risk Reduction
Engineering Laboratory, Cincinnati,
OH, to announce key findings of the
research project that is fully
documented in a separate report of
the same title (see Project Report
ordering information at back).
Introduction
For the study summarized herein,
inhalation and dermal worker exposures
as well as chemical releases were
characterized at an electronic
manufacturing plant. The parameters
(exposures and releases) were measured,
and the aspects of the operation believed
to influence these parameters were
documented over four filtration cycles.
Each cycle was composed of three
stages: sludge filtering, filter cake drying,
and filter cake removal.
This assessment study is part of a joint
research effort undertaken by the U.S.
Environmental Protection Agency and
Southwest Research Institute. The overall
goal of the cooperative agreement is to
develop database models for use in
predicting chemical releases and worker
exposures from select filtration and
drying unit operations. The database
models developed will be applicable for
the Premanufacture Notice (PMN) review
system. For each study the chemical
monitored is a surrogate for a
hypothetical PMN new chemical in order
to evaluate the worker exposures and
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chemical releases from the unit
operation. Thus, there is no requirement
to select an operation which has a toxic
chemical, provided that the physical
properties of the chemical can be
extrapolated to the hypothetical PMN
new chemical. The surrogate chemical at
Plant 50 is total copper.
The sludge was from a metal rinse
stream. Because the metal with the
highest concentration was copper, total
copper (both soluble and insoluble) was
selected to evaluate worker exposures
and chemical releases.
For each unit operation cycle, sludge
was pumped from a storage tank to a
recessed chamber filter press. In the
sludge filtering stage, the solids (filter
cake) were collected in the chambers of
the press while filtrate exited the press
through spigots on the side of each plate
into an open collection trough. The filtrate
further drained into a sump and was then
pumped to an effluent storage tank. This
process continued until the press was
(approximately) filled with cake.
Once the press was filled, the cake was
blown with compressed air (the filter cake
drying stage). The air entered the press
through the same port as the sludge and
exited the press through the same
spigots as the filtrate. The discharging
compressed air created a mist in the
vicinity of the press.
After the drying stage, the filter cake
was removed. As the press was opened,
one plate at a time, the filter cake
dropped into a collection hopper. The
filter cake was transported with a screw
auger to a collection trailer. Cleaning the
last chamber of the press completed the
filter cake removal stage.
Two filter presses were housed in a
separate room next to the main waste
treatment area. The recessed chamber
filter press used in this study had 23
plates (or 22 chambers), which were each
approximately 1 m in length and width
and 4.5 cm thick. (The other press did
not operate during this study.) The total
filtration surface area was 34.8 m2, and
the total filtration volume was 0.70 m3.
The overall size of the press was 5.0 m
long by 1.6 m wide by 2.3 m tall. The
press was equipped with a hydraulic ram
closure mechanism and an automatic
plate shifting device.
Procedure
All data were categorized according to
the three filtration stages mentioned
above. Worker exposures were assessed
during four cycles of the filtration
operation, and chemical release
measurements were taken during the first
three cycles. The emissions from sealing
points were evaluated during the sludge
filtering stage in the fourth cycle. For all
four cycles, the sludge came from a
single, isolated storage tank.
Background, area, and personnel air
samples were collected with the use of
battery-operated pumps, duPont P4LCs*,
to pull air through 0.8 p mixed-cellulose,
ester membrane filters. The background
air samples were collected where air
either entered into or exited from the filter
press room. Two area samples were
located at the ends of the filtration
collection trough and one by a control
panel. The personnel sample collection
cassettes were attached to each
operator's shirt collar.
Wipe samples were collected on two
flat horizontal areas of the filter press,
one at each end of the filter press.
In conjunction with measuring the
volumes of sludge feed and filtrate, as
well as weighing a chamber of the filter
cake, bulk samples were taken of the
sludge feed, filtrate, and filter cake The
sludge feed samples were grabbed from
the storage tank immediately before the
start of the sludge filtering stage. The
filtrate samples were collected at the
outlet of the collection trough discharge
pipe. Small fragments of filter cake were
selected from the chamber that was
weighed.
