United States
Environmental Protection
Agency
Municipal Environmental
Research Laboratory
Cincinnati OH 45268
Research and Development
EPA-600/S2-84-069 May 1984
SER& Project Summary
Removal of Giardia lamblia Cysts
by Drinking Water Treatment
Plants
Foppe B. DeWalle, Jogeir Engeset, and William Lawrence
A pilot study was conducted at the
University of Washington to evaluate
the removal of Giardia lamblia cysts and
cyst-sized particles from Cascade
Mountain waters. Methods included
coagulation/sedimentation and filtra-
tion, or direct filtration using three
2.3-L/min (0.6-gpm) pilot treatment units
and diatomaceous earth (DE) filtration
with a 3.8-L/min (1-gpm) DE pilot filter.
Results were verified by use of a
75-L/min (20-gpm) pilot unit (Waterboy,
Neptune Microfloc*) in field trials at Ho-
quiam and Leavenworth, Washington.
Granular media filtration tests yielded
greater than 99.9% removal of spiked
cysts under optimum conditions, al-
though removal percentages decreased
greatly at lower spiking levels. Both the
pilot unit and the field unit established
the importance of a minimum alum
dosage (10 mg/L), an optimum pH
range, and intermediate flow rates of 4.9
to 9.8 m/hr (2 to 4 gpm/ft1). Effluent tur-
bidity and cyst-sized particles passing
the filter increased rapidly when the
above conditions were not attained or
when sudden changes occurred in plant
operation. When no coagulants were
used during filtration, the process
removed only 48% of the spiked cysts
and 47% of the turbidity. A cyst spike
in the pilot unit in Hoquiam using alum
as coagulant resulted in an 81% cyst
removal, and the spike at Leavenworth
using a polymeric flocculant gave a 72%
removal. Producing a low-turbidity filter
effluent with alum or polymeric floc-
culant was difficult when the water
temperature was less than 3°C. Further
research on low-temperature direct
filtration is necessary to improve the
removal efficiency under these con-
ditions.
DE filtration proved effective both for
turbidity, particle, and cyst removal. The
addition of 0.0075 mg/L nonionic poly-
mer showed some improvement in effi-
ciency. Cyst removals generally ranged
from 99% to 99.99%.
This Project Summary was developed
by EPA's Municipal Environmental Re-
search 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
A study was undertaken to evaluate the
removal of Giardia lamblia cysts and cyst-
sized (8- to 12-fjm) particles by drinking water
plants. The first phase of the study was
devoted to a laboratory-scale evaluation of
Giardia removal efficiency by coagulation,
flocculation, and filtration. In addition, a
diatomaceous earth filter was tested. The
second phase consisted of a pilot- and full-
scale evaluation of Giardia removal from
drinking water plants where cysts might be
present in the raw water.
All laboratory water treatment plant ex-
periments were conducted with unfiltered
Seattle tap water to which cysts were added.
The cysts that were used to spike the water
were isolated from the feces of human giar-
diasis patients. The cysts were recovered
from the spiked water using membrane filtra-
tion techniques. Giardia cysts present in the
membrane retentate were enumerated with
a hemacytometer and a Coulter Counter.
This project was of considerable sig-
nificance in the State of Washington
-------
because waterborne giardiasis outbreaks had
occurred in Camas in 1976 and in Leaven-
worth in 1980. The latter community was
selected as one of the sites for field testing
with the 75-L/min mobile pilot plant.
Experimental Procedures
The Giardia cysts were collected from the
feces of human giardiasis patients. The cysts
were separated from the feces using a
sucrose gradient technique. During testing,
the cyst suspension was added to the in-
fluent of the unit process to be studied. The
cysts were recovered from the process ef-
fluent by filtering 10 to 100 L through a 5-^m-
pore-size, 293 mm Nuclepore membrane
filter at 10 psi. The cysts were removed from
the filter by agitation, and the washwater
was concentrated to 5 mL by centrifugation.
