United States
Environmental Protection
Agency
Air and Energy Engineering
Research Laboratory
Research Triangle Park NC 27711
Research and Development
EPA/600/S7-85/008 May 1985
Project Summary
Performance Evaluation of an
Improved Street Sweeper
Michael Duncan, Roop Jain,
Shui-Chow Yung, and Ronald Patterson
Dust emissions from paved streets
can be controlled by street cleaning,
but the commonly used broom and
vacuum street sweepers are ineffec-
tive in removing small particles from
the street surface, and they disperse
the dust into the air during sweeping.
A.P.T. improved a commercial va-
cuum sweeper under a previous EPA
contract, and in limited testing
showed that the Improved Street
Sweeper (ISS) cleans the street better
and disperses less dust.
In this study, an extensive evalua-
tion of the ISS was carried out in
Bellevue, WA, and in San Diego, CA.
The cleaning performance of the ISS
was compared with that of broom
sweepers and a vacuum sweeper. The
ISS cleaned streets better than the
other sweepers. Typically, the broom
sweepers removed 20% of the street
solids, the vacuum sweeper, 70%, and
the ISS, 80%. Additionally, the ISS
was the only sweeper tested that
gave a constant, low level of residual
street solids that was independent of
the initial amount of street solids.
This Project Summary was devel-
oped by EPA's Air and Energy Engi-
neering Research Laboratory, Re-
search Triangle Park, NC, to an-
nounce 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
Dust on urban streets can cause air
pollution because of redispersion of the
dust and water pollution from rain water
runoff. One way to minimize these pollu-
tion problems is to clean the streets
regularly. The existing types of street
sweepers have been primarily designed to
remove trash and the larger solids. They
have low to moderate efficiency for
removing fine dust from streets. In addi-
tion, most street sweepers disperse some
of the street dust into the air during
sweeping.
Under a previous U.S. EPA contract,
A.P.T. evaluated the problems with pres-
ent sweepers and modified a vacuum
sweeper by adding partial hoods to the
gutter brooms, and venting an air stream
through a spray scrubber.
This improved street sweeper (ISS) was
subjected to a limited testing program in
San Diego and Los Angeles during the
previous contract. Results clearly in-
dicated that the ISS could eliminate the
the dust plume during sweeping and give
a cleaner street. However, additional
research work was needed to refine the
design and to demonstrate its capability.
Under this contract, extensive tests
were conducted to determine the im-
proved street cleaning performance and
the effectiveness for reducing fugitive par-
ticle emissions from the ISS.
Objectives
The ISS and conventional street
sweepers were tested in operation under
identical conditions in the City of
Bellevue, Washington, and in San Diego,
California. The objectives for this study
were:
1. Compare the street cleaning abilities
of the following street sweepers:
a. A.P.T. ISS.
b. Tymco Model 600 regenerative air
sweeper.
c. Mobil broom sweeper.
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d. FMC broom sweeper.
2. Compare the dust dispersions of the
ISS and Tymco sweepers.
3. Determine particle emissions from
the ISS.
4. Evaluate the effects of street clean-
ing on water runoff. This portion of
work was performed in cooperation
with the City of Bellevue, which
studied the effect of street sweeping
on urban water runoff quality (under
contract with the Municipal En-
vironmental Research Laboratory of
the U.S. EPA). The results were
reported by the City of Bellevue and
are not included in this report.
Street Sweeper Descriptions
Street sweepers can be categorized into
two major groups according to the
mechanism that they use to pick up solids
from the street. These two groups are
broom sweepers and vacuum sweepers.
The ISS is a vacuum sweeper with equip-
ment added by A.P.T. for performance
improvement. Brief descriptions of the
four sweepers evaluated in this study are
presented below.
Mobil and FMC Sweepers
Both the Mobil and the FMC sweepers
are four-wheeled broom sweepers with
similar features. They use rotating gutter
brooms to move the dirt from the area
near the curb to the area under the
sweeper. From there, the dirt is swept
onto a squeegee-type dirt elevator by a
large, cylindrical, pickup broom that
rotates about a horizontal shaft at the rear
of the sweeper. The dirt elevator lifts the
dirt into a collection hopper.