Copper analyses of the sludge, filter
cake, wipe, and filtrate samples were
done by direct aspiration flame atomic
absorption spectrophotometry, employing
Method 220.1 of Methods for Chemical
Analyses of Water and Wastes (EPA
600/4-79/020). Method 160.3 of the same
reference was used to analyze total
residue. NIOSH Method 7029 was used
to analyze the air samples for copper,
except that graphite furnace atomic
absorption spectrophotometry was used
for greater sensitivity.
A Kurz 441 M Air Velocity Meter
measured air velocities. Smoke tubes
indicated gross air movement within the
filter press room.
Results
Worker inhalation exposure measure-
ments for airborne copper were
performed for four filtration operation
cycles using three operators, A-1, B-1,
and C-1 [the first operator (A-1) was
monitored twice]. The geometric mean
exposure, the average duration of the
'Use of trade names or commercial products does
not constitute endorsement or recommendation
for use
stage, and the average duration of
operator's involvement during each si
as well as the entire unit operation
summarized in Table 1 (the minimi
and maximums are also presented).
total copper concentrations in the slu
feed and the filter cake w
approximately 0.1% and 1.0% by wei
respectively. Total copper was in a hi'
insoluble form with a low vapor pressi
The head, neck, and lower arm a
comprised the exposed skin surfaces
all of the operators. Since the sec
operator (B-1) did not wear any gl<
(and operators A-1 and C-1 did),
hands were also potential sites for de
exposure. The routes by which co|
was deposited on the skin were airb
aerosols and contact with surfaces (w
had visible deposits of green dust) ir
filter press room.
The air and wipe sampling res
indicate the airborne copper con'
trations made aerosol deposition
exposed skin surfaces a neglig
consideration. Deliberate contact
surfaces occurred when the oper<
opened and closed valves, turned on
off pumps, grabbed the outer edge
some of the plates and slid them slii
forward to ensure they were corn
aligned with the filter cloths,
occasionally held onto the side of
press for support while peering intc
press to inspect the filter cloths for
residue. Incidental contact occurred \
the operators hit their lower arms
hands for operator B-1) on vai
surfaces.
No direct contact with the slu
filtrate, or filter cake was observed.
The ventilation measurements sh<
that air movement through the filter |
room was relatively constant at a i
location throughout the study, but tr
velocities varied from location to loci
Smoke tube studies showed most c
air that entered the room via the
doorway flowed directly towards the
doorway. (These doorways were lo<
towards the front of the room on the
wall. There were no other entrance
the air, except through leaks in the v\
the lower level, and only one other
the south wall exhaust fan.) As th
moved from east to west, very litt
from the work area by the filter pn
became entrained into this mai
current. The operators, however.
most of their time in the other porti
the room where the filter press
located and in which ventil
stagnation occurred.
An overall mass balance approach
appropriate samples taken for
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Table 1. Operators' Geometric Mean Inhalation Exposure to Airborne Copper
Duration of the Stages and Operators' Involvement
Stage
Sludge Filtering
Cake Drying
Cake Removal
Entire Operation (TWA)
Geometric
Mean
Exposure,
fig/m3
4.1
1.6
30
6.4
Minimum
Exposure,
}ig/m3
3.8
0.8
11
3.1
Maximum
Exposure,
fig/m3
4.8
2.6
130
25
Average
Stage
Operation
Duration,
min
39
57
17
113
Minimum
Duration,
min
26
49
15
98
Maximum
Duration,
min
57
64
20
141
Average
Duration of
Operator
Involvement,
min
11
3
17
31
Minimum
Duration,
min
9
3
15
27
Maximum
Duration,
min
13
3
20
33
Table 2. Mass Balance Results
Sample Site
Mass Total, Kg
Mass of Total Copper, Kg
Influent
Sludge feed
Cycle 1 Cycle 2 Cycle 3 Cycle 1 Cycle 2 Cycle 3
2150 1570 1660 2.9 2.0 1.9
Effluent
Filtrate
Filter cake
Total Effluent
1720
338
2058
1210
335
1545
1120
339
1459
0.001
5.3
5.3
0.001
3.0
3.0
0.0009
2.1
2.1
copper, was used to quantitate chemical
releases. Table 2 summarizes the results
(for the three filtration operational cycles).
Although the average percent
difference between the overall effluent
and influent masses was -6.3% (range of
-1 6% to 13% with a sample standard
deviation of 5.9%), the average percent
difference between the total copper
masses in the effluent and influent was
+ 36% (range of 10% to 59% with a
sample standard deviation of 24%).