The average recovery of cysts at initial
concentrations ranging from 103 to 105
cysts/ml measured with the hemacytometer
was 20% using the Millipore membrane and
85% with the Nuclepore membrane, in-
dicating that the membrane structure may
have had an effect when using the 293-mm
membrane. At concentrations below 1
cysts/mL, the recoveries became highly
variable because of the low number of cysts
that could be enumerated. For example, the
recovery of duplicate runs at 0.1 cyst/mL
was 75% and 23%, respectively.
Two counting techniques were used for
the enumeration of the G. lamblia cysts. The
first technique was microscopic counting
using different counting chambers, and the
second was an electric current displacement
technique using a ZBI Coulter Counter and
Channelyzer (Coulter Electronics, Hialeah,
Florida) calibrated to measure particle den-
sities in the Giardia size range (8 to 12 pirn).
Both methods exhibited some nonlinearity
for the more diluted suspensions. Although
the Coulter Counter was more precise and
had a lower detection limit, only the
hemacytometer method was specific for
cysts. The Coulter Counter could not dif-
ferentiate between cysts and other particles
of a similar size, so counts from that system
are referred to as cyst-sized particles.
Tests for electrophoretic mobility (EM) and
zeta potential (ZP) were carried out to deter-
mine how they varied for formalin-fixed Giar-
dia cysts at different pH values using a Zeta
Meter (Zeta Meter, Inc., New York, New
York). The ZP values for the fixed G. lamblia
cysts clearly showed a decreasing potential
at decreasing pH values. But, even at low
pH values, the cysts retained their negative
charge. The ZP was always more negative
Mention of trade names or commercial products does
not constitute endorsement or recommendation for
than -20 mv in the range of pH 5 to 10.
Thus alum and cationic polymers would be
appropriate coagulants.
The pH was measured with a Model 5 Cor-
ning pH meter (Corning Glass, Corning, New
York) standardized daily with pH buffer. Tur-
bidity was measured with a continuously
recording low-range Hach 1720A turbidity
meter (Hach Chemical, Loveland, Colorado)
and standardized daily as suggested in the
manual. To verify the readings of the flow-
through turbidimeters, grab samples of the
influent and effluent were analyzed daily on
a DRT-100 (H.F. Instruments, Ft. Meyers,
Florida) bench-top turbidimeter.
The pilot plant built at the University of
Washington (UW) for this study had rapid
mixing, flocculation, sedimentation, and
filtration in three parallel treatment trains
with flow rates of 2.3 L/min each. The
10.8-cm diameter Plexiglas filter columns
contained 50.8 cm of 0.92-mm effective size
(e.s.) anthracite with a uniformity coefficient
(u.c.) of 1.28 and 25.4 cm of 0.40-mm e.s.
sand (u.c. = 1.30). The columns had
headloss taps at 10.2-cm (4-in.) intervals.
The DE test filter was a 0.1-m2 (1-ft2)
pressure filter operated at 3.8 L/min (1.0
gpm). The operation of the filter consisted
of three steps: Precoating, filtration, and
filter cleaning. Precoating was accomplished
by adding a measured amount of diatomite
to tap water and recirculating the slurry
through the filter. During the runs, body feed
diatomite was added to the raw water. The
thickness of the filter cake increased during
the run. Filter runs were terminated when
headloss exceeded 30 psi. The filter cake was
removed from the septum, and the spent
diatomite was discharged to waste. Septum
and filtration chamber were carefully sluic-
ed to make the filter ready for a new
precoating.
Several different grades of diatomite (ob-
tained from the Manville Products Corp.,
Denver, Colorado) were used. The amounts
of precoat material applied to the septum
ranged from 0.5 to 1.2 kg/m2 (0.1 to 0.24
Ib/ft2). The results indicated that 1.0 kg/m2
(0.2 Ib/ft2) would be an adequate precoat
thickness for all grades of diatomite, in-
cluding Celite 560, the coarsest in the group.