Tymco Sweeper
The Tymco model 600 sweeper is a
vacuum sweeper which uses a regenera-
tive air system to recirculate the air from
vacuuming the street dirt. A gutter broom
moves the street dirt from the curb
toward the center of the sweeper. A
blower forces air through a slot in the
pickup head which rides on and seals
against the street surface. The slot directs
a high-velocity blast at the street surface,
loosening the dirt. The dirt is then
vacuumed up and is carried to a hopper
through a vacuum hose. In the hopper,
paper and leaves are removed from the air
stream by a screen, and large particles are
removed by a centrifugal separator. The
air then enters the blower to complete the
cycle.
A.P.T. Improved Street
Sweeper
The ISS is the above Tymco sweeper
with modifications to maximize the collec-
tion of fine particles. The modifications in-
clude:
1. Installing a partial hood around each
gutter broom and venting the hood
to the hopper.
2. Increasing the vacuum in the pickup
head by venting about 1000 cfm
(28,317 L/min) of air out of the
regenerative air system.
3. Installing a scrubber to clean the
vent air. The scrubber was originally
a charged spray scrubber. It was
changed in this study to a low pres-
sure drop venturi scrubber because
the spray scrubber was too small
and had substantial water drop loss
on the walls. In addition, the
charged spray scrubber system was
too complicated and its efficiency
differed little from a regular spray
scrubber because electrostatic aug-
mentation only improves collection
efficiency for particles smaller than 3
/imA diameter and there were not
many particles smaller than 3 /imA
diameter in the vent air stream.
Test Methods
Four sweeper performance parameters
were measured in this study: the ability of
a street sweeper to remove solids from a
street surface, the relative dust disper-
sions of the ISS and the Tymco
sweepers, and the mass rate and size-
distribution of the ISS scrubber emis-
sions. The measurement methods are
summarized below.
Street Solids Removal
The ability of a street sweeper to
remove solids from a street was deter-
mined by measuring the amount of street
solids on the street before and after
sweeping. Each test was performed on a
test section of street that was from 160 to
320 m (0.1 to 0.2 mile) long. The width of
each test section was from the street
centerline to the curb, on only one side of
the street. Each test involved only one
sweeper, making one sweeping pass next
to the curb.
Each street dust sample was taken by
vacuuming 5 to 60 randomly selected 13.3
cm wide strips. Two types of samples
were taken: half-of-street strips from the
curb to the street centerline, and strips of
the sweeping lane. The half-of-street
samples were taken to express sweeper
performance in terms of commonly used
street sweeping practice; which is sweep
the street by passing the sweeper once on
one side of the street near the curb.
Sweeper performance based on half-of-
street samples may be penalized because
part of the sampled area is not swept.
The sweeping lane samples were taken to
accurately determine the ability of a
sweeper to remove the solids from its
path.
The street dust sampler consisted of a
triangular vacuum pickup head, two
vacuum cleaners in parallel, and a cascade
impactor sampling system. During sampl-
ing, the pickup head contacted the street
and the leading edge was elevated
manually 0.3 cm above the street surface
to permit an adequate air flow and to col-
lect the large solids. The dirt was col-
lected in each vacuum cleaner canister,
and the vacuum cleaner air was filtered by
a pair of cloth filters in each canister. The
canister sample was later sized by sieve
analysis.
The particles smaller than 15 pmA
diameter were sized with a cascade im-
pactor sampling train. A sample probe
was inserted into the vacuum hose of the
vacuum cleaner, and an air sample was
withdrawn isokinetically. The sample
passed through a precutter to remove the
particles larger than 15 to 20 /*mA
diameter and then through a University of
Washington Mark III cascade impactor for
size tractionation.
Dust Dispersion
The mass concentration of the dust
dispersed by the Tymco and the ISS was
determined with two glass-fiber filters
mounted on the top of the pickup head at
its leading edge. Since the total volume of
the dust-laden air is not known, the
measurement results are only an indica-
tion on the relative amount of dust
dispersed by the Tymco sweeper and ISS.