In addition to the overall mass balance
approach, spills and leaks were observed
and documented. These leaks and spills
represent releases that would not have
been included in the other mass
measurements. The five releases
observed were: (1) the air valve to the
press leaked 1 drop of sludge onto the
floor (of the lower level) every 10 sec
during the sludge filtering stage, (2) the
recessed chamber plates dripped liquid
into the cake hopper; six leaks flowed at
a rate of 1 drop every 2 sec, (3) the valve
to the sludge feed pump leaked sludge
onto the floor at a rate of 1 drop every
minute, (4) the fine mist generated during
the cake drying stage from the filtrate
spigots fell onto the floor (of the lower
level), which dampened an area of
approximately 1.5 m2, and (5) the small
fragments of filter cake that missed the
hopper fell onto the floor (of the lower
level) as the recessed chambers were
emptied during the cake removal stage;
the fragments of cake averaged 5 cm3 in
volume. It should be noted that the
^ludge dripping from the leaks in
jmbers 1 through 3 was somewhat
clearer in appearance compared with the
murky, green color of the sludge.
Therefore, the residue and copper
concentrations in these leaks may have
been lower than those in the original
sludge. During each filtration cycle, these
spills and leaks released approximately
1.1 g of total copper. The total copper
released in the filtrate waste stream
averaged 1 g per filtration cycle. An
estimated 23 mg of copper was present
in the air exhausted from the filter press
room during each filtration cycle.
Consequently, the total chemical releases
from each filtration operation was
approximately 2.1 g of copper, or slightly
less than 0.1% of the total copper
processed through the filter press.
The sealing point evaluation was
performed to measure the aerosol
concentration generated by the operation.
No aerosol was detected above the total
background levels (0.05 mg/m3) at any of
the pumps, valves, or connections.
Aerosol was detected at the 23 open-
ended spigot lines and the filtrate
collection trough. The aerosol
concentration detected was 0.4 mg/m3.
An aerosol concentration of 1.0 mg/m3
was also recorded for the open-ended
line discharging filtrate into the sump. It
must be noted that the measurements
were for the total aerosol concentration;
identification of a particular species (e.g.,
copper aerosol) was not possible.
Discussion
The total average duration of the
filtration cycle was 113 min. Of this time,
the operator was actively involved in the
operation for 31 min on average (or
27%). If an operator were to be
responsible for multiple filter presses, the
"free times" within the various stages
could permit the operator to stagger the
stages of the individual presses and
operate them simultaneously. With
presses similar to ones in this study, an
operator could perform the various tasks
on three presses and finish in a 147-min
period. During this span of time, the
operator would accrue a total exposure
duration of 93 min (three presses at 31
min each), which is equivalent to 63% of
the total time. Therefore, to determine the
worker exposure during the total filtration
cycle, the number of filter presses
operated by the worker must be known.
Based on a geometric mean inhalation
exposure, 72% of an operator's exposure
to copper occurred during the cake
removal stage of the filtration operation.
Fifteen percent of an operator's time was
spent during this stage. An operator's
time weighted average (TWA) exposure,
based on the geometric mean, was 6.4
pg/m3.
To determine an operator's exposure,
the following formula could be used
(assuming the worker only operated one
press).
o
HgTc _ ngTc (TWA) 1.25m
day 3 hr
hr of operation # cycles
x - x
cycle
day
-------
where Tc = target chemical.
For this study, the operator's exposure
would be (assuming an 8 hr shift per
day),
g
Hg copper _ 6.4 pg copper 1.25 m
day 3 hr
m
(113/60) hr 4 cycles
x x -
cycle day
61 jig copper
~
Observations of the workers indicated
any dermal exposure incurred during the
sludge filter and filter cake drying stages
was the result of casual or incidental
contact of the hands with contaminated
surfaces, which resulted in very minimal
exposure. The filter cake removal stage
did provide a greater opportunity for
dermal exposure since the workers were
in contact with the filter press and were in
proximity to the filter cake. No direct
contact with the filter cake was observed,
however.
The protective equipment each
operator wore included chemical safety
goggles at all times in the filter press
room and hearing protection devices
during the cake drying stage. Operators
A-1 and C-1 also wore cotton gloves. In
addition, operator C-1 wore a disposable,
half-face dust respirator.