The last part of the study was used to
compare the laboratory results with field data
by using a mobile pilot plant. In addition, the
mobile pilot plant results were compared
with results of the treatment plants at Ho-
quiam and Leavenworth. The trailer-
mounted unit was a U.S. Environmental Pro-
tection Agency (EPA) drinking water pilot
plant, a Waterboy-27 (Neptune Microfloc,
Corvallis, Oregon) that was modified by ex-
tending the length of the sand filter compart-
ment by 83.8 cm (33 in.) to provide for more
headloss buildup. The treatment train con-
sisted of three static in-line mixers. Model
2-50-541-5 (Kenecs, Danver, Massachu-
setts), a flocculator with 8 min of detention
time, and a mixed media filter. The filter had
45.7 cm (18 in.) anthracite, (e.s. 1.0 to 1.1
mm, u.c. < 1.7), 22.9cm (9 in.) of sand (e.s.
0.42 to 0.55 mm, u.c. < 1.8), 7.6 cm (3 in.)
of fine garnet (e.s. 0.18 to 0.28 mm, u.c. <
2.3), 7.6 cm (3 in.) of coarse garnet, (1 to
2 mm size), 10.2 cm (4 in.) of 0.95 cm
(3/8-in.) gravel, and 12.7 cm (5 in.) of 1.9-cm
(3/4-in.) gravel (Neptune Microfloc, Cor-
vallis, Oregon). Capacity was approximately
75 L/min, giving a filtration rate of 12 m/hr
(5 gpm/sf).
Granular Media Filtration Results
Granular media filtration was studied first
in experiments with the UW pilot plant. The
raw water source was unfiltered Seattle tap
water from the Tort Reservoir. The first seven
runs for Giardia cyst removal were made
using the coagulation/sedimentation unit
followed by filtration. Runs made thereafter
were direct filtration runs bypassing the
sedimentation unit. The cyst spiking results
of the first seven runs generally showed high
(96% to 99.9%) cyst removals at cyst levels
of 23 to 1100 cysts/L. The removal efficiency
seemed to decrease at low spiking levels.
Removal was only 30% at a cyst concentra-
tion of 2.3 cysts/L in raw water. Results are
listed in Table 1.
A large number of runs were made with-
out addition of cysts. The filter runs were
conducted at different alum dosages, pH
values, and flow rates. The main parameters
measured during the testings were removal
of particles in the Giardia size range, turbidity
removal, length of filter run, headloss
buildup at different depths in the filter, and
particle distribution at different filter depths.
The importance of using an'adequate alum
dose was established. Best removal of cyst-
sized particles and turbidity occurred in the
7- to 15-mg/L range of alum doses. Highest
particle removals were obtained at pH 6.5,
although acceptable results could be attained
in a pH range of 5.6 to 7.0. Sudden pH
changes could cause filtrate quality to
deteriorate. When the filtration rate was in-
creased above 17 m/hr, filtered water qual-
ity deteriorated and headloss buildup
increased sharply.
After the direct filtration runs had es-
tablished operating conditions for effective
removal of cyst-sized particles, additional
runs were made with G. lamblia cysts. Dur-
ing most of these filter runs, about 20 million
cysts per run were added to the raw water.
These tests established the importance of
good coagulation practice. Results appear in
Table 2.
-------
Table 1. Performance of Each Filter Run with Cysts Added Directly to Filter
Run No.
3
4
5
6
7
Filter
Loading
Rate
m/hr
5
6
6
6
6
pH
6.7
6.3
(no lime)
7.2
(lime used)
6.4
(no lime)
7.2
(lime used, low
spiking level)
Cyst
Dosage
9841 L Fitter B
622/L Filter C
1093/L Filter C
231 L Filter C
SOIL Filter C
2.3/L Filter C
% Cyst-
sized
Particle
Removal
93. J
91.5
31
95.6
95.2
% Cyst
Removal
99.96
99.95
96.74
96.67
30
At optimum conditions, cyst removal was
consistently high. An alum dosage of 12
mg/L, pH 6.2, and a filter loading rate of 4.9
m/hr (2 gpm/ft2), would give a 99.73%
removal of cysts at the end of the 1-hr filter
ripening period. Later in the run, cyst reduc-
tion was 99.94% and the effluent turbidity
was constant at 0.02 ntu. The influent tur-
bidity was 1.2 ntu. A filter run with a higher
loading rate to 9.8 m/hr (4 gpm/ft2) did not
show any adverse effect on the filter's abil-
ity to remove cysts.