/SS Scrubber Emission
The mass emission rate and the particle
size distribution of the ISS scrubber ex-
haust were determined by sampling the
scrubber outlet with a cascade impactor.
Results
Test Areas and Sweepers
In Bellevue, sweepers were tested at
two areas: SE 30th St. (in a light-
industrial area) and Surrey Downs (a
residential neighborhood). The ISS, Tym-
co, and Mobil sweepers were tested at
both areas.
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In San Diego, tests were made at two
areas: Mission Blvd. (in a commercial-
residential-recreational area) and Morena
Blvd. (in a commercial area). At Mission
Blvd., the ISS, Tymco, Mobil, and FMC
sweepers were tested. At Morena Blvd.,
the ISS, Tymco, and FMC sweepers were
tested.
Distribution of Street Solids
Comparison of the initial half-of-street
and sweeping lane samples revealed that
70 to 100% of the street solids were
within the sweeping lane. The mass me-
dian diameters of the street solids were
found to vary from 200 to 500 ^m.
This distribution of street dust agrees
with the measurement results reported by
the city of Bellevue. The city of Bellevue
measured the distribution of street solids
on 110th Avenue SE. They found that: 45
to 55% of the solids were within 0.51 m
of the curb, 75 to 80% were within 1.2 m
of the curb, and 85 to 95% were within
2.4 m of the curb.
Street Sweeper Cleaning
Performance
The street cleaning performance of a
street sweeper cannot be expressed in
terms of removal efficiency because the
efficiency depends on the amount of
solids on the street, the size distribution
of the solids, and the street surface
characteristics. Instead, the sweeper per-
formance was evaluated based on plots of
residual versus initial solids on the street.
The effect of particle size on sweeper per-
formance was determined from plots for
various particle size ranges. To eliminate
the effects of street surface characteristics
on sweeper performance, each graph is
for only one test site.
Figure 1 shows typical results for half-
of-street samples of total street solids.
Depending on initial street dust loading,
the broom sweepers removed 0 to 40% of
the solids, the Tymco, 30 to 55%, and
the ISS, 30 to 60%. Therefore, based on
half-of-street results, the Tymco was only
slightly less effective than the ISS, but
each was more effective than the broom
sweeper.
Figure 2 shows typical results for
sweeping lane samples of total street
solids. It reveals larger differences in per-
formance between the sweepers than the
half-of-street graphs, because the solids
of the unswept area were not included in
the residuals. The broom sweepers
removed about 5.0 to 45% of the solids
and their sweeper curves usually have
slopes of about 1. The Tymco removed
200
750
I
i
to
•v^
CQ
700
50
1 1
Mobil TYMCO ISS
Symbol O A D
Correlation
Coefficient 0.976 0.912 0.989
Y-lntercept 4.26
Slope 0.901
9.86 5.86
0.397 0.398
' Mobil
Residual = Initial
Surrey Downs
Bellevue, WA
50 100 150
Initial Solids, kg/curb-km
200
250
Figure 1. Total solids performance at Surrey Downs from half-of-street samples.
about 50 to 75% of the solids, and its
performance curve slopes are about 0.25.
The ISS removed 50 to 85% of the solids
and its curves have slopes of zero. This
indicates that the ISS gave a constant
residual level that was independent of the
amount of initial street solids.
Results from sieve analysis showed that
the broom sweepers were only effective in
removing large particles (larger than 2,000
/tm diameter). They were not effective in
removing particles smaller than 125 /tm
diameter. In some cases, there were more
small particles on the street after sweep-
ing than before sweeping!
The performance difference between
the Tymco and the ISS was not great for
particles larger than 500 /tm diameter. In
half of the test site, the Tymco performed
as well as the ISS. For solids with a
diameter smaller than 500 /tm, the Tymco
did not pick up as much solids as the ISS
(Figure 3). The curves of the Tymco have
slopes from 0.2 to 0.5. The ISS has the
best performance curves, with slopes of
about zero.