Total copper was a very small portion
of the material being processed. As such,
the methods used to accomplish a mass
balance were too insensitive to accurately
or precisely quantitate the mass of total
copper.
Conclusions
The workers' TWA exposures to total
copper over the 113-min average
duration of the unit operation ranged from
3.1 to 25 u,g/m3. The ACGIH's 1987-88
TLV for 8-hr exposures to copper dust
and mist is 1 mg/m3.
The total copper concentrations in the
sludge feed and the filter cake were
approximately 0.1% and 1.0% by weight,
respectively. Therefore, it is uncertain
whether the low worker exposures
measured were solely attributed to the
operational characteristics of the filter
press or were a reflection of the low total
copper concentrations.
The area of the room most frequently
occupied by the workers was also the
area that received the least air circulation.
The air flow rate and distribution pattern
inside the filter press room remained
relatively constant throughout the study.
Data from this research also indicate
that a worker's technique in removing the
filter cake may be an important factor in
determining a worker's exposure to within
one order of magnitude. The range of
inhalation exposures during the cake
removal stage was 11 ng/m3 to 130
jig/m3. A noticeable difference in worker
techniques was recorded for the high and
low exposure readings.
The sludge filtering stage showed great
variability among the work paths taken by
the filter press operators but little
difference among their resultant
exposures (geometric mean exposure for
the four sludge filtering stages was 4.1
u.g/m3). The sludge filtering stage
comprised roughly one-third of the 113
min needed to complete an average
filtration cycle.
The filter cake drying stage, which
comprised slightly more than 50% of the
time for the filtration cycle, was largely
unattended by the operators and,
therefore, contributed very little to their
exposures. The working time was 3 min,
and the geometric mean of the inhalation
exposures to airborne copper was 1 .6
Although manual removal of filter cake
from the chambers of the filter press
comprised only 15% of the time in an
average filtration cycle, it produced 72%
of the workers' exposures to copper
during the filtration operation.
Dermal exposures to total copper were
not quantitated. Observations of the
operators' work practices indicated that
their dermal exposures were probably
very low and effectively eliminated
through their use of work gloves when
removing the filter cake.
Total chemical releases from the filter
press were estimated to be 2.1 g of
copper or 0.1% of the total copper mass
that was processed through the u
operation. Although the mass of chemi
in the filtrate could be measured, 1
mass of chemical released in spills
leaks of the feed material and filter Ce
could not be quantified. The study's d
indicate that leaks or spills of fe
material or filter cake can be a gres
potential source of chemical releas
than from the total filtrate effluent
insoluble filter cake products.
Using a mass balance to calculate tc
copper processed through the filter pr<
was not an effective method
measuring the individual chemi<
releases. The sampling and analyti
errors associated with the mass balar
measurements did not permit accur
calculations of the relatively sir
masses represented by the individ
chemical releases.
Recommendations
The in-plant assessment study o
filter press unit operation yielded d
that provided insight into worl
exposures and chemical releases. Pi
scale experiments should be conduc
using different worker scenarios i
target chemicals to quantify ranges
exposures and chemical releases t
can occur by varying these two variabl
For a future in-plant assessment sti
of a filter press, any one or more of
following criteria should be consideret
the selection process-
A liquid, high-molecular-weight, orge
chemical should be studied.
An operation with a more concentre
chemical (cake product) in the fi
stream should be used.
A larger filter press (one requiring
operators to remove the filter a
should be used.
This report was submitted in pa
fulfillment of Cooperative Agreem
CR813355 by Southwest Resea
Institute under the partial sponsorshii
the U.S. Environmental Proteci
Agency.
-------
James Scott, Keith Sherban, and Mary Marshall are with Southwest Research
Institute, San Antonio, TX 78284.
Dennis Tlmberlake is the EPA Project Officer (see below).
The complete report, entitled "Assessing Chemical Releases and Worker
Exposures from a Filter Press," (Order No. PB 90-119 587/AS; Cost: $23.00,
subject to change) will be available only from:
National Technical Information Service
5285 Port Royal Road
Springfield, VA 22161
Telephone: 703-487-4650
The EPA Project Officer can be contacted at:
Risk Reduction Engineering Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
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