A reduction in the coagulant dosage led,
as expected, to an increase in the number
of cysts passing through the filter. When the
alum dose was 4 mg/L, the filter-ripening
period increased to 2 hr, and only 64% of
the cysts added to the plant after 2.5 hr of
operation were removed in the filter. The ef-
fluent turbidity was 0.5 ntu, but was slowly
decreasing. The effluent turbidity at 72.5 hr
remained relatively high at 0.4 ntu, whereas
the cyst removal had increased to 91.8%. As
expected, when no coagulant was added to
the water, the filter performed poorly with
regard to both cyst removal and turbidity
reduction. More than half the cysts (52%)
passed through the filter, and the effluent
turbidity remained relatively high.
For the raw water being studied, cyst
removal exceeded 99% at pH 5.6 and pH
6.2, but it dropped to just over 95% when
pH was raised to 6.8.
An examination of Table 2 shows that fil-
tered water turbidity could be used as a
guide to cyst removal efficiency. Cyst
removal exceeded 99.0% ten times. In seven
of the ten instances, the filtered water tur-
bidity was less than 0.10 ntu. Cyst removal
was less than 99% on five occasions, and
each time the filtered water turbidity ex-
ceeded 0.10 ntu (actual range was 0.19 to
0.52 ntu).
To confirm information developed in the
UW pilot plant, field tests were performed
with the EPA's 75-L/min mobile pilot plant
at Hoquiam and at Leaven worth. In each
case, the data were also compared with ac-
tual plant operating data to provide guidance
to local plant operators. Thirty pilot plant
runs were made at Hoquiam between May
and September 1980. Another 19 runs were
made at Leavenworth from September
through November 1980.
At Hoquiam, the most effective particle
and turbidity removal occurred with an alum
dose of at least 8 mg/L. The optimum pH
was 6.7, with acceptable performance in the
range of 6.4 to 7.0, according to pilot plant
results. Actual treatment plant practice
before the study resulted in turbidity and
cyst-sized particle removals that were some-
what erratic. The high removal variability was
primarily due to fluctuations in pH during
coagulation and flocculation. The pH ranged
from 6.6 to 7.4, and the lower removals were
observed at the higher pH values. The ap-
parent inability of alum to affect the overall
performance of the plant at dosages above
those found effective in the pilot plant was
related to the treatment plant's operation at
high pH values. Some operational changes
at the plant were considered as a result of
the pilot plant work. One change, a closer
monitoring of the raw water pH as it entered
the flocculator, was well under way toward
the end of the study, and it included reduc-
ing the amount of soda ash added to the raw
water. Instead, additional soda ash was
Table 2. Cyst Removal During Direct Filtration at UW Pilot Plant
Run
No.
72
73
74
76
77
78
79
80
81
82
Alum
Coagul.