Relative Dust Dispersed by
Tymco and ISS
The mass concentrations of dust
measured at the pickup head of the ISS
and the Tymco were scattered. Therefore,
it cannot be concluded that the ISS
dispersed less dust during sweeping.
However, based on visual observations,
the ISS did have a smaller dust plume.
ISS Scrubber Emissions
The mass median diameter of the par-
ticles in the ISS scrubber exhaust was
about 2 /jnA, and 94% of the emissions
were smaller than 10 /tmA. The mass
emission rate of the ISS scrubber is plot-
ted against initial solids on the street
which were smaller than 10 /*mA in Figure
4. Depending on the amount of initial
dust on the street, the emissions varied
from 0.005 to 0.4 kg/curb-km, which cor-
responds to 2 to 40% of the initial street
solids which were smaller than 10 /unA
diameter. The average was about 10%.
The venturi scrubber was limited to a
maximum pressure drop of 15 cm W.C.
because of limitations of the existing fan
on the sweeper. The scrubber emission
could be lowered if this fan were replaced
with a higher pressure drop fan.
Conclusions
The ISS was evaluated along with other
conventional sweepers in Bellevue,
Washington, and in San Diego, Califor-
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nia. The results show that the ISS
removes more street solids than the same
sweeper without the improvements (and
also better than broom sweepers).
Typically, a broom sweeper removes 20%
of the street solids, the Tymco sweeper,
70%, and the ISS, 80%. Additionally, the
ISS was the only sweeper tested that
gave a constant, low level of residual
street solids that was independent of the
initial amount of solids on the street.
However, the residual level does depend
on the street surface characteristics.
Based on visual observations, the ISS
dispersed less dust during sweeping.
However, the data from measurements of
the dust concentration at the pickup head
of the Tymco and the ISS were too scat-
tered to allow statistical verification.
Recommendations
This evaluation shows that the ISS
cleans streets better than conventional
sweepers especially in the fine particle
range. Its effects on ambient air quality
have not been measured. To complete the
evaluation of the ISS, the emission fac-
tors of the ISS and conventional
sweepers need to be measured. This
could be accomplished by sampling am-
bient air upwind and downwind of streets
during and between sweepings. A fugitive
emissions measurement program would
reveal the contribution of fine particles
into the air from street sweeping and how
much this dust loading would be reduced
using the design principles developed by
A.P.T.
I
i
u
I'
I
1
I
100
90
80
70
60
50
40
30
20
10
\ I T
I T
-- Mobil Sweeper
--- TYMCO Sweeper
Residual = Initial
Sweeping Lane Width = 3.0 m
Surrey Downs,
Bellevue. WA
I 1
I I
0 10 20 30 40 50 60 70 80 90 100
Initial Solids, kg/curb-km
Figure 2. Total solids performance at Surrey Downs from sweeping lane samples.
50
40
30
.
1
10
O FMC
A TYMCO
n iss
Residual = Initial
10 20 30 40 50
Initial Solids, kg/curb-km
60
70
Figure 3. Performance on 63 to 500 fjm sweeping lane samples at Morena Blvd.
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1.0
0.001
IIII
I I I 1 I I I
Emission
Rate
O SE 30th St. -
O Surrey Downs -
A Mission Blvd.
O Morena Blvd.
i i I i i i i
0.1 1.0 10 100
Initial Sweeping Lane Solids Smaller Than 10^mA, kg/curb-km
Figure 4. ISS scrubber emissions.
M. Duncan. R. Jain, S-C. Yung. andR. Patterson are withA.P.T., Inc., San Diego,
CA 92109.
Dale L. Harmon is the EPA Project Officer (see below).
The complete report, entitled "Performance Evaluation of an Improved Street
Sweeper, "(Order No, PB 85-169 845/AS; Cost: $20.50, 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:
Air and Energy Engineering Research Laboratory
U.S. Environmental Protection Agency
Research Triangle Park, NC 27711
. GOVERNMENT PRINTING OFFICE: 1985/559 111/10834
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Environmental Protection Information
Agency Cincinnati OH 45268
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