and
Dosage
(mg/L)
None
12.0
12.0
12.0
7.0
4.0
12.0
12.0
12.0
CatFloc
T-1
5.0
pH
6.5
6.2
6.2
6.2
6.2
6.2
6.8
5.6
5.6
6.4
Filter
Loading
Rate
(m/hr)
6.1
6.1
4.3
9.7
9.4
9.7
8.6
10. J
8.6
9.7
8.3
9.7
9.7
9.7
9.7
Total
Dosage
2.0- 10*
12.7-10"
20.0- 10*
15.5- 10*
19.0- 10*
19.2- 10*
20.4- 10*
21.4- 10*
20.2- 10*
21. 5- 10*
21.5- 10*
20.4- 10*
20.4- 10*
20.1-10*
20.1-10*
Filter
Influent
Dosage
6.6- 10*
3.8- 10*
4.2- 16*
7.3- 10*
8.7-10*
9.8- 10*
9.4- 10*
10.7-10*
8.8- 10*
10. 3- 10*
8.4- 10*
10.0- 10*
9.8- 10*
9.8- 10*
9.8- 10*
Cyst
Removal
(%)
48
99.73
99.943
99.936
99.979
99.75
99.87
64
91.8
95.4
99.41
99.83
99.84
95.9
99.911
Elapsed
Time
(Hr:Min)
4:30
1:15
26:00
1:00
7:00
1:00
16:00
2:30
72:30
1:00
10:00
1:00
7:00
1:00
21:00
Cyst Addition
Influent
Turbidity
(ntu)
0.73
1.24
1.19
1.37
1.14
1.94
0.81
1.31
1.35
0.95
1.02
1.73
1.78
0.92
0.80
Effluent
Turbidity
(ntu)
0.39
0.03
0.19
0.04
0.02
0.24
0.03
0.52
0.37
0.28
0.04
0.03
0.02
0.23
0.27
Turbidity
Removal
(%)
47
98
84
97
98
88
96
60
73
71
96
98
99
75
66
-------
2
1
o
I
-S
.o
100
80
60
40
20
0
100
80
60
40
20
0
100
80
60
40
20
Polymer
Alum
Effluent
Turbidity
< 0.05 NTU
0.05-
-------
effective at 3°C, a cationic polymer was
tried. Removals were comparable with those
experienced with alum at this low tempera-
ture. Maximum turbidity removal of 59%
was realized at a polymer dose of 0.2 to 0.4
mg/L, compared with 43% removal with no
coagulant. Particle removal decreased at low
temperatures from 45% to 12% when 0.2 to
0.4 mg/L of polymer was added. To achieve
optimum particle removal under these con-
ditions, a polymer dosage of 3.5 mg/L was
required. But this dose decreased turbidity
removal to 35%, apparently a result of the
polymer's restabilization of very fine colloids
that were smaller than the size being
measured by the particle counter but large
enough to cause light scatter (turbidity).
To determine the ability of the pilot plant
to remove cysts, 1.25 x 10* cysts were added
to the raw water over a 20-min period, and
the filter influent and effluent were sampled
and analyzed for cysts. Before the cyst ad-
dition, a salt solution had been added and
traced through the plant to determine suit-
able sampling times. The plant was operated
at a 10.7-m/hr (4.4 gpm/ft2) filtration rate
with 1.2 mg/L Cat Floe T as the coagulant.
The raw water turbidity was 0.33 ntu, and
the temperature was 1 °C. During the cyst
addition, the effluent turbidity was 0.19 ntu,
a 42% reduction. The three filter influent
samples recovered a calculated 867 cysts,
and 242 cysts were recovered from the ef-
fluent corresponding with a 72% removal.
Cyst-sized particle removal was 53%.
Removal of turbidity and particles at
Leavenworth was greater when alum was
used as the coagulant instead of a cationic
polymer. Lower filtered water turbidities
were attained with alum (Figure 2), and the
lowest turbidity ranges more frequently were
associated with very high removal per-
centages.
The Leavenworth treatment plant used
cationic polymer as the primary coagulant.
Both the raw water and filtered water tur-
bidities were below 1.0 ntu, but some equip-
ment problems associated with filter control
values prevented the plant from operating at
maximum efficiency. These problems were
later corrected, and new equipment was in-
stalled to improve the rapid mixing process.
il
IS
100
80
60
II 40
II
II
g 20
o>
0
WO
S 80
"5 c
a. a
60
| 40
S 20
0.01 -< 0.025 NTU Effluent Turbidity
0.025 -< 0.05
0.05 -<0.10
0.10 -<0.20
0.20 -<0.30
2 10 25 50 75
Percent of Measurements
With Less Than Indicated Particle Removal
Figure 2. Frequency distribution of particle removal at different effluent turbidities during
alum and polymer treatment at Leavenworth.
Diatomaceous Earth Filtration
Results
Numerous DE filter runs were performed
without addition of cysts to develop general
information on filter performance. The re-
sults from the initial runs showed that the
cyst-sized particle removal by the DE filter
was generally better than the reduction in
turbidity. This result was expected, because
irticles 6 ^m or smaller are generally more
abundant than particles in the 7- to 12-^m
range. Of the several types'of filter aids
tested, the best performers were the finer
grades, especially in the very beginning of
the run. Later in the run, when the cake was
thick, no grade of DE specifically out-
performed the others for removal of turbidi-
ty and cyst-sized particles.
The most noticeable difference between
these runs was the rate of headloss buildup,
which was slowest for the coarsest grades.
This result was also manifested by Ibnger
filter runs. The length of the run depended
not only on the type of diatomite used, but
to a significant degree on the amount of
body feed added to the filter. The body feed
rate ranged from 10 to 40 mg/L. Though the
raw water used for these runs was of high
quality, with turbidity normally ranging from
0.6 to 0.9 ntu during this time of the year,
5
-------
body feed rates of 10 or 40 mg/L resulted
in shorter filter runs than did application of
20 mg/L of body feed. This result indicated
that the 10 mg/L was an inadequate body
feed dose, but 40 mg/L was excessive.
During one of the runs when Hyflo Super-
Cel was used as a filter aid, a nonionic
polymer (Magnifloc 985ISI, American Cyan-
amid Co., Wayne, New Jersey) was added
to the raw water. The most noticeable ef-
fect of the 0.0075-mg/L polymer addition
was a significant improvement in the effluent
quality in the very beginning of the run. As
the run progressed, the efficiency of the DE
filter seemed to be similar to earlier runs
where no polymer had been added. When
the run was terminated, it was approximately
25% shorter than similar runs where no
polymer was added. The single most impor-
tant factor for the decrease in run duration
was assumed to be the polymer addition.
In the DE filtration research on Giardia cyst
removal, the cysts were added to the raw
water at the same location as the body feed,
either as a slug or as a constant continuous
dosage. The slug contained a total of 3.0 x
106 cysts, added in 10 sec. For continuous
addition, the cysts were metered into the raw
water line with a peristaltic pump. Raw water
cyst concentrations used during these runs
ranged from 1.5 x 105 to 9.0 x 10s cysts/L.
Because data on DE filter run length and
removal of turbidity and cyst-sized particles
had already been obtained, runs with Giar-
dia cysts were conducted only long enough
to dose the cysts and obtain information on
cyst removal efficiency.
The filter effluent sampling schedule was
determined from a series of tests in which
a salt solution was added to the raw water
in place of cysts. The conductivity of the
filter effluent was monitored continuously to
determine (1) how fast a 10-sec slug would
pass through the filter, and (2) the time re-
quired to reach a constant effluent concen-
tration when a continuous dosage was
added to the filter influent. Results showed
that the entire slug would have reached the
filter effluent in 10 min. Thus to trap all the
cysts escaping the filter, a 38-L sample would
need to be collected. This volume was not
an unreasonably large one to process by the
technique developed for this study. When
a constant dosage was added to the raw
water, the effluent concentration had at-
tained its maximum and constant level after
10 min. By adding cysts for 15 min and sam-
pling the filter effluent during the last 5 min,
a 19-L sample containing an average effluent
concentration of cysts was collected.
All cyst runs used Hyflo Super-Cel as a
filter aid. Based on results from preceding
runs without cyst addition, a 1.0-kg/m2
(0.2-lb/ft2) precoat and 20-mg/L body feed
was judged most suitable for the 3.8-L/min
filtration rate and raw water quality. During
two of the four runs, a 0.0075-mg/L dosage
of the 985N polymer was added to the raw
water for the duration of the run. Results ap-
pear in Table 3. Diatomaceous earth filtra-
tion proved to be very effective for Giardia
cyst removal, with more than 99% of the
cysts removed in every one of the 12 filtered
water samples analyzed in this series of tests.
Conclusions
High cyst removals (above 99%) can be
attained by properly operated granular media
filters, but close attention must be given to
maintaining the unit processes at optimum
conditions.
When a plant operates with alum as the
coagulant, an adequate alum dose is essen-
tial for effective removal of turbidity and
cysts. Close monitoring of pH during the
coagulation and flocculation processes is
also necessary. For the waters studied in this
investigation, the pH optimum under most
conditions was 6.7. Changes in raw water
quality could cause a shift in the pH op-
timum, as was demonstrated during the field
operation.
The polymers tested as primary coagulants
did not perform as well as alum. On the other
hand, the filter runs were longer, and the
necessity for close pH monitoring experi-
enced during alum treatment was not re-
quired.
UW pilot plant data on cyst removal and
mobile pilot plant data on removal of cyst-
sized particles suggested that the highest
removal percentages for cysts and for 8- to
12-^m particles usually tended to be as-
sociated with production of low turbidity
water. Best particle removal results were
seen for filtered water with turbidities of 0.05
ntu or lower.
Table 3. Filter Runs with Cysts Using DE Filter
An increase in filter-loading rate beyond
the 10 m/hr (4.1 gpm/ft2) used for many of
the filter runs could be detrimental. The ef-
fluent water quality would normally suffer,
and because of the more rapid headless
buildup and hence shorter filter run, the
amount of water produced per run was often
less than at the more moderate filtration
rates.
Low temperatures can greatly affect the
coagulation and flocculation process when
alum is used. A similar phenomenon can
occur with polymers. Increasing the floccula-
tion time beyond the 8 min that were avail-
able in the mobile pilot plant might have
improved the plant's ability to treat the cold
water at Leaven worth. The optimum op-
erating conditions attained during the period
of low water temperature would most likely
have changed with an increase in the floc-
culation time.
Diatomite filtration was very effective in
removing G. lamblia cysts, even in the very
beginning of the filter run, when the precoat
acted as the only barrier. As the run pro-
gressed and the body feed caused the
thickness of the filter cake to increase, the
removal of cysts improved. The only de-
crease in the filter's ability to trap the cyst
particles was recorded when the dosage at
the end of the run was increased six times.
This decrease in performance was less evi-
dent when a polymer was added to the raw
water. The polymer addition generally im-
proved the removal efficiency, but it tended
to shorten the filter run because of a more
rapid rate of headloss buildup, especially
toward the end of the run.
The full report was submitted in fulfillment
of Grant No. R806127 by the University of
Washington under the sponsorship of the
U.S. Environmental Protection Agency.
Cyst Addition
Run
No.
63
64
65
66
Number Added
Polymer Continuous
Added Slug (Cysts/L)
3.0- 10*
3.0- 10s
No
3.0- 10°
1.5- 10s
9.0- 10s
3.0- JO1
3.0- IP
Yes
3.0- 10*
1.5- JO1
9.0- 10s
No 4.5- 10s
Yes 4.5- 10s
Elapsed
Time
(Hr:Min)
0:05
0:20
2:00
2:30
3:00
0:05
0:20
2:00
2:30
3:00
3:00
3:00
Removal IR)
(%)
99.35 99.65
R> 99.65
99.61 99.65
K> 99.65
R> 99.65
99.48
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Foppe B. DeWalle, Jogeir Engeset, and William Lawrence are with the University
of Washington, Seattle, WA 98195.
Gary S. Logsdon is the EPA Project Officer (see below).
The complete report, entitled "Removal ofGiardia lamblia Cysts by Drinking Water
Treatment Plants," (Order No. PB 84-162 8 74; Cost: $13.00, 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:
Municipal Environmental Research Laboratory
U.S. Environmental Protection Agency
Cincinnati, OH 45268
United States
Environmental Protection
Agency
Center for Environmental Research
Information
Cincinnati OH 45268
Official Business
Penalty for Private Use $300
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U.S. GOVERNMENT PRINTING OFFICE: 1984-759-102/952 I